Cast TiAl alloys with high Nb content are subject of extensive research with the aim to develop material with low density, good corrosion resistance and high strength at elevated temperatures. Disadvantage of their broad applications is restricted workability, machinability and low fracture toughness especially at room temperature. Improvement of properties of TiAl based materials can be achieved by tailoring the microstructure by modification of chemical composition. For this purpose 5 types of TiAl alloys with 7 at.% of Nb were prepared having variable content of Mo and/or C. Addition of Mo and/or C resulted in three types of microstructure and different phase composition. All modified alloys contain colonies consisting of thin lamellae of α and γ phases sometimes complemented by γ and/or β phase at the grain boundaries. Variable microstructure and phase composition resulted in differences in mechanical behaviour. The most promising tensile properties at both room and elevated temperature were observed for alloy doped with 2 at.% of Mo having the mixed microstructure containing β phase and for alloy doped with 0.5 at.% of C with nearly lamellar microstructure without β phase. 2Mo alloy exhibited reasonably good ductility while 0.5C alloy reached the highest tensile strength. Also low cycle fatigue behaviour of these two materials was the best of all five materials under investigation. Fatigue deformation characteristics were better in the case of 2Mo alloy while 0.5C alloy exhibited higher cyclic stresses. Fracture mechanisms were determined using fractographic analysis. The major fracture mode of all alloys was trans-lamellar.Keywords: TiAl, microstructure, mechanical properties, effect of alloying, fractography
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