Effect of Protective Coating Layer and Overlapping Factor on the Microstructure and Mechanical Properties of Rene-80 Ni-Based Superalloy in Laser Shock Peening Process

The evolution of microstructures resulting from plastic deformation plays a crucial role in enhancing the mechanical properties of superalloys treated with laser shock peening (LSP). In this study, the Rene-80 Ni-based superalloy underwent LSP in two modes: with and without a protective layer, across three different overlap levels. The investigation focused on analyzing the microstructure, surface attributes, and mechanical properties. The findings revealed a maximum residual stress of − 482 MPa at a 66% overlap, with a notable reduction as the overlap factor decreased. The absence of a protective layer led to component melting, increased surface roughness, and reduced compressive residual stresses. Scanning electron microscopy (SEM) showed that the γ' precipitates were distorted and transformed into a non-cubic state due to dislocation slip and intense plastic deformation induced by the laser plasma, both with and without the protective layer. Electron backscattering diffraction (EBSD) analysis revealed that severe plastic deformation on the sample surface caused a 33% reduction in average grain size, from 750 to 500 μm. Additionally, there was a 35% increase in low-angle grain boundaries and a 65% increase in high-angle grain boundaries, indicating heightened dislocation activity and grain boundary formation, as well as the development of twins near the surface. These microstructural changes led to a 26% increase in surface hardness after LSP. Due to the gradient nature of the applied strain, the increases in hardness and grain refinement diminished with increase in distance from the surface.