EFFECT OF MN DOPING ON CHARGE-DENSITY IN GAMMA-TIAL BY QUANTITATIVE CONVERGENT-BEAM ELECTRON-DIFFRACTION

The intermetallic compound TiAl with and without 5 at.% manganese, has been studied by energy filtered convergent beam electron diffraction (CBED) in a transmission electron microscope. The addition of Mn is known to be beneficial for the mechanical properties of this material. The aim has been to investigate whether this effect is followed by detectable changes in electronic structure, with the focus on bonding. From the positions of high-order Laue zone lines in the centre disc, the lattice tetragonality is found to decrease with the addition of Mn. By ALCHEMI studies, Mn is found to substitute randomly on Ti and Al sites. The structure factors are determined using multiparameter least-square minimization based on fitting between experimental and calculated intensity profiles. The X-ray structure factors for the nine lowest order reflections have been derived for doped and undoped material. The uncertainty is typically 0.3%, and is best for the strong, lowest order reflections. The electron deformation density maps show that the effect of doping with Mn is to draw charge away from nearest-neighbour covalent bonds and redistribute it more uniformly between second nearest neighbours which may enhance ductility.