Cubic Boron Nitride and Boron Based Tool Coatings: Mechanical and Tribological Properties

Due to their broad range of mechanical properties, from very soft e.g. hexagonal boron nitride, to very hard, e.g. titanium diboride or especially cubic boron nitride (cBN), boron based coatings can be applied in a wide range of cutting operations. The soft coatings can be used as a dry lubricant for cutting operations. The very hard modifications are suitable for wear resistant coatings on cutting tools for highly abrasive machining operations. After a short overview of the relevance of cBN in production engineering and future trends we will present in detail the current status of development of cBN coatings. Different ways for cBN deposition will be discussed, including the research results of the Fraunhofer IST. Using a modified sputter technique and a special B-C-N gradient interlayer, an essential adhesion improvement of the cBN top layer has been achieved. Our new process allows to prepare cBN films thicker than 2 m on silicon and nearly 1 m on cemented carbide cutting inserts. Measurements of mechanical properties like hardness and Young s modulus reveal that the properties of the cBN films are nearly identical to those of cBN bulk material. Results of cutting and machining tests for cBN and other boron based tool coatings will be presented.