Phase-Field Simulation of γ′-Co3 (Al, W) Evolution Kinetics with Antiphase Boundaries in Co-Based Monocrystal Superalloys

Antiphase boundaries (APBs) of L1(2) ordered gamma '-Co-3 (Al, W) precipitates have an essential effect on the high-temperature strength of Co-based monocrystal superalloys. In this work, the antiphase boundaries and their effects on the evolution kinetics of gamma ' phase are studied with the phase-field model. The formation of APBs between gamma ' phases with different crystallographic variants induces a sharp increase in free energy; the width of APBs measured by the edge-to-edge distances of the gamma ' phase is consistent with the experimental results of superalloys. Also, a coupling behavior of Ostwald ripening and APB's migration in the coarsening of the gamma ' phase is revealed. In addition, the volume fraction of the gamma ' phase with four antiphase domains is lower than that of the single-domain gamma ' phase, and the time exponent of the particles' number density of the gamma ' phase at the steady coarsening stage changes from -0.99 of single domain to -0.8 of APBs. The results show that the high-energy APBs can reduce the coarsening rate of gamma ' phases, which are significant in the microstructure and composition designing of the ordered precipitates with APBs in Co-based superalloys.