Abstract
Co-plating of Cu-Ni coatings by supercritical CO2 (sc-CO2) and conventional electroplating processes was studied in this work. 1,4-butynediol was chosen as the surfactant and the effects of adjusting the surfactant content were described. Although the sc-CO2 process displayed lower current efficiency, it effectively removed excess hydrogen that causes defects on the coating surface, refined grain size, reduced surface roughness, and increased electrochemical resistance. Surface roughness of coatings fabricated by the sc-CO2 process was reduced by an average of 10%, and a maximum of 55%, compared to conventional process at different fabrication parameters. Cu-Ni coatings produced by the sc-CO2 process displayed increased corrosion potential of ~0.05 V over Cu-Ni coatings produced by the conventional process, and 0.175 V over pure Cu coatings produced by the conventional process. For coatings ~10 µm thick, internal stress developed from the sc-CO2 process were ~20 MPa lower than conventional process. Finally, the preferred crystal orientation of the fabricated coatings remained in the (111) direction regardless of the process used or surfactant content.
Highlights
Cu and Cu-rich alloys are popular engineering materials due to their many technological and metallurgical uses
Current Efficiency (CE) was improved by the addition of even a small quantity of 1,4-butynediol for both processes. 1,4-butynediol is known to undergo hydrogenation under a supercritical CO2 (sc-CO2) environment [25], so it is possible that the surfactant could bind with extra H+ that initially reduced the current efficiency of the plating processes
This work reports the fabrication of Cu-Ni alloy co-plating with 1,4-butynediol as a surfactant in sc-CO2 electroplating at low direct current (DC) settings
Summary
Cu and Cu-rich alloys are popular engineering materials due to their many technological and metallurgical uses. Alper et al [5] reported electroplating using a three-electrode setup supplying negative potential and adjusting pH values, which affected the surface morphology and magnetic properties of the samples. Even though adding 1,4-butynediol makes the plated surfaces smoother, the conventional process showed a disadvantage when the sample surface has a complex morphology This reduces the ability of the electrolyte to flow smoothly, increases viscosity, and creates residual H+ in the coating during electroplating. 1,4-butynediol was introduced to the sc-CO2 electroplating process to reduce both internal stresses and surface roughness, and to study the co-plating of Cu-Ni coatings under a pressure of 15 MPa and temperature of 50 ◦ C. Various analyses of mechanical and chemical properties were performed, which will be described in more detail in the sections below
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