THE POSSIBILITY OF COATING CUBIC BN FILMS ON VARIOUS SUBSTRATES

A cubic BN (c-BN) film with stoichiometric composition has been prepared on a silicon wafer using a hot cathode plasma discharge in a parallel magnetic field. However, the film does not show good adhesion because of internal stress. The effect of variation in nitrogen concentration across the film thickness on adhesion has been examined to attempt to produce good adhesion of the film on a silicon wafer. A stainless steel substrate was also used. In this case it was necessary to use a dual layer deposition technique in which a titanium base layer or first layer was deposited followed by a second layer of graded BN (nitrogen concentration varied across the film thickness). The same idea was then applied to more practical tool materials, i.e. WC-Co alloy and high speed steel; these two materials were also successfully deposited with c-BN with good adhesion by using a first layer of titanium. Furthermore, it was observed that, for a silicon substrate with a diamond coating, a c-BN film could be directly deposited on the substrate without using the graded BN layers or the interlayer of titanium.