Doped CVD Al2O3 coatings for high performance cutting tools

Today, high performance applications of cemented carbide cutting tool inserts demand coatings with enhanced wear resistance. Chemical vapour deposited coatings based on Ti(C,N) and Al2O3 are the systems of choice for these applications. The influence of experimental variables on process stability and Al2O3 modification and structure was investigated. Deposition characteristics of Al2O3 as a function of doping combinations, generated by additional gases (TiCl4, BCl3), and deposition temperature are reported. The Al2O3 coatings were deposited in the temperature range of 930–1030 °C at atmospheric pressure. Doping element concentrations and distribution were investigated by inductively coupled plasma mass spectrometry, energy-dispersive X-ray spectra and scanning transmission electron microscopy. Microstrain and substructure were evaluated by high temperature X-ray diffraction analysis and discussed in consideration of doping element type and deposition temperature and phase stability in the application temperature range of 800–1100 °C. The investigations have shown that the deposition rates can be enhanced by doping with Titanium. The temperature range of κ-Al2O3 phase stability during deposition is extended by Boron. Ti-and B-doped κ-Al2O3 exhibited lower full width half maximum values at temperatures above 1000 °C. It was concluded that the kinetic of the κ→α-Al2O3 transformation is affected thereby and results in enhanced wear resistance for high temperature applications of κ-Al2O3 coated cutting tool inserts.