Symposium Organizers
Chong Long Fu Oak Ridge National Laboratory
Helmut Clemens University of Leoben
Masao Takeyama Tokyo Institute of Technology
Joerg Wiezorek University of Pittsburgh
David Morris CENIM CSIC
II1: Iron and Nickel Aluminides
Session Chairs
Monday PM, November 27, 2006
Commonwealth (Sheraton)
9:30 AM - **II1.1
Strengthening Mechanisms for Fe-Al-based Alloys with Increased Creep Resistance at High Temperatures.
Martin Palm 1 , André Schneider 2 , Gerhard Sauthoff 1
1 , MPI f. Eisenforschung GmbH, Düsseldorf Germany, 2 , Salzgitter Mannesmann Forschung GmbH, Duisburg Germany
Show Abstract10:00 AM - II1.2
The Effects of Strain Rate and Temperature on the Mechanical Properties of the High-strength Spinodal Alloy Fe30Ni20Mn25Al25..
Ian Baker 1 , Taniquea Boyd 1 , James Hanna 1 , George Gray 2
1 Thayer School of Engineering, Dartmouth College, Hanover, New Hampshire, United States, 2 Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractA spinodal alloy, Fe30Ni20Mn25Al25, was produced by casting followed by hot extrusion. The microstructure, as characterized using transmission electron microscopy consisted of coherent, 50-60 nm wide rods aligned along <100>, consisting of alternating B2 and b.c.c. phases. The mechanical properties were determined under compression over a range of temperatures and at different strain rates. The as-extruded room-temperature yield strength was ~1400 MPa, and yield strengths of up to 2350 MPa were found after heat treatment at 823 K, when a Fe-Mn phase with the β-manganese formed. Strengths of over 200 MPa were found at temperatures of 1073 K, the highest test temperature. The yield strength was found to be very strain rate dependent, even at room temperature. This presentation will attempt to correlate the microstructures with the mechanical properties in attempt to understand the origin of the high strengths in this alloy. Research supported by NIST grant 60NANB200120 and NSF grant DMR 0552380
10:15 AM - II1.3
Microstructure Control Using Precipitate Phases for the Development of Heat Resistant Fe3Al-based Alloys.
Satoru Kobayashi 1 , Stefan Zaefferer 1
1 , Max-Planck-Institute fuer Eisenforschung GmbH, Duesseldorf Germany
Show Abstract10:30 AM - II1.4
Strengthening at High Temperatures in an Iron-aluminium Alloy by the Precipitation of Stable and Coherent Intermetallic Particles.
David Morris 1 , Maria Munoz-Morris 1 , Luis Requejo 1
1 Physical Metallurgy, CENIM,CSIC, Madrid Spain
Show Abstract10:45 AM - II1.5
High Cohesive Special Boundaries in Boron-free Fe-40%at. Al.
Anna Fraczkiewicz 1 , Tiphaine Cordonnier 1
1 UMR CNRS 5146, Ecole Nationale Superieure des Mines, St-Etienne France
Show Abstract11:00 AM - II1: Fe-Ni-Al
BREAK
11:15 AM - II1.6
Effects of Dislocation and Microstructure on Pseudoelasticity in D03-Type Fe3Al Single Crystals.
Yukichi Umakoshi 1 , Takashi Nakajima 1 , Hiroyuki Yasuda 2 1
1 Division of Materials and Manufacturing Science, Graduate School of Engineering, Osaka University, Osaka Japan, 2 Research Center for Ultra-High Voltage Electron Microscopy, Osaka University, Osaka Japan
Show AbstractFe3Al single crystals with the D03 structure exhibited significant pseudoelasticity depending on chemical composition, microstructure and testing temperature. The pseudoelasticity was found to be based on a reversible motion of 1/4<111> superpartial dislocations dragging the nearest-neighbor anti-phase boundaries (NNAPB). During unloading, the NNAPB pulled back the superpartials resulting in the pseudoelasticity. The amount of strain recovery showed a maximum at 23.0at.%Al. The fine ordered domain structure at 23.0at.%Al led to the individual motion of 1/4<111> superpartials resulting in the large pseudoelasticity. In Fe-23.0at.%Al crystals oriented for {101}<111> single slip, deformation proceeded accompanied with a formation of slip bands parallel to {101} plane, while the slip bands disappeared after unloading. The loading axis of the crystals tended to rotate toward <111> slip direction without phase transformation and twinning. The recovery ratio of Fe-23.0at.%Al crystals exceeded 80% in the wide temperature range from 223 to 473K. In the temperature range, the yield stress decreased monotonically with increasing temperature in contrast to the conventional shape memory materials. These results strongly suggested that the pseudoelasticity was based on the dislocation motion.
11:30 AM - II1.7
Pseudoelasticity and Shape Memory in Single Crystal Fe3Al.
Saurabh Kabra 1 , Hongbin Bei 1 2 , Easo George 2 1
1 Department of Materials Science and Engineering, University of Tennessee, Knoxville, Knoxville, Tennessee, United States, 2 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show Abstract11:45 AM - II1.8
Microstructure and Mechanical Behaviour of a Duplex fcc-B2 Fe-Ni-Al Alloy.
Maria Munoz-Morris 1 , David Morris 1
1 Physical Metallurgy, CENIM,CSIC, Madrid Spain
Show Abstract12:00 PM - II1.9
Texture Memory Effect During Heat Treatment in the Heavily Cold Rolled Ni3Al Foils.
Masahiko Demura 1 , Ya Xu 1 , Kyosuke Kishida 2 , Toshiyuki Hirano 1
1 Fuel Cell Materials Center, National Institute for Materials Science, Tsukuba, Ibaraki, Japan, 2 Department of Materials Science and Engineering, Kyoto University, Sakyo-ku, Kyoto, Japan
Show AbstractThin foils of boron-free Ni3Al intermetallics have been developed for high-temperature micro systems (Demura et al., 2001). We have recently found an interesting texture evolution during heat treatment in the cold-rolled Ni3Al foils (Demura et al., 2004). That is, the cold-rolled texture changes into a complicated one after the primary recrystallization and then returns to the original cold-rolled texture during the grain growth. This two-step texture evolution can be denoted as texture memory effect. In this paper, we examined the mechanism of the texture memory effect, paying attention to the orientation relationship between the cold-rolled and the recrystallized textures. The 84% cold-rolled foils with the Goss texture were heat-treated and the grain orientation was determined by the electron backscatter diffraction (EBSD) method.The EBSD measurements revealed that the major component in the primary-recrystallization texture had a 40°<111> rotation relationship to the cold-rolled Goss texture. Beside, there were the Goss and other grains surrounded by the 40°<111> rotated grains though they were minor. It is known in fcc metals that the 40°<111> grain boundary (GB) has a high mobility than others. Assuming the high mobility of the 40°<111> GB in Ni3Al similarly, the texture memory effect can be explained as follows. In the primary recrystallization, the 40°<111> rotated grains grow immediately after nucleation to consume the deformed matrix, thus the 40°<111> rotated texture being formed. In the grain growth, the Goss grains grow preferentially since they are surrounded by the 40°<111> rotated grains, thus having a high mobility GB. Consequently, it can be concluded that the texture was memorized through the special 40°<111> rotation relationship.
12:15 PM - II1.10
Microstructure and High Temperature Mechanical Behavior of B2 Ni-Al-Ru Ternary Alloys.
Fang Cao 1 , Tresa Pollock 1
1 Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States
Show AbstractRu-modified NiAl-based bond coats have the potential to improve the durability of Superalloy - Thermal Barrier Coating systems (TBCs) for advanced gas turbine engines. An understanding of the deformation and creep mechanisms across the Ni-Al-Ru B2 field is essential to the development of these new bond coats for TBCs. The objective of this study was to investigate the high temperature mechanical behavior of five ternary alloys with compositions located within the B2 field across the NiAl-RuAl phase region of the ternary. The microstructure and phases present in these alloys were analyzed by standard analysis techniques, including scanning electron microscopy (SEM), X-ray powder diffraction (XRD), electron microscope analysis (EMPA), and transmission electron microscopy (TEM). Mechanical properties, including compression tests over temperature range from 25 to 700 °C and compression creep tests from 950 to 1050 °C were investigated. At room temperature, brittle failure was observed in the Al-deficient, Ni-rich alloys in compression, while improved strength and ductility were observed in Ru-rich alloys at temperatures up to 700 °C. Exceptional creep strength was observed in these alloys, as compared to NiAl. The creep resistance increases dramatically as the Ru/Ni ratio increases, with a Al50Ni5Ru45 alloy having a creep strength approximately 25 times greater than hard-oriented NiAl at a creep rate of 10-7 s-1. Activation energies and stress exponents were measured and compared to binary NiAl. The dislocation substructures formed in those alloys after compression and creep were observed by TEM and deformation mechanisms were characterized as a function of Ru/Ni ratio.
12:30 PM - II1.11
Modifications of Surface Microstructure and Properties Induced by High Current Pulsed Electron Beam (HCPEB) Treatments of Intermetallics.
Thierry Grosdidier 1 , JianXin Zou 1 2 , XiangDong Zhang 2 1 , ShengZhi Hao 2 , Chuang Dong 2
1 Material Science - LETAM, University Paul Verlaine, Metz France, 2 Material Science, Dalian University of Technology, Dalian China
Show AbstractHigh current pulsed electron beam (HCPEB) is a fairly new technique for surface modifications[1]. The pulsed electron irradiation induces (i) a rapid heating and cooling of the surface together with (ii) the formation of thermal stress waves. As a result, improved surface properties of the material, often unattainable with conventional surface treatment techniques, can be obtained fairly easily. This is particularly true for corrosion and tribological properties. The present contribution will review the use of this technique for modifying different types of intermetallics or intermetallic containing alloys. In particular, the potential of the technique for structure modifications associated with the use of the pulsed electron beam under “heating” and “melting” conditions will be highlighted. Under the “melting” mode, it will be shown that the treatment induces the formation of an ultra fine grained layer formed by rapid solidification [2]. Via the study of NiTi and superalloys, it will be demonstrated that “non conventional solidification textures” are also associated with this treatment. The HCPEB treatment has a high potential in the field of bio-materials development; as demonstrated by the significant improvement in corrosion resistance of NiTi alloys within a simulated body fluid [3, 4].The use of the “heating” mode, for which the top surface of the material remains in the solid state during the overall treatment, is less “conventional” but does provide with substantial interesting surface modifications. A detailed analysis of a FeAl alloy will demonstrate grain size refinement, hardening and texture modification in the suface layer without any modification of the surface geometry. These processes will be discussed with respect to the conbined effects of the heavy deformation and recrystallisation/recovery mechanisms taking place during the HCPEB treatment.[1] Proskurovsky DI, Rotshtein VP, Ozur GE, Ivanov YuF, Markov AB., Surface and Coating Technology, 125, 49, 2000.[2] Zou J.X., Grosdidier T., Zhang K.M., Dong C., in the press of Acta Materialia.[3] Zhang K.M., Zou J.X., Grosdidier T., Gey N., Hao S.Z., Dong C., Yang D.Z., in the press of Journal of Alloys and Compounds.[4] Zou J.X., Zhang K.M., Dong C, Qin Y., Hao S.Z., Grosdidier T.. accepted by Applied. Physic. Letters.
12:45 PM - II1.12
Three-dimensional Imaging of Ordering Alloys using DFTEM Tomography.
Satoshi Hata 1 , Kousuke Kimura 2 , Gao Ye 2 , Syo Matsumura 2 , Tomokazu Moritani 3 , Minoru Doi 3
1 Department of Applied Science for Electronics and Materials, Kyushu University, Kasuga, Fukuoka Japan, 2 Department of Applied Quantum Physics and Nuclear Engineering, Kyushu University, Fukuoka, Fukuoka Japan, 3 Department of Materials Science and Engineering, Nagoya Institute of Technology, Nagoya, Aichi Japan
Show AbstractII2: Theory
Session Chairs
Monday PM, November 27, 2006
Commonwealth (Sheraton)
2:30 PM - **II2.1
First-principle Thoery of Phase Stability, Phase Equilibria and Phase Transition of Ordered Compounds.
Tetsuo Mohri 1
1 Materials Science and engineering, Hokkaido University, Sapporo Japan
Show AbstractFirst-principles theory of alloys is based on electronic structure calculation at the ground state and statistical mechanics calculation at finite temperatures. The former clarifies the stablity of an ordered compound aganst competing phases and the latter is employed mainly to derive a phase diagram. The author performed a series of first-principles investigations on binary alloy systems including noble metal alloys, semiconductor alloys and Fe-based alloy systems by combining FLAPW electronic structure total energy calculations with Cluster Variation Method. Recently, the theoretical framework is extended even to calculate microstrucutral evolution process. By exemplifying Fe-based alloy systems,the progress of the fisrt-principles investigation is reviewed and future prospect is discussed.
3:00 PM - II2.2
Predicting the Crystal Structure of Intermetallics using Data Mining and Quantum Mechanics.
Chris Fischer 1 , Kevin Tibbetts 1 , Dane Morgan 2 , Gerbrand Ceder 1
1 Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Department of Materials Science and Engineering, University of Wisconsin, Madison, Wisconsin, United States
Show AbstractPredicting crystal structure is a critical problem for computational materials science. When computing the properties of both existing and genuinely new materials, it is essential that one know the stable structure of the material of interest.To predict crystal structure from first principles both an accurate energy model, and an efficient algorithm to search through the space of possible crystal structures are required. Traditionally the limiting factor in this approach was the accuracy of the energy model, but with sustained increases in both computational power and advances in basic materials theory, the primary challenge is now searching through the unwieldy space of possibilities in an informed way.We have developed a new approach to the prediction of crystal structure utilizing correlations present in existing experimental data. The correlations implicitly encode well-known heuristic rules such as size-mismatch, but do so without explicitly stating what constitute relevant physical parameters. These correlations are then used to efficiently guide accurate quantum mechanical calculations providing a practical solution to the problem of crystal structure prediction.
3:15 PM - II2.3
Structural Transformations and Improved Ductility in Ordered FeCo and ZrCo Intermetallics.
Maja Krcmar 1 2 , Chong Long Fu 1 , James Morris 1 3
1 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Physics Department, Grand Valley State University, Allendale, Michigan, United States, 3 Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee, United States
Show AbstractThere is a growing evidence that common understanding of ductility fails to explain the behavior of many B2 intermetallics: the brittleness of B2 FeCo remains a puzzle given its symmetry, weak ordering and <111> deformation mode. In contrast, the strongly-ordered line compound ZrCo exhibits unusually good ductility. Using first-principles calculations, we find that under <100>(001) elastic shear, the B2 FeCo can transform into the low-symmetry L10 structure. At realistic shear angles, for Fe-rich FeCo and stoichiometric FeCo, the L10 structure is metastable, with energy considerably higher than that of the B2 structure. Since the stored mechanical energy cannot fully dissipate in these alloys, it can cause the initiation and propagation of cracks. In contrast, for Co-rich FeCo, the L10 structure is stable, with energy lower than that of the B2 structure. In this case, transformation toughening can occur as the stress energy is fully dissipated by the decrease in the electronic energy due to the structural phase transformation into a lower energy structure, before the local stress concentrations become high enough to initiate a crack. We suggest that improved ductility in Co-rich FeCo alloys may originate from the transformation toughening. Our first-principles calculations also find that elastic stress can induce B2 B33 martensitic phase transformation in ZrCo alloys, where B33 is the stable structure. Potential source of the improved ductility in ZrCo is therefore transformation toughening due to the stress induced B2 B33 transformation. This work is sponsored by the Division of Materials Sciences and Engineering, the US DOE, under contract DE-AC05-00OR22725 with UT-Battelle, LLC.
3:30 PM - II2: Theory
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4:30 PM - **II2.4
Multiscale Phase Field Modeling of γ′Precipitation and Deformation in Ni-Base Superalloys.
Chen Shen 1 , Ju Li 1 , Mike Mills 1 , Yunzhi Wang 1
1 Materials Science and Engineering, The Ohio State University, Columbus, Ohio, United States
Show Abstract5:00 PM - II2.5
The Effect of Constraints on Plastic Deformation.
Vaclav Paidar 1
1 , Institute of Physics, Praha 8 Czech Republic
Show Abstract5:15 PM - II2.6
Precipitation-Induced Nano-Twinning.
Franz Fischer 1 , Fritz Appel 2 , Helmut Clemens 3
1 Institute of Mechanics, Montanuniversität Leoben, Leoben Austria, 2 Institute for Materials Research, GKSS Research Centre, Geesthacht Germany, 3 Department of Physical Metallurgy and Materials Testing, Montanuniversität Leoben, Leoben Austria
Show AbstractIntermetallic alloys as γ(TiAl) may be strengthened by Ti3AlC precipitates, which reduces the creep resistance by about one orders of magnitude. Ti3AlC are "cigar"-shaped nanoinclusions with the typical geometrical parameters, diameter of 2 nm, length of 20 nm and separation distance 80 nm. The precipitates show an anisotropic volume change with an isotropic component of 0.058 and an additional anisotropy term in the longitudinal direction of -0.036. The elastic contrast between the matrix and the precipitate amounts C=1.66. This significant misfit together with the mismatch in the elastic constants is accommodated by an elastic straining of the precipitate and its neighbour material by distinct dislocations and faults starting from the surface of the precipitate. Experimental work is demonstrated identifying these faults, which according to our knowledge was not reported before. Since the fault can be characterized by band of a distinct length l and a height h, being equal to the distance of two atomic planes, we consider it as a precipitation induced precursor for mechanical twins. Based on thermodynamics of displacive phase transformations a thermodynamical mechanical driving force (MDF) is opposed to a set of restrictive forces. A sudden generation of a nano-twin occurs if the MDF is going to overcome the restrictive forces, consisting of a dissipative term proportional to the product of a critical shear stress and twinning shear (being 0.707), the additionally produced interface energy and the elastic strain energy. It can be shown that the sum of the restrictive forces is a non-convex function of the ratio l/h. This means that a metastable situation may happen where short as well very long nano-twins are possible. An actual configuration is studied and compared with experimental results.Finally both an experimental as well as micro-mechanical (thermodynamical) explanation is given for the existence of such nano-twins which may form larger twins in the case of provision of an additional driving force, e.g. by an external load stress state.
5:30 PM - II2.7
Anomalous Equilibrium Volume Change of Magnetic Fe-Al Crystals.
Martin Friak 1 , Jörg Neugebauer 1
1 , Max-Planck-Institut für Eisenforschung, GmbH, Duesseldorf Germany
Show AbstractIron aluminides represent a very promising class of intermetallic materials with great potential for substituting stainless steels at elevated and high temperatures. Experiments observed an anomalous equilibrium-volume behavior as a function of concentration in Fe-rich compounds [1]. This effect has been tentatively assigned to be due to an order-disorder transition [1]. In order to clarify this phenomenon we have studied the role of magnetism in Fe-Al crystals employing density functional theory (DFT) within the generalized gradient approximation (GGA). The excess energies, equilibrium lattice parameters and magnetic states have been determined for a dense set of different iron concentrations and a large variety of atomic configurations. Both external and internal relaxations were allowed.The spin-polarized calculations for ordered ferromagnetic Fe-rich compounds nicely reproduce the anomalous volume behavior, i.e. the effect is not related to an order-disorder transition. Analyzing different magnetic states we identified the change in magnetism to be the driving force. In fact, performing the same calculations but switching off magnetism removed the anomalous volume dependence and showed a clear linear dependence. Based on these results the importance of order-disorder transition in Fe-Al systems is revisited.[1] R. A. Buckley and S. Kaviani, Mat. Sci. Eng. A258, 173 (1998).
5:45 PM - II2.8
Applications of Zintl Intermetallics: SrAl2 a Wetting Layer for 2D Growth in Heterogeneous Stacks.
Alexander Demkov 1
1 Department of Physics, University of Texas-Austin, Austin, Texas, United States
Show Abstract
Symposium Organizers
Chong Long Fu Oak Ridge National Laboratory
Helmut Clemens University of Leoben
Masao Takeyama Tokyo Institute of Technology
Joerg Wiezorek University of Pittsburgh
David Morris CENIM CSIC
II3: Ferromagnetic Shape Memory Alloys and Magnetic Intermetallics
Session Chairs
Peter Mullner
Wolfgang Pfeiler
Tuesday AM, November 28, 2006
Commonwealth (Sheraton)
9:30 AM - **II3.1
Magnetoplasticity and Nano-Magneto-Mechanics of Magnetic Shape-Memory Alloys.
Peter Mullner 1 , Zak Clark 2 , Linda Kenoyer 2 , William Knowlton 2 , Gernot Kostorz 3
1 Department of Materials Science and Engineering, Boise State University, Boise, Idaho, United States, 2 Departments of Materials Science & Engineerng and Electrical & Computer Engineering, Boise State University, Boise, Idaho, United States, 3 , ETH Zürich, Zürich Switzerland
Show AbstractMagnetoplasticity is the plastic response of a material to a magnetic field, usually implying the motion of twin boundaries. Magnetoplasticity has been found in ferromagnetic materials such as rare-earth metals and a number of intermetallic compounds. The martensitic phases of Ni2MnGa have especially attracted particular attention. Twinning disconnections are the elementary carriers of twin-boundary motion. Depending on the martensite structure, twinning disconnections may dissociate into partial twinning disconnections in various ways. Mutual interaction of twinning disconnections and their interaction with interfaces control magnetic-field-induced deformation and fracture initiation. In singly twinned crystals, twinning disconnections run through the entire crystal, and the full twinning shear may be released. In polysynthetically twinned crystals, the path of twinning disconnections is geometrically limited, and the twinning shear is only partially released. Atomic-force microscopy (AFM), magnetic-force microscopy (MFM), and nanoindentation experiments were performed on a Ni-Mn-Ga single crystal with orthorhombic (14M) martensite. The surface relief was characterized and used to identify the orientation of individual twin variants. It was shown that ab- and bc-twinning modes are present. The magnetic domains are elongated along the crystallographic c direction. Twin variants with the c direction perpendicular to the surface exhibit an out-of-plane magnetization which can be identified through a strong contrast in the MFM image. The deformation caused with nanoindentation is recoverable to a large degree. No trace of deformation twinning was found after unloading. It is concluded that although the residual deformation is due to dislocation activity, it is likely that pseudo-elastic twinning took place during loading and unloading. The results indicate a size effect on deformation twinning under localized loading.
10:00 AM - **II3.2
Control of Microstructure Driven by Magnetic Field in Ferromagnetic Intermetallics.
Tomoyuki Kakeshita 1 , Takashi Fukuda 1
1 Department of Materials Science and Engineering, Graduate School of Engineering, Osaka University, Suita Japan
Show AbstractMagnetic field has been known to be effective in solidification processes. Recently, however, it has been revealed that the magnetic field is also effective for controlling the arrangement of variants, which are formed in association with a solid-solid transformation, in some ferromagnetic intermetallic-based alloys with a large magnetocrystalline anisotropy. In this presentation, we will show two of such cases: one is the rearrangement of martensite variants by magnetic field in intermetallic-based ferromagnetic shape memory alloys (Ni2MnGa and Fe3Pt), and the other is formation of mono-variant state by ordering heat-treatment under magnetic field in a L10-type CoPt. The former process is diffusionless and proceeds by the movement of twinning plane under a magnetic field. The latter is a diffusion controlled process. For both the cases, a large magnetocrystalline anisotropy is essentially important for controlling the arrangement of variants, although kinetics of the two processes is quite different each other.
10:30 AM - II3.3
Systematic Investigation of Magnetostrictive and Ferromagnetic Shape Memory Alloys in the FePdGa Ternary System.
Jason Hattrick-Simpers 1 , Samuel Lofland 2 , Antonio Orozco 3 , Lee Knauss 3 , Manfred Wuttig 1 , Ichiro Takeuchi 1
1 Materials Engineering, University of Maryland, College Park, Maryland, United States, 2 Department of Physics and Astronomy, Rowan University, Glassboro, Maryland, United States, 3 , Neocera, Beltsville, Maryland, United States
Show Abstract10:45 AM - II3.4
Acoustic Attenuation in Ferromagnetic Shape Memory Alloy Polymer Composites Embedded with Double PZT Sensors.
Manickam Mahendran 1 , Jorge Feuchtwanger 1 , Bradley W.Peterson 1 , Robert C.O'Handley 1
1 Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show Abstract11:00 AM - II3: FSMA
BREAK
11:15 AM - **II3.5
L10 Ordered Intermetallics for Ultrahigh Density Magnetic Recording Media: Phase Formation and the Role of Alloy Chemistry and Composition.
Katayun Barmak 1
1 Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States
Show Abstract11:45 AM - II3.6
Cold-Deformation and Annealing of equiaxed L1o-ordered FePd Intermetallics.
Aniridha Deshpande 2 , Jörg Wiezorek 1
2 High Intensity Discharge, GE (Lighting Technology), Willoughby, Ohio, United States, 1 MSE, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
Show Abstract12:00 PM - II3.7
Kinetics of L10 Long-range Ordering in FePd Thin Film.
Chaisak Issro 1 , Veronique Pierron-Bohnes 2 , Wolfgang Püschl 1 , Rafal Kozubski 3 , Wolfgang Pfeiler 1
1 Faculty of Physics, University of Vienna, Vienna Austria, 2 , Institut de Physique et Chimie des Matériaux de Strasbourg, Strasbourg France, 3 M. Smoluchowski Institute of Physics, Jagellonian University, Cracow Poland
Show AbstractDue to their high magnetic anisotropy L10-ordered intermetallics bear a potential as high density magnetic recording materials. In this case the c-axis of the tetragonally distorted structure is the easy axis of magnetization. We present preliminary results on the details of ordering kinetics on FePd films (thickness 100 nm) epitaxially co-deposited on MgO substrates.As known from previous experiments, FePd film epitaxially grown on MgO(001) is already highly ordered in the as-prepared state and shows a nearly single-crystalline structure (c-axis perpendicular to sample surface). It also turned out that (quasi) residual electrical resistivity (REST) measurement is well suited for the detection of atom jumps in intermetallic thin films due to its high resolution for configurational changes. Here we report first results from a more detailed study of ordering kinetics by measuring REST in-plane during isothermal small-step annealing. This heat treatment along a sequence of closely neighboring temperatures leading from one equilibrium state of order to a slightly different one - so called ‘order-order relaxations’ - allows a detailed view of the ordering process, the change of the degree of order with temperature, and the corresponding activation energy, which can be related to self diffusion. An ordering activation energy of about 2.3 eV results, which is slightly below the value obtained in a previous investigation on bulk material.
12:15 PM - II3.8
Microstructural Evolution during Post Deposition Annealing of Pulsed Laser Deposited Fe(100-x) Pdx Thin Films.
Andreas Kulovits 1 , John Leonard 1 , Jorg Wiezorek 1
1 MSE, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
Show AbstractFePd belongs to a group of L1o - intermetallics with attractive uniaxial hard-ferromagnetic properties. In this study thin FePd films of different composition Fe-Xat%Pd, X=34, 50, 61, were deposited by pulsed laser deposition (PLD) on amorphous SiO2 and single crystalline NaCl. The as deposited state will be characterized in terms of topography, morphology, grain size, texture and presence of short-range order. The effect of the substrate will be discussed. Furthermore the microstructural evolution during the different order/disorder phase-transformations will be carefully studied by means of AFM, SEM, XRD and TEM. The change in degree of order has been monitored by means of VSM measurements. Differences in microstructural evolution due to different ordering reactions FCC to L1o ordering and concomitant phase separation of α – Fe vs. FCC to L1o ordering vs. FCC to L12 ordering upon heat treatment will be contrasted. The relationships between magnetic properties and microstructure will be discussed. Support from NSF-DMR-Metals is gratefully acknowledged.
12:30 PM - II3.9
Magnetic Anisotropy in Cubic Fe3Pd.
Yi Qi 1 , Liyang Dai 1 , James Cullen 1 , Manfred Wuttig 1 , John Cumings 1
1 Materials Science and Engineering, University of Maryland, College Park, College Park, Maryland, United States
Show Abstract12:45 PM - II3.10
In-Situ Studies of Phase Transformation in Ferromagnetic Shape-Memory Bulk Polycrystals and Nanoparticles.
Yandong Wang 1 , Yang Ren 2 , Hahn Choo 3 , Peter K. Liaw 3
1 , Notheastern University, Shenyang China, 2 , Argonne National Laboratory, Argoone, Illinois, United States, 3 , The University of Tennessee, Knoxville, Tennessee, United States
Show AbstractII4: Thermoelectric and Shape Memory Alloys
Session Chairs
Haruyuki Inui
Yukichi Umakoshi
Tuesday PM, November 28, 2006
Commonwealth (Sheraton)
2:30 PM - **II4.1
Defect Control and Defect Engineering of Transition-metal Silicides.
Haruyuki Inui 1
1 Department of Materials Science & Engineering, Kyoto University, Kyoto Japan
Show AbstractThere are some semiconducting transition-metal silicides that exhibit interesting physical properties for industrial applications. Their interesting physical properties often stems from the unique crystal structures. A defect silicide formed with rhenium is one of them, seeking for thermoelectric applications accompanied by a narrow band-gap. Although Re disilicide has been believed to have the tetragonal C11b structure that is isomorphous to MoSi2, we have recently found out that Re disilicide does not reside at the composition of ReSi2 but has a stoichiometry formulated to be ReSi1.75. We have identified the crystal structure of ReSi1.75 be monoclinic with the space group Cm (mc44) due to an ordered arrangement of vacancies on Si sites in the underlying C11b lattice. The vacancy concentration as well as their arrangements can be controlled by ternary additions. Depending on the valence electron number of ternary elements, the Si vacancy concentration of the silicide decreases or increases, leading sometimes to the improved thermoelectric properties. This is accompanied by the introduction of two different kinds of shear structures with displacement vector of [100] either on (107) or (10-9) planes. If such shear operation occurs every unite cell of the silicide, the so-called adaptive structure, which is basically an incommensurate structure, is formed. The largest improvement in the properties so far observed is obtained with the adaptive structure. A sesquisilicide formed with Ru is another example to show that the thermoelectric properties are largely altered by defect engineering. In this case, the lattice parameter of the Si sublattice with respect to that of the Ru sublattice is the subject for the defect engineering. The crystal structure of the high-temperature phase of Ru2Si3 is one of the simplest form of the so-called chimney-ladder structure, which is, in general, composed of transition metal (M) atoms in a tetragonal β-Sn arrangement (chimneys) and group-14 or 13 atoms (X) in a coupled helical arrangement (ladders), with both the chimney and ladder being aligned along the [001] direction of the tetragonal unit cell. Once Re is added, a series of chimney-ladder phases are formed over a wide composition range, with each of chimney-ladder phases having different lattice parameters of the Si sublattice with respect to those of M sublattice so that the Si/(Ru+Re) ratio of the chimney-ladder phases increases with the increase in the Re content. The observed deviation of the chimney-ladder structure from the idealized composition and the possibility of adjusting the semiconducting properties of these chimney-ladder structures are discussed in terms of the valence electron concentration per metal atom.
3:00 PM - II4.2
Solid-State Synthesis of Magnesium Base Thermoelectric Alloys via Bulk Mechanical Alloying.
Tatsuhiko Aizawa 1 2 , Renbo Song 3
1 Department of Materials Science and Engineering, University of Toronto, Toronto, Ontario, Canada, 2 , Osaka Prefecture UNiversity, Osaka Japan, 3 , University of Science and Technology Beijing, Beijing China
Show AbstractMagnesium binary and ternary alloy systems have been popular as a thermoelectric light-weight alloy to be working in the medium temperature range. In particular, pseudo binary alloy systems among Mg2Si, Mg2Ge, Mg2Sn and Mg2Pb have been explored to improve the absolute figure-of-merit ZT and to reduce the initial cost for fabrication of thermoelectric materials. Difficulty in materials processing and manufacturing of these alloys becomes a main issue to be solved toward further research and development: high vapor pressure of magnesium, chemical reactivity of Mg, Si or Ge with crucible and vial and various contaminations in processing . Solid state synthesis via bulk mechanical alloying succeeded in fabrication of various intermetallic compounds and alloys in bulk. In the present paper, the solid-state reactivity via the bulk mechanical alloying is first stated for synthesis of Mg2Si and Mg2Sn: nucleation-controlled and diffusion-controlled processes. This processing is applied to directly synthesize ternary thermoelectric alloys Mg2Si1-xGex, Mg2Si1-ySny and Mg2Sn1-zPbz for 0.0 < x, y, z < 1.0 and to evaluate their thermoelectric properties. Hot pressing is used to make full-dense billets and samples for thermoelectric measurement. In particular, the effect of germanium and tin contents on their Seebeck coefficient and band-gap is investigated to describe the p-n transition behavior and to understand the change of electric structure with solid solution formation.
3:15 PM - II4.3
Thermoelectric Properties of Half-Heusler Compounds N-type MNiSn and P-type MPtSn (M = Hf, Zr).
Yoshisato Kimura 1 , Tomoya Kuji 1 , Akihisa Zama 1 , Yoshinao Mishima 1
1 Materials Science and Engineering, Tokyo Institute of Technology, Yokohama Japan
Show Abstract3:30 PM - II4.4
Thermoelectric Properties of ZrNiSn based half-Heusler Compounds.
Shinsuke Yamanaka 1 , Hiroaki Muta 1 , Ken Kurosaki 1
1 Graduate School of Engineering, Osaka University, Suita, Osaka, Japan
Show Abstract3:45 PM - II4.5
Thermoelectric Properties of Ba-Ge based type-III Clathrate Compounds.
Jung-Hwan Kim 1 , Norihiko Okamoto 1 , Katsushi Tanaka 1 , Haruyuki Inui 1
1 Materials Science and Engineering, Kyoto University, Kyoto Japan
Show Abstract4:15 PM - II4.6
Thermoelectric Figure of Merit Enhancement of FeSi2 Thin Film with [100] Orientation.
Hirofumi Kakemoto 1 , Tohru Higuchi 2 , Hajime Shibata 3 , Satoshi Wada 1 , Takaaki Tsurumi 1
1 , Tokyo Institute of Technology, Meguro, Tokyo, Japan, 2 , Tokyo University of Science, Shinjuku, Tokyo, Japan, 3 , National Institute of Advanced Industrial Science and Technology, Tsukuba Central 2, Tsukuba, Japan
Show Abstract4:30 PM - II4.7
Classification and Characterization of the Shape Memory Binary Alloys.
Mitsuo Notomi 1 , Krystyn Van Vliet 2 , Sidney Yip 2
1 Mechanical Engineering, Meiji university, Kawasaki, Kanagawa, Japan, 2 Materials Science and Engineering, MIT, Cambridge, Massachusetts, United States
Show AbstractFor more than forty years from the discovery of TiNi SMA, it was found that the some kinds of alloys exhibited shape memory behaviors and many researchers tried to reveal the mechanisms of SME. Consequently, in some SMA, especially TiNi and its based alloys, most of the controversies have been solved according to the outstanding review related to the TiNi and its based SMA by Otsuka and Ren. The basic requirement conditions for SME were as follows,1.Ordered crystal structure of the parent phase,2.Thermoelastic martensitic transformation,3.Internal twinning in the martensite. Furthermore, Otsuka and Shimizu revealed the mechanisms of shape recovery on the advantage of B2 crystal. It is well known that the conditions are applicable to explain SME. Nevertheless, there are some problems still remain to be solved or clarified. For example, some kinds of alloys exhibit the shape recovery via reverse MT although its MT is not thermoelasticity. This martensite of MT is classified as faulted martensite and the alloys are not considered to belong to the category of exact SMA in the view of less thermoelastic transformation by some researchers. The mechanisms of SME in disordered fcc In-Tl alloys are still unclear although the alloys is one of well-known SMA that was found early and several explanations were applied. In this papers the physical properties and features related to SME of all shape memory binary alloys (SMBA) that exhibit not only perfect shape recovery but also partial shape recovery are compiled from published papers and then classified according to the crystal structures of austenite and martensite phases. Meanwhile, we focus on the binary alloys, not trinary and more, in order to avoid the arguments and efforts to be too complicated. The shape recovery, MT temperature, combination and solubility of each element of SMBA are investigated in detail, and consequently reconsideration for the conditions of SME. Consequently, 30 kinds of SMBA can be divided into three groups, B2 type, A2 type and A1 type according to the crystal structures of parent phase. On B2 type SMBA there are two categories reduced from the combination of elements. The alloy has the ordered crystal structure at parent phase and exhibits thermoelastic martensitic transformation might take higher performance of shape recovery. The advantage of twinning deformation on B2 and A2 type SMBA is considered that the identity of plane and direction between twinning and slipping. On A1 type SMBA except for In-based SMBA the movement of an atom stop at the partial dislocation site since the constraint is induced due to magnetization. The stopping movement means twinning instead of slipping. This classification is useful for considering the character of SMBA.
4:45 PM - II4.8
Meta-stable Behavior of Cu-Al-Ni Functional Intermetallics, Studied by Mechanical Spectroscopy and "in situ" TEM Heating.
Jose San Juan 1 3 , Alfonso Ibarra 2 , Angel López-Echarri 1 , Eduardo Bocanegra 2 , Maria Nó 2
1 Fisica Materia Condensada, Universidad del Pais Vasco, Bilbao Spain, 3 Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Fisica Aplicada II, Universidad del Pais Vasco, Bilbao Spain
Show Abstract5:00 PM - II4.9
High-throughput Characterization of Ternary Ni-Ti-X Shape Memory Thin Films using Automated Temperature-dependent Resistivity Measurements.
Robert Loebel 1 2 , Sigurd Thienhaus 1 2 , Alfred Ludwig 1 2
1 Combinatorial Materials Science, caesar, Bonn Germany, 2 Institute of Materials, Ruhr-University, Bochum Germany
Show AbstractShape memory alloy (SMA) thin films are used as actuator materials in MEMS due to their high energy density. Whereas binary thin films with compositions close to Ni50Ti50 are well-established, ternary systems like NiTiCu, NiTiPd, NiTiHf are less studied. Furthermore new alloys are developed which show a magnetic shape memory effect, e.g. NiMnGa. Here, we present a fast and reliable characterization technology for the optimization of known and the development of new SMA thin films, which yields rapidly the transformation temperatures (i.e. martensite and austenite start and finish temperatures and the thermal hysteresis of the investigated thin films) over a whole wafer. In this paper, automated temperature-dependent resistivity measurements from ternary Ti-Ni-X thin films (X=Cu, Pd, Au, Fe) deposited in the form of materials libraries, are presented. The development goal in theses systems is to achieve a minimized thermal hysteresis and adjustable transformation temperatures.
5:15 PM - II4.10
Control and Characterization of Grain Boundary in B2 Type Ti-Ni Alloy.
Minoru Nishida 1 , Mitsuhiro Matsuda 1 , Akinori Kakisaka 1 , Sadahiro Tsurekawa 2
1 Materials Science and Engineering, Kumamoto University, Kumamoto Japan, 2 Mechanical Engineering, Tohoku University, Sendai Japan
Show Abstract5:45 PM - II4.12
Internal Structure of B19 Martensite in TiAu Shape Memory Alloy.
Tomonari Inamura 1 , Ryosuke Tachi 2 , Kenji Wakashima 1 , Hideki Hosoda 1
1 Precision and Intelligence Laboratory, Tokyo Institute of Technology, Yokohama Japan, 2 Graduate Student, Tokyo Institute of Technology, Yokohama Japan
Show AbstractInternal structures of B19 martensite in TiAu binary alloy were examined by transmission electron microscopy (TEM) observation and phenomenological theory of martensite crystallography (PTMC) in this study.The equi-atomic TiAu alloy has the B2-B19 martensitic transformation at about 900K. Our group have confirmed that TiAu alloys exhibit shape memory effect (SME) and superelasticity (SE). SME and SE properties are essentially determined by the crystallography of the martensitic transformation. There are, however, few reports of crystallographic features of martensite in this alloy system. X-ray diffraction (XRD) analysis at room temperature (RT) showed that crystal structure of the martensite is B19 (orthorhombic) with lattice parameters of 0.294nm, 0.490nm and 0.463nm for equi-atomic TiAu. The lattice parameter of B2 phase was extrapolated to be 0.326nm for RT. The principal strains were calculated with assuming AuCd type lattice correspondence and were diag{-0.098, +0.063, +0.004}. PTMC analysis showed that the martensite plate becomes 'stress-free' relative to the surrounding matrix when internal twin of {111} type I twin or <211>type II twin is introduced with volume fraction of about 0.1. Internal structure of the martensite was examined by TEM and obtained results were discussed on the basis of the crystallographic theory.
II5: Poster Session
Session Chairs
Helmut Clemens
David Morris
Masao Takeyama
Jörg Wiezorek
Wednesday AM, November 29, 2006
Exhibition Hall D (Hynes)
9:00 PM - II5.1
On the Massive Transformation in High Niobium Containing TiAl Alloys.
Christina Scheu 1 , Limei Cha 1 , Harald Chladil 1 , Helmut Clemens 1 , Arno Bartels 2 , Walter Wolf 3 , Raimund Podloucky 4 5
1 Department of Physical Metallurgy and Materials Testing, University of Leoben, Leoben Austria, 2 Materials Science and Technology, TU-Hamburg-Harburg, Hamburg Germany, 3 , MaterialsDesign s.a.r.l, Le Mans France, 4 Institut für Physikalische Chemie, University of Vienna, Vienna Austria, 5 , Center for Computational Materials Science, Vienna Austria
Show Abstract9:00 PM - II5.10
Synthesis of FeAl Hetero-Nanostructured Bulk Parts via Spark Plasma Sintering of Milled Powder.
Thierry Grosdidier 1 , Gang Ji 1 , Frederic Bernard 2 , Sebastien Launois 3
1 Material Science - LETAM, University Paul Verlaine, Metz France, 2 Material Science - LRRS, University of Dijon, Dijon France, 3 Département de Technologie pour l'Energie et les Nanomatériaux, Commissariat à l'Energie Atomique, Grenoble France
Show Abstract9:00 PM - II5.11
TEM Observation of Vacancy Clustering Process in FeAl Single Crystal.
Masafumi Tsunekane 1 , Kyosuke Yoshimi 1 , Kouichi Maruyama 1
1 Graduate School of Environmental Studies, Tohoku University, Sendai Japan
Show AbstractNanoporous surfaces were formed in B2-type FeAl single crystals by quenching into iced water, followed by surface treatment and aging heat treatment. It was indicated from our previous works that the nanoporous phenomenon is caused by the clustering of supersaturated thermal vacancies. The clustering process of supersaturated thermal vacancies was systematically observed by transmission electron microscopy (TEM). The pore size and density were changed with changing heat treatment parameters such as quenching temperature, aging temperature and aging time. An exothermic irreversible peak was detected in as-quenched specimens by differential scanning calorimetry (DSC). The isochronal change of surface morphology and substructure around the exothermic peak temperature was further observed by TEM. Average pore size monotonously increased with increasing the temperature. A certain number of dislocations whose Burgerse vectors are parallel to <100> existed in the isochronally heated single crystals, and dislocation density was changed corresponding to the temperature. On the other hand, there was no dislocation zone just from surface to several tens nanometers in depth. These results confirm that the nanoporous phenomenon is caused by the clustering of supersaturated thermal vacancies. A growth model of vacancy clusters is proposed based on the obtained results.
9:00 PM - II5.12
Surface and Bulk Characterization of a Fe-40Al (% at.) Intermetallic in as-cast Condition.
Roberto Diaz 1 , Julio Islas 1
1 , UNAM, Mexico DF Mexico
Show Abstract9:00 PM - II5.13
Line Width Broadening, Peak Shifts and the Equation of State of Plastically Deformed Solids Under Uniaxial Stresses.
John Vassiliou 1 , J. Otto 2 , G. Frommeyer 3
1 Physics, Villanova University, Villanova, Pennsylvania, United States, 2 , Joint Research Center for the European Commission, Brussels Belgium, 3 , MPI Eisenforschung, 40237 Dusseldorf Germany
Show Abstract9:00 PM - II5.14
Synthesis, Microstructure, and Mechanical Properties of FeCo-VC Composites.
Hongbin Bei 1 2 , Easo George 1 2
1 Materials Science and Technology Division, Oak Ridge national Labortory, Oak Ridge, Tennessee, United States, 2 Materials Science and Engineering, The Unversity of Tennessee, Knoxville, Tennessee, United States
Show Abstract9:00 PM - II5.15
Atomic Disorder and its Relation to the Magnetic Behavior in CoFe1-xAlx Alloys.
Tetsuya Fujiwara 1 , Shigeyuki Kikuchi 1 , Hiroki Ishibashi 1 , Mineo Kogachi 1
1 Department of Physical Science, Graduate School of Science, Osaka Prefecture University, Sakai, Osaka, Japan
Show Abstract In recent experimental study of CoFe1-xAlx system, we have reported an appearance of the B2-phase over wide ranges of composition x and temperature and that of the Heusler-phase around x=0.5 (Co2FeAl) at low-temperature. Further, the mean magnetic moment obtained as a function of quenching temperature TQ showed a decrease with increasing TQ in the B2-phase in x<0.4, while it remained constant in the Heusler-phase. For understanding such magnetic behavior, in the present study, degree of atomic disorder is investigated for both phases in CoFe1-xAlx alloys. Integrated intensity measurements of appropriate reflections in X-ray diffraction are performed for B2 and Heusler alloys quenched from various temperatures (773K to 1173K) for determining the long-range order parameters S1 and S2. S1 gives a measure of degree of atomic disorder on the Co-site (Co-type disorder) and S2 gives that of atomic disorder between the Fe- and Al-sites (Fe-Al-type disorder). In the B2-phase alloy (x=0.30), S1 shows a decrease with increase in TQ, indicating that the Co-type disordering proceeds with increase in temperature (in this phase, S2=0 because of complete disorder between the Fe- and Al-sites). In the Heusler-phase region (x=0.45, 0.50 and 0.55), no difference in S1 is found between two samples quenched from TQ=773K and 873K (the value of S1 is 1, i.e., Co atoms exclusively occupy the Co-site), while S2 for 873K is smaller than that for 773K, indicating that the Fe-Al-type disordering mainly proceeds with increase in temperature. From present results, it is shown that the Fe-Al-type disorder does not affect the magnetic moment of the Heusler-phase alloys but the Co-type disorder leads to its reduction in the B2-phase alloys. These are discussed noting the recent theoretical studies of atomic disorder effect on the magnetism in Co-based Heusler alloys Co2YZ (e.g., Y=Cr, Mn and Z=Al, Si).
9:00 PM - II5.16
Evolution and Interaction of Dislocations in B2 Intermetallics: Fully Anisotropic Discrete Dislocation Dynamics Simulations.
Qian Chen 0 , Bulent Biner 0
0 Ames Laboratory, Iowa State University, Ames, Iowa, United States
Show Abstract9:00 PM - II5.17
Phase Equilibria among α-Fe, γ-Fe and Fe2Mo Phases and Stability of the Laves Phase in Fe-Ni-Mo Ternary System at Elevated Temperatures.
Shigehiro Ishikawa 1 , Shingo Okamoto 1 , Takashi Matsuo 1 , Masao Takeyama 1
1 Metallurgy and Ceramics Science, Tokyo Institute of Technology, Tokyo Japan
Show Abstract9:00 PM - II5.18
UFG to NC FePd by Combined Reaction Transformation Mode of Severely Plastically Deformed gamma – FePd.
Vincent Sokalski 1 , Andreas Kulovits 1 , Jorg Wiezorek 1
1 MSE, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
Show AbstractPrevious studies have shown that equiaxed ultra fine grained (UFG) L1o-ordered FePd can be produced by ordering phase transformation of heavily cold-rolled austenitic fcc-FePd. As the magnetic properties can be improved by suppression of the polytwinned micro-constituent formed by the conventional ordering mode it is anticipated that further grain refinement from UFG scale leads to further property enhancement. In order to reduce the grain size further fcc-severely plastically deformed austenitic FePd has been phase transformed during isothermal annealing after severe plastic deformation by equal channel angular pressing (ECAP). The property, defect and texture evolution during the deformation process and during the morphological changes accomplished by the phase transformation during isothermal annealing below the ordering temperature have been monitored using SEM, XRD, TEM, hardness and magnetic property measurements. Processing-structure-property relations are discussed and compared to previous studies using other deformation processing routes. Support from NSF-DMR-Metals is gratefully acknowledged.
9:00 PM - II5.19
Microstructural Characterization of the Novel Alloys in the FeCoMnAl System.
Johnathan Loudis 1 , I. Baker 1 , S. Lish 1 , C. Zhang 1
1 Thayer School of Engineering, Dartmouth College, Hanover, New Hampshire, United States
Show AbstractThere is interest in developing soft magnetic alloys suitable for high-temperature, magnetic-mechanical applications. To this end, we have investigated several FeCoMnAl alloys. Some of these alloys have been found to display coercivities of ~1 Oe and magnetizations of ~ 200 emu/g at room temperature, and coercivities <5 Oe and magnetizations of ~160 emu/g up to 700 degrees Celcius. TEM studies have shown evidence of microstructures resulting from both precipitation and growth mechanisms as well as spinodal decomposition. Precipitates often display a Beta-Mn structure within a B2 matrix. The alloys formed by spinodal decomposition consist of a fine nanostructure of alternating B2 and BCC phases. This poster summarizes the microstructures for various alloy compositions and heat treatments, and the resulting magnetic and mechanical properties. This project was funded by an NSF Graduate Research Fellowship and NIST grant 60NANB2D0120.
9:00 PM - II5.2
Compression and Compressive Creep Behaviors in Titanium Aluminides alloyed with Vanadium comprizing Gamma+Beta Dual Phase Microstructures.
Tohru Takahashi 1 , Yohji Kojima 2 , Koshiro Otsuka 2
1 Dept. Mechanical Systems Engg., Tokyo Univ. Agric. & Tech., Koganei, Tokyo, Japan, 2 Graduate Student, Tokyo Univ. Agric. & Tech., Koganei Japan
Show AbstractFine grained gamma+beta dual phase microstructures were obtained in aluminum-titanium-vanadium ternary alloys containing 40 at.% aluminum and 60 at.% (titanium and vanadium). Average grain size was about 5, 3, and 2 micrometers in the recrystallized materials containing 20, 30, and 40 at.% vanadium, respectively. The phase constitution was around 50 vol.% gamma phase and 50 vol.% beta phase. Compression behavior was investigated at temperatures ranging from the room temperature up to 1200K, and compressive creep tests were carried out at 1050-1200K in order to characterize the temperature and chemical composition dependence of strength and deformation. These gamma+beta microduplex materials showed very high strength at room temperature; 0.2% proof stress was around 1200MPa. The compression deformability decreased from about 0.2 to 0.05 true strain with increasing vanadium content. The grain size effect was not clarified yet, but it was rather disappointing that smaller-grained material with Al40Ti20V40 composition did not show effective improvement either in strength or in deformability. The 0.2% proof stress showed a considerable weakening at temperatures higher than 900K; the onset temperature of softening became lower as the vanadium content increased. In the Al40Ti40V20 material with about 5 micrometer grains, both gamma and beta grains were flattened up to 1000K, however, above 1100K the gamma grains showed no significant shape change even after a heavy deformation. This is probably because the gamma grains were relatively stronger than the beta grains. The gamma grains showed tendency toward agglomeration, which is similar to the rafting of precipitate particles in superalloys. Surface relief was observed after high temperature deformation suggesting activity of boundary sliding on grain boundaries and interfaces. Compressive creep behavior was investigated under a constant true stress in vacuum. Creep curves consisted of a small amount of normal primary transient, the minimum creep rate region, and a steady or slightly accelerating creep region. Stress exponent decreased to about 2 with decreasing vanadium content. It was rather unexpected that smaller grained Al40Ti20V40 material showed larger stress exponent around 3.
9:00 PM - II5.20
Plastic Deformation Behavior of Oriented Ni3V Crystals with D022 Structure.
Koji Hagihara 1 , Mayumi Mori 1 , Yukichi Umakoshi 1
1 Division of Materials and Manufacturing Science, Graduate School of Engineering, Osaka University, Suita, Osaka, Japan
Show AbstractThe Ni3X-type intermetallic compounds are known to crystallize in various geometrically close-packed (GCP) crystal structures depending on the kind on X atom. We recently found that the yield stress anomaly (YSA) appears not only in L12-Ni3Al but also in other hcp-based GCP compounds such as D0a-Ni3Nb, D024-Ni3Ti and D019-Ni3Sn. Therefore, they also have a possibility for a strengthening phase. The multi-phase alloys composed of these GCP compounds have been investigated as a new class of high-temperature structural material [For example, Y. Nunomura, Y. Kaneno, H. Tsuda, T. Takasugi; Acta materialia, 54 (2006) 851.]. In this study, the plastic deformation behavior of Ni3V with the D022 structure, which is an important component in the Ni-based multi-phase alloys, was examined using the oriented crystals grown by the floating zone (FZ) method. The temperature dependences of plastic behavior, operative slip system and dislocation structure were investigated, and these properties were discussed comparing with other Ni-based GCP compounds. Master ingots with a composition of stoichiometric Ni-25at.%V were prepared by arc-melting. Single crystals were grown by the FZ method at a growth rate of 2.5 mmh-1 under an Ar gas flow. The gained crystals are regarded to be single crystals when indexed as fcc-based crystal, but it was clarified in the TEM observation that the crystals contain three variants of Ni3V whose c-axes aligned perpendicular to each other, due to the ordered-disordered transformation of Ni3V at 1318K. The volume fraction of the three variants was not equal in the FZ-grown crystals. Two of three variants particularly formed the lamellar structure with the interface on {101] in the FZ-grown crystals and the volume fraction of another variant was very small. Rectangular specimens with dimensions of approximately 2x2mm2x5mm were prepared from the as FZ-grown crystals, and compression tests were performed in a temperature range from 77 to 1173K in vacuum. Several different loading axes were chosen and the orientation dependence of plastic deformation behavior was examined. Dislocation structures were observed in a JEOL JEM-3010 transmission electron microscope (TEM) operated at 300kV.Three operative deformation modes of {111}1/6<112] twinning, {111}<110] and {111}1/2<112] slips were identified. The former two systems were dominantly operative at low temperatures and the latter was operative at high temperatures above 873K. The slip on (001) was not macroscopically observed in this study. The effect of microstructure on the plastic behavior and the yield stress was also examined with the annealed crystals with different variant morphology.
9:00 PM - II5.21
Microstructural Evolution of Dual Multi-Phase Intermetallic Alloys Composed of GCP Ni3Al and Ni3V Phases Containing Ti.
Takayuki Takasugi 1 2 , Yasuyuki Kaneno 1 , Hiroshi Tsuda 1
1 Department of Materials Science, Graduate School of Engineeering, , Osaka Prefecture Univrersity, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka Prefecture, Japan, 2 Osaka Center for Industrial Materials Research, Institute for Materials Research, Tohoku University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka Prefecture, Japan
Show AbstractThe microstructural evolution of intermetallic alloys, which have dual two-phase microstructure composed of Ni3Al (L12) and Ni3V (D022) phases, was investigated as a function of aging time at 1273K, using transmission electron microscopy and X-ray diffraction. Even from early aging time, the lower (i.e. eutectoid) microstructure showed structurally decomposed clusters composed of L12 phase and three D022 variant structures. With proceeding aging time, the decomposed L12 and D022 phases coarsened and transformed to lamellar-like microstructures where two types of interfaces between the L12 and D022 phases, and between two different D022 variant structures were developed. At longer aging time, the L12 phase disappeared from the lamellar-like microstructure and alternatively the D022 phase composed of two different variant structures prevailed over the lamellar-like microstructures. Corresponding to this microstructural change, the direction of the lamellar and its interfacial plane rotate (i.e. change) from <001> to <011> and from {001} to {011}, respectively. At a final aging stage, a specific set of two different D022 variant structures tend to expend other set of two different D022 variant structures.
9:00 PM - II5.22
Wear Behavior Related to Microstructures of Ni3Al-based Materials.
Karin Gong 1 , Heli Luo 2 , Erik Strom 1 , Changhai Li 1
1 Materials and Manufacturing Technology, Chalmers University of Technology, Göteborg Sweden, 2 Structural Materials Research, Central Iron & Steel Research Institute, Beijing China
Show Abstract9:00 PM - II5.23
Role of Topologically Close Packed Phase Precipitates in Ductilizing Cr-Re and Mo-Re Alloys.
Oleg Kontsevoi 1 , Nadezhda Medvedeva 2 , Yuri Gornostyrev 3 , Arthur Freeman 1
1 Physics & Astronomy, Northwestern University, Evanston, Illinois, United States, 2 , Institute of Solid State Chemistry, Ekaterinburg Russian Federation, 3 , Institute of Metal Physics, Ekaterinburg Russian Federation
Show Abstract9:00 PM - II5.24
Combustion Synthesis of Single-Walled Carbon Nanotube Reinforced Nickel Aluminides.
Lori Groven 1 , Brian Glover 2 , Jan Puszynski 1
1 Chemical and Biological Engineering, SDSM&T, Rapid City, South Dakota, United States, 2 Electrical Engineering, SDSM&T, Rapid City, South Dakota, United States
Show AbstractCombustion synthesis method was investigated for fabrication of single-walled carbon nanotube (SWNT) reinforced nickel aluminide composites using both uncoated and electrolessly nickel coated SWNT's. Simultaneous combustion synthesis and densification experiments were carried out in a uniaxial press to obtain dense SWNT reinforced composites with densities greater than 92 % of the theoretical one. It was demonstrated that SWNT's are not damaged during a short exposure to high temperature generated during the gasless combustion synthesis of SWNT-nickel aluminide composites. It has been demonstrated that SWNT's act as a diluent and simultaneously inhibit grain growth while adding structural reinforcement. The effect of several key processing parameters such as initial size of reactants (nanometer to micron), weight fraction of SWNT loading, SWNT coating characteristics, and temperature-pressure conditions on morphology of combustion synthesized product, their phase composition, residual porosity, and microhardness were investigated and will be discussed in detail.
9:00 PM - II5.25
Tensile Property of Cold-Rolled Foils of Ni-Based and Co-Based L12 Intermetallic Alloys.
Yasuyuki Kaneno 1 , Takayuki Takasugi 1 2 , Tadamichi Myoki 1
1 Department of Materials Science, Osaka Prefecture University, Sakai, Osaka, Japan, 2 Osaka Center for Industrial Materials Research, Institute for Materials Research, Tohoku University, Sakai, Osaka, Japan
Show AbstractPolycrystalline L12-type Ni3(Si,Ti), Ni3Al and Co3Ti prepared through the thermomechanical process of arc-melted ingots were successfully cold-rolled to thin foil with a thickness of below 200μm. The cold-rolling with over 90% reduction in thickness was possible without any intermediate annealing. Tensile property of the rolled foils was investigated as a function of annealing temperature as well as testing temperature. These three alloys showed high tensile strength (~2GPa) at room temperature due to heavily cold-rolling although no plastic elongation was observed. When the rolled foils were annealed, tensile strength generally decreased, accompanied with a certain level of tensile elongation. Tensile elongation increased with increasing annealing temperature, and reached to ~30-40% by high temperature annealing at 1173K. In the case of Ni3(Si,Ti) foil, intermediate temperature annealing (i.e. around at 873K) yielded an extremely high tensile strength and proof strength (over 2GPa) with a reasonable tensile elongation. On the other hand, it was found that the fully-recrystallized foils of Ni3(Si,Ti) and Co3Ti showed a strength anomaly at intermediate testing temperature (i.e., positive temperature dependence of proof strength). The observed tensile properties, especially tensile strength at low temperature as well as at high temperature for the present L12 intermetallic foils were found to be superior to those for the conventional alloys such as stainless steels and nickel based alloys.
9:00 PM - II5.26
Phase-separations of Coherent Precipitates of Ordered Phases in Elastically Constrained Alloys.
Minoru Doi 1 , Hiroshi Kumagai 1 , Kanako Nakashima 1 , Takao Kozakai 1
1 Materials Science and Engineering, Nagoya Institute of Technology, Nagoya Japan
Show Abstract9:00 PM - II5.27
Microstructure and Mechanical Properties of Dual Multi-Phase Intermetallic Alloys Composed of GCP Ni3Al and Ni3V Phases containing Nb.
Wataru Soga 1 , Yasuyuki Kaneno 1 , Takayuki Tkasugi 1 2
1 , Department of Materials Science, Graduate School of Engineering, Osaka Prefecture University, Sakai, Osaka, Japan, 2 , Osaka Center for Industrial Materials Research, Institute for Materials Research, Tohoku University, Sakai, Osaka, Japan
Show AbstractDual multi-phase intermetallic alloys, which are composed of Ni3Al (L12) and Ni solid solution (A1) phases at high temperature annealing and are additionally refined by a eutectoid reaction at low temperature aging, according to which the Al phase is transformed into the Ni3Al (L12)+Ni3V (DO22) phases, were prepared based on the pseudo-ternary system Ni3Al-Ni3Nb-Ni3V. The high-temperature tensile deformation, fracture behavior, and compression and tension creep were investigated using polycrystalline and single crystalline materials. The alloys with such a novel microstructure show extremely high yield and tensile strength with good temperature retention, and also reasonable tensile ductility, when compared with conventional Ni-based superalloys. The creep test conducted at high temperature showed extremely low creep rate and long creep rupture time when compared with conventional Ni-based superalloys. The obtained results are promising for the development of a new-type of high-temperature structural material.
9:00 PM - II5.28
The Broadening of Crystallographic Orientation Distribution in Crept Ni-base Superalloys.
Toru Inoue 1 , Katsushi Tanaka 1 , Haruyuki Inui 1
1 Materials Scinence and Engineering, Kyoto University, Kyoto Japan
Show Abstract9:00 PM - II5.29
Formation Process of Rhenium-Base Diffusion Barrier on a Nickel-Base Superalloy.
Yongming Wang 1 , Takanori Suda 1 , Shigenari Hayashi 1 , Somei Ohnuki 1 , Toshio Narita 1
1 , Hokkaido University, Sapporo Japan
Show Abstract9:00 PM - II5.3
Effect of Cooling Rate and Composition on Lamellar Microstructure and Creep Resistance of TiAl Alloys.
Hanliang Zhu 1 , Dongyi Seo 2 , Kouichi Maruyama 1 , Peter Au 2
1 Graduate School of Environmental Studies, Tohoku University, Sendai Japan, 2 Institute for Aerospace Research, National Research Council Canada, Ottawa, Ontario, Canada
Show Abstract9:00 PM - II5.30
Effect of Heat Treatment on the Ductility of Ni(γ)/Ni3Al(γ') Two-phase Alloy Foils.
Motonori Nakamura 1 2 , Toshiyuki Hirano 2 1 , Masahiko Demura 2 , Ya Xu 2
1 Graduate School of Pure and Applied Physics, Unibersity of Tsukuba , Tsukuba, Ibaraki, Japan, 2 Fuel Cell Materials Center, National Iustitute for Materials Science, Tsukuba, Ibaraki, Japan
Show Abstract We have developed thin foils of Ni(γ)/Ni3Al(γ') two-phase alloys by cold rolling for high-temperature micro chemical reactors. As-rolled foils are brittle, showing low tensile elongation less than 1%, and thus poor in formability.However, we consider that it is possible to improve the ductility by heat treatment, similar to the case in γ' single-phase Ni3Al foils (Cui et al. 2005). In the present paper, we examine the effect of heat treatment on the mechanical properties of the γ/γ’ two-phase alloys foils. The 95% cold-rolled foils of the γ/γ’ two-phase alloys (Ni-18.0 at.% Al) were heat-treated at temperature ranging from 873 K to 1273 K for 0.5 h. The microstructure was observed by optical microscopy and scanning electron microscopy (SEM). The orientations of recrystallized grain were measured by the electron backscatter diffraction (EBSD) method. The cold-rolled and the recrystallized textures were measured by the X-ray Schultz back reflection method. Tensile tests were preformed at room temperature in air at a nominal strain rate of 8.3 × 10-4 s-1. Recrystallization started at 873 K: equiaxed grains were partly observed and the recrystallization texture was different from that of the cold-rolled texture. The SEM observation and the EBSD measurements revealed that the recrystallization completed at 1273 K. The recrystallization rate is slow in the two-phase foils, compared with the single-phase foils where recrystallization completed at 873 K/0.5 h. The recrystallized grains contained coherent precipitates of γ’ in the γ matrix. In tensile test, the cold-rolled foils fractured without showing yielding. They became ductile by heat treatment. The foils showed a fracture elongation of 0.6% after heat treatment at 873 K and that of about 10% after heat treatment at 1073 K. In the fully recrystallized foils, which were heat-treated at 1273 K, the fracture elongation reached about 14% associated with large decrease in yield stress. Thus, it turned out that the ductility is improved in the γ/γ’ two-phase foils as the recrystallizaion progresses. This is in marked contrast to the behavior of the γ' single-phase foils: they are brittle just after the recrystallization and the ductility improvement is achieved with the subsequent grain growth.
9:00 PM - II5.31
Dynamics of Ultrafast Laser Induced Damage in Single Crystal Ni-based Superalloy During Machining.
Joel McDonald 1 , Shuwei Ma 2 , John Nees 3 , Chi-Sheng Yu 2 , Katsuyo Thornton 2 , Tresa Pollock 2 , Steven Yalisove 2
1 Applied Physics, University of Michigan, Ann Arbor, Michigan, United States, 2 Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States, 3 Center for Ultrafast Optical Science, University of Michigan, Ann Arbor, Michigan, United States
Show AbstractPump-probe imaging of ultrafast-pulsed laser ablation was performed to investigate mechanical shock induced damage in an intermetallic alloy (CMSX-4) during femtosecond laser machining. Mechanical shock is generally observed during ultrafast ablation in materials. Previously, this has been studied with interferometric techniques such as VISAR or with shadowgraph imaging of the air shock that forms at the backside when a shock wave exits a material. This permits the measurement of the amplitude of the shock wave after dispersion though the material. Measurement of the pressure at the front of the material has been elusive. We will demonstrate a method to infer the pressure-time relationship at the (remaining) surface during ablation. Measuring the amount of material removed by the ablation event and also measuring the velocity of the ejected material provides the momentum transfer away from the front surface of the material. This, in turn, permits the determination of momentum transfer (pressure) into the material. The velocity of the material front is provided by shadowgraphic imaging along with dual-pulse laser induced breakdown spectroscopy and front-view pump-probe interference imaging of the ablation (time range: 0 – 10 nanoseconds following onset of ablation, time resolution: 150 femtoseconds). Atomic force microscopy (AFM) images of the crater left in the material after the ablation event provides a measurement of the mass removed. These data are compared to a one-dimensional radiation hydrodynamic model (HYADES) in a Ni sample. In addition, focused ion beam prepared cross section samples, directly below the irradiated zone, are studied in a transmission electron microscope. The defects that are observed will be discussed in the context of the dissipative component of the mechanical shock as it traverses a material.
9:00 PM - II5.32
Microstructure and Mechanical Properties of Multi-Phase Intermetallic Alloys Composed of GCP Ni3X (X:Si, Ti and Nb) Phases.
Masayoshi Fujita 1 , Yasuyuki Kaneno 1 , Takayuki Takasugi 1 2
1 , Department of Materials Science, Graduate School of Engineering, Osaka Prefecture University, Sakai, Osaka, Japan, 2 , Osaka Center for Industrial Materials Research, Institute for Materials Research, Tohoku University, Sakai, Osaka, Japan
Show AbstractMicrostructure, high-temperature tensile deformation and fracture behavior of multi-phase intermetallic alloys, which were based on Ni3Si-Ni3Ti-Ni3Nb pseudo-ternary alloy system and composed of geometrically close packed (GCP)-L12, D024 and D0a phases, were investigated. It was found that Ni3Si (L12) alloys were age-hardenable due to the precipitation of the Ni3Ti(D024) and/or Ni3Nb(D0a) phases. The plate-like, i.e.,Widmansttaten-like Ni3Ti (D024) phases were precipitated from L12 matrix by a solid-state reaction at high temperature, accompanied with a certain orientation relationship and habit plane, and consequently resulted in an increase and a subsequent peak of hardness or strength. The Ni3Si-based intermetallic alloys with such an optimized multi-phase microstructure showed favorable yield and tensile strength, and also reasonable tensile ductility over a wide range of temperatures.
9:00 PM - II5.33
Microstructure Control of Nb-Si Alloy Doped with Zr and Mg through Eutectic and Eutectoid Reactions and its Deformation Behavior.
Seiji Miura 1 , Yuki Murasato 1 , Kenji Ohkubo 1 , Yoshisato Kimura 2 , Nobuaki Sekido 3 , Yoshinao Mishima 2 , Tetsuo Mohri 1
1 Mat. Sci. and Eng., Hokkaido University, Sapporo, Hokkaido, Japan, 2 Mat. Sci. and Eng., Tokyo Institute of Technology, Yokohama, Kanagawa, Japan, 3 Mat. Sci. and Eng., University of Wisconsin-Madison, Madison, Wisconsin, United States
Show Abstract9:00 PM - II5.34
Effect of Hf and Cr Additions on the Phase Equilibria of the Nb-Si and Nb-Ti-Si Systems.
Bernard Bewlay 2 , Ying Yang 1 , Y. Chang 3
2 , GE global research center, Niskayuna, New York, United States, 1 , CompuTherm LLC, Madison, Wisconsin, United States, 3 , University of Wisconsin-Madison, Madison, Wisconsin, United States
Show AbstractNb-silicide based in-situ composites are promising materials for future high-temperature structural applications. Nb-silicide composites are typically alloyed with Hf, Ti, Cr and Al to provide a balance of mechanical and environmental properties. Phase equilibria of the Nb-Ti-Si system have been extensively studied in literature. However, effect of Hf and Cr additions on the phase equilibria of the Nb-Si and Nb-Ti-Si systems is not well understood. In the present study, thermodynamic descriptions of Nb-Ti-Si-Hf and Nb-Si-Cr were developed based on available binary and ternary experimental data using the CALPHAD approach. Effect of Hf and Cr additions on the phase equilibria of the Nb-Si and Nb-Ti-Si systems was illustrated by the calculated phase equilibria from the developed thermodynamic descriptions. The calculated phase equilibria can be validated by available experimental results.
9:00 PM - II5.35
Toughening Effect and Oxidation Behavior of MoSi2 -ZrO2 Composites.
Karin Gong 1 , Erik Strom 1
1 Materials and Manufacturing Technology, Chalmers University of Technology, Göteborg Sweden
Show AbstractTransformation toughening effect of ZrO2-addition has been recognized as an important toughening mechanism in MoSi2-based materials. In this study, the influence of particle size and volume percentage on toughening effect in MoSi2-matrix composites reinforced by unstabilized ZrO2-addition were investigated. The observed data indicated that the fine particle size of less than 1 μm and 15-25 vol.% addition showed effective toughening results. Three different sintering processes: pressure-less sintering (PLS), hot-press sintering (HPS) and PLS + HIPing sintering, were used to prepare the testing composites in this investigation. The measured data on sintered density, RT-hardness and RT-toughness revealed that the PLS process could be a practical and economical method for producing MOSi2-ZrO2 composites in industry. Oxidation behavior of MoSi2-ZrO2 composites was also observed in the work. Clearly, the ZrO2-addition made the composites having a low oxidation resistance, which means that a low ZrO2-addition should be used in the composites, as far as an acceptable toughening effect was reached.
9:00 PM - II5.36
Thermal Stability of Binary Cr-Cr3Si and Ternary NiAl-Mo Eutectic Alloys.
Aravind Gali 1 , Hongbin Bei 1 2 , Easo George 2 1
1 Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee, United States, 2 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show Abstract9:00 PM - II5.37
Crystal Structures and Thermoelectric Properties of Ru1-xRexSiy Chimney-Ladder Compounds.
Akira Ishida 1 , Norihiko Okamoto 1 , Kyosuke Kishida 1 , Katsushi Tanaka 1 , Haruyuki Inui 1
1 Department of Materials Science and Engineering, Kyoto University, Kyoto Japan
Show AbstractSemiconducting Ruthenium sesquisilicide, Ru2Si3 has been attracting a large attention as a high-temperature thermoelectric material because of its high Seebeck coefficient and low thermal conductivity. Ru2Si3 crystallizes into two different types of structures: the tetragonal-type high-temperature (HT) phase and the orthorhombic-type low-temperature (LT) phase. The HT Ru2Si3 phase has the so-called chimney-ladder structure, which is composed of two types of subcell: transition metal (M) atoms in a tetragonal β-Sn arrangement and group 14 or 13 atoms (X) in a coupled helical arrangement, with both the chimney and ladder being aligned along the c-axis of the tetragonal unit cell. This chimney-ladder compound has a composition (X/M ratio) that is related to the c-axis dimension of the X subcell (CX). Since the chimney-ladder compounds are known to be electron compounds following an valence electron counting rule: VEC=14, the crystal structure and therefore intrinsic physical properties are expected to be controlled by alloying with a substitutional element, especially when the number of valence electrons of alloying element is different from that of Ru. In this study, we investigated the phase relationship of Re-alloyed Ru2Si3 and studied the variations of the crystal structures and thermoelectric properties of the Ru1-xRexSiy chimney-ladder compounds as a function of the Re concentration.
The Ru1-xRexSiy chimney-ladder phases are confirmed to be formed in a wide compositional range by a stabilization of the HT Ru2Si3 chimney-ladder phase through the substitution of Ru with Re. Compositional formula of the chimney-ladder phases are determined to be Ru1-xRexSi1.5386+0.1783x (0.14≦x≦0.76), which are deviated from the idealized composition conforming the valence electron counting rule: VEC=14. Using the VEC=14 rule for predicting the semiconducting behavior, adjustment of the group number of the M-site elements might be used to alter the VEC, producing p-type semiconductors for VEC<14 and n-type for VEC>14, with the carrier concentration related to the deviation from VEC=14. Thermoelectric properties measured using single crystals with different compositions are consistent well with this predicted behavior, with n-type semiconducting behavior at low Re concentrations and p-type semiconducting behavior at high Re concentrations.
9:00 PM - II5.38
Thermoelectric Properties of ZrNiSn Based p-type Half-Heusler Compounds.
Yoshikatsu Goda 1 , Hiroaki Muta 1 , Takanori Kanemitsu 1 , Ken Kurosaki 1 , Shinsuke Yamanaka 1
1 Graduate School of Engineering, Osaka University, Suita, Osaka, Japan
Show Abstract9:00 PM - II5.4
Characterization of β-Ti Phase Precipitated Within Lamellae along The Transformation Pathway of α → γ and β in Gamma TiAl Alloys.
Masao Takeyama 1 , Hiroaki Fukushima 1 , Takashi Matsuo 1
1 Metallurgy and Ceramics Science, Tokyo Institute of Technology, Tokyo Japan
Show AbstractOur phase diagram study revealed the composition region with a transformation pathway from β-Ti (bcc) → α-Ti (hcp) through β+α two-phase region, followed by α→β+γ-TiAl(L10) through α+γ during cooling in any Ti-Al-M ternary system (M: β stabilizing elements). This phase transformation involving β phase enables us to tailor high strength wrought gamma alloys. The high-temperature β phase above the α single phase region is effective in facilitating hot working processes. In contrast, the low-temperature β phase below the α phase region plays a role in toughening the alloys since it can be finely dispersed within the lamellar microstructure by designed heat treatment using the decomposition of α phase (α→α+γ→β+γ). In this study, the formation mechanism of the bcc-β-Ti phase precipitated within the lamellae will be presented briefly, and the focus will be mainly placed on the characterization of the precipitated β phase in terms of transmission electron microscopy. The β phase nucleates at γ/γ interfaces in addition to the α/γ interfaces. The supersaturated M in the prior formed γ phase is responsible for the nucleation and growth of β phase. The observed β phase is bar shaped grown along six different directions on the γ/γ interfaces. The crystallographic orientation relationship between the two phases is Kurdjumov-Sachs (<1–11>β//<1–10>γ, {110}β//{111}γ). The electron tomography of the β phase revealed two sets of facets on either side of the γ phase along the preferred growth direction (PGD), and thus the morphology of the β phase is rectangular prism. The PGO is irrational of [–223]β, which is about 11° rotated from the <111>β//<1–10]γ toward [001]β. This direction is the least misfit direction, in good agreement with the calculation based on the lattice invariant theory.
9:00 PM - II5.40
Control of the Si Vacancy Concentration and Arrangement in ReSi1.75 by Al and P Additions.
Shunta Harada 1 , Kyosuke Kishida 1 , Katsushi Tanaka 1 , Haruyuki Inui 1
1 Department of Material Science & Engineering, Kyoto University, Kyoto Japan
Show AbstractSemiconducting rhenium disilicide ReSi1.75 is known as a promising material for thermoelectric applications. Binary ReSi1.75 exhibits significantly anisotropic thermoelectric properties such that the value of Seebeck coefficient along [100]C11b is positive (230μV/K at 330 K) while it is negative (-300μV/K at 600 K) along [001]C11b. This may result from the highly anisotropic electronic structure of ReSi1.75. The dimensionless figure of merit (ZT) for binary ReSi1.75 is as high as 0.7 at 1073 K when measured along [001]C11b while the ZT value along [100]C11b is moderate (0.15 at 900 K). So it is important to clarify the change of the crystal structure caused by substituting with the third element to improve this high dimensionless figure of merit.Various kinds of research results have been reported for the ReSi1.75 stoichiometry and the crystal structure. The crystal structure of rhenium disilicide has been reported as a tetragonal C11b (MoSi2-type, space group I4/mmm) structure and the stoichiometry was thought to be Re:Si=1:2. According to our recent analysis by electron diffraction and high-angular annual dark field scanning transmission electron microscopy (HAADF-STEM), however, the crystal structure is monoclinic with the space group of Cm due to an ordered arrangement of vacancies in Si sites in the underlying (parent) C11b structure. The semiconductive nature of this compound is explained by the value of VEC (Valence Electron Concentration for each metal atom).Moreover, upon substituting an element of rhenium and/or silicon with others, a concentration of Si vacancies changes so as to retain the average number of valence electron; the concentration of Si vacancies increase (decrease) upon substituting silicon with other elements having more (less) number of valence electron. Due to the change in the concentration of Si vacancies, the arrangement of Si vacancies is also changed. In this work, by using the HAADF-STEM method, we investigate the change in the arrangement of Si vacancies upon substituting silicon with aluminum and phosphorus. When silicon is substituted with aluminum, the concentration of Si vacancies decreases so as to compensate the less number of valence electron possessed by an aluminum atom. On the other hand, the concentration of Si vacancies increases upon substituting silicon with phosphorus because a phosphorus atom has more number of valence electron than silicon.
9:00 PM - II5.41
LnPdX (Ln = Lanthanide; X = Sb or Bi): High Performance Thermoelectric Intermetallics.
Takeyuki Sekimoto 1 , Ken Kurosaki 1 , Hiroaki Muta 1 , Shinsuke Yamanaka 1
1 , Division of Sustainable Energy and Environmental Engineering, Graduate School of Engineering, Osaka University, Suita, Osaka, Japan
Show Abstract9:00 PM - II5.42
Thermoelectric and Electrical Properties of InSb Thin FilmsPrepared by Metalorganic Chemical Vapor Deposition.
Masashi Matsumoto 1 , Jun Yamazaki 1 , Shigeo Yamaguchi 1 2
1 EEIE, Kanagawa University, Yokohama Japan, 2 HRC, Kanagawa University, Yokohama Japan
Show Abstract9:00 PM - II5.43
A Theoretical Investigation of Germanides of Pt and Ni: The Electronic Structure, Elastic Properties, Surface Energetics, and Work Functions.
Manish Niranjan 1 , Leonard Kleinman 1 , Alexander Demkov 1
1 Department of Physics, University of Texas at Austin, Austin, Texas, United States
Show AbstractAs scaling of traditional silicon based technology reaches its physical limits, a germanium channel field effect transistor (FET) is generating a lot of interest. To fully exploit transport properties of germanium, a low resistance contact technology will have to be developed based on metal germanides, much in the same way that self aligned metal silicides are used in a standard complimentary metal oxide semiconductor (CMOS) process today. Thus germanides with low n- and p-type Schottky barriers (for the use in NMOS and PMOS devices) to germanium channel need to be identified. Unfortunately, in spite of their new practical importance experimental studies of germanides are scarce, and, to our knowledge, no theoretical work exists in the literature. Germanides have complex phase diagrams with partial solubility and a combination of multiple eutectic and peritectoid behavior, and we find ab-initio calculations extremely useful in providing fundamental understanding of the structure-property relations between the crystal structure, chemical composition and atomic structure of the alloy/semiconductor interface on one hand and the Schottky barrier height on the other hand. In deep submicron regime (22 nm and below) PtGe, NiGe and their alloys appear to be promising as low barrier contacts to p-type germanium. Using density functional theory we have studied bulk electronic structure of NiGe and PtGe. Our calculated lattice constants are within 1-2% of recently reported experimental values. We also report nine elastic constants for each metal. We perform a comprehensive study of work functions, and surface energies as a function of the surface orientation. Theoretical work functions for the (001) surfaces of NiGe and PtGe are 4.6 and 4.9 eV, respectively, suggesting that NiGe, PtGe or their alloys indeed can be used as contacts to p-type germanium. We identify the growth conditions necessary to stabilize this orientation. Also we will discuss the stability of the monogermanide MnP-type phase of the NixPt1-xGe alloy with respect to decomposition into other phases.
9:00 PM - II5.44
Lanthanide Based Ternary Intermetallics as Advanced Thermoelectric Materials.
Ken Kurosaki 1 , Takeyuki Sekimoto 1 , Kenta Kawano 1 , Hiroaki Muta 1 , Shinsuke Yamanaka 1
1 Graduate School of Engineering, Osaka University, Suita, Osaka, Japan
Show Abstract9:00 PM - II5.45
Synthesis of Magnetic Nanoparticles by Sputtering.
Mai Miyata 1 , Kyosuke Kishida 1 , Katsushi Tanaka 1 , Haruyuki Inui 1
1 Department of Materials Science and Engineering, Kyoto-university, Kyoto Japan
Show AbstractMagnetic nanoparticles are attracting considerable attention due to their potential application as a data storage medium with the ultimate goal of storing one data bit per a particle. Since magnetic stability of an individual particle scales with KuV (where Ku is the anisotropy constant and V is the particle volume), magnetic materials with a high magnetic anisotropy constant is required to decrease the individual particle volume. FePt and SmCo5, which have higher magnetic anisotropy constants compared with the currently used Co-Cr-based alloys, are promising candidates for future high density magnetic recording media applications. The thermodynamic equilibrium structure of FePt is a chemically ordered L10 phase with high anisotropy. However, particles made by both chemical and physical method are disordered fcc phase. FePt nanoparticles must be annealed at a high temperature after deposited onto a substrate to induce the phase transformation from the disordered fcc to the ordered L10 phase. Such post-deposition annealing induces thermal degradation of the substrates. In order to avoid these difficulties, we employ a sputtering apparatus with relatively higher gas pressure equipped with sintering furnace. The apparatus is composed of a nucleation chamber, sintering furnace and a deposition chamber. The particles are generated by sputtering in a continuous Ar gas flow that carries the particle through the sintering furnace to the deposition chamber. The particles are annealed in the sintering furnace prior to their deposition onto a substrate. Ar gas pressure and gas flow are controlled separately. We synthesis ordered L10 FePt and SmCo5 nanoparticles by this apparatus, and observe the morphology changes of the particles in different experimental condition. FePt and Sm-Co nanoparticles are obtained by optimizing the gas pressure and gas flow rate. Their morphologies predominantly depend on Ar gas pressure. Most of the FePt nanoparticles, which are annealed in the sintering furnace, have ordered phase. This suggests pre-deposition annealing is effective to obtain ordered FePt nanoparticles.
9:00 PM - II5.46
Investigation of AuNi5 Films Deposited by Pulsed Laser Deposition for RF MEMS Switch Contacts.
Noha Farghal 1 , Moustafa Ghannam 2 , Amr Shaarawi 1 3 , Hussein El Samman 3 , Philippe Soussan 4 , Kris Baert 4
1 Youssef Jameel Science and Technology Research Center, American University in Cairo, Cairo Egypt, 2 College of Engineering and Petroleum, Kuwait University, Kuwait City Kuwait, 3 Physics Department, American University in Cairo, Cairo Egypt, 4 , IMEC, Leuven Belgium
Show Abstract9:00 PM - II5.47
Epitaxial Growth and Magnetic Properties of Fe3Si Thin Films.
Kensuke Akiyama 1 , Satoru Kaneko 1 , Yasuo Hirabayashi 1 , Azusa Kyoduka 2 , Yutaka Sawada 2 , Hiroshi Funakubo 3
1 , Kanawaga Industrial Technology Center, Ebina, Kanagawa Japan, 2 , Tokyo Polytechnic University, Astugi, Kanagawa Japan, 3 , Tokyo Institute of Technology, Yokohama, Kanagawa Japan
Show AbstractIn iron-silicon binary phase diagram, there are semiconducting phase (β-FeSi2), metallic phase (α-FeSi2) and ferromagnetic phase (Fe3Si) as a thermally stable compound, and electrical band structure and electron spin are controlled by composition ratio and crystal structure. In those phases, β-FeSi2 and Fe3Si phases are expected to grow epitaxially on Si substrate because of the similarity of its crystal structure. We have succeeded in the epitaxial growth of β-FeSi2 films on some kinds of single crystals, for example Si and yttria-stabilized zirconia (YSZ) substrates, and investigated the crystal structure of those epitaxial films. Furthermore, when the epitaxial growth of Fe3Si thin film is realized, stacking layer's structure would lead to the advanced devices such as spin transistor.In this study, we succeeded in the epitaxial growth of Fe3Si thin film as a ferromagnetic metal on the Si with buffer-layer and oxide insulating single crystal by magnetron-sputtering method. Those oxide insulators have been reported to epitaxially grow on Si substrate. We also investigated the effect of crystal structure, crystal orientation and the lattice strain on the magnetic properties of Fe3Si thin films.Polycrystalline Fe3Si phases were prepared on (001)Al2O3 substrate, while amorphous Fe-Si films deposited on (102)Al2O3 substrates. On the other hand, (100)-oriented and (110)-oriented epitaxial Fe3Si films were grown on (100)MgO and (111)MgO substrates, respectively. In spite of the fact that the lattice matching is generally important to hetero epitaxial growth of the film, the epitaxial growth of Fe3Si film was affected not only by the lattice matching but also by other factors, such as arrangement of anion and cation. Magnetic hysteresis loops of all the films revealed soft-magnetism, and the saturation magnetization (Ms) was large in the order of epitaxial, amorphous and polycrystalline Fe3Si films. However, the Ms of the epitaxial film was strongly influenced by the lattice strain.
9:00 PM - II5.49
Magnetic Behavior due to Quenching Temperature in Co-based Heusler-type Alloys Co2MnZ (Z=Si, Ge, Sn).
Shigeyuki Kikuchi 1 , Tetsuya Fujiwara 1 , Hiroki Ishibashi 1 , Mineo Kogachi 1
1 Department of Physical Science, Graduate School of Science, Osaka Prefecture University, Sakai, Osaka, Japan
Show Abstract Co-based Heusler-type Co2YZ alloys (e.g., Y= Cr, Mn and Z=Si, Ge, Sn, Al) are prospective candidates for application in the spintronics devices because these are theoretically predicted to be half metal ferromagnets with 100% spin polarization at the Fermi level. However, as well recognized, atomic disorder leads to degradation of the half metallicity and also the magnetism, preventing the practical application. In the present study, we investigate the magnetic behavior in Co2MnZ alloys (Z=Si, Ge and Sn) as a function of quenching temperature TQ. The mean magnetic moment is obtained at 4.2K for alloys quenched from TQ= 773K to 1273K by using a SQUID magnetometer. Changes in observed mean magnetic moment with quenching temperature are quite different among three systems. It decreases with increase in TQ in Co2MnSi and Co2MnGe, steeply for the former and gradually for the latter. Further, in Co2MnSn, it remains almost constant. According to the recent theoretical studies of Heusler Co2YZ alloys, Y-Z-type disorder (atomic disordering between the Y- and Z-sites) does not significantly affect the magnetism, while Co-Y-type disorder leads to its degradation as well as the half metallicity. From these, we can suppose that degradation of the magnetism observed in Co2MnSi and Co2MnGe is due to the Co-Mn-type disorder but this degradation is not caused by the Mn-Sn-type disorder in Co2MnSn. Therefore, Co2MnSn can be expected to be one of the most prospective candidates for fabrication of the spin-devices. Further, the lattice constant is also obtained by X-ray diffraction measurement. It decreases with increase in TQ up to 1073K, very slightly in Co2MnSi and steeply in Co2MnGe and Co2MnSn, indicating a noticeable contrast to the changes in magnetic moment. Correlation to the magnetic behavior is discussed.
9:00 PM - II5.5
Insitu Creep Deformation Observations in Ti-15Al-33Nb-xB (at%) and Ti-22Al-26Nb-xB (at%) Alloys.
C. Cowen 1 , C. Boehlert 1
1 Chemical Engineering and Materials Science, Michigan State University, East Lansing, Michigan, United States
Show Abstract9:00 PM - II5.50
Effect of Ti3Si on Texture in Ti-Nb Based Shape Memory Alloys.
Ryutaro Shimizu 1 , Yusuke Fukui 1 , Kei Masumoto 1 , Tomonari Inamura 2 , Kenji Wakashima 2 , Shuichi Miyazaki 3 , Hideki Hosoda 2
1 graduate school, Tokyo Institute of Technology, Yokohama 226-8503 Japan, 2 , Precision and Intelligence Laboratory, Tokyo Institute of Technology, Yokohama 226-8503 Japan, 3 , Institute of Materials Science, University of Tsukuba, Tsukuba 305-8573 Japan
Show Abstract9:00 PM - II5.51
Effects of Aging on Microstructures and Shape Memory Properties of TiAu Containing 18mol%Co.
Yasuhito Tsugane 1 , Tomonari Inamura 2 , Kenji Wakashima 2 , Hideki Hosoda 2
1 Graduate student, Tokyo Institute of Technology, Yokohama Japan, 2 Precision and Intelligence Laboratory, Tokyo Institute of Technology, Yokohama Japan
Show Abstract9:00 PM - II5.52
Microstructures and Hydrogen Permeability of Nb-NiTi Eutectic Alloys Prepared by Directional Solidification.
Yuji Yamaguchi 1 , Kyosuke Kishida 1 , Katsushi Tanaka 1 , Sho Tokui 2 , Kazuhiro Ishikawa 2 , Kiyoshi Aoki 2 , Haruyuki Inui 1
1 Department of Materials Science and Engineering, Kyoto University, Kyoto Japan, 2 Department of Material Science, Kitami Institute of Technology, Kitami Japan
Show Abstract9:00 PM - II5.53
Microstructure and Hydrogen Permeability of Duplex Phase M-Zr-Ni (M=V, Nb, Ta) Alloys.
Kazuhiro Ishikawa 1 , Naoshi Kasagami 2 , Tomoyuki Takano 2 , Kiyoshi Aoki 1
1 Materials Science, Kitami Institute of Technology, Kitami, Hokkaido, Japan, 2 Graduate Student, Kitami Institute of Technology, Kitami, Hokkaido, Japan
Show Abstract9:00 PM - II5.54
Anisotropic Microstructure and Hydrogen Permeability of Nb-Ti-Ni Duplex Phase Alloy Prepared by Rolling and Annealing.
Sho Tokui 1 , Kazuhiro Ishikawa 1 , Kiyoshi Aoki 1
1 Materials Science, Kitami Institute of Technology, Kitami, Hokkaido, Japan
Show Abstract9:00 PM - II5.6
Change in Creep Deformation of PST Crystals with Different Stress Axis.
Xiaohua Min 1 , Eisaku Sakurada 1 , Masao Takeyama 1 , Takashi Matsuo 1
1 Metallurgy and Ceramics Science, Tokyo Institute of Technology, Tokyo Japan
Show AbstractThe creep features of TiAl single crystal with fully lamellar structure, designated as PST crystal, have been clarified to depend strongly on the angle between the lamellar plate and the stress axis, designated as Φ. These features are derived by the fact that the predominant creep deformation of the γ plate continues by suppressing effect of the α2 plate on the slip systems not parallel to the γ plate. The change in the stress axis of the PST crystal with creep deformation has been investigated by EBSD using the PST crystals with various stress axes, and it is confirmed that the initial stress axis located within the standard stereographic triangle moves for the [001]-[-111] line, and then turns its direction for the [-111] pole by accepting the creep deformation. These moving features of stress axis indicate that the first slip system of <-101>(111) continues near the [001]-[-111] line, then, the first slip system turns to the second one of <-110>(111). The reason that the steep decrease in creep rate follows the gradual decrease in creep rate is interpreted by the additional operation of the second slip system. According to this conception, it is supposed that the strain making steep decrease in creep rate is directly correlated with the distance from the [001]-[-111] line to the initial stress axis. Therefore, in this study, the difference in the creep deformation of the two PST crystals with different initial stress axes from the [001]-[-111] line in the standard stereographic triangle was investigated. The PST crystal with Φ of 31° has nearer to the [001]-[-111] line than the PST crystal with Φ of 34°. The constant stress tensile creep tests were conducted at 1148k—68.6 MPa. And such unexpected result is obtained that the steep decrease in creep rate of the PST crystal with Φ of 31° occurs at 200 h, which is longer than that of the PST crystal with Φ of 34°. Since the initial creep rate of the PST crystal with Φ of 31° is smaller than that of the PST crystal with Φ of 34°, therefore, the time is not adequate parameter to compare the difference in the onset of the steep decrease in creep rate. Then, the strain when the steep decrease in creep rate appeared is compared, that strain of the PST crystal with Φ of 31° is 0.12, which is half value of 0.21 in the PST crystal with Φ of 34°. In addition, the strain at the minimum creep rate of the PST crystal with Φ of 31° is 0.37, which is also smaller than that of 0.63 in the PST crystal with Φ of 34°. Consequently, the supposition that the strain showing the steep decrease in creep rate is directly correlated with the distance from the [001]-[-111] line was confirmed.
9:00 PM - II5.7
Phase Transitions and Recrystallization in a Ti-46at%Al-9at%Nb Alloy as Observed by In-situ High-Energy X-ray Diffraction.
Klaus-Dieter Liss 2 , Helmut Clemens 1 , Arno Bartels 3 , Andreas Stark 3 , Thomas Buslaps 4
2 Bragg Institute, Australian Nuclear Science and Technology Organisation, Menai, New South Wales, Australia, 1 Department of Physical Metallurgy and Materials Testing, University of Leoben, Leoben Austria, 3 Department of Materials Science and Technology, Hamburg University of Technology, Hamburg Germany, 4 , European Synchrotron Radiation Facility, Grenoble France
Show Abstract9:00 PM - II5.8
Magnetron Sputtered Intermetallic Al-Au and Al-Zr Coatings for the Oxidation Protection of γ-TiAl.
Martin Moser 1 , Paul Mayrhofer 1 , Ian Ross 2 , Mark Rainforth 2 , Lars Hultman 3 , Fredrik Eriksson 3
1 Physical Metallurgy and Materials Testing, University of Leoben, Leoben Austria, 2 Department of Engineering Materials, University of Sheffield, Sheffield United Kingdom, 3 Thin Film Division, Department of Physics (IFM), Linköping University, Linköping Sweden
Show Abstract9:00 PM - II5.9
High Temperature Sulfidation Resistance of DO3 and B2 Ordered FeAl Tested in H2S-rich Gases.
Pierre-Yvan Thery 1 , Anna Fraczkiewicz 1 , Francois Ropital 2 , Xavier Longaygue 2
1 UMR CNRS 5146, Ecole Nationale Superieure des Mines, St-Etienne France, 2 Departement Materiaux, Institut Francais du Petrole, Rueil-Malmaison France
Show AbstractThe sulfidation resistance of Fe-Al alloys, containing different contents of Al (25 and 40 at. % Al ; DO3 or B2-ordrered, respectively), some of them containing 2 % of niobium, was tested in a highly corrosive atmosphere (15% H20, 13% N2, 42% H2, 30% H2S) during 600 h at 700 °C. After corrosion tests, sample gain mass was measured and compared to standards (AISI 321 stainless steel and Al2O3). Corrosion mechanisms were analyzed from microstructural observations (SEM, XRD, TEM).In general, studied alloys presented a good corrosion resistance in comparison with AISI 321 stainless steel which exhibited a 2 to 3 order of magnitude larger gain mass. Fe-40Al-based alloys presented gain mass nearly identical to that of plain Al2O3 : this excellent sulfidation resistance was attributed to the protective layer of alumina formed on their surface. In Fe-25Al-based alloys, large amount of iron sulfides FeS that grow over the alumina layer, is responsible for a lesser sulfidation resistance. Still, the resistance of this group of alloys could be significantly improved by an oxidation treatment prior to corrosion test.The corrosion resistance of Fe-40Al-based alloy was shown to be highly improved by a careful preparation of sample surface, to avoid superficial cracks, which play the role of nucleation sites for sulfides.The addition of Nb in iron aluminides was supposed to enhance sulfidation resistance through preventing growth of harmful FeS particles. Yet, the corrosion scales on niobium-containing alloys show only a small amount of Nb3S4 which did not prevent efficiently the formation of FeS. Moreover, alloying of Fe-25Al with Nb even resulted in an important harmful modification of the microstructure during sulfidation through an intense diffusion of S inwards the specimen and precipitation of niobium sulfides in the bulk.
Symposium Organizers
Chong Long Fu Oak Ridge National Laboratory
Helmut Clemens University of Leoben
Masao Takeyama Tokyo Institute of Technology
Joerg Wiezorek University of Pittsburgh
David Morris CENIM CSIC
II6: Silicides and Other Intermetallics
Session Chairs
Martin Heilmaier
Sharvan Kumar
Wednesday AM, November 29, 2006
Commonwealth (Sheraton)
9:30 AM - **II6.1
Creep Effects on Monotonic and Cyclic Crack Growth Response of a Two-Phase Mo-Si-B Alloy.
Sharvan Kumar 1 , Amruthavalli Alur 2 1
1 Engineering, Brown University, Providence, Rhode Island, United States, 2 , Intel Corporation, Chandler, Arizona, United States
Show AbstractMo-Si-B alloys are being considered as possible candidates for high-temperature applications beyond the capabilities of Ni-based superalloys. Thus, their high-temperature properties including strength, toughness and fatigue properties are of interest. On a more fundamental note, crack growth behavior during monotonic and cyclic loading at elevated temperatures is affected by creep and by environment, and their influence on toughness and fatigue properties must be understood. In this presentation, we report on the effect of loading rate on fracture toughness at high temperatures and understand the observed response by examining 1) the interaction of the advancing crack with the two-phase microstructure, and 2) the evolution of microstructure ahead of the crack-tip as a consequence of the crack-tip field. Parallel studies were also performed under cyclic loading conditions at 1200°C and 1400°C by subjecting compact tension specimens to sinusoidal and trapezoidal loading waveforms and by varying the dwell times in the trapezoidal cycles. Interrupted tests were conducted and fracture surfaces were examined to develop an appreciation for crack interaction with microstructure following various levels of Delta K at the crack tip. The monotonic and cyclic tests were instrumental in identifying regimes (temperature, time, loads) where the microstructure ahead of the crack tip revealed several instabilities that were localized including recrystallization, grain growth, and creep cavitation. Finite element analysis of the field ahead of a sharp crack in a two-phase microstructure subjected to monotonic three-point bend loading revealed strain localization “pockets” ahead of the crack tip, rising as a consequence of the presence of second phase particles that were heterogeneously distributed. The localized strains are thought to provide the driving force for recrystallization (and the particle matrix interfaces provide preferred nucleation sites for new grains) that occur in isolated pockets in the vicinity of the growing crack but not elsewhere in the specimen.
10:00 AM - II6.2
Effect of C11b-Stabilized Element on Deformation Mode in C40-Type (Nb1-x,Mox)Si2 (X=0-0.85) Single Crystals.
Takayoshi Nakano 1 , Koji Hagihara 1 , Yukichi Umakoshi 1
1 Division of Materials and Manufacturing Science, Graduate School of Engineering, Osaka University, Suita, Osaka, Japan
Show AbstractPlastic deformation behavior and dominant deformation mode in ternary (Nb1-x,Mox)Si2 (X=0-0.85) single crystals with the C40 structure were examined focusing on the phase stability between the C40 and C11b structures. Temperature dependence of CRSS for the (0001) <2-1-10] is strongly influenced by Mo concentration accompanied with the change in deformation mode from the co-planar type to the synchroshear type. In the ternary crystals with x=0-0.30, anomalous strengthening clearly appeared and the peak stress increased up to 1873K with an increase in Mo content. The Mo atoms may gather and form a dragging atmosphere around 1/3<2-1-10] dislocations containing a super lattice intrinsic stacking fault (SISF), resulting in anomalous strengthening. In the crystals with x=0.60-0.85, in contrast, high CRSS was obtained with fracture in a brittle manner at low temperatures, and the stress decreased remarkably with an increase in test temperature. HRTEM observation showed that the synchroshear type dissociation of each super partial dislocation, 1/6<2-1-10], occurred on the neighboring slip planes, accompanied with much wider separation distance of SF than that in the ternary crystals with the low content Mo. This change in plastic deformation behavior may be closely related to the decrease in phase stability of the C40 structure with addition of the C11b-stabilized element, Mo. The phase stability can be represented by the ratio of (h/b), where the h is the (0003) spacing and the b is the amplitude of 1/3<2-1-10]. As the (h/b) ratio increases with the Mo addition, the dissociation mode changes from the co-planar type to the synchroshear type at the ratio of 0.465.
10:15 AM - II6.3
High Temperature Compression and Tension Response of a Mo-Si-B Solid Solution Alloy.
Padam Jain 1 , K. Kumar 1
1 Engineering, Brown University, Providence, Rhode Island, United States
Show AbstractThe increasing demand for materials that can perform at high temperatures beyond the capabilities of Ni-base superalloys has generated interest in refractory metal-based systems (Mo-based and Nb-based), and within the family of Mo alloys, three-phase alloys at the Mo-rich end of the Mo-Si-B system have drawn recent attention. Previous studies on two- and three-phase alloys have confirmed the central role of the Mo-rich solid solution phase in affecting creep resistance and low temperature toughness in these multiphase alloys. Thus, compression and tension tests were conducted on a Mo-Si-B solid solution Mo-3Si-1.3B (at.%) alloy that contained a very low fraction (~3 %) of the T2 phase. Compression response was evaluated in vacuum at 1000 and 1200 oC over a strain rate regime spanning 10-4 - 10-7 s-1. The strengthening of Mo solid solution due to presence of Si in it was confirmed and the role of the matrix in controlling compression behavior of Mo-Si-B alloys was explained. Uniaxial tensile tests were conducted at 1000 oC and 1100 °C at nominal strain rates of 10-4 and 10-6 s-1 and resulting fracture surfaces were characterized. These results will be presented and their implications with respect to the response of the multiphase alloys will be discussed.
10:30 AM - II6.4
Structure and Oxidation Behavior of Mo/Mo5SiB2 Composites Produced by MA-SPS Process.
Akira Yamauchi 1 , Kyosuke Yoshimi 2 , Kazuya Kurokawa 1
1 Center for Advanced Research of Energy Conversion Materials, Hokkaido University, Sapporo Japan, 2 Graduate School of Environmental Studies, Tohoku University, Sendai Japan
Show AbstractIn this study, Mo5SiB2 has been synthesized from elemental powders by mechanical alloying (MA), and Mo/ Mo5SiB2 composites have been fabricated by spark plasma sintering (SPS) process. MA was carried out in acetone to avoid oxidation with a planetary ball mill (Fritsch P7) at the rotation speed of 500 rpm. Structural changes during MA were examined as a function of MA time by using X-ray diffractometry (XRD) and scanning electron microscopy (SEM).The XRD and SEM results showed that the MA process of longer than 50 hr led to the synthesis of Mo5SiB2. The Mo5SiB2 powder was successfully consolidated with Mo powder by the SPS technique, resulted in fabrication of fully-dense compacts of Mo/Mo5SiB2 composites. The formation of SiO2 inclusions that were caused by the oxidation of the MAed powder was considerably suppressed by C addition into Mo5SiB2 powder. Moreover, isothermal oxidation behavior of the fabricated compacts was investigated at 1073, 1273 and 1473 K in air. Sintered Mo/Mo5SiB2 compacts showed an improvement of oxidation resistance compared to arc-melted Mo/Mo5SiB2 composites.
10:45 AM - II6: Mo-Nb-Si
BREAK
11:00 AM - **II6.5
A Review Of Very High-Temperature Nb-Silicide Based Composites.
Bernard Bewlay 1 , P. Subramanian 1 , L. Cretegny 1
1 , GEGRC, Niskayuna, New York, United States
Show Abstract11:30 AM - II6.6
High Temperature Deformation Behavior of a Mechanically Alloyed Mo Silicide Alloy.
Martin Heilmaier 1 , Holger Saage 1 , Pascal Jehanno 2 , Mike Böning 2
1 Institute for Materials and Joining Technology, University Magdeburg, Magdeburg Germany, 2 Technology Center, Plansee SE, Reutte Austria
Show AbstractMo-Si-B alloys consisting of Mo solid solution and the intermetallic phases Mo3Si and Mo5SiB2 hold promise as structural materials for ultra-high temperature applications in excess of 1100°C in air, taking advantage of (i) the beneficial oxidation resistance of the silicides and (ii) the outstanding mechanical properties of molybdenum. A typical alloy composition that showed balanced properties was given as Mo–8.9Si–7.7B (in at.%) [1, 2]. However, Berczik [1] reported that wrought processing of such alloys with conventional grain sizes for making semi-finished products needed temperatures as high as 1760°C. To circumvent these difficulties, we suggest in the present contribution to employ mechanical alloying as the crucial processing step. After consolidation via cold compaction, sintering in dry hydrogen atmosphere and final hot isostatic pressing at 1500°C, one obtains an ultra-fine microstructure with a nearly continuous Mo(ss) matrix and the sizes of all phases being in the sub-micron range. This finding also demonstrates the extraordinary high thermal stability of this 3-phase Mo-silicide alloy. Tensile tests were carried out on round button-head samples in vacuum at initial strain rates ranging from 10-4 to 10-2 s-1 whereas the temperature varied in the range from 1200 to 1400°C.With a stress exponent of about 2 and the activation energy being close to that of Mo-self diffusion the material exhibits superplasticity at temperatures as low as 1300°C with tensile strain to failures of 200-400% at strain rates as high as 10-3s-1, thus, making sound wrought processing on industrial-scale facilities at temperatures much lower than reported in [1] feasible. Finally, to enhance creep resistance at high temperatures required for structural applications the alloys were annealed at 1700°C for 10h leading to significant coarsening of the microstructure and, hence, to a considerable reduction in minimum creep rate.[1] D.M. Berczik, US Patent 5,595,616, 1997.[2] T.A. Parthasarathy, M. Mendiratta, D.M. Dimiduk, Acta Mater. 50 (2002) 1857.
11:45 AM - II6.7
The Nature of Laves Phases - Case Studies on Selected Binary and Ternary Transition Metal Systems.
Frank Stein 1 , Martin Palm 1 , Oleg Prymak 1 , Daniel Gruener 2 , Alim Ormeci 2 , Guido Kreiner 2 , Andreas Leineweber 3 , Dieter Fischer 4 , Gerhard Sauthoff 1 , Georg Frommeyer 1 , Dierk Raabe 1 , Erik Mittemeijer 3 , Martin Jansen 4 , Yuri Grin 2
1 , Max-Planck-Institut fuer Eisenforschung GmbH, Duesseldorf Germany, 2 , Max-Planck-Institut fuer Chemische Physik fester Stoffe, Dresden Germany, 3 , Max-Planck-Institut fuer Metallforschung, Stuttgart Germany, 4 , Max-Planck-Institut fuer Festkoerperforschung, Stuttgart Germany
Show Abstract12:00 PM - II6.8
Pseudoelastic Behavior of Fe3Ga Single Crystals with D03 Structure.
Hiroyuki Yasuda 1 2 , Mitsuhiro Aoki 2 , Yukichi Umakoshi 2
1 Research Center for Ultra-High Voltage Electron Microscopy, Osaka University, Osaka Japan, 2 Division of Materials and Manufacturing Science, Graduate Scool of Engineering, Osaka University, Osaka Japan
Show Abstract Pseudoelastic behavior of Fe3Ga single crystals was investigated focusing on the dislocation structure and the phase constituent. Fe3Ga single crystals annealed in the D03 single phase region at 873K exhibited large pseudoelasticity of 5% recoverable strain. However, a thermoelastic martensitic transformation was confirmed to never occur in the crystals by a differential scanning calorimetry and a transmission electron microscopy. In D03-ordered Fe3Ga single crystals, uncoupled and paired 1/4[111] superpartial dislocations moved dragging the nearest-neighbor (NN) and next-nearest neighbor (NNN) anti-phase boundaries (APBs) during loading, respectively. During unloading, these APBs pulled back the superpartials resulting in large pseudoelasticity, which is similar to D03-ordered Fe3Al crystals. The strain recovery of Fe3Ga single crystals at higher strains was larger than that of Fe3Al crystals because of the higher back stress of both the NNAPB and NNNAPB. Moreover, the precipitation of the thermally stable L12 phase at low temperatures was so slow that the metastable D03 phase developed even if the crystals were annealed in the (α+L12) phase field in the Fe-Ga equilibrium phase diagram. The metastable D03 phase also demonstrated large pseudoelasticity of which recovery ratio was above 90%. In contrast, the crystals aged in the (α+D03) phase region showed small strain recovery.
12:15 PM - II6.9
Ferromagnetic Behavior of Nanostructured Mechanically-Alloyed FeCo-based Powders.
Qi Zeng 1 , Ian Baker 1 , Viginia McCreary 2
1 Thayer School of Engineering, Dartmouth College, Hanover, New Hampshire, United States, 2 Department of Materials Science and Engineering, Columbia University, New York, New York, United States
Show AbstractFeCo-based nanostructured powders with B2 structures were prepared by mechanical alloying and subsequently heat-treated in order to optimize their magnetic properties. The microstructures of the powders were characterized by XRD, DSC, SEM and MFM, and the magnetic properties were measured using both a VSM and a SQUID. Although the annealed powders had grain sizes less than the magnetic exchange length, neither a low coercivity nor a (grain size)6 dependence of the coercivity, as expected from Herzer’s random magnetic anisotropy model, were found. Measurements of the temperature dependence of magnetic properties from 10-300 K indicated that both the magnetic interaction between the individual powder particles and the irregularities in particle morphology and size produced the relatively high room temperature coercivity of ~15 Oe.Research sponsored by NIST grant 60NANB2D0120.
12:30 PM - II6.10
The Role of Phase Stability in Ductile, Ordered B2 Intermetallics.
James Morris 1 2 , Y. Ye 3 , Maja Krčmar 1 4 , Chong Fu 1
1 Materials Science & Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Materials Science & Engineering, University of Tennessee, Knoxville, Tennessee, United States, 3 Materials & Engineering Physics, Ames Laboratory, Ames, Iowa, United States, 4 Physics Department, Grand Valley State University, Allendale, Michigan, United States
Show Abstract12:45 PM - II6.11
Room Temperature Ductility of B2-Type CoZr Intermetallic Compounds.
Yasuyuki Kaneno 1 , Takayuki Takasugi 1 2 , Mitsuhiko Yoshida 3 , Hiroshi Tsuda 1
1 Department of Materials Science, Graduate School of Engineering, Osaka Prefecture University, Sakai, Osaka, Japan, 2 Osaka Center for Industrial Materials Research, Institute for Materials Research, Tohoku University, Sakai, Osaka, Japan, 3 Department of Materials Science and Engineering, Miyagi National College of Technology, Natori, Miyagi, Japan
Show AbstractB2-type CoZr intermetallic alloys with different chemical compositions (i.e. Co-49.0Zr, -49.5Zr, -50.0Zr, -50.5Zr and Co-51.0Zr (at.%)) were hot-rolled and subsequently recrystallized to evaluate tensile properties as a function of temperature. Microstructures of Co-49.0Zr, -49.5Zr and -50.0Zr alloys were composed of the B2-matrix containing C15-type Co2Zr Laves dispersions, while those of Co-50.5Zr and -51.0Zr were composed of the B2-matrix containing C16-type CoZr2 Laves dispersions. These homogenized ingots were successfully hot-rolled without edge cracks, except for Co-51.0Zr. The recrystallized Co-49.5Zr, -50.0Zr and -50.5Zr alloys exhibited a notable tensile elongation of ~10-20% at room temperature and ~60-80% at elevated temperatures. Also, the recrystallized Co-50.0Zr alloy was capable of cold rolling up to 70% reduction. In addition, tensile ductility was most prominent in just-stoichiometric Co-50.0Zr alloy in which the amount of second phase dispersions was minimum among the investigated alloys. These results suggested that the B2 phase CoZr was inherently ductile. TEM observations for Co-50.0Zr alloy that was tensile-deformed at room temperature revealed that the type of activated dislocations was <001> dislocations by which the von Mises’ criterion was not satisfied. Moreover, neither phase transformation by deformation such as martensitic transformation nor mechanical twinning was observed.
II7: Titanium Aluminides and Other Intermetallics
Session Chairs
Fritz Appel
Bernard Bewlay
Wednesday PM, November 29, 2006
Commonwealth (Sheraton)
2:30 PM - **II7.1
Texture Formation in High Niobium Containing TiAl Alloys.
Arno Bartels 1 , Andreas Stark 1 , Frank-Peter Schimansky 2 , Helmut Clemens 3
1 5-06 Materials Science, TUHH, Hamburg Germany, 2 , GKSS Research Centre, Geesthacht Germany, 3 Physical Metallurgy and Materials Testing, University of Leoben, Leoben Austria
Show Abstract3:00 PM - II7.2
Mechanical Properties of Hot-Worked Gamma TiAl Alloys with BCC β-Ti Phase.
Kentaro Shindo 1 , Toshimitsu Tetsui 1 , Masao Takeyama 2
1 Nagasaki R&D Center, Mitsubishi Heavy Industries,LTD., Nagasaki, Nagasaki, Japan, 2 Department of Metallurgy and Ceramics Science, Tokyo Institute of Technology, Tokyo, Tokyo, Japan
Show AbstractMechanical properties of a hot-worked TiAl alloy with a composition of 42Al-8V(at%), consisting of lamellar, γ and β grain of which the hot workability was improved by introducing β phase, has been Investigated using tensile test at high temperature, Plane bending fatigue test and foreign object attack test. Since microstructure has a large influence on the mechanical properties of TiAl alloy, microstructural control is a promising avenue for countermeasures. This in turn has led to a focus on hot-working, enabling wide-ranging microstructural control, and hot-worked TiAl alloys were developed with Ti-Al-V ternary systems. These alloys can be hot-extruded or hot-forged, with various structural control possible in conjunction with subsequent heat treatment. This study presents the results of consideration of mechanical properties of these alloys. Hot-worked TiAl alloys feature the introduction of β phase with a high deformability at high- temperature, achieved through the addition of β-stabilizing elements such as V, Mn, Cr, and Nb serving to improve hot-workability.The tensile strength of 42Al-8V(at%) at 673K is high at 752MPa. The Spesific strength of this alloy is higher than that of Inconel713C from room temperature to 973K. High strength is observed until about 973K. Given that the strength of precision cast TiAl alloy is normally under 600MPa, it can be seen that the strength is comparatively grater. However, strength declines at high temperatures. This decline is due to the influence of the β phase. This alloy would be suitable for lower temperature blades or structural components. High-cycle fatigue strength of this alloy for plane bending fatigue test at 270MPa is more than 10^8 cycles at room temperature. In foreign object attack test with taper plate specimen modified turbine blade and brass ball as foreign object, the relation between impact damege and thickness of specimen at attack point is investgatied. A limite of impact energy, at which there isn't a crack on buck of attack point, is obtained with each thickness about hot-forged TiAl alloy and from the relationship between impact energy and plate thickness at the point of collision, a safe region was indicated in which impact fracture was not reached.
3:15 PM - II7.3
The Influence of Nb on the Transition Temperatures of Titanium Aluminides.
Harald Chladil 1 , Helmut Clemens 1 , Masao Takeyama 2 , Rainer Gerling 3 , Ernst Kozeschnik 4 , Sascha Kremmer 5
1 Department of Physical Metallurgy and Materials Testing, University of Leoben, Leoben Austria, 2 Department Metallurgy and Ceramics Science, Tokyo Institute of Technology, Tokyo Japan, 3 Institute for Materials Research, GKSS Research Centre, Geesthacht Germany, 4 Institute for Materials Science, Welding and Forming, Graz University of Technology, Graz Austria, 5 , Boehler-Schmiedetechnik GmbH&CoKG, Kapfenberg Austria
Show Abstract3:30 PM - II7.4
Synchrotron Techniques to Analyze Deformation Mechanisms in Two Phase (α2+γ)-TiAl Alloys.
Francisco Garcia-Pastor 1 , Mallikarjun Karadge 1 , Hui Jiang 2 , David Hu 2 , Xinhua Wu 2 , Michael Loretto 2 , Philip Withers 1 , Michael Preuss 1
1 School of Materials, The University of Manchester, Manchester United Kingdom, 2 IRC in Materials, The University of Birmingham, Birmingham United Kingdom
Show Abstract3:45 PM - II7.5
Evolution of Antiphase Domains and Gamma Lamellae in Ti-39at%Al Single Crystals.
Yuichiro Koizumi 1 , Kazuki Iwamoto 1 , Takayuki Tanaka 1 , Yoritoshi Minamino 1 , Nobuhiro Tsuji 1
1 Adaptive Machine Systems, Osaka University, Suita Japan
Show Abstract4:00 PM - II7: TiAl
BREAK
4:15 PM - II7.6
Nano-Scale Design of TiAl Alloys Based on beta-Phase Decomposition.
Fritz Appel 1 , Michael Oehring 1 , Jonathan Paul 1
1 Institute for Materials Research, GKSS Research Centre Geesthacht, Geesthacht Germany
Show AbstractPhase decomposition and ordering reactions in beta/í2-phase containing TiAl alloys were utilized to establish a novel, previously unreported, type of laminate microstructure. The characteristic constituent of this microstructure are laths with a nanometer-scale substructure that are comprised of several stable and metastable phases. Microstructural control can be achieved by conventional thermomechanical processing and leads to a structurally and chemically very homogeneous material with excellent mechanical properties. The physical metallurgy of this novel type of alloy has been assessed by high resolution transmission electron microscopy and mechanical testing. Particular emphasis is paid on transformation induced toughening mechanisms.
4:30 PM - II7.7
Development of New TiAl Alloys by Spark Plasma Sintering.
Alain Couret 1 , Guy Molénat 1 , Jean Galy 1 , Marc Thomas 2
1 , CEMES/CNRS, Toulouse France, 2 , DMMP/ONERA, Chatillon France
Show Abstract4:45 PM - II7.8
Mechanical Properties of E21 Ti3AlC-base Alloy.
Hideki Hosoda 1 , Tomonari Inamura 1 , Kenji Wakashima 1
1 Precision and Intelligence Laboratory, Tokyo Institute of Technology, Yokohama, Kanagawa, Japan
Show Abstract5:00 PM - **II7.9
Catalytic Properties of Ni3Al Foils for Hydrogen Production.
Toshiyuki Hirano 1
1 , National Institute for Materials Science, Tsukuba Japan
Show AbstractMechanical properties have extensively been studied in Ni3Al in terms of high-temperature structural applications. In contrast catalytic properties have scarcely attracted attention so far. However since Ni3Al contains high concentration of Ni which is active, some catalytic property can be expected. Recently we for the first time succeeded in fabricating thin foils of Ni3Al using cold rolling, and found that the foils exhibit a high catalytic activity for methane decomposition, leading to hydrogen production. The results indicate that Ni3Al foils are functioned both as catalysts and as high-temperature structural materials, which is advantageous to the micro reactor for hydrogen production. There is a possibility that the foils can be used both as catalysts and as vessel. In this paper, we present the catalytic properties of thin foils of Ni3Al for catalytic methanol decomposition.We developed thin foils of Ni3Al, 30 micrometer-in thickness, by cold rolling of the single crystals. We briefly introduce the fabrication process and the mechanical properties of the foils, and then describe the catalytic properties as follows. The catalytic properties were examined over the foils in flowing methanol. The catalytic activity emerged above 713 K, i.e., methane decomposed into hydrogen and carbon monoxide. Interestingly it increased with increasing reaction time and reached a steady state of methane conversion larger than 98%. Usually high catalytic activity cannot be achieved from flat metallic foils because of their low surface area. This characteristic behavior is attributed to the spontaneous formation of fine Ni particles dispersed on the foils.
5:30 PM - II7.10
Modeling Water on Intermetallic Surfaces: Theoretical Studies in an Electrochemical Environment.
Chinmoy Ranjan 1 , Christopher Taylor 2 , Sally Wasileski 2 , Hector Abruna 1 , Francis DiSalvo 1 , Matthew Neurock 2 , Roald Hoffmann 1
1 Chemistry, Cornell University, Ithaca, New York, United States, 2 Chemical Engineering, University of Virginia, Charlottesville, Virginia, United States
Show AbstractElectrochemical reactions are generally carried out at a metallic surface under an applied potential. Under these operating conditions, reactions may proceed in pathways different from what one might predict for ultra-high-vacuum conditions. We wish to link theoretical calculations to actual electrochemical events at an electrode surface. We have done calculations on some Pt intermetallics containing Pb. Some of which (i.e. PtPb) are useful anode catalysts for Fuel Cells. Using Theoretical calculations we achieve insights into actual surface chemical species that might be present on an electrode around the operating potentials and thus elucidate mechanistic clues about specifics of a reactions i.e. oxidation of electrodes, removal of poisons from electrode surfaces.
5:45 PM - II7.11
High Throughput Screening Methods for Fuel Cell Electrocatalysts.
Jing Jin 1 2 , Mark Prochaska 3 2 , Maxim Kostylev 1 2 , Hector Abruna 1 2 , Francis DiSalvo 1 2 , R. Bruce van Dover 3 2
1 Department of Chemistry and Chemical Biology, cornell University, Ithaca, New York, United States, 2 Cornell Fuel Cell Institute, Cornell University, Ithaca, New York, United States, 3 Department of Material Science and Engineering, Cornell University, Ithaca, New York, United States
Show Abstract