Microstructure Homogeneity, Crack Propagation and Self-Toughening of Solidified TiC-TiB<sub>2</sub> Composite Prepared by Combustion Synthesis in Enhanced High-Gravity Field

Abstract

A series of solidified TiC-TiB2were prepared by combustion synthesis in enhanced high-gravity field, and the ceramics were comprised of TiB2primary phases, irregular TiC secondary phases, a few of Al2O3inclusions and Cr-based metallic phases. Because of the accelerated phase separation of Al2O3droplets from the molten reaction products, the enhanced high-gravity field not only caused both Al2O3inclusions and shrinkage cavities to be sharply reduced, but also brought about the refined microstructure and the improved homogeneity in the solidified ceramic. As high gravity acceleration reached 2500 g, the ultrafine-grained microstructure with the thickness of TiB2platelets smaller than 1 μm was achieved, and FESEM fractographs showed a whole of ultrafine TiB2platelets almost accomplished the pullout process, and the maximum fracture toughness of 16.5 ± 1.0 MP · m0.5was achieved, whereas the maximum flexural strength of 982 ± 20 MPa was also simultaneously obtained as a coupled result of sharply-reduced defects, the refined microstructure, the improved homogeneity and the high defect tolerance achieved in the near-full-density composite.