Deposition of Ni Coatings by Electrolytic Plasma Processing

Abstract

Electrolytic Plasma Processing (EPP) is an emerging cleaning and coating technology capable of high deposition rates while being relatively simple and environmentally friendly. In the present study, Ni coatings were deposited via EPP on low carbon steel substrates. Initially, experiments were carried out at different processing conditions to determine their effect on the coating characteristics and select the most appropriate conditions for Ni deposition. The coated samples were characterized by Scanning Electron Microscopy (SEM), X-ray Diffraction, and Transmission Electron Microscopy. EPP Ni depositions were conducted at the selected processing conditions for 10, 20 and 30 s. EPP produced high purity Ni coatings with an approximate grain size of 20 nm at a deposition rate of 166 nm/s. The corrosion properties were assessed in 3.5 % NaCl aqueous solution using open circuit potential measurements, potentiodynamic polarization testing and Electrochemical Impedance Spectroscopy (EIS). The microstructure and coating characteristics, both before and after corrosion testing, were studied using SEM. In spite of the short deposition time, EPP-coated Ni was shown to increase the corrosion resistance of the steel substrate by increasing the corrosion potential and significantly decreasing the corrosion rate. The EIS studies revealed that a similar corrosion mechanism prevails between pure Ni and EPP-coated Ni. Best corrosion behavior was obtained with a coating deposition time of 30 s, showing a positive shift in the corrosion potential by ~200 mV and more than an order of magnitude reduction in the corrosion rate of the low carbon steel.