Solvent diffusion in various alloys was studied using the Kriukow-Shukowitzky method and the substitute tracer, Co (table 176). The enhancement of solvent diffusion was almost linear for the substitutional alloys at low concentrations but became non-linear at much higher impurity concentrations. It was suggested that second-order complexes governed the diffusion behavior and that the free enthalpy of the C atoms was considerably reduced if 2 adjacent impurity atoms were bound to each other and to a vacancy. This led to a strong attractive impurity-impurity-vacancy interaction, whereas impurities with a positive excess charge repelled each other but were also attracted by the vacancy.

C.Kostler, F.Faupel, T.Hehenkamp: Scripta Metallurgica, 1986, 20[12], 1755-9

Table 176

Diffusion of 60Co in Ni-C Alloys at 1366K