In this experimental study the corrosion characteristics (rates and mechanisms) of two thermally-sprayed cermet coatings have been examined in a static saline environment (synthetic seawater). The coatings have complex microstructures where the ceramic hard-phase constituents are embedded in a metallic matrix. Their electrochemical response during accelerated corrosion DC polarisation tests reflects this
complexity. The test protocol has enabled the mechanisms of corrosion occurring on the WC/CrC cermet and the WC-Cr-Ni cermet to be compared and contrasted. A 'critical' temperature has been defined for the WC-Cr-Ni coating similar to the critical pitting temperature (CPT) for stainless steels. Electrochemical behavior, which can not be simply described as truly 'passive' behavior, is displayed by the WC/CrC coating and such a well-defined 'critical' temperature is not apparent. The contrasting mechanisms of corrosion, identified during post-test examination, can be correlated to the contrasting electrochemical response.
Keywords: corrosion, thermal spray, coating, cermet, electrochemistry.