Papers by Author: A. Stark

Abstract: In this study texture and microstructure formation in high-Nb containing TiAl alloys during lab-scale compression experiments and “near conventional” forging on an industrial scale are investigated. The deformation temperatures range from 700 °C up to temperatures close to the α transus temperature (Tα = 1295 °C). Depending on the deformation conditions, the texture of the tetragonal γ-TiAl phase is formed by pure deformation components, components related to dynamic recrystallization, or transformation components. This changing corresponds with microstructural observations. The hexagonal phases α2-Ti3Al and α-Ti(Al) show a similar texture as it is known for Ti and Ti-base alloys after compressive deformation at elevated temperatures. In contrast to the γ texture, no significant change of the α/α2 texture was observed in the investigated temperature range. In the alloy with a composition of Ti-45Al-10Nb (in at.%) even deformation textures of ternary intermetallic phases, as the hexagonal ωo-Ti4Al3Nb and the cubic βo-TiAl(Nb) phase, respectively, were measured and analyzed.

Abstract: High-energy synchrotron X-ray diffraction is a novel and powerful tool for bulk studies of materials. In this study, it is applied for the investigation of an intermetallic γ-TiAl based alloy. Not only the diffraction angles, but also the morphology of reflections on the Debye-Scherrer rings are evaluated in order to approach lattice parameters and grain sizes as well as crystallographic relationships. An in-situ heating cycle from room temperature to 1362 °C has been conducted starting from massively transformed γ-TiAl which exhibits high internal stresses. With increasing temperature the occurrence of strain relaxation, chemical and phase separation, domain orientations, phase transitions, recrystallization processes, and subsequent grain growth can be observed. The data obtained by high-energy synchrotron X-ray diffraction, extremely rich in information, are interpreted step by step.