Effect of temperature and phase constitution on kinetics of La diffusion

The diffusion of La in ε-Fe_2-3N(ε) and γ'-Fe₄N(γ') phase produced by plasma nitriding was studied. It is found that with increasing nitriding time, the ε phase continuously decomposes into γ' one under employed experimental conditions and compared with γ' phase or ε+γ' ones, the mono one ε has an impedient effect on depth of La diffusion. The growth of La layer in dual phases and mono one follows an approximate exponential law and a parabolic one, respectively, and this kinetics law does not change with increasing temperature. The effect of increasing temperature in the range of 520 to 560°C on La diffusion depth is less than that of phase consitution change such as the decomposition of ε phase into γ' one.