Microstructures and Properties of TiC-TiB2 Composites Prepared by Combustion Synthesis in Enhanced High-Gravity Field

By taking combustion synthesis in enhanced high gravity field with increasing acceleration from 500 g to 2500 g at intervals of 500 g, a series of TiC-66.7 mol%TiB₂ composites were prepared through liquid forming and rapid solidification. The ceramics were composed of TiB₂ primary phases, TiC secondary phases and a few of Al₂O₃ inclusion and Cr metallic phases. Increasing high gravity acceleration not only promoted the combustion mode transfer from steady SHS mode to explosive one through enhancing the deposition of liquid product toward unreacted blend, but also accelerated liquid-liquid separation of TiC-TiB₂ / Al₂O₃ droplets and subsequent formation of layered melt through enhancing Stokes flow in mixed liquid products, thereby reducing sharply Al₂O₃ inclusions and shrinkage cavities in solidified TiC-TiB₂ composite. Meanwhile, the enhanced Stokes flow brought about constitutional uniformity through enhancing atomic diffusion in TiC-TiB₂ liquid, not only refining the microstructure of the solidified ceramic, but also improving the homogeneity of the ceramic by inducing TiB₂ primary phases to grow at similar velocity. As a result, hardness, flexural strength and fracture toughness of the composite increased greatly in enhanced high-gravity field.