Surface modification of TiAlSiCN coatings to improve oxidation protection

Coatings with high thermal stability and oxidation resistance are highly anticipated for various high-temperature applications. In this work we compare three different approaches to increase the oxidation resistance of nanocomposite TiAlSiCN coatings with exceptionally high thermal stability: (i) deposition of a thin Al top-layer, (ii) Al ion implantation into their topmost surface, and (iii) deposition of a thin AlOx top-layer. The coatings were annealed in air at 1000, 1100, and 1200 °C for 1 h and their oxidation was studied using scanning electron microscopy and glow discharge optical emission spectroscopy. The obtained results demonstrate that the deposition of a thin top-layer of amorphous AlOx increases the oxidation resistance of the TiAlSiCN coatings from 1000 to 1100 °C. This decreases the gap between the high thermal stability (1300 °C) and oxidation resistance of the TiAlSiCN coatings, which is particularly important for high-speed and dry cutting applications. In contrast, the deposition of either a thin Al top-layer or Al ion implantation resulted in a negative effect. The factors affecting the rapid oxidation of such coatings at 1000 and 1100 °C are discussed.