Engineering Relationships for Computational and Analytical Prediction of Coating Wear during Tribological Tests

The work sets the task of determining the conditions for tribological testing of coatings in which the coating realizes its potential of physical, mechanical, and tribological properties regardless of the substrate. A standard method of tribological testing was used on a friction machine according to the pin–disk scheme with a circular motion of a spherical indenter pin. Experimental data are presented on the study of the structure and properties of vacuum ion-plasma nitride coatings of TiN, TiAlN, and CrAlSiN. The coatings had a thickness of 0.8–4.0 μm and were applied to plate steel samples intended for testing in a friction machine. The wear process of coatings is considered from the perspective of contact fracture mechanics and fatigue theories. A calculation and analytical model is proposed for quantitative assessment of contact and wear parameters during 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 critical thickness of the coating, which excludes its deflection. To assess the wear of coatings in this case, it is recommended to use fatigue failure models with the construction of a Woehler fatigue curve and determination of the fatigue limit based on the Murokami–Endo theory. The implementation of the recommended approach was carried out for the nitride coatings using a database of the authors’ experimental data.