Post-process lasering improves strength-ductility tradeoff and fatigue limit of additively manufactured stainless steels

Although stainless steels fabricated via additive manufacturing exhibit higher strength in comparison to their conventionally manufactured counterparts, they often suffer from lower ductility and poorer fatigue limit. In this work, post-process micron-sized lasering is used to re-engineer additively manufactured stainless steel microstructures close to the sample surface in order to improve their overall performance. The key idea is to use smaller spot sizes and faster scan speeds during post-process lasering compared to the fabrication process. Using a novel coupling between a continuous-wave laser and a scanning electron microscope, single line scans were performed to optimise the lasering parameters. The optimised parameters were then used to treat the surface of the entire sample. The result is an intragranular structure refinement near the surface, exhibiting nearly an order of magnitude reduction in microsegregation cell and dislocation structure size, and increase in dislocation density. The ensuing microstructure demonstrates a higher yield strength without ductility loss and significant enhancement of the fatigue limit due to reduced surface roughness and intragranular structure refinement. The proposed technique has tremendous potential to improve the mechanical response of alloys fabricated either via additive manufacturing or any other manufacturing technique.