Growth rate of fine grains formed by diffusion induced recrystallization in Ni layer of Cu/Ni/Cu diffusion couples

Abstract

Diffusion induced recrystallization (DIR) in the Ni(Cu) system was experimentally studied. The notation Ni(Cu) means that Cu atoms diffuse into a pure Ni or binary Ni-Cu phase. The Cu/Ni/Cu diffusion couples consisting of pure Cu single crystals with the same crystallographic orientation and a pure Ni polycrystalline specimen were annealed at 923 and 1023 K for various times between 1.8 × 103 and 1.76 × 105 s. The penetration of Cu in the Ni phase was found to occur at rates three orders of magnitude greater than the ones evaluated from the volume diffusion. This unusually rapid penetration is due to DIR. DIR was observed to take place only in the Ni phase from the interfaces in all the diffusion couples annealed at 923 and 1023 K. The observations indicate that the thickness l of the DIR region increases with increasing annealing time t according to the relationships l=4.9 × 10-8(t/t0)0.41 and l=1.8 × 10-7(t/t0)0.37 at 923 and 1023 K, respectively. Here, l and t are measured in m and s, respectively, and t0 is unit time, 1 s. The analysis using the kinetic equation proposed by Li and Hillert could account for the observations quantitatively.