Reactive hot-pressing induced low temperature densification of (Zr,Ta)B2-SiC ceramics: microstructure and strengthening

In view of the high sintering temperature and difficulty in densification of the ultra-high temperature ceramics(UHTCs), a novel reactive hot-pressing process was designed to achieve the low temperature densification of high strength (Zr,Ta)B 2 -SiC ceramics. It was found that the mechanical properties were closely associated with the microstructure, being dependent on the sintering temperature. The microstructure characterization revealed that the main phases of ceramic were incompletely solid soluted borides and SiC at the sintering temperature of 1600 °C; while at 1700 °C, the boride ceramics were completely solid soluted (Zr,Ta)B 2 and formed an interlocking structure with SiC. The evaluation of mechanical properties indicated that the flexural strength of the ceramics increased from 470.2 MPa to 736.7 MPa when the sintering temperature increased from 1600 °C to 1800 °C. Correspondingly, the fracture toughness increased from 3.54 MPa·m 1/2 to 4.10 MPa·m 1/2 . The improvement of mechanical properties were mainly attributed to the interlocking structure formed by the solid solution (Zr,Ta)B 2 and SiC, which caused the crack propagation path becoming tortuous along the interface of different phases.