Validation of Multicomponent Diffusivities Using One Diffusion Couple

An experimental method involving one diffusion couple is described for measuring a column of coefficients in the matrix of a multicomponent, square root diffusivity. An example is given for a quaternary Ni-4at.%Cr-6at.%Al-4at.% Mo alloy at 1100 °C in which coefficients from the Mo column were determined and compared with those measured using three diffusion couples. For two of the diffusion coefficients, the agreement was within 1%, while for the third coefficient there was nearly a 40% difference. That difference was directly related to an error in one of the diffusion couple alloy compositions. A discussion is given as to how the single column of square root diffusivities can be used to partially validate a predicted diffusivity obtained from semi-empirical thermodynamic and mobility databases.