Rapid surface modification of SLM-fabricated GH3625 superalloy by micro-scale laser shock peening without coating

Selective Laser Melting (SLM) has shown great potential in the design and fabrication of complex metallic components. However, SLM-fabricated parts generally suffer from poor surface quality, resulting in inferior fatigue performance. Although post-treatments such as heat treatment (HT) and machining are commonly applied, their effectiveness is limited for complex geometries or narrow regions. In this study, a rapid surface modification method by micro-scale laser shock peening without coating (μLSPwC) is proposed to improve the surface quality and fatigue performance of SLM-fabricated GH3625 Ni-based superalloy. The surface characteristics and fatigue performance of the SLMed, HT + polished, LSP, LSPwC and μLSPwC treated specimens are compared. Results indicate that μLSPwC effectively reduces surface roughness from 7.75 μm to 5.63 μm through micro-scale laser-induced thermal effect. Simultaneously, the mechanical effect of the laser-induced shock wave introduces a compressive residual stress (CRS) layer with a depth of approximately 340 μm and a hardened layer of about 245 μm. Moreover, the average grain size in the near-surface region is refined from 69.04 μm to 41.51 μm. As a result, the μLSPwC specimen exhibits the most pronounced improvement in fatigue performance, with a fatigue life approximately 41.7 times longer than SLMed specimens.