Influence of Milling Mechanism on Synthesis of TiB_2 and TiB/TiB_2 Composites

摘要

We present an investigation of the effects of milling mechanism on structural and phase evolution during reactive milling of Ti and B. Using the magneto-milling technique, powders were milled under conditions of (ⅰ) ball-particle shear and (ⅱ) ball particle impact. It was found that TiB_2 formed under shear via a combustion synthesis reaction occurring within 240 hours. However, for the same powder charge, milling rate and milling time, it was found that TiB_2 did not form under the more highly energetic impact mode of milling. The more sluggish reaction kinetics for the formation of TiB_2 under impact are believed to be related to higher Fe contamination levels in samples milled under impact mode, and an increase in activation energy for reaction with B when the Ti contains dissolved Fe. This was confirmed with follow up investigations involving milling with deliberate Fe additions. Hot compaction and densification of nanostructural precursor powders was aided by the presence of Fe and resulted in monolithic structures comprising TiB, TiB2 and small amounts of TiFe-based binder phases.