Influence of isothermal post-treatment on tribocorrosion behaviour of laser powder bed fusion-processed β-type Ti-Nb alloy

Ti-Nb alloys are well-regarded implant materials thanks to their high corrosion resistance and good biocompatibility. Nonetheless, their cast and solution-treated forms suffer from limited mechanical strength. LPBF-processed Ti-Nb alloys hold significant potential for customized implants. Applying post-heat treatments, particularly isothermal age-hardening, can strengthen these alloys and improve their resistance to the biomechanical loads encountered in service. However, load-bearing implants are prone to tribocorrosion due to the relative motion between implant components or between the implant and surrounding tissue in body fluids. This study investigates the mechanical, corrosion, and tribocorrosion properties of post-treated LPBF-produced β-type Ti-42Nb alloys, and compares their performance with both as-built LPBF Ti-42Nb and conventional Ti-6Al-4V ELI. Results show that isothermal heat treatment is effective in increasing the mechanical properties by introducing ω iso precipitates for Ti-42Nb (LPBF-300 °C 30 h) and α iso ’’ precipitates for Ti-42Nb (LPBF-450 °C 30 h) to the single β-phase microstructure. Tribocorrosion behavior was investigated under open circuit potential (OCP) and anodic potentiostatic polarization conditions (0.6 V vs. Ag|AgCl) in phosphate-buffered saline (PBS) using a reciprocating pin-on-disk tribometer. The formation of precipitates does not adversely affect the passive film, indicating that its stability is maintained by the strong passivating nature of Ti-Nb alloys. However, the tribocorrosion resistance declines following isothermal heat treatment, likely due to the rapid detachment of hard and brittle precipitates, leading to increased material loss. Nevertheless, controlling the distribution of precipitates in LPBF-fabricated Ti-42Nb alloys may enhance their performance for implant use.