Microstructures and Properties of Solidified TiC-TiB_2 Ceramic Composites with increasing Cr Metallic Binder Prepared by Combustion Synthesis in High-gravity Field

摘要

By increasing addition amount of (CrO_3 + Al) subsystem in (B4C + Ti) system, the solidified TiC-TiB_2 composites with a series of mass fraction of Cr binder were achieved by combustion synthesis in high-gravity field. The microstructures of the solidified ceramics presented a number of fine TiB_2 platelets embedded in TiC grains, Cr-Ti alloy or between TiC grains and Cr-Ti alloy. The increased Cr binder in the ceramic not only brought about the enhanced densification of the ceramic due to fill-up of Cr-Ti liquid in shrinkage cavities between solidified TiC and TiB_2 phases, but more importantly made fine-grained even ultrafine-grained microstructure achieved because of the accelerated nucleation and the decelerated growth of TiB_2 at initial stage of material solidification. As a result of the achievement of fine-grained even ultrafine-grained microstructure along with the enhanced toughneing mechanisms contributed by the refined TiB_2 platelets and the increased plastic phases of Cr-Ti alloy, the solifidied TiC-TiB_2 composite containing 20.7 % Cr binder presented the maximun values of 1045 ±25 MPa and 21.5 ± 1.6 MPa · m~(0.5), simultaneously, inflexural strength and fracture toughness along with the moderate hardness of 17.5 ± 2.2 GPa.