Effects of annealing on microstructure and mechanical properties of nano-grained Ni-based alloy produced by severe cold rolling

Nano-grained (NG) Ni-based alloy with average grain size about 50 nm was produced via severe cold rolling at room temperature. Compared to the solution-treated alloy prepared for rolling, the cold-rolled (CRed) NG alloy exhibited approximately 475%, 130% and 180% increase in the average yield strength (YS), ultimate tensile strength (UTS) and microhardness, respectively. Effect of the annealing on mechanical properties and microstructure of this NG Ni-based alloy were investigated systematically. The annealed-CRed alloys possessed NG (90 nm) and ultrafine-grained structure (200 nm) after 60 min annealing at 700 and 800 °C, respectively, suggesting high thermal stability of the nanostructure. Peak YS and UTS of 2047.5 and 2142 MPa, respectively, were obtained with appropriate annealing temperature and time. The mechanisms of variations in mechanical properties were analyzed based on phase composition and microstructure evolution of the annealed NG Ni-based alloy. Both the high thermal stability and strength are due to the formation of the γ′ precipitates and slight grain growth of the NG matrix.