Kinetics of Ordering in the Alloy AuCu

Abstract

The kinetics of ordering in AuCu has been studied using electrical resistivity as the index of order. A purely phenomenological analysis of isothermal resistivity-time curves showed that ordering in this alloy is a process characterized by a single constant activation energy of 29 kcal. For further kinetic analysis, it is necessary to transform the raw data into isothermal order parameter-time curves. This was accomplished via Muto's theoretical relation between resistivity and the Bragg-Williams order parameter, S. A consistent kinetic picture was obtained in terms of S, with the ordering process accurately described by a simple third-order rate equation with all the kinetic constants fully evaluated. The usual ln (rate constant) versus 1/T plot gave an activation energy of 28.5 kcal in excellent agreement with the phenomenological activation energy. Further experiments showed that the proposed kinetics predicts correctly the response to complex time temperature sequences.