Effect of temperature on microstructure and residual stresses induced by surface treatments in Inconel 718 SPF

In this study, Inconel 718 (IN718SPF) samples were treated with three surface modification techniques: laser shock peening (LSP), cavitation shotless peening (CSP) and ultrasonic nanocrystalline surface modification (UNSM). Subsequently, these samples were exposed to temperatures between 550 °C–650 °C for different time intervals. Residual stresses on the sample surfaces were measured using XRD to compare the thermal relaxation behavior of samples treated with different surface treatments. The results show that surface compressive residual stresses induced by all three surface treatments are stable at high temperatures after initial relaxation. Further, TEM micrographs were obtained from surface treated samples that were exposed to 550 °C for 5 min and 24 h. A comparison of microstructures before and after thermal exposure is presented. The study quantifies activation enthalpy for residual stresses relaxation in LSP, CSP and UNSM treated IN718SPF and a relaxation mechanism is proposed. [Display omitted] •Surface treatment induced residual stress relaxation at high temperature in few minutes•Gradual reduction in magnitude of residual stresses after initial relaxation•Microstructural changes including formation of dislocation cells, reduction in dislocation density•Activation enthalpy for relaxation of residual stress: UNSM