核壳型MoSi2基高温结构材料的可控制备及强韧化机理研究

MoSi2 is a very important high temperature structural candidate materials. At present, there are still problems of poor toughness and low high temperature strength. This project devotes to resolving the problems by designing a core-shell structured composites by employing MoSi2, ZrO2 and Nb constituents. Such a composite design is expected to be able to take the advantages of the three constituents in their properties. The composite powders of MoSi2@ZrO2 and Nb@ZrO2 core-shell structure will be controllably synthesized by the solvent thermal method. The ZrO2 shells of the core-shell structures will be modified by surfactants to make the the core-shell structures form a stable solution. Through electrostatic attraction, the MoSi2@ZrO2 and Nb@ZrO2 will be used as precursors for the self-assembly fabrication of a multi-layer core-shell structure. The MoSi2 and Nb can be separated by the ZrO2 shell, which avoid the growth, diffusion and oxidation of the MoSi2 and Nb particles. The MoSi2 based block materials with the core-shell structure are obtained after drying and the microwave pressure sintering. The relationship between the mechanical properties of the composite materials and its composition, content, size and shell structure will be studied in details. The mechanism of controlling the grain growth of the MoSi2 will be discussed during sintering of the MoSi2 based composite materials and the mechanisms of strengthening and toughening of the MoSi2 base core shell materials will be clarified to realize the controllable of the structure and properties of the MoSi2 base core-shell materials. It provides an important theoretical basis and practical approach for the development of high strengthening and toughening properties of the MoSi2 base composites.

MoSi2是潜在的高温结构材料，针对目前仍存在室温韧性差、高温强度低等问题。本项目以MoSi2、Nb和ZrO2为组元，进行核-壳结构设计，利用不同组元性能上的优势来提高MoSi2综合力学性能。采用溶剂热法可控制备MoSi2@ZrO2和Nb@ZrO2核壳复合粉。利用表面分散剂修饰ZrO2壳，形成均匀稳定溶液；利用静电作用使MoSi2@ZrO2和Nb@ZrO2自组装成多层核-壳结构。ZrO2壳分隔MoSi2和Nb，避免MoSi2和Nb晶粒长大，相互扩散和氧化，经过干燥和微波热压烧结，获得MoSi2基复合块材。系统研究该复合块材的力学性能与其组成、含量、尺寸和壳层结构之间的关系。探讨MoSi2基复合材料烧结过程中核壳结构抑制MoSi2晶粒长大的机理，阐明MoSi2基核壳材料强韧化机理，实现MoSi2基核壳材料结构、组织和性能的可控。为研制高强韧性的MoSi2基复合材料提供重要理论基础和实际途径。

MoSi2室温断裂韧性差，高温强度低以及低温抗氧化能力不足，影响其作为高温零部件的可靠性和安全性，提高MoSi2材料韧性、强度、低温抗氧化能力成为该材料研究的核心问题。.本项目以MoSi2、Nb和ZrO2为组元，进行了核-壳结构设计，采用水热法可控制备了MoSi2@ZrO2和Nb@ZrO2核壳复合粉，采用静电自组装制备了MoSi2@ZrO2@Nb@ZrO2核壳结构复合粉体，采用微波烧结法制备了MoSi2基复合材料。研究了MoSi2@ZrO2@Nb@ZrO2核壳结构复合材料的力学性能与其组成、含量、尺寸和壳层结构之间的关系。探讨了MoSi2基复合材料烧结过程中核壳结构抑制MoSi2晶粒长大的机理，阐明了MoSi2基核壳材料强韧化机理，实现了MoSi2基核壳材料结构、组织和性能的可控。.结果表明：ZrO2/Nb复相添加并形成核壳结构比单相添加更能提高MoSi2基复合材料的综合力学性能。与常规烧结相比，微波烧结大幅缩短烧结时间，显著降低烧结温度，提高致密度。当Nb含量为15wt%，ZrO2含量为20wt%时，1550℃，30min微波烧结制备的多壳层MoSi2@ZrO2@Nb@ZrO2核壳结构复合材料综合力学性能较优，相对密度为99%，显微硬度为13.3GPa，断裂韧性为8.98MPa·m1/2，抗弯强度为560.4Mpa。MoSi2@ZrO2@Nb@ZrO2核壳结构烧结块体500℃和600℃循环氧化72小时增重分别为1.98%和13.78%，表明，MoSi2@ZrO2@Nb@ZrO2核壳结构更能有效抑制了MoSi2的pest现象。MoSi2@ZrO2@Nb@ZrO2核壳结构复合材料存在多种增韧机制，在多相复合添加剂作用下，引起的裂纹桥联、偏转、晶粒拔出，起到了协同增韧的作用，而且效果大于单一相添加增韧效果；同时沿晶与穿晶混合也是提高断裂韧性的重要因素。.本项目的研究对复合技术与制备工艺的结合以及多种增韧机制协同作用改性MoSi2材料具有一定参考价值和科学意义。