Cubic boron nitride based coating systems with different interlayers for cutting inserts

Due to its outstanding properties, cubic boron nitride (c-BN) has a high application potential, in particular as a super hard cutting tool coating. Unfortunately until now there have been no c-BN tool coatings available at an industrial scale. The preparation of c-BN coatings with a film-thickness in the µm range is challenging and succeeded only by few research groups in the last few years. In the Fraunhofer IST a PVD sputtering process was used employing a boron carbide target in an argon/nitrogen atmosphere. By this PVD process c-BN films with a thickness between 1 and 2 µm were deposited on pre-coated cemented carbide cutting inserts. The pre-coating is an important part of the interlayer system design which is used to improve the adhesion of the c-BN film and therefore is crucial for a successful application as a cutting tool coating. Several TiAlN based coatings were deposited on cemented carbide cutting inserts and tested as interlayers for the c-BN layer system. High temperature experiments at ambient air show a high oxidation resistance of c-BN with a very high remaining hardness after heat treatment. Furthermore investigations of adhesion and wear will be presented as well as morphology and composition analysis.