Abstract
Amorphous boron nitride (aBN) powders were prepared for planetary milling of hexagonal BN and phase transformation behavior under high pressure and high temperature was studied. Since aBN was extremely reactive with humidity in the ambient atmosphere, two types of aBN powders were prepared: one was hydrated and the other was free from humidity, prepared in a dry nitrogen atmosphere. Phase transformation to cBN from aBN with humidity took place under similar conditions previously reported for aBN, while the formation of cBN from dry aBN was more difficult compared to that starting from other crystalline phases of BN. It was suggested that fine-grained cBN powders and their sintered texture could be obtained by appropriate HP/HT conditions by using aBN.
