Transformation behavior of PdAuSi metallic glasses

Abstract

The transformation behavior of roller-quenched amorphous Pd 0.82− x Au x Si 0.18 and Pd 0.835− x Au x Si 0.165 alloys, where x ⩽ 0.10, after rapid heating to temperatures near to or above T g, is reported. The calorimetrically determined glass ( T g) and kinetic crystallization ( T c) temperatures both increased with x up to x ≈ 0.04. With increasing x, at x ⩾ 0.04, T c decreased rapidly while T g varied little. Binary Pd 0.82Si 0.18 alloys crystallized to an fcc phase without apparent composition segregation. The tendency to phase separate at T near T g, as manifested by small- (SAXS) and large-angle X-ray scattering and calorimetry, increased with increasing Au substitution. Pd 0.8Au 0.035Si 0.165 alloy apparently phase separated by a nucleation and growth mechanism, with a growth rate limited by the melt viscosity, to form an fcc phase dispersed in an amorphous phase which later crystallized. Pd 0.74Au 0.08Si 0.18 alloy phase separated initially to two melts, each of which later crystallized in turn. The initial separation behavior was generally consistent with the predictions of the spinodal theory but with some deviation from Cahn's linear relation.