Ti-Zr-B-C四元系复相陶瓷中的固溶反应耦合机理及显微组织与性能调控

Ultrahigh-temperature ceramics such as borides (MB2) and carbides (MC) of transition metals (Ti, Zr, Hf)have excellent physicochemical properties such as high hardness, high modulus, high temperature resistance, oxidation resistance and ablation resistance，which has broad application prospects in extreme conditions such as ultra-high temperature. This project is based on the unclear question of interdiffusion, solid solution and reaction coupling mechanism between M1B2-M2C, during sintering process of quaternary multiphase ceramics (M1B2-M2C). In this project, Ti-Zr-B-C quaternary multiphase ceramics are chosen to carry out the basic research. ZrB2-TiC and TiB2-ZrC are selected as the reference system to investigate the influence of the types of raw materials, chemical composition, sintering process and other parameters on the solution-coupled reaction, densification behavior, microstructure and properties of ceramics. Combining with thermodynamic calculation and study of diffusion couple, the reaction thermodynamics and diffusion kinetics will be clarified and also boride / carbide solution reaction model shall be established and as a result the interaction of anion and cation diffusion, solid solution and the reaction mechanism of coupling as well as the densification mechanism of sintering multiphase ceramics, significant microstructure evolution law and toughening mechanism will be revealed to obtain excellent mechanical properties of Ti-Zr-B-C quaternary system of multiphase ceramics. The completion of this project will enrich the methods of ultra-high temperature ceramic sintering and also provide the theoretical basis for the design and preparation of high-performance multiphase ceramics.

以过渡金属Ti、Zr、Hf等的硼化物和碳化物为代表的超高温陶瓷具有高硬度、高模量、耐高温、抗氧化、耐烧蚀等优异的性能，在极端环境具有广阔的应用前景。本项目基于四元系硼化物-碳化物复相陶瓷（M1B2-M2C）烧结过程中两相互扩散、固溶和反应耦合机制尚不清楚的问题，以四元系Ti-Zr-B-C复相陶瓷为对象开展相关基础研究。选择ZrB2-TiC和TiB2-ZrC为对照系，探究原料种类、化学成分、烧结工艺等参数对陶瓷的固溶反应耦合行为、致密化行为、显微组织和性能的影响规律，结合热力学计算与扩散偶研究，阐明反应热力学和扩散动力学，建立硼化物/碳化物固溶反应模型，揭示阴阳离子的互扩散、固溶与反应的耦合作用机理，进而揭示复相陶瓷的烧结致密化机理、显微组织演化规律和强韧化机理，获得力学性能优异的Ti-Zr-B-C四元系复相陶瓷。本项目的完成将丰富超高温陶瓷烧结途径，为高性能复相陶瓷设计、制备提供理论基础。

本项目针对硼化物、碳化物超高温陶瓷烧结难、脆性大、可靠性差等缺点，提出基于固溶和反应耦合效应主导的互扩散机制促进硼化物-碳化物复相陶瓷烧结的新思路。以ZrB2-TiC和TiB2-ZrC为对照系，进行了ZrB2与TiC间的固溶反应规律及扩散热力学和动力学研究，探索固溶反应耦合效应；系统研究了原料配比、烧结工艺等参数对复相陶瓷致密化、微结构和性能的影响规律，阐明复相陶瓷烧结致密化机理、显微组织演化规律和强韧化机制；获得综合性能优异的Ti-Zr-B-C四元系复相陶瓷。. 研究结果表明，ZrB2-TiC和TiB2-ZrC具有相同的热力学终态，即(Ti, Zr)B2-(Zr, Ti)C。但混粉烧结和扩散偶试验均表明ZrB2-TiC体系比TiB2-ZrC体系具有更高的烧结活性。TiB2-ZrC的固溶过程基于金属原子的纯扩散；而ZrB2-TiC体系以B和C原子扩散主导的反应为主，反应过程同步促进了金属原子互扩散的固溶过程。ZrB2-TiC反应与固溶过程主导的互扩散传质促进了材料致密化。ZrB2-TiC体系在1800 °C/1 h/30 MPa热压烧结工艺下即可实现充分反应和快速致密化，烧结激活能为531 ± 16 kJ/mol，致密化控制因素为Ti和Zr原子的晶格扩散。. 1750℃烧结制备的完全致密的四元系陶瓷平均晶粒尺寸仅为~0.3 μm，晶粒生长激活能为933 kJ/mol，约为典型硼化物-碳化物复相陶瓷材料的1/5，细小的晶粒尺寸主要归因于低温原位反应中晶粒重新形核。复相陶瓷力学性能随烧结温度升高先增加再降低, 存在细晶强化、固溶强化、板状晶强韧化等多重机制。1800 °C烧结ZrB2-TiC复相陶瓷具有最佳力学性能，其硬度、抗弯强度和断裂韧性分别为27.9 GPa、705MPa和5.3 MPa·m1/2。复相陶瓷氧化过程受扩散控制，抗氧化性能随碳化物含量增多而变差，ZrB2-10 mol.% TiC具有最佳的抗氧化性能，其在1300 °C氧化4 h后比表面积氧化增重~2.4 mg·cm-2。. 本项目为硼化物-碳化物复相陶瓷优化设计及强韧化提供了新的思路，打破了硼化物-碳化物复相陶瓷研究中将碳化物相作为添加剂的惯性思维模式，为高性能复相陶瓷构件的制备提供了新的途径。