MXene/Si-B-C-N复相陶瓷的强韧化和氧化机制

Si-B-C-N ceramics have great potential applications in the fields of high-temperature structural and multifunctional heat-resistant ceramics because of their good high-temperature properties and machinability. However, the intrinsic brittleness has been one of the bottleneck questions restricting their widespread applications in industry. MXene, one of the new two-dimension materials beyond graphene, has the morphological features similar to graphene and the integrated characteristics of metals and ceramics thereby improving the fracture toughness and widening the operating temperatures of the ceramics, which has been proved by the preliminary findings of the proposer of this project. Therefore, the novel design idea is proposed that the new two-dimension materials, represented by MXene, can be incorporated into structural ceramics. Ti3C2 and Cr2C, typical of the transition metal carbide, and Ti2N, typical of metal nitride, will be chosen to be the models of MXene for the development of MXene/Si-B-C-N composite monoliths by the spark plasma sintering (SPS). The mechanisms of strengthening and toughening will be discussed by investigating the relationship between the components, process routes, microstructures and properties. The oxidation mechanism will be also clarified by studying the oxidation resistance so as to develop MXene/Si-B-C-N ceramics having good comprehensive mechanical properties and oxidation resistance in the nearly full temperature range. This work will provide the technical and theoretical supports for the applications of the structural parts of Si-B-C-N ceramics in the fields of high-temperature structural and multifunctional heat-resistant materials, and serve as the general guidance to the development of the new system of high-temperature ceramics.

硅硼碳氮（Si-B-C-N）陶瓷具有优良的耐高温性能和可机械加工性，在航空航天多功能防热和高温结构领域极具应用潜力。但是，本征脆性仍是制约该陶瓷在工程上得到广泛应用的瓶颈问题之一。MXene具有类似石墨烯的形貌特征，且兼具金属与陶瓷性质，（申请人前期研究表明）可改善陶瓷脆性甚至拓宽其使用温度范围。因此本项目提出将MXene与结构陶瓷复合的新思路：（1）选取过渡金属碳化物（Ti3C2和Cr2C）和氮化物（Ti2N）三种MXene模型材料，采用放电等离子烧结技术制备MXene/Si-B-C-N复相陶瓷；（2）研究材料组分-组织结构-力学性能之间的关系及界面问题，阐明强韧化机制；（3）研究抗氧化性能，阐明氧化机制，进而研发综合力学性能以及全温域抗氧化性能优良的陶瓷。本研究将为Si-B-C-N陶瓷在多功能防热和耐高温构件上的应用提供理论与技术支持，且对整个新型耐高温陶瓷体系的研发具有普遍指导意义。

现代空天技术的快速发展对陶瓷材料的耐高温性能提出了更高的要求，同时硅基结构陶瓷的本征脆性仍是制约其在工程中广泛应用的瓶颈问题之一。本项目采用超声-速冻-冷冻干燥-放电等离子烧结技术将新型二维材料MXene引入到典型的耐高温结构陶瓷Si-B-C-N中，系统研究了非晶Si-B-C-N粉体的合成机制、MXene/Si-B-C-N陶瓷的物相、微观结构、力学性能以及抗氧化性能及相关机制。研究结果表明：硅-氮化硼-石墨混合物实现晶态到非晶态转变是晶粒细化诱导的非晶化过程，原子扩散起很大作用，晶粒细化导致形成更多的晶界、内应变以及缺陷，进而为原子扩散提供更多的通道，加速纳米晶-非晶转变。随着球磨时间的延长，颗粒尺寸先减小至亚微米，然后略微增大，再然后一次颗粒尺寸减小至纳米级直至最终达到平衡态。由于晶体结构的本质属性，与硅相比，氮化硼与石墨更容易实现非晶化。硼原子稀释了硅和碳原子的浓度，在一定程度上阻碍了硅与碳原子间的扩散以及机械化学反应，因此，与硅-石墨混合物相比，硅-氮化硼-石墨混合物更容易实现非晶化。MXene(Ti3C2Tx)的引入有效改善了Si-B-C-N陶瓷的力学性能，引入3.0 wt% Mxene可以将陶瓷的断裂韧性提高至~7.6 MPa‧m1/2，与相同成分的Si-B-C-N陶瓷性能相比提高~36%，主要增韧机理为纳米片拔出、裂纹桥连与偏转；MXene的含量对氧化后陶瓷的物相组成没有明显影响，但是对抗氧化性能影响很大。引入≤3.0 wt% Mxene的复相陶瓷在低温（900°C）与中温（1100°C）范围内的抗氧化性能与Si-B-C-N的性能不相上下。得益于高熔点棒状TiO2晶粒镶嵌在SiO2层中形成的锚定效应，引入3.0 wt% Mxene可以有效改善复相陶瓷的抗高温（1600°C）氧化性能，但是过少的MXene不能改善甚至会恶化Si-B-C-N陶瓷的抗高温氧化性能。以上研究结果对耐高温硅基结构陶瓷的研发提供了理论和技术支持。