Densification Mechanism of TiB₂-1%CoB and TiB₂-5%TaB₂-1%CoB Systems

Abstract

Sintered TiB₂-1%CoB and TiB₂-5%TaB₂-1%CoB materials have high density and high trasverse rupture strength. In the present study, the densification mechanism of the above materials has been investigated. It has been found that even a small amount (1 wt% or less) of CoB added to TiB2 or to TiB₂-5%TaB₂ has a remarkable effect on densification, and that the mixture of TiB₂-1%CoB shows remarkable shrinkage during sintering under the die pressure of 200 kg/cm₂ even at 1400°C which is lower than the melting point of CoB. These results suggest that the densification of these materials is caused mainly by an activated sintering process under die pressure. In this process, atoms on the surface of TiB₂ (or TaB₂) grains dissolve into the CoB phase so that a carrier phase may be formed in the contact area between the TiB₂ (or TaB₂) grain and the CoB phase. Then, the surface atoms on any TiB₂ (or TaB₂) grain can diffuse rapidly to other grains through the carrier phase.