Development of moderate temperature CVD Al2O3 coatings

Chemically vapor deposited Al2O3 coatings, due to their high hardness and chemical inertness, are currently the state of art in the cutting tool industry. The conventional high deposition temperature of about 1050 °C for Al2O3 coatings, based on the water-gas shift process, has to a great extend restricted the development of several hybrid coatings, such as TiC/TiN/TiCN/Al2O3. To overcome this limitation, alternate systems to deposit Al2O3 at moderate temperatures have been investigated. Systems using NO-H2, H2O2, NO2-H2 and HCOOH were identified and thermodynamic calculations were performed to evaluate them as potential sources of oxygen donors to form Al2O3 in the moderate temperature range of 700-950 °C. Preliminary results have clearly demonstrated that it is possible to grow moderate temperature alumina (using such alternate sources) on the TiC/TiN coated cemented carbide substrates.