Effect of deposition strategy on SS316L–Inconel 718 bimetallic structures fabricated by WAAM: microstructure, mechanical properties, and wear performance

This research systematically examines the influence of the deposition strategy on the microstructural evolution and mechanical behaviour of SS316L-Inconel 718 bimetallic structures produced by Wire Arc Additive Manufacturing (WAAM). Uni- and bidirectional deposition strategies were compared using comprehensive microstructural, mechanical, and tribological characterisation. The bidirectional method, which involves changes in the deposition direction back and forth, led to a repeating thermal cycling that yielded a refined morphology (predominantly equiaxed grains), which was different from the coarse columnar dendrites in the unidirectional build. This approach also encouraged better elemental diffusion across the phase boundary, leading to wider and more homogeneous metallurgical transition zones. Therefore, the bidirectional structure exhibited excellent mechanical performance, such as an 18% higher ultimate tensile strength (602.65 MPa vs. 509.45 MPa), three times greater ductility (15.18% vs. 5.15% fracture strain), and a 15–20% higher hardness. In tribological tests, the bidirectional structure showed a reduction of 41.7% in dry sliding wear mass loss, with a lower and more stable coefficient of friction. Worn surface analysis confirmed that there was a transition from severe abrasive/delamination wear in the unidirectional structure to mild abrasive wear in the bidirectional counterpart.