An investigation of cadmium, hard chromium and their possible replacement coatings for aerospace applications

High velocity oxygen fuel (HVOF) thermally sprayedWC/Co/Cr coating is considered as an electroplated hard Cr (EHC) coating replacement and Al-based coatings including electrodeposited Al (EDAl), flame sprayed Al (FSAl) and SermeTel 962 are considered as electrodeposited Cd (EC) coating replacements. This is due to the environmental issues surrounding the continued use of the latter two systems. All these coatings were characterised in terms of composition, morphology, microstructure, porosity and corrosion resistance (electrochemical linear polarisation resistance). Surface analytical techniques used included scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS) and focused ion beam scanning electron microscopy (FIBSEM). The feasibility of these coatings to replace EHC and EC coatings has also been identified. [Continues.]