Atom location by channeling enhanced microanalysis study of site distributions of alloying elements in titanium aluminides

The original equation of Spence and Tafto for quantitative determination of site occupancy using atom location by channeling enhanced microanalysis me thod has been extended to take into account both delocalization effect and the influence of point defects (antisite atomic distribution and vacancies) . The outcome of this treatment suggests that, for crystals free of antisit e defects, the accuracy of site occupancy is influenced by delocalization e ffect but is independent of both thermal and structural vacancies. For crys tals free of structural vacancies, the accuracy of site occupancy is influe nced by both delocalization effect and antisite defects, but is independent of thermal vacancies. The delocalization effect was shown to vary with cha nneling strength at a given channeling condition. For a binary ordered phas e in which at least one of the host elements exhibits weak delocalization e ffect las is the case for many transition-metal aluminides), a tangent-line method for obtaining the value of k (a parameter necessary for the calcula tion of site occupancy) was proposed, allowing the determination of the del ocalization correction factor for the other host element. Application of th is method to estimating the delocalization effect of Al in Ti3Al and TiAl u nder axial and planar channeling conditions, respectively, was demonstrated .