Diffusion paths and structures in multiphase Cu−Ni−Zn couples at 775°C

Abstract

Multiphase diffusion was investigated in the Cu−Ni−Zn system at 775°C for the development of diffusion structures involving two interfaces. Selected series of diffusion couples characterized by a common γ (cubic) terminal alloy joined to a set of α (fcc) alloys developed an intermediate β (bcc) phase with two interfaces, α/β and β/γ. The α/β interface showed transitions from planar to nonplanar and back to planar morphology, as the copper concentration of the α terminal alloy was decreased from 100 to about 30 at. pct. Planar β/γ interfaces were observed for all but two of the couples. The compositions on either side of planar α/β interfaces were consistent with those based on equilibrium tielines, while the compositions at nonplanar α/β interfaces differed from those of equilibrium. Selected series of couples assembled with γ and β alloys were also investigated for the development of interface instability at the β/γ interface. The diffusion paths of γ/β couples were consistent with those of γ/α couples.