Hot deformation induced microstructure evolution of a novel as-extruded Ni-based P/M superalloy
Y.L. Wang, Y. Li, H. Zhang, Jianzheng Guo
Abstract
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 <101> 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 γ′ phases enlarged after hot deformation through an Ostwald ripening process and varied from ∼142.5 to ∼235.0 nm in different conditions while their initial sizes were ∼137.2 nm. The effect of strain rate on the particle size of γ′ phases was much greater than the deformation temperature that exhibited a stronger influence on their area fraction.