Investigations of the bonding layer in commercial CVD coated cemented carbide inserts

The effects of processing parameters on the bonding layer structure between the cemented carbide substrate and the Al2O3 coating were investigated by depositing thick bonding layers under commercial production conditions. Different from the belief in the literature that the bonding layer is a cubic Ti(C,N,O) phase, titanium oxides were observed. Energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) measurements were used to determine the compositions and structures of the bonding layer and the Al2O3 layer. It was found that the α-Al2O3 phase formed when there is a bonding layer, and the κ-Al2O3 phase formed without the bonding layer. Thermodynamic calculations were conducted to explore the effects of processing parameters on the formation of various oxides. It was suggested that the decomposition efficiency of the gas precursors plays a critical role in the formation of oxides.