Intermetallic γ‐TiAl‐based alloys represent a new class of light‐weight structural materials for use at high temperatures. Because of their unique properties these alloys are considered for applications in aerospace and automotive industries. During the last decade both, alloy development and materials processing progressed significantly. New materials and powder metallurgy (PM) have formed a symbiosis since many decades. In fact, PM is an ancient technology which has been used for the processing for almost every metal or ceramic material. Therefore, it is hardly surprising that PM plays an important role in research and development of γ‐TiAl‐based alloys.

a b s t r a c tA b-solidifying TiAl alloy with a nominal composition of Tie43.5Ale4Nbe1Moe0.1B (in at.%), termed TNMÔ alloy, was produced by a powder metallurgical approach. After hot-isostatic pressing the microstructure is comprised of fine equiaxed g-TiAl, a 2 -Ti 3 Al and b o -TiAl grains. By means of two-step heat-treatments different fine-grained nearly lamellar microstructures were adjusted. The evolution of the microstructure after each individual heat-treatment step was examined by light-optical, scanning and transmission electron microscopy as well as by conventional X-ray and in-situ high-energy X-ray diffraction. The experimentally evaluated phase fractions as a function of temperature were compared with the results of a thermodynamical calculation using a commercial TiAl database. Nano-hardness measurements have been conducted on the three constituting phases a 2 , g and b o after hot-isostatic pressing, whereas the hardness modification during heat-treatment was studied by macro-hardness measurements. A nano-hardness for the b o -phase is reported for the first time.

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The C distribution within the -TiAl-phase of a Ti-45Al-5Nb-0.5C alloy with near- microstructure has been studied by atom probe tomography. In most areas the C atoms are homogenously distributed, and only a few C enriched features were detected which are presumably Cottrell atmospheres surrounding dislocation cores. The C concentration within the -phase was measured to be approximately 0.25 at.%, which is a factor of ten higher than the solubility limit reported for other TiAl alloys. The reason for this unusually high C solubility is explained by an existing model which relates the number of octahedral sites consisting of six Ti atoms to the solubility limit of interstitials. The large amount of C in solid-solution can explain the results of a recent study which showed that the C-containing alloy had an approximately 30% increase in yield strength when compared with a C-free sheet containing the same Ti, Al and Nb concentration.

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