Microstructure evolution in a Fe-Ni-Si alloy during heat treatment and electron irradiation

Experiments have been made on studying structural and phase changes by the residual resistivity method in a Fe-Ni-Si alloy during annealing and electron irradiation. Thermal diffusion starts above 600 K and ensures decomposition of the solid solution up to 700 K; at higher temperatures it provides homogenization of the solid solution with the dissolution of intermetallic compounds in accordance with the equilibrium phase diagram. It is shown that, upon irradiation with electrons above 240 K, vacancy clusters are formed in both the aged and quenched alloys. Dissociation of clusters occurs at temperatures ranging between 350 and 500 K and leads to solid solution decomposition under the influence of diffusion caused by migrating vacancies with the formation of intermetallic precipitates. Irradiation at 423 K causes migration of vacancies and decomposition of the solid solution. In alloys irradiated at both temperatures above 700 K, as well as in unirradiated alloys, the precipitates dissolve in accordance with a single equilibrium dependence.