Process Development for the Orientation Control of the(α_2+γ)Lamellar Microstructure in TiAl Intermetallic Compounds

本文对利用α_2+γ相成分控制TiAl基合金片层组织取向的两种基本工艺进行了理论和实验研究。首先在α单相区进行高温变形，然后在α_2+γ区进行退火和变形。α单相区的单轴压缩导致纤维织构的形成，但发生了动态再结晶。压缩面最大极密度出现在α_2相（0001）处约35°处。热处理后形成反映α单相区单轴变形织构的片层组织。在α单相区变形和两相区退火形成的全片层组织中，试样发生了加工软化。两相区的变形引起了片层的旋转。在真应变约为-0.8变形后，片层界面与压缩面基本平行。第二种工艺是在织构钛箔和铝箔之间反应扩散的基础上设计的。热过程由四个加热阶段和一个冷却阶段组成。用EDX对热处理后的相进行了检测。结果表明，40 ~ 60%的片层取向受初始钛箔织构的支配。结果表明，反应扩散与热处理相结合是制备具有取向层状组织的TiAl片材的有效方法。

Two basic processes designed for controlling the orientaion of lamellar microstructure of with the constituents of α_2+γ phases in the TiAl based alloys are theoreticall and experimentally examined. The first process consists of the high-temperature deformation in α single phase region followed by the annealing and deformation in α_2+γ region. The uniaxial compression in the α single phase region resulted in the formation of a fiber texture, though dynamic recrystallization occurred. The maximum pole density for the compression plane appeared about 35 degrees away from(0001)of α_2 phase. The heat treatment generates the lamellar microstructure reflecting the texture formed by the uniaxial deformation in the α single phase region. Work softening was observed at the deformation of the specimen with fully lamellar microstructure formed by the deformation in the α single phase region and the annealing in the two phase region. The deformation in the two phase region brought about the rotation of the lamellae. The lamellar interface lied almost parallel to the compression plane after the deformation of about-0.8 in true strain.The second process is designed on the basis of the reactive diffusion between the textured titanium foils and aluminum foils. Thermal process consists of four heating stages and a cooling stage for lamellar construction. The phases are examined after the heat treatments by EDX.It was found that 40-60% of the orientations of the lamellae are dominated by the texture of the starting titanium foils. It was concluded that the combination of the reactive diffution process and the thermomechanical treatment described above is promising for the manufacturing process of TiAl sheet materials with the oriented lamellar microstructure.