Peculiar microstructural evolution and tensile properties of β-containing γ-TiAl alloys fabricated by electron beam melting

Abstract

The microstructure and tensile properties of β-containing Ti–44Al–4Cr alloy rods additively manufactured by electron beam melting (EBM) process were examined as a function of input energy density determined by the processing parameters. To the best of our knowledge, this is the first report to demonstrate that two types of fine microstructures have been obtained in the β-containing γ-TiAl alloys by varying the energy density during the EBM process. A uniform α 2 /β/γ mixed structure containing an α 2 /γ lamellar region and a β/γ dual-phase region is formed at high energy density conditions. On the other hand, a lower energy density leads to the formation of a peculiar layered microstructure perpendicular to the building direction, consisting of a ultrafine α 2 /γ lamellar grain layer and a α 2 /β/γ mixed structure layer. The difference in the microstructures originates from the difference in the solidification microstructure and the temperature distribution from the melt pool, which are dependent on the energy density. Furthermore, it was found that the strength of the alloys is closely related to the volume fractions of the β phase and the ultrafine α 2 /γ lamellar grains which originates from the massive α grains formed by rapid cooling under low energy density conditions. The alloys with high amounts of these peculiar microstructures exhibit high strength comparable to and higher than the conventional β-containing γ-TiAl at room temperature and 1023 K, respectively.