棒状硼化锆粉体的制备及其流延合成高性能织构化硼化锆陶瓷的研究

This project is aimed at improving the toughness of zirconium diboride ceramicsby texture technology. Firstly, we will combine sol-gel method and microwave sintering technology to achieve the preparation of rod-like zirconium diboride powders with controllable morphology, size distribution, and length-diameter ratio. Moreover, the aforementioned oriented rod-like zirconium diboride powders can serve as "die crystal", and distributing in sphere-like type of zirconium diboride powders with preferred orientation through tape casting technology. Highly oriented zirconium diboride ceramics could then be obtained via hot pressure sintering process. This uniqueinterlocking structure of rodlike crystal organization can realize the deflection, bridging, and bifurcation of cracks, thus improving the fracture toughness of zirconium diboride ceramic. In addition, systematic study will be performed to explore how sol-gel process and microwave sintering parameters could impact the morphology and composition of rod-like zirconium diboride powders, then exploring the thermodynamics and dynamics laws during the formation of rod-like zirconium diboride powders with controllable morphology, size distribution, and length-diameter ratio can be revealed, it followed by the clarification of oriented Growth mechanism of rod-like zirconium diboride powders in high temperature liquid phase system. Subsequently, preparation process and formation mechanism of textured zirconium diboride ceramics was studied, the relationship between the phase composition, grain size, texture, grain boundary structure and strength, toughness and high temperature properties of textured zirconium diboride ceramics was established, and inherent mechanism of toughening properties effected by the microstructure was revealed. This project will provide the reference and theoretical guidance for ultra-high-temperature ceramics, which has important scientific significance and practical value.

针对硼化锆陶瓷韧性差的缺点，本项目拟采用织构化技术，在溶胶凝胶法结合微波技术实现形貌、大小、长径比可控的棒状硼化锆粉体制备的基础上，将具有取向的棒状硼化锆粉体作为“模晶”，利用流延技术使"模晶"能择优取向地分布在近球状硼化锆粉体中，并采用热压烧结制备具有高度取向的硼化锆陶瓷，这种互锁结构的棒晶组织能实现裂纹偏转、分叉和桥联, 从而提高硼化锆陶瓷的断裂韧性。通过系统研究溶胶凝胶和微波对棒状硼化锆粉体形貌和组成的影响，旨在探索形貌、大小和长径比可控棒状硼化锆粉体形成的热力学和动力学内在规律，阐明棒状硼化锆粉体高温液相中定向生长的机制。并通过对织构化硼化锆陶瓷的流延和热压制备工艺的研究，建立织构化硼化锆陶瓷的强度、韧性与材料的相组成、织构化和微观结构的关系，揭示织构化结构的形成机理及织构化强韧化力学性能的内在机制。本项目的开展将为超高温织构化研究提供借鉴和理论指导，具有重要的科学意义和实用价值。

材料的强韧性差是航空航天领域使用的超高温材料急需解决的最关键的基础性问题之一。本项目以硼化锆超高温陶瓷为研究对象，采用溶胶凝胶结合微波烧结的技术，制备了具有棒状晶结构的硼化锆粉体，并研究了凝胶注模成型结合烧结的技术制备了具有部分织构化的硼化锆陶瓷以增强硼化锆陶瓷的强度和韧性。首先，采用新的聚合模版法制备了ZrB2粉体。通过在前驱体成胶过程中引入近球状硼化锆粉体，近球状硼化锆粉体的引入起到晶种和提供原料的作用，利用硼化锆各个方向的晶体生长速率是不同的，在c方向有较高的生长的速度，通过液相作用下的溶解再结晶机制，在c轴的生长的速率被进一步增大，从而实现单分散长棒状晶硼化锆粉体的制备。通过将凝胶注模成型的方法引入硼化锆陶瓷的成型制备，实现了硼化锆陶瓷的净尺寸成型，通过调节工艺得到了有一定取向的陶瓷素坯。探讨了三种不同分散剂对成型性能的影响，获得了制备硼化锆陶瓷最佳的成型工艺条件：分散剂选择PAANH4、料浆的pH值为9、PAANH4添加量为2wt%、球磨时间为12h、固含量为45vol%、单体（AM）含量为4wt%。将自制的棒状硼化锆粉体引入硼化锆陶瓷烧结中，通过对硼化锆陶瓷烧结性能研究发现，引入含量为5%的棒状硼化锆粉体，烧结的温度制度为1900度，保温10min得到了部分取向的ZrB2陶瓷，自制棒状形貌的ZrB2粉体具有促进ZrB2织构的形成，实现ZrB2陶瓷的织构化烧结。该项目制备的不同形貌硼化锆粉体和织构化陶瓷，将为其它取向性陶瓷粉体制备和高强度和韧性的高温陶瓷的制备提供借鉴和理论指导。