The influence of thermal oxidation on the microstructure, fatigue properties, tribological and in vitro behaviour of laser powder bed fusion manufactured Ti-34 Nb-13Ta-5Zr-0.2O alloy

This study innovatively investigates the feasibility of thermal oxidation (TO) for improving the wear and fatigue properties of TNT5Zr-0.2O alloys manufactured by laser powder bed fusion (LPBF). Static chemical etching (CE) as a pre-treatment for TO successfully removed the LPBF induced surface adhered powders. A mixture of rutile, Nb2O5, Ta2O5, and ZrO phases were formed as an oxide layer after TO. It can be found a better wear resistance was retained in this β-titanium alloy after TO, as demonstrated by the wear scar features with ploughing grooves changing into brittle peeling of oxides. Plain fatigue strength of CE treated alloy (150 MPa) was 1.5 times higher than the value of CE+TO treated alloy (60 MPa), as a result of multiple premature fatigue cracks possibly developing in the compounds region after TO. In vitro biocompatibility results showed no significant differences in metabolic activity of pre-osteoblasts seeded on the treated surfaces. In addition, early and late mineralisation assays revealed similar levels of 14-day ALP activity, and 28-day mineral deposits formed on the two biocompatible TNT5Zr-0.2O alloy surfaces. Overall, though the oxide layer is corrosion-resistant in the aggressive environment (3 M HCl solution), showing a potential application of TO in additively manufactured titanium medical devices. However, TO should be cautiously exploited due to the deterioration of mechanical properties.