TiN被覆したステンレス鋼の硫酸水溶液での耐食性

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TiN films were deposited under various conditions onto SUS304 stainless steel substrates by a hollow cathode discharge (HCD) type ion plating process. The corrosion resistance of the TiN-coated specimens in the active region was estimated in aqueous solutions of sulfuric acid, mainly by an electrochemical method. Measurements of the anodic polarization curves showed that the critical current density for passivation of the TiN-coated specimens was smaller than that for specimens without a TiN coating, that is, that active dissolution was retarded by TiN coating. The cathodic reaction tended to be similarly retarded by TiN coating. The corrosion resistance of the TiN-coated specimens was further improved by Ti undercoating and TiC coating under the TiN coating layer. This is attributed to the fact that the Ti undercoating and TiC coating decreased the number of defects that penetrate through the coating layers to the stainless steel substrate, that is, increased the intercepting effect of the coating layers from its surroundings. The intercepting effect of the coating layer from the surroundings of the specimens treated at 300°C was superior to that of the specimens treated at 450°C. The effect of hydrogen on the crack morphology of the TiN films was remarkable, and in the case of TiN films put into a hydrogen surroundings, cleavage fractures occurred.
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