Laser Shock Peening of Laser Based Directed Energy Deposition and Powder Bed Fusion Additively Manufactured Parts: A Review.

The tensile residual stress (TRS) generated due to large thermal gradient during the laser directed energy deposition (DED) and laser based powder bed fusion (PBF) is one of the major concerns. TRS leads to lower tensile, fatigue strength, distortion, reduced corrosion resistance, pores, etc. This concerns can be mitigated using laser shock peening (LSP). The basic principles and characteristics of each process i.e., PBF, DED, and LSP process, followed by popular metallic materials used by PBF and LDED processes are discussed. The applications and drawbacks of each process are presented. This review paper discusses the recent progress on the LSP of laser based PBF/DED manufactured samples. Different approaches and challenges to hybrid AM + LSP are also presented in this paper i.e. LSP after every certain layer and LSP after the whole part is manufactured. Even though the LSP after every certain layer offers deep CRS inside a part, it is a very time-consuming and difficult process as constant removing, polishing, and resetting of the samples compromising the parts' accuracy. Frequent change of workstation between LSP and AM is also a major problem while benefits of LSP after the whole part is manufactured are limited to the surface. The introduction of finer grains after LSP led to an increased microhardness and reduced pores thus increasing the tensile and fatigue life of the parts. The challenges and future scope are delineated. [ABSTRACT FROM AUTHOR]