Interdiffusion of the platinum-group metals in nickel at elevated temperatures

Rates of interdiffusion of the platinum group metals Ir, Pd, Pt, Rh and Ru with nominally pure nickel have been characterised. Interdiffusion coefficients are estimated by analysing the measured diffusion profiles. In the composition range studied (no greater than 10 wt.% of the platinum group metal), the interdiffusion coefficients display little concentration dependence, but the values can differ by an order of magnitude. In order to rationalise the dependence of the interdiffusion coefficient on atomic number, the data are compared with values for other elements which are already in the literature. A systematic trend is observed: elements furthest from the centre of the period display the largest values and elements at the centre the smallest. It appears therefore that the magnitude of the interdiffusion coefficient correlates strongly with the atomic radius of the interdiffusing transition metal species. Our results suggest the existence of a binding energy between the vacancies and the impurity species. We believe that the interdiffusion data are of considerable use to those designing new and novel grades of superalloy for high temperature applications.