Development of matrix microstructure in polycrystalline cubic boron nitride ceramics

Abstract

The development of matrix microstructure in polycrystalline cubic boron nitride cutting tool materials has been investigated by X-ray diffraction and scanning and transmission electron microscopy combined with energy dispersive X-ray spectrometry. The materials had a matrix based on Ti(C,O,N) and Al and were fabricated from powder mixtures milled with either WC-Co cemented carbide or (Ti,W)(C,N)-Co cermet milling media. The introduction of WC-Co debris resulted in the formation of an Al- and W-rich liquid phase during high pressure high temperature sintering. Crystalline intergranular phases rich in W partitioned from this liquid. Debris from the cermet milling media resulted in the formation of intergranular Co2B; the W was retained in the (Ti,W)(C,N) structure during sintering. Al-rich reaction zones on cBN grain surfaces developed locally during high pressure high temperature sintering.