Mechanical properties and toughening mechanisms of SiC_w/ZrO₂ (6% mol Y₂O₃) ceramic composites

Microstructure, mechanical properties and toughening mechanisms of hot pressed SiC_w/ZrO₂ (6% mol Y₂O₃) ceramic composites were investigated by means of XRD, SEM, TEM and EPMA. The results show that the high density (98%) of the composites was obtained and Vickers hardness and fracture toughness increased with increasing SiC_w content. With 10% wt SiC_w the hardness and fracture toughness increased from 14·6 GPa and 3·7 MPa √m of the ZrO₂(Y₂O₃) matrix to 17·2 GPa and 5·5 MPa √m of the composite, respectively. TEM observations show that a glassy phase containing Zr, Y and Si was formed at interfaces between some whiskers and the matrix. SEM observations of crack propagation revealed the following toughening mechanisms: (1) some whiskers were pulled out, bridging the two sides of the cracks which propagated straightly; (2) some cracks were deflected on meeting with the whiskers; (3) the whiskers fractured with matrix together and the cracks propagated straightly; (4) the cracks were branched and microcracks were formed in front of the main crack tip.