Effect of power density on microstructure characterization and fatigue behavior of laser shock peened Rene-80 Ni-based superalloy

Abstract

The microstructure plays a crucial role in determining the mechanical properties and performance of materials, particularly in high-strength alloys such as Rene-80. This study focuses on the microstructure characterization of Rene-80 nickel-based superalloy after undergoing Laser Shock Peening (LSP), an advanced surface treatment technique imparting beneficial residual stresses and improving fatigue life. The primary objective of this research is to investigate how varying power densities during the LSP process affect the microstructure of the Rene-80 superalloy. The power density in LSP is a critical parameter that influences the intensity of shock waves imparted onto the material’s surface, consequently impacting the microstructure. Through advanced microscopy techniques and analysis, the study explores the resulting microstructural changes, including surface roughness, dislocation density, and the presence of defects like dislocations and dislocation cells. These alterations are vital indicators of the material’s mechanical properties, such as tensile and fatigue strength. LSP samples were characterized using various techniques, including field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), and X-ray diffraction (XRD) analysis. Additionally, the mechanical performance of the samples was assessed through low-cycle fatigue tests and tensile tests, both conducted before and after LSP treatment. The optimal power density for Laser Shock Peening is determined to be 2.5 HEL. At this power density, the shock wave generated does not create a molten layer on the surface but accumulates defects, resulting in maximum compressive residual stress at the surface. LSP induces intense plastic deformation in the sample, distorting γ’ precipitates. Higher power densities lead to the formation of cross-linked sets of slip bands, highlighting defect slip as the main mechanism of plastic deformation in the LSP process. Understanding these effects is essential for optimizing the LSP process parameters to achieve desired mechanical properties and enhance the performance and longevity of components made from Rene-80 nickel-based superalloy in high-stress applications. It was found that the fatigue life of the samples increased by 500% and optimizing the effect of power density on the LSP process led to an improvement in the fatigue life of the Rene 80 samples.