An Investigation on Corrosion Behavior of Duplex Hard ChromiumCoatings

摘要

In this study, the corrosion and mechanical properties of single hard chromiumrncoatings obtained by direct and pulse current compared with duplex (I.e. a hard layerrnon top of a crack-free sub-layer with the ratio 25/75, 50/50, 75/25) chromium coatingsrnelectrodeposited on a mild steel substrate have been investigated. The corrosionrnresistances have compared through electrochemical polarization (in 3.5% NaClrnsolution) and salt spray tests. The results of corrosion testing shows that crack-freerncoatings of hard chromium coatings obtained by pulse current, better corrosionrnresistance than ordinary hard chromium coatings obtained by direct current. Their icorrrnin 3.5% NaCl solution is lower than in ordinary hard chromium coatings.rnIn addition, the duplex coatings with the ratio 25% hard layer/75% crack-free layerrnshowed the best corrosion resistance in comparison with another duplex coatings.rnNo visible corrosive products in the crack-free coatings of hard chromium obtained byrnpulse current have occurred after the salt spray tests. Electron microscopy techniquernSEM and optical microscopy were used to observe the surface morphology, damagernand crack origin sites.