| 초록 |
Cubic boron nitride (c-BN) is a promising coating material for cutting tools due to its extremely high hardness, high temperature stability compare to diamond and its chemical resistance for working with iron containing materials like steel. Recently some research groups have succeeded in producing thick (＞1 µm) c-BN coatings on silicon and metal substrates by physical vapor deposition (PVD) and chemical vapor deposition (CVD) methods. Our Lab was succeed thick c-BN films on cemented carbide cutting tools by R.F. (13.56 MHz) diode sputtering apparatus and multi layer system. The aim of this study is the optimization of c-BN film deposition processes for commercial application. The thick c-BN layer was coated on with utilizable TiAlN interlayer (2~5 µm), boron carbide (~1 µm) and B-C-N gradient layer (10~15 nm) system. In spite of high residual stress, c-BN top layers of a thickness of more than 2 µm could be deposited on cemented carbide substrates using the multi layer system without an essential reduction of stresses. Moreover, we succeed ~3 µm adhesive and stable c-BN films with a suitable interlayer and gradient layer system. The c-BN top layer had a micro hardness of 65 GPa, and showed a range of 30 - 40 N for the critical load depending on the different grain size of tool substrates. Moreover, the boron nitride layer consisted to more than 90 % of c-BN and X-ray diffraction showed that (111) growth direction was preferential in the film. In addition, the prepared layer system showed excellent cutting performance in turning test. |
