Microstructural Degradation and the Effects on Creep Properties of a Hot Corrosion-Resistant Single-Crystal Ni-Based Superalloy During Long-Term Thermal Exposure

摘要

In the present study, the kinetics of microstructural degradation during long-term thermal exposure (LTTE) and the effects on creep deformation mechanisms of a hot corrosion-resistant single-crystal Ni-based superalloy with a low gamma' volume fraction and gamma/gamma' lattice misfit were investigated in detail. The kinetic of gamma' coarsening in the experimental alloy conforms well to the Lifshitz-Slyozov-Wagner theory during LTTE at 900 degrees C up to 10,000 hours. The evolution of gamma/gamma' lattice misfit during the LTTE was also investigated by a first attempt. The focused research emphasized on the influences of gamma/gamma' lattice misfit evolution after the LTTE on the microstructural degradation, dislocation motion, and different creep mechanisms during high-temperature low-stress creep and high-temperature high-stress creep. The results show that the decreasing of the absolute values of gamma/gamma' lattice misfit and change of gamma' size and morphology after the LTTE contribute to the weakening of barrier to the dislocation cutting process into gamma' precipitates during creep and the sharp reduction of stress-rupture lifetime at 950 degrees C/280 MPa after 1000 hours exposure. As the applied stress decreased to 230 MPa at 950 degrees C, the creep mechanisms change from the dislocation cutting through gamma' precipitates at high applied stress to the dislocation glide and climb around gamma' precipitates. The dislocation glide and climb by-pass deformation mechanism were not significantly influenced by the change of gamma' precipitates morphology and magnitude of gamma/gamma' mismatch within 1000 hours thermal exposure, and the minimum creep rate and creep lifetime after 1000 hours thermal exposure were similar to that of the original heat-treated samples. (C) The Minerals, Metals & Materials Society and ASM International 2018