Kinetics of the formation of Fe_2B layers in gray cast iron: Effects of boron concentration and boride incubation time

摘要

The growth kinetics of Fe_2B layers formed at the surface of gray cast iron were evaluated in this study. The pack-boriding process was applied to produce the Fe_2B phase at the material surface, and the variables included three temperatures (1173,1223 and 1273 K) and four exposure times (2,4,6 and 8 h). Taking into account the growth fronts obtained at the surface of the material and the mass balance equation at the Fe_2B/substrate interface, the boron diffusion coefficient on the borided phase was estimated for the range of treatment temperatures. Likewise the parabolic growth constant, the instantaneous velocity of the Fe_2B/substrate interface, and the weight gain in the borided samples were established as a function of the parameters τ(t) and α(C), which are related to the boride incubation time (t_0(T)) and boron concentration at the Fe_2B phase, respectively. Observation of the growth kinetics of the Fe_2B layers in gray cast irons suggest an optimum value of boron concentration that is in good agreement with the set of bonding experimental conditions used in this work.