Oxidation processes in vanadium-based single-layer and nanolayer hard coatings

We studied the oxidation resistance of CrVN single-layer, CrN/(Cr,V)N nanolayer and CrN/(Cr,V)N/VN nanolayer hard coatings with respect to the Cr:V atomic ratio. All the coatings were deposited by DC magnetron sputtering in an industrial deposition system. Using different target configurations we were able to prepare a series of samples with various Cr:V ratios. The following target arrangements were used: a) two sources with triangle-like, segmental Cr/V targets for depositing a single-layer CrVN coating with different Cr:V atomic ratios; b) two triangle-like, segmental Cr/V targets and two chromium targets for depositing the nanolayer CrN/(Cr,V)N coating; and c) two triangle-like, segmental Cr/V targets, one chromium and one vanadium target for depositing the nanolayer CrNi(Cr,V)N/VN coating. The analysis of the oxidation mechanisms for all three types of coatings showed that the formation of a thin chromium oxide layer slows down the diffusion of vanadium towards the surface. However, at the locations where the growth defects were present the vanadium kept diffusing at high rates and formed V2O5 dendritic structures at the surface. Vanadium oxide is known to have good lubricating properties at elevated temperatures, thus (Cr,V)N-based hard coatings could potentially be useful for the protection of hot-forging tools operating at high temperatures. (C) 2017 Elsevier Ltd. All rights reserved.