Rapid nickel diffusion in cold-worked carbon steel at 320-450 °C

The diffusion coefficient of nickel in cold-worked carbon steel was determined with the diffusion couple method in the temperature range between 320 and 450 degrees C. Diffusion couple was prepared by electro-less nickel plating on the surface of a 20% cold-worked carbon steel. The growth in width of the interdiffusion zone was proportional to the square root of diffusion time to 12,000h. The diffusion coefficient (D-Ni) of nickel in cold-worked carbon steel was determined by extrapolating the concentration-dependent interdiffusion coefficient to 0% of nickel. The temperature dependence of D-Ni is expressed by D-Ni = (4.5+5.7/-2.5) x 10(-11) exp (-146 +/- 4 kJ mol(-1)/RT) m(2)s(-1). The value of D-Ni at 320 degrees C is four orders of magnitude higher than the lattice diffusion coefficient of nickel in iron. The activation energy 146 kJ mol(-1) is 54% of the activation energy 270.4 kJ mol(-1) for lattice diffusion of nickel in the ferromagnetic state iron.