Characteristics of microstructure evolution of surface treated IN718 superalloy by warm laser shock peening during long-term aging at high temperatures

The microstructure evolution behavior and its mechanism of the surface treated IN718 superalloy by laser shocking peening (LSP) and warm laser shocking peening (WLSP) followed by long-term aging at high temperature ranging from 600 °C to 680 °C were investigated in the present study. It was found that the substructure evolution behavior, compressive residual stress reduction and γ″ phase coarsening of the hardened surface layer of WLSP sample could be effectively inhibited at high temperature, in comparison with those of LSP counterpart. Owing to the formation of complex structure of γ″ phase and high-density dislocation with stacking faults (SFs) and micro-twins in γ″ phase in the hardened layer of WLSP alloy, more stable and higher density geometrically necessary dislocations (GNDs) were developed around γ″ phase, which changed the micro-stress distribution of the hardened layer and produced more stable hetero-deformation induced strengthening effects. The findings of the present study provide a new cognition for further deepening the micro-mechanism of strengthening and toughening of hardened surface layer in WLSP treated IN718 superalloy at high temperature, promoting the more practical application of WLSP technology in the manufacturing field of key components of superalloys.