On the Mechanical Behavior and Microstructural Evolution of a TiAl Alloy under Quasistatic and Dynamic Compression

摘要

The mechanical behavior 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 two-phase duplex microstructure (γ + α _2) with the presence of a minor third phase B2. Quasistatic compression tests (ε = 10~(-3) s~(-1)) were performed on a universal testing machine while dynamic compression tests (ε ≥ 2 10~3 s~(-1)) were conducted on an split-Hopkinson bar equipment. The tests were made at temperatures ranging from 20 °C to 500 °C. The microstructural observations on transmission electron microscope were made in order to correlate the mechanical properties to the microstructure of the material. The duplex alloy presents a good combination of mechanical resistance and ductility. The duplex alloy is sensitive to the strain rate which can be correlated to the twinning activity. The flow stress shows a positive temperature dependence known as strength anomaly. This anomaly is connected to the pinning of mobile dislocations by different obstacles. In this paper it is shown that a high density of twin and their intersections can contribute to the occurrence of the anomaly.