热处理工艺对SiC/Al_2O_3陶瓷裂纹愈合及强度的影响

采用压痕法在热压烧结的SiC/Al2O3复合陶瓷试样表面制造裂纹,对含有裂纹的试样在1 000～1 400℃进行不同时间的愈合处理,研究了愈合工艺对材料抗弯强度的影响规律,同时探索了愈合机理.结果表明,随着愈合处理温度的升高和时间的延长,表面裂纹逐渐愈合,长度缩短,材料的抗弯强度逐渐恢复.经1 300℃保温4 h愈合处理后,抗弯强度恢复至583.6 MPa,与完好试样的抗弯强度值(600.6 MPa)非常接近.继续提高处理温度或和延长时间,生成的大量CO(或CO2)气体难以从试样中逸出或在表面产生气孔,在试样表面形成新的缺陷,反而不利于抗弯强度的恢复;抗弯强度的恢复反应是SiC+O2→SiO2+CO(CO2),生成的SiO2填充了裂纹.

Effect of heat treatment on crack-healing and strength of SiC/Al_2O_3 composites

The cracks were prepared on the surface of hot pressed and sintred SiC/Al2O3 composite sample by indentation methed.SiC/Al2O3 composite with surface cracks was treated for healing cracks at 1 000-1 400℃ for different time.The effects of heating processes on bending strength were investigated,and the healing mechanism was studied.The results show that as the treatment temperature and time increase the cracks on the sample surface tend to be healed up and shortened,thus the bending strength increases.The bending strength of samples healing at 1 300℃ for 4h restores up to 583.61MPa which is close to 600.6MPa of intact samples.While further increase the healing temperature and holding time,large amount of CO(or CO2)gas generated can be hardly released or leads to the formation of pores on the surface,which is unfavourable to recovery of the bending strength.The improved bending strength is attributed to the mechanism of SiO2 derived from reaction of SiC+O2→SiO2+CO(CO2)to fill in the cracks.