Precipitation study on Mg-12 wt% Ti alloy obtained by physical vapour deposition

Abstract

The thermal stability of Mg-12 wt% Ti alloy processed by physical vapour deposition has been studied using differential scanning calorimetry (DSC) and transmission electron microscopy. The alloy in the as-deposited condition is a solid solution of titanium in magnesium. During DSC experiments, three exothermal transformations have been observed. The first at 430 K is related to the stress relaxation of defects introduced during the growth process. The second transformation is associated with the precipitation of titanium in the magnesium matrix, which occurs in two stages. In the first stage, small coherent precipitates around 1 nm in size are present in the basal plane. The second stage has been associated with the growth of the titanium precipitates along the [0001] direction. The activation energies for these transformations are 144 and 155 kJ mol-1 respectively. At higher temperatures, above 703 K, an increase in heat flow takes place that is related to the strong oxidation of the magnesium matrix.