Thermal oxidation of Ti6Al4V: a pathway to enhanced anti-corrosion, anti-wear, and bioactive properties

Titanium and its alloy Ti6Al4V have gained attention as advanced biomaterials in healthcare due to the presence of a native amorphous titanium oxide layer on their surface. This inherent amorphous layer with a thickness restricted to 3-7 nm imparts improved biocompatibility and corrosion resistance to the material. However, this limited thickness constrains its functional performance. This work is aimed at improving the functionality of Ti6Al4V by creating an oxide layer of suitable thickness on its surface through controlled heat treatment. Samples were oxidized at three different temperatures-400 °C, 600 °C, and 800 °C-for 1 h, and alterations in morphology, oxygen content, crystallization of the oxide layer, surface energy, surface roughness, and micro-hardness of the samples were investigated. Electrochemical analysis revealed a systematic lowering in the corrosion rate with increasing temperature. Notably, the corrosion rate of the sample heated at 800 °C was 0.52 mil y^-1, which is one-fourth times lower than that of the pristine sample (2.04 mil y^-1). Tribology analysis showed a significant enhancement in wear resistance. The wear rate of pristine Ti6Al4V (7.56 × 10^-3mm³Nm^-1) reduced by two orders for the sample heat treated at 800 °C (9.59 × 10^-5mm³Nm^-1) when tested against a stainless steel counterpart. Furthermore, samples subjected to higher thermal oxidation exhibited superior bioactivity, as evidenced by increased apatite growth and a calcium to phosphorus ratio closer to the optimum value reported in the literature. The improved performance of the thermally oxidized sample is attributed to an increase in the rutile phase of crystalline titanium oxide on the Ti6Al4V surface post heat treatment.