Crystal Growth, Fracture Behavior and Toughening of Rapidly-Solidified TiC-TiB_2 Prepared by Combustion Synthesis in High-Gravity Field

摘要

Micro-nanocrystalline microstructures characterized by TiB_2 platelets of the average thickness close to or smaller than 1 μm, were achieved in full-density solidified TiC-TiB_2 composites by combustion synthesis in high-gravity field. XRD, FESEM and EDS results showed that a large number of fine TiB_2 platelets were uniformly embedded in irregular TiC grains, a few Cr-Al metallic phases or in between those phases. The achievement of micro-nanocrystalline microstructures results from low-velocity faceting growth of TiB_2 crystal, high-velocity non-faceting growth of TiC solid and high diffusion rate of C relative to B in liquid TiC-TiB_2. The relative density, Vickers hardness, flexural strength and fracture toughness of TiC-TiB_2 composites measured 99.3%, 21.5 ± 1.5 GPa, 845 ± 35 GPa and 16.8 ± 1.5 MP · m~(0.5), respectively. High flexural strength of the materials benefits mainly from the achievement of micro-nanocrystalline microstructure in the full-density solidified ceramic and high fracture toughness contributed from intensive coupled toughening mechanisms by a large number of fine TiB_2 platelets and a few Cr-Al metallic phases.