Additive manufacturing (AM) processes increasingly establish themselves as an alternative manufacturing route to investment casting and conventional forging for making complex aircraft components out of γ-TiAl alloys.
Due to the process-related high and short-time energy input, extremely fast cooling rates occur and internal stresses can result. For high niobium containing multiphase alloys, major problems and questions arise with regard to understanding the process and the processing parameters. An understanding of the phase evolution and phase transformations that take place cannot be accomplished using classical metallographic methods.

This study investigates the effect of different cooling and heating cycles on phase formation and phase evolution in a high niobium containing Ti-46Al-9Nb (composition in at.%) alloy. We performed in situ high-energy X-ray diffraction experiments at the Hereon beamline HEMS at Petra III at DESY, Hamburg. Using in situ experiments, it was possible to determine the influence of the cooling rate on the lattice parameters, phase fractions, and to observe structural changes in the crystal structure and site occupation for all phases present α/α₂, β/β_o and γ/γ_m. In addition, it was possible to investigate the development of internal stresses directly as a function of the cooling rate.