Polycrystalline compacts, earth-boring tools including such compacts, and methods of fabricating polycrystalline compacts

1. A polycrystalline compact, comprising:

diamond;

cubic boron nitride; and

at least one hard material selected from the group consisting of aluminum nitride, gallium nitride, silicon nitride, titanium nitride, silicon carbide, titanium carbide, titanium boride, titanium diboride, and aluminum boride;

wherein the diamond, the cubic boron nitride, and the hard material are intermixed and interbonded to form a polycrystalline material, and

wherein the polycrystalline compact at least one of comprises from about 3 atomic percent to about 15 atomic percent boron or has a density of at least about 3.30 g/cm 3 ; and

wherein the polycrystalline compact comprises at least one composition selected from the group consisting of:

from about 65 atomic percent to about 95 atomic percent carbon;

from about 5 atomic percent to about 10 atomic percent boron;

from about 3 atomic percent to about 15 atomic percent nitrogen; and

from about 0.05 atomic percent to about 5.0 atomic percent of an element selected from the group consisting of aluminum, gallium, silicon, and titanium.

2. The polycrystalline compact of claim 1 , wherein the polycrystalline compact has a density of at least about 3.40 g/cm 3 .

3. The polycrystalline compact of claim 1 , wherein the polycrystalline compact comprises from about 65 atomic percent to about 95 atomic percent carbon.

4. The polycrystalline compact of claim 1 , wherein the polycrystalline compact comprises from about 5 atomic percent to about 10 atomic percent boron.

5. The polycrystalline compact of claim 1 , wherein the polycrystalline compact comprises from about 3 atomic percent to about 15 atomic percent nitrogen.

6. The polycrystalline compact of claim 1 , wherein the polycrystalline compact comprises from about 0.05 atomic percent to about 5.0 atomic percent of an element selected from the group consisting of aluminum, gallium, silicon, and titanium.

7. The polycrystalline compact of claim 1 , wherein the at least one hard material selected from the group consisting of aluminum nitride, gallium nitride, silicon nitride, titanium nitride, silicon carbide, titanium carbide, titanium boride, titanium diboride, and aluminum boride comprises aluminum nitride.

8. The polycrystalline compact of claim 1 , wherein the polycrystalline compact is substantially free of metallic phases comprising cobalt, nickel, iron, and alloys thereof.

9. A method of fabricating a polycrystalline compact, comprising:

forming a mixture comprising diamond, non-cubic boron nitride, and a metal or semimetal, the metal or semimetal selected from the group consisting of aluminum, gallium, silicon, and titanium;

encapsulating the mixture in a container; and

subjecting the encapsulated mixture to a pressure of at least 5.0 GPa and a temperature of at least 1,100° C. for a period of time from about 1 second to about 5 minutes to form a polycrystalline material from the mixture, the polycrystalline material comprising the diamond, cubic boron nitride formed from the non-cubic boron nitride, and at least one hard material selected from the group consisting of aluminum nitride, gallium nitride, silicon nitride, titanium nitride, silicon carbide, titanium carbide, titanium boride, titanium diboride, and aluminum boride;

wherein the diamond, the cubic boron nitride, and the hard material are intermixed and interbonded within the polycrystalline material.

10. The method of claim 9 , wherein forming the mixture comprising diamond, non-cubic boron nitride, and the metal or semimetal comprises mixing the diamond with the non-cubic boron nitride and aluminum powder.

11. The method of claim 9 , wherein forming the mixture comprising diamond, non-cubic boron nitride, and the metal or semimetal comprises mixing diamond having an average particle size from about 50 nm to about 40 μm with the metal or semimetal and the non-cubic boron nitride.

12. The method of claim 9 , wherein forming the mixture comprising diamond, non-cubic boron nitride, and the metal or semimetal comprises mixing non-cubic boron nitride having an average particle size from about 1 μm to about 40 μm with the diamond and the metal or semimetal.

13. The method of claim 9 , wherein subjecting the encapsulated mixture to the pressure of at least 5.0 GPa and the temperature of at least 1,100° C. comprises subjecting the encapsulated mixture to a pressure of at least about 7.5 GPa.

14. The method of claim 9 , wherein subjecting the encapsulated mixture to the pressure of at least 5.0 GPa and the temperature of at least 1,100° C. comprises subjecting the encapsulated mixture to a temperature of at least about 1,400° C.

15. A polycrystalline compact, comprising:

diamond;

cubic boron nitride; and

at least one hard material selected from the group consisting of aluminum nitride, gallium nitride, silicon nitride, titanium nitride, silicon carbide, titanium carbide, titanium boride, titanium diboride, and aluminum boride;

wherein the diamond, the cubic boron nitride, and the hard material are intermixed and interbonded to form a polycrystalline material, and

wherein the polycrystalline compact at least one of comprises from about 3 atomic percent to about 15 atomic percent boron or has a density of at least about 3.30 g/cm 3 ; and

wherein the polycrystalline compact has a Young's modulus of at least about 700 GPa.

16. An earth-boring tool, comprising:

a bit body; and

at least one polycrystalline compact secured to the bit body, the polycrystalline compact comprising:

diamond;

cubic boron nitride; and

at least one hard material selected from the group consisting of aluminum nitride, gallium nitride, silicon nitride, titanium nitride, silicon carbide, titanium carbide, titanium boride, titanium diboride, and aluminum boride;

wherein the diamond, the cubic boron nitride, and the hard material are intermixed and interbonded to form a polycrystalline material, and

wherein the at least one polycrystalline compact comprises a material having a Young's modulus of at least about 700 GPa; and

wherein the polycrystalline compact at least one of comprises from about 3 atomic percent to about 15 atomic percent boron or has a density of at least about 3.30 g/cm 3 .

17. A method of fabricating a polycrystalline compact, comprising:

forming a mixture comprising diamond, non-cubic boron nitride, and a metal or semimetal, the metal or semimetal selected from the group consisting of aluminum, gallium, silicon, and titanium;

encapsulating the mixture in a container; and

subjecting the encapsulated mixture to a pressure of at least 5.0 GPa and a temperature of at least 1,100° C. to convert at least a portion of the non-cubic boron nitride from a wurtzitic phase to a cubic phase and form a polycrystalline material from the mixture, the polycrystalline material comprising the diamond, the wurtzitic phase boron nitride, and at least one hard material selected from the group consisting of aluminum nitride, gallium nitride, silicon nitride, titanium nitride, silicon carbide, titanium carbide, titanium boride, titanium diboride, and aluminum boride;

wherein the diamond, the wurtzitic phase boron nitride, and the hard material are intermixed and interbonded within the polycrystalline material.

18. A method of fabricating a polycrystalline compact, comprising:

forming a mixture comprising diamond, non-cubic boron nitride, and metal or semimetal particles having an average particle size from about 50 nm to about 1μm, the metal or semimetal selected from the group consisting of aluminum, gallium, silicon, and titanium;

encapsulating the mixture in a container; and

subjecting the encapsulated mixture to a pressure of at least 5.0 GPa and a temperature of at least 1,100° C. to form a polycrystalline material from the mixture, the polycrystalline material comprising the diamond, cubic boron nitride formed from the non-cubic boron nitride, and at least one hard material selected from the group consisting of aluminum nitride, gallium nitride, silicon nitride, titanium nitride, silicon carbide, titanium carbide, titanium boride, titanium diboride, and aluminum boride;

wherein the diamond, the cubic boron nitride, and the hard material are intermixed and interbonded within the polycrystalline material.