Eliminating anisotropy and unlocking ultra‑high strength in TA15 via in‑situ nitrogen microalloying during micro laser powder bed fusion

Abstract Titanium alloys are vital for lightweight aerospace structures. Yet their application in micro-architected components using laser-powder bed fusion (L-PBF) is constrained by pronounced anisotropy and inadequate as-built strength, which typically requires post-processing. Here, we introduce an in-situ microalloying strategy using reactive micro-LPBF (µ-LPBF) for TA15 (Ti-6Al-2Zr-1Mo-1 V), supported by multiphysics modeling. This approach leverages nitrogen to simultaneously trigger isotropic grain refinement and activate synergistic strengthening mechanisms. Compared to the anisotropic pure Ar counterparts, optimized 5 vol% N 2 specimens exhibit superior isotropic mechanical responses tailored for micro-bearing environments: achieving a record-breaking ultimate compressive strength of 2266 MPa (vs. 1827 MPa) and a hardness of 5.58 GPa (vs. 4.09 GPa), while maintaining a high strain-to-failure of 22.9%. The enhanced performance originates from the multifaceted role of nitrogen: increasing the molten pool’s energy absorptivity and inducing an obvious constitutional supercooling related to a high growth restriction factor for promoting a columnar-to-equiaxed transition of prior β-grains. At the atomic level, interstitial nitrogen promotes dislocation multiplication and in-situ polygonization into low-angle grain boundaries while stimulating deformation twinning. This coordinated “Solid Solution + Recovery” pathway enhances strength-plasticity synergy, providing a post-processing-free strategy for manufacturing high-performance, isotropic titanium components.