酚醛树脂对反应烧结碳化硅显微结构与性能的影响

Effect of phenol-formaldehyde resin on microstructure and properties of reaction-bonded silicon carbide

以碳化硅(w(SiC)=99%,d50=5μm)、炭黑(w(C)=99.8%,d50=0.38μm)和单质硅(w(Si)=98.6%)为原料,无水乙醇(w(乙醇)=99.6%)、热塑性酚醛树脂(0.074μm、工业级)为结合剂,乌洛脱品为固化剂,以50 MPa的单向压力,分别将采用干混工艺、湿混工艺混合、干燥后的物料压制成型为50 mm×5 mm的生坯,在N2保护下经800℃焙烧、炭化处理,有机物热降解后得到陶瓷素坯。研究了酚醛树脂在不同加入量(其质量分数分别为4%、8%、10%、12%、16%)及混练工艺(干混、湿混)对反应烧结碳化硅素坯强度和烧结体显微结构的影响,并采用SEM和光学显微镜分析了试样的显微结构和断面形貌。结果表明:当酚醛树脂加入量为12%时,采用湿混工艺可以制备出具有良好可浸渗性且抗折强度高达45 MPa的素坯,完全可以满足复杂异型件在烧成以前进行机械加工的要求,烧结体的抗折强度最高可达455 MPa。与干混工艺相比,用湿混工艺制成烧结体的显微结构更加均匀,晶粒更加细小,裂纹扩展更加曲折。

The ceramic biscuit was prepared using silicon carbide（w（SiC）=99%,d50=5 μm）,carbon black（w（C）=99.8%,d50=0.38 μm） and silicon（w（Si）=98.6%） as starting materials,anhydrous alcohol（99.6%） and thermosetting phenol-formaldehyde resin（0.074 μm,industrial grade） as binder,hexamethylene tetramine as solidified agent,by dry mixing and wet mixing,respectively,pressing into Ф50 mm×5 mm at 50 MPa,firing at 800 ℃ in N2 with carbonization treatment and organic thermal degradation.The influences of different additions（4%,8%,10%,12% and 16%） and different mixing processes of phenol-formaldehyde resin on the strength and the sintered microstructure of the reaction-bonded silicon carbide biscuit were studied.The fracture morphology and the microstructure of the specimen were also analyzed by SEM and optical microscope.The results indicated that：when the addition of phenol-formaldehyde resin was 12wt%,the modulus of rupture of the specimen prepared by wet mixing could reach 45 MPa with good penetrability,which could satisfy the requirements of machining for irregular shape components before firing,and the modulus of rupture of the fired specimen could reach 455 MPa.The microstructure of the specimen prepared by wet mixing was more uniform,the grain was finer and the crack propagation was more flexural,compared with the specimen prepared by dry mixing.