Creep behaviors of fine-grained Ni-base powder metallurgy superalloys at elevated temperatures

In this work, the high temperature creep properties of three newly developed P/M superalloys with fine grains were investigated under conditions of 650 °C/1100 MPa, 750 °C/690 MPa, and 815 °C/550 MPa. The creep behavior associated with microstructure were analyzed, considering the interactions of dislocation with grain boundaries and γ′ phase. The results indicated that the cracks were more likely to initiate at grain boundaries, resulting in intergranular cracking. Moreover, the dislocation movement in grains was strongly related with testing temperature and applied stress, which is explained by theoretical calculation on the composition-dependent critical stresses (CSs) to trigger various mechanisms, including dislocation shearing the γ′ phase by stacking faults (SFs) or APB coupled dislocation pairs, and dislocation climbing.