碳化硅陶瓷及其复合材料的热等静压氮化

NITRIDATION OF SiC CERAMICS AND SiC BASED COMPOSITESBY HOT ISOSTATIC PRESSING

通过对ＳｉＣ陶瓷、ＳｉＣ－ＴｉＣ复相陶瓷以及ＳｉＣ晶须补强ＳｉＣ基复合材料在氮气氛中进行高温氮化处理，成功地实现了这些材料的开口气孔与表面裂纹的愈合。有关研究表明：热等静压氮化工艺可以显著提高ＳｉＣ陶瓷及其复合材料的抗弯强度，对断裂韧性也有较大的改善作用。对于热等静压（ＨＩＰ）烧结ＳｉＣ陶瓷（添加３％Ａｌ２Ｏ３，以质量计），在１８５０℃和２００ＭＰａ氮气压力氮化处理１ｈ后，其抗弯强度和断裂韧性分别由５８２ＭＰａ和５．７ＭＰａ·ｍ（１／２）提高到９０７ＭＰａ和８．４ＭＰａ·ｍ（１／２）；对于预烧结密度为３．４５ｇ／ｃｍ３的ＳｉＣ－ＴｉＣ复相陶瓷，经ＨＩＰ氮化处理后，其室温强度由３５４提高到６８６ＭＰａ，断裂韧性由６．９提高到７．９ＭＰａ·ｍ（１／２）；对于ＨＩＰ烧结５％（ｖｏｌ）ＳｉＣ晶须补强ＳｉＣ基复合材料，ＨＩＰ氮化处理后，其抗弯强度与断裂韧性分别高达９３１ＭＰａ和８．５ＭＰａ·ｍ（１／２）。

SiC monolithic ceramics and SiC-TiC multiphase ceramics as well as SiC whisker-reinforced SiC based composites were nitrided by hot isostatic pressing in a N2 atmosphere at high temperatures. The possibility to heal surface cracks and open pores was experimentally verified by HIP-nitridation, and the influences of which on bulk density, flexural strength and fracture toughness were investigated. The results show that the sur face cracks and open pores can be healed and the mechanical properties can be obviously improved by HLP-nitridation. For hot isostatically pressed SiC ceramics with addition of 3%(mass) Al2O3, the flexural strength and fracture toughness are increased from 582MPa to 907 MPa and 5. 7MPa·m(1/2) to 8. 4MPa·m(1/2) respectively when HIP-nitridation is performed under 200 MPa in N2 at 1850 ℃ for 1h. For SiC-TiC multiphase ceramics with bulk density of 3. 45g/cm3, the room-temperature strength and fracture toughness are increased from 354MPa to 686MPa and 6.9MPa·m(1/2) to 7.9MPa·m(1/2) respectively by HIP-nitridation. For 5%(vol)SiC whisker-reinforced SiC based composites, the flexural strength and fracture toughness are as high as 931 Mpa and 8. 5MPa·m(1/2), respectively,after HIP-nitridation under a N2-pressure of 200 MPa at temperature of 1850 ℃ for 1h.