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Growth and characterization of thick cBN coatings on silicon and tool substrates

: Bewilogua, K.; Keunecke, M.; Weigel, K.; Wiemann, E.


Thin solid films 469-470 (2004), pp.86-91
ISSN: 0040-6090
Journal Article
Fraunhofer IST ()
cubic boron nitride; sputter deposition; mechanical property; cutting tool; turning test

Recently some research groups have achieved progress in the deposition of cubic boron nitride (cBN) coatings with a thickness of 2 µm and more, which is necessary for cutting tool applications. In our laboratory, thick cBN coatings were sputter deposited on silicon substrates using a boron carbide target. Following a boron carbide interlayer (few 100 nm thick), a gradient layer with continuously increasing nitrogen content was prepared. After the cBN nucleation, the process parameters were modified for the cBN film growth to a thickness of more than 2 µm. However, the transfer of this technology to technically relevant substrates, like cemented carbide cutting inserts, required some further process modifications. At first, a titanium interlayer had to be deposited followed by a more than 1-µm-thick boron carbide layer. The next steps were identical to those on silicon substrates. The total coating thickness was in the range of 3 µm with a 0.5- to nearly 1-µm-thick cBN top layer. In spite of the enormous intrinsic stress, both the coatings on silicon and on cemented carbide exhibited a good adhesion and a prolonged stability in humid air. Oxidation experiments revealed a stability of the coating system on cemented carbide up to 700 °C and higher. Coated cutting inserts were tested in turning operations with different metallic workpiece materials. The test results will be compared to those of well-established cutting materials, like polycrystalline cubic boron nitride (PCBN) and oxide ceramics, considering the wear of coated tools.