Atomic scale studies of the mechanisms of internal oxidation

Jang, Ho Won; Chan, D. K.; Seidman, David N.; Merkle, K. L.

doi:10.1016/0956-716x(93)90256-r

Cited by 8 publications

(2 citation statements)

References 17 publications

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“…8) and the elemental profiles (Figs. 9 and 10) suggest that selective oxidation might have occurred as internal Cr 2 O 3 formation with scattered nuclei of oxides on the surface, which is supported by the theoretical conditions for internal oxidation: [18][19][20][21][22] (i) the chemical affinity of oxygen for Cr is higher than that for Fe; (ii) there is no passive oxide layer; and (iii) oxygen has a higher permeability (c O D O ) than Cr (c Cr D Cr ) in bcc Fe-Cr alloy, i.e. c O D O 54610 211 cm 2 s 21 (in bcc-iron at 800uC 23,24 ) and c Cr D Cr 54610 212 cm 2 s 21 (in Fe-16Cr at 800uC 25 ).…”

Section: Heat Treatments In N 2 -H 2 Gas Mixtures -Annealingmentioning

confidence: 66%

Effects of heat treatments on near surface elemental profiles of Fe–15Cr polycrystalline alloy

Park¹,

Spiegel²

2005

Corrosion Engineering, Science and Technology

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For the development of optimised surface modification of Fe-Cr alloys, the surface chemistry of an Fe-15 at.-%Cr alloy specimen during the initial stage of oxidation was investigated as well as the effects of hydrogen during annealing and following oxidation. Samples were exposed to various heat treatment atmospheres at 800uC: annealing in N 2 -H 2 gas mixtures, oxidation in air and annealing then oxidation. After the heat treatments, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were employed to characterise the morphology, elemental depth profiles and the chemical states of the elements. In the initial stage of oxidation, the chemistry of the oxide layer on the surface transformed in the following sequence: Fe rich oxide R Duplex oxide layer (outer Fe rich and inner Cr rich) R Cr rich mono-phase layer (M 2 O 3 ). In the transformation, the reaction rate for the formation of the Cr rich oxide layer was controlled by the diffusion of cations. Annealing in H 2 -containing atmospheres increased the Cr content at the surface. An increase in hydrogen content in the atmosphere further increased both the Cr to Fe ratio in the near surface region, and the thickness of the layer affected by the heat treatment. Selective oxidation of chromium occurred as internal Cr 2 O 3 formation, as a function of the Cr content rather than the oxygen partial pressure. Hydrogen facilitated the diffusion of chromium, probably by cleaning of fast diffusion paths. The addition of hydrogen to the annealing atmosphere before the oxidation was beneficial to obtain a Cr rich oxide layer on the surface. a Cr total /Fe total atomic ratio; b Oxygen content 10 Depth profiles of annealed samples 11 Diffusion profiles of Cr Park and Spiegel Effects of heat treatments on near surface elemental profiles of Fe-15Cr alloy Corrosion Engineering, Science and Technology 2005 VOL 40 NO 3

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Section: Heat Treatments In N 2 -H 2 Gas Mixtures -Annealingmentioning

confidence: 66%

Effects of heat treatments on near surface elemental profiles of Fe–15Cr polycrystalline alloy

Park¹,

Spiegel²

2005

Corrosion Engineering, Science and Technology

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“…[15][16][17] On the other hand, a method without the procedure of adding Y 2 O 3 powder has been explored for fabrication of some other ODS alloys, for example, Ni, Cu, Co and Pt based alloys. [18][19][20][21] On the field of Fe based alloy, Schneibel and Shim has fabricated intermetallic compounds (Fe 17 Y 2 and Fe 11 TiY) to characterise the oxidation of Ti and Y in these compounds. 22 However, this method has not been widely used in the fabrication of ODS RAFM steels up to now.…”

Section: Introductionmentioning

confidence: 99%

Segregation and precipitation formation for in situ oxidised 9Cr steel powder

Wang

Liu

et al. 2016

Materials Science and Technology

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Powder and sintered bulk materials of a reduced activation steel with oversaturated Ti and Y are prepared by gas atomisation and sintering. Segregation on both the surface and interior of the powder particles are observed after an thermal treatment. The oxidation of the segregates promotes formation of clusters of large Y oxide crystals and thick continuously distributed Ti oxide layers on the surface of the powder particles. The oxidation also occurs within the powder particles and mainly forms larger Ti oxide dispersoids in the grain boundaries of the powder. The coarsening and aggregation of the oxide dispersoids occur with increasing duration of the thermal treatment. Yttrium is also segregated and precipitated in the grains of the powder particles.

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