Abstract
The mechanical behaviour of a γ-TiAl alloy and its microstructural evolution are investigated in this work. The alloy has a nominal composition of Ti-46.5Al-4(Cr, Nb, Ta, B) (at. %) and presents twophase near lamellar microstructure (y-TiAl + α 2 -Ti 3 Al) with the presence of a minor third phase B2. Quasistatic compression tests (e = 10 -3 s -1 ) were performed on a universal testing machine while dynamic compression tests (i: ≥ 2 10 3 s -1 ) were conducted on a split-Hopkinson bar. The tests were realised at temperatures ranging from 20°C to 600°C. The microstructure evolution has been studied by transmission electron microscopy. The plastic deformation has been mainly localised in the γ-TiAl phase. The latter is characterized by high density of twins and dislocations. A quantitative analysis of these defects has been managed to correlate the mechanical properties to the microstructure of the material. It has been stated that the alloy presents a good balance between strength and ductility. The near lamellar structure is sensitive to the strain rate which can be related to the dislocations and twinning activity. The flow stress shows positive temperature dependence known as strength anomaly. This anomaly is connected to the pinning of mobile dislocations by obstacles. The high density of twins and their intersections contribute to the occurrence of the anomaly.
Published Version
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