Development of moderate temperature CVD Al 2O 3 coatings

Abstract

Chemically vapor deposited Al 2O 3 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 Al 2O 3 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/Al 2O 3. To overcome this limitation, alternate systems to deposit Al 2O 3 at moderate temperatures have been investigated. Systems using NO–H 2, H 2O 2, NO 2–H 2 and HCOOH were identified and thermodynamic calculations were performed to evaluate them as potential sources of oxygen donors to form Al 2O 3 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.