Degradation of Ion–Plasma Nitride Coatings at Different Scale Levels under Frictional Wear Conditions

In tribological tests of coatings, cyclic loads enable to evaluate the relationships between their wear, the kinetics of the initiation and propagation of cracks, as well as fatigue failure. For such purposes, a concept of degradation at different scale levels was developed. This made it possible to reveal that wear of the ion–plasma nitride coatings involved six stages, which depended on their microstructure. The widths of wear tracks were utilized as indicators of the degradation stages, while the internal morphologies reflected the fatigue mechanisms. Stepwise fragmentation of the coatings, as the most extensive stage and actual from a self–organization perspective, was analyzed in detail. In addition, the morphologies of the wear tracks were examined at different degradation stages.