Martin Kathrein

On the effect of Ta on improved oxidation resistance of Ti–Al–Ta–N coatings

Formation of protective oxide scales is the main reason for the high oxidation resistance of TiAlN based coatings. Here the authors report on further improvement in the oxidation resistance of TiAlN by Ta alloying. An industrial-scale cathodic arc evaporation facility was used to deposit Ti–Al–Ta–N coatings from powder metallurgically produced Ti38Al57Ta5 targets. After oxidation in ambient air, a significantly reduced oxide layer thickness in comparison to unalloyed TiAlN reference material was observed. Energy-dispersive x-ray spectroscopy line scans and secondary ion mass spectroscopy depth profiling showed that the oxide scale consists of an Al-rich top layer without detectable amount of Ta and a Ti–Ta-rich sublayer. Transmission electron microscopy investigations revealed α-Al2O3, rutile-type TiO2, and anatase-type TiO2 as the scale forming oxides. Furthermore, the Ti–Ta-rich sublayer consists of a porous layer at the oxide-nitride interface but appears dense toward the Al-rich top layer. The improve...

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 Al 2 O 3 are the systems of choice for these applications. The influence of experimental variables on process stability and Al 2 O 3 modification and structure was investigated. Deposition characteristics of Al 2 O 3 as a function of doping combinations, generated by additional gases (TiCl 4 , BCl 3 ), and deposition temperature are reported. The Al 2 O 3 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 K-Al 2 O 3 phase stability during deposition is extended by Boron. Ti-and B-doped K-Al 2 O 3 exhibited lower full width half maximum values at temperatures above 1000 °C. It was concluded that the kinetic of the K →α-Al 2 O 3 transformation is affected thereby and results in enhanced wear resistance for high temperature applications of K-Al 2 O 3 coated cutting tool inserts.

Combinatorial synthesis of Cr1−xAlxN and Ta1−xAlxN coatings using industrial scale co-sputtering

For a comprehensive understanding of the scientific relations between composition, microstructure and properties of hard coatings usually a multitude of deposition runs is necessary. Within the present work, a combinatorial deposition approach using triangular shaped segmented sputter targets was adapted for an industrial scale sputter system. Owing to the position of the substrates relative to the target segments, a wide range of compositions can be achieved within a single deposition run. To verify this concept, Cr1 − xAlxN reference coatings and Ta1 − xAlxN coatings, each with a base layer of TiAlN (i.e. a bilayer configuration), were synthesised. The effect of the varying chemical compositions on the structure and mechanical as well as tribological properties was investigated. This approach enables to efficiently identify promising coating compositions.

Sputtered Coatings Based on the Al 2 Au Phase

Transition metal nitride-based, wear-resistant hard coatings on cutting tools and other substrates often lack distinct colorations allowing product differentiation and self-lubricating properties. In the present work, the possibility of achieving these objectives for sputtered coatings based on the purple-red Al2Au phase within the Al-Au system was investigated. Coatings were characterized with respect to morphology, chemical and phase composition, hardness, optical, oxidation and tribological properties. Al2Au-containing coatings were deposited with dense, fine-grained structures yielding a hardness of 4 GPa and pink coloration. The coatings were stable up to about 850°C, where the onset of oxidation occurs. Low friction coefficients against alumina were achieved between 500 and 700°C. The concept of applying Al2Au-containing coatings as a colored self-lubricating layer on top of a hard coated cemented carbide tool warrants further investigations.