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 ∼22.4 %, and their uniform elongation was also increased by ∼10.8 %. By utilizing in-situ formed TiC_xN_y 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 Σ3 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 Σ3 twin boundaries. The novel strategy developed in this study provides an efficient solution for developing metals with exceptional strength-ductility synergy.