Microstructure and mechanical properties of hot-pressed ZrB₂-SiC-ZrO_2f ceramics with different sintering temperatures

Effect of the hot-pressing temperature (1750-1950°C) on the microstructure and mechanical properties of the hot-pressed ZrB₂-SiC-ZrO_2f ceramics was investigated in detail. It was indicated that when the hot-pressing temperature was above 1900°C, ZrO₂ fibers were instable in ZrB₂-SiC matrix which would degenerate into particles and the grain size of ZrO₂ particles was bigger than the upper critical grain size so that the phase transformation of tetragonal to monoclinic phase would occur spontaneously during cooling process. The optimal hot-pressing temperature for this material system should be 1850°C to obtain high performance of the ZrB₂-SiC-ZrO_2f ceramics. The flexural strength and fracture toughness were enhanced to 1086±79MPa and 6.9±0.4MPam^1/2, respectively. The toughness mechanism was mainly attributed to densification, phase transformation toughening, crack deflection, fibers fracture, fibers pull-out and fibers debonding.