Thick c-BN coatings – Preparation, properties and application tests

Due to the outstanding properties of cubic boron nitride (c-BN) – c-BN is the second hardest of all known materials, has a high wear resistance and a high thermal stability – this material is very promising for a broad range of applications, especially for cutting tools, both as bulk and as a coating material. The state-of-the-art is the use of sintered cutting inserts with c-BN grains. Such c-BN grains are synthesized in an expensive high-pressure–high-temperature process.The requirements for cutting tools continuously increase in production engineering and this leads to a strong demand for new super hard tool coatings. Cubic boron nitride coatings could be an attractive solution. Unfortunately, the preparation of thick c-BN coatings, on the μm scale, is difficult, due to some serious drawbacks and has been successful only in the last years for a few research groups worldwide.PVD processes allow the preparation of c-BN films thicker than 2 μm on silicon and 1 μm c-BN top layers on pre-coated cemented carbide cutting inserts. Measurements of mechanical properties like hardness and Young's modulus reveal that the properties of the c-BN coatings, with hardness of about 60 GPa, are nearly identical to those of c-BN bulk material.Results of systematic turning and milling tests of different coatings in combination with a c-BN top-layer on cemented carbide cutting inserts will be presented in detail. The new results confirm the high potential of c-BN coatings on cutting tools.