Pressureless densification, microstructure tailoring and properties of Ta0.8Hf0.2C-based composites

Ta0.8Hf0.2C (TH) ceramics are desirable for applications in ultra-high temperature environments, but they are difficult to be sintered pressurelessly. TH ceramics were densified up to 98.8% from commercial powders via pressureless sintering (PLS) at 2473 K. SiC was introduced as secondary phase to tailor microstructures and improve properties of TH. The influence of SiC volume fraction on the densification, microstructure evolution and room-temperature properties of TH-based ceramics were examined. Average grain size of TH was refined from 13.6 down to 2.0 μm. 10 vol% SiC addition contributed to densification of Ta0.8Hf0.2C-SiC (THS) composites with a relative density of 99.6%. The mechanical properties of THS were fairly good, and thermal properties of sintered THS displayed a remarkable improvement compared with TH: the coefficient of thermal expansion (CTE) showed a reduction of 8.6% while the thermal conductivity increased from 18.6 to 41.5 W/m K.