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Quantitative Characterisation and Microstructural Anisotropy of a Hot-Extruded TiAl Alloy
In the present paper we present quantitative microstructural investigations of a hot-extruded 3rd generation intermetallic γ-titanium aluminide alloy (TNBV5) with duplex microstructure. We characterised the microstructures of samples taken perpendicular and parallel to the extrusion direction by scanning and transmission electron microscopy, determining the grain areas of lamellar and globular grains, the fraction of lamellar colonies, the fraction of the twinned γ-grains, and the mean lamellar spacing of the lamellar regions. Our results indicate that the lamellar interfaces are predominantly aligned parallel to the extrusion direction. Preliminary creep tests performed on differently oriented samples highlight that the observed microstructural anisotropy affects the creep behaviour of the alloy under uniaxial loading. The metallographic methods described here in detail allow quantifying the influence of microstructural anisotropy on the mechanical properties and the creep behaviour of titanium aluminides.