Surface enhanced polycrystalline diamond composite cutters

A polycrystalline diamond cutter comprising:

• a cemented metal carbide body having a face;
• a polycrystalline diamond layer on the body face wherein at least part of the polycrystalline diamond layer is used to engage earth formations;
• and
• a non-diamond refractory metal compound coating covering at least part of the polycrystalline diamond face used to engage earth formations and wherein the coating is substantially only applied to the face of the polycrystalline diamond layer used to engage earth formations.

A polycrystalline diamond cutter comprising:

• a cemented metal carbide body having a face;
• a polycrystalline diamond layer on the body face wherein at least part of the polycrystalline diamond layer is used to engage earth formations;
• and
• a coating on the polycrystalline diamond surface, wherein the polycrystalline diamond surface has a residual tensile stress and wherein the coating reduces the magnitude of the residual tensile stress.

A drill bit for cutting rock formations comprising:

• a bit body;
• and
• a plurality of polycrystalline diamond cutters embedded in the bit body, each of the cutters comprising:
• a cemented tungsten carbide body,
• a layer of polycrystalline diamond on a cutting face of the body, and
• a coating over the polycrystalline diamond, the coating consisting essentially of a non-diamond refractory metal compound selected from the group consisting of titanium nitride, titanium carbide, titanium carbonitride, titanium aluminum carbonitride, titanium aluminum nitride, boron carbide, chromium carbide, chromium nitride, zirconium carbide and any of the transition metals or Group IV metals combined with either silicon, aluminum, boron, carbon, nitrogen or oxygen.