A bimodal γ′ phase precipitation in Ni-Al alloys with preaging and continuous cooling: phase-field simulation

A bimodal precipitation with primary and secondary gamma ' phase in Ni-17 at.% Al alloys was produced via preaging and continuous cooling. The morphology and composition evolution of gamma ' phase during cooling process were studied by using phase-field simulation, the bimodal precipitation mechanism was declared. The content of Al in secondary gamma ' phase is lower than the equilibrium composition because of the slower atom diffusion during continuous cooling. With the increase of cooling rates, the volume fraction and average radius of primary and secondary gamma ' phase are reduced, the number density of secondary gamma ' phase increases; in addition, the inter-distance of particle size distribution of primary and secondary gamma ' phase is widen. A long time of isothermal preaging reduces the precipitation and growth of secondary gamma ' phase. The hybrider precipitates with bimodal size distribution of gamma ' phase help optimizing the precipitates morphology of nickel based alloys.