PURPOSE: To have an inexpensive diamond cutting tool with a long service life by forming a polycrystal diamond film in a sticking manner on a substrate which is excellent in close contactness with a diamond synthesized in gas phase and has a coefficient of thermal expansion close to that of diamond by a gas phase synthesizing method.
CONSTITUTION: On a substrate 2 composed of sintered body having SiC or Si3N4 as its main gradient, a polycrystal diamond film 1 is formed by a gas phase synthesizing method. This film 1 is bonded onto a cutting tool base 3 together with the substrate 2 by means of a bonding layer 4. The thickness of the film 1 is preferably in a range of 20 - 100μm. If is exceeds 100μm, the close contactness between the substrate 2 and the film 1 decreases thereby resulting in separation. If it is too thin a warp is generated in the substrate 2 during the formation of the film 1 while if too thick there is a problem in the manufacture of cutting tool. A ratio between the strength of polycrystal diamond measured by a Maran spectral method and the strength of carbon with free form is prefarably 0.25 or less as for the film quality of polycrystal diamond 1 because if it exceeds the wear resistance is reduced remarkably.
TANABE KEIICHIRO
IKEGAYA AKIHIKO
FUJIMORI NAOHARU
