Microstructural Characterization And Oxidation Performance Of A Novel Rare Earth Elements-Modified Chromizing Coating

A novel RexOy-modified chromizing coating has been developed on a mild carbon steel by two steps: the first one is composite electrodeposition of Ni and RexOy particles, followed by the second one of chromizing on the Ni-RexOy composite using pack cementation method at 1120℃ for 4 hours. The coating is composed of the major portion of an outer layer with RexOy dispersion and the minor portion of an inner layer without RexOy. For comparison, chromizing was also performed in the same condition on the low carbon steel and the one with electroplated Ni film but without RexOy addition. Cyclic oxidation at 840℃ for 120h and oxidation at 940 for 90 hours showed the RexOy-modified chromizing coating has a superior oxidation resistance, as compared to the other two RexOy-free coatings. Samples before and after oxidation were investigated using OM,XRD,SEM/EDAX and EPMA, the results indicated that the chromia scale formed on RexOy-dispersed coating was thinner and finer-grained. The effect of RexOy on the microstructure and the oxidation of the chromizing coating is discussed in this work.