In-situ Ti-O-N reaction-induced nanoparticles for synergistic enhancement of mechanical and corrosion properties in laser powder bed fusion stainless steel

In metal additive manufacturing, one of the biggest challenges is achieving integrated manufacturing that simultaneously fulfils structural and performance requirements. The performance of the stainless-steel components is primarily determined by mechanical properties and corrosion resistance. This study utilises laser-gas-powder synergy to generate TiO₂ and TiN nanoparticles through in-situ Ti-O-N chemical reactions in the laser powder bed fusion process. These particles simultaneously refine grains and suppress sensitisation, thereby significantly improving mechanical properties and the corrosion resistance of the stainless steel. The grain size is markedly refined from 16.5 μm to 0.68 μm, resulting in an increase in yield strength from 537 MPa to over 1 GPa, while maintaining an elongation of 31.4%. The corrosion current density is reduced from 3.122 × 10−⁷ A·cm−² to 5.068 × 10−⁸ A·cm−², which is attributed to the suppression of sensitisation via the adsorption of impurity elements by titanium. Additionally, the innovative use of an N2 atmosphere ensures the complete conversion of residual titanium to TiN, effectively preventing titanium segregation and promoting microstructural homogeneity. This study demonstrates the potential of in-situ Ti-O-N chemical reactions to strengthen stainless steel for use in extreme environments, including nuclear reactors and marine equipment.