Microstructural evolution of intermetallic compound layers formed in Fe/Zn binary diffusion couples

Abstract

The microstructural evolution of intermetallic compound layers formed in Fe/Zn diffusion couples (DCs) was examined by optical and scanning electron microscopies and electron-probe microanalysis. In the solid-Fe/liquid-Zn DCs at 450°C, the δp phase nucleates between the δp and ζ phases after dipping for about 100 s and every intermediate phase seems to obey the square root law individually before and after the appearance of the δp phase at 100 s. In the concentration-penetration profiles, a composition gap is observed in the δp phase of the solid-Fe/liquid-Zn DCs dipped for a long time at temperatures ranging from 450 to 550°C, while only a singular point, but no gap, is obtained in the DCs dipped at elevated temperatures over 575°C. On the other hand, in the case of the solid-Fe/solid-Zn DCs at 400°C, the δk phase instead of the δp phase appeares later between the δp and Γ phases and finally covers the whole δ region.