Synthesis of corrosion-resistant nanocrystalline nickle-copper alloy coatings by pulse-plating technique

Bright and smooth nanocrystalline Monel-type Ni-Cu alloy gets deposited from complex citrate electrolyte by pulse electrolysis. Transmission electron microscopy studies have revealed that the deposited Ni-Cu alloy was nanocrystalline in nature and it comprised a two-phase (fcc+L1(o)) mixture. The presence of twins could be seen in the nanocrystals. The Ni-Cu alloys prepared by pulse electrolysis were finer grained (similar to 2.5-28.5 nm) than those deposited by direct current method. Nelson-Riley function has been used to calculate the lattice parameters for both the pulse current-plated and direct current-plated alloys from x-ray diffraction analysis. The microhardness values for pulse current-plated alloys were higher than for the direct Current-plated alloys. The internal stresses of both the pulse current-deposited and the direct current-deposited alloys have also been measured; the values were lower for pulse current-plated alloys. Potentiodynamic polarisation studies were carried out in aerated and deaerated neutral 3.0 Wt per cent NaCl solution and instantaneous corrosion current density of the plated alloy was determined and compared with the Monel-400 alloy. It was found that nanocrystalline pulse current-Ni-35.8 Wt per cent copper alloy exhibited lower instantaneous value of corrosion current density than that of specimens with direct current method and Monel-400 alloy. The dissolution behaviour of the deposited nanocrystalline material was found to be more like general corrosion rather than localised corrosion as in the case of Monel-400 alloy.