Study On SiC-Al₂O₃ Composite Ceramic Preparation And Its Crack-healing Properties

SiC-Al₂O₃ composite ceramic was prepared by hot-press sintering with Al₂O₃ powder and SiC powder as materials; A diamond-shaped indentation was introduced to the center of the tensile surface of standard SiC-Al₂O₃ composite ceramic sample being 3mm×4mm×36mm using Vicker's indenter method; the ceramic samples with introduced crack were individually crack-healed in conditions of different temperatures and different healing times. SEM, XRD and three-point bending so forth methods were used to investigate the character of the above material. Investigation as followed:The elastic modulus of SiC-Al₂O₃ composite ceramic increase with sintering temperature lifting, and when sintering temperature is above 1800℃, the density starts reducing; but the density decreases with the SiC content decrease, and the Young's modulus decreases when SiC content exceeds 20%.The bending strength changing tendency of SiC-Al₂O₃ composite ceramic with sintering temperature is as same as that of fracture toughness, they two begin decreasing when sintering temperature is above 1800℃; similarly, the bending strength changing tendency and fracture toughness changing tendency with SiC content are also the same, and they two begin decreasing when SiC content is above 20%; when sintered at the condition of 1800℃and SiC content 20%, the bending strength and fracture toughness reach the maximums simultaneously, individually 770MPa and 6.9MPa·m^1/2.The crack mode of SiC-Al₂O₃ composite ceramic is mixed crack mode of inter-granular crack and trans-granular crack by microstructure investigation.When SiC-Al₂O₃ composite ceramic is healed for 2h, 4h and 6h, its bending strength increases with healing temperature from 1000℃to 1400℃; the bending strength begin going down when healed at 8h and temperature higher than 1200℃; the bending strength exhibits a notable rising tend when healed at 1000℃and 1200℃with healing time from 2h to 8h; But the bending strength show a decreasing tend as healing temperature further stands up to 1300℃and 1400℃.Bending strength analytical results of SiC-Al₂O₃ composite ceramic show that the average bending strength of samples healed is up to 583.61MPa, near 600.6MPa level of perfect samples, which is two times higher than that of non-healed samples,It is showed that chemical reactions are occurred when the samples are healed in air by XRD: SiC+O₂→SiO₂+CO₂(CO),SiO₂+Al₂O₃→3Al₂O₃·2SiO₂; The bending strength of SiC-Al₂O₃ composite ceramic samples healed is improved because the production SiO₂ and 3Al₂O₃·2SiO₂ fill the cracks and make them healed.