Structural Utilization of the Intermetallic Compound TiAl - an Attempt to Ductilize TiAl by Controlling its Lamellar Structure -

富钛TiAl是公认的高强度/高密度比的高温结构材料。一个主要的问题也已被认识到，在环境温度下的延展性差。本课题组成功地控制了TiAl化合物定向凝固过程中的组织演变。我们对具有这种受控组织的TiAl进行了单轴变形和轧制的研究，得到的结果可以概括如下。(1)当层板平行或垂直于加载轴时，屈服应力很高，而对于中间取向，屈服应力很低。(2)当片层平行或垂直于加载轴时，剪切变形穿过片层边界进行，而剪切变形平行于中间取向的片层边界发生。(3)对于拉伸轴与片层边界呈511 °倾斜的试样，获得了约20%的室温拉伸伸长率。(4)双相组织TiAl的变形机制为{111}型真孪晶和沿着<110]滑移。(5)当具有受控显微组织的双相TiAl化合物即使在室温下也可以被轧制到多达50%的厚度压下量时。(6)当TiAl化合物在室温下轧制并随后在900 ℃范围内退火时，显微硬度的恢复分两个阶段发生。第一和第二阶段分别对应于位错的重排和湮灭以及形变孪晶的退火。(7)冷轧PST晶体的再结晶方式取决于轧制压下量。当轧制压下量小于20%时，发生再结晶而不干扰片层组织特征。因此，通过连续的轧制和退火工艺，应该可以获得高于50%的轧制压下量。

Ti-rich TiAl has been recognized as a high-temperature structural material of high strength/density ratio. A major problem has also been recognized, poor ductility at ambient temperatures. The present authors' group has succeeded in controlling the micro-structure evolution during the unidirectional solidification of TiAl compounds. We have made a study of the uniaxial deformation and rolling of TiAl with such a controlled microstructure and obtained the results which can be summarized as follows.(1) Yield stress is high when the lamellae are parallel or perpendicular to the loading axis and it is very low for intermediate orientations.(2) When the lamellae are parallel or perpendicular to the loading axis, shear deformation proceeds across the lamellar boundaries, while shear deformation occurs parallel to the lamellar boundaries for intermediate orientations.(3) A room temperature tensile elongation of about 20%, was obtained for a specimen whose tensile axis is inclined at 511 to the lamellar boundaries.(4) Deformation mechanisms of TiAl with the TAl two phase structure are found to be the true twinning of the {111}-type and slip along <110].(5) When the two-phase TiAl compounds with the controlled microstructure can be rolled to as much as 50% reduction in thickness even at room temperature.(6) When TiAl compounds are rolled at room temperature and subsequently annealed in the range 900, recovery in microhardness occurs in two stages. The first and the second stages correspond respectively to the rearrangement and annihilation of dislocations and the annealing-out of deformation twins.(7) Recrystallization mode of cold-rolled PST crystals depends on rolling reduction. When the rolling reduction is smaller than 20%, recrystallization occurs without disturbing the lamellar structure characteristics. Therefore, it should be possible to attain a rolling reduction higher than 50% thrrough successive roll-and-anneal process.