Microstructure characterization of localized corrosion wear of Cr/Cr2N+ a-C:H/a-C:H:Cr multilayer coatings on carbon fiber composites

The use of carbon fiber composites (CFC) for different applications is widespread. Carbon-based materials show, however, significant oxidative degradation in air. Modern materials are subjected to aggressive, corrosive environment. This type of environment may strongly reduce their mechanical properties. For the protection of CFC, it was necessary to apply coatings to the composite surface. In the presented paper, a chromium/chromium nitride (Cr/Cr2N) multilayer structure has been selected as the inner part. The outer part of the coating was a hydrogenated amorphous carbon (a-C:H), gradually implanted by Cr nanocrystals. The application of transmission electron microscopy (TEM) indicated that the proposed deposition method allowed the formation of a Cr/Cr2N multilayer of Λ = 150 nm, topped with a-C:H+ Cr23C6 composite of a varied carbides density. The micro-hardness of the deposited coatings was up to 14 GPa (at a load of 2 and 5 mN). The microstructure of the deposited coatings was described in detail by means of TEM in the authors’ recently published paper [1]. This paper is a continuation thereof, aimed at describing microstructure changes after a localized corrosion process. In order to study localized corrosion in coatings, particularly in metallic (Cr) interlayers, the potential measurements and voltammetry experiments were performed in a Ringer solution. The open-circuit potential reaches stable values after a sufficient time period. The results indicated that the presence of a-C:H+Cr23C6, the outer part of the coating, speeds up the localized corrosion process in Cr interlayers in the inner part of a coating.