Interdiffusion in the Ti-rich phases of the Ti-Al system

The interdiffusion coefficient ((D) over tilde) has been measured in the temperature range from 1442 to 1639 K as a function of the composition in the alpha (hexagonal close-packed, A3), alpha(2) (ordered hexagonal, D0(19)), beta (body-centred cubic, A2) and gamma (ordered face-centred cubic, L1(0)) phases of the Ti-Al system. The concentration profiles were obtained by electron probe microanalysis, and the chemical diffusivity was extracted from the concentration profiles by the Boltzmann-Matano procedure. In all the phases the interdiffusion coefficients increase with increasing Al contents. This increase is large in the disordered phase alpha, but much smaller in the ordered phases alpha(2) and gamma.