Shot peening coverage effect on laser powder bed fused steel

Abstract

Developing effective strategies for enhancing the damage tolerance of laser powder bed fusion (LPBF) components remains a formidable challenge in the disruptive additive manufacturing field. The typical shot-peening (SP) is a promising and efficient post-treatment procedure owing to its capability to introduce compressive residual stress, enhance the surface integrity, shrinkage the subsurface lack-of-fusion (LoF) defects of LPBF components. However, there is still a significant gap in understanding the appropriate utilization of the SP procedure to enhance fatigue performance, hindering its full potential in practical applications. This study systematically investigated the influence of surface coverage (150 %, 300 %, and 450 %) on surface characteristics, subsurface characteristics, and mechanical properties of LPBF 304L austenitic steel. Though evaluating the feasibility of severe shot peening and observing post-deformed microstructures, the process-microstructure-performance relationship of shot-peened LPBF austenitic steel was preliminarily established for the first time. The results indicated that increasing surface coverage up to a threshold (300 % in this work) could effectively enhance the strength and fatigue performance without significantly sacrificing ductility, primarily attributed to the increased gradient strain generated by the gradient deformation structures as well as the shrinkage of detrimental near-the-surface defects. The excessive surface coverage may be detrimental to ductility and fatigue performance, as it directly increases the severe plastic deformation and near-saturated micro-defects in the gradient deformation layer, substantially weakening the strain gradient's capability to accommodate dislocation flow during deformation. The findings suggested careful selection of shot peening coverage to balance enhanced mechanical properties and minimal introduction of detrimental defects.