Phase-field simulation of rafting kinetics in a nickel-based single crystal superalloy

Abstract Directional coarsening (rafting) of the γ ′ precipitate phase during creep in a nickel-based single crystal superalloy is simulated using the phase-field method. Both the morphological change of the γ ′ phase and the microstructure-dependent heterogeneous creep of the γ matrix phase are modeled in the simulation. In three-dimensional simulations considering a single γ ′ particle at 1273 K under tensile stresses of 130 MPa and 100 MPa along the [001] crystallographic direction, the γ ′ phase coarsens toward the direction perpendicular to the applied stress axis. The simulated macroscopic creep rate–time curve in the initial stage of creep is consistent with the experimental data. The time to rafting increases with decreasing magnitude of the applied external stress. Furthermore, the external stress is removed at an arbitrary strain in the simulation at 1273 K, and the occurrence of rafting during the subsequent heat treatment without external stress is confirmed. The simulation results show that the threshold value of macroscopic strain for inducing rafting ( ɛ th ) is ɛ th = 0.12 % – 0.16 % in the stress range of 100–160 MPa. Moreover, rafting can be accelerated by removing the external stress of 100–160 MPa when the macroscopic strain exceeds ɛ th .