Growth Kinetics of Boronized Layers and the Diffusion Zone in the Iron-Based A286 Superalloy with the Taylor Expansion Model

This work addresses the modelling of growth kinetics for FeB, Fe₂B, and the diffusion zone formed after the solid boriding of the iron-based A286 superalloy. A novel kinetic model was developed to analyze the boron diffusion in this multi-layer system, with a non-linear boron distribution in each phase. The boron concentration profile within each phase was expressed as a function expanded in a second-order Taylor series. Subsequently, the proposed model was used to assess the boron diffusion coefficients in the FeB and Fe₂B layers, as well as in the diffusion zone (DZ), using experimental data from the literature. As a result, the boron activation energies in the FeB, Fe₂B, and DZ layers were determined to be 176.69, 201.05, and 207.80 kJ mol^–1, respectively. Additionally, the experimentally measured layer thicknesses were compared with the predicted values, validating the developed model.