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Tolpygo, V.K.; Viefhaus, H.

doi:10.1023/a:1018818906559

Cited by 28 publications

(14 citation statements)

References 24 publications

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“…The effect of Pt on S segregation in b-NiAl has also been investigated, and Pt was found to reduce S segregation to the free surface [18][19][20] and even eliminate S at the interface [18]. Hf, a reactive element, is expected to reduce, if not eliminate, S segregation to the interface, as has been found for Zr in Fe 3 Al [21] and Y in FeCrAl [22][23][24]. Hf has been shown to segregate to the Al 2 O 3 /NiAl interface (K. L. More, private communication, unpublished results), but whether it stops S segregation has yet to be determined.…”

Section: Introductionmentioning

confidence: 99%

Sulfur Segregation at Al2O3/γ-Νi + γ′-Ni3Al Interfaces: Effects of Pt, Cr and Hf Additions

2009

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The interfacial chemistry that developed as a result Al 2 O 3 -scale growth on c-Mi ? c 0 -Ni 3 Al alloys at 1150°C was studied using scanning Auger microscopy after the oxide layer was scratched to spall under ultra-high vacuum. The extent of scale spallation was used to evaluate semi-quantitatively the interfacial strength. The alloys investigated were primarily c 0 in structure, containing 22 at.% Al plus further additions of Pt, Cr and/or Hf. In the case of the binary c ? c 0 alloy, it was found that a sub-monolayer of sulfur segregated at the alloy/scale interface. Platinum reduced and hafnium eliminated sulfur segregation, but chromium enhanced it through Cr-S cosegregation, even on Pt-and Hf-containing alloys. Platinum also segregated slightly at the alloy/scale interface. The interface strength was a strong function of the sulfur content. Beyond the effect of eliminating S segregation, Pt and Hf both showed additional beneficial effects on alumina scale adhesion.

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Section: Introductionmentioning

confidence: 99%

Sulfur Segregation at Al2O3/γ-Νi + γ′-Ni3Al Interfaces: Effects of Pt, Cr and Hf Additions

2009

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“…Further, little sulfur segregation at the scale/coating interface occurs, but due to the limitation of the SEM sensitivity, it is difficult to detect the existence of such sulfur segregation. It is true that sulfur segregation, at monolayer thickness, but up to 50% concentration, are typically demonstrated by some highly sensitive, surface- analytical techniques, such as Auger [11][12][13][14][16][17] and XPS, 15 rather than EDS over the years. Smeggil et al 8 reported a small interfacial sulfur peak on a 10-20 ppm sulfur alloy by scanning-electron-microprobe techniques.…”

Section: Methodsmentioning

confidence: 99%

“…In recent years, many researchers in hightemperature oxidation of metals have focused their attention on sulfur segregation at the interface between thermally grown Al 2 O 3 scales and various heat-resisting alloys including Fe-Cr-Al and Ni-Cr-Al. [10][11][12][13][14][15][16][17] Many studies support the proposed ''the sulfur-effect'' model, including some indirect results showing that sulfur removal from an alloy by H 2 -annealing greatly improves the oxide-scale adhesion. [18][19][20][21][22] Smialek has suggested that for single-crystal superalloys the sulfur content should be lower than 0.2 ppm to maximize scale adhesion for a 1 mm-thick sample.…”

Section: Introductionmentioning

confidence: 99%

Effect of Nanocrystallization on Sulfur Segregation in Fe–Cr–Al Alloy during Oxidation at 1000°C

Yang

Wang

2006

Oxid Met

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From the 1980's a theory named ''the sulfur effect'' has been applied to explain the scale adhesion and the reactive-element effect (REE) during high-temperature oxidation. It claims that the bond between the oxide scale and the metal substrate is intrinsically strong and that impurity sulfur in the metal segregates at the oxide scale/substrate interface and weakens the bond, and that REs getter the sulfur impurity and prevent it from segregating to the interface. In the present study, a cast polycrystalline sulfur-containing Fe-25Cr-5Al-1S (wt.%) alloy and its magnetron-sputtered nanocrystalline coating were oxidized at 1000°C, and the specimens were examined by XRD and SEM. The scale formed on the cast alloy was cracked and detached from the substrate even after isothermal exposure, and obvious sulfur enrichment was detectable at the scale/substrate interface. While, the scale formed on the nanocrystalline coating was very adherent after 100 cycles oxidation. Here, sulfur was preferentially distributed in the outer scale and internal oxides rather than at the scale/substrate interface. These results provide evidence that nanocrystallization can prevent sulfur segregation at the scale/substrate interface, hence enhance scale adhesion.

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“…The analyzed areas are oxide imprints, and segregation could only have happened before the separation. Using Auger electron spectroscopy, Tolpygo and Viefhaus [19] also detected S at an intact FeCrAl/Al 2 O 3 interface, with a coverage of 50 at.%. According to these authors, the driving force of this segregation is plastic stress and strain to the interface.…”

Section: Adherence Loss At An Intact Interfacementioning

confidence: 99%

Characterization of Sulfur Distribution in Ni-Based Superalloy and Thermal Barrier Coatings After High Temperature Oxidation: A SIMS Analysis

et al. 2009

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Sulfur segregation was characterized by secondary ion mass spectrometry (SIMS) in uncoated single-crystal Ni-based AM1 superalloys with various S contents and on NiPtAl, NiAl and NiPt bondcoats of complete TBC systems. In spite of technical difficulties associated with diffuse sputtered interfaces, an original sample preparation technique and a careful choice of analysis conditions enabled a chemical characterization of S distribution below metal/oxide interfaces. An initial heterogeneous distribution of S in as-received high S (3.2 ppmw) AM1 was measured. After oxidation, a S depletion profile formed, with a slope that depended on the initial bulk S content. GDMS measurements enabled a quantitative distribution of S in oxidized low S (0.14 ppmw) AM1 to be constructed and discussed in relation to equilibrium surface segregation of S on Ni. The quantity of S integrated in the thermally grown oxide (TGO) was estimated and found to be very similar to that measured from depletion found in the metal. Localized S enrichments in Pt-containing coatings are related to a possible beneficial trapping mechanism of Pt on the adherence of oxide scales.

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Cited by 28 publications

References 24 publications

Sulfur Segregation at Al2O3/γ-Νi + γ′-Ni3Al Interfaces: Effects of Pt, Cr and Hf Additions

Sulfur Segregation at Al2O3/γ-Νi + γ′-Ni3Al Interfaces: Effects of Pt, Cr and Hf Additions

Effect of Nanocrystallization on Sulfur Segregation in Fe–Cr–Al Alloy during Oxidation at 1000°C

Characterization of Sulfur Distribution in Ni-Based Superalloy and Thermal Barrier Coatings After High Temperature Oxidation: A SIMS Analysis

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