Kinetic features of diffusion induced recrystallization in the Cu(Ni) system at 873 K

The kinetics of diffusion induced recrystallization (DIR) in the Cu(Ni) system was experimentally studied at 873 K. Ni/(CuNi)/Ni diffusion couples were prepared by a diffusion bonding technique using a pure Ni specimen and binary CuNi alloys with mol fractions of Ni of y0=0, 0.114 and 0.231, and then annealed at 873 K for various times between 1 and 72 h (3.6×103 and 2.59×105 s). After annealing, a fine grain region (DIR region) alloyed with Ni was observed to form at the interface owing to DIR and to grow mainly towards the Cu phase. The thickness l of the DIR region monotonically increases with increasing annealing time t according to the relationship l=k(t/t0)n, where t0 is unit time, 1 s. The exponent n takes a constant value of 0.45 independent of the composition y0. On the other hand, as the composition y0 increases from 0 to 0.231, the proportionality coefficient k decreases from 5.7×10−8 to 4.5×10−8 m. The experimental results were theoretically analyzed using a kinetic model proposed by the present authors. The growth behavior of the DIR region was explained well by the analysis. This means that the chemical driving force due to the compositional difference between the Cu phase and the DIR region is the most important driving force for DIR in the Cu(Ni) system under the present experimental conditions.