Pulse co-electrodeposition and characterization of NiW-WC composite coatings

The present study investigates the influence of pulse current parameters on the structure and hardness of the co-deposited nickel tungsten alloys incorporated by tungsten carbide particles (NiW-WC) for environmentally friendly alternatives to chromium deposits. While a minimum average current density of about 0.04 A/cm(2) is required for sufficient co-deposition kinetics, a decrease of duty cycle from 50% to 10% and a reduction of pulse frequency from 100 Hz to 10 Hz generally result in the increase of the carbide content in the deposits. Furthermore, these pulse parameters also affect the content of tungsten alloyed in the nickel matrix. NiW-WC of high hardness exceeding that of hard chromium coating by about 40% is achieved in the deposits with uniform structure, and with 31 at.% W and 13 wt.% WC particles. The mechanisms controlling the co-electrodeposition process and the corresponding hardness are discussed. (C) 2010 Elsevier B.V. All rights reserved.