Recrystallization and phase transitions in a γ-TiAl-based alloy as observed by ex situ and in situ high-energy X-ray diffraction

High-energy synchrotron X-ray diffraction is a novel and powerful tool for bulk studies of materials and is applied to the investigation of a high Nb-bearing gamma-TiAl-based alloy. The results determined from ex situ diffraction patterns of differently heat-treated samples are compared with those from metallographic examinations. The diffraction angles and also the morphology of reflections on the Debye-Scherrer rings are evaluated in order to determine lattice parameters and grain sizes as well as crystallographic correlation. An in situ heating cycle from room temperature to 1362 degrees C has been conducted starting from massively transformed gamma-TiAl. 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. Finally, a fully lamellar structure, well oriented with respect to the high-temperature phase, is formed. The data obtained by high-energy synchrotron X-ray diffraction, which contain extremely rich information, are interpreted step by step and relate well with the ex situ observations and metallographic examinations. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.