Study of microstructure and mechanical properties of cBN coatings on nanocrystalline diamond transition layer prepared by magnetron sputtering

Cubic BN (cBN) coating is a promising protective coating in dry cutting because of its good properties in the future. However, due to the large difference in physical properties between the coating and the substrate material, the coating is easy to fall off, which limits the wide application of cBN coating. In this work, high quality cBN coating was prepared on the nanocrystalline diamond transition layer by RF magnetron sputtering technology. The effects of substrate bias and nitrogen partial pressure on microstructure and mechanical properties of cBN were analyzed. The results show that with the increase of bias pressure, the coating becomes denser, and the cubic phase content can reach up to 72.2%. With the increase of nitrogen partial pressure, the amount of Ar+ decreases, and the compactness of the coating becomes worse. The weakening of the bombardment effect is conducive to reducing the residual stress. When the bias pressure is −150 V and the partial pressure of nitrogen is 30%, the cubic phase content reaches a maximum of 74%, and the hardness and elastic modulus of the cBN coating reached their maximum values of 37 and 421 GPa, respectively. This study has a guiding significance for the application of cBN coated tools in dry machining.