Effect of c-BN Size and Content on the Self-Propagating High-Temperature Synthesis of c-BN Composites Bonded with Ti-Al-C System Multiphase Products

Abstract

A mixture of Ti, Al, graphite and c-BN powders was used as raw material to fabricate Ti2AlC matrix-bonded c-BN composite using the self-propagating high-temperature synthesis (SHS) method. The effect of c-BN size and content on the fabrication of the composites was investigated. The results show that Ti2AlC matrix-bonded c-BN composites can be obtained by SHS. c-BN content and size evidently affected the phase composition and microstructure characteristic of the composites. At 10-30% c-BN (120/140 mesh) content, the product phases were Ti2AlC, Ti3AlC2, Al3Ti, TiN, TiC, AlN, graphite and TiB2. A dense transition layer with a thickness of about 10 μm showed the interface between c-BN and the matrix. However, Al peaks appeared, and the titanium aluminium carbide peak became weak in the samples containing 40% and 50% c-BN. c-BN was unequally enwrapped by one coating with a thickness of about 2 μm. The main product phases of the samples were Ti2AlC, Ti3AlC2, Al3Ti, TiN, TiC, AlN, graphite and TiB2 in the products with different c-BN sizes. The addition of coarse c-BN particles (80/100, 120/140 and 170/200 mesh) yielded a transition layer with a thickness of approximately 10 μm on the interface and Ti2AlC main phase matrix. The finer the particle size, the greater the reaction activity. When c-BN was finer (20 μm), c-BN more easily reacted with Ti and Al to form TiN, AlN and TiB2. The synthesis of Ti2AlC was obviously inhibited.