Effect of laser shock peening (LSP) on the microstructure, residual stress state and hardness of a nickel based superalloy

Efforts have been made here to understand the effect of laser shock peening (LSP) on the phase, microstructure, residual stress and hardness of a nickel (Ni) based superalloy. A 10 J Nd:YAG laser was used for the LSP operation. Following LSP detailed microstructural, surface topography, phase and compositional analyses, along with residual stress and hardness studies were undertaken. A parametric window was first established to explore the relationship between LSP process parameters and the respective surface and bulk properties. The effects of an ablative medium on the properties of the modified layer was also investigated. Qualitative and quantitative information on dislocation density was obtained using X-ray diffraction (XRD) analysis and correlated with the processing parameters. Residual stress developed following LSP was measured using the XRD technique. Nanocrystallization of the Ni matrix was observed following LSP under optimized laser operating parameters. An increase in the hardness of the Ni based superalloy was observed due to the microstructural refinement. The residual stress state on the surface of the laser shock peened Ni based superalloy showed a maximum compressive stress of 166 MPa, which gradually decreased with depth from the surface. A detailed microstructure-property relationship was established to understand the mechanism of property enhancement. Further optimization of the LSP process to surface treat the Ni-based superalloy will open up new avenues for the material’s applicability, particularly in the aerospace sector.