Development of a Protective Coating for Evaluating the Sub-surface Microstructure of a Worn Material

Abstract

AbstractIn the current study, electrolytic deposition using two different electrodes, copper (Cu) and nickel (Ni) was investigated with the aim of protecting the worn surface during mechanical sectioning and polishing, for a posterior examination of the sub-surface microstructure. The efficacies of the two coatings were visually assessed based on its adhesivity and the ability to protect the wear tracks of an as-cast 26% Cr high chromium cast iron (HCCI) alloy. It was observed that electrodeposition using Cu as the electrode was ineffective owing to a poor adhesivity of the coating on the HCCI surface. The coating had peeled off at several regions across the cross-section during the mechanical sectioning. On the other hand, Ni electroplating using Ni strike as the electrolyte was successfully able to protect the wear track, and the sub-surface characteristics of the wear track could be clearly visualized. A uniform coating thickness of about 8 µm was deposited after 30–40 min with the current density maintained between 1 and 5 A/dm2. The presence of the Ni coating also acted as a protective barrier preventing the ejection of the broken carbide fragments underneath the wear track.