Microstructure and indentation damage resistance of ZrB ₂ ‐20 vol.%SiC ipo‐eutectic composites

Abstract Zirconium diboride with 20 vol.% silicon carbide bulk composites were fabricated using directionally solidification ( DS ) and also by spark plasma sintering ( SPS ) of crushed DS ingots. During the DS the cooling front aligned the c ‐axis of ZrB ₂ grains and its Lotgering factor of f _{(00 l )} was high as 0.98. The Vickers hardness was anisotropic and it was high as 17.6 GP a along the c ‐axis and 15.3 GP a when measured in an orthogonal direction. On both surfaces, even when using 100 N indentation load, no cracks were observed, suggesting a very high resistance to crack propagation. Such anomalous behavior was attributed to the hierarchical structure of DS sample where the ZrB ₂ phase was under strong compression and the SiC phase was in tension. In the SPS ed sample, the microstructure was isotropic respect to the direction of applied pressure. Indentation cracks appeared around the indent corners but not emanated from the diagonals, confirming high damage resistance.