Tribological and oxidation behaviour of TiAlCN/VCN nanoscale multilayer coating deposited by the combined HIPIMS/(HIPIMS-UBM) technique

A TiAlCN/VCN nanostructured multilayer coating with a bi-layer thickness of 2.2 nm and a total thickness of 2.6 μm was deposited by mixed High Power Impulse Magnetron Sputtering and Unbalanced Magnetron Sputtering (HIPIMS-UBM) technique. HIPIMS was utilized in both surface pretreatment as well as coating deposition steps. The ionic composition of the HIPIMS plasma as a function of discharge current was analysed by plasma sampling using energy-resolved mass spectrometery. The spectral intensities have shown high metal ion concentration of Ti+, V+, and Al+ in the plasma. A significant amount of C+ ions were also observed due to the decomposition of the reactive methane (CH4) gas. High ionisation of the condensing species resulted in formation of a highly dense microstructure. This was confirmed through the cross-sectional TEM analysis. Thermo-gravimetric analysis showed a significant rise in the onset of rapid oxidation temperature to ≈ 780 °C. In contrast, the carbon-free TiAlN/VN multilayer coating starts oxidising rapidly at 638 °C. Dry sliding wear tests were conducted on the coatings at room temperature and at elevated temperatures of 200 °C, 450 °C, and 650 °C. The friction coefficient was found to be μ = 0.45 at room temperature, whereas the coefficient steadily decreased from 0.7 at 200 °C, to 0.5 at 450 °C and 0.4 at 650 °C respectively. Raman spectra taken in the wear track of the coating suggested the presence of Magneli phase oxides of the form, V2O5, VO2, TiO2, and AlVO4. These Raman results were compared with previously reported XRD studies performed on the oxidised surface of the TiAlCN/VCN coating at above mentioned consecutive temperatures.