Preparation of alumina coatings by chemical vapour deposition

A short survey is given of improvements in the performance of cemented carbide tools for steel cutting as a result of a coating. The preparation of Al 2O 3 coatings by chemical vapour deposition is discussed in terms of nucleation, growth, preferred orientations and equilibrium growth shapes of the Al 2O 3 crystals as well as the influence of impurities on the layer formation. It is also pointed out that, although impurities can in principal have beneficial effects, they usually seem to be detrimental.