Wei Xiaoyu, Yang Hui, Zhao Hongsheng, Liu Xiaoxue, Zhang Kaihong, Li Ziqiang, Gao Yuan, Liu Bing
Institute of Nuclear and New Energy Technology, Tsinghua University, Beijing 100084, China.
Materials (Basel). 2022 Apr 28;15(9):3203. doi: 10.3390/ma15093203.
SiC/MoSi-SiC-Si coatings for nuclear graphite spheres with different Si-Mo ratios were prepared through two-step pack cementation. XRD, SEM and EDS techniques were used to analyze the composition and microstructure of the coatings. The oxidation resistance performance of the composites at 1773 K, in static air, was investigated. The results showed that the SiC-MoSi-Si coating could be divided into a denser inner layer and a loose outer layer, as free Si would infiltrate into the inner micropores of the coating under capillary force. When the Si/Mo ratio of the second pack cementation was 7:1, the thickness of the denser inner layer basically reached the maximum and exhibited excellent oxidation resistance ability, with a weight gain of 0.19% after 200 h oxidation. The performance improvement was analyzed as a result of the addition of SiC and C powder in the pack cementation process, effectively increasing the phase interfaces to relax the thermal stress in the coating. With different Si-Mo ratios, the content of residual Si and the formation rate of SiO glass layer on the coating surface were also different, thus affecting the anti-oxidation performance. The main reactions occurring at different stages of the oxidation curve were also discussed.
通过两步包埋渗金属法制备了具有不同硅钼比的核石墨球用碳化硅/硅化钼-碳化硅-硅涂层。采用X射线衍射（XRD）、扫描电子显微镜（SEM）和能谱仪（EDS）技术分析涂层的成分和微观结构。研究了复合材料在1773K静态空气中的抗氧化性能。结果表明，碳化硅-硅化钼-硅涂层可分为致密的内层和疏松的外层，因为游离硅会在毛细力作用下渗入涂层的内部微孔。当第二次包埋渗金属的硅/钼比为7:1时，致密内层的厚度基本达到最大值，并表现出优异的抗氧化能力，氧化200h后的增重为0.19%。分析了由于在包埋渗金属过程中添加碳化硅和碳粉导致性能提升的原因，其有效地增加了相界面以缓解涂层中的热应力。随着硅钼比的不同，涂层表面残余硅的含量和二氧化硅玻璃层的形成速率也不同，从而影响抗氧化性能。还讨论了氧化曲线不同阶段发生的主要反应。
