High temperature friction and galling properties of nanolayered (Cr,V)N coatings and effect of V content

Abstract

Chromium nitride (CrN) coating is considered as one of the best candidates for wear protection in many forming application where adhesive wear and galling dominate. However, its relatively high coefficient of friction against soft metals hinders its applicability. Vanadium nitride (VN), on the other hand has attracted increasing interest as VN is easily oxidized to form Magneli phase vanadium oxides with easy slipping shear planes, on one hand leading to self-lubricating properties but also to deteriorated wear resistance. This can be overcome by forming CrVN coatings. However, there is a lack of information how such coatings perform in terms of galling resistance and V-concentration in typical forming conditions and against soft metals.Therefore, the aim of this work was to study friction properties of nano-layered PVD (Cr,V)N coatings at room and elevated temperature and how V-content influences on friction and galling resistance against typical work materials. Nanolayered (Cr,V)N coatings with V in concentrations from 15 to 30 % were deposited by industrial DC magnetron sputtering system and tested using Load-Scanner against AA2024 aluminum alloy and low-carbon steel at room and elevated temperature of 300 °C and 600 °C, respectively. Results were evaluated in terms of coefficient of friction level and stability, critical loads for galling initiation and volume of adhered work material. Results show that (Cr,V)N coatings do not necessarily improve galling resistance, being strongly dependent on V concentration and contact temperature. For forming Al alloys positive results are obtained with coatings containing 20–25 at.% V and for low-carbon steels above 25 at.%, with marked improvement obtained only at elevated temperatures.