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

An earth-boring tool, comprising:

• a bit body;
• and
• at least one polycrystalline diamond compact secured to the bit body, the polycrystalline diamond compact comprising:
• diamond grains;
• cubic boron nitride grains;
• and
• grains of an additional nitride, carbide, or boride 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 grains, the cubic boron nitride grains, and the grains of the additional nitride, carbide, or boride are intermixed and interbonded to form a polycrystalline material, and
• wherein the at least one polycrystalline diamond compact has a density of at least about 3.40 g/cm3.

A method of fabricating a polycrystalline compact, comprising:

• forming a mixture comprising diamond grains, non-cubic boron nitride grains, 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 form a polycrystalline material from the mixture, the polycrystalline material comprising the diamond grains, cubic boron nitride grains formed from the non-cubic boron nitride grains, and grains of an additional nitride, carbide, or boride 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 grains, the cubic boron nitride grains, and the grains of the additional nitride, carbide, or boride are intermixed and interbonded within the polycrystalline material.