Grain Boundary Segregation of Yttrium in Chromia Scales

Przybylski, K.; Garratt‐Reed, Anthony J.; Yurek, G. J.

doi:10.1149/1.2095646

Cited by 139 publications

(47 citation statements)

References 21 publications

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“…Evidence for the role of grain-boundary segregation of reactive elements in C r 2 0 3 was given by the experiments [36,37]. STEM measurements revealed that segregation of yttrium at the chromia grain boundaries does indeed occur.…”

Section: Alteration In the Number And Character Of Short-circuit Diffmentioning

confidence: 96%

The reactive element effect; ionic processes of grain-boundary segregation and diffusion in chromium oxide scales

Polman¹,

Fransen²,

Gellings³

1989

J. Phys.: Condens. Matter

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Abstract. The transport processes in chromium oxide reviewed here, are related to the basic ionic processes in oxides. Solid state science has been effective in describing the complicated diffusion-controlled oxide growth of chromium and chromia-forming alloys. Additions of reactive elements to chromia-forming alloys have a remarkably beneficial effect and this effect is also related to ionic transport processes in crystal lattices. Chromia-forming alloys are widely used in coal handling and conversion systems due to their good high-temperature corrosion properties; for industrial applications the requirement is that a good adherent protective oxide with a low diffusion of defects is formed. Recently, improved knowledge has been gained of the identity of the moving species and the values of the corresponding diffusion coefficients in chromia scales. STEM measurements give experimental support for the theory of grain-boundary segregation and blocking of grain-boundary diffusion by reactive elements.In this paper the current ideas on the transport processes in chromia and the role of rare earth additions on the corrosion behaviour are reviewed. In addition calculations on crystal lattices and grain boundaries are discussed. The calculations on chromia have been beneficially influenced by earlier theoretical considerations on nickel oxide. Consequently, results on (doped) nickel oxide as well as chromium oxide are discussed.

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Section: Alteration In the Number And Character Of Short-circuit Diffmentioning

confidence: 96%

The reactive element effect; ionic processes of grain-boundary segregation and diffusion in chromium oxide scales

Polman¹,

Fransen²,

Gellings³

1989

J. Phys.: Condens. Matter

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“…Research has shown yttria segregation at the grain boundaries [28]. However, here yttria is homogeneously distributed within the W matrix at atomic level.…”

Section: Importance Of Nano-scale Effects For Understanding the Oxidamentioning

confidence: 78%

“…The fact that small amounts of active elements, such as Y, substantially improve the adherence of oxide scales, was discovered in 1937 [25]. Since then Y has been added to various alloys and studies on the role of Y have been conducted [23,24,[26][27][28][29][30][31][32].…”

Section: Introductionmentioning

confidence: 99%

On Oxidation Resistance Mechanisms at 1273 K of Tungsten-Based Alloys Containing Chromium and Yttria

Klein

Wegener

Litnovsky

et al. 2018

Metals

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Tungsten (W) is currently deemed the main candidate for the plasma-facing armor material of the first wall of future fusion reactors, such as DEMO. Advantages of W include a high melting point, high thermal conductivity, low tritium retention, and low erosion yield. However, was an accident to occur, air ingress into the vacuum vessel could occur and the temperature of the first wall could reach 1200 K to 1450 K due to nuclear decay heat. In the absence of cooling, the temperature remains in that range for several weeks. At these temperatures, the radioactive tungsten oxidizes and then volatilizes. Smart W alloys are therefore being developed. Smart alloys are supposed to preserve properties of W during plasma operation while suppressing tungsten oxide formation in case of an accident. This study focuses on investigations of thin film smart alloys produced by magnetron sputtering. These alloys provide an idealistic system with a homogeneous distribution of the elements W, chromium (Cr), and yttrium (Y) on an atomic scale. The recommended composition is W with 12 weight % of Cr and 0.5 weight % of Y. Passivation and a suppression of WO 3 sublimation is shown. For the first time, the mechanisms yielding the improved oxidation resistance are analyzed in detail. A protective Cr 2 O 3 layer forms at the surface. The different stages of the oxidation processes up to the failure of the protective function are analyzed for the first time. Using 18 O as a tracer, it is shown for the first time that the oxide growth occurs at the surface of the protective oxide. The Cr is continuously replenished from the bulk of the sample, including the Cr-rich phase which forms during exposure at 1273 K. A homogenous distribution of yttria within the W-matrix, which is preserved during oxidation, is a peculiarity of the analyzed alloy. Further, an Y-enriched nucleation site is found at the interface between metal and oxide. This nucleation sites are deemed to be crucial for the improved oxidation resistance.

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“…The use of reactive elements, especially rare earths (RE) to improve high temperature oxidation resistance of chromium dioxide and alumina forming alloys is quite well documented. [1][2][3][4][5][6][7][8][9][10][11][12][13][14] The improvements are in the form of reduced oxidation rates and increased scale adhesion. The RE can be added to the alloy in elemental form or as oxide dispersions.…”

Section: Introductionmentioning

confidence: 99%

“…It can also be applied as an oxide coating to the alloy surface. [3][4][5][6][7]15 Various mechanisms have been proposed to explain the effect of reactive elements in improving oxidation resistance and the most widely accepted mechanism attributes it to segregation of the reactive elements to the interface or to the oxide scale grain boundaries and blocking of Cr ion diffusion though the oxide scale [8][9][10][11] Studies carried out by Seo et al, about the effect of addition of Ce, La and Y to a Fe-22Cr-0.5Mn alloy on the oxidation behavior of the alloy at 800 °C, indicated that Y was the most effective element to reduce the growth rate of the oxide scale. 12 In recent years a number of studies have been carried out to exploit the benefits of rare earth additions on oxidation behavior of chromium dioxide and alumina forming alloys.…”

Section: Introductionmentioning

confidence: 99%