炭素鋼の腐食疲労強度に及ぼす窒化チタン被覆の影響

抄録

In order to investigate the effect of titanium nitride (TiN) coating on corrosion fatigue behavior of metal, cantilever-type rotating bending corrosion fatigue tests were carried out in 3.0% saline solution by using the round bar specimens of 0.37%C carbon steel, JIS S35C, coated with TiN by the physical vapour deposition (PVD) method or the chemical vapour deposition (CVD) method. From the experimental results, obvious improvement of corrosion fatigue strength was observed in TiN coated specimens, as compared with those without coating. The corrosion fatigue crack propagation rate observed on the surface of coated specimens was equivalent to that without coating. Fracture surface observations with a scanning-electron microscope revealed that the corrosion fatigue crack propagated from small corrosion pits formed at the base metal under the coating layer due to aqueous solution transmitted throughout the small pinhole or flaw of the coating. The causes of the improvement in the corrosion fatigue resistance of TiN coated material were elucidated that the TiN layer does not peel off from the substrate surface owing to its enough adhesion and corrosion resistance of the layer itself is more excellent than that of the substrate metal.