A method of forming a non-metallic coating on a metallic substrate involves the steps of positioning the metallic substrate in an electrolysis chamber and applying a sequence of voltage pulses of alternating polarity to electrically bias the substrate with respect to an electrode. Positive voltage pulses anodically bias the substrate with respect to the electrode and negative voltage pulses cathodically bias the substrate with respect to the electrode. The amplitude of the positive voltage pulses is potentiostatically controlled, wheras the amplitude of the negative voltage pulses is galvanostatically controlled.