Effect of Product Shape on Microstructure and Mechanical Properties of Ti-48Al-2Cr-2Nb Alloys Fabricated by Additive Manufacturing

Additive manufacturing is one of highly efficient processes to fabricate TiAl low pressure turbine blade. In the present study, large triangular prisms and small cylindrical rods of Ti-48Al-2Cr-2Nb alloys were prepared by electron beam powder bed fusion (EB-PBF) to examine the effect of product shape on the microstructure and mechanical properties. The microstructure after EB-PBF depends on the process parameter such as beam current and scanning speed. Under an optimum condition, peculiar banded structure composed of duplex-like structure and equiaxed γ grains (γ band). Such microstructure is homogeneously formed in cylindrical rods 10 mm in diameter. On the other hand, in the case of the triangular prisms, the microstructure vary from area to area. In the thick area, the banded structure is formed, while typical lamellar structure composed of the α₂ and γ phases can be seen in the thin area. It is also noted that hardness distribution was also inhomogenous depending on the microstructure. In EB-PBF process, an electron beam moves showing a snake pattern. In the thin area, the beam moves forth and back quickly, resulting in an increase in temperature. This leads to the formation of the lamellar structure. In order to get homogeneous microstructure throughout the triangular prisms, the process parameter is changed from area to area. As a result, homogeneous microstructure consisting of the banded structure was formed and the hardness distribution of the triangular prisms also became homogeneous.