On the stability and composition of oxide layers on pre-treated titanium

This paper discusses the stability and the adhesion properties of oxide layers after different surface treatments on Ti6Al4V. The surface treatments investigated consist of a three step procedure: a conditioning step (alkaline cleaning and acidic or alkaline etching) for cleaning and texturing the surface, a pre-treatment (sulphuric acid anodising) for adhesion promotion and a final painting. UV/vis-spectroscopy, XPS and SEM were used for the analysis of the resultant oxide layers. To evaluate the long-term stability of the oxide layers, different aging tests were carried out. The adhesion properties were determined by using the cross-cut test.The obtained oxide layers comprise TiO2 after the conditioning process. The aging applied to these surfaces causes an oxide layer growth. The oxide layers of the anodised samples contain titanium(II)oxide, titanium(III)oxides and titanium dioxide. In case of the applied conditions, the surface colours of the anodised samples are the result of the suboxides in the layer. The results show that the titanium(III)oxides are instable. Due to the aging test applied they were oxidised to titanium(IV)oxide. The found instabilities of the investigated oxide layers correspond to the paint adhesion results. The investigations show that the paint adhesion decreases due to the instability of the oxide layer.