1998 MRS Fall Meeting & Exhibit

Chairs

Akihisa Inoue, Tohoku Univ
William Johnson, California Inst of Technology
C.T. Liu, Oak Ridge National Laboratory

Symposium Support 

• Alps Electric Co., Ltd., Japan
• Amorphous Technologies, USA
• JEOL Ltd., Japan
• Makabe R&D Co., Ltd.
• Oak Ridge National Laboratory
• U.S. Department of Energy 

1998 Fall Exhibitor 

* Invited paper

SESSION MM1: ATOMIC AND ELECTRONIC STRUCTURE I 
Chairs: Robert J. Gottschall and William L. Johnson 
Tuesday Morning, December 1, 1998 
Fairfax A/B (S)

8:30 AM OPENING REMARKS 
8:45 AM *MM1.1 
STRUCTURE AND PHASE STABILITY OF BULK METALLIC GLASSES. D.M.C. Nicholson , G.M. Stocks, W.A. Shelton, Oak Ridge National Laboratory, Oak Ridge, TN; J.C. Swihart, Physics Dept., Indiana Univ., Bloomington, IN; Yang Wang, Pittsburgh Supercomputing Center, Pittsburgh, PA. 

By surveying the list of observed bulk amorphous metals one may infer that their formation depends on the presence of at least three atomic species of different sizes. This can be attributed to either formation of particularly compact stable amorphous structures, increased entropy of mixing, or inhibition of diffusion toward more stable crystalline forms. The relationship between structure and stability will be the focus of this paper. Electronic structure techniques such as the locally self-consistent multiple scattering (LSMS), tight-binding-bond, and linear muffin-tin orbital methods can be used to asses the relative stability of competing amorphous and crystalline structures. They also provide information about the electronic states that can be compared to XPS spectra and specific heat measurements. A review of the structural information available from experiment and model building efforts will be given. Typical models of amorphous metals employ hundreds to thousands of atoms. The status of electronic structure methods for such large complex structures will be discussed, illustrations will be drawn from LSMS calculations for amorphous Ni-Pd-P and Zr-Ni-Al.

9:15 AM MM1.2 
OXYGEN DISTRIBUTION IN Zr-BASED METALLIC GLASSES. D.H. Ping , K. Hono, Materials Physics Devision, National Research Institute for Metals, Tsukuba, JAPAN; A. Inoue, Institute of Metal Research, Tohoku University, Sendai, JAPAN. 

Recent finding of Zr-based amorphous alloys with excellent glass forming ability enables to fabricate bulk amorphous alloy by the conventional casting process. As Zr has a large affinity with oxygen, impurity oxygen is introduced into the Zr-based amorphous alloys during melting, which influence the glass forming ability as well as the crystallization kinetics greatly. However. no direct observation of impurity oxygen dissolution and redistribution during the crystallization process has been reported so far in a microscopic scale. This paper reports the oxygen behavior in the as-cast amorphous and nanocrystallized Zr-Cu-Pd-Al alloys observed by a three-dimensional atom probe (3DAP) technique. Oxygen impurity (about 0.1 at.%) is dissolved uniformly in the as-quenched Zr-Cu-Pd-Al amorphous alloy even if oxygen is not added intentionally. When the alloy is crystallized, oxygen redistribution occurs; it is rejected from the primary  crystals and partitioned in the subsequently crystallized phases. Oxygen atoms are observed to enrich in the crystalline phase, and the concentration is approximately 4 at.%, virtually no oxygen is dissolved in the remaining amorphous phase. This demonstrates that oxygen redistribution occurs during the crystallization reaction thereby influences the kinetics of crystallization. The oxygen behavior in Zr-Ni-Cu-Al and Zr-Ti-Cu-Ni-Al metallic glasses will also be reported. 

9:30 AM MM1.3 
DECOMPOSITION IN Pd₄₀Ni₄₀P₂₀ BULK METALLIC GLASS. M. K. Miller , Oak Ridge National Laboratory, Metals and Ceramics Division, Oak Ridge, TN; R. B. Schwarz and Yi He, Center for Materials Science, Los Alamos National Laboratory, CMS, Los Alamos, NM. 

An atom probe field ion microscope and 3 dimensional atom probe characterization of the solute distribution in a bulk Pd₄₀Ni₄₀P₂₀ metallic glass in the as-cast state and after annealing has been performed. Statistical analysis of the atom probe atom-by-atom data detected the presence of short range ordering in the as-cast alloy. Phase separation at the nanometer level is observed in glassy samples after annealing above the glass-transition temperature. Crystallization proceeds by phase separation into three distinct crystalline phases. Atom probe analysis of the alloy annealed for 1 h at 410C revealed that the primary phosphide phase (orthorhombic) had an average composition of 47.6  0.3% Ni, 28.3  0.3% Pd and 24.2  0.3% P, the palladium-rich phosphide phase (orthorhombic) had an average composition of 69.8  0.6% Pd, 8.6  0.4% Ni and 21.6  0.6% P, and the palladium-nickel (face centered cubic) solid solution had an average composition of 44.7  0.4% Pd, 39.8  0.4% Ni and 15.6  0.3% P. 
This research was sponsored by the Division of Materials Sciences, U. S. Department of Energy, under contract DE-AC05-96OR22464 with Lockheed Martin Energy Research Corp., and contract W-7405-ENG.36 with the University of California. This research was conducted utilizing the Shared Research Equipment (SHaRE) User Program facilities at Oak Ridge National Laboratory. 

9:45 AM MM1.4 
A LOCAL PROBE INTO THE ATOMIC AND ELECTRONIC STRUCTURE OF METALLIC GLASSES USING EELS. F.M. Alamgir , Y. Ito, D.B. Williams, H. Jain, Lehigh University, Dept. of Material Science and Engr., Bethlehem, PA. 

The local atomic and electronic structure of bulk glass-forming metal alloys have not yet been unambiguously determined. One important reason for this is the lack of element-specific information available on the atomic coordination environment and the electronic density of states in these glasses.
In this light the Pd-Ni-P bulk glass-former and the Ni-P glass have been studied using electron energy-loss spectroscopy (EELS). The energy-loss near-edge structure (ELNES) of EELS provides local density of unoccupied states. The chemical environments around Ni in the glasses were compared to those of standard Ni compounds. In order to obtain the spatial distribution of the atoms in these two glass systems the extended energy-loss fine structure (EXELFS) of EELS was examined beyond ionization events in Pd and Ni atoms. EXELFS data were processed to obtain partial radial distribution functions (PRDFs) of Ni and Pd. Preliminary PRDFs obtained from the Pd M-edge shows the splitting of the second peak characteristic of the random-packing-of-hard-spheres model. 

10:30 AM *MM1.5 
VOLUME EFFECTS IN THE FORMATION OF BULK METALLIC GLASSES. A.R. Yavari , CNRS umr 5614, Institut National Polytech. de Grenoble, St-Martin-d'Heres, FRANCE; A. Inoue, IMR, Tohoku Univ., Sendai, JAPAN. 

In the early 1980s, it was proposed that one of the criteria for easy glass formation is the smallness of the volume change Vls of crystallisation of the undercooled liquid alloy [J. Chimie Physique 1982]. Usually any excess volume released into the liquid due to formation of denser crystallites is quickly evacuated to the external surfaces but in highly viscous undercooled liquids this process is slow and it was argued that Vls released at the crystallite growth interfaces will act as free volume, locally reducing the melt viscosity and increasing diffusion and crystal growth rate. It would then be expected that the less Vls is released in this manner, the easier the glass formation. Such a correlation has recently been confirmed by the very small values of Vls measured for bulk glasses developed in Sendai. 
It has also been found that elemental additions such as that of aluminium with sp outer electrons to transition metal and actinide-based glass-forming alloys with d and f unfilled bands result in significant densification and strongly negative volumes of mixing Vmix. It is argued that the strongly negative Vmix will modify the repulsive branch of the interatomic potentials and increase the activation energy for diffusive jumps thus contributing strongly to bulk glass formation by lowering of atomic mobility in the liquid alloy. 

11:00 AM MM1.6 
MÖSSBAUER STUDY OF THE EVOLUTION OF THE INTERNAL MAGNETIC HYPERFINE FIELD OF AN AMORPHOUS METALLIC GLASS. Raul Gomez , Vivianne Marquina, R. Ridaura, Sergio Aburto, M. Jimenez, UNAM, Dept of Physics, MEXICO. 

We present the temperature variation of the hyperfine field of a sample of amorphous Metglas 2605 SC, from 12 K up to 673 K, where the system becomes paramagnetic (Curie temperature) as measured by Mössbauer Spectroscopy (MS). The hyperfine field varies as predicted by the molecular field theory of Weiss with a total spin moment of 5/2, indicating that the Fe atoms in the amorphous state of this metallic glass are in a 3+ state. On the other hand, the temperature variation of the isomer shift shows the typical linear decrease associated with a quadratic Doppler shift. However, near the Curie temperature of the amorphous phase, a significant deviation of linearity is observed, probably due a change in the electronic distribution caused by the shut off of the long range magnetic coupling, with a concomitant change in the electronic shielding effects. 

11:15 AM MM1.7 
EXELFS OF METALLIC GLASSES. Yasuo Ito , Faisal M. Alamgir, David B. Williams, Himanshu Jain, Dept of Materials Science and Engineering, Lehigh University, Bethlehem, PA. 

The feasibility of using extended energy-loss fine structure (EXELFS) (the electron analog of extended x-ray absorption fine structure (EXAFS)) obtained from  1 nm² regions of metallic glasses to study their short-range order has been examined. The ability to obtain structural information with such a high spatial resolution is not possible with x-ray based techniques, which therefore cannot directly access, for example, the early stages of nucleation and phase separation. Ionization edges of the metallic glasses in the electron energy-loss spectrum (EELS) have been obtained from PdNiP and NiP metallic glasses using a fine electron probe (1 nm diameter) in a dedicated scanning transmission electron microscope (STEM). The partial radial distribution function (RDF) at a specific elemental site has been obtained by Fourier transforming the oscillatory part of the EXELFS. The spectrometer (GATAN 666 PEELS attached to a VG HB 501 STEM) is capable of acquiring the K ionization-edge of the lighter elements (Z  22). In practice, it is limited to about Z = 17 due to the poor signal-to-noise ratio in higher energy loss ranges, beam damage, contamination and instrumental stability. In this paper, we have attempted to analyze EXELFS of L- and M-edges of heavier elements (Ni and Pd) in order to extend the applicability of the technique to heavier elements. 

11:30 AM MM1.8 
SIMULATION OF STRESS DISTRIBUTION AND MECHANICAL RESPONSE OF METALLIC GLASSES. Yoshiaki Kogure , Masao Doyama, Teikyo Univ. of Science & Technology, Uenohara, Yamanashi, JAPAN. 

Atomic structure and stress distribution in metallic glasses are simulated by the molecular dynamics method. The embedded atom method potential is applied to express the atomic interaction. Glassy states of pure metals and binary alloys are produced by quenching the molten states. The atomic structures in the glasses are investigated by means of the radial distribution function and the simulated x-ray diffraction patterns.
The distributions of internal strain in the glass structures are evaluated from the correlation of atomic volume distribution. The long range correlation can be related with the elastic strain. The short range correlation in a few atomic distance may be related with the deformation potential of defect in the glasses, which causes the characteristic property of glasses seen at very low temperatures, such as the excess specific heat, the phonon scattering, the resonance absorption of sound, and so on. 
The external stresses are applied, and the changes of the local strain associated with the displacement of atoms are investigated. The experimental results of mechanical response of glasses by the ultrasonic measurement are usually analyzed on the basis of elastic model, and the distributions of double well potentials or quantum mechanical two level systems have been speculated. A purpose of the present study is to present a microscopic interpretation for the fundamental mechanism of stress interaction. 

11:45 AM MM1.9 CALCULATION OF THERMODYNAMIC, MECHANICAL AND TRANSPORT PROPERTIES OF MODEL GLASS FORMERS. Tahir Çagin, Yue Qi, Hao Li and William A. Goddard, III, Materials Simulation Center, Caltech, Pasadena, CA, Hideyuki Ikeda, William L. Johnson, Materials Science Department, Caltech, Pasadena, CA, Yoshitaka Kimura, Nippon Steel, JAPAN. 

Recently, we have parametrized Sutton-Chen type empirical many body force fields for FCC transition metals to study the thermodynamic, mechanical, transport and phase behavior of metals and their alloys. We have utilized these potentials in lattice dynamics calculations and molecular dynamics simulations to describe the structure, thermodynamic, mechanical and transport properties of pure metals and binary alloys in solid, liquid and glass phases. Here, we will describe these applications: equation of state of pure metals, mechanical properties of their binary alloys and viscosity of a binary alloy, (Au-Cu), as a function of composition, temperature, and shear rate, crystal-liquid, liquid-crystal phase transformation in (Ni-Cu), liquid to glass transformation in a model glass former, (Ag-Cu). We will discuss the microscopic structure, thermal and mechanical properties of this model glass. 

SESSION MM2: ATOMIC AND ELECTRONIC STRUCTURE II 
Chairs: Akihisa Inoue and Hans-Joerg Fecht 
Tuesday Afternoon, December 1, 1998 
Fairfax A/B (S)

1:30 PM *MM2.1 
THERMODYNAMICS AND BULK GLASS FORMING ABILITY FROM THE LIQUID STATE. P.J. Desre . 

Abstract Not Available 

2:00 PM MM2.2 
VISCOSITY MEASUREMENTS FOR La-Al-Ni ALLOYS BY AN OSCILLATING CRUCIBLE METHOD. Tohru Yamasaki , Tomohiro Tatibana, Yoshikiyo Ogino, Himeji Institute of Technology, Dept of Materials Science and Engineering, Himeji, JAPAN; Akihisa Inoue, Tohoku University, Institute for Materials Research, Sendai, JAPAN. 

Lanthanum-based and Aluminum-based La-Al-Ni amorphous alloys have a large glass-forming ability. In the glass-forming process from the liquid, the most important factor is the temperature dependence of the viscosity of the supercooled liquid. In the present study, the viscosity of Aluminum-based and Lanthanum-based La-Al-Ni liquid alloys and La-Al-Ni-Co-Cu alloy has been measured by an oscillating crucible method in the temperature range from melting temperature, Tm, up to about 1400 K. The viscosity below Tm was estimated from the Fulcher relation. 
Al90-XLaXNi10 (X=0-10 at., La55Al45-XNiX (X=10-40 at. and La55Al25Ni10Co5Cu5 alloys were treated in the present study. The oscillating crucible method of the inverse suspending type was used for measuring the viscosity under a purified helium atmosphere. The logarithmic decrement was found by measuring successive time intervals as the reflected beam the distance between two phototransistors. In the case of La55Al45-XNiX alloys, the viscosity increased with increasing Ni content up to about 20 at.  Ni and then decreased with increasing the Ni content, while the activation energy for viscous flow decreased to a minimum value at about 20 at.  Ni. This composition is well inconsistent with that of the La-Al-Ni alloy having largest glass-forming ability. When Co and Cu are added in La-Al-Ni alloys, the liquid viscosity tended to increase while the activation energy for viscous flow tended to decrease. The viscosity, , of the alloys can be well expressed by the Fulcher relation, i.e., ln  0.432+194.3/(T-466.2) for La55Al25Ni20 alloy, and ln  0.554+280.5/(T-454.3) for La55Al25Ni10Co5Cu5 alloy where h is given in mPa…s and T in K. 

2:15 PM *MM2.3 
SYNTHESIS AND PROPERTIES OF Pd-CONTAINING BULK GLASSY ALLOYS. R. B. Schwarz , Tong de Shen, and Joe D. Thompson, Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, NM . 

Bulk amorphous alloy ingots, a few inches in length and at least 7 mm diameter, have been prepared in the Pd-Ni-P, Pd-Cu-P, Pd-Cu-Ni-P, and Pd-Ni-Fe-P systems using a flux melting and water quenching technique. For these glasses, the difference between the crystallization temperature T_x, and the glass transition temperature T_g, T = T_x - T_g, ranges from 53 to 110 K. These large values of T open the possibility for the fabrication of amorphous near net-shape components using techniques such as injection molding. The molar volume, thermal, elastic, and magnetic properties of these alloys have been studied. For the iron containing bulk glasses, the partial molar volume of Fe in the Pd­Ni­ Fe-P bulk glasses is significantly larger than the molar volume of (metastable) fcc Fe, suggesting chemically selective Fe-Pd bonding. Both static and dynamic magnetic properties suggest that a spin glass is achieved for bulk amorphous Pd₄₀Ni_40-xFe_xP₂₀ alloys with x  5. A field­dependent re-entrant spin glass behavior is also observed for x = 17.5. Above the spin freezing temperature, the amorphous Pd₄₀Ni_40-xFe_xP₂₀ alloys (x  5) become superparamagnetic and subsequently paramagnetic with increasing temperature. 

3:15 PM *MM2.4 
NANOPHASES IN BULK METALLIC GLASSES. M. Weiss, N. Geier, M. Moske and K. Samwer , Institut f. Physik, Universitaet Augsburg, Augsburg, GERMANY. 

The bulk metallic glasses provide a new class of materials to study the thermophysical properties of undercooled liquids near the so called calorimetric glass transition. Viscosity measurements show that these systems have a fragilitiy index close to strong glass formers.This compares nicely with the KWW-exponent at the glass transition deducted from anelastic relaxation time measurements and can be related with models of dynamic heterogenities (solid-like and liquid-like clusters) in the liquid. In this concept the jump of the thermal expansion coefficient at the glass transition is expected and has been found experimentally. 

3:45 PM MM2.5 
IN-SITU ELECTRON DIFFRACTION STUDY OF STRUCTURAL CHANGE IN THE SUPER-COOLED LIQUID REGION IN AMORPHOUS La-Al-Ni ALLOY. Tadakatsu Ohkubo, Takashi Hiroshima, Yoshihiko Hirotsu , Osaka Univ, Inst of Sci & Ind Res, Osaka, JAPAN; Akihisa Inoue, Tohoku Univ, Inst of Mater Res, Sendai, JAPAN. 

It is known that amorphous La₅₅Al₂₅Ni₂₀ alloy has an excellent superplasticity in the stable supercooled liquid state between temperatures from about 470 to 515K¹⁾. These temperatures, 470 and 515K, correspond to those of the glass tarnsition(Tg) and the crystallization(Tx), respectively. T (=Tx-Tg) the supercooled liquid temperature range. Two-stage glass-transitions have been observed in the T range by measuring the changes in storage and loss moduli²⁾. However, no investigation has been made about atomic structures in the T range and also at temperatures before and after the galss transition. In this study atomic structures before and after Tg and in the T range on annealing have been investigated by in-situ electron diffraction using specimen-heating stage in TEM and the imaging-plate (IP) intensity recording. HRTEM imaging was also performed using IP in the annealing process. No local structural change was observed by HRTEM before and after Tg. From the analysis of atomic radial distribution functions, increases in interatomic distances of La-La, La-Al and La-Ni from about 2 to 4% were clearly observed at temperatures higher than Tg, which exhibits one of the natures of the supercooled liquid state. Just before the crystallization, the interatomic distance of La-La further increased. Atomic coordination number for La-La changes inversely in accordance with the change of La-La distance. It is confirmed that in the supercooled liquid state a stepwise atomic structural change occurs during heating up to the crystallization temperature. The two-stage structural change corresponds to the two-stage glass-transitions²⁾. 

4:00 PM MM2.6 
FREE-VOLUME CHANGES IN THE BULK METALLIC GLASS Zr_46.7Ti_8.3Cu_7.5Ni₁₀Be_27.5 AND THE UNDERCOOLED LIQUID. C. Nagel , K. Ratzke, E. Schmidtke, and F. Faupel, Univ. of Kiel, Dept. of Materials Science and Engineering, Kiel, GERMANY. 

Annealing of excess free-volume during structural relaxation has been investigated in splat quenched and slowly cooled bulk Zr_46.7Ti_8.3Cu_7.5Ni₁₀Be_27.5. Positron lifetime spectroscopy and density measurements clearly show a decrease of quenched-in excess free-volume at annealing temperatures below the glass transition temperature T_g. Isothermal measurements between 180 and 230C revealed the well-known Kohlrausch behavior for structural relaxation (). The effective activation energy is 0.7 eV. Structural relaxation is not accompanied by severe embrittlement. Quenching from temperatures above T_gshows a distinct increase in free-volume for thick bulk samples, whereas no increase could be found for thin splat samples. This geometry effect indicates that the outer sample surface plays a crucial role in annealing of excess volume. The increase in free-volume above T_g is in agreement with changes in the effective activation energy observed in diffusion and viscosity measurements. 
The Zr_46.7Ti_8.3Cu_7.5Ni₁₀Be_27.5 samples were provided by U. Geyer, Univ. of Göttingen, Germany. 

4:15 PM MM2.7 
DENSITY INHOMOGENEITY, GLUSTER PROPERTIES AND GLASS TRANSITION. Mo Li , Dept of Materials Science and Engineering, The Johns Hopkins University, Baltimore, MD. 

Is glass transition kinetic? Why the relaxation time for glasses nonexponential? What's the entropy of the undercooled liquid? How to rationalize the fragile and strong glasse's viscosity of undercooled liquid? Is it possible to have a universal criterion to predict the glass formibility? These questions will be addressed with an emphasis on their connections to the density inhomogeneity and cluster properties in glass forming systems. Some recent experimental results will be briefly reviewed and further detailed information on the microscopic level from molecular dynamics simulations will be presented. The connection to the glass transition and glass properties will be established. 

4:30 PM MM2.8 
STRUCTURE AND GLASS-FORMING ABILITY OF METALLIC MELTS. Vladimir Manov , Edward Brook-Levinson, Peter Popel, Vladislav Molokanov, Advanced Metal Technologies Ltd., Even Yehuda, ISRAEL. 

The properties of glass-forming metallic melts versus temperature were measured during samples heating above the melting point and their subsequent cooling. The following was found: 1) cooling and heating curves do not coincide below some temperature T; 2) curves slopes changes and the properties jumps occur at some temperature during the melt heating below T; 3) surface tension positive temperature coefficient at both heating and cooling and non-ideal forms of the cooling curves. The anomalies 1) reflect the melt structure irreversible changes near T. We relate it to destruction of microheterogeneities inherited from initially heterogeneous materials and stabilized by excess interface free energy. After heating above T the melt becomes a true solution and inclines to deeper undercoollng below liquidus. The anomalies 2) can be linked to the melt heterogeneous structure transformation. The non-ideal temperature dependencies of the properties following the melt transformation into a true solution, indicates complicated structure of the systems. It demonstrates that the melt structure before casting strongly influences the glass forming ability in preparation of Bulk Amorphous Alloys. 

4:45 PM MM2.9 
PROBING SLOW ATOMIC MOTIONS IN METALLIC GLASSES USING NMR. Yue Wu , Xiao-Ping Tang, Department of Physics and Astronomy, University of North Carolina, Chapel Hill, NC; Ralf Busch and William L. Johnson, Keck Laboratory of Engineering Materials, California Institute of Technology, Pasadena, CA. 

The nuclear magnetic resonance (NMR) technique of ⁹Be alignment echo is explained and it is demonstrated that this technique is an excellent tool for detecting ultraslow atomic motions in Zr-Ti-Cu-Ni-Be metallic glasses. Atomic motions can be detected by this technique in the timescale between the spin-spin relaxation time (about 1 ms) and several times of the spin-lattice relaxation time.