Toughening Effect of ZrB2 in Al2O3-ZrB2 Nanocomposite Ceramics

The Al2O3-ZrB2 nanocomposite ceramics were prepared and the mechanical properties of the process parameters' effect were studied. The results show that for various applied sintering temperatures of Al2O3 ceramics, a maximum Vickers hardness of 18 970 MPa and high reliability are attained at 1500 °C and at atmosphere sintering. The fracture toughness is (5.2±0.3) MPa·½. In addition, the sample is not well densified at the sintering temperature. Scanning electron microscopy (SEM) shows that fine ZrB2 particles disperse and are pinned at grain boundaries to inhibit grain boundary movement effectively. While larger ZrB2 particles distribute between A12O3 particles uniformly and occupy Al2O3 particles growing space to hinder the matrix grains, which greatly promote the densification of the ceramic and improve the microstructure. 20% ZrB2/Al2O3 composite ceramics exhibit a relative density above 98% at (450 °C, Vickers hardness of 18 070 MPa, and fracture toughness of (6.7±0.2) MPa·½ Fracture morphology indicates that trans-granular fracture occurs in the nanocomposite ceramic with high toughness.