Deposition, microstructure and properties of texture-controlled CVD α-Al2O3 coatings

The influence of nucleation on the microstructure and properties of CVD Al2O3 was investigated. The experimental α-Al2O3 layers were deposited (a) without nucleation control and (b) with nucleation steps resulting in pronounced 〈101¯2〉, 〈101¯4〉 and 〈101¯0〉 growth textures. The experimental layers were characterised using X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Wear properties of the textured coatings were evaluated in turning. The chemistry of the nucleation surface appeared to be an important factor in pre-determining the phase content and growth textures of the Al2O3 layers. Optimised nucleation resulted in substantially improved wear properties and these kinds of α-Al2O3 layers were typically composed of relatively small, defect-free grains exhibiting no porosity. The 〈101¯4〉 textured α-Al2O3 layer showed the best wear resistance.