Fast Penetration of Cu in Ni of Cu/Ni/Cu Diffusion Couples Due to Diffusion Induced Recrystallization

Abstract

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 1023 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 l of the DIR region in the Ni phase increases in proportion to the square root of the annealing time 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 l is described as a function of the annealing time t by the equation l=2√D^ht. The temperature dependence of D^h has been obtained from the experimental results and then compared with that of the volume diffusion coefficient D^v 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.