Assessment of gradient and nanogradient PVD coatings behaviour under erosive, abrasive and impact wear conditions

PVD coatings are of great interest due to their high hardness, wear and oxidation resistance, thermal stability and lubricity. Gradient deposition technology allows improving adhesion to substrate and mechanical properties of the coating-substrate system by elimination of the mismatch in materials properties at the interface and reduction of residual stresses. The present study aims at the assessment of performance of the nano-composite gradient superhard AlTiN/Si3N4 and also TiN, TiCN, TiAlN, AlTiN gradient PVD coatings deposited onto cemented carbide substrate. Erosive, abrasive and impact wear tests were conducted to obtain the insight into qualitative and quantitative aspects of PVD coatings resistance to wear. Microstructural analysis has indicated that gradient deposition technology allows reducing the risk of coatings decohesion due to weak adherence. The fracture of AlTiN/Si3N4 and other coating systems investigated under all conditions is initiated at the defect areas (such as pores and protuberances). The performance of nano-composite gradient superhard AlTiN/Si3N4 coating is superior under abrasive wear; very good under erosive wear; and quite good under impact wear.