Effect of long-range interaction on diffusion in copper-nickel composition-modulated alloys

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Abstract
Vapor deposited Cu–Ni films were produced containing composition modulations with wavelengths between 0.8 to 5.0 nm. The foils, deposited on mica substrates, exhibited a strong 〈111〉 texture and produced satellite peaks in the x-ray diffraction patterns. The interdiffusivities in the range of 375–450 °C, which were measured from the decay rate of the x-ray diffraction satellite intensities, yielded an activation energy of 2.7×105 J/mol. This value is in good agreement with that obtained by tracer diffusivities at high temperatures. The effective diffusion coefficient D̃B at 400 °C [as a function of the dispersion relation B2(h)] showed a minimum at a wavelength of about 1.5 nm in contrast with the linear or monotonic behavior of several other systems. A new formulation of D̃B in a power series of B2 was developed and the first six interaction energies were calculated from short-range order parameters.