Electrochemical methods and Mott-Schottky analysis in conjunction with the point defect model (PDM) for oxide films have been used to investigate the semiconductor properties of the oxide films formed on the surface of cobalt-tungsten alloy coatings in 1 mol•L^－1 NaOH electrolyte. The donor density (N_D), the flatband potential (U_fb) and the oxygen vacancy diffusion coefficient (D₀) of the oxide films on the coatings with different tungsten contents under three different anodization potentials were calculated from the Mott-Schottky plots, respectively. The results indicated that the Mott-Schottky plots of the oxide films were linear with a positive slop, and showed behaviour of the N-type semiconductor. The donor density (N_D) of the oxide films increased with the rising of anodization potential or with the decrease of the tungsten content in the alloy coatings, therefore, the chances of oxide films breakdown and pitting initiation increased. The flatband potential of the oxide films dropped with the decrease of anodization potential or with the decrease of the tungsten content in the alloy coatings. Therefore, the corrosion resistance of the anodic oxidation films enhanced. The oxygen vacancy diffusion coefficient (D₀) of the anodic oxidation films which formed on the surface of cobalt-tungsten alloy coatings with different tungsten contents at three different anodization potentials were (1.543～8.533)×10^－14 cm²•s^－1.

Key words: Co-W alloy, oxide films, Mott-Schottky analysis, point defect model, oxygen vacancy diffusion coefficient