Oxygen Diffusion in Alumina. Application to Synthetic and Thermally Grown Al<sub>2</sub>O<sub>3</sub>

S. Chevalier, B. Lesage, C. Legros, G. Borchardt, G. Strehl, M. Kilo Laboratoire de Recherches sur la Reactivite des Solides, CNRS UMR 5613, Universite de Bourgogne, F-21078 Dijon, France Laboratoire d’Etudes des Materiaux Hors Equilibre, CNRS UMR 8647, Universite Paris XI, F-91405 Orsay, France. Institut fur Metallurgie, TU Clausthal, Robert Koch Strasse 42, D38678 Clausthal-Zellerfeld, Germany. * sebastien.chevalier@u-bourgogne.fr

Role of Minor Element Addition in the Formation of Thermally Grown Alumina Scales

The Role of Zr in the High-Temperature Oxidation of Fe<sub>3</sub>Al

The paper describes an examination of the effect of the addition of zirconium as a third element on the heat-resisting properties and explains the high temperature oxidation mechanism of Fe3Al intermetallic compounds. The Fe3Al and Fe3Al-0,05Zr specimens have been isothermally oxidized in the temperature range of 1173-1473 K in synthetic air for 100 hrs. The formed oxide layer, about 1,5-2 μm thick, was Al2O3. An examination of the cross-sectioned scales by SEM-EDS showed that the alumina layer consisted of a small inner columnar layer and an outer equiaxed grain layer. Additionally, very fine (50-150 nm) oxide grains rich in Zr, further identified as ZrO2, were found across the alumina sca…

Influence of the mode of introduction of a reactive element on the high temperature oxidation behavior of an alumina-forming alloy. Part I: Isothermal oxidation tests

Several routes of yttrium introduction were applied to test the high temperature oxidation performance of a FeCrAl alloy. Isothermal oxidation tests were described in a previous paper (Part I of this paper in this journal, 2004, 55, 352). Cyclic oxidation tests were performed in air under atmospheric pressure on blank specimens, Y 2 O 3 sol-gel coated-, Y 2 O 3 metal-organic chemical vapor deposited (MOCVD)-, yttrium ion implanted-alloys, as well as on a steel containing 0.1 wt.% of yttrium as an alloying element. For the 20 hours cycles, all the samples, except FeCrAl-0.1Y, exhibit weight losses after a few cycles, indicating drastic spallation of the oxide scales. The MOCVD coated specime…

MOCVD deposition of YSZ on stainless steels

Abstract Yttria stabilized zirconia was deposited on stainless steel using the metal–organic chemical vapor deposition (MOCVD) technique, from β-diketonate precursors. The variation of the evaporation temperatures of yttrium and zirconium precursor allowed to control the level of Y within the film. Over the temperature range 125–150 °C, the Y content increased from 2.5 to 17.6 at.%. X-ray diffraction (XRD) analyses evidenced tetragonal phase of zirconia when the Y content was below 8 at.%, and cubic phase for higher concentration. Sputtered neutral mass spectrometry (SNMS) profiles confirmed that the control and stability of Y precursor temperature were of major importance to guarantee the …

Study of the electronic and atomic structure of thermally treated SrTiO3(110) surfaces

The electronic structure of heated SrTiO3(110) surfaces was investigated with metastable impact electron spectroscopy and ultraviolet photoelectron spectroscopy (He(I). Scanning tunnelling microscopy and atomic force microscopy (AFM) were used to study the topology of the surface. The crystals were heated up to 1000 °C under reducing conditions in ultrahigh vacuum or under oxidizing conditions in synthetic air for 1 h, respectively. Under both conditions microfacetting of the surface is observed. The experimental results are compared with ab initio Hartree-Fock calculations, also presented here, carried out for both ideal and reconstructed SrTiO 3(110) surfaces. The results give direct evid…

Mechanisms Involved by Reactive Elements upon High Temperature Chromia Scale Growth

The influence of Y 2 O 3 , Pr 2 O 3 , Nd 2 O 3 , Sm 2 O 3 and Yb 2 O 3 coatings on Fe-30Cr alloy oxidation behaviour was investigated at 1000°C in air under atmospheric pressure. Isothermal exposures indicated that the Y 2 O 3 coating was the most protective after 100 hours. Pr 2 O 3 , Nd 2 O 3 and Sm 2 O 3 coatings were less effective, but the less beneficial effect was observed when Yb 2 O 3 coating was applied onto the Fe-Cr alloy surface. Two-stage oxidation experiments in 16 O 2 and then 18 O 2 were performed to get information about the chromia growth phenomena with and without reactive elements. The 18 O-tracer distribution was determined by secondary ion mass spectrometry (SIMS) and…