Microstructure and tribological properties of cubic boron nitride films on Si3N4 inserts via boron-doped diamond buffer layers

• Cubic BN films are deposited on Si3N4 inserts via boron-doped diamond interlayers.
• The doping level of diamond layers affects the quality of cubic BN films.
• The cubic BN coatings show ultrahigh hardness and excellent tribological properties.

Cubic boron nitride (cBN) coatings were deposited on silicon nitride (Si3N4) cutting inserts through conductive boron-doped diamond (BDD) buffer layers in an electron cyclotron resonance microwave plasma chemical vapor deposition (ECR MPCVD) system. The adhesion and crystallinity of cBN coatings were systematically characterized, and the influence of doping level of BDD on the phase composition and microstructure of the cBN coatings were studied. The nano-indentation tests showed that the hardness and elastic modulus of the obtained cBN coatings were 78 GPa and 732 GPa, respectively. The tribological properties of the cBN coatings were evaluated by using a ball-on-disc tribometer with Si3N4 as the counterpart. The coefficient of the friction and the wear rate of the cBN coatings were estimated to be about 0.17 and 4.1 × 10− 7 mm3/N m, respectively, which are remarkably lower than those of titanium aluminum nitride (TiAlN) coatings widely used in machining ferrous metal. The results suggest that cBN/BDD coated Si3N4 inserts may have great potentials for advanced materials machining.