Importance

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Abstract

A cubic boron nitride (cBN) polycrystallite includes: a fine-grained cBN crystal of 10-60 nm in grain size; a coarse-grained cBN crystal of 100-250 nm in grain size; and a lamellar crystal consisting of stacked plate-like crystals of cBN with the maximum length perpendicular to the stacking direction not larger than 1000 nm and an aspect ratio smaller than 3, where the aspect ratio is defined as the maximum length divided by a maximum length in the stacking direction, and a mean grain size of the fine-grained, coarse-grained and lamellar crystals is not larger than 80 nm. This cBN polycrystallite can be obtained by performing, under 10 GPa or lower, heating a material made of hexagonal system boron nitride to a first temperature within 1300°-1600° C., maintaining it for a first predetermined period, heating it to a second temperature within 1700°−2100° C., maintaining it for a second predetermined period, and cooling it.

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First Claim