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 °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 12,000 h. The diffusion coefficient (DNi) of nickel in cold-worked carbon steel was determined by extrapolating the concentration-dependent interdiffusion coefficient to 0% of nickel. The temperature dependence of DNi is expressed by DNi = (4.5 + 5.7/−2.5) × 10−11 exp (−146 ± 4 kJ mol−1/RT) m2s−1. The value of DNi at 320 °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.