Effect of intrinsic properties of ceramic coatings on fatigue behavior of Cr–Mo–V steels

The effect of intrinsic properties of ceramic coatings such as TiN, TiCN and TiAlN films on fatigue behavior has been studied on the commonly used rotor steel, Cr–Mo–V steel, in which test samples were deposited with ceramic coating layers of 2.5–5 μm thick by a filtered arc ion plating. The coating layer micro-hardness, film characteristics and residual stresses of coating films by X-ray diffraction were investigated, and the high-cycle fatigue tests were conducted under rotary bending and axial constant amplitude loading. The hardness of coating layers increased approximately 5–10 times more than that of uncoated substrate dependent on the coatings, and large compressive residual stresses appeared on the coating layers. It is also shown that the fatigue strength of coated specimens is superior to those of uncoated substrate, in particular at long fatigue life. Based on detailed observation of crack initiation, growth and fracture surfaces, it has been concluded that the improved fatigue strength of ceramic-coated material is mainly attributed to the retardation of crack initiation of the substrate by hard coating layers, compared with the influence of crack growth resistance by ceramic coatings.