Thermal stability of doped CVD κ-Al2O3 coatings

The application of wear-resistant alumina-containing coating systems is a common approach to improve cutting performance of cemented carbide cutting inserts. This work focuses on the influence of B- and Ti-B-doping on the thermal stability of kappa-Al2O3 deposited at high temperature and low pressure by chemical vapor deposition. The investigated coating architecture includes a kappa-Al2O3 bilayer, separated by a TiN/TiCN interlayer, and a TiCN base-layer grown on cemented carbide substrates. The transformation from kappa-Al2O3 to alpha-Al2O3 was examined with high-temperature X-ray diffraction at 1030 and 1000 degrees C as well as glancing angle X-ray diffraction after different heat treatment times at 1000 degrees C. Chemical composition and coating morphology were determined with glow discharge optical emission spectrometry and scanning electron microscopy, respectively. In general, doping retarded the kappa-alpha-transformation. Ti-B- and, to a lower degree, B-doping entailed a slower diffusion of base-layer and substrate species through the kappa-Al2O3 bilayer, thus retarding the formation of segregated species on the sample surface. In addition, the heat treatment atmosphere decisively affected the kappa-alpha-transformation. (c) 2010 Elsevier B.V. All rights reserved.