Hot deformation induced microstructure evolution of a novel as-extruded Ni-based P/M superalloy

Hot extrusion (HEX) and isothermal forging (ITF) are two critical processing methods in manufacturing of Ni-based powder metallurgy (P/M) superalloys. Hot compressions with different parameters were performed on a novel Ni-based P/M superalloy in as-extruded condition to simulate ITF and the related microstructure evolution. The results revealed that the as-extruded alloy was fully recrystallised with no preferred orientation, while hot deformation at relatively high strain rate could induce the formation of texture. Low-angle grain boundaries were formed due to the rearrangement of deformation-induced dislocations. The existence of high-angle grain boundaries led to dislocation pile-ups and resultant local stress concentration. The grains were remarkably refined after hot deformation due to dynamic recrystallisation and corresponding reduction of average grain size varied from 20 to 67%. The average particle size of gamma ' phases enlarged after hot deformation through an Ostwald ripening process and varied from similar to 142.5 to similar to 235.0 nm in different conditions while their initial sizes were similar to 137.2 nm. The effect of strain rate on the particle size of gamma ' phases was much greater than the deformation temperature that exhibited a stronger influence on their area fraction.