Influence of Depositing Parameters on Microstructure of Ni-Co Pulse Plating

Abstract:

Influence of the pulse currents, the pulse frequency and CoSO₄ content of plating solution on Co content of Ni-Co alloy coatings are investigated by environmental scanning electronic microscopy and field emission scanning electronic microscope. The result shows that Co content of Ni-Co alloy coating increases as the increase of CoSO₄ content and pulse frequency. Co content of Ni-Co alloy coating increases when the current density decrease. When CoSO₄ content of plating solution and the pulse frequency increase, the coating surface become smoother, microstructure become denser and coating grain refinement. when current density is small, coating crystalline grains size are tiny and the coating crystalline grains arrangement is relatively close. In the Ni-Co electrodepositing process, the combining of Ni²⁺ and Co²⁺ generates [CoNi (Ⅱ)] intermediate products, then the decomposion of [CoNi (Ⅱ)] generate Co and Ni²⁺. This hinders sedimentation of Ni²⁺ ions and increases sedimentary speed of Co²⁺ ion. Polarization of electrodeposited cobalt is lager than polarization of electrodeposited nickel. So as the current density increases, nickel deposition relative faster than cobalt, thus leads to the cobalt content of coating decreased. The recovering frequency of metal ion concentration in pulse spread layer rise at the fixed time as pulse frequency increases.

• Periodical: Applied Mechanics and Materials (Volumes 84-85)
• Pages: 86-90
• DOI: https://doi.org/10.4028/www.scientific.net/AMM.84-85.86
• Online since: August 2011
• Authors: Ji Cheng Gao, Hui Ming Jin, Ji Qun Zhang, Jun Shi, Lu Li
• Keywords: Depositing Parameters, Microstructure, Ni-Co Pulse Plating

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DOI: 10.1016/j.surfcoat.2006.06.017