Observations on diffusion-induced recrystallization in binary Ni/Cu diffusion couples annealed at an intermediate temperature

Diffusion-induced recrystallization (DIR) was experimentally studied using diffusion couples consisting of a pure Cu single crystal and a binary Ni–Cu polycrystalline alloy. The (Ni–Cu)/Cu diffusion couples were annealed at 873 K for various times between 1 and 72 h (3.6×103 and 2.59×105 s). During annealing, a fine grain region (DIR region) was observed to form at an interface of each diffusion couple due to DIR and to grow mainly towards the Cu phase. The thickness l of the DIR region increases with increasing annealing time t according to the relationship l=kl(t/t0)n, where t0 is unit time, 1 s. The proportionality coefficient and the exponent take constant values of k=2.18×10−8 m and n=0.55, respectively, independent of the composition of the Ni phase within experimental uncertainty. The compositional differences across the moving boundaries of the DIR region on both the Cu phase and Ni phase sides decrease in inverse proportion to the almost fourth root of the annealing time. At each annealing time, the compositional difference Δxc on the Ni phase side monotonically decreases with increasing Cu concentration x0 in the Ni phase, whereas there is no clear relationship between the compositional difference Δxi on the Cu phase side and the Cu concentration x0.