The effects of heat treatments on hardness and wear resistance in Ni-W alloy coatings

The relationship of processing parameters, microstructure, and mechanical responses of the electrodeposited nickel-tungsten alloys exposed to elevated temperatures in the range 700-1100 degrees C are investigated. Reverse pulse electrodeposition technique is employed to control the tungsten content and nanocrystalline grain size of the deposits. The application of heat treatment at 700 C on the alloy with high tungsten content (22 at.%) and small grain size (3 nm) gives hardness enhancement and a small decrease in wear resistance. Prolonging annealing duration and increasing annealing temperature promote more grain growth and reductions of both hardness and wear resistance, despite the formations of secondary phases. For alloys with lower tungsten contents (6% and 13%) and larger grain sizes (13 and 56 nm), higher degrees of grain growth coupled with monotonic decline of hardness are observed. The study indicates that the electrodeposited nickel-tungsten alloys with a high tungsten content potentially serve as strong candidates for high temperature applications. (C) 2011 Elsevier B.V. All rights reserved.