Structure and growth kinetics features of ceramic coatings produced on Ti-6Al-4V alloy by plasma arc oxidation

Ceramic coatings were fabricated by plasma arc oxidation on Ti-6Al-4V alloy in phosphate-containing solution. The growth rate, microstructure and phase composition of ceramic coatings were investigated using coating thickness gauge, scanning electron microscope (SEM) and X-Ray diffraction (XRD). After plasma arc oxidation treatment, the microstructure of the remained Ti-6Al-4V alloy substrate remains unchanged and no hardening zone in the substrate is found. Ceramic coating formed on Ti-6Al-4V alloy surface by alternating-current plasma arc oxidation contains two layers: an outer layer and an inner layer. The outer layer coating consists of a large amount of rutile and a little anatase. But in the inner layer, anatase becomes a main phase while the rutile fraction obviously decreases, which indicates that phase transformation of anatase into rutile occurs in the duration of oxidizing process. In the mean time, with increasing treatment duration, coating growth varies from rapidness to tardiness accompanied by gradually roughening in appearance.