Influence of input energy density on morphology of unique layered microstructure of γ-TiAl alloys fabricated by electron beam powder bed fusion

Abstract

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 fac-tors 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/mm 3 . It is in-teresting 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 α 2 / 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 α 2 / 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.