Ion‐beam mixing at Ni‐Si interfaces was studied as a function of dose, temperature, and dose rate. In the temperature range 10–443 K, the thickness of the mixed Ni‐Si layer grew proportionally to the square root of dose for 250‐keV Ar+and 280‐keV Kr+irradiations. The apparent diffusion coefficient for mixing during irradiation comprises temperature‐dependent and independent contributions. The activation enthalpy for the temperature‐dependent part is ∼0.09 eV. Varying the dose rate by a factor of ∼20 had little effect upon mixing at either 80 or 368 K. Analysis of these results using chemical rate theory showed that the low activation enthalpy for diffusion was not associated with point‐defect motion. More likely the temperature dependence of mixing in Ni‐Si is associated with the effect of temperature on compound formation. The results for mixing at 10 K in Ni‐Si were compared with those in Ni‐Al, at 10 K, to study the effect of crystal structure on displacement mixing.