Microstructure and properties of CVD γ-Al2O3 coatings

This work deals with the microstructures and wear properties of chemical vapour deposited γ-Al₂O₃. The γ-Al₂O₃ coatings were deposited at 800 °C on TiN and Ti(C,N) pre-coated cemented carbide substrates. The microstructures developed in the γ-Al₂O₃ coatings and the influence of the nucleation surface on the growth of γ-Al₂O₃ were characterised using transmission electron microscopy, electron energy-loss spectroscopy and X-ray diffraction. The γ-Al₂O₃ coatings were fine-grained with a high density of {1 1 1} growth twins and contained some residual sulphur. γ-Al₂O₃ was found to grow epitaxially on the investigated substrates. The mechanical properties were evaluated in metal cutting and were compared with those of κ-Al₂O₃ coated tools. As compared with the κ-Al₂O₃ coatings, the γ-Al₂O₃ coatings exhibited slightly worse adhesion and tendency for edge chipping. However, the γ-Al₂O₃ coatings showed better crater wear resistance on the rake face than κ-Al₂O₃ coatings.