Cubic boron nitride coatings - sputter deposition, properties and application tests

Because of their high hardness and thermal stability, cubic boron nitride (cBN) coatings are highly attractive for cutting tool applications, especially for ferrous materials. However, there are still some obstacles to overcome before cBN coatings will meet an industrial level. Today sufficiently thick (up to 2 µm and more) and well adhering cBN films can be prepared on cemented carbide cutting inserts. Deposition processes were carried out in laboratory scale equipment by reactive sputtering using boron carbide B4C targets and Ar/N2 gas mixtures. As adhesion improving interlayers hard coatings like TiN and TiAlN were prepared. The coating properties were very similar to those known for bulk cBN. Cutting tests under conditions near to actual practice revealed the high potential of the cBN coatings. There are indications that the coatings behavior will be influenced by the grain structure and composition of the cemented carbide substrate. The consequences in view of cBN deposition on three dimensional tools and to an up scaling to industrial machine dimensions will be discussed.