Influence of Deposition Mode on Microstructural and Mechanical Properties of Wire Arc Additive Manufactured 308L Stainless Steel Structures

The aim of this study is to investigate the impact of different metal deposition modes—spray (S), pulse (P), and pulse-switchback (PS)—on the metallurgical and mechanical properties of SS308L structures in wire arc additive manufacturing (WAAM). Three thin-walled structures were deposited using optimal process variables and inter-layer time delay. Through metallographic examination, it was found that the P-mode had the highest homogeneity (88.94%) in terms of grain size and phase fraction, followed by the S-mode (86.03%) and the PS-mode (74.68%). Based on micro-hardness data, the P-mode had the highest average hardness value (272.51 HV along BD and 276.99 HV along TD). However, the PS-mode (83.46%) had a more homogeneous hardness distribution compared to the S-mode (83.11%) and P-mode (78.59%). In tensile tests, the P-mode showed higher tensile strength (823 MPa) and more homogeneous (98.68%) properties than the PS-mode and S-mode. However, the P-mode exhibited the highest variability (21.14%) in terms of elongation, followed by PS-mode (20.82%) and S-mode (16.30%). It was also found that the P-mode induced the maximum stress-induced phase transformation from γ-phase to α'-phase, followed by PS-mode and S-mode. This study provides valuable insights for determining the optimal deposition mode for SS308L structural components in the WAAM process.