Method for making diamond coated cutting tool

A process for making a diamond coated cutting tool, the process comprising the following steps:

• providing a sintered substrate, the sintered substrate comprising tungsten carbide and cobalt, the sintered substrate having an average tungsten carbide grain size of between about 3 micrometers and about 20 micrometers;
• re-sintering the sintered substrate to produce a re-sintered substrate, the re-sintered substrate having a surface, and the re-sintered substrate having a surface region beginning at and extending inwardly from the surface, the re-sintered substrate having a bulk region inwardly of the surface region, and the surface region of the re-sintered substrate having an average tungsten carbide grain size of between about 12 micrometers and about 60 micrometers, the bulk region of the re-sintered substrate having an average tungsten carbide grain size of between about 3 micrometers and about 20 micrometers, and wherein the average tungsten carbide grain size in the surface region is greater than the average tungsten carbide grain size in the bulk region;
• subjecting the re-sintered substrate to a chemical treatment for the removal of cobalt at the surface of the re-sintered substrate to produce a treated substrate, and wherein the treated substrate has a surface with a cobalt peak/tungsten peak ratio of less than 0.2 and there being an absence of continuous porosity below the surface of the treated substrate;
• and
• adherently depositing a diamond coating to at least a portion of the surface of the treated substrate.