Bimetallic additively manufactured structure (BAMS) of Inconel 625 and austenitic stainless steel: effect of heat-treatment on microstructure and mechanical properties

This study presents a bimetallic additively manufactured structure (BAMS) of Inconel 625 (In625) and austenitic stainless steel 316L (SS316L) manufactured by a gas-metal-arc-welding (GMAW) based on wire-arc additive manufacturing (WAAM) technology. A BAMS was heat treated at 970 °C for improvement of the mechanical properties. The heat treatments resulted in a microstructural change from delta-ferrite to austenite in SS316L and enhanced tensile strength compared to the as-built sample. The same crystal structure and similar lattice constant between In625 and SS316L led to an epitaxial growth at bimetallic interface, which developed coherent columnar grains with the same crystallographic orientation. During the heating and cooling sequence, different thermal expansion coefficients of both materials generated localized strains at the bimetallic interface, from which dynamic strain hardening was achieved exhibiting a higher hardness at the interface.