CHEMICAL-VAPOR-DEPOSITION OF AL2O3 ON TIO

This paper is a study of the phase content and morphology of Al2O3 grown by the AlCl3/H-2/CO2 process on a chemical vapour deposition (CVD) TiO layer. The results were compared with the results of CVD of Al2O3 on Ti2O3, Ti3O5 and TiO2 from an earlier investigation. The reason for this study is that it has been suggested that the presence of titanium oxides on a TiC surface promotes the formation of alpha-Al2O3 resulting in inferior wear properties of cemented carbide cutting tools. The present investigation showed that alpha-Al2O3 was the only aluminium oxide polymorph obtained on intact layers of TiO as well as of Ti2O3, Ti3O5 and TiO2. The layers consisted of well-shaped crystallites with many cracks. The formation of titanium oxides upon oxidation of a TiC surface in a H2O/H-2 atmosphere was studied thermodynamically. At a pressure of 6.7 x 10(3) Pa and very low H2O concentrations TiO was obtained, while higher concentrations yielded both Ti2O3 and Ti3O5.