GENERAL-ASPECTS OF THE THERMOMECHANICAL TREATMENT OF 2-PHASE INTERMETALLIC TIAL COMPOUNDS

This article represents a survey on the thermomechanical treatment (TMT) of two-phase intermetallic TiAl compounds. Nearly all of the important parameters, such as temperature, cooling rate, forging ratio, and direction, of the TMT steps were examined. The aim of this investigation was to understand the effects of the different parameters and thus to provide the knowledge of how to achieve all desired types of microstructures depending on the application purpose. Along the way, it was necessary to overcome the brittleness of TiAl compounds in order to permit further working and deformation processes, such as near net shape forming and sheet rolling. We obtained the best ductility with homogeneous equiaxed microstructures with true plastic tensile strains at room temperature of more than 6 pct for Ti-48Al-2Cr (atomic percent). In the case of equiaxed microstructures, the Hall-Petch relationship could be confirmed for both the yield and the fracture stress. Therefore, the microstructures causing highest strength and high ductility and the way to achieve these properties were elaborated and are discussed in detail here.