Influence of Input Energy Density on Morphology of Unique Layered Microstructure of γ-TiAl Alloys Fabricated by Electron Beam Powder Bed Fusion

Microstructure and tensile properties of Ti–48Al–2Cr–2Nb (at%) rods fabricated by electron beam powder bed fusion (EB-PBF) process were investigated by changing input energy density (ED) which is one of the important factors affecting formation of the melt pool. We found that unique layered microstructure consisting of an equiaxed γ grain layer (γ band) and a duplex region can be formed by EB-PBF with ED in the range of 13 to 31 J/mm3. It is interesting to note that the width of the γ band and the volume fraction of the γ phase in the duplex region decrease with increasing ED. On the other hand, the α2/γ lamellar grain in the duplex region increases with increasing ED. These morphological changes in the layered microstructure are attributed to variation of temperature distribution from melt pool caused by increasing ED. Moreover, we also found for the first time the strength of the alloys can be improved by decreasing width of the γ band and increasing of the α2/γ lamellar grain in the duplex region. Whereas, the width of the γ band and the fraction of the equiaxed γ grain in the duplex region should be increased to enhance ductility of the alloys.