Relationship Between Microstructure and Mechanical Properties of β-Containing TiAl Alloys Fabricated By Additive Manufacturing

In recent years, TiAl alloys containing the β phase are expected to expand the application scope of the alloys due to their superior mechanical properties at high temperatures. Electron beam powder bed fusion (EB-PBF) that is one of the additive manufacturing processes for metallic materials has attracted much attention as a fabrication process of TiAl alloy parts for aerospace applications with complex geometries. Furthermore, it is possible to obtain unique microstructures by repeated and rapid fusion and solidification during the EB-PBF process, resulting in excellent mechanical properties. In the present study, relationships between microstructure and mechanical properties of β-containing TiAl alloys prepared by the EB-PBF process were investigated focusing on the influence of the input energy density. Specimens fabricated at low energy densities contain ultrafine lamellar structure composed of the α₂ and γ phases, together with the β/γ cells discontinuously precipitated at the lamellar grain boundary. The ultrafine lamellar grains and the β/γ cells are effective in increasing strength and ductility of the alloys, respectively. In addition, we developed new heat treatment processes to control the morphology of the microstructure. The alloys subjected to optimum heat treatments exhibit higher strength and larger ductility at 1023 K, compared with the cast alloys.<br/><br/>This work was supported by Council for Science, Technology and Innovation(CSTI), Cross-ministerial Strategic Innovation Promotion Program (SIP), “Materials integration” for revolutionary design system of structural materials” (Funding agency: JST).