Selectively leached, polycrystalline structures for cutting elements of drill bits

1. A method of fabricating a sintered polycrystalline diamond structure, comprising:

forming a compact comprising diamond grit;

sintering the compact in the presence of a catalyst to thereby form a diamond structure comprising an integral mass of sintered polycrystalline diamond (PCD) exhibiting diamond-to-diamond bonding, the metal catalyst occupying voids therein; and

partially leaching the sintered diamond structure by removing the catalyst from an area within the sintered diamond structure adjacent to a working surface of the structure;

wherein the sintered diamond structure comprises at least one region interspersed with at least one additive for increasing the permeability of the PCD or acceptance of the PCD to a leaching solution within portions of the compact as compared to at least one other region of the diamond structure containing less of said at least one additive; and

wherein said at least one additive is selected from a group consisting of, but not limited to, titanium diboride (TiB 2 ), wurtzite boron nitride (w-BN), cubic boron nitride (c-BN), zirconium diboride (ZrB 2 ), wurtzite silicon carbide, and electrically conductive carbon allotropes, wherein said at least one additive is not a fullerene.

2. The method of claim 1 , wherein the catalyst is comprised of metal.

3. The method of claim 1 , wherein the sizes of the grains of said additive are less than 60 microns.

4. The method of claim 1 , wherein the sizes of the grains of diamond grit are less than 60 microns.

5. The method of claim 4 , wherein the sizes of the grains of diamond grit are less than 30 microns.

6. The method of claim 4 , wherein the sizes of the grains of diamond grit are less than 100 nanometers in at least one dimension.

7. The method of claim 1 , wherein said at least one additive comprises less than 10% by volume of the at least one region of the diamond structure.

8. The method of claim 7 , wherein said at least one additive comprises less than 5% by volume of the at least one region of the diamond structure.

9. The method of claim 7 , wherein said at least one additive comprises less than 1% by volume of the at least one region of the diamond structure.

10. The method of claim 7 , wherein the amount of said at least one additive in the at least one region of the diamond structure comprises an amount of between 0.05% and 0.5% by volume of the at least one region of the diamond structure.

11. The method of claim 1 , wherein the compact has a plurality of surfaces, at least one of which is a working surface; and wherein the compact has at least one discrete region that is adjacent the working surface that contains the at least one additive, and at least one region not containing the at least one additive.

12. The method of claim 1 , wherein the compact is formed with a plurality of surfaces, at least one of which is a working surface and at least one of which is a bottom surface; and wherein the compact is formed with at least two layers of PCD, a first layer of PCD having grains of a first size or size range adjacent the working surface, and a second layer nearer the bottom surface having grains of PCD larger than the first size or size range.

13. The method of claim 1 , further comprising leaching metal catalyst from the diamond structure.

14. The method of claim 1 , wherein,

the compact has a plurality of surfaces, at least one of which is a working surface;

the compact has at least one discrete region that is adjacent the working surface that contains the at least one additive, and at least one region not containing the at least one additive; and

the method further comprises leaching catalyst from the diamond structure, including from the at least one discrete region containing the mixture.

15. The method of claim 1 , wherein said at least one additive is dispersed into the at least one region of the diamond structure by mixing said at least one additive into the diamond grit and forming the compact with the mixture comprising the diamond grit and said at least one additive in the at least one region.

16. The method of claim 1 , wherein said at least one additive is dispersed into the at least one region of the compact, after the compact is formed and before the compact is sintered.

17. A method of fabricating a sintered polycrystalline diamond structure, comprising:

forming a compact comprising diamond grit;

sintering the compact in the presence of a catalyst to thereby form a diamond structure comprising an integral mass of sintered polycrystalline diamond (PCD) exhibiting diamond-to-diamond bonding, the metal catalyst occupying voids therein; and

partially leaching the sintered diamond structure by removing the catalyst from an area within the sintered diamond structure adjacent to a working surface of the structure;

wherein the sintered diamond structure comprises at least one region interspersed with at least one additive for increasing the permeability of the PCD or acceptance of the PCD to a leaching solution within portions of the compact as compared to at least one other region of the diamond structure containing less of said at least one additive; and

wherein the at least one additive is located in at least one, discrete region within the compact, and wherein the compact has at least one other region with PCD devoid of additive.

18. A method of fabricating a sintered polycrystalline diamond structure, comprising:

forming a compact comprising diamond grit;

sintering the compact in the presence of a catalyst to thereby form a diamond structure comprising an integral mass of sintered polycrystalline diamond (PCD) exhibiting diamond-to-diamond bonding, the metal catalyst occupying voids therein; and

partially leaching the sintered diamond structure by removing the catalyst from an area within the sintered diamond structure adjacent to a working surface of the structure;

wherein the sintered diamond structure comprises at least one region interspersed with at least one additive for increasing the permeability of the PCD or acceptance of the PCD to a leaching solution within portions of the compact as compared to at least one other region of the diamond structure containing less of said at least one additive; and

wherein the at least one additive has a first proportion of additive to PCD, and wherein the method further comprises mixing grains of diamond grit mix with grains of said at least one additive in a second proportion different from the first proportion, and wherein forming the compact comprises at least one discrete region of the mixture with the first proportion of the additive and PCD and at least one discrete region of the mixture of said at least one additive and PCD in the second proportion.

19. A method of fabricating a sintered polycrystalline diamond structure, comprising:

forming a compact comprising diamond grit;

sintering the compact in the presence of a catalyst to thereby form a diamond structure comprising an integral mass of sintered polycrystalline diamond (PCD) exhibiting diamond-to-diamond bonding, the metal catalyst occupying voids therein; and

partially leaching the sintered diamond structure by removing the catalyst from an area within the sintered diamond structure adjacent to a working surface of the structure;

wherein the sintered diamond structure comprises at least one region interspersed with at least one additive for increasing the permeability of the PCD or acceptance of the PCD to a leaching solution within portions of the compact as compared to at least one other region of the diamond structure containing less of said at least one additive; and

wherein,

the compact has a plurality of surfaces, at least one of which is a working surface;

the compact has at least one discrete region that contains the at least one additive and a region not containing the at least one additive; and

the method further comprises leaching from the diamond structure metal catalyst from the working surface, the leaching occurring within at least a portion of both the at least one discrete region containing the at least one additive and the region not containing the at least one additive.

20. A method of fabricating a sintered polycrystalline diamond structure, comprising:

forming a compact comprising diamond grit;

sintering the compact in the presence of a catalyst to thereby form a diamond structure comprising an integral mass of sintered polycrystalline diamond (PCD) exhibiting diamond-to-diamond bonding, the metal catalyst occupying voids therein; and

partially leaching the catalyst from an area within the sintered diamond structure adjacent to a working surface of the structure;

wherein the sintered diamond structure comprises at least one region interspersed with at least one additive for increasing the permeability of the PCD or acceptance of the PCD to a leaching solution within portions of the compact as compared to at least one other region of the diamond structure containing less of said at least one additive; and

wherein said at least one additive is dispersed into the diamond structure by backfilling or ion deposition after sintering the compact and prior to partially leaching the diamond structure.

21. A method of fabricating a sintered polycrystalline diamond structure, comprising:

forming a compact comprising diamond grit with at least one region interspersed with at least one additive;

sintering the compact by infiltrating a metal catalyst to form the diamond structure comprising an integral mass of sintered polycrystalline diamond (PCD) exhibiting diamond-to-diamond bonding, the metal catalyst occupying voids therein; and

partially leaching the sintered diamond structure to remove the metal catalyst from an area within the sintered diamond structure adjacent to a working surface of the structure;

wherein the additive increases the permeability to a leaching solution within portions of the sintered diamond structure as compared to at least one other region of the sintered diamond structure containing less of said at least one additive and wherein the at least one additive is not a fullerene.

22. The method of claim 21 , wherein said additive is comprised of one or more hydrophiles.

23. The method of claim 21 , wherein said at least one additive is selected from the group consisting of, but not limited to titanium diboride (TiB 2 ) wurtzite boron nitride (w-BN), cubic boron nitride (c-BN), zirconium diboride (ZrB 2 ), wurtzite silicon carbide, and electrically conductive carbon allotropes.

24. A method of fabricating a sintered polycrystalline diamond structure, comprising:

forming a compact comprising diamond grit;

sintering the compact in the presence of a catalyst to thereby form a diamond structure comprising an integral mass of sintered polycrystalline diamond (PCD) exhibiting diamond-to-diamond bonding, the metal catalyst occupying voids therein; and

partially leaching the sintered diamond structure by removing the catalyst from an area within the sintered diamond structure adjacent to a working surface of the structure;

wherein after leaching the leached portion of the diamond structure has less of the metal catalyst that remains after sintering than adjacent areas of the PCD because the leached portion of the diamond structure contains at least one additive for increasing permeability of the PCD or acceptance of the PCD to a leaching solution; and

wherein said at least one additive is selected from a group consisting of, but not limited to, titanium diboride (TiB 2 ), wurtzite boron nitride (w-BN), cubic boron nitride (c-BN), zirconium diboride (ZrB 2 ), wurtzite silicon carbide, and electrically conductive carbon allotropes, wherein said at least one additive is not a fullerene.

25. The method of claim 24 , wherein after leaching, the leached portion of the diamond structure has at least 50% of the catalyst that remains after sintering removed by leaching.

26. The method of claim 25 , wherein after leaching, the leached portion of the diamond structure is substantially devoid of metal catalyst.