The microstructure of cBN-metal composites synthesized from hBN with metallic solvents

Cubic boron nitride (cBN)-metal composites were synthesized from hexagonal boron nitride (hBN) using Co–Cr–Al, Co–V–Al and Co–Cr–V–Al as infiltration solvents under high pressure and high temperature conditions (5.6 GPa and 1700 °C for 30 min). The alloy compositions employed in the present study were (in weight percent) Co70–Cr22–Al8, Co80–V10–Al10, Co84–V6–Al10 and Co70–Cr19–V3–Al8. It was found that the size of cBN grains in the composites synthesized using Co–V–Al solvent was relatively finer compared with the ones synthesized using Co–Cr–Al. It was also confirmed that the grain growth of cBN could be suppressed by adding a small amount of V to the Co–Cr–Al solvent. We suggest that V might be used as an additive in the metal solvent during sintering of fine grains cBN compact, where the microstructure homogeneity and the cBN abnormal grain growth are the important issues.

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► cBN was synthesized from hBN using Co–V–Cr–Al metal solvent under HPHT condition.
► Adding V or Cr into the Co–Al solvent lowered the pressure region of cBN synthesis.
► V in the Co–Al system suppressed the growth of cBN grain during synthesis process.