On the Kinetics of the Disorder-Order Transformation in Cu3Au

Abstract

The isothermal order‐dependent change in the Young's modulus of a single crystal of Cu₃Au is measured as a function of time at various temperatures in the range 279.3°C to 384.3°C. These temperatures were reached by quenching rapidly from an equilibrium state 28.2°C above the critical temperature (386.0°C). The time variations of Young's modulus indicate two distinct stages of the disorder‐order transformation. The initial stage starts immediately and is completed a few minutes after quenching, while the later stage requires a few minutes before starting and then proceeds very slowly toward an equilibrium state. ``Relative relaxation times'' are associated with each of them. In conformance with the work of Sykes and Evans and others, the initial stage is described as the formation of contiguous, antiphase, ordered domains by means of normal atomic interdiffusion. The later stage consists of the coalescence of these domains and requires at least two different geometrically constrained diffusion processes.