傾斜組成を有するNi-Cuめっき膜の作製とその硬さ

摘要

イオン化傾向の異なる2種類の金属イオンを含む電解液を用いた電気めっきでは，析出物の組成が負荷電位に依存する.したがって，異なる電位を交互に与えることによって，2つの異なる金属を交互に積層させることができる．構成層の層厚さをナノメートルスケールまで減少させたナノ多層膜は，優れた引張強度や硬さを示すことが報告されている.このようなナノ多層膜を表面に電気めっきした材料では疲労特性や摩耗特性の向上が見られ　その応用が期待されている．%A Ni-Cu alloy film with high composition gradient was fabricated by electrodeposition technique. Because the chemical composition of the electrodeposit depends on the applied electrochemical potential in solution containing nickel and copper ions, we could grow the gradient-composition Ni-Cu alloy film by applying a continuously variable potential wave. To obtain a relatively thick film on a substrate, the Ni-Cu layers with high positive and negative gradients were stacked alternately during the electrodeposition. In X-ray diffraction analyses, the gradient-composition film exhibited a very broad peak lying between Ni and Cu peaks, although two diffraction peaks appeared in an electrodeposited Ni/Cu multilayer fabricated using a rectangular potential wave. This broad X-ray peak was consistent with the gradient composition. Vickers hardness of the gradient-composition film was higher than that of the Ni/Cu multilayer with 100 nm layer thickness, by a factor of 1.8. The strength increment in the gradient-composition film could be explained by high-density misfit dislocations which uniformly distributed in the film.