Formation of a Zr+ZrxNy+(Zr+TiBSiNi)N+(TiBSiNi)N Gradient-Layered Coating Based on Physical and Tribotechnical Characteristics of Constituent Layers

Abstract

In order to promote the research on vacuum-arc coating deposition using vaporable TiBSiNi SHS-cathodes, a design of a Zr+Zr_xN_y+(Zr+TiBSiNi)N+(TiBSiNi)N gradient-layered hardening coating is proposed. Its constituent layers are selected relying on the results of a comparative study of their physical, mechanical and tribotechnical properties. The coating architecture is based on the tribological theory and the analysis of basic requirements to protective-hardening coatings. A comparison of the coating parameters with those of its layers demonstrates that most of them exceed the latter. In particular, its hardness is found to be 40.2 ± 2.0 GPa against that of a ZrN coating equal to 31.5 ± 2.3 GPa and is at the level of the hardest (TiBSiNi)N coating layer (41.9 ± 3.6 GPa). The adhesion (strength of cohesion to substrate) of the gradient-layered coating exceeds those of its constituent layers – ZrN, (TiBSiNi)N, and (Zr+TiBSiNi)N. An annealing treatment of this coating at 700°C in air for 60 min demonstrates its high thermal stability. The proposed gradient-layered coating exhibits a higher hardness (14.8 GPa) compared to the other coating types (5.8–9.1 GPa) after annealing, which, according to the XRD analysis, can be attributed to the availability of zirconium nitrides and harder titanium nitrides in its composition. The principal criteria of the designed gradient-layered coating are its tribo-engineering tests demonstrating both a lower friction coefficient and a higher wear resistance over those of the other coatings. Its wear parameter is found to be 5.4∙10^–6 mm³N^–1m^–1 in coupling with a 100Cr6 steel counterbody compared to that of a conventional ZrN zirconium nitride coating – 43.0∙10^–6 mm³N^–1m^–1. There are also some advantages of the gradient-layered coating revealed in its wear resistance in comparison with the constituent multi-component layers – both with a 100Cr6 steel counterbody and in a tribo-couple with a superhard silicon carbide, SiC.