UC Davis

The effect of a dc on the interdiffusivity D in the Cu-Ni system was investigated over the temperature range of 650-850 degrees C and at current densities in the range of 0-1000 A cm(-2). Interdiffusivities were calculated using the Sauer-Freise-den Broeder method and the values calculated in the absence of a current were in agreement with previously published results. The influence of the current on D depended on its direction relative to the two interfaces in the trilayered Cu-Ni-Cu samples. When the electronic flow was from Ni to Cu (cocurrent interface), the interdiffusivity showed a marked increase relative to copper content but was unchanged when the electronic flow was from Cu to Ni (countercurrent interface). The increase of D in the cocurrent interface depended on concentration and temperature. At lower temperatures, the increase becomes significant at higher copper concentrations but for the same value of current density, the increase is apparent at lower concentrations. The effective activation energy of interdiffusivity depended on concentration and decreased with the application of a current. The decrease was largest for higher copper concentrations. The results are interpreted in terms of a proposed vacancy-atom interaction for copper with the implication that the electron wind effect on Cu is counteracted by the effect of vacancies. (c) 2007 American Institute of Physics.