Crack Propagation Properties and Toughening of Wrougt TiAl Alloys based on Our Design Principle

采用单晶和多晶材料，系统地研究了片层取向和β-Ti相的存在对具有片层组织的TiAl合金增韧和强化的影响。从单晶实验来看，裂纹的萌生和扩展行为强烈地依赖于剪切分量平行于加载方向的片层取向，并且可以通过最小化剪切分量来实现增韧。根据我们设计的变形合金的设计原则进行的多晶实验表明，片状晶界上的β相是可变形的，不会裂纹扩展，因此具有有效的增韧作用。合金的蠕变强度与目前使用的镍基合金相当。因此，决定蠕变强度的不是β相的存在，而是蠕变过程中的组织稳定性。

The effects of lamellar orientation and presence of beta-Ti phase on toughening and strengthening of TiAl alloys with lamellar microstructure using single and polycrystalline materials were systematically investigated. From the single crystal experiments, crack initiation and propagation behavior depends strongly on the lamellar orientation with shear component parallel to the loading direction, and toughening can be achieved by minimizing the component. From the polycrystalline experiments based on our design principle of the wrought alloys, the beta phase present on the lamellar colony boundaries is deformable and resistant to crack propagation, thereby effective in toughening. The creep strengths of the alloys were found to be comparable to the currently used Ni-based alloys. Thus, it is not the presence of beta phase but microstructure stability during creep that governs the creep strength.