Calculation and Analytical Prediction of Coating Wear during Tribological Tests Based on Models of Contact Fatigue Failure

The work examines the conditions of tribological tests of steel samples with nitride ion-plasma coatings. A calculation and analytical model is proposed for quantitative assessment of contact and wear parameters during sliding friction tests: the size of the contact area, the depth of contact approach, the depth of the plastic zone, stresses in the coating, fatigue limit, and the critical thickness of the coating, which excludes its deflection. It has been shown that coatings with a thickness above critical realize their potential for physical, mechanical, and tribological properties regardless of the substrate. If the coating thickness is insufficient, the result of tribological tests is determined by the behavior of the “coating–substrate” system, a high-hard nitride coating on a ductile steel substrate experiences deflection and premature brittle failure. To assess the wear of coatings in this case, it is recommended to use fatigue failure models with construction of the Wöhler fatigue curve and determination of the fatigue limit based on the Murakami–Endo theory. The implementation of the recommended approach was carried out for the studied nitride coatings using a database of our own experimental data.