  Diffusion in ternary, multiphase systems was studied theoretically and
experimentally in Ni-Cr-Al system at 1200C. The samples were prepared by the
multiple method. It has been shown that the method allows obtaining good
quality, planar, reproducible and oxide-free diffusion couples. For the first
time the concentration profiles were measured by the wide-line EDS analysis.
Two models were applied: 1) multi-phase multi-component model based on the
bivelocity method in R1 and 2) dual-scale two-phase model, that includes
interdiffusion in matrix (global scale in R1) and the diffusion between matrix
and precipitates (local scale in R3). The models were used in numerical
experiments in which the diffusion paths, the local entropy production rate and
the volume fractions of the phases present in the system were calculated. For
the first time the Kirkendall plane shift in two-phase system was computed and
compared with experimental findings. It has been shown that both models are
consistent. The multi-phase, multi-component model was applied to simulate
diffusion and the results were compared with experiment. Experimental and
numerical results are in agreement. It has been found that: 1) the type 0
interphase boundary (IB) moves during diffusion, contrary to the Morral
theorem, 2) in the case when the terminal compositions of the two-phase alloys
are close to the phase boundary then the single beta-phase zone can grow
between two-phase zones and diffusion path enters the single-phase region, 3)
the diffusion path strongly depends on the shape of the phase boundary line and
the accuracy of thermodynamical data is a key factor in modelling and 4) the
recently reported occurrence of the local extrema in the distribution of
entropy production at the IBs is a result of numerical errors and can be
eliminated as is shown in dual-scale two-phase model.
