Assessment of the capability of Zr, Y, La, Gd, Dy, C, and Si to enhance the creep strength of gamma titanium aluminide alloys based on their effect on flow stress and thermal activation parameters

Abstract

The present work examines the capacity of the elements Zr, Y, La, Gd, Dy, C, and Si to increase the structural stability and creep strength of γ titanium aluminide alloys. The elements were alloyed for this purpose to the base material Ti-44at.%Al-5at.%Nb, and were transformed into four different states of precipitate dispersions via thermomechanical treatment. The resulting materials were deformed in compression at room temperature as well as at 1023 and 1173 K. Strain-rate cycling was performed during the tests to determine the associated flow stresses and the reciprocal activations volumes of plastic deformation. This information has been used to estimate the impact of the precipitates on the athermal component of the flow stress, which significantly influences the creep properties. The results indicate that only the elements C and Si are able to effectively enhance the creep strength in the long term. The element C forms Ti3AlC precipitates, which lead to a considerable increase of the athermal stress component, whereas Si forms Ti5Si3 precipitates leading to a moderate increase of the athermal stress component but a comparatively stable microstructure. Moreover, it appears that the strengthening effects could be increased by using higher additions of C or Si.