Boron containing combination tool coatings - characterization and application tests

The requirements for durable tool coatings continuously increase. In many cases, tool coatings combining different phases or several layers could provide an improvement in tool life. The broad range of mechanical properties of materials in the B-C-N and Ti-B-N ternary systems, from very soft to superhard, presents many possibilities to generate various combination coatings. Such coatings were prepared using reactive sputter techniques with different target materials. An outstanding example is a superhard 3 µm thick coating system with a 0.5 to 0.8 µm thick cBN top layer deposited on cutting inserts. Soft coatings like hexagonal boron nitride were found to be essential for machining operations under dry conditions. The coatings were characterized with respect to hardness, abrasive wear rate and friction coefficients. The correlation between properties and composition was revealed. Application test results of B-C-N and Ti-B-N coating systems on tools obtained under near production conditions will be reported. Specifically, turning tests performed with cemented carbide cutting inserts coated with a superhard coating system with a cBN top layer will be discussed.