Corrosion Resistance and Corrosion Fatigue Strength of Carbon Steel Coated with Chromium Nitride by Multistage PVD Method.

Abstract

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