Rolling contact fatigue behavior of Ti/TiN coated ADI by cathodic arc deposition

The results show that the surface hardness, residual stresses and coating adhesion strength of the samples increase as TiN layer thickness increases while surface roughness, coating hardness and elastic modulus do not vary significantly with the TiN layer thickness. Regarding the RCF tests, two failure mechanisms were observed in the coated samples, coating delamination and substrate spalling. Coating delamination turned out to be the most predominant mechanism and occurred at fewer loading cycles than substrate spalling. The EDS analysis revealed that inside the delaminated areas the Ti interlayer remained adhered to the substrates in all the cases. Extended tests on delaminated samples show growing delamination until final failure by substrate spalling occurred. The Weibull analysis indicates that the RCF life of the coated samples seems to have a tendency to increase with the TiN layer thickness and, in the case of the thicker TiN layer, to exceed the life of uncoated ADI after the extended tests. However, due to the number of samples employed, the statistic analysis does not show significant differences in the RCF behavior of the uncoated and coated samples.