초록

Cutting elements having coarse grain substrates and ultra hard material layers are provided. The substrates are formed from coarse grain size particles of tungsten carbide. A method of forming such cutting elements and a drag bit incorporating such cutting elements are also provided.

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What is claimed is: 1. A shear cutter comprising: a substrate having an end surface, wherein the substrate is formed by the consolidation of a composition comprising tungsten carbide and a binder material, the substrate after consolidation not having a double cemented microstructure and having at l

What is claimed is: 1. A shear cutter comprising: a substrate having an end surface, wherein the substrate is formed by the consolidation of a composition comprising tungsten carbide and a binder material, the substrate after consolidation not having a double cemented microstructure and having at least one substrate property selected from the group consisting of a median particle size of at least 6 μm, a Rockwell A hardness less than 86, and an impurity content of the tungsten carbide being not greater than about 0.1% by weight; and an ultra hard material layer over the end surface of the substrate, wherein the ultra hard material comprises ultra hard material particles, wherein the median particle size of the ultra hard particles is approximately the same as the median particle size of the substrate. 2. The shear cutter as recited in claim 1 further comprising at least one intermediate layer between the substrate and the ultra hard material layer. 3. The shear cutter as recited in claim 1 wherein the substrate has a median particle size of at least about 9 μm. 4. The shear cutter as recited in claim 1 wherein the substrate has a fracture toughness after consolidation of at least about 18 ksi(in)0.5. 5. The shear cutter as recited in claim 1 wherein the substrate has a hardness after consolidation in the range from about 83 to about 85 Rockwell A. 6. The shear cutter as recited in claim 1 wherein the substrate end surface is non-planar. 7. The shear cutter as recited in claim 1 wherein the ultra hard material layer comprises an ultra hard material selected from the group consisting of diamond, cubic boron nitride and a mixture thereof. 8. The shear cutter as recited in claim 1 wherein after consolidation the substrate has a fracture toughness of at least about 18ksi(in)0.5 and a hardness in the range from about 83 to about 85 Rockwell A. 9. A shear cutter comprising: a substrate having an end surface, wherein the substrate is formed by the consolidation of a composition comprising tungsten carbide and a binder material, the substrate after consolidation not having a double cemented microstructure and having at least one substrate property selected from the group consisting of a median particle size of at least 6 μm, a Rockwell A hardness less than 86, and an impurity content of the tungsten carbide being not greater than about 0.1% by weight; and an ultra hard material layer over the end surface of the substrate, wherein the substrate comprises at least a 6% concentration of particles having a grain size of at least 7 μm or more. 10. The shear cutter as recited in claim 9 further comprising at least one intermediate layer between the substrate and the ultra hard material layer. 11. The shear cutter as recited in claim 9 wherein the substrate has a median particle size of at least about 9 μm. 12. The shear cutter as recited in claim 9 wherein the substrate has a fracture toughness after consolidation of at least about 18 ksi(in)0.5. 13. The shear cutter as recited in claim 9 wherein the substrate has a hardness after consolidation in the range from about 83 to about 85 Rockwell A. 14. The shear cutter as recited in claim 9 wherein the substrate end surface is non-planar. 15. The shear cutter as recited in claim 9 wherein the ultra hard material layer comprises an ultra hard material selected from the group consisting of diamond, cubic boron nitride and a mixture thereof. 16. The shear cutter as recited in claim 9 wherein after consolidation the substrate has a fracture toughness of at least about 18 ksi(in)0.5 and a hardness in the range from about 83 to about 85 Rockwell A. 17. A cutting element comprising: a substrate having an end surface, wherein the substrate is formed by the consolidation of a composition comprising tungsten carbide and a binder material, the substrate after consolidation having at least one substrate property selected from the group consisting of a median particle size of at least 6 μm, a Rockwell A hardness less than 86, and an impurity content of the tungsten carbide being not greater than about 0.1% by weight; and an ultra hard material layer over the end surface of the substrate, wherein the ultra hard material comprises ultra hard material particles, and wherein the median particle size of the ultra hard particles is approximately the same as the median particle size of the substrate. 18. A cutting element comprising: a substrate having an end surface, wherein the substrate is formed by the consolidation of a composition comprising tungsten carbide and a binder material, the substrate after consolidation having at least one substrate property selected from the group consisting of a median particle size of at least 6 μm, a Rockwell A hardness less than 86, and an impurity content of the tungsten carbide being not greater than about 0.1% by weight, wherein the substrate comprises at least a 6% concentration of particles having a grain size of at least 7 μm or more; and an ultra hard material layer over the end surface of the substrate. 19. The cutting element as recited in claim 18 further comprising at least one intermediate layer between the substrate and the ultra hard material layer. 20. The cutting element as recited in claim 18 wherein the substrate has a median particle size of at least about 9 μm. 21. The cutting element as recited in claim 18 wherein the substrate has a fracture toughness after consolidation of at least about 18 ksi(in)0.5. 22. The cutting element as recited in claim 18 wherein the substrate has a hardness after consolidation in the range from about 83 to about 85 Rockwell A. 23. The cutting element as recited in claim 18 wherein the substrate end surface is non-planar. 24. The cutting element as recited in claim 18 further wherein the ultra hard material layer comprises an ultra hard material selected from the group consisting of diamond, cubic boron nitride and a mixture thereof. 25. The cutting element as recited in claim 18 wherein after consolidation the substrate has a fracture toughness of at least about 18 ksi(in)0.5 and a hardness in the range from about 83 to about 85 Rockwell A. 26. The cutting element as recited in claim 18 wherein the ultra hard material comprises ultra hard material particles, wherein the median particle size of the ultra hard particles is approximately the same as the median particle size of the substrate. 27. The cutting element as recited in claim 18 wherein the substrate comprises at least a 6% concentration of particles having a grain size of at least 7 μm or more. 28. The cutting element as recited in claim 18 wherein the substrate comprises cobalt and wherein the impurity content of the tungsten carbide is controlled to provide a thermal conductivity after consolidation not less than a value Kmin as determined by the following equation: description="In-line Formulae" end="lead"K min=0.38-0.00426X, where X in the substrate cobalt content in weight %. description="In-line Formulae" end="tail" 29. The cutting element as recited in claim 18 wherein the substrate comprises cobalt and wherein the substrate composition has a minimal Rockwell A scale hardness Hmin after consolidation defined by the equation: description="In-line Formulae" end="lead"H min=91.1-0.63X, where X is the substrate cobalt content in weight %. description="In-line Formulae" end="tail" 30. The cutting element as recited in claim 18 wherein the substrate comprises cobalt, wherein the impurity content of the tungsten carbide is controlled to provide a thermal conductivity not less than a value Kmin as determined by the following equation: description="In-line Formulae" end="lead"K min=0.00102X2-0.03076X+0.5454, description="In-line Formulae" end="tail" where X is the substrate cobalt content in weight %, and K min is in the units of cal/cm쨌s쨌K. 31. The cutting element as recited in claim 18 further comprising a transition layer between the substrate and the ultra hard material layer.