Flexural strength and fracture behavior of ZrB2-SiC ultra-high temperature ceramic composites at 1800°C

ZrB2-15 vol.%SiC and ZrB2-30 vol.%SiC composites with smaller starting particle sizes in which the particle sizes of ZrB2 and SiC are 2 mu m and 0.5 mu m, respectively, demonstrated marked plasticity and significant reduction in the flexural strength at 1800 degrees C. The flexural strengths of these two composites are 112 +/- 12 MPa and 48 +/- 10 MPa, respectively, and their corresponding strength retentions are 13% and 7%, respectively. Large ZrB2 grains were commonly observed in the samples containing 15 vol.%SiC, which are always the sites for the crack initiation. Cavities were found in the samples containing 30 vol.%SiC and the grain boundaries arc the main sites for the crack and cavity nucleation. To improve ultra-high temperature strength, larger starting particle sizes (ZrB2 and SiC are 5 mu m and 2 mu m, respectively) were used for the preparation of ZrB2-15 vol.%SiC. This sample fractured in an elastic manner up to 1800 degrees C and showed a very high strength with a value of 217 +/- 16 MPa. (C) 2009 Elsevier Ltd. All rights reserved.