Rafting and redissolution of γ' phase in Ni-Al alloy under external stress.

The volume fraction and rafting degree of the γ'-NiAl phase under stress and high temperature are the key characteristics of mechanical properties in Ni-based superalloys, the rafting and redissolution of γ' phase caused by the creep at high temperature damage the morphology and properties of Ni-based superalloys. The phase-field simulation is performed to study the rafting accompany with the redissolution of γ' phase under high temperature and loading stress in Ni-Al alloy, the driving force and kinetics evolution of the γ' rafting were revealed. During the rafting under continuous heating, the elastic energy in the vertical γ channel is different to that of the horizontal γ channel, this difference in elastic energy drives the elements diffusion directionally to form the γ' rafts morphology. With the increased tensile stress, the decrease of specific surface of the γ' phase slows down the redissolution, a higher volume fraction is reserved for the rafted γ' phase. With temperature increases, the interface of γ/γ' phase becomes more diffusional and wider under stress. The results give an insight on the rafting mechanism of γ' phase and the kinetics evolution in Ni-based superalloys under excess temperature.