METASTABILITY AND THERMOPHYSICAL PROPERTIES OF METALLIC BULK GLASS-FORMING ALLOYS

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 properti es of the metastable glassy and undercooled liquid states have been me asured below and above the glass transition temperature. These measure ments include specific heat, viscosity, volume, and elastic properties as a function of temperature. As a result, it becomes obvious that th e maximum undercooling for these alloys is given by an isentropic cond ition before an enthalpic or isochoric instability is reached. Alterna tively, these glasses can also be produced by mechanical alloying, thu s replacing the thermal disorder by static disorder and resulting in t he same thermodynamic glass state. During heating through the undercoo led liquid, a nanoscale phase separation occurs for most glasses as a precursor of crystallization.