Diffusion of tungsten in α-iron

Tracer diffusion coefficient of 181W in α-iron has been determined in the temperature range between 833 and 1173 K using a serial sputter-microsectioning method. The temperature dependence of the diffusion coefficient, D, over the whole temperature range of α-iron across the Curie temperature (T C = 1043 K), can be expressed by where s is the ratio of the spontaneous magnetization at T K to that at 0 K. The factor 0.086 in the above equation is smaller than 0.156 for the self-diffusion, showing that the influence of the magnetic transformation on the diffusion of tungsten in α-iron is smaller than that on the self-diffusion. The activation energy 287 kJ/mol for tungsten diffusion in the paramagnetic iron is much higher than 250.6 kJ/mol for the self-diffusion. Atomic size effect is predominant in the activation energies for diffusion of transition elements in the paramagnetic α-iron.