Influence of the nucleation surface on the growth of epitaxial Al2O3 thermal CVD films deposited on cemented carbides

This work aims at understanding the nucleation and growth of alumina films grown on Ti(C,N)-based layers using an industrial-scale CVD system. Firstly, Al2O3 layer was deposited on Ti(C,N)-based layers without any nucleation treatment, pure alpha-Al2O3 is obtained, whereas no orientation relationship at the Ti(C, N)/alpha-Al2O3 layers interface can be observed. Secondly, Al2O3 layer was deposited on the bonding layer consisting of rutile TiO2, which is obtained by oxidizing the uppermost part of Ti(C,N)-based layers. Herein, alpha-Al2O3 single-phased layer is obtained, and the epitaxial growth of alpha-Al2O3 on rutile is observed. The orientation relationships can be found as:((1) over bar 20) (alpha-Al2O3)//(10 (1) over bar)(rutile), (003) alpha-Al2O3 //(010)(rutile) and [210]alpha-Al2O3 //[101](rutile). Finally, Al2O3 layer was deposited on the bonding layer, produced from a TiCl4-H2-N-2-CH4-CO-AlCl3 gas mixture. Regarding this intermediate layer, despite additions of CO and AlCl3, no evidence for oxide phases, e.g. TiO2 and Al2O3 can be found, while Ti(C,N) needle-shaped grains develop. In this case, kappa-Al2O3 is epitaxially grown on Ti(C,N), with the orientation relationships found as:.(013)kappa-Al2O3//((2) over bar 20)(Tio(C,N)), (100)kappa-Al2O3//(1 (1) over bar1)(Tio(C,N)) and [031]kappa-Al2O3//[112](Tio(C,N)). Since processing parameters for the alumina depositions were always the same, it is revealed that the nucleation of alpha-Al2O3 and kappa-Al2O3 can be accurately controlled with deposition of specific bonding layers. (C) 2022 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

This study investigates the nucleation and growth of alumina films on Ti(C,N)-based layers using an industrial-scale CVD system. It is found that the deposition of Al2O3 layer without nucleation treatment results in pure alpha-Al2O3, while no orientation relationship is observed at the Ti(C,N)/alpha-Al2O3 interface. However, when the Al2O3 layer is deposited on a bonding layer consisting of rutile TiO2, alpha-Al2O3 single-phased layer is obtained with epitaxial growth on rutile. Furthermore, when the Al2O3 layer is deposited on a bonding layer produced from a TiCl4-H2-N-2-CH4-CO-AlCl3 gas mixture, kappa-Al2O3 is epitaxially grown on Ti(C,N). The nucleation of alpha-Al2O3 and kappa-Al2O3 can be accurately controlled by depositing specific bonding layers.