Effects of ZrO<sub>2</sub> Addition on the Mechanical Properties of TiB<sub>2</sub> HIP'ed Compacts

Abstract

Ceramic TiB2 composites with up to 40wt% ZrO2 or 2mol% Y2O3-ZrO2 were fabricated by hot isostatic pressing (HIP) with glass encapsulation. The effect of addition on the mechanical properties and microstructure of TiB2 HIP'ed bodies was investigated. The addition of ZrO2 or 2mol% Y2O3-ZrO2 was very effective in improving the 3-point bending strength of TiB2. The 3-point bending strengths of TiB2 containing 10wt% ZrO2 and 10-20wt% (2mol% Y2O3-ZrO2) were 1160-1200MPa, which were about three times higher than that of monolithic TiB2 (450MPa). The 3-point bending strength was dependent on the monoclinic ZrO2 ratio (monoclinic ZrO2/monoclinic ZrO2+tetragonal ZrO2) and the monoclinic ZrO2 content in the HIP'ed bodies. To obtain HIP'ed bodies with strengths higher than 1000MPa, the ratio of monoclinic ZrO2 must be less than 60% and the monoclinic ZrO2 content must be less than 10wt% in HIP'ed bodies. Vickers hardness and fracture toughness were also affected by the addition of ZrO2 and 2mol% Y2O3-ZrO2. The Vickers hardness of HIP'ed bodies decreased with increasing ZrO2 and 2mol% Y2O3-ZrO2 content. On the other hand, the fracture toughness increased linearly with increasing ZrO2 and 2mol% Y2O3-ZrO2 content. The fracture toughness of TiB2 containing 30wt% ZrO2 was 8.2MPa⋅m1/2. This toughning was caused by crack deflection, however, stress induced transformation was not observed. TEM observation showed no grain boundary phase which was resulted from the reaction between TiB2 and ZrO2. However, EDS analysis showed that Ti and Zr existed in the ZrO2 and TiB2 grains, respectively, indicating that diffusion occured between TiB2 and ZrO2.