A method of creating adherent surface coatings on carbide cutting tools or other workpiece substrates through the development of polycrystalline diamond coatings or composite coatings comprising a refractory metal carbide and polycrystalline diamond is described. The coating is deposited through a sequenced chemical vapor deposition process, first using a specified gas mixture of hydrogen and a refractory metal halide to deposit a base layer of a refractory metal carbide. This step is followed by a second step in which polycrystalline diamond is deposited from a gas mixture comprising a hydrocarbon and hydrogen. Co-deposition of refractory metal carbide and diamond in the second step to create a toughened diamond coating is also contemplated.