Kinetics of Reactive Diffusion in the Co/Zn System at Solid-State Temperatures

Abstract

The kinetics of reactive diffusion in the Co/Zn system was experimentally examined at solid-state temperatures. In this experiment, sandwich Zn/Co/Zn diffusion couples were prepared by a diffusion bonding technique, and then isothermally annealed in the temperature range of 523–573 K for various times up to 211 h. Owing to annealing, an intermetallic layer consisting of the γ, γ₁ and γ₂ phases was formed at the original interface in the diffusion couple, where the thickness is much smaller for the γ and γ₁ phases than for the γ₂ phase. Thus, the γ₂ phase predominantly governs the overall growth of the intermetallic layer. The total thickness of the intermetallic layer increases in proportion to a power function of the annealing time. The exponent of the power function takes values of 0.54–0.56 at 523–548 K and that of 0.85 at 573 K. Consequently, volume diffusion mainly controls the layer growth at 523–548 K, but interface reaction as well as volume diffusion contributes to the rate-controlling process at 573 K.

Fig. 3 The total thickness l of the intermetallic layer versus the annealing time t at T = 523, 548 and 573 K shown as open rhombuses, squares and circles, respectively.