Kinetic study of the precipitation in physical vapour depositedMg–12% wt. Ti alloy

Abstract

Kinetic parameters of titanium precipitation in Mg–12 wt.% Ti obtained by physical vapour deposition (PVD) have been studied using the Johnson–Mehl–Avrami equation extended to a non-isothermal transformation. The titanium precipitation takes place in two stages: the first corresponds to the nucleation and growth of the precipitates by diffusion along the basal plane and the second to their coarsening along the [0001] direction. The Avrami exponent, n, has been calculated from the differental scanning calorimtery curves for the two stages. In both cases values of n around 1 were obtained, which indicate a diffusion process dominant in one dimension. Furthermore, at the last stage of titanium nucleus formation, a decrease in Avrami exponent has been observed associated to a fast and progressive saturation of nucleation sites.