1.4 Fe2B layer's thicknesses

The estimation of the Fe2B layers' thicknesses can be determined through the Eqs. (35) and (36).

• Steady state diffusion model

$$\mathbf{v} = \sqrt{\begin{pmatrix} 3.33 \times 10^{-3} \\ \end{pmatrix} \begin{pmatrix} 2444 \times 10^{-3} \\ \end{pmatrix} \begin{pmatrix} \text{exp} & -\frac{165.0329 \text{ kJ mol}^{-1}}{RT} \end{pmatrix}} \begin{pmatrix} \text{[m]} & \text{(35)} \end{pmatrix}$$

• Non-steady state diffusion model

$$\mathbf{v} = \sqrt{\begin{pmatrix} 8.33 \times 10^{-3} \\ \end{pmatrix} \begin{pmatrix} 2(072 \times 10^{-3}) \\ \end{pmatrix} \begin{pmatrix} \text{exp} & -\frac{164.999 \text{ kJ mol}^{-1}}{RT} \end{pmatrix}} \mathbf{d} \begin{pmatrix} \text{m} \end{pmatrix}} \tag{36}$$

Hence, Eqs. (35) and (36) can be used to estimate the optimum boride layer thicknesses for different borided ferrous materials.
