Oxidation at 900 °C of the chromized coatings on A3 carbon steel with the electrodeposition pretreatment of Ni or Ni-CeO2 film

Chromized coatings developed on a mild carbon steel (A3) using a conventional halide-activated pack cementation method at 1120 degrees C inevitably formed chromium carbides in the surface zone, which is the crucial factor giving the coatings a fast scaling rate in 5 pct O(2) + N(2) at 900 degrees C, and simultaneously a severe scale spallation during cooling. No chromium carbides were seen in the chromized coatings, when the steel was pretreated with a similar to 80-mu m-thick precursor film of electrodeposited Ni Without or with dispersions of similar to 5.5 wt pct CeO(2) nanoparticles. However, during oxidation of the chromized, Ni-film-treated coating in 5 pet O(2) + N(2), fresh chromium carbides were intensively precipitated in the Coating near-surface zone. The carbides' oxidation caused the formation of the scale, with an increased susceptibility to cracking and spalling. For the chromized, Ni-CeO(2)-nanocomposite-treated A3, chromium carbides were sporadically precipitated throughout the entire coating during oxidation, and the negative effect of the carbides on oxidation was prevented. This, together with the reactive element effect (REE) of the added CeO(2) during oxidation, is proposed for this coating, for the purpose of thermally forming a chromia scale with a noticeably reduced growth rate and also an enhanced adhesion.