Application of ultrasonic nanocrystal surface modification for improving surface profile of DEDed AISI 316L

This study investigated the effect of ultrasonic nanocrystal surface modification (UNSM) on the deteriorated surface of AISI 316L deposited using the direct energy deposition (DED) technology. After UNSM treatment, the coarse DEDed surface was fined, and a regular micro-surface profile was implemented. Compared to the case before UNSM treatment, the waviness and roughness of the surface after UNSM treatment decreased by up to 73.8 % and 86.2 %, respectively, and reduced further as the UNSM interval was decreased. Surface severe plastic deformation (S2PD) was induced in the dendrite structure of the UNSM-treated DEDed sample surface. The microstructure was deformed till a depth of up to 92.13 mm from the surface and was significantly affected by the interval. After UNSM treatment, the hardness improved by up to 71.5 % and gradually decreased from the surface to the inside; the hardness was improved by UNSM up to a maximum depth of 400 μm. Although the UNSM interval condition had a significant effect on the DEDed surface, it barely affected the relationship between the directions of DED deposition and UNSM treatment. This study confirmed that the UNSM technology can effectively improve a DEDed surface.