Overcoming the strength-ductility trade-off in additively manufactured super austenitic stainless steel matrix composites via grain boundary engineering and heterogeneous structures

The development of high-strength metals is vital for various industrial applications, but avoiding a reduction in their ductility remains a challenge. In this study, an innovative combination of grain boundary engineering and multiple heterogeneous structures was proposed to significantly enhance the strength-ductility synergy of metals using laser powder bed fusion (LPBF) technique, and a novel super austenitic stainless steel (SASS) matrix composite with significantly enhanced strength-ductility synergy was demonstrated. Compared to as-built SASSs, the ultimate tensile strength of as-built novel SASS matrix composites was increased by similar to 22.4 %, and their uniform elongation was also increased by similar to 10.8 %. By utilizing in-situ formed TiCxNy nanoparticles induced by micron-sized TiC particles and introducing 2507 super duplex stainless steels (SDSSs) to manipulate the stacking fault energy of AL-6XN SASSs, bimodal austenite grains were created. Substantial Sigma 3 twin boundaries and some nanotwins were generated, and fine duplex grains were produced in some areas. Significantly enhanced strain hardening rate was obtained in as-built novel SASS matrix composites, which was mainly attributed to the production of bimodal grains, duplex grains, nanotwins, nanoparticles, and Sigma 3 twin boundaries. The novel strategy developed in this study provides an efficient solution for developing metals with exceptional strength ductility synergy.