Electrodeposition of Ni-Fe-Mo-W Alloys - 13th Quarter Report
13th Quarterly Report - AESF Research Project #R-117. This NASF-AESF Foundation research project report covers the 13th quarter of project work (January-March 2016).
Yujia Zhang and E.J. Podlaha-Murphy*
Boston, Massachusetts, USA
Editor’s Note: This NASF-AESF Foundation research project report covers the 13th quarter of project work (January-March 2016). Progress on the previous quarters has been published in summary in the NASF Report in Products Finishing and in full at www.pfonline.com.** A printable PDF version is available by clicking HERE.
Beginning in January 2013, the NASF, through the AESF Foundation Research Board, funded a three-year project on alloy plating at Northeastern University, in Boston, under the direction of Dr. Elizabeth Podlaha-Murphy, with emphasis on nickel-molybdenum-tungsten deposits. In 2016, a one-year extension was granted to examine the influence of oxide particulates codeposited with different combinations of Ni, Mo and W alloys on the resulting deposit composition in the generation of novel alloy composites. What follows is the first report on this new work.
Electrodeposition of Ni-W-TiO2 composites
Metal matrix composite coatings combine a second phase particle into a metal, and can address the need for advanced materials with tailored properties. There are many reports of different particle types electrodeposited with metals, with several good reviews available.1,2 Generally, the particle is dispersed in an electrolyte, commonly by mechanical means through stirring, and captured into a growing film as the metal ion is reduced at the electrode surface. In particular, electrodeposited Ni-W alloys with titania particles have been previously reported with an emphasis on how the particle affects one of the deposit properties and its structure. Kumar, et al.3 examined the corrosion resistance and hardness of nickel-rich Ni-W deposits with small amounts of titanium. The hardness was improved with the inclusion of particles and the corrosion resistance was enhanced, particularly for pulsed deposition of the composite. Goldasteh and Rastegari,4 also reported improved hardness for a similar Ni-W-TiO2 composite compared to a Ni-W alloy. They used nano-sized titania particles leading to grain refining. Only when their composite was pulse deposited was there an enhancement of corrosion resistance in a 0.5M NaCl electrolyte. Other oxide particle types have been demonstrated with Ni-W alloy matrices as well, including nano-scaled alumina and zirconia. Yari and Dehghanian5 found that the alumina particle did not change the surface morphology, phase or texture of the Ni-W, but decreased the tungsten content and the rate of deposition. Beltowska-Lehman, et al.6 reported an enhancement of hardness with Ni-W-ZrO2 compared to similarly deposited Ni-W. They utilized ultrasonic agitation that can help to disperse the particles in the electrolyte and found that it had a positive effect on the amount of particle in the deposit.
Typically, Ni-W is electrodeposited from ammonium-containing electrolytes, and results in nickel-rich alloys, as in the cited examples above. Without ammonium ions in the electrolyte, the amount of tungsten in an electrodeposited film has been shown to be higher in Ni-W alloys, although with a loss in current efficiency.7 Presented here is an examination of adding titania particles to an ammonia-free Ni-W electrolyte, resulting in high amounts of tungsten in the deposit. Our goal is in determining if the particle changes the rates of deposition (i.e., partial current densities), hence composition and current efficiency, and if the inclusion of particles affects the morphology.
A citrate-boric acid electrolyte was used in this study and contained 0.1M nickel sulfate, 0.15M sodium tungstate and 0.285M trisodium citrate, 1.0M boric acid, at a pH of 8 adjusted with sodium hydroxide, with and without 12.5 g/L micron-size titanium dioxide (particle diameters less than 44 microns, -325 mesh, Acros Organics). The determination of polarization curves and actual deposition were carried out at room temperature on copper covered brass cylinder electrodes, having a diameter of 0.6 cm. A copper tape, (3M Copper Conducting Tape, SPI supplies), typically used for SEM analysis, was used to cover the electrode so that the film could be readily removed for further analysis and the cylinder current collector re-used. The polarization data was scanned from the open circuit potential to a large enough overpotential to achieve a current density that is reached in a rotating Hull cell configuration. During the polarization scan a three-electrode cell configuration was used with a platinum mesh anode and a saturated calomel reference electrode (SCE). The curves were corrected for ohmic drop with impedance spectroscopy. The rotating Hull cell, shown in Fig. 1, used the same diameter rod, with a length of 8 cm, and an average current density of 50 mA/cm2. A plastic cylinder placed between the anode and the cathode, create a current distribution. The plot in Fig. 1 provides a way to estimate the current distribution. The calculated values assume a primary current distribution. The rotation rate was 500 rpm. A Solartron 1287A potentiostat/galvanostat current generator was used for both linear sweep voltammetry and deposition.
The composition and thickness were measured using x-ray fluorescence. The deposit surface morphology was inspected with scanning electron microscopy (SEM) obtained using a Hitachi 4800 at different magnifications.