Investigation of Growth Kinetics of Fe₂B Layers on AISI 1518 Steel by the Integral Method

Abstract

The AISI 1518 steel was pack-borided in the temperature range 1123–1273 K for a treatment ranging from 2 to 8 h. A compact single boride layer (Fe2B) was formed at the surface of the AISI 1518 steel using the mixture of powders composed of 20 % B4C, 10 % KBF4 and 70 % SiC. The following experimental techniques such as scanning electron microscopy coupled with EDS analysis and X-ray diffraction analysis were employed to characterize the pack-borided AISI 1518 steel. An alternative model, based on the integral mass balance equation, was used to estimate the boron diffusion coefficients in the Fe2B layers in the temperature range 1123–1273 K. Finally, the value of activation energy for boron diffusion in the AISI 1518 steel was estimated and compared with the literature data. Furthermore, the present model was validated by comparing the experimental value of Fe2B layer thickness, obtained at 1253 K for 2 h of treatment, with the predicted value.

Boriding Kinetics of FeB and Fe2B Layers on AISI M2 Steel by the Integral Diffusion Model

“…A particular solution of the resulting DAE system from the integral method was developed to estimate the values of boron diffusion coefficients in the FeB and Fe2B layers on AISI M2 steel in the temperature range 1173-1323 K. Recently, the integral model was successfully applied to analyze the kinetics of formation of Fe2B layers on different substrates [17][18][19][20][21][22]. The value of boron diffusivity in Fe2B was found to be directly proportional to the square of parabolic growth constant at the considered interface.…”

“…The two ordinary differential equations given by Equations (18) and (19) are obtained from the integration of Second Fick's law between the two limits 0 and u(t) for FeB, and between u(t) and v(t) for Fe2B.…”

“…In the same manner, the second algebraic constraint can be obtained from the continuity equation at the (Fe2B/substrate) interface as follows: (17), (18), (19), (20) and 21constitute a DAE system to be solved. The variables a1(t), a2(t), b1(t), b2(t), u(t) and v(t) should verify the algebraic constraints given by Equation (16), (17), (20) and (21) at boride incubation time t0(T) if the values of boron diffusion coefficients in FeB and Fe2B are known.…”

Characterization and Boronizing Kinetics of EN-GJL-250 Lamellar Gray Cast Iron

“…This kinetic approach, based on the integral diffusion model, Türkmen et al [12] was adopted to be applied for the growth kinetics of entire boride layer (FeB+Fe2B) formed on the lamellar gray cast iron substrate. The integral diffusion model has been successfully used to simulate the kinetics of Fe2B layers on different substrates [12][13][14][15][16][17][18]. The developed boron concentration-profile through the entire boride layer is schematically shown in Figure 1.…”

“…The assumptions considered during the formulation of this diffusion model were given elsewhere [12][13][14][15][16][17][18]. The initial and boundary conditions for this diffusion problem are represented as:…”