Effect of Al Addition on Corrosion Protection of Ti-39Nb-6Zr Alloy for Biological Applications.

For metals to be used as biomaterials, there must not be harmful reaction between the corrosion product of metal or eluted ion, and bio-tissue. Titanium is one of the excellent bio-compatible materials and generally it has tendency to have a small amount elution of Ti ions inside the body. Titanium alloy need to have low elastic modulus for reducing the stress shield effect. Ti-39Nb-6Zr alloy which is consist of biocompatible element such as Nb and Zr, has low elastic modulus with below 60 GPa, but it shows lower yield stress and tensile stress compared with Ti-6Al-4V alloy. In order to increase the strength of Ti-39Nb-6Zr alloy, aluminum was added in this alloy. Since aluminum elements are reported to lead to Alzheimer disease in human, high corrosion resistance is required to use Ti-39Nb-6Zr-0.45Al alloy containing a small amount of Al. In this study, corrosion behaviors were investigated under the solution of three conditions of 0.9% NaCl (pH 7), 0.1% NaF (pH 3) and 0.1% NaF (pH 5). The behaviors were stable under all the conditions. But Ti-39Nb- 6Zr-0.45Al alloy had better corrosion resistance than Ti-39Nb-6Zr alloy in all the conditions. This is because oxide mixtures such as Al₃Ti5O₂, Al₂TiO5 are formed inside the surface layer, which results in forming more stable oxide film than TiO₂ surface film. Ti-39Nb-6Zr-0.45Al alloy has high corrosion resistance and can reduce the concern about aluminum ion elution inside the body.