Mechanical behavior and microstructure of SiC and SiC/TiB₂ ceramics

Toughness characteristics and associated microstructural behavior in two kinds of SiC and TiB₂ particulate-reinforced SiC composites were studied. From indentation-strength tests, the Al₂O₂-doped, high volume fraction β-SiC/TiB₂ showed a distinctive flaw tolerance and a higher retained strength in the long-crack region, as compared with β-SiC alone. On the other hand, the boron- and carbon-doped, low volume fraction, α-SiC/TiB₂ exhibited a higher retained strength without an apparent improvement in flaw tolerance, as compared with α-SiC. Crack bridging and sliding and pullout of TiB₂ particulates toughened the β-SiC/TiB₂, while only crack bridging by TiB₂ occurred in α-SiC/TiB₂ with difficulty in grain sliding and pullout. A quantitative evaluation of the indentation-strength data revealed a sharp rising toughness curve for β-SiC/TiB₂. The enhanced long-crack toughness originated from the weak interface created by the TiB₂ and sintering additives.