Creep behaviors of multiphase Ni3Al-based intermetallic alloy after 1000 °C-1000 h long-term aging at intermediate temperatures

The microstructure evolutions during 1000 degrees C-1000 h long-term aging and relevant 800 similar to 840 degrees C/220 similar to 300 MPa creep behaviors of a novelly designed multiphase Ni3A1-based intermetallic alloy were investigated. Results showed this alloy presented excellent intermediate temperature creep properties even after 1000 degrees C-1000 h long-term aging. A kind of bimodal R-type gamma' rafting structures were observed in the 800 degrees C/220 MPa creep process of the long-term aged alloy, and the creep resistance levels of three kinds of gamma' rafting structures were evaluated to be in the order of bimodal R-type gamma' rafting structures > R-type gamma' rafting structure > N-type gamma' rafting structure. The 1000 degrees C-1000 h long-term aging can promote the inhomogeneous precipitation of Cr4.6MoNi2.1 phase at the edge gamma'-gamma dendrite area, which can play the role of pinning dislocations and inhibiting the further rafting and coarsening of the R-type gamma' rafts during creep. Differed from Ni-based alloys and other Ni3Al-based alloys, this long-term aged alloy exhibited abnormal four-stage creep characteristics, which consisted of atypical short steady-state creep stage with step fluctuant feature and atypical long accelerated creep stage with creep rate increasing at a constant rate.