Multi-scale hybrid reinforced super duplex stainless steel matrix composites with high strength and ductility via laser powder bed fusion and an in-situ synthesis strategy

The emergence of nanoparticle-reinforced metal matrix composites represents a promising method for efficiently enhancing material strength without significant compromise in ductility. Nevertheless, the homogeneous distribution of nanoparticles in matrix remains a technical challenge. To address this issue, this study designed an advanced method to create a multi-scale hybrid to reinforce super duplex stainless steels (SDSSs) by coupling laser powder bed fusion (LPBF) technique with an in-situ synthesis strategy and optimizing post heat treatment. For as-built composites, both TiCxNy and M23C6 nanoparticles were generated in-situ by the introduction of micron-sized TiC particles into SDSSs, and their microstructure was mainly composed of fine ferrite grains. The post quenching treatment enabled heat-treated composites to possess micro-duplex matrix grains with a multi-scale hybrid, including micron-sized TiC, in-situ sub-micron M23C6 particles, and in-situ TiCxNy nanoparticles. Particularly, the obvious agglomeration phenomenon of in-situ TiCxNy nanoparticles was not observed. In comparison with heat-treated SDSSs (ultimate tensile strength (UTS): ~839 MPa; uniform elongation (UE): ~20.6%), heat-treated composites processed by 1090 °C obtained a higher UTS (~992 MPa) with only 0.8% reduction in UE. The great ductility of heat-treated composites was primarily attributed to their relatively high strain hardening rate, facilitated by grain refinement and the formed multi-scale hybrid. The successful creation of a multi-scale hybrid sets the stage for producing high-performance metallic components via LPBF and in-situ strategy.