A cinematographic study of the massive transformation in CuGa alloys

Abstract

The massive transformation in five CuGa alloys, containing between 22.8 and 24.3 at. % Ga, has been studied cinematographically during heating and cooling in a hot-stage assembly. The rate of heating and cooling varied between 4 and 30°C/sec. The cinematographic work was supplemented by metallographic and X-ray work at room temperature. It is concluded that under the conditions of the present study the major part of each transformation occurred by the propagation of incoherent boundaries of the massive phase in a manner expected for a diffusion-controlled process. The speed of the massive transformation was some 100 times faster than that of a diffusional process that produced equilibrium structures. In many cases the advancing transformation front became planar, particularly in regions where plastic deformation in the parent phase produced temporary barriers to further transformation. Plastic deformation was also in part responsible for the occurrence of the ledge-type of growth in the bulk, and for slip markings observed on the surface. It is concluded that growth of the massive phase grains occurs both with and without the existence of an orientation relationship between the parent and massive phases. The growth of (101̄1) twins and of other planar boundaries is reported.