Surface heterostructuring of 316L stainless steel manufactured by laser powder bed fusion and hot isostatic pressing

Metal additive manufacturing (AM), offering high freedom of design, has garnered attention as a cutting-edge manufacturing technology. Commonly, hot isostatic pressing (HIP), as post-processing, is utilized to remove undesirable defects in AM parts to obtain fully dense components. However, excessive heating during HIP can result in the deterioration of mechanical properties, limiting their potential for structural industry applications. Herein, we propose a new strategy to obtain an optimized gradient structure to achieve a substantial synergistic effect through ultrasonic nanocrystal surface modification (UNSM) on the HIP-processed AM substrate. The resulting microstructure shows an extended gradient layer reaching the center of the substrate with significant mechanical incompatibility between adjacent domains, showing an excellent combination of strength and ductility. Our study suggests that the optimized gradient structure with superior mechanical properties can be achieved by strategically exploiting HIP-induced effects, which are generally avoided in structural materials due to their deleterious effect on strength.