Hardness, adhesion strength, and tribological properties of adaptive nanostructured ion-plasma vacuum-arc coatings (Ti,Al)N–Mo2N

Abstract

The properties of nanostructured multilayered coatings of the composition (Ti,Al)N–Mo₂N, which were fabricated by the ion-plasma vacuum-arc deposition (arc-PVD), are investigated. The thickness of coating layers is comparable with the grain size, which is about 30–50 nm. The coating hardness reaches 40 GPa with relative plastic deformation work of about 60%. It is established by measuring scratching that the cohesion destruction character of the coating occurs exclusively according to the plastic deformation mechanism, which evidences its high fracture toughness. The local coating attrition to the substrate takes place under a load on the order of 75 N. The coating friction coefficient in testing conditions according to the “pin-on-disc” layout using the Al₂O₃ counterbody under a load of 5 N is 0.35 and 0.50 at temperatures of 20 and 500°C, respectively. The coating is almost unworn because of the formation of MoO₃ oxide (the Magneli phase) operating as the solid lubricant in the friction zone. An increase in the friction coefficient and noticeable wear are observed with the further increase in the testing temperature, which is associated with the sublimation intensification of MoO₃ from the working surfaces and lowering its operational efficiency as the lubricant.