Observation on Isothermal Reactive Diffusion between Solid Ni and Liquid Sn

Abstract

The kinetics of the reactive diffusion between solid Ni and liquid Sn was experimentally examined using Ni/Sn diffusion couples. The diffusion couples were prepared by an isothermal bonding technique and then immediately annealed in the temperature range of T = 533-623 K for various times up to t = 14.4 ks (4 h). During annealing, a compound layer of Ni 3 Sn 4 is formed at the original Ni/Sn interface in the diffusion couple and grows mainly into the liquid Sn specimen. The mean thickness of the compound layer is proportional to a power function of the annealing time. The exponent n of the power function takes values between 0.31 and 0.43. Since there is no systematic dependence of n on T, we may consider that n is insensitive to T within experimental uncertainty. When growth of a compound layer with uniform thickness is controlled by volume diffusion, n is equivalent to 0.5. If boundary diffusion contributes to the layer growth and grain growth occurs in the compound layer, however, n becomes smaller than 0.5. Since grain growth practically takes place in the compound layer, it is concluded that the layer growth of Ni 3 Sn 4 is mainly controlled by boundary diffusion at T = 533-623 K.

Compound Growth due to Reactive Diffusion between Solid-Ni and Liquid-Zn

“…A polycrystalline commercial rod of pure Ni with diameter of 8 mm and purity higher than 99% were cut into columnar specimens with length of 5 mm as previously described. 25) The annealing and the mechanical polishing of each columnar Ni specimen were conducted by the technique reported in a previous article. 25) Polycrystalline columnar specimens with length of 30 mm were cut from a commercial rod of pure Zn with diameter of 6 mm and purity of 99.9%.…”

“…25) The annealing and the mechanical polishing of each columnar Ni specimen were conducted by the technique reported in a previous article. 25) Polycrystalline columnar specimens with length of 30 mm were cut from a commercial rod of pure Zn with diameter of 6 mm and purity of 99.9%. A pair of the columnar Zn specimen and the polished Ni specimen was encapsulated in an evacuated silica capsule with inner diameter of 8.5 mm.…”

“…A pair of the columnar Zn specimen and the polished Ni specimen was encapsulated in an evacuated silica capsule with inner diameter of 8.5 mm. The silica capsule was isothermally preheated and bonded to prepare a solid-Ni/ liquid-Zn diffusion couple by an isothermal bonding (IB) technique 25) in the temperature range between 773 K and 923 K. The diffusion couple was isothermally annealed for various times up to 10.8 ks (3 h) at each constant temperature in this temperature range, followed by water quenching with breaking the capsule. Hereafter, T shows the annealing temperature, and t indicates the annealing time.…”

“…24) Attention was focused on the compound growth in a previous study. 25) In that study, 25) the reactive diffusion between solid Ni and liquid Sn was experimentally examined at temperatures of T = 533623 K using an isothermal bonding (IB) technique. 25) In the IB technique, preheating and subsequent isothermal bonding-and-annealing are conducted at an equivalent temperature in a vacuum.…”

“…25) In that study, 25) the reactive diffusion between solid Ni and liquid Sn was experimentally examined at temperatures of T = 533623 K using an isothermal bonding (IB) technique. 25) In the IB technique, preheating and subsequent isothermal bonding-and-annealing are conducted at an equivalent temperature in a vacuum. Thus, unlike a usual immersion technique, the compound growth during really isothermal reactive diffusion is reliably observed in the experiment using the IB technique.…”