Mitigation of Stress Corrosion Cracking in Additively Manufactured Stainless Steel by Laser Shock Peening

Abstract

Use of laser powder bed fusion (LPBF) stainless steel in corrosive environments is attractive due to material's high corrosion resistance and fine feature resolution, which is advantageous for fluidic applications. For this implementation to be optimized, LPBF stainless steel parts must have reduced susceptibility to stress corrosion cracking (SCC), a failure mode that is of high risk for stainless steels. Laser shock peening (LSP) surface processing has been used to improve SCC resistance in wrought metals and has also been used to improve other material properties of additively manufactured metals. However, LSP has yet to be investigated for the improvement of SCC behavior in LPBF stainless steel. This article demonstrates that not only does LSP improve time to crack initiation of LPBF 316L stainless steel in SCC testing but also improves SCC behavior differently when applied to different surfaces of the build. To explain these results, residual stress, texture, dislocation distribution, hardness, microstructure, and fracture surfaces are investigated, linking different hydrogen embrittlement mechanisms to each of the two build orientations as well as the peened and un-peened conditions. These results are supported by matching the observed crack morphologies to those simulated with dynamic crack modeling, thereby demonstrating the impact of residual stress and plastic versus brittle failure upon the observed outcome.