The accuracy of this equation, when used to deduce grain-boundary diffusion coefficients from experimentally determined solute distributions, was studied for various ranges of the experimental variables:  = [(D’/D)-1]a/Dt and  = y/Dt. The accuracy was assessed by first obtaining the value of  which was found by applying the LeClaire relationship to a solute distribution that had been numerically estimated from Whipple’s exact solution to the diffusion problem. The calculated value was then compared with the true  value upon which the gradient had been based. The relative errors which resulted from the application of LeClaire’s equation were found to be less than 10% over the range of conditions ( greater than 10, / between 2 and 20) which constituted the claimed field of applicability. It was found that the method yielded very inaccurate grain-boundary diffusivities when  and / were less than 2. It was concluded that especial care had to be taken, when selecting ranges of  and /, if the application of LeClaire’s relationship was to provide reliable values of the grain-boundary diffusion product, aD’, on the basis of measured diffusion gradients.

Y.C.Chung, B.J.Wünsch: Materials Letters, 1996, 28[1-3], 47-54