Ti–48Al–2Cr–2Nb alloys prepared by electron beam selective melting additive manufacturing: Microstructural and tensile properties

Abstract

Here, an electron beam selective melting (EBM) technique was employed to shape Ti–48Al–2Cr–2Nb alloy to combat its intrinsic brittleness and insufficient hot workability. Through process optimization, high-density samples (4.2327 g/cm3) were produced. First, the mechanism of interaction between phase transformation and microstructural evolution of EBM-formed Ti–48Al–2Cr–2Nb alloy was investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), and electron backscattering diffraction (EBSD). And then, the mechanism of interaction between tensile properties and microstructural evolution of EBM-formed Ti–48Al–2Cr–2Nb alloy was discussed. Based on the results, the microstructure consists of coarse equiaxed grains and fine lamellar grains, which gradually coarsen from upper to bottom. As the thickness of the layer increases from upper to bottom, the content of the B2 phase increases continuously, with a predominant component of TiAl and a small amount of Ti3Al and B2 phases. The majority of the γ-TiAl phase does not exhibit significant texture, while the α2-Ti3Al phase shows a texture of (0001) with 19.32 times the random intensity, and its c-axis is parallel to the deposition direction. Benefiting from its unique structure features, the maximum room temperature tensile strength of as-deposited Ti–48Al–2Nb–2Cr alloy reaches 854.6 MPa with an elongation of over 2%. And the maximum high-temperature tensile strength of EBM-formed Ti–48Al–2Nb–2Cr alloy reaches 707 MPa at 650 °C with an elongation over 3.5%. According to these results, the mechanical properties of our EBM Ti–48Al–2Cr–2Nb alloy are superior to those previously reported.

Keywords

• Electron beam selective melting
• TiAl alloys
• Microstructure evolution
• Phase transformation
• Mechanical properties