The Thermal Stability of Ti-Al-C Pvd Coatings

While (Ti,Al)N coatings are well known and established in wear applications like drilling and milling, the corresponding TiC based metastable system Ti-Al-C is not well examined. This paper investigates the phase stability and the phase transition behaviour of post-deposition heat-treated Ti-Al-C coatings. The samples were annealed in a temperature range from 600–1400 °C in a high vacuum furnace. The influence of deposition parameters like coating compositions via the Ti/Al ratio and the metal/metalloid ratio on the properties were investigated. Another very important parameter in this investigation is the carbon carrier gas. Examined gases were methane, ethane, ethylene and ethine. The changes in microhardness, lattice parameters and particle sizes were analysed with respect to their temperature dependence. The phase formation depends on the target composition and on the reactive gas. A formation of a metastable (Ti,Al)C phase can be observed. A higher C:H ratio of the reactive gas leads to better incorporation of carbon into the coating. An Al-loss independent of the coating composition begins 1000 °C. The microhardness increases with higher annealing temperature and decreases with higher Al-content.