氮化硼-氧化锆复合材料的低温致密化行为与抗钢水侵蚀机理

Boron nitride (BN) ceramic has a unique set of properties, including an extremely high melting point, exceptional chemical inertness, excellent thermal shock resistance, solid self-lubricant and non-wettability with molten metal. Due to this combination of properties, BN ceramic has been widely applied in aerospace, electronic equipment, precision chemistry, metallurgy, etc. Background of side dams used in thin-strip casting process, This project foucs on the intrinsic characteristics of BN ceramic such as poor sintering ability, low mechanical properties and imited corrosion resistance against molten steel. A novel processing combining liquid phase sintering and reaction sintering has been proposed for fabricating dense BN-ZrO2 composite at low sintering temperature (<1400℃), by using B2O3 as transient viscous phase and designing reaction process for transforming from low-melting sintering additive to high-melting sintering additive. The influence of the reactant component, reaction process and sintering process on densification behavior, microstructure and mechanical properties has been also analyzed and discussed. Based on the results, the sintering mechanism has been proposed. Furthermore, corrosion properties of composites with different composition under various corrosion condition ( corrosion time and temperature) have been evaluated systematically, and clarifies the detail evolvement and conversion process of microstructure of residual corrosion layer. A simple schematic of corrosion process would be constructed, and then the corrosion mechanism of BN composites against molten steel has been proposed. The accomplishment of the project will provide a new method of low-costing fabrication and performance optimization of BN composites, and guide the research and development of BN composites as side dams. It will have a wonderful academic value and potential prospect in practice.

氮化硼陶瓷具有高熔点、化学稳定、抗热震、高温自润滑及与熔融金属不浸润等优点，在航空航天、电子、化工、冶金等领域有广泛的应用前景。本项目以钢铁薄带连铸侧封板为应用背景，针对氮化硼陶瓷存在的烧结困难、力学性能低、抗钢水侵蚀性能差等问题，针对氮化硼-氧化锆复合材料体系，提出以氧化硼为过渡相，设计合理反应途径，完成低熔点烧结助剂向高熔点烧结助剂转化，发挥液相烧结与反应烧结的协同作用，实现氮化硼复合材料的低温(<1400℃)烧结的新思路。系统研究反应物种类和配比、反应途径及烧结工艺对材料致密化行为、组织结构和力学性能的影响规律，揭示其致密化机理；研究物相组成和侵蚀条件(时间和温度)对材料抗钢水侵蚀性能的影响，阐明侵蚀残留层微结构演变规律，构建侵蚀模型，揭示钢水侵蚀机理。本项的完成将为氮化硼复合材料的低成本制备和性能优化设计提供有效途径，指导氮化硼基侧封板的研制，其具有重要的学术价值和潜在的工程应用前

本项目针对项目以钢铁薄带连铸侧封板为应用背景，针对氮化硼陶瓷存在的烧结困难、力学性能低、抗钢水侵蚀性能差等问题，针对氮化硼-氧化锆复合材料体系，设计过渡塑性相烧结工艺实现氮化硼基陶瓷材料的低温烧结致密化，通过对添加剂的反应动力学计算、反应产物随温度的转变过程，烧结致密化曲线变化趋势的分析。提出以氧化硼为过渡相，设计合理反应途径，实现低熔点烧结助剂向高熔点烧结助剂转化，发挥液相烧结与反应烧结的协同作用，使氮化硼基复合材料的烧结温度降低近500℃，在1300~1500℃即可获得致密的氮化硼基陶瓷材料。在相同压力条件下，1300℃的复合材料力学性能优于1200℃所制备的复合材料。烧结温度为1300℃，热压压力为100MPa时所得材料综合性能最优，其抗弯强度为228.2MPa，断裂韧性为4.14MPa，维氏硬度为2.46GPa。研究了Ti3SiC2对BN-ZrO2-Ti3SiC2复合材料力学性能的影响，抗弯强度随Ti3SiC2添加量的增加先提高后降低，S4T4成的抗弯强度最高，达到316.8MPa，比起未添加Ti3SiC2的复合材料（292.6MPa），提高了8.3%；复合材料的抗钢水侵蚀性能随着Ti3SiC2含量增加而提高。Ti3SiC2的存在有助于在侵蚀过程中形成更为致密的ZrO2或(ZrTi)O2侵蚀层，抵御钢液对材料的进一步侵蚀。随着Ti3SiC2含量提高，材料因钢水侵蚀造成的尺寸变化减小。Ti3SiC2含量为8%的材料在1600℃侵蚀40min后，侵蚀层厚度为184μm，侵蚀深度仅为204μm，具有最佳的抗钢水侵蚀性能。. 本项目为氮化硼基陶瓷复合材料优化设计及低温致密化提供新的思路，为高性能氮化硼基陶瓷侧封板低成本制备提供有效途径，阐明了氮化硼基陶瓷复合材料抗钢水侵蚀机制，为进一步优化设计抗热震耐腐蚀氮化硼基陶瓷侧封板奠定了理论基础和实验依据。实现了氮化硼基陶瓷侧封板的国内自主化研制，通过试验线中试，并有望替代国外进口产品。