Synergistic integration of laser shock peening and heat treatment for refined microstructure and enhanced mechanical properties in additively manufactured 17–4PH stainless steel

Abstract

This study explores the combined effects of laser shock peening (LSP) and heat treatment (HT) on the microstructure, residual stress, and mechanical behaviour of selective laser-melted 17–4 precipitation-hardened (PH) stainless steel. Subsequently, laser shock peening (LSP) was performed on both as-printed (AP) and heat-treated (HT) sample surfaces, and their microstructure, residual stress, and mechanical behaviour were evaluated. The severe plastic deformation (SPD) resulted in significant compressive residual stresses (CRS) in the surface layer of the AP+LSP (-879 MPa) and AP+HT+LSP (-850 MPa) samples. Laser peening caused dislocation accumulation and micro-level grain refinement in the sample's deformed layers, improving its mechanical properties. The AP+HT+LSP sample shows significant improvements over the as-printed (AP) sample. The fraction of high-angle grain boundaries (HAGBs) and high misorientation angles were higher in the AP+HT+LSP sample, and its effect is revealed in the microhardness data. The collective contribution of precipitation strengthening, Hall-Petch, CRS, dislocation strengthening, and increased fraction of HAGBs is observed in mechanical and microstructural aspects of laser shock peened specimens.