Abstract: TiAl alloys fabricated by electron beam powder bed fusion (EB-PBF) usually exhibit special microstructures with alternating fine-grained (FG) regions and coarse-grained (CG) bands. In previous studies, the CG microstructures were equiaxed γ phases, and the FG microstructures presented three types: near gamma, duplex, and nearly lamellar. However, the rule for controlling FG microstructures has not been found. Hence, a method needs to be built to find the rule for controlling FG microstructures. Here, we established a normalized process diagram by combining Al-equivalent and dimensionless process parameters. Based on the normalized process diagram, we successfully control the FG microstructures and customize three FG microstructures of the Ti-48Al-2Cr-2Nb alloy. Meanwhile, the average tensile yield strength reaches 756 MPa when the FG microstructure is near gamma. The yield strength is higher than the previous data for the Ti-48Al-2Cr-2Nb alloy. This is attributed to the strong interface-strengthening effect between FG near-γ microstructures and CG γ bands. These findings can help shorten the research time of the other TiAl alloys fabricated by EB-PBF, improving the mechanical properties of the other EB-PBF-built TiAl alloys in the future.

Key words: TiAl alloy, Additive manufacturing, Electron beam powder bed fusion, Normalized process diagram, Microstructure, Tensile strength