Phase Formation in Cr–Si Mixture during Mechanical Activation and Annealing

A chromium-silicon mixture of the CrSi₂ atomic composition is subjected to mechanical activation in a high-energy planetary mill for 9–60 min at a ball to material ratio of 20 : 1. Silicide formation during mechanical activation begins already after 9 min of milling, and only the highest silicide CrSi₂ is observed up to 60 min. During the milling, a roll-shaped structure is formed from alternating layers of Cr and Si, which become thinner with increasing activation time, reaching the diffusion path lengths of each other’s components in some places. With subsequent rapid (~6°C/s) heating of the activated mixtures to a temperature of 1000°C, starting from a milling time of 45 min, a state close to phase equilibrium is established, in which the content of CrSi₂ is maximal, but CrSi, Cr₅Si₃, and Si are also present (up to 10% in total). The diffusion nature of silicide formation is confirmed both during mechanical synthesis and during subsequent rapid heating. In this case, the observation of only one highest silicide CrSi₂ during milling is probably due to the abnormally large coefficient of interdiffusion of components in this silicide at low temperatures compared to other silicides, the layers of which in the “diffusion pie” are significantly thinner and are not detected in X-ray diffraction analysis.