Investigating the correlation between mechanical properties and gradient microstructures in laser shock peened CrCoNi alloy

In this study, laser shock processing (LSP) was used to enhance the mechanical properties of CrCoNi medium-entropy alloys (MEAs) by introducing the gradient microstructures (GS) within the material. Extensive microstructural characterizations confirmed a progressive distribution of nanocrystalline grains, dislocations, and deformation twins along the material's depth. Quantitative measurements of microstructural parameters at varying depths were conducted. Near the surface, the predominant microstructural evolutions were high dislocation density, twins, and grain refinement. At deeper regions, the key behaviors were nanoscale grain refinement and twin collisions. Nanoindentation and micro-pillar compression tests were employed to characterize the hardness distribution and mechanical properties at the microscale. It was found that LSP significantly improved hardness and yield strength. A quantitative relationship between GS and mechanical properties was developed, with theoretical calculations showing good agreement with experimental results. The contributions of different microstructural evolutions to hardness were individually assessed, revealing that multi-stage twins and grain refinement were the primary strengthening factors after one and ten impacts, respectively.