Improving the oxidation resistance of TiAlN/CrAlO coatings through CrAlON interlayer

Physical vapor deposition nitride and oxide hard coatings are essential for cutting tools. The combination of nitride and oxide layers benefits adhesion improvement on tool substrates and holds great technological importance. Here, an investigation was conducted to examine the high-temperature oxidation resistance of TiAlN, TiAlN/CrAlO, and TiAlN/CrAlON/CrAlO coatings deposited by cathode arc evaporation. The oxidation resistance of a single TiAlN coating is quite poor, as it undergoes complete oxidation at a temperature of 900 °C. The top layer of CrAlO experiences grain coarsening and possesses a considerable degree of capability to impede the inward diffusion of oxygen. Hence, the TiAlN/CrAlO bi-layered structure can endure temperatures of 900 °C without experiencing substantial oxidation. The CrAlON acquired a nano-multilayered configuration comprising sublayers rich in oxygen and nitrogen through deposition in a mixed O2 and N2 atmosphere. When exposed to air at elevated temperatures, a low oxygen level at the CrAlO/CrAlON interface induces the formation of an amorphous AlO scale produced by the CrAlON interlayer. This slow-growing amorphous scale protects the underlying coating from further intense oxidation. Therefore, the TiAlN/CrAlON/CrAlO coating demonstrated higher resistance to oxidation at a temperature of 950 °C.