GLASS TEMPERATURE AND SOLID - LIQUID TRANSITION OF METALLIC GLASSES

Thermal and electric properties of metallic glasses and of crystalline reference samples have been measured starting from room temperature u p to the liquid state using a high-speed calorimeter. High heating rat es phi = dT/dt are required to prevent the crystallization of the glas ses. The glass temperature T(g) is found to increase continuously with phi from a lower limit T(go) at phi < 0.1 K/s to an upper limit T(gin finity) less-than-or-equal-to 1.25 T(go) reached at phi almost-equal-t o 10(4) K/s and remaining constant for higher phi. Two empirical relat ions exist between the entropy of fusion of a crystalline alloy, DELTA AS(m) = DELTAH(m)/T(m) (enthalpy of fusion/melting temperature) and th e properties T(ginfinity) and DELTAH(cro) (enthalpy of crystallization ) of the corresponding glass: DELTAS(m) = DELTAH(m)/T(m) almost-equal- to (DELTAH(m) -DELTAH(cro))/T(ginfinity) almost-equal-to 3Rln(Tm/T(gin finity)). These and related experimental results suggest that Tg(infin ity) is the melting temperature of a glass, whereas T(go) marks the be ginning of a thermally activated process in the solid glass, probably homogenization, whence the relation T(ginfinity)/T(go) less-than-or-eq ual-to 2 1/3 almost-equal-to 1.26 is derived.