Title: The Sputter-Induced Solute Segregation in the Surface Layer of Cu-Ni Alloys during Argon Ion Bombardment at Elevated Temperatures
Abstract: In order to study the mechanism of sputter-enhanced solute segregation, surface and matrix compositions of Cu-Ni alloys were measured after Ar ion bombardment up to 873 K by means of Auger electron spectroscopy (AES) and X-ray micro analysis (XMA). Sputtering at a high dose rate resulted in nickel enrichment on surface at all temperatures and all alloy compositions. At low dose rate, however, copper was segregated in the surface. The thickness of segregated copper layer was 4∼6 nm at 873 K that was too thick to be the Gibbsian equilibrium segregation. A layer depleted in copper ∼70 nm in thickness was observed beneath it. In order to know the deth profile, the composition change was analyzed and the enhanced diffusion was measured with a 40 at% coarse grained specimen (1∼2 mm in diameter). The enhancements of diffusion coefficients were 3.6×108, 1.3×104 and 19 at 573, 723 and 873 K, respectively. The apparent activation energy was only 22.6 kJ/mol. The small value suggested that the surface segregation was caused by the interstitial type diffusion mechanism.