The Effect of Deposition Parameters on Tensile Properties of Pulse-Plated Nanocrystalline Nickel
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The Effect of Deposition Parameters on Tensile Properties of Pulse-Plated Nanocrystalline Nickel K. L. Morgan, Z. Ahmed, and F. Ebrahimi Department of Materials Science and Engineering, University of Florida, Gainesville, FL 32611, U.S.A. ABSTRACT The microstructure and tensile properties were investigated for pulse-plated nanocrystalline nickel electrodeposits prepared from an additive-free sulfamate-based solution. Square-wave cathodic current densities were varied from 25 to 75 mA/cm2. The samples deposited at 25 mA/cm2 showed the smallest grain size (d ~ 12 nm), and the grain size was found to increase with increasing current densities. The grain size of the electrodeposits ranged from approximately 27 to 12 nm. Tensile results indicated that the yield strength of the specimens increased with decreasing grain size. Scanning electron microscopy revealed that all electrodeposits fractured through a ductile mechanism.
INTRODUCTION Electrodeposition has successfully been used to fabricate metallic nanostructures [1]. The commercial plating industry has recently adopted the pulse-plating deposition technique due to its ability to produce finely grained coatings with less surface roughness. Pulse-plating differs from conventional plating in that it utilizes interrupted DC current to deposit metal ions onto a substrate. A series of equal-amplitude DC pulses are delivered for a short time (ton), and separated by longer times (toff) of zero current. Generally, as the current density delivered to the working electrode increases, the overpotential at the electrode increases, which increases the driving force for nucleation. Therefore, by using the pulsed electrodeposition technique and increasing the current density, deposits with increasingly finer grain sizes are expected to be produced. The objective of this study has been to investigate the effect of pulsed-current density on the microstructure and tensile properties of electrodeposited nanocrystalline nickel fabricated without the use of grain-refining organic additives.
EXPERIMENTAL PROCEDURES A conventional three-electrode cell with a copper rotating disk working electrode, a parallel Pt foil anode, and a saturated calomel reference electrode (SCE) was used in this study. The copper substrate (diameter = 35 mm) was annealed at 150°C and electropolished before deposition. The working electrode was rotated at a speed of 400rpm. Pulsed current densities of 25, 50, and 75 mA/cm2 were used in the investigation. The pulse cycles were composed of ton = 1ms and toff = 9ms. The deposition ran for 54 to 72 hours to achieve a deposit thickness of ~ 25 µm. The electrolyte used in the study was a sulfamate solution containing 90 g/L Ni, 15 g/L boric acid, and .075 g/L sulfamate-nickel-anti-pit (SNAP). The pH of the solution was adjusted to 4.7 through additions of nickel carbonate. After adding nickel carbonate, the solution was B3.11.1
vacuum-filtered. Prior to deposition, the electrolyte was deaerated with nitrogen for one hour. During all depositions, the solution tempera
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