PURPOSE: To firmly bond a diamond layer to a sintered material and to improve the abrasion resistance and toughness of the sintered material by dissolving and removing a metal from the surface layer of a sintered diamond containing a small amount of a metal and depositing a diamond film on the surface by vapor-growth technique.

CONSTITUTION: Diamond particles containing a small amount of a metal such as Cr, Ni or Co are sintered to form a sintered material having excellent toughness. The metal in the surface layer of the sintered material is dissolved and removed e.g. by the acid treatment of the material. A diamond film is deposited on the treated material by vapor-phase growth technique. A blade of a cutting tool having excellent abrasion resistance, peel resistance and toughness can be produced by the process.