Evaluation of the effective diffusion coefficient of boron in the Fe2B phase in the presence of chemical stresses

Abstract

Abstract In this work, the effective diffusion coefficient of boron in the Fe2B phase was evaluated by considering the effect of chemical stresses in the case of paste-boriding of AISI 4140 steel. Two kinetic approaches were proposed to evaluate the diffusion coefficient of boron in the Fe2B phase in the temperature range of 1 123–1 273 K, and considering the effect of the boride incubation times. By applying the mass balance equation at the (Fe2B/substrate) interface and the theory of elasticity, it is possible to determine the effective diffusion coefficient of boron in the Fe2B phase. The obtained value of activation energy of boron diffusion in the presence of chemical stresses was estimated as 158.78 kJ mol−1 using the experimental parabolic growth constants taken from the literature. In addition, the simulated values of effective diffusion coefficients of boron in the Fe2B phase are found to be sensitive to the change in the boriding temperature and to the increase in the upper boron content in the Fe2B phase within its composition range