Phase and structural transformations in the Ni65Mo20Cr15 alloy at changing the temperature of heat treatment

The ternary Ni65Mo20Cr15 alloy was studied using TEM after heat treatment at different temperatures. It has been shown that the tendency to phase separation which exists in the Ni/Mo diffusion couple at high temperatures leads to precipitation of crystalline particles of Mo atoms in the liquid solution. At lowering the heat treatment temperature to 1200 °C, a phase transition ordering - phase separation occurs in the Ni/Mo diffusion couple, which results in dissolution of the particles of Mo atoms. At 650 °C, there takes place precipitation of Ni2Mo phase particles, which can initiate intercrystalline embrittlement of Hastelloy-type alloys.