Effect of substrate grain size and surface treatments on the cutting properties of diamond coated Co-cemented tungsten carbide tools

Three sets of triangular (TPGN 160308) WC-6wt.%Co inserts having different average grain size (1, 3 and 6 µm) were submitted to surface roughening either by wet etching with Murakami's reagent or by a heat treatment in the hot filament chemical vapor deposition (HFCVD) reactor. The heat treatment was performed in a monohydrogen-rich atmosphere at substrate temperatures as high as 1000 degrees C. X-Ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) showed that this pre-treatment led to surface recrystallization of tungsten carbide and to a lower surface Co concentration. The fractional density and the bulk properties of the substrates, as determined by saturation magnetization and coercitivity measurements, were not affected by the thermal treatment. Prior to deposition, all inserts were etched with an acid solution of hydrogen peroxide. Diamond coatings were deposited by HFCVD. The coated inserts were tested by dry machining of MMC (Al-20% SiC) bars. Turning tests showed that a proper combination of substrate pretreatment and microstructure was necessary to maximize the life of diamond coated tools.