准连续网状Ti5Si3/TiAl复合材料设计制备与蠕变机制研究

针对TiAl基合金加工成形困难与800℃以上抗蠕变能力不足的瓶颈问题，本项目创新性地将“先成形后反应合成”与“构型复合化”思想相结合，提出高抗蠕变TiAl基复合材料板材制备与成形一体化方法：首先利用真空压力浸渗法将Al-Si合金液渗入多孔钛粉预制体中以获得Ti-(Al-Si)双金属复合体，随后进行轧制获得双金属板材，再利用多级反应热处理技术调控Ti颗粒与Al-Si合金的反应扩散，实现原位自生Ti5Si3增强相呈准连续网状分布即构型复合化，优化制备参数，制备出准连续网状Ti5Si3/TiAl复合材料板材；建立“制备参数—网状结构—力学性能”关系，阐明Ti5Si3/TiAl复合材料网状结构调控规律与变形断裂特性，优化出最佳抗蠕变性能；建立蠕变本构方程并阐明蠕变变形过程中组织演变规律，揭示准连续网状Ti5Si3/TiAl复合材料蠕变机制。项目实施将为TiAl基复合材料薄板制备奠定理论与实验基础。

In order to solve the bottleneck problems of weak formability and lack in creep properties over 800℃ of titanium aluminide (TiAl) based alloys, in this project the two design concepts “Forming first and then reaction synthesis” and “Microstructural architecture” are innovatively combined and thus an integrated technique of preparation and forming of TiAl matrix composite sheet is proposed: Firstly, molten Al-Si alloys are infiltrated in porous preform of spherical pure titanium particles by vacuum pressure infiltration technique, and hence Ti-(Al-Si) bimetallic billet is prepared. And then the Ti-(Al-Si) bimetallic billet is subjected to hot rolling in order to obtain the desired Ti-(Al-Si) bimetallic sheet. Subsequently, the multi-step reaction heat treatment is employed to regulate the chemical reaction between Ti particles and Al-Si alloys, and in situ synthesized Ti5Si3 reinforcements present in form of a quasi-continuous network distribution. As a result, Ti5Si3/TiAl composite sheet with a quasi-continuous network architecture is successfully produced by optimizing the preparation parameters mentioned above. In addition, the relationship among fabrication parameters, network structure and mechanical properties is established, and regulation mechanism of the quasi-continuous network microstructure and deformation and fracture characteristic of Ti5Si3/TiAl composite are clarified and thereby the quasi-continuous network Ti5Si3/TiAl composite with the optimal creep properties is obtained. Finally, creep constitutive equation is constructed, moreover, scan electron microscope, transmission electron microscope and X-ray tomography technique are used to investigate the microstructure evolution of Ti5Si3/TiAl composite in the process of creep deformation, and thus the creep mechanism of quasi-continuous network Ti5Si3/TiAl composite will be revealed. The findings of this project will lay a theoretical and experimental foundation for thin sheet forming of TiAl matrix composites.