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Abstract

Due to their low density and high strength, TiAl-based intermetallics are promising candidate materials for high-temperature applications. Nb additions in the latest generation of these alloys further improve strength, creep resistance and oxidation resistance at elevated temperatures. In the present study, uniaxial tensile and biaxial (double shear) creep experiments in the temperature range between 700 and 800°C were conducted on a hotextruded Ti-45Al-5Nb-0.2B-0.2C (at.-%) alloy. Initial and creep deformed duplex microstructures were quantitatively analyzed by scanning electron microscopy (SEM), electron back scatter diffraction (EBSD), and transmission electron microscopy (TEM). EBSD and TEM results indicate the presence of both texture and a microstructural anisotropy, where lamellar grains are predominantly oriented parallel to the extrusion direction. This anisotropy has a distinct effect on the uniaxial creep behaviour of specimens with different orientations. However, no influence of specimen orientation with respect to the extrusion direction was found in double shear creep curves. We demonstrate that microstructural anisotropy must be appreciated when uni- and multiaxial creep data of TiAl are compared. And we discuss the interaction of different microstructural processes (dislocation plasticity, twinning, dynamic recrystallization) that govern the creep behaviour of TiAl.