Zero-flux planes and flux reversals in the Cu- Ni- Zn System at 775 °C

Abstract

Ternary diffusion in the Cu-Ni-Zn system was investigated at 775 °C for the development of zero-flux planes (ZFP) and flux reversals of the individual components. ZFP’s, where the interdiffusion flux of either Cu, Ni, or Zn goes to zero, were identified in several series of single phase and multiphase solid-solid diffusion couples assembled with a (fcc),β (bcc), or γ (cubic) Cu-Ni-Zn alloys and characterized by terminal alloys of similar thermodynamic activity for one of the components. Profiles of interdiffusion fluxes were directly determined from concentration profiles. The diffusion path for a single phase couple with a ZFP was experimentally found to be invariant with diffusion time. The locations of ZFP’s within the diffusion zone of a couple corresponded to sections where the activity of a component was the same as its activity in either of the terminal alloys of the couple. Couples developing ZFP’s showed regions where a component diffused up its own activity gradient. The diffusional interactions among the components described by the ratios of cross to main ternary interdiffusion coefficients were determined directly from the slopes of the diffusion paths at various ZFP compositions. In several multiphase couples, discontinuous flux reversals for the components were also identified at theβ/a and γ/β interfaces. A discontinuous flux reversal for a component was observed at a planar interface, when the activity of the component at the interface corresponded to its activity in one of the terminal alloys of the couple.