Diffusion model for growth of Fe₂B layer in pure iron

A simple diffusion model is proposed to estimate the growth kinetics of Fe₂B layers created at the surface of pure iron. This model employs the mass balance equation at the Fe₂B/substrate interface to evaluate the boron diffusion coefficient (D_Fe2B) in the boride layer. The Fe₂B layers were formed using the paste boriding process, at four temperatures with different exposure times. Analysing the results, the evolution of the parabolic growth constant (k) of the Fe₂B layer is presented as a function of boron concentration and boride incubation time [t0(T)]. Furthermore, the instantaneous velocity of the Fe₂B/substrate interface and the weight gain of borided pure iron were estimated for different boriding temperatures. Finally, to validate the diffusion model, the boride layer thicknesses were predicted and experimentally verified for two boriding temperatures and for different treatment times.