On the reasons for the effects of dispersions of stable oxides and additions of reactive elements on the adhesion and growth-mechanisms of chromia and alumina scales-the ?sulfur effect?

Lees, D. G.

doi:10.1007/bf00656731

Cited by 189 publications

(39 citation statements)

References 16 publications

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“…It has been suggested that sulfur influences scale growth, both for alumina 74 and chromia 75 . Using scanning transmission electron microscopy, Fox el al 75 have found sulfur at Cr 2 O 3 scale grain boundaries, and Lees 76 proposed that the presence of sulfur there promotes cation transport at oxide grain boundaries. Whether this is true needs to be confirmed by more studies.…”

Section: Sulfurmentioning

confidence: 99%

Impurity Effects on Alumina Scale Growth

Hou¹

2003

Journal of the American Ceramic Society

141

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Most high temperature resistant alloys oxidize to form an external alumina layer, or scale, whose slow growth protects the underlying alloy from continued aggressive oxidation. The growth of the Al 2 O 3 scale is controlled by the transport of oxygen inward and aluminum outward through it, with the rate dominated by the fastest diffusing specie down the fastest path. Components in the alloy can be incorporated into the growing Al 2 O 3 layer, hence affect the transport rates of oxygen and/or aluminum. This paper summarizes existing experimental data to assess the possible effect of these incorporated impurities on the growth rate and transport properties of Al 2 O 3 scales formed on Fe, Ni and Pt based alloys. The amount and distribution of the alloy base metal, sulfur impurity and reactive elements, such as Hf, Y, Zr and Ce, in the alumina scale are evaluated. Their effect on the oxidation and transport rates through the scale are discussed and compared with Al and O diffusion rates deduced from creep studies.

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Section: Sulfurmentioning

confidence: 99%

Impurity Effects on Alumina Scale Growth

Hou¹

2003

Journal of the American Ceramic Society

141

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“…The segregation of indigenous sulfur impurity from an alloy to the Ah03 scale/alloy interface during high temperature oxidation is often considered the major cause that weakens the interface [1][2][3][4]' Systematic studies of the chemical changes at Ah03/alloy interfaces as a function of oxidation time have in recent years been carried out for FeCrAI [5], Fe3AI and FeAI [6,7], where the alloys normally contain about 20 ppm of sulfur. Although sulfur was found to be the major segregant at these scale/alloy interfaces, the segregation behavior, in terms of rate and amount, varied significantly with different alloys and differed from surface segregation.…”

Section: Introductionmentioning

confidence: 99%

Interfacial Segregation, Pore Formation, and Scale Adhesion on NiAl Alloys

2005

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Ni-40 and 50at%AI alloys were oxidized at 1000°C for various times in oxygen. Auger electron microscopy was used to study the interface chemistry after scale spallation in ultra high vacuum. The interfacial failure stresses were determined using a tensile pull tester and related to the interface chemistry, pore area and density. Results showed that sulfur started to segregate to areas ofthe Ah03INi40AI interface where the scale was in contact with the alloy after a complete layer of a-Ah03 developed there; the concentration then gradually increased to a steady level of~2 at%. However, sulfur did not segregate to similar areas of the Ah03INi50AI interface even after extended oxidation when it was amply present on interfacial void faces. This behavior demonstrated a strong dependence of interface segregation on NiAI alloy composition. Interfacial failure stress was found to decrease with increasing sulfur content between voids and with higher interface porosity. The level of porosity was strongly related to the sulfur content in the alloy. When Ni40AI was doped with excess sulfur, the segregation behavior did not change, but the interfacial pore density increased significantly. The detrimental effect of sulfur on scale adhesion is two-fold: to weaken the interface and to enhance interfacial pore formation.

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“…9,10) S content at the interface was previously measured by Auger analysis, for example on NiAl alloy with 3-4 ppm S after 10 h of oxidation at 1 000°C was reported to be about 2 at%.…”

Section: Discussionmentioning

confidence: 97%