成分及工艺对常压烧结碳化硅组织及性能的影响

Effects of Boron and Carbon Contents and Sintering Conditions on Microstructure and Mechanical Properties of Pressureless-Sintered SiC

本文采用工业α-SiC粉料经球磨和酸洗处理后,以B和C为助烧结剂,进行了常压烧结试验,对烧成试样进行了宏观力学性能和微观组织分析。实验结果指出,少量B和C的存在,对SiC烧结后期的致密化过程有显著促进作用,B、C过多时,以疏松第二相存在于SiC品界,阻止了烧结休密度的进一步提高.以0.5wt%B+4wt%C为助烧结剂,2100℃,保温60min,获得了SiC的致密烧结体,密度为96.8%TD。抗弯强度达441MPa。经抛光和电解腐蚀后的金相组织中,首次观察到了一种板状结构,并用热力学分析了其形成和生长的条件。

The sintering behavior of commercial α--SiC powders with additions of B and C was studiedThe effects of B and C contents and sintering conditions on microstructure and mechanical proper-ties of the SiC bodies were also discussed. Experiment results showed that little amounts of B and Caccelerated densincation. In case of overdose of B and C, an cmorphous grain--boundary phase waspresent at three--grain junctions which would prevent increasing the density of the sintered SiC bod-ies. Silicon carbide dense bodies with sintering additives of 0.5wt%B+4wt%C were obtained at2100℃ for 60 minutes, which had a relative density of 96.8% and a bending strength of 441 MPa. Aspecial platclike structure was observed for the first time in the optical micrographs ora polished andelectrolysis--etched SiC bodies' surface. Its forming and growing conditions were discussed bythermodynamics analysis. Two critical values for radias of the plates were determined as R_0 and R_1.If R>R_0 the isometric grains began growing to plates. If R>1, the plates began thickening.