Two ZrB2-based composites were fabricated by hot-pressing with vacuum. ZrB2+20vol%SiC and ZrB2+20vol%SiC+8vol%TiB2 were selected as the starting compositions. The microstructures and phase constitutions of the composites were investigated and compared to these of monolithic ZrB2 material. For the ZrB2-based composites, with the addition of SiC particles, the excessive growth of ZrB2 materials is restricted and grain structure is refined. Meanwhile the fracture modes are changed, namely, from transgranular to mixed inter/transgranular. Strengthening mechanism is grain refining and the toughening mechanism is crack deflection, crack branching and grain refining. The role of TiB2 as an addition to the ZrB2 matrix was also examined and discussed.

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In this paper, we analyze the influence of surface effects including residual surface stress, surface piezoelectric and surface elasticity on the buckling behavior of piezoelectric nanobeams by using the Timoshenko beam theory and surface piezoelectricity model. The critical electric potential for buckling of piezoelectric nanobeams with different boundary condition is obtained analytically. From the results, it is found that the surface piezoelectric reduces the critical electric potential. However, a positive residual surface stress increases the critical electric potential. In addition, the shear deformation reduces the critical electric potential, and the influence of shear deformation become more significant for a stubby piezoelectric nanobeam.

SiC whisker-reinforced ZrB2 matrix ultra-high temperature ceramic were prepared at 2000°C for 1 h under 30MPa by hot pressing and the effects of whisker on flexural strength and fracture toughness of the composites was examined. The flexural strength and fracture toughness are 510±25MPa and 4.05±0.20MPa⋅m1/2 at room temperature, respectively. Comparing with the SiC particles-reinforced ZrB2 ceramic, no significant increase in both strength and toughness was observed. The microstructure of the composite showed that the SiC whisker was destroyed because the SiC whisker degraded due to rapid atom diffusivity at high temperature. The results suggested that some related parameters such as the lower hot-pressing temperature, a short sintering time should be controlled in order to obtain SiC whiskerreinforced ZrB2 composite with high properties.