Author/Editor		Milošev, I; Abels, JM; Strehblow, HH; Navinšek, B; Metikoš-Huković, M
Title		High temperature oxidation of thin CrN coatings deposited on steel
Type		članek
Source		J Vac Sci Technol A
Vol. and No.		Letnik 14, št. 4
Publication year		1996
Volume		str. 2527-34
Language		eng
Abstract		High temperature oxidation of thin (0.34 micro m) CrN (PVD) coatings deposited on steel substrate was studied in the temperature range from 450-750 degrees C in an oxygen flow by surface analytical methods (XPS, AES, EDS, SEM, AFM). The formation of a very thin surface overlayer of chromium oxynitride was observed even at room temperature. After oxidation at temperatures higher than 450 degrees C the formation of a thick separate Cr2O3 layer on top of the nitride coating was observed. The thickness and morphology of Cr2O3 layer depend on the temperature. It is suggested that the oxidation of CrN proceeds by progressive replacement of nitrogen by oxygen. Parallel to the formation of a Cr2O3 layer, diffusion of iron, as the main constituent of the substrate, occurs. After oxidation at temperatures >-600 degrees C localislands of FeO are observed at the surface and identified by the combined application of surface analytical techniques with high lateral resolution, i.e., small area XPS, point AES, and EDS. Diffusion ofiron probably starts at the pinholes in the coating, although in the later stage or at higher temperatures diffusion through the pinholes is no longer the dominanting mechanism. it is suggested that the difference in the thermal expansion coefficients between the nitride coating and the substrate leads to thermal stresses which affect the adhesion at the coating/substrate interface. The interface becomes permeable at some local defects, thus enabling a fast diffusion of iron. Penetration of iron results in the formation of local pits at the surface where the ion oxide deposites are formed with the oxygen of the gas phase. These local islands of iron(II) oxide are surrounded by the continous protecting layer of Cr2O3.
Descriptors		STEEL CHROMIUM ALLOYS CORROSION SPECTROMETRY, X-RAY EMISSION