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 degrees 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 degrees C, the coating showed low friction coefficient at mu <= 0.6 and low wear rate in the scale of 10(-17) m(3) N(-1) m(-1) dominated by mild oxidation wear. From 100 to 200 degrees C, a progressive transition to higher friction coefficient occurred. After that, the coating exhibited high friction of mu = 0.9 at temperatures between 200 and 400 degrees C, and simultaneously higher wear rates of (10(-16) to 10(-15)) m(3) N(-1) m(-1). The associated wear mechanism changed to severe wear dominated by cracking and spalling. From 500 degrees 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 mu = 1.1 at 500 degrees C, and then to fast deterioration of the coating despite the lowest friction coefficient of mu < 0.3 at 700 degrees C. (C) 2011 Elsevier B.V. All rights reserved.