Ordering and disordering of β/βo-phase in γ-TiAl based alloys investigated by neutron diffraction

TiAl based alloys are desirable materials for turbine blades in aircraft engines. Depending on alloy composition and temperature additionally disordered β-Ti(Al) (A2 structure) or ordered βo-TiAl (B2 structure) can occur. Unfortunately little is known about the exact order/disorder transformation temperatures of β/βo. We used the good contrast of neutron diffraction for ordering and disordering of TiAl alloys to determine the order/disorder temperatures, which are not accessible by other methods like DSC measurements. Several binary TiAl alloys as well as alloys with additional alloying elements were used to investigate the influence of different Al concentrations and alloying additions on the occurring ordering/disordering reactions and phase transformations. As a result ordered βo phase was found only in selected ternary alloys.