Modelling boron diffusion for Fe₂B layer formation: comparative kinetics analysis in pack-boronized AISI 4147 steel

Abstract

In this current research paper, the modelling of boron diffusion during the powder-pack boronizing was achieved by utilizing two kinetics approaches: the integral method and average diffusion coefficient (ADC) method. This integral method used a general solution of algebraic differential equations (DAEs) system. The powders mixture composed of: 33.5 wt% B4C, 5.4 wt% KBF4 and 61.1 wt% SiC was employed to generate the Fe2B layers on AISI 4147 steel in the interval of 1123–1273 K for 2–8 h. The obtained surface layers have been characterized by Scanning electron microscopy (SEM) to examine the growth front with a typical saw-toothed morphology. The crystalline nature of boride phase has been verified by X-ray diffraction technique (XRD). The calculation results arising from the two models led to the similar boron activation energy in Fe2B equal to 196.19 kJ mol−1. Additionally, both models were checked out empirically by selecting three extra boronizing conditions obtained at 1273 K for increasing times (2.5, 4.5 and 8.5 h). The predicted layers’ thicknesses were found to be in line with the experimental results.