CORROSION MECHANISMS AND ELECTROCHEMICAL BEHAVIOUR OF THERMAL SPRAY COATINGS (WC-Cr-Ni AND WCCrC)

摘要

In this experimental study the corrosion characteristics (rates and mechanisms) of two thermally-sprayedcermet coatings have been examined in a static saline environment (synthetic seawater). The coatingshave complex microstructures where the ceramic hard-phase constituents are embedded in a metallicmatrix. Their electrochemical response during accelerated corrosion DC polarisation tests reflects thiscomplexity. The test protocol has enabled the mechanisms of corrosion occurring on the WC/CrCcermet and the WC-Cr-Ni cermet to be compared and contrasted. A 'critical' temperature has beendefined 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 bythe WC/CrC coating and such a well-defined 'critical' temperature is not apparent. The contrastingmechanisms of corrosion, identified during post-test examination, can be correlated to the contrastingelectrochemical response.