Repairing additive-manufactured 316L stainless steel using direct energy deposition

Powder bed fusion (PBF), a 3D printing process, is widely used for manufacturing 316L stainless steel parts. When these PBF parts are damaged or worn severely during service, they can be repaired by conventional repair processes such as GTAW welding, metal spraying, brazing etc. However, these processes have several disadvantages such as creating a large heat affected zone and repair defects (pores and cracks). In contrast, directed energy deposition (DED) provides good metallurgical bonds, minimal dilution, and a small heat-affected zone. In this study, to verify the applicability of DED to repair of damaged PBF parts, we repaired sample parts and observed their tensile properties, hardness, and metallurgical characteristics. First, we designed hot-rolled and PBF specimens with trapezoidal grooves of varying depth. After filling the groove using DED, the specimens were tested for tensile properties. We found that in specimens with large groove depths (1 mm and 2 mm), cracks occurred around the repair due to thermal stresses and oxide inclusion. For this reason, strength and elongation were lower in these specimens. We also found that the micro-hardness of the deposition zone is greater than the original hot-rolled specimens and similar to the PBF specimens. The microstructure of the repaired area is mainly composed of complicated dendrite structures due to irregular nucleation. In addition, dimples were observed in the fracture surfaces, indicating that ductile fracture occurred. We conclude that the DED process can be employed to repair damaged 316L stainless steel parts, with the low severity of the damage to be repaired.