A kinetic model for estimating the boron activation energies in the FeB and Fe_2B layers during the gas-boriding of Armco iron: Effect of boride incubation times

摘要

The present work deals with a simulation of the growth kinetics of boride layers grown on Armco iron substrate. The formed boride layers (FeB + Fe_2B) are obtained by the gas-boriding in the temperature range of 1073-1273 K during a time duration ranging from 80 to 240 min. The used approach solves the mass balance equations at the two growing fronts: (FeB/Fe_2B) and (Fe_2B/Fe) under certain assumptions. To consider the effect of the incubation times for the borides formation, the temperature-dependent function Φ(T) was incorporated in the model. The following input data: (the bonding temperature, the treatment time, the upper and lower values of boron concentrations in FeB and Fe_2B and the experimental parabolic growth constants) are needed to determine the boron activation energies in the FeB and Fe_2B layers. The obtained values of boron activation energies were then compared with the values available in the literature. Finally, a good agreement was obtained between the simulated values of boride layers thicknesses and the experimental ones in the temperature range of 1073-1273 K.