Characterization of hot-pressed short ZrO2 fiber toughened ZrB2-based ultra-high temperature ceramics

Two different ZrB2-based ultra-high temperature ceramics were produced by hot pressing: ZrB2 + 20 vol.% SiC particle + 15 vol.% ZrO2 fiber and ZrB2 + 20 vol.% SiC whisker + 15 vol.% ZrO2 fiber. The microstructures were analyzed by using transmission electron microscopy and high-resolution transmission electron microscopy. It was shown that a clean interface without any impurities was identified in ZrB2-based hybrid ceramics with SiC whiskers and ZrO2 fibers, which would significantly improve the toughening mechanism. The results of high-resolution transmission electron microscopy showed that stacking faults in SiC whiskers resulted from an insertion of a (111) layer, which would be one of the main reasons for material anisotropy. However, the interface between the SiC particle and ZrO2 fiber was found to be ambiguous in ZrB2-based hybrid ceramics with SiC particles and ZrO2 fibers due to the slight reaction. The orientation relationship between t-ZrO2 and m-ZrO2 phases obeyed the classical correspondence: (100)m//{100}t and [001]m//〈001〉t, which further verified the feasibility of phase transformation toughening mechanism.