Interdiffusion in ternary Co-Cr-AI alloys

The description of interdiffusion in a ternary system requires four composition-dependent diffusion coefficients which together form a coefficient matrix. The values of this matrix have been determined for a wide rangeof compositions in the cobalt solid solution of the Co-Cr-AI system at 1100°C. This was achieved by annealing infinite diffusion couples between appropriate pairs of alloys and determining the resulting concentration profiles by electron-probe X-ray microanalysis. The diffusion coefficients obtained agreed with expectations based on the results of previous studies of related systems. All four coefficients were found to vary systematically with composition, as illustrated by contour maps. However, this did not fit theoretical predictions based on the Wagner dilute solution model. Certain anomalous results were explained on the basis of the formation of non-equilibrium vacancy concentrations.