Degradation Features of Ion-Plasma Nitride Coatings under Sliding Friction

The paper studies nitride coatings of the TiAlN and CrAlSiN systems with a thickness of 0.8…4.0 μm deposited by the vacuum ion-plasma technology. Specimens of nitrided 38Cr2MoAl and cemented 12Cr2Ni4 steels were used as substrates for coating deposition. Experimental data are derived on the physical and mechanical properties of the coatings by various indentation methods, including scratch tests, as well as on their tribological properties in sliding friction tests. The results of microstructural (SEM) and energy-dispersive X-ray (EDX) analysis of the coatings are also presented, including electron microscopic data on coating wear in tribological tests. It is shown that none of the physical and mechanical characteristics (hardness H, elastic modulus E, and their ratios H/E, H³/E²) determined by continuous or dynamic (for example, critical load F^c_N for coating spallation in scratch tests) indentation can separately describe the coating resistance to wear under the test conditions. This is the methodological problem that does not allow an accurate prediction of the coating wear. The problem is solved by the joint use of the calculated specific work of coating spallation from the substrate G and the coating resistance to plastic deformation H³/E², which together determine not only the coating degradation process, but also the loss of stability of the entire coating–substrate system.