Advanced post-processing of Ti–6Al–4V alloy fabricated by selective laser melting: A study of laser shock peening and ultrasonic nanocrystal surface modification

In this study, individual and combined applications of laser shock peening (LSP) and ultrasonic nanocrystal surface modification (UNSM) technologies were applied to Ti–6Al–4V alloy manufactured by the selective laser melting (SLM) process. This study aims to investigate the effects of individual LSP and UNSM technologies, and their sequential combinations in a different order (LSP + UNSM and UNSM + LSP) on the microstructure, grain size, hardness, residual stress, mechanical and tribological properties of Ti–6Al–4V alloy. It is crucial to analyze how the sequential or combined application of LSP and UNSM technologies affects the surface finish of the AM Ti–6Al–4V alloy, which typically has rougher surfaces than traditionally manufactured parts. Results indicated that UNSM technology reduced the surface roughness by about 12 times, introduced a high level of compressive residual stress (CRS), and demonstrated better mechanical and tribological performances than LSP technology. Additionally, the combination of UNSM + LSP technologies, in which LSP technology was subsequently performed on the UNSM-treated sample, was found to be more effective than that of the combination of LSP + UNSM technologies, where the UNSM technology was subsequently performed on the LSP-treated sample.