Solidification characteristics of high Nb-containing γ-TiAl-based alloys with different aluminum contents

The effect of Al content on the microstructure and solidification characteristics of Ti–Al–Nb–V–Cr alloys in as-cast and isothermally treated states was investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) equipped with energy dispersive spectroscope (EDS), and transmission electron microscopy (TEM). The typical solidification characteristics are due to the joint influence of both the crystal temperature range and the solidification path. The wide crystallization temperature range contributes to obtaining coarse dendrites in the as-cast Ti47Al7Nb2.5V1.0Cr (at%) alloy solidifying through the peritectic reaction. The β-solidifying Ti46Al7Nb2.5V1.0Cr (at%) alloy with the narrow crystallization temperature range is attributed to the formation of a homogeneous fine-grained microstructure. However, the crystallization temperature range of Ti48Al7Nb2.5V1.0Cr (at%) alloy is equivalent to that of Ti46Al7Nb2.5V1.0Cr alloy, but it is solidified by peritectic reaction, leading to the formation of finer dendrites.