Influence of the substrate hardness on the cavitation erosion resistance of TiN coating

Nanocrystalline TiN coating was deposited by means of the cathodic arc method on stainless steels types X6CrNiTi18-10 and X39Cr13. Both steels were subjected to thermal treatment in order to obtain substrates of different hardness: 1.7 GPa, 2.8 GPa and 4.6 GPa. The TiN coating was 3.7 μm thick. The TiN coating has strong (1 1 1) crystallographic orientation and fine crystalline structure of δ-TiN phase. The TiN coating is characterized by high hardness (25.4 GPa) and good adhesion. The adhesion increases with the substrate hardness. The evaluation of TiN coating resistance to cavitation erosion is based on the investigation performed in a cavitation tunnel with a slot cavitator and tap water as a medium. The estimated cavitation resistance parameters of coating were the incubation period of damage and the total mass loss after the whole test. It has been confirmed that the incubation periods of the coated steels were from 2 to 4 times longer than that of the uncoated steels. The mass losses of the coated steels decrease approximately 2.5 times in comparison with the uncoated steels. The scanning microscope analysis indicates that the damage of TiN coating is mainly due to its delamination. The character of the coating and substrate damage in multiple locations indicates that the hard coating micro-particles torn off during the cavitation bubbles implosion hit against the coating and the revealed areas of substrate. As a result, the coating and especially the substrate of relatively low hardness beside cavitation erosion are subject to solid particle erosion with the hard torn off micro-particles of coating.