Temperature dependent friction and wear of magnetron sputtered coating TiAlN/VN

In this paper, a magnetron sputtered nano-structured multilayer coating TiAlN/VN, grown on hardened tool steel substrate, has been investigated in un-lubricated ball-on-disk sliding tests against an alumina counterface, to study the friction and wear behaviours at a broad range of testing temperatures from 25 to 700 °C, followed by comprehensive analysis of the worn samples using FEG-SEM, cross-sectional TEM, EDX, as well as micro/nano indentations. The experiment results indicated significant temperature-dependent friction and wear properties of the coating investigated. Below 100 °C, the coating showed low friction coefficient at μ ≤ 0.6 and low wear rate in the scale of 10−17 m3 N−1 m−1 dominated by mild oxidation wear. From 100 to 200 °C, a progressive transition to higher friction coefficient occurred. After that, the coating exhibited high friction of μ = 0.9 at temperatures between 200 and 400 °C, and simultaneously higher wear rates of (10−16 to 10−15) m3 N−1 m−1. The associated wear mechanism changed to severe wear dominated by cracking and spalling. From 500 °C and so on, accelerated oxidation of the TiAlN/VN became the controlling process. This led first to the massive generation of oxide debris and maximum friction of μ = 1.1 at 500 °C, and then to fast deterioration of the coating despite the lowest friction coefficient of μ < 0.3 at 700 °C.