The biocompatibility and the corrosion resistance are strongly
related to the surface oxide layer that covers the metallic materials.
The cpTi oxide layer is mainly composed of TiO2 with small amounts
of TiO and Ti2O3 [35]. In Ti-6Al-4 V alloy, the surface oxide layer is composed
by a variety of oxides (TiO, Ti2O3, and TiO2) with amounts of
Al2O3, hydroxyl groups, and water [37]. When the alloy elements Al
and V are added to cpTi to produce the Ti-6Al-4 V alloy, the mechanical
resistance is improved, but the corrosion resistance decreases.