Influence of bias voltage on residual stresses and tribological properties of TiAlVN-coatings at elevated temperatures

The extension of tool life is a crucial goal for heat resistant forming tools. Therefore, the industry is interested to reduce the friction and wear for these tools. The employment of metals, polymeric composites, and ceramics as solid lubricants increases the production as well as maintenance costs. Thus, the thin film technology and especially new self-lubricating coatings will become increasingly important. Titanium aluminum vanadium nitride as a self-lubricating coating has a high potential to improve the tribological behavior of heat resisting tool surfaces and has good mechanical properties such as a high hardness (more than 40 GPa). In this study, TiAlVN coatings were deposited on HS6-5-2C high speed steel substrates by using a magnetron sputtering system. After annealing at 650 °C, a V2O5 (Magnéli phase) which adds self-lubricating qualities to the coatings could be detected in the TiAlVN layer. Due to the influence of adhesive and cohesive damage processes, resulting from the residual stress behavior in the layer close to the substrate area, it is critical to measure residual stresses in order to increase the wear resistance. In addition to the phase analyses, residual stress measurements were investigated by means of x-ray diffractometry as well. An experimental method, based on the traditional sin²ψ-method and utilizing a grazing-incidence diffraction geometry was used in order to enhance the irradiation volume of thin film samples. This resulted in a higher intensity for high-angle Bragg peaks than for the Bragg–Brentano geometry. Furthermore, the mechanical and tribological properties of the TiAlVN coatings were characterized at elevated temperatures. The required results were provided by a high temperature ball-on-disk device and a nanoindenter.

► TiAlVN-coating with self-lubricating properties.
► Hardness increased with increasing bias voltage up to 43 GPa and decreased to 18 GPa at 500 °C.
► Residual stresses of the TiAlVN-coating decreased slightly with increasing temperature.
► At 650 °C self-lubricating V2O5 Magnéli-phases were detected, which influenced the friction behavior positively.