Effect of TiN coating on corrosion fatigue strength of carbon steel

In order to investigate the effect of titanium nitride (TiN) coatings on corrosion fatigue behavior cantilever-type rotating bending corrosion fatigue tests were carried out in 3.0% saline solution using round bar specimens of 0.37% C carbon steel, JIS S35C, coated with TiN by physical vapour deposition (PVD) or chemical vapour deposition (CVD). Improvement of corrosion fatigue strength was observed in TiN coated specimens compared with those without coatings. The corrosion fatigue crack propagation rate observed on the surface of a coated specimen 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 small pinholes or flaws of the coating. The TiN layer does not peel off from the substrate surface owing to its adhesion, and corrosion resistance of the layer itself is greater than that of the substrate metal.