Microstructural Changes during Interfacial Diffusion at the Sm<sub>2</sub>Fe<sub>17</sub>–Zn Interface

The microstructural changes and interdiffusion coefficients at the Sm2Fe17–Zn interface were investigated in this study. Sm2Fe17–Zn diffusion couples were annealed for 10 min at 320, 350, and 400°C, which are below the melting temperature of Zn (419°C), resulting in the interdiffusion of Zn, Fe, and Sm. At the interface annealed at 400°C, three diffusion regions were identified between the Sm2Fe17 and Zn phases. The thickest region was a Zn-rich region composed of polycrystalline δ- and ζ-Zn–Fe binary alloy phases and a ThMn12-type Sm(Zn,Fe)12 ternary alloy phase. The annealing time dependence of the thickness of the Zn-rich region at 400°C was measured, and the interdiffusion coefficient was evaluated as 7.3 × 10−13 m2s−1 using the Einstein–Smoluchowski equation. At the surface of the Sm2Fe17 phase, a region with a fiber-like microstructure was observed that consisted of two phases, α-(Zn,Fe) and Sm(Zn,Fe)12. Interestingly, these two phases exhibited a specific crystal orientational relationship of α-FeZn(10-1)[111]//Sm(Zn,Fe)12(01-1)[011]. Between these two diffusion regions, a third region composed of nanosized polycrystalline grains of Γ-FeZn, α-FeZn, and Sm(Zn,Fe)12 was observed.