Effect of Scan Speed on Microstructure and Tensile Properties of Ti–48Al–2Cr–2Nb Alloys Fabricated via Additive Manufacturing

Abstract

The morphology of microstructure and tensile properties of Ti–48Al–2Cr–2Nb (at%) alloy rods fabricated by the electron beam powder bed fusion (EB-PBF) process were investigated with a particular focus on the influence of scan speed of the electron beam. Homogeneous near lamellar structure composed of the α₂ and γ phases can be obtained in the rod fabricated under the slowest scan speed. The fine lamellar spacing which contributes to the high strength of the alloy is derived from the fast-cooling rate of EB-PBF. On the contrary, a layered microstructure comprising a duplex-like region and an equiaxed γ grain layer (γ band) perpendicular to the building direction is obtained when increasing scan speeds. We observed for the first time that an increase in the scan speed results in a narrow width of the γ band. We also found that these microstructural changes have a significant influence on the mechanical properties of the rods. The near lamellar structure exhibits higher strength compared to the layered microstructure. Whereas, the rods with the layered microstructure show large ductility at room temperature. The elongation of each rod strongly depends on the width of the γ band owing to the preferential deformation of the γ band.