Effect of shot peening on residual stress stability and high-temperature mechanical properties of powder metallurgy Ni-based superalloy

This study examines the effects of shot peening on the microstructure and high-temperature creep behavior of a powder metallurgy Rene 95 nickel-based superalloy. The alloy was processed by hot isostatic pressing, followed by solution treatment and two-stage aging. Shot peening introduced a high compressive residual stress of ~1200 MPa near the surface, along with local plastic deformation and grain refinement. Subsequent heat treatments (400–800 °C) showed minimal changes in grain size and local misorientation by EBSD, but residual stresses relaxed rapidly above 700 °C. This relaxation is attributed to the dissolution of fine tertiary γ′ precipitates, which alters dislocation behavior and reduces microstructural stability. Tensile testing revealed that yield and ultimate strengths were maintained up to 650 °C but declined significantly above 700 °C. High-temperature creep tests at 650 °C under 1034 MPa demonstrated that shot-peened specimens exhibited an approximately 82% longer creep life than the base material. These results indicate that compressive residual stresses from shot peening can partially mitigate high-temperature degradation mechanisms, thereby improving the creep performance of Rene 95 for high-temperature applications.