The effect of heterogeneous precipitation behavior on the mechanical properties of IN718 superalloy after laser shock peening and heat treatment processes

Precipitation strengthening and severe plastic deformation (SPD) processes are the main ways to improve the strength of precipitation-reinforced alloys. Nevertheless, the improved strength is at the expense of the alloy's ductility. The combined strengthening effects of the different processes have received much attention from re-searchers. In this study, a combination of laser shock peening (LSP) and heat treatment (HT) processes introduces gradient microstructure in IN718, including sub-grain and dislocation pile-up and precipitated phases inside the grain. The precipitated phase effectively inhibits the thermal reversion of the grains, and the microstructure produced by LSP was retained. Further TEM observations show that the volume fraction of the precipitated phase shows a heterogeneous distribution from the grain edge to the center. This heterogeneous microstructure significantly changes the degree of hardening from the grain edge to the center while improving the plasticity in the LSP-hardened region. Thus, the overall plasticity of the material is maintained after HT. The results indicate that the gradient microstructure and inhomogeneous distribution of precipitation phases induced by the LSP and HT combined process can lead to excellent mechanical properties.