Fast penetration of Cu in Ni of Cu/Ni/Cu diffusion couples due to diffusion induced recrystallization

Rapid penetration of Cu in Ni owing to diffusion induced recrystallization (DIR) in the Ni(Cu) system was experimentally examined using the Cu/Ni/Cu diffusion couples consisting of pure Cu single crystals and a pure Ni polycrystalline specimen annealed at 923 and 1 023 K in previous studies. The experimental results have been theoretically analyzed to find a new criterion for the occurrence of DIR in the present study. According to the experimental results, the thickness I of the DIR region in the Ni phase increases in proportion to the square root of the annealing lime t Thus, if we define the parameter D (h) as the hypothetical diffusion coefficient which gives the overall penetration rate of Cu across the DIR region, the thickness I is described as a function of the annealing time t by the equation l=2 root D(h)t. The temperature dependence of Dh has been obtained from the experimental results and then compared with that of the volume diffusion coefficient DV of Cu in Ni. From the comparison, it is concluded that the ratio D-h/D-V should be greater than thirty in order for DIR to take place in the Ni(Cu) system.