Chemical vapour deposition of alumina on cutting tool inserts from AlCl 3-H 2-CO 2 mixtures: Influence of the chemical vapour deposition parameters and the nature of the inserts on the morphology and wear resistance of the coatings

Abstract

Alumina coatings were deposited by chemical vapour deposition (CVD) from an AlCl 3-H 2-CO 2 gas mixture on TiC-precoated cemented carbide or sintered alumina cutting tool inserts. The influence of both the CVD conditions (temperature, total pressure, feed gas composition) and the nature of the heat treatments of the substrates on the morphology, adherence and wear resistance of the coatings was studied. The deposits usually consisted of conducting non-stoichiometric α-Al 2O 3. The growth rate of the coating increases with increasing temperature, total pressure and tends toward a maximum for α = P H 2 in P CO 2 in ≈ 1 and P AlCl 3 ≈ 10 −3 atm. The best results were obtained with deposits that were prepared at medium temperature and low pressure. Heat treatment of the TiC-precoated cemented carbide inserts, before alumina deposition, increases adherence. An alumina CVD deposit on sintered alumina inserts enhanced their wear resistance. When the black α-Al 2O 3 deposits are heated in air, oxygen vacancies are eliminated and they become insulators.