Due to their low density (4 g per cm3), good oxidation and corrosion resistance and high specific tensile and creep strength, γ-TiAl based alloys recently have started to replace Ni-based superalloys as a material for turbine blades in aircraft engines. TiAl alloys in the range of 39 – 45 at.% Al usually contain the ordered phases γ and α2 at lower and disordered alpha at higher temperatures. Depending on alloy composition and temperature additionally disordered β-Ti(Al) (A2 structure) or ordered βo-TiAl (B2 structure) can occur. The ductile high temperature β phase is important for the processing of the material while the low temperature βo phase is said to embrittle the material at service temperature.
We used the good contrast of neutron diffraction for ordering and disordering of TiAl-based alloys to determine the order/disorder temperatures which are not accessible by other methods like DSC measurements. Three binary TiAl alloys (Ti-xAl with x = 39, 42 and 45) and five alloys with additional alloying elements (Ti-42Al-2Y with Y = Nb, Mo, Ta, Cr and Fe) were used to investigate the influence of different Al concentrations and alloying additions on the kinetics of the occurring ordering/disordering reactions and phase transformations. In the presentation new results of neutron diffraction experiments and microstructure investigations by scanning electron microscopy will be shown.