层状多孔TiAl合金板材反应合成机理与强韧化机制

In order to solve the bottleneck problem of low strength and toughness of porous TiAl alloys used in metallic thermal protection system, Ti foils and Al-Nb composite foils are used as starting materials to prepare controlled-porous laminated TiAl alloys. The formation of the porous is based on the Kirkendall effect. Strengthening of porous TiAl alloys will be achieved by forming a continuous dense TiAl layer and introduction of Nb elements in the porous layers. Effects of starting material and technological parameters on the laminated pore structure and microstructure are studied. The synthesis mechanism of laminated porous TiAl alloys will be clarified. Furthermore, the mechanical properties of laminated porous TiAl alloys are tested, and the relationship between mechanical properties and laminated porous structures will be constructed. The deformation behavior of the laminated porous TiAl alloys are characterized to uncover the strengthening and toughening mechanisms of the alloys. Finally, the heat-conducting properties of the laminated porous alloys are characterized to uncover the mechanism of thermal protection. The implementation of this project will provide a technique and theory support to solve the problems for forming high-performance porous TiAl plate, and promote the application of porous TiAl plate.

本项目针对多孔TiAl合金作为金属热防护系统材料强度低、韧性差的关键问题，提出选用Ti箔与Al-Nb复合箔材为原材料，利用Kirkendall效应反应合成孔结构可控的层状多孔TiAl合金，通过形成连续致密TiAl合金层及在多孔层中引入合金元素Nb，实现对多孔TiAl合金的强韧化。研究原材料及反应合成工艺参数对TiAl合金组织及层状多孔结构的影响规律，揭示层状多孔TiAl合金的反应合成机理；测试不同孔结构参数材料的力学性能，建立孔参数-力学性能之间的关联关系，通过对变形组织的分析，揭示其强韧化机制；在此基础上，研究层状多孔TiAl合金的导热性能，揭示其热防护机理。项目的实施可望为高性能多孔TiAl合金板材的制备提供有效技术及理论支撑，推进多孔TiAl合金的实用化。

本项目旨在通过层状结构设计实现TiAl金属间化合物强韧化，选用Ti箔与Al-Nb(Al-Si)复合箔材为原材料，通过控制原始箔材层厚参数及反应退火工艺(反应温度及压力)制备了孔结构可控的等轴晶组织和片层组织交替排列层状多孔TiAl复合板材，孔洞位于等轴晶层的中间位置，且Nb元素及原位自生的Ti5Si3增强相主要分布于该层。随着压力的增加多空层中孔洞数量和大小均减少，等轴晶层层厚减小，全片层层厚和片层团簇尺寸变大，在5MPa压力下制备出的复合板密度为3.750g/cm3，抗拉强度在800℃高达到565.4MPa，延伸率为6.25%，在AO加载模式下室温断裂韧性最高达到15.8MPa·m1/2。压力为3 MPa时密度为3.142g/cm3，复合板的延伸率较高，850℃达到33.8%，且抗拉强度保持在384MPa。层状结构实现了TiAl复合板强度和塑性完美结合。这是由于在变形过程中复合板在层界面处的等轴晶粒中沿法向(ND)存在应变梯度，且越靠近界面的位置取向差越大。随着变形的进行全片层中的应力通过传递至等轴晶层的方式缓解全片层中的应力集中，通过孔洞和层状结构来抑制微裂纹的扩展，从而使复合板的强韧性得到提高。因此，本项目提出的层状结构TiAl复合板材组织构型化设计及制备为TiAl复合材料实用化提供了有效的理论与技术支撑。