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

Abstract

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 (CH 4) 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, V 2O 5, VO 2, TiO 2, and AlVO 4. 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.