Processing, toughness improvement and microstructural analysis of SiC platelet-reinforced Al2O3/Y-TZP nano-ceramic matrix composites

Hexagonal SiC platelet-reinforced Al2O3/Y-TZP ceramic matrix composites having sub-micron grains were fabricated. Slip casting was used as a wet colloidal processing route to minimize the processing defects and obtain preferred orientation with platelets. The effect of platelet volume fraction and aspect ratio on fracture toughness, strength, mode and microstructure of the final composite were examined. The fracture toughness and flexural strength of the reinforced-composites were evaluated using indentation in bending and four-point bending tests, respectively. High resolution scanning electron microscopy (HRSEM) and transmission electron microscopy were used to determine the microstructural details and the dominant toughening mechanisms that occurred. Mechanical tests and detailed microstructural results have led to the conclusion that multiple-toughening behavior via transformation toughening, microcracking, crack deflection, load transfer and platelet pull-out as well as thermal residual stresses have a significant contribution to improving the fracture toughness. A fracture toughness value as high as 11.2 MPa m1/2 was achieved for a specimen sintered at 1600°C for 3 h with a platelet addition of 30 vol.%.