A method for forming a polycrystalline compact comprising grains of a hard material, the method comprising: introducing coarse grains of hard material, fine grains of the hard material, and a catalyst material to a press, the coarse grains and the fine grains not yet interbonded; elevating to a plateau temperature a system temperature to which the grains (26, 28) are subjected; elevating to a plateau pressure a system pressure to which the grains (26, 28) are subjected; after holding, during a plateau stage (308A, 309A), the system temperature at the plateau temperature and the system pressure at the plateau pressure, spiking at least one of the system temperature and the system pressure to form inter-granular bonds between the grains (26, 28), the spiking comprising: elevating the at least one of the system temperature and the system pressure to a peak condition (316, 317); and returning the at least one of the system temperature and the system pressure from the peak condition (316, 317) to a respective one of the plateau temperature and the plateau pressure; after the spiking, holding, during another plateau stage, the system temperature at the plateau temperature and the system pressure at the plateau pressure; after the another plateau stage (308B, 309B), lowering the system temperature to a final system temperature and the system pressure to a final system pressure; and removing the polycrystalline compact from the press, the polycrystalline compact comprising the coarse grains of hard material and the fine grains of the hard material interbonded by inter-granular bonds and comprising the catalyst material in interstitial spaces. introducing coarse grains of hard material, fine grains of the hard material, and a catalyst material to a press, the coarse grains and the fine grains not yet interbonded; elevating to a plateau temperature a system temperature to which the grains (26, 28) are subjected; elevating to a plateau pressure a system pressure to which the grains (26, 28) are subjected; after holding, during a plateau stage (308A, 309A), the system temperature at the plateau temperature and the system pressure at the plateau pressure, spiking at least one of the system temperature and the system pressure to form inter-granular bonds between the grains (26, 28), the spiking comprising: elevating the at least one of the system temperature and the system pressure to a peak condition (316, 317); and returning the at least one of the system temperature and the system pressure from the peak condition (316, 317) to a respective one of the plateau temperature and the plateau pressure; elevating the at least one of the system temperature and the system pressure to a peak condition (316, 317); and returning the at least one of the system temperature and the system pressure from the peak condition (316, 317) to a respective one of the plateau temperature and the plateau pressure; after the spiking, holding, during another plateau stage, the system temperature at the plateau temperature and the system pressure at the plateau pressure; after the another plateau stage (308B, 309B), lowering the system temperature to a final system temperature and the system pressure to a final system pressure; and removing the polycrystalline compact from the press, the polycrystalline compact comprising the coarse grains of hard material and the fine grains of the hard material interbonded by inter-granular bonds and comprising the catalyst material in interstitial spaces.