A model for studying the kinetics of the formation of Fe2B boride layers at the surface of a gray cast iron

The present work estimates, using a kinetic model, the growth kinetics of Fe2B boride layers generated at the surface of a gray cast iron via the powder-pack boriding considering three different temperatures (1173, 1223 and 1273 K) and four treatment times (2, 4, 6 and 8 h). By the use of the mass balance equation at the (Fe2B/substrate) interface under certain assumptions and considering the effect of the boride incubation time, it was possible to estimate the corresponding parabolic growth constant in terms of two parameters α(CupFe2B) and β(T) depending on the boron content in the Fe2B phase and on the process temperature, respectively. The mass gain at the material surface and the instantaneous velocity of the (Fe2B/substrate) interface were also estimated. A fairly good agreement was observed between the experimental parabolic growth constants taken from a reference work (Campos-Silva et al., Characterization of boride layers formed at the surface of gray cast irons, Kovove Mater. 47 (2009) 1-7.) and the simulated values of the parabolic growth constants. Furthermore, the boride layer thicknesses were predicted and experimentally verified for three process temperatures and four treatment times.