The growth kinetics of intermetallic compounds by the fast diffusion path at the interface of Co and molten Zn

Abstract

This study investigates the growth and microstructure formation of intermetallic compounds at the solid/liquid interface of a Co/Zn diffusion couple prepared using an isothermal bonding method and annealed isothermally at 703 K, 723 K, and 743 K for up to 48 h. The experimental observations and analysis revealed the formation of three Zn-rich intermetallic compounds: γ (Co5Zn21), γ1 (CoZn7), and γ2 (CoZn13). The γ2 phase, having the highest Zn content, formed the thickest layer, while the γ and γ1 phases exhibited slower growth. The total thickness of these layers increased proportionally to the annealing time, following a power function. The growth of intermetallic compounds was predominantly controlled by interdiffusion, with the γ2 phase forming island-like structures that merged over time, creating fast diffusion paths of liquid Zn. The annealing temperature had a minimal impact on the growth rate, with slightly faster growth observed at lower temperatures due to finer needle-like interfaces within the molten Zn, which created more efficient diffusion paths. These findings underscore the importance of understanding the kinetics and mechanisms of intermetallic compound formation for optimizing material properties and processing conditions in industrial applications.