Composition dependence of ordering kinetics in Cu₃Pt

Abstract

The effect of alloy composition on the ordering kinetics in L1₂ Cu₃ Pt, ranging from 13 at.% to 23 at.% Pt, is investigated. It is confirmed that ordering in the alloys proceeds in two stages. Stage I is associated with heterogeneous nucleation and growth-type ordering and stage II with homogeneous ordering. Each stage of ordering is characterized by the associated anti-phase domain (APD), i.e. the stripe-like APD for the heterogeneous ordering and the maze- or swirl-like morphology for the homogeneous ordering. Differential thermal analysis (DTA) has revealed that the relative dominancy between stage I and stage II ordering depends on the alloy composition and that stage I ordering is most dominant in Cu-15 at.% Pt. The temperature regime for each stage of ordering has been determined over the range of compositions investigated. The activation energy for each stage of ordering as a function of alloy composition has been evaluated by two methods (1) through the change in intensity ratio during isothermal ordering obtained by X-ray measurements, and (2) through the DTA results upon continuous heating. The compositional dependence of the activation energy is discussed in terms of the ordering mechanism at each stage which involves different types of vacancy to assist the ordering.