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Session Chairperson: Dr. Robert J. Gottschall, Division of Materials Science (ER-13), U.S. Department of Energy, Germantown Building, 19901 Germantown Road, Germantown, MD 20874-1290
8:30 am INVITED
INTRODUCTORY REMARKS: Robert J. Gottschall, Division of Materials Science (ER-13), U.S. Department of Energy, Germantown Building, 19901 Germantown Road, Germantown, MD 20874-1290
8:45 am INVITED
FERROMAGNETIC BULK AMORPHOUS ALLOYS: Akihisa Inoue, Institute for Materials Research, Tohoku University, Katahira 2-1-1, Sendai 980-77, Japan
Since the discoveries of bulk amorphous alloys in Ln-Al-TM, Mg-Ln-TM and Zr-Al-TM (Ln=lanthanide metal, TM=transition metal) systems for the last several years, great attention has been paid to bulk amorphous alloys. It was subsequently reported that bulk amorphous alloys were formed in Ti-Zr-TM, Zr-Ti-TM-Be and Pd-Ni-Cu-P systems. The maximum thickness reaches 40 mm and the critical cooling rate is of the order of 1K/s. However, there have been no data on bulk amorphous alloys with ferromagnetism at room temperature. We have derived three empirical rules for the achievement of large glass-forming ability from previously reported bulk amorphous alloys. Based on the three rules, we have searched new ferromagnetic bulk amorphous alloys and succeeded in finding several ferromagnetic bulk amorphous alloys in Fe-, Co- and Ln-based systems. The Fe-based bulk amorphous alloys exhibit good soft magnetic properties of 1.3 T for magnetization, 2 A/m for coercive force (Hc), 7000 for permeability at 1 kHz and 21x10-6 for magnetostriction. The Ln-based bulk amorphous alloys were prepared in the diameter range up to 15 mm and exhibited rather good hard magnetic properties of high Hc of 400 kA/m and maximum energy products of 20 kJ/m3. These discoveries seem to be promising for future progress of bulk amorphous alloys.
9:25 am INVITED
THERMODYNAMIC AND KINETIC ASPECTS OF BULK METALLIC GLASS FORMING ALLOYS: William L. Johnson, W.M. Keck Laboratory of Engineering Materials 138-78, California Institute of Technology, Pasadena, CA 91125
The development of several families of multicomponent alloys which form metallic glasses at relatively low cooling rates has triggered renewed interest in thermodynamic and kinetic properties of undercooled liquid metals as well as glass formation. Results of studies of atomic diffusion, viscosity, specific heat, liquid phase separation, and crystallization kinetics will be surveyed for alloys in the Zr-Ti-Ni-Cu-Be and Zr-Ti-Ni-Cu-Al systems. Containerless processing studies of the undercooled melts using electrostatic and electromagnetic levitation will be described. Liquid phase separation, impurity effects, and heterogeneous crystal nucleation are found to play an important and often unanticipated role in the crystallization kinetics. This has led to new understanding of the factors which govern glass formation in these bulk glass forming materials.
10:05 am INVITED
PHASE SEPARATION, CRYSTALLIZATION AND FORMATION OF QUASICRYSTALS IN BULK Zr-BASED AMORPHOUS ALLOYS: Uwe Köster, Department of Chemical Engineering, University of Dortmund, D-44221 Dortmund, Germany
Crystallization occurs by nucleation and growth. Growth may be primary, eutectic or polymorphic. Crystallization statistics as performed by TEM indicate heterogeneous nucleation with large transient times below the glass transition; nucleation and growth rates obey Arrhenius equations with activation energies typical for diffusion. Above glass transition homogeneous nucleation has been found and kinetics can be described best by Vogel-Fulcher-Tammann equations. From Crystallization studies typical metal-metalloid glasses are fragile, but the new bulk amorphous alloys are strong glasses. Amorphous phase separation prior to crystallization not only increases the glass forming ability, but also leads to the formation of nanocrystalline structures. Phase separation might be responsible for the strong influence of oxygen and hydrogen on the crystallization of Zr-based metallic glasses. Some bulk amorphous alloys transform into quasicrystals. Their nucleation and growth rates are measured in detail. The relation between glass-forming ability, existence of Laves phases and formation of quasicrystals will be discussed.
10:45 am BREAK
11:00 am INVITED
BULK NANOCRYSTALLINE AND AMORPHOUS REFRACTORY ALLOYS AND THEIR PROPERTIES: S.J. Poon, G.J. Shiflet, D.J. Li, K.J. Doherty, Department of Physics, Department of Materials Science, University of Virginia, Charlottesville, VA 22901
Synthesis of bulk samples of refractory metal alloys containing nanocrystalline and amorphous phases via conventional casting and their structural and physical properties will be reported. First, we will present results on (Fe, Ni, Cu, Nb)95Zr5 systems. Key factors for forming the titled phases will be discussed. Then we will report recent results on titanium alloys, with emphasis on structure and phase transformation.
11:40 am INVITED
BULK AMORPHOUS METALLIC ALLOYS: SYNTHESIS BY FLUXING TECHNIQUES AND PROPERTIES: Yi He, Ricardo B. Schwarz, Center for Materials Science, MS-K765, Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM 87545
Fluxing techniques have been used to study the undercooling and vitrification of glass-forming binary, ternary and quaternary alloy melts. By reducing and neutralizing heterogeneous nucleation centers, molten Pd10Fe30Ni40P20 were undercooled to 303 K or 0.26 Tm below its melting temperature Tm, while bulk amorphous Pd-Ni-P and Pd-Cu-P alloy rods with diameters ranging from 7 to 25 mm were synthesized over a wide composition range. The crystallization temperatures Tx and the glass transition temperatures Tg of these bulk amorphous alloys were determined by differential scanning calorimetry (DSC). For most bulk amorphous Pd-Ni-P alloys, the difference T=Tx-Tg is larger than 90 K, and bulk amorphous Pd40Ni40P20 cylinders with 25 mm in diameter can be easily fabricated. T for bulk amorphous Pd-Cu-P alloys is smaller than for amorphous Pd-Ni-P alloys, and exhibits a dependence on the phosphorus concentration which peaks near 20 at.% P. The glass formability of Pd-Cu-P was increased substantially when part of Cu was placed by Ni. Our results demonstrate that the critical cooling rates for glass formation in Pd-Ni-P and Pd-Cu-Ni-P alloys are the lowest among all known bulk metallic glass forming systems. The density, microhardness, elastic properties, specific heat and the glass formation range of these alloys will be reported.
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