In-situ alloying of titanium nitride nanoparticles via laser powder bed fusion for fabricating high-strength, ductile titanium alloys

Alpha-titanium is renowned for its exceptional ductility but has been overlooked due to its limited strength. Alloying with other elements is a common strategy to enhance its strength. Nitrogen, the most potent hardening element in titanium, has been neglected because its hardening effect typically results in a significant sacrifice of ductility. In this study, we integrate alloy design with additive manufacturing processes to demonstrate the utilization of nitrogen for achieving outstanding tensile properties. We employed two scales of TiN powder as a nitrogen source during in-situ alloying via laser powder bed fusion and discovered that the addition of micron-sized TiN (15–53 μm) resulted in leftover TiN particles in as-printed samples, which adversely affect ductility. Nonetheless, with the incorporation of nano-sized TiN powder (<100 nm), all nitrogen constituents manifest as interstitial nitrogen and distributed evenly. By incorporating compositional and process design, we achieved over a 60 % improvement in yield strength with almost no loss of elongation in the titanium-nitrogen alloy. A systematic exploration of deformation mechanisms suggests that the incorporation of nitrogen significantly refines grains, inhibits variant selection, and activates more <c+a> dislocations, thereby synergistically strengthening the titanium-nitrogen alloys. These findings advance the development of solid solution-strengthened titanium alloys and provide novel insights for the exploration and creation of cost-effective, high-performance titanium alloys.