Microscopic phase-field simulation for precipitation behavior of Ni-Al-Cr alloy during two-step aging

Based on the microscopic phase-field model, the pre-aging temperature effects on the precipitation mechanism and microstructure evolution during two-step aging for Ni75Al9Cr16 alloy were simulated. The results show that the early precipitation mechanism of Ll(2) phase is the mixed mechanism of spinodal decomposition and non-classical nucleation growth, whereas the early precipitation mechanism of DO22 phase is spinodal decomposition when the pre-aging temperature is 873 K. The early precipitation mechanism of Ll(2) phase is non-classical nucleation growth, whereas the early precipitation mechanism of DO22 phase is spinodal decomposition when the pre-aging temperature is 973 K. Under the effects of elastic strain energy, the cubic particles exhibit directional alignment along [100] and [010] directions during the late precipitation. which is more obvious at lower pre-temperature. DO,, phases appear earlier than Ll(2) phases under these two kinds of precipitation processes; and the nucleation incubation time becomes long with the increase of pre-temperature.