Dual-Wire Plasma Arc Additively Manufactured SS 316L-Inconel 625 Functionally Graded Material: Microstructure Evolution and Mechanical Properties

Functionally graded material (FGM) is an appropriate response to high-performance and multi-functional applications. In this research, dual-wire plasma arc welding can be used to fabricate SS 316L-Inconel 625 FGM with a composition gradient of 50 wt.% by adjusting the volume fraction of welding wire delivered to the melt pool. The phase evolution, microstructure, composition, microhardness and tensile properties of different composition regions along the building direction were analyzed. The results show that good bonding in the bi-metallic interface region and defect-free microstructure. The microstructure along the deposition direction is mainly columnar and equiaxed dendritic structure, and the grain growth direction is mainly along the deposition direction. The existence of Laves phases is proved by EDS mapping and point detection. Due to remelting, an error is existed between the actual composition distribution and the designed discrete gradient. The microhardness value decreases first, and reaching a minimum at the bi-metallic interface of the 100-50 wt.% SS 316L, and then increase gradually (157 HV-208 HV). The ultimate tensile strength, yield strength and elongation are 554.12 +/- 7.44 MPa, 340.79 +/- 4.13 MPa and 26.65 +/- 0.27%, respectively. From the feasibility study, the dual-wire plasma arc welding provides a novel additive manufacturing process for the FGMs.