Properties, composition and structure of multilayer gradient (Zr,Nb)N coatings prepared by vacuum arc deposition method

Abstract

This paper presents the results of synthesis of the multilayer gradient (Zr,Nb)N coatings, synthesized by the vacuum-arc deposition at the evaporation of (Zr and Nb) pure metal cathodes. The niobium concentration gradient through the thickness was obtained by varying the arc current with a niobium cathode in the range of 80–150 A under the constant pressure of the working argon-nitrogen gas mixture and constant current of arc discharge with a zirconium cathode. The formed gradient coatings were studied by SEM, TEM, XRD analysis, micro- and nanoindentation, and tribological measurements. It was found, that the synthesized coatings have high hardness of up to 36.2 GPa, relatively low Young’s modulus of 222 GPa, relatively high H/E ratio of ? 0.2, high degree of elastic recovery of 69%, low arithmetic average surface roughness of 0.03 ?m, low friction coefficient of 0.31, and relatively low wear rate of 1.3·10–6 mm3N–1m–1. The coatings have a multiphase and multilayer nanocrystalline structure with alternation of layers with higher and lower niobium concentration. The multilayer gradient (Zr,Nb)N coating consists mainly of the ZrN crystallites with a cubic crystal lattice, and Zr0.5Nb0.5N, Nb, NbN crystallites with the volume fraction of up to 23% and 3% of crystallites of the following phases: Nb2N, Nb4N3, ZrN0.28, NbO2, Nb2O5, and ZrO2.