Metastability and thermophysical properties of metallic bulk glass forming alloys |
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Authors: | R K Wunderlich H J Fecht |
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Affiliation: | (1) Materials Science and Engineering Department, Technical University Berlin, D-10623 Berlin, Germany;(2) the Materials Science Department, University of Ulm, D-89081 Ulm, Germany |
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Abstract: | The absence of crystallization over a wide time/temperature window can be used to produce bulk metallic glass by relatively
slow cooling of the melt. For a number of alloys, including several multicomponent Zr-based alloys, the relevant thermodynamic
and thermomechanical properties of the metastable glassy and undercooled liquid states have been measured below and above
the glass transition temperature. These measurements include specific heat, viscosity, volume, and elastic properties as a
function of temperature. As a result, it becomes obvious that the maximum undercooling for these alloys is given by an isentropic
condition before an enthalpic or isochoric instability is reached. Alternatively, these glasses can also be produced by mechanical
alloying, thus replacing the thermal disorder by static disorder and resulting in the same thermodynamic glass state. During
heating through the undercooled liquid, a nanoscale phase separation occurs for most glasses as a precursor of crystallization.
This article is based on a presentation made in the “Structure and Properties of Bulk Amorphous Alloys” Symposium as part
of the 1997 Annual Meeting of TMS at Orlando, Florida, February 10–11, 1997, under the auspices of the TMS-EMPMD/SMD Alloy
Phases and MDMD Solidification Committees, the ASM-MSD Thermodynamics and Phase Equilibria, and Atomic Transport Committees,
and sponsorship by the Lawrence Livermore National Laboratory and the Los Alamos National Laboratory. |
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