Effect of laser shock peening on surface morphology and microstructure of Inconel 625 alloy

The surface microstructure of Inconel 625 alloy is refined through the application of laser shock peening （LSP） technology， aiming at optimizing its surface morphology.The microstructural characteristics are examined using laser scanning confocal microscopy， electron backscatter diffraction （EBSD）， and transmission electron microscopy （TEM）. Vickers microhardness testing is employed to analyze hardness variations. The results show that suitable LSP conditions can eliminate impact pits and enhance surface quality. Furthermore， the microstructure gradually transitions， with the surface layer evolving into ultrafine lamellae and grains under LSP treatment. The surface layer is predominantly composed of substructures and deformed grains， whereas the transition layer features a mix of deformed grains and recrystallized structures. As the depth increases， the population of deformed grains decreases， and recrystallized grains increases. A quantitative assessment of the geometrically necessary dislocation density （ρGND） for the alloy after five LSP treatments show that the surface ρGND reaches 2.91×1014 m-2， compared to 0.61×1014 m-2 for the untreated layer， indicating a significant increase post LSP. This alteration in dislocation density results in a shift in microhardness， which escalates with the number of LSP cycles and diminishes with depth. This trend can be attributed to LSP-induced changes in the proportion of large-angle grain boundaries， with the grain boundary strengthening effect in Inconel 625 alloy adhering to the Hall-Petch relationship.