Polycrystalline compacts including in-situ nucleated grains, earth-boring tools including such compacts, and methods of forming such compacts and tools

An earth-boring tool, comprising:

• a body;
• and
• at least one polycrystalline compact attached to the body, the at least one polycrystalline compact comprising:
• a hard polycrystalline material comprising:
• a plurality of in situ nucleated smaller grains of hard material having a first average grain size, the in situ nucleated smaller grains formed during an HTHP (high-temperature, high-pressure) process;
• and
• a plurality of larger grains of hard material having a second average grain size, the plurality of in situ nucleated smaller grains and the plurality of larger grains being interspersed and inter-bonded.

A method of forming a polycrystalline diamond compact, comprising:

• mixing a plurality of nucleation particles with a plurality of larger diamond grains, a carbon source, and a catalyst for catalyzing the formation of diamond material;
• subjecting the mixture to an HTHP (high-temperature, high-pressure) process at a pressure greater than about five gigapascals (5.0 GPa) and a temperature greater than about 1,000° C.;
• forming a plurality of in situ nucleated smaller diamond grains during the HTHP process by catalyzing the formation of diamond material on the plurality of nucleation particles using the carbon source and the catalyst;
• and
• catalyzing the formation of diamond-to-diamond bonds between the diamond grains of the plurality of larger diamond grains and the plurality of in situ nucleated smaller diamond grains during the HTHP process to form a polycrystalline diamond material comprising the plurality of in situ nucleated smaller diamond grains and the plurality of larger diamond grains, the plurality of in situ nucleated smaller diamond grains and the plurality of larger diamond grains being interspersed and inter-bonded.