Low Temperature Diffusion in Polycrystalline Thin-Film Gold–Nickel Couples

Diffusion in the gold–nickel system has been studied by isothermally annealing polycrystalline thin film gold-nickel couples in the temperature range 400°–750° C. X-ray diffractometer traces were taken of the couples after each annealing interval. The diffusion data are interpreted in terms of a model in which microcrystalline alloy aggregates of wide compositional range are formed in the grain boundaries of each layer. These aggregates become richer in diffused metal until compositions at the miscibility boundary are reached. Supersaturation and subsequent precipitation then occur to yield the terminal condition in which the couple becomes a uniform mixture of nickel-rich and gold-rich alloys.