Behaviors of residual stress and high-temperature fatigue life in ceramic coatings produced by PVD

To investigate the effect of ceramic coatings on fatigue characteristics at room and elevated temperatures, residual stress measurements using the X-ray diffraction (XRD) method and high cycle fatigue tests were performed. The fatigue test for the uncoated and TiAlN-coated specimens was carried out at room temperature, 400 and 538 deg. C, respectively, while the residual stress and hardness variation of the TiAlN-coated layer were measured according to the temperature of the stress relief (SR) treatment. As a result, high compressive residual stress was measured in the coating, which decreased relative to the SR temperature. The cracks in the fatigue test, at both room and elevated temperatures, started from inclusions in the substrate near the interface between the base material and the coated ceramic. There was no hardness degradation in the coatings relative to the SR conditions. Therefore, it was concluded that the improvement in the fatigue life for the coated specimens was mainly due to compressive residual stress rather than surface constraints due to the higher hardness of the layer