Bernard Bewlay General Electric Company
Martin Palm Max-Planck Institut fuer Eisenforschung GmbH
Sharvan Kumar Brown University
Kyosuke Yoshimi Tohoku University
N1: Intermetallic Shape Memory Allloys
Monday AM, November 29, 2010
Room 203 (Hynes)
10:00 AM - N1.2
Micromechanical Testing and Modeling of Shape Memory Behavior in Ni-Ti Based Alloys.
Matthew Bowers 1 , John Carpenter 1 , Michael Mills 1 , Peter Anderson 1 , Sivom Manchiraju 1 Show Abstract
1 Materials Science and Engineering, The Ohio State University, Columbus, Ohio, United States
Micromechanical testing of single crystal Ni-Ti based shape memory alloys is being performed in an effort to understand the effects of specimen size and crystal orientation on martensite-induced pseudoelastic and shape memory response. The primary goal in this investigation is to determine the means by which the matrix accommodates the large strain associated with the martensitic transformation. This information is critical in extending the working life of components under cyclic loading and/or heating. It is theorized that the accommodation may take place by matrix plasticity and/or by inducing additional transformation variants, however no experimental verification exists. FIB-machined, micron-scale pillars of several crystallographic orientations chosen on the basis of Schmid factor calculations have been tested in compression and stress-strain data has been collected. Post-mortem TEM analysis has been done to analyze the resulting microstructure and dislocation substructure, including the presence of any residual martensite. Crystallographic theory of martensite and micromechanics-based stress field calculations are being used to explain the results. We demonstrate through this method the study of isolated martensitic transformations using direct mechanical response measurements for individual variants. Also, we investigate whether the shape memory response may be enhanced given select specimen dimensions and crystallographic orientations.
10:15 AM - N1.3
The Origins of Microstructural Instability in NiTi Shape Memory Alloy Actuators.
Nicholas Jones 1 , David Dye 1 Show Abstract
1 Dept of Materials, Imperial College London, London United Kingdom
Shape memory alloy (SMA) based actuators are currently of great interest to the aerospace industry as they offer the potential for dynamic components, which will be beneficial in the drive to reduce emissions. For these components to be structurally useful, they require the application of significant bias loads on the SMA. However, despite successful demonstrator components, the cyclic instability of the martensitic transformation continues to prevent the transfer of this technology into full scale production components. Here we present in situ synchrotron X-ray diffraction results investigating the microstructural evolution of a near equiatomic NiTi SMA over several thermal cycles using different uniaxially applied loads. Despite being cycled under a nominally elastic load, an accumulation of strain is observed. Certain crystallographic orientations are found to align with the sample tensile axis and we observe that the martensitic microstructure evolves during cycling. It would appear that this alteration is driven by an attempt to minimise the effect of the externally applied load. The reasons for this are explored, based on the fundamentals of the transformation process.
10:30 AM - N1.4
Characterization and Properties of a Near Stoichiometric NiTiPt High Temperature Shape Memory Alloy.
Fan Yang 1 , Libor Kovarik 1 3 , Ronald Noebe 2 , Anita Garg 2 , Michael Mills 1 Show Abstract
1 , The Ohio State University, Columbus, Ohio, United States, 3 , Pacific Northwest National Laboratory, Richland, Washington, United States, 2 , NASA Glenn Research Center, Richmond, Virginia, United States
Aging of the high-temperature shape memory alloy Ti50Ni30Pt20(at.%) results in precipitation of a previously unidentified phase. The precipitate phase has been analyzed with electron diffraction, high-resolution STEM HAADF imaging and 3-D atom probe tomography (L. Kovarik, F. Yang, A. Garg, D. Diercks, M. Kaufman, R.D. Noebe, M.J. Mills, Acta Materialia 2010, article in press). It is shown that the precipitates have a unique structure due to their non-periodic character along one of the primary crystallographic directions. It will be shown that the structure can be explained in terms of random stacking of three variants of a monoclinic crystal that is closely related to the structure of high temperature cubic B2 phase; the departure of the structure from the B2 phase can be attributed to the ordering of Pt atoms on the Ni sublattice and relaxation of the atoms (shuffle displacements) from the B2 sites. The shuffle displacements and the overall structural refinement were deduced from ab initio calculations. The effects of aging on mechanical and shape memory properties were investigated, with an emphasis on transformation strain, work output and dimensional stability by means of cyclic load biased tests. The precipitate has been shown to play a key role in achieving overall optimal shape memory properties.
10:45 AM - N1.5
Self-assembled NiTi Nanowires.
Xu Huang 1 , Yuriy Chumlyakov 2 , Ainissa Ramirez 1 Show Abstract
1 Mechanical Engineering, Yale University, New Haven, Connecticut, United States, 2 Physics of Plasticity and Strength Materials Laboratory, Siberian Physical and Technical Institute, Tomsk Russian Federation
Self-assembled NiTi nanowires were fabricated by electro-polishing single crystal NiTi alloys. The resulting NiTi nanowires were approximately 480 nm by 480 nm in cross section, with lengths of 50 µm, which were found to lengthen with increasing etching time. Most of the nanowires grew perpendicularly along the <110> and <100> planes of the single crystal substrate, while a few of the wires presented an inclined at a specific angle. The nanowires composition was determined using microprobe, and the electrical properties were investigated using four-point probe measurements. Their phase transformation properties were evaluated by testing the resistivity as a function of temperature using a sample heating stage. These methods for producing NiTi nanowires could provide new routes for smart nano-structures.
11:00 AM - N1.6
Computational Studies of the NiTi Alloy System: Bulk, Supercell, and Surface Calculations.
Amanda Stott 1 2 , David Dixon 1 , Chris DellaCorte 2 , Stephen Pepper 2 , Phillip Abel 2 Show Abstract
1 The Deparment of Chemistry, The University of Alabama, Tuscaloosa, Alabama, United States, 2 Tribology and Mechanical Components Branch, NASA Glenn Research Center, Cleveland, Ohio, United States
Tailoring the microstructure of the NiTi alloy by increasing the Ni atomic to ~ 55% leads to alloys with increased dimensional stability which can be used in bearing applications while maintaining tribological performance equal to that of traditional tool steels in friction tests. Unlike traditional tool steels, which are magnetic and may corrode in harsh environments, Ni55Ti45 is non-corrosive and non-magnetic, both of which are desirable properties currently not found in any bearing material. A density functional theory study of the constituent phases NiTi, Ni4Ti3, and Ni3Ti in the NiTi alloy system was performed for the bulk phase, supercell, and surface structures using the Vienna Ab-Initio Simulation Package (VASP 5.2). From these calculations, a detailed theoretical analysis of the microstructure, site-projected band structure, and density of states (DOS) was performed. The NiTi surface heats of formation are comparable to bulk-phase values. The heat of formation of NiTi is predicted to be lower in the bulk than in the supercell. In contrast, the supercell heats of formation for Ni4Ti3 and Ni3Ti are lower than in the bulk. The combined experimental and computational results suggest that Ni4Ti3 and Ni3Ti act to stabilize the parent NiTi phase. The predicted DOS shows a significant contribution of Ti states at higher energies (less stable) and Ni at lower energies (more stable). A pseudogap exists in the NiTi DOS, as often observed in ceramic materials. This pseudogap is due to NiTi phase stabilization from the partial occupancies between d-d or d-p hybridization orbital interactions. In Ni4Ti3 no pseudogap is present, and the Ni and Ti contributions occur at approximately the same energy range, although the peak apex of the Ti d-states occurs at a higher energy than the peak apex of the Ni d-states, indicating delocalized metallic bonding. In Ni3Ti, a narrow gap exists at the Fermi level, with Ni and Ti contributions occurring over this energy range. The Ni and Ti in the Ni3Ti d-states are similar to those in Ni4Ti3, consistent with delocalized metallic bonding. The band structure and charge density results show the d-orbital character of Ni4Ti3 and Ni3Ti to be highly symmetric compared to NiTi, also indicating these phases act to stabilize the parent NiTi matrix. The mixed phase composition of the bearing surface and the Ni-rich composition of the alloy are both factors in the positive lubrication behavior of Ni55Ti45. The delocalized metallic bonding found in the DOS calculations and the negative charge accumulation at Ni lattice sites could be responsible for this behavior.
11:30 AM - **N1.7
Pseudoelasticity of D03-Type Fe3Al and Fe3Ga-based Alloys.
Hiroyuki Yasuda 1 , Yukichi Umakoshi 1 Show Abstract
1 Division of Materials and Manufacturing Science, Osaka University, Osaka Japan
The pseudoelastic behavior of Fe3Al and Fe3Ga alloys with the D03 structure is reviewed. In general, pseudoelasticity which shape memory alloys exhibit is based on a thermoelastic martensitic transformation. However, pseudoelasticity regardless of the martensitic transformation is found to take place in D03-ordered Fe3Al and Fe3Ga alloys. For instance, a 1/4〈111〉 superpartial dislocation in Fe3Al alloys moves independently dragging an antiphase boundary (APB). During unloading, the APB pulls back the superpartial to decrease its energy resulting in pseudoelasticity, which is called “APB pseudoelasticity”. Moreover, three types of pseudoelasticity based on martensitic transformation, twinning and dislocation motion appear in Fe3Ga alloys depending on degree of D03 order, loading axis and stress sense. The mechanism of the pseudoelasticities in the D03-type intermetallics is discussed based on some in situ observations.
12:00 PM - N1.8
Thin Films of AuCuAl Shape Memory Alloy for Use in Plasmonic Nano-actuators.
Vijay Bhatia 1 , Annette Dowd 1 , Michael Cortie 1 , Gordon Thorogood 2 Show Abstract
1 Institute for Nanoscale Technology, University of Technology Sydney, Broadway, New South Wales, Australia, 2 , Institute of Materials Engineering, Australian Nuclear Science and Technology Organisation, Menai, New South Wales, Australia
The beta-phase shape memory alloy (SMA) with a composition in the vicinity of Au7Cu5Al4 has been shown to be relatively resistant to aging and martensite stabilization compared to copper-based SMAs. However, although Au7Cu5Al4 has been studied in the bulk form, there has been no attempt yet to prepare thin film actuators of it. In contrast, films of the better known TiNi SMA have been extensively studied for use in thin film actuators, however their use in nano-sized actuators has been limited due to the oxidation of films of less than 100 nm thickness. The Au7Cu5Al4 SMA is relatively resistant to oxidation due to its high gold content and may therefore be a better candidate for use in nanoscale SMA actuators. Another advantage of this alloy is that its dielectric properties suggest that it can support a surface plasmon in the visible spectrum. This has the potential to enable a range of interesting new functionalities in which the shape memory effect and plasmonics are combined. Here we describe the synthesis and characterisation of films of Au7Cu5Al4 and related alloys produced by magnetron sputtering. The microstructure of the films was controlled by varying the Al content, while keeping the Au:Cu ratio fixed. In this way, the microstructure could be controlled to produce alpha, beta or gamma phases according to position on the pseudobinary transect, however it is only the beta structured intermetallic phase that has the SMA property. The films were characterised by XRD, SEM, TEM, resistance measurements, x-ray reflectometry and SPM. These techniques showed that films of correct crystal structure and composition were produced and that they exhibited the reversible austenite to martensite phase transition required of a SMA. Attainment of of this property is the key prerequisite for the development of a SMA opto-mechanical nano-actuator.
12:15 PM - N1.9
Surface Modification of Ni-Ti for Biomedical Applications by Plasma-immersion Ion Implantation.
Rui M. Martins 1 2 , Nuno Barradas 1 2 , Eduardo Alves 1 2 , Dietmar Henke 3 , Helfried Reuther 3 , Maria Carmezim 4 5 , Teresa Silva 4 6 , Joao C. Fernandes 4 Show Abstract
1 , Instituto Tecnológico e Nuclear (ITN), Sacavém Portugal, 2 , Centro de Física Nuclear da Universidade de Lisboa (CFNUL), Lisboa Portugal, 3 Institute of Ion Beam Physics and Materials Research, Forschungszentrum Dresden- Rossendorf, Dresden Germany, 4 ICEMS/DEQB/IST, TULisbon, Lisboa Portugal, 5 ESTSetúbal, Instituto Politécnico de Setúbal, Setúbal Portugal, 6 ISEL, Instituto Politécnico de Lisboa, Lisboa Portugal
The enormous elasticity of Ni-Ti is becoming integral to the design of a variety of new medical products. The wide spectrum of application in implantology imposes special requirements on the biocompatibility of Ni-Ti. The biological response to implant materials is a property directly related to their surface conditions and an optimum surface layer is thus desired. The plasma-immersion ion implantation (PIII) technique was used to modify and improve the surface of a Ni-Ti alloy (~ 50.2 at.% Ni, superelastic at body temperature) for biomedical applications. The main goal has been the formation of a Ni-depleted surface, which should serve as a barrier to out-diffusion of Ni ions from the bulk material. Ion implantation of oxygen was carried out. The depth profiles of the elemental distribution in the alloy surface region, obtained by Auger electron spectroscopy (AES), confirm the formation of a Ti-rich oxide layer. The working plan also comprised ion implantation of nitrogen. In this case, the formation of titanium oxynitride (TiNxOy) was observed. The AES depth profiles clearly show a Ni-depleted fraction for experiments performed with 40 keV.The deposition of a coating by a PVD technique would have disadvantages due to the interface between the coating and the bulk (lower adhesion). PIII creates a graded interface between the modified surface and the bulk. Techniques like thermal oxidation and nitriding could also lead to an improved corrosion resistance and Ni-depleted Ni-Ti surface. However, the high temperature necessary for the experimental procedure would lead to modification of the phase transformation characteristics and loss of specific mechanical properties of the alloy. Heat treatments tests performed at temperatures above 350C led to a shift of the transformation temperatures of the Ni-Ti alloy used in this work. Moreover, the R-phase is then present at body temperature, which is not the case for Ni-Ti samples modified by the PIII technique. This technique only changes the properties of the Ni-Ti alloy top layer.
12:30 PM - N1.10
Correlation of Specific Resistance and Phase Structure in the 3D Porous Nitinol after Laser Assisted Manufacturing.
Igor Shishkovsky 1 , Vladimir Sherbakov 1 Show Abstract
1 Laboratory of Technological lasers, Lebedev Physics Institute of Russian Academy of Sciences, Samara branch, Samara Russian Federation
The main goal of this study is a Shape Memory Effect (SME) in a porous titanium nickelide (- NiTi intermetallic phase referred to as nitinol) fabricated via the Selective Laser Sintering/Melting (SLS/SLM) process. Phase and structural transformation behavior of the intermetallide is characterized by scanning electron microscopy, EDX and X-ray analysis. The influence of the laser sintering parameters and additional heating on the phase content and the thermally dependence of the electrical resistivity are discussed. Peaks and humps of the electrical resistivity are found to correspond to the start and finish temperature of the austenite-to-martensite-and-back phase transitions and that knowledge can be used for the SME estimation and optimization. Advantages and drawbacks of the application of this porous material as the bio-MEMS are considered.Keywords: Selective laser sintering/melting (SLS/SLM), nitinol, shape memory effect (SME), micro-electro-mechanical systems (MEMS).
12:45 PM - N1.11
Simulating the Thermal Cycling Response of Stressed Polycrystalline NiTi.
Sivom Manchiraju 1 , Peter Anderson 1 , Darrell Gaydosh 2 , Ronald Noebe 2 Show Abstract
1 , The Ohio State University, Columbus, Ohio, United States, 2 , N. A. S. A. Glenn Research Center, Cleveland, Ohio, United States
A challenge in modeling of shape memory alloys is to capture the load biased thermal cycling response. Experiments show that the transformation strain is a strong function of the bias stress. It is observed that the transformation strain is small under small bias stress, increases steadily with increasing bias stress and ultimately starts to decrease at large bias stress due to intervention of plastic deformation. Though this dependence has been simulated by phenomenological macroscopic models, detailed microstructure based models which track the volume fraction of individual martensite variants have been unable to capture the experimental observations. This work discusses three key modifications to a microstructure based FEM model in order to capture the load biased thermal cycling. First, the model couples deformation due to martensitic phase transformation and plastic deformation in austenite . The model captures the grain-to-grain redistribution of stress caused by both plasticity and phase transformation, thereby allowing each mechanism to affect the driving force for the other. This leads to a decrease in transformation strain at large bias stress. Second, the martensite plate interaction energy approximation proposed in  is modified to include a plate “self-hardening” term. This enables formation of multiple martensite plate types in the grains of polycrystal upon thermal cycling under small bias stress. Thus, a less textured martensite and a small transformation strain is predicted at small bias stress, similar to experimental observations. Third, the elastic anisotropy effects are rigorously captured using crystallographic theory of martensite in conjunction with the FEM model by using the recent first principle calculations of monoclinic martensite stiffness.The model is calibrated and validated rigorously with macroscopic load-bias and pseudoelastic experiments for solutionized polycrystalline NiTi (55wt% Ni). Preliminary results show that the transformation strain and texture predicted by the model is in good agreement with the experiments. Despite these improvements, the model predicts the onset of plastic strain at bias stress levels much higher than that observed in the experiments. Reasons for this discrepancy will be discussed.References:1.S. Manchiraju and P. M. Anderson, 2010, International Journal of Plasticity, doi:10.1016/j.ijplas.2010.01.009 2.E. Patoor, A. Eberhardt, M. Berveiller, 1996, J. de Physique, 6, 277.
N2: Iron Aluminides
Monday PM, November 29, 2010
Room 203 (Hynes)
2:30 PM - **N2.1
Processing Iron Aluminides by Heavy Deformation for Improved Room Temperature Strength-ductility and for High Temperature Creep Strength.
David Morris 1 , Maria Munoz-Morris 1 Show Abstract
1 Physical Metallurgy, CENIM, CSIC, Madrid Spain
Iron aluminides show many interesting properties, but still show relatively poor ductility at room temperature and only moderate creep resistance at temperatures above about 600C. Processes of severe plastic deformation have been investigated for a wide range of ductile alloys over the past decade, but have hardly been considered for intermetallics. This presentation discusses processing of a Fe3Al alloy by heavy cold rolling, followed by recovery-recrystallization anneals with an objective of refining grain size to improve strength at the same time as ductility. The high strength and poor ductility of the work hardened material leads to a danger of cracking during rolling. Such rolling, combined with some recovery annealing, can, nevertheless, lead to strong materials with some plastic ductility. A different technique of multidirectional, high-strain and high-temperature forging applied to a boride-containing Fe3Al alloy produces a material with large grain size and refined dispersion of boride particles. These lead to a considerable increase in creep strength under conditions of moderate stresses at temperatures around 700C. This high-strain forging technique can be seen as an intermediate processing method between conventional wrought metallurgy and mechanical-alloying powder metallurgy.
3:00 PM - N2.2
Fatigue Resistance and Elastic Properties of Fe3Al-Based Alloys.
Manja Krueger 1 , Florian Gang 1 , Alexandra Laskowsky 1 , Heike Ruehe 1 , Joachim Schneibel 1 , Martin Heilmaier 2 Show Abstract
1 Mechanical Engineering, Institute for Materials and Joining Technology, Otto-von-Guericke University Magdeburg, Magdeburg Germany, 2 Materials Science, Technical University Darmstadt, Darmstadt Germany
Iron aluminide alloys based on Fe3Al are of interest in applications where excellent corrosion and oxidation resistance, adequate strength at elevated temperatures and a low density are required. While fatigue can become an important issue in many structural applications of iron aluminides, it has not received much attention to date: publications on this topic deal either with high cycle fatigue (HCF) or fatigue crack growth behaviour.In this presentation the low cycle fatigue (LCF) behaviour of two cast as well as two hot extruded Fe3Al alloys (with and without Cr) is investigated at room temperature and 300°C in air. The LCF tests were carried out in strain control with strain amplitudes in the range of εa = 0.1-0.7% strain with frequencies of 1 or 3 Hz. In all cases strong cyclic hardening, much stronger than the hardening in a normal tensile test, was observed. Surprisingly, the addition of Cr did not improve the tensile and LCF properties of iron aluminide. For cycle numbers less than about 10000, the LCF fatigue resistance at 300°C was higher than that at room temperature. It is shown that the LCF behaviour of Fe3Al at 300°C is significantly better than that of Al-Si casting alloys. This feature makes Fe3Al competitive with Al alloys at temperatures of 300°C and above.
3:15 PM - N2.3
The Effect of Fine M2C (M: Mo, Cr, Fe) Particles on the High Temperature Strength and Recrystallization Temperature of Warm Rolled Fe3Al Base Alloys.
Satoru Kobayashi 1 , Takayuki Takasugi 2 1 Show Abstract
1 , Tohoku university, Sakai Japan, 2 , Osaka prefecture university, Sakai Japan
The effect of fine M2C carbide particles on the high temperature strength and recrystallization temperature of warm rolled Fe3Al base alloys containing Cr, Mo and C was investigated. Fe-27Al-1.2C-2Cr-xMo (x: 0, 0.3, 0.6, 0.9 at.%) alloys were arc melted, warm rolled and annealed. The 0.2% proof stress at 600 degree C increased from 280 MPa to 390 MPa with increasing Mo content from 0 to 0.9. TEM observations have revealed the presence of finely dispersed M2C particles in the alloys with the Mo contents higher than 0.6%, indicating that both Mo solid solution and the particles contribute to the strengthening. The recrystallization temperature also increased from 730 degree C to 810 degree C with increasing Mo content from 0.3 to 0.9. TEM observations have revealed that the M2C particles pin subgrain boundaries formed during recovery process, indicating that the particles stabilize the deformed structure at high temperatures. The stability of M2C particles against long term exposures at high temperatures will also be presented.
3:30 PM - N2.4
In-situ TEM Straining Study of the Yield Anomaly in L21-ordered Fe2MnAl Single Crystal.
Yifeng Liao 2 , Ian Baker 1 Show Abstract
2 Materials Science and Engineering, Northwestern University, Evanston, Illinois, United States, 1 Thayer School of Engineering, Dartmouth College, Hanover, New Hampshire, United States
Fe2MnAl adopts the L21 structure (ordered B2) at lower temperatures and disorders to the B2 structure (ordered b.c.c.) at 890 K. It shows a positive temperature dependence of its yield strength at intermediate temperatures with a peak at 700 K. In order to unravel the reason for the anomalous yield strength behavior, TEM in-situ straining of Fe2MnAl single crystals was performed at room temperature, 700-800 K (peak temperature) and 900 K (above the peak temperature). Four-fold dissociated superdislocations with a/4<111> Burgers vectors were observed to glide during room temperature straining. The separation between the outer partials was ~5 nm, whereas the separation of the inner partials was ~20 nm. The two outer pairs were found to had separated at 700 K-800 K due to the decrease in the degree of L21 order. The motion a dislocation with a total slip vector of 1/2<111> must trail a 1/2<111>-type anti-phase boundary (APB) that increases the energy of the matrix. Above 900 K the motion of two-fold paired dislocations does not produce any APBs as the matrix disorders to the B2 structure. The increasing number of separated superdislocations at elevated temperatures below 700 K could be one of the reasons for the anomalous yield strength. This research was supported by National Science Foundation Grant DMR 0552380.
3:45 PM - N2.5
Attempts at Obtaining Fine-grained Ordered Fe-Al Alloys.
Anna Fraczkiewicz 1 , Jerzy Bystrzycki 2 , Sanaa Najjar 1 , Izabela Kunce 2 , Radoslaw Lyszkowski 2 , Frank Montheillet 1 Show Abstract
1 Centre SMS, UMR CNRS 5146, Ecole des Mines de St-Etienne, St-Etienne France, 2 Faculty of Advanced Technology and Chemistry, Military University of Technology, Warsaw Poland
Main limitation of the so-sought industrial development of ordered Fe-Al alloys is nowadays the cost of their processing. Obtaining of fine-grained materials, with a micron-range grain size, has been shown to be the only possible way to avoid the material’s room temperature brittle fracture. Moreover, the presence of a second phase (mainly oxides) intergranular precipitates is necessary to prevent grain growth. Unfortunately, this kind of microstructure can only be obtained through powder-metallurgy based methods, too expensive if not leading to a net-to-shape processing.In this work, we show the results of different attempts of obtaining fine-grained structures in different FeAl alloys through severe plastic deformation processing. Ternary Fe-40Al (B2), alloyed with Mn (2%) and doped with B (100 ppm) has been laboratory deformed in severe compression tests, on a wide range of temperatures (800 to 1100°C) and strain (up to epsilon=2). Binary Fe-28Al has been tested in multiaxis compression (MaxStrain system). Present work deals with the use of the latter system to process Fe-40Al alloys. Evolution of deformed microstructures has been studied as a function of severe deformation conditions. Only extreme conditions of available deformation, giving the maximal “charge” of the material, allow obtaining the sought fine-grained structure. At lower “charges” (temperature and strain), different features are progressively observed: the microstructure transformation starts with a localized deformation, than, a local (“collar”) recrystallisation takes place; finally, an uniform microstructure can be obtained.
4:30 PM - N2.6
Microstructure and Mechanical Behavior of Two-phase Fe30Ni20Mn20Al30 Alloy.
Xiaolan Wu 1 , Ian Baker 1 , Michael Miller 2 , Karren More 2 , Ai Serizawa 2 Show Abstract
1 Thayer School of Engineering, Dartmouth College, Hanover, New Hampshire, United States, 2 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
The microstructure and mechanical properties of Fe30Ni20Mn20Al30, which has a room-temperature yield strength of 1200 MPa, are described. Transmission electron microscopy (TEM) and atom probe tomography (APT) were used to characterize the microstructures of the alloy in both as-cast (AS) and annealed conditions. Upon casting, the alloy had a fine (phase width ~5 nm) two-phase (B2/L21) microstructure, possibly formed by spinodal decomposition. After annealing for 72 h at 823 K the microstructure had coarsened substantially so that the phase widths were ~25 nm. Energy dispersive X-ray spectroscopy (EDS) and APT results showed that the B2 phase is rich in Fe and Mn, whereas the L21 phase is rich in Ni and Al. Room temperature hardness tests on the alloy annealed f