A study of rolling-contact fatigue of bearing steel coated with physical vapor deposition TiN films: coating response to cyclic contact stress and physical mechanisms underlying coating effect on the

摘要

The effect of physical vapor deposition (PVD) TiN coatings of different thicknesses on the rolling-contact fatigue (RCF) life of coated specimens is studied experimentally. Based on the results ofconventional three-ball-on-rod testing, the optimum film thickness is found to be about 0.75μmThinner coatings do not significantly affect the fatigue life, while much thicker ones have a negativeeffect on it. These trends agree with the findings of prior studies. Using a progressive testing technique,the mode of localized damage experienced by thick TiN coatings under cyclic contact stressconditions is established. The fatigue life reduction observed with such coatings is explained bycomparison of the coated surface roughness in the damaged and the intact portions of the rolling track.Progressive testing results also indicate that the stress-affected material volume plays an importantrole in near-surface initiated rolling-contact fatigue. By modifying fatigue test conditions, the fatiguelife enhancement observed with some PVD TiN coatings is demonstrated to result from loading ballpolishing by the hard coating. The present experimental observations agree with the predictions of acompanion theoretical study.