ZrB2-SiC纳米织构陶瓷熔体生长、取向控制与强韧化机理

ZrB2-based ultra-high-temperature ceramics are the ones of the most important advanced ultra-high-temperature structural materials in the field of hypersonic aircrafts due to their excellent high-temperature properties. Controlling microstructures and optimizing phase interface structures to obtain highly dense and ultra fine nano-texture composite ceramics are new vital ways to greatly improve the material property. In order to overcome the fatal preparation drawbacks including low densification, coarse particle and interface amorphous phase as well as poor fracture toughness for conventional solid sintered ZrB2-based composite ceramic, this propose is devoted to develop the melt growth method to prepare the highly densed ZrB2-SiC nano-texture ultra-high-temperature eutectic composite ceramic by using the novel laser floating zone remelting method based on the melt solid-liquid phase transformation and ceramic composition design theories. The ultra-fine nanoeutectic structure with uniform distribution and high growth orientation will be prepared and adjusted by accurately controlling the unidirectional thermal flow and solidification process, and introducing seed crystal as well as the third composition additions, accordingly improving the strength and fracture toughness.The effects of solidification processing parameters,seed crystal orientation and third composition additions on the eutectic microstructure, solid-liquid interface and preferred growth orientation as well as the phase interface structure will be systematically investigated, thereby establishing the melt growth and orientation controlling method for the ultra-high temperature boride-based eutectic composite ceramics. The eutectic growth model for the faceted boride phase with strong growth anisotropy is going to be obtained. The strengthening and toughening mechanisms as well as ant-oxidization behaviors for the nano-textured boride-base eutectic composite ceramics are to be revealed. The fundamental investigation of this project is to provide theoretical foundation and technical support for developing superior ultra-high-temperature composite ceramics with high densification, high strength and toughness, and to further enrich and develop eutectic solidification theory.

ZrB2基超高温陶瓷以其优异的高温综合性能成为高超飞行器领域重要的先进结构材料。采用微结构调控，优化相界面结构，获得全致密、超细化的纳米织构复相陶瓷是改善和提高性能的重要新途径。针对传统烧结方法制备ZrB2基陶瓷难致密化、晶粒长大、界面存在玻璃相及韧性差等问题，本项目将熔体液固相变与ZrB2基复相陶瓷成分设计相结合，拟采用激光悬浮区熔高梯度定向凝固技术，通过精确控制单向热流和凝固过程、引入籽晶及第三组元，原位制备组织超细化、相分布均匀、取向精度高的高强韧ZrB2-SiC纳米织构共晶复合陶瓷，探明凝固工艺、籽晶取向及第三组元对凝固组织、液固界面、生长取向和相界面结构的影响规律，建立超高温硼化物共晶陶瓷熔体取向生长与组织控制方法，构建强各向异性硼化物小平面相共晶生长模型，揭示多元复相纳米织构硼化物共晶陶瓷的强韧化机理和氧化行为，为发展高致密、强韧化超高温陶瓷及其凝固制备技术提供理论和技术基础。

ZrB2基超高温陶瓷以其优异的高温综合性能成为高超飞行器领域重要的先进结构材料。本项目突破传统烧结技术，将熔体液固相变与ZrB2基复相陶瓷成分设计相结合，提出并发展了以激光表面区熔和光悬浮区熔高梯度定向凝固技术快速制备高致密度、纳米织构共晶陶瓷的新思路和新方法，实现了ZrB2-SiC共晶复相陶瓷熔体取向生长调控与凝固组织的优化，揭示了多元复相纳米织构ZrB2-SiC共晶陶瓷的强韧化及抗氧化机理，为实现高致密、高强高韧性超高温硼化物复相陶瓷的设计和凝固制备提供了新途径。主要研究结果如下：.1) 建立了硼化物共晶复相陶瓷成分设计准则，发展了适于激光区熔且致密度匹配的高纯硼化物共晶预制体制备工艺。.2) 突破了硼化物陶瓷致密化难的瓶颈，实现了表面光滑、高致密度(>99%)、无裂纹和孔洞的ZrB2-SiC共晶陶瓷的快速制备。.3) 探明了ZrB2-SiC共晶复合陶瓷凝固组织特征、微结构控制及演化规律。定向凝固ZrB2-SiC共晶陶瓷呈现典型的非规则共晶组织，随激光扫描速率的增加，共晶组织逐渐细化。.4) 揭示了ZrB2-SiC共晶复合陶瓷取向生长、相界面调控及共晶生长机理。低扫描速率下激光水平区熔时，随扫描速率的增加，ZrB2-SiC共晶陶瓷凝固组织由非规则块片状共晶组织转变为较规则的骨架状共晶组织。.5) 激光水平区熔定向凝固ZrB2/SiC共晶陶瓷硬度达到24.2±0.6 GPa，断裂韧性为7.4±0.5 MP m1/2。断裂形式以脆性穿晶断裂为主，沿晶断裂为辅。凝固组织细化及裂纹偏转、桥接、分叉和多道裂纹相互作用是主要增韧机制。.6) 揭示了定向凝固ZrB2/SiC共晶复合陶瓷的高温抗氧化机制。在1400℃和1500℃下氧化气氛下，定向凝固ZrB2-SiC共晶陶瓷表面形成平整连续的富SiO2玻璃层，能够有效阻止氧向基体的扩散，并能及时愈合气泡破裂后的共晶组织，恢复其良好的抗氧化性能。.. 本项目相关研究结果发表学术论文25篇，其中SCI收录22篇，包括本领域TOP1期刊J. Eur. Ceram. Soc. 4篇和Scripta Mater. 3篇。获授权发明专利6项。参加学术会议20次，其中特邀报告12次。