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

Abstract

In the current study, electrolytic deposition using two diferent 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 efcacies 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 inefective owing to a poor adhesivity of the coating on the HCCI surface. The coating had peeled of 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 prevent ing the ejection of the broken carbide fragments underneath the wear track.