Effect of stabilising heat treatment on characteristics of electrolytic alumina coating on ferritic stainless steel

The effect of stabilising thermal treatment on the characteristics of conve rsion coatings modified by electrolytic alumina deposits have been studied using SIMS analysis and X-ray diffraction in grazing incidence. Before heat ing, alumina deposit obtained is in form of amorphous boehmite gel. Heat tr eatment at 800 degrees C in air lends to a very uniform coating morphology and induces diffusion phenomena. After heating (24 h), the coating is const ituted of two layers: an alumina (delta-Al2O3) outer layer and a chromium o xide (alpha-Cr2O3) inner layer. At the coating/steel interface mixed oxide (iron, chromite) are present. The electrolytic alumina deposit blocks the c hromium oxide in the deep zone.