Corrosion resistance and corrosion fatigue strength of carbon steel coated with chromium nitride by multistage PVD method

Chromium nitride(CrN) exhibits good corrosion resistance in addition to excellent electrical and mechanical properties. A decrease in the number of defects such as pinholes or voids formed during deposition is required for improvement of corrosion resistance and corrosion fatigue strength of coated materials. A multistage physical vapor deposition (PVD) method was proposed in order to fabricate dense thin-coating films. In an electrochemical anodic polarization test in aerated 2%H2SO4 solution, 0.37 wt%C steel that was coated with CrN thin film using the multistage PVD method showed better corrosion resistance than a specimen coated by a conventional method, This is due to a decrease in the number of small defects in the coating film deposited using the multistage PVD method. Evaluation of the corrosion fatigue strength of multistage-coated steel was performed by means of a cantilever-type rotating-bending fatigue test in 3%NaCl solution. The corrosion fatigue strength of multistage-coated steel was improved compared with that of the uncoated steel; however, the increase in fatigue strength was less in the multistage-coated specimen than in the specimen coated by the conventional method, contrary to the experimental results obtained from the anodic polarization test. It was pointed out that corrosion fatigue strength is dependent on not only the number of defects but also the shape of large defects in the coating film.