Tribological behavior and thermal stability of TiC/a-C:H nanocomposite coatings

Advanced TiC/a-C:H nanocomposite coatings have been produced via reactive deposition in a closed-field unbalanced magnetron sputtering system (Hauzer HTC-1200). These wear-resistant coatings are targeted for automotive applications where high load-bearing capacity and thermal stability, low friction, and wear resistance are the primary requirements. In this article the tribological behavior of the nanocomposite coatings is scrutinized by means of ball-on-disk tribotests at elevated temperature or after annealing in the temperature range of 150-400 deg. C. The thermal stability of the coatings in terms of critical temperatures, at which the degradation of wear resistance and friction of the coatings starts, is monitored with depth profiling of oxygen content using Auger spectroscopy in conjunction with detailed examinations of the mechanical properties of the annealed coatings. A striking result is that a coating thermally stable up to 350 deg. C may fail at much lower temperatures during elevated-temperature tribotests. The origin of failure is attributed to the interfacial delamination due to the discontinuity in mechanical properties between the coatings and substrates at elevated temperatures. It indicates a stringent requirement to optimize the interlayer of advanced tribological coatings developed for high temperature applications