High temperature oxidation behavior of yttrium dioxide coated Fe-20Cr alloy

Abstract

Long term isothermal and cyclic oxidation behavior of yttrium dioxide (Y2O3) coated Fe-20Cr alloy was studied. Oxidation tests were carried out in air for periods of up to 200 hours at 1000°C and the oxidation behavior of the alloy was evaluated gravimetrically. The Y2O3 coating reduced markedly the mass gain of the alloy. Energy dispersive spectroscopic analysis of scale sections on oxidized Y2O3 coated specimens revealed a Cr rich layer close to the metal/oxide interface and the presence of Y and Cr near the oxide/air interface, indicating diffusion of Cr through the Y2O3 layer. Further evidence of this diffusion was seen as change in colour of the Y2O3 coating from white to green after prolonged oxidation. X-ray diffraction analysis of the scale revealed perovskite-type YCrO3.This study attributes the increased oxidation resistance of the Y2O3 coated Fe-20Cr alloy to increased oxygen ion diffusion through the Cr2O3 scale due to YCrO3 formation and grain boundary segregated Y ion blocking alloy cation diffusion.