Microstructure and properties of TiAl processed via an electron beam powder bed fusion capsule technology

Titanium aluminide (TiAl) alloys are considered for high-temperature applications at a progressive rate and processing issues become increasingly important. Especially β-solidifying TiAl alloys are subjected to extensive research activities. In our research, we assessed a novel manufacturing technique combining electron beam powder bed fusion (PBF-EB/M) for manufacturing near net shape capsules and hot isostatic pressing (HIP) for consolidating sintered powder particles inside the capsule. This novel processing route is intended to overcome the disadvantages from PBF-EB/M process (heterogeneous aluminum evaporation during melting) and HIP process (formation of shell structures at particle boundaries). The formation of shell structures at previous particle boundaries (PPB) is a phenomenon typically related to powder metallurgy (PM). In this study a β-solidifying TiAl alloy, termed TNM, with a nominal composition of Ti-43.5Al–4Nb–1Mo-0.1B (in atomic percent, at.%) is used as raw material. Additively manufactured capsules containing sintered powder particles are hot isostatic pressed to the final part dimension. Microstructures from both, powder particles as well as consolidated material, are presented in detail regarding aluminum (Al) evaporation and the formation of shell structures. The mechanical properties of produced specimen are compared to results from conventional manufacturing techniques. In summary, our results reveal the capability of the novel PBF-EB/M capsule technology approach. •Fabrication of TiAl by an electron beam powder bed fusion capsule technology.•Microstructure heterogeneity.•Shell formation results from a reduced Al content.•Al depleted zone is caused by Al evaporation in the heating step of PBF-EB/M.