Crystal plasticity phase-field simulation of creep property of Co-base single crystal superalloy with pre-rafting

Abstract

Co-base superalloys with γ′-Co3(Al,W) precipitates show attractive properties in high temperature, while the creep concomitant with rafting of γ′ precipitates is a critical problem for this newly developed alloy. Creep properties and rafting morphology in Co-10 Al-9 W (at.%) alloy at 1173 K were studied by the creep damage crystal plasticity phase-field model coupled with sublattice free energy. Creep strain and strain rate increase with the creep stress changing from 237 MPa to 397 MPa, whereas the creep life is shortened, the simulation results consist well with the general creep laws. With the accumulation of creep strain, the creep strain and creep rate increase in the later stage of creep. N-type pre-rafting enhances the tensile creep resistance of Co-10 Al-9 W (at.%) alloy under 1173 K/237 MPa in the first and second creep stage, while such an enhancement effect disappears for the large stress of 297 MPa. The large stress induces the topology inverse of N-type pre-rafting to the P-type rafting, heterogeneous distribution of diffusion potential induced by stress provides the driving force for element diffusion during topology inverse. The results show the methods and mechanisms for improving the creep property via the pre-rafted morphology in Co-base superalloy.