SiO2f/SiO2复合材料表面碳热还原反应及润湿性提高机理研究

In order to address the issues of the undesirable wettability of the AgCuTi braze filler on the surface of SiO2f/SiO2 composites and discontinuous metallurgical reaction layer, which was found in previous studies, a method of carbothermal reduction on the surface of SiO2f/SiO2 composites is proposed. The surface structure of the composites were optimized and regulated in order to improve the wettability of the AgCuTi braze alloy on SiO2f/SiO2 composite and the interfacial metallurgical bonding. The subject first employed a magnetron sputtering method to prepare a carbon layer with controllable thickness on the SiO2f/SiO2 surface. Then the SiO2f/SiO2-graphite interfacial reaction was achieved by a high-temperature treatment. The SiC phase which was more easily metallurgical bonded with the AgCuTi braze alloy formed. Based on the thermodynamic calculation, the crystal growth and formation mechanism of SiC were investigated. Finally, the wetting and metallurgical reaction evolution of the AgCuTi-SiO2f/SiO2 system were studied under different SiC ratios and layer thicknesses on the surface of SiO2f/SiO2 composites. The mechanism of improved wettability and interfacial metallurgical reaction were proposed. The research of this project will provide a new idea on the enhancement of the interfacial wettability and the metallurgical bonding in brazing. Besides, a necessary theoretical basis will also be provided on the interfacial reaction mechanism.

本课题针对前期研究中发现的AgCuTi钎料在SiO2f/SiO2复合材料表面润湿困难、冶金反应层不连续的问题，提出了SiO2f/SiO2复合材料表面碳热还原的方法，对复合材料进行表面结构的优化与调控，以实现AgCuTi钎料对SiO2f/SiO2复合材料润湿及冶金结合的增强。课题首先通过磁控溅射的方法在SiO2f/SiO2复合材料表面实现层厚可控的石墨层的制备。再通过高温处理实现SiO2纤维/石墨的界面反应，以制备更易与AgCuTi发生冶金结合的SiC相。以热力学计算为理论依据对SiC的晶体生长及生成机理进行探究。最后研究SiO2f/SiO2复合材料表面获得不同SiC比例及层厚的条件下，AgCuTi钎料与复合材料的润湿及冶金反应演变，提出该体系润湿性提高及界面冶金反应的机理。本项目的研究为钎焊中界面润湿性及冶金结合的提高提供了一种全新的思路，并从界面反应机理上提供必要的理论基础。

项目提出一种基于有机物热解实现SiO2f/SiO2复合材料表面碳热还原的方法，重点研究了碳化温度、保温时间、酚醛树脂浓度对碳层形貌、成分及厚度的影响。通过优化工艺参数，制备了厚度约为4 μm非晶碳层。通过表面结构调控，制备从表面至芯部为高碳含量层/SiC/SiO2、低碳含量层/SiC/SiO2及SiO2/SiC共3种不同的改性后的SiO2f/SiO2复合材料。结果表明表面结构为SiO2/SiC/C时，AgCuTi钎料在复合材料表面润湿铺展效果最优，体系接触角仅为40，相比于未处理降低了66%，反应层致密而连续。采用TEM确定了表面碳热还原反应后的润湿界面典型结构，即SiO2f/SiO2复合材料/Ti5Si3+TiO2/树脂碳层+TiC/Ti5Si3/Cu3Ti3O /TiCu+Ag(s,s)+Cu(s,s)。研究了复合材料表面粗糙度对AgCuTi润湿铺展影响，结果表明粗糙度降低有利于促进润湿铺展。测试了有无碳热还原反应的SiO2f/SiO2复合材料自身连接强度，结果表明碳热还原反应后，接头抗剪强度达到19 MPa，与未处理相比提升170%，该方法可促进润湿界面生成连续反应层、有利于钎料润湿、填缝，最终实现接头性能提升，为合金钎料在惰性陶瓷表面润湿铺展能力提升提供理论基础与技术支持。