Phase-field simulation of γ(A1) + γ′(L12) + γ"(D022) three-phase microstructure formation in Ni-base superalloys

The calculation of gamma(A1) + gamma'(L1(2)) or gamma(A1) + gamma(D0(22)) two-phase microstructure changes in Ni-base superalloys has been one of the main subjects in the phase-field method, because the morphology of these two-phase microstructures crucially influences the high temperature mechanical properties of Ni-base super alloys. In this study, more complicated phase decomposition behavior, in which three phases, gamma(A1), gamma'(L1(2)) and gamma ''(D0(22)) are simultaneously included, is modeled on the basis of the conventional phase-filed method. The results obtained are as follows: The present simulation model reasonably reproduces the complex feature of microstructure changes including gamma, gamma' and gamma '' three phases, e. g. the characteristic morphology of the gamma' particles covered with gamma '' phase is simulated realistically. The morphology of the microstructure is mainly controlled by the elastic strain energy induced from the lattice mismatches among these three phases. In particular, the magnitude relation among the lattice parameters of the three phases is a key factor to control and understand the morphological changes of the complex microstructure including gamma, gamma' and gamma '' three phases.