Structural Aspects of Wear Resistance of Coatings Deposited byPhysical Vapor Deposition

This study examines TiAlN and CrAlSiN coatings with a thickness of 0.8–4.0 μm deposited by plasma-assisted physical vapor deposition in vacuum on nitrided and carburized steel substrates. The coatings have different structural morphologies: a homogeneous monolayer structure, a multilayer structure with different-thickness layers, and a heterogeneous multiphase structure. A range of coating mechanical properties, including hardness H and elastic modulus E, as well as special properties characterizing the resistance to elastic H/E and plastic H3/E2 deformation is studied by indentation testing at different loads. The applicability of PVD coatings for increasing the wear resistance of splines in heavily loaded friction pairs is investigated. Tribological tests were conducted on a friction machine at a load comparable to the working loads in the spline contact region. A multilayer coating showed better mechanical characteristics than a monolayer one. The strength of the multilayer coating deposited on a solid substrate increased with decreasing layer thickness. The most structure sensitive mechanical characteristic is the plastic deformation resistance H3/E2, which increases considerably at a nanoscale layer thickness (<100 nm), while the hardness H and elastic deformation resistance H/E depend weakly on the layer thickness. Unlike the mechanical properties, the structure of the coatings is not always a significant wear resistance parameter. The dominant factor in the conducted tests is the wear mechanisms. TiAlN coatings are shown to rapidly degrade and wear out due to oxidative wear. CrAlSiN coatings under the same test conditions wear off by the fatigue mechanism. The coatings with a heterogeneous multiphase nanostructure exhibit the best mechanical properties and high wear resistance under severe friction conditions.