1996 年 45 巻 1 号 p. 26-31
Chromium nitride (CrN) has good properties, such as high hardness, good wear resistance, relatively good adhesion of the film and an attractive color, in addition to corrosion resistance. The superior properties of CrN thin film may be useful to surface improvement of metals. In order to investigate the effect of CrN coating on the corrosion fatigue behavior of metals, cantilever-type rotating bending fatigue tests were carried out in 3% saline solution by using the round-bar specimens of 0.37% carbon steel coated with CrN by a physical vapor deposition method. Obvious improvement of corrosion fatigue strength was observed for the CrN coated specimens, as compared with those without coating. Also, it was observed that the improvement of corrosion fatigue strength depended on the thickness of coated film, because small pores and pinholes in the coating were produced during coating process and these defects decreased with increasing film thickness. The quantitative evaluation of defects in the coating film was made from the current density determined by the electrochemical polarization method. The open pores in the coating acted as a small anode area which accelerated the corrosion of base metal, and the corrosion fatigue strength was controlled by the defect size in the coating.