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

本文从理论和实验上研究了控制TiAl基合金中α_2 + γ相层状组织取向的两种基本工艺。第一个过程是先在α单相区高温变形，然后在α_2 + γ区退火和变形。在α单相区的单轴压缩导致纤维织构的形成，但发生动态再结晶。压缩面的最大极密度出现在距α_2相（0001）约35 °处。热处理产生的片层组织反映了α单相区单轴变形形成的织构。在α单相区变形和两相区退火形成的全层片组织中，试样变形时出现加工软化现象。两相区的变形引起了薄片的转动。在真应变为-0.8左右的变形量下，片层界面几乎平行于压缩面。第二种工艺是基于织构钛箔与铝箔之间的反应扩散设计的。热处理包括四个加热阶段和一个冷却阶段，用于层状结构。用能谱仪分析了热处理后的相组成，发现40 - 60%的层片取向由原始钛箔的织构控制。结果表明，反应扩散工艺与形变热处理工艺相结合，是制备具有取向层状组织的TiAl板材的有效方法。

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.