Adhesion strength of diamond films on heat-treated WC-Co cutting tools

摘要

The adhesion strength and deposition behavior of diamond films with different grain size onto heat-treated WC-Co cutting tool inserts were investigated. The diamond film was deposited on WC-6 percent Co cutting tool inserts by the hot-filament chemical vapor deposition method, with H_2/ 3 percent CH_4 mixed gas. The N_2 gas was incorporated in the mixed gas to refine the grain size of the deposited diamond film (nanocrystalline diamond: NCD). Pores were observed in the interface region between the micrometer-size diamond film (MCD) and the WC-Co cutting tool insert. This suggested that the growth of diamond grains on top of elongated WC grains, which was induced by heat treatment to improve the adhesion strength of the deposited film, hindered the deposition of diamond in the valley area between the elongated WC grains. By contrast, in the case of the NCD film with a grain size of less than 50 nm obtained by addition of N_2 gas, no pores were observed, due to the fact that the refined diamond grains filled the interface region regardless of the existence of the elongated WC grains. The adhesion strength of the NCD film was likely to be greater than that of the MCD film on the heat-treated WC-Co cutting tool insert, which was explained by the full coverage with small diamond grains at the rough interface region.