Cutting elements having non-planar cutting faces with selectively leached regions, earth-boring tools including such cutting elements, and related methods

1. A cutting element, comprising:

a substrate; and

a volume of polycrystalline diamond material affixed to the substrate at an interface, the volume of polycrystalline diamond material comprising:

a front cutting face comprising:

a first substantially planar portion located adjacent to a lateral side surface of the cutting element;

a second, discrete substantially planar portion located in a central region of the front cutting face; and

at least one recess located at least partially between the first and second substantially planar portions, the at least one recess extending from a plane defined by the first and second substantially planar portions to a first depth in the volume of polycrystalline diamond material in an axial direction parallel to a central axis of the cutting element;

a region including a catalyst material disposed in interstitial spaces between diamond grains of the volume of polycrystalline diamond material, the region including the catalyst material extending through the volume of polycrystalline diamond material from the interface to an exposed surface of the volume of polycrystalline diamond material within the at least one recess of the front cutting face; and

a first region substantially free of the catalyst material, wherein the first region substantially free of the catalyst material extends from the first substantially planar portion of the front cutting face to a second depth in the volume of polycrystalline diamond material in the axial direction; and

a second region substantially free of the catalyst material, wherein the second region substantially free of the catalyst material extends from the second substantially planar portion of the front cutting face to a third depth in the volume of polycrystalline diamond material in the axial direction, the second region substantially free of the catalyst material discrete from and separated from the first region substantially free of the catalyst material by the region including catalyst material, wherein the second depth and the third depth are greater than the first depth.

2. The cutting element of claim 1 , wherein the first region substantially free of the catalyst material extends to an exposed surface of the volume of polycrystalline diamond material proximate a cutting edge formed between the front cutting face and a generally cylindrical lateral side surface of the cutting element.

3. The cutting element of claim 1 , wherein the second depth and the third depth are substantially equal.

4. The cutting element of claim 1 , wherein the second depth is at least about ten percent (10%) greater than the first depth.

5. The cutting element of claim 1 , wherein the second depth is greater than the first depth by at least about 0.0254 mm (0.001 inch).

6. The cutting element of claim 1 , wherein the third depth is less than the second depth.

7. An earth-boring tool, comprising:

a body; and

the cutting element of claim 1 affixed to the body.

8. The earth-boring tool of claim 7 , wherein the earth-boring tool is a fixed-cutter drill bit.

9. A cutting element, comprising:

a substrate; and

a volume of polycrystalline diamond material affixed to the substrate at an interface, the volume of polycrystalline diamond material comprising:

a front cutting face with at least one substantially planar portion and at least one recess, the at least one recess extending from a plane defined by the at least one substantially planar portion a first depth into the volume of polycrystalline diamond material in an axial direction parallel to a central axis of the cutting element;

a region including a catalyst material disposed in interstitial spaces between diamond grains of the volume of polycrystalline diamond material; and

at least one region substantially free of the catalyst material, wherein the at least one region substantially free of the catalyst material extends from the at least one substantially planar portion of the front cutting face a second depth into the volume of polycrystalline diamond material in the axial direction, and wherein the at least one region substantially free of the catalyst material extends from a lowermost region of an exposed surface of the volume of polycrystalline diamond material within the at least one recess a third depth into the volume of polycrystalline diamond material in the axial direction, wherein the second depth and the third depth are greater than the first depth.

10. The cutting element of claim 9 , wherein the third depth is less than the second depth.

11. The cutting element of claim 9 , wherein the at least one region substantially free of catalyst material extends substantially continuously over a surface of the volume of polycrystalline diamond material defined by the front cutting face.

12. The cutting element of claim 11 , wherein the at least one region substantially free of catalyst material and the region including the catalyst material meet at a substantially planar boundary extending substantially continuously through the volume of polycrystalline diamond material.

13. The cutting element of claim 12 , wherein the substantially planar boundary extends normal to the axial direction.

14. An earth-boring tool, comprising:

a body; and

the cutting element of claim 9 affixed to the body.

15. A method of fabricating a cutting element, comprising:

affixing a volume of polycrystalline diamond material to a substrate at an interface, the volume of polycrystalline diamond material comprising:

diamond grains and a catalyst material disposed in interstitial spaces between the diamond grains;

a front cutting face comprising:

a first substantially planar portion located adjacent to a lateral side surface of the cutting element;

a second, discrete substantially planar portion located in a central region of the front cutting face; and

at least one recess located at least partially between the first and second substantially planar portions, the at least one recess extending from a plane defined by the first and second substantially planar portions to a first depth in the volume of polycrystalline diamond material in an axial direction parallel to a central axis of the cutting element; and

a region including the catalyst material extending through the volume of polycrystalline diamond material from the interface to an exposed surface of the volume of polycrystalline diamond material within the at least one recess of the front cutting face; and

forming a first region substantially free of the catalyst material within the volume of polycrystalline diamond material, the at least one region extending from the first substantially planar portion of the front cutting face to a second depth in the volume of polycrystalline diamond material in the axial direction, wherein the second depth is greater than the first depth; and

forming a second region substantially free of the catalyst material within the volume of polycrystalline diamond material, wherein the second region substantially free of the catalyst material extends from the second substantially planar portion of the front cutting face to a third depth in the volume of polycrystalline diamond material in the axial direction, the second region substantially free of the catalyst material discrete from and separated from the first region substantially free of the catalyst material by the region including catalyst material, wherein the second depth and the third depth are greater than the first depth.

16. The method of claim 15 , wherein forming at least one region substantially free of catalyst material within the volume of polycrystalline diamond material comprises:

applying a mask material resistant to a leaching agent to a surface of the volume of polycrystalline diamond material within the at least one recess of the front cutting face; and

introducing at least a portion of the volume of polycrystalline diamond material and the mask material to the leaching agent.

17. The method of claim 16 , further comprising removing at least a portion of the mask material from the at least one recess and subsequently reintroducing at least a portion of the previously masked portion of the volume of polycrystalline diamond material to the leaching agent.