Tailoring microstructure and mechanical properties of an LPBF-processed beta Ti-Nb alloy through post-heat treatments.

[Display omitted] • The influence of aging on the microstructural and mechanical properties of LPBF-processed Ti-42Nb alloy was investigated. • The formation of the metastable orthorhombic α i s o ' ' phase was revealed. • A clear influence of the as-built microstructure on the number, size, and morphology of the precipitates was demonstrated. • A preferential hardening of the grain boundary regions was shown. • An exceptional improvement (∼50 %) in the tensile strength was achieved compared to the as-built state. This study provides a comprehensive analysis of a Ti‑42Nb alloy produced via laser powder bed fusion (LPBF) with varying post-heat treatment durations within the α + β phase range at 723 K. Synchrotron XRD analysis revealed the formation of the metastable orthorhombic α iso ' ' phase during heat treatment, acting as an intermediate to the stable α phase. With prolonged heat treatment, the α iso ' ' phase fraction increased, reaching approximately 25 % after 108.0 ks. SEM analysis identified β grain boundaries as primary sites for early α iso '' precipitation, while intragranular α i s o ' ' precipitation was delayed. Up to 28.8 ks, volume fraction and size of intragranular precipitates exhibited notable variations due to minor Nb content fluctuations from LPBF processing, resulting in an increased spread of hardness and Young's modulus on the micro scale. Tensile tests revealed significant strength enhancement through post-heat treatment for 108 ks compared to the as-built state, achieving a yield strength of around 1060 MPa (50 % increase) and ultimate tensile strength of 1125 MPa (55 % increase). Extended growth of the α i s o ' ' phase led to an increased Young's modulus, reaching 87 GPa after 108.0 ks. These findings provide valuable insights for developing post-heat treatment strategies for LPBF-produced Ti‑42Nb implants, including both bulk materials and lattice structures. [ABSTRACT FROM AUTHOR]