Plasma electrolytic oxidation of titanium has been investigated using a phosphate/silicate electrolyte witha square waveform and a frequency of 50 Hz. A range of constant rms current densities, duty cycles and negative-to-positive current ratios was employed. The resultant coatings were examined by analytical scanning and transmission electron microscopies and X-ray diffraction. The coatings, which were limited in thickness to similar to 40 to 50 mu m, contained anatase, rutile, Ti2O5 and silicon-rich, amorphous material. The tribological behaviour was investigated using a ball-on-disc test, revealing a coefficient of friction against steel of similar to 0.8, which reduced to similar to 0.4 by incorporation of ptfe particles from the electrolyte. However, due to the composition and morphology of the coatings, their wear life was relatively short. (C) 2014 The Authors. Published by Elsevier B.V.