The influence of chromium addition on the toughness of γ-Niα-Al2O3 interfaces

Gaudette, F.; Suresh, S.; Evans, A.G.; Dehm, Gerhard; Rühle, M.

doi:10.1016/s1359-6454(97)00064-5

Cited by 60 publications

(39 citation statements)

References 22 publications

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“…There are also a number of published studies directed at slow crack growth at metal-alumina interfaces and which have determined values of interface toughness, r j [22][23][24][25][26]. There is also an implicit or explicit relationship between toughness and moisture (in air) or sulfur segregation.…”

Section: Discussionmentioning

confidence: 99%

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Delayed alumina scale spallation on Rene'N5+Y: moisture effects and acoustic emission

Smialek

Morscher

2002

Materials Science and Engineering: A

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The single crystal superalloy Rene'N5 (with Or without V-doping and hydrogen annealing) was cyclically oxidized at 1 150°C for 1000 hours. After considerable scale growth (~500 hr.), even the adherent alumina scales formed on Y -doped samples exhibited delayed interfacial spallation during subsequent water immersion tests, performed up to 1 year after oxidation. Spallation was characterized by weight loss, the amount of spalled area, and acoustic emission response. Hydrogen annealing (prior to oxidation) reduced spallation both before and after immersion, but without measurably reducing the bulk sulfur content of the Y -doped alloys. The duration and frequency of sequential, co-located acoustic emission events implied an interfacial crack growth rate at least 10-3 mis, but possibly higher than 10 2 mls. This is much greater than classic moisture-assisted slow crack growth rates in bulk alumina (10-6 to 10-3 m!s), which may still have occurred undetected by acoustic emission. An alternative failure sequence is proposed: an incubation process for preferential moisture ingress leads to a local decrease in interfacial toughness, thus allowing fast fracture driven by stored strain energy.

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Section: Discussionmentioning

confidence: 99%

“…There is also an implicit or explicit relationship between toughness and moisture (in air) or sulfur segregation. Some pertinent aspects and results are summarized in Table IV 2 , respectively, when tested in dry N2 [22,23]. A stress corrosion mechanism was operative.…”

Section: Discussionmentioning

confidence: 99%

Delayed alumina scale spallation on Rene'N5+Y: moisture effects and acoustic emission

Smialek

Morscher

2002

Materials Science and Engineering: A

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“…Both contain Cr, Pt and Hf, and both have scales of similar thickness and composition, but the latter had significantly lower interface strength due to higher S level at the interface. This alloy also had Cr enriched at the interface ( and Ni20Cr/Al 2 O 3 interfaces that the enrichment of Cr can profoundly increase the interfacial fracture toughness [47]. It cannot be concluded that the same result takes place for thermally grown scale/alloy interfaces; however, even if it were the case, any positive effect of Cr must have been overwhelmed by the negative effect of sulfur.…”

Section: Effect Of S Hf and Pt On Interface Strengthmentioning

confidence: 95%

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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“…Interface cracks that debonded in room air at mixed mode fracture energies as low as 10 J/m 2 were found to blunt significantly in a dry nitrogen environment; such cracks would not grow at driving forces up to 100 J/m 2 [9]. Furthermore, a study investigating the mode I fracture of sapphire/nickel interfaces in a dry environment revealed that considerable crack blunting (CTOD ~ 140 nm) could be measured prior to the final failure at ~ 70 J/m 2 [24].…”

Section: Metal/ceramic Interface Studiesmentioning

confidence: 99%

“…While no evidence of moisture assisted slow crack growth under static loading has been found for the aluminum/alumina system, such behavior has been observed for sapphire/gold [19], sapphire/nickel [9], and glass/copper [37,38] interfaces in sandwich specimens. Additionally, it is known that both polycrystalline alumina and sapphire are susceptible to moisture assisted crack growth under static loading in a humid environment [60,61].…”

Section: Constraint Effects In the Alumina/aluminum Systemmentioning

confidence: 99%

Interfacial and near interfacial crack growth phenomena in metal bonded alumina

Kruzic

2001

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This study examines the mechanisms of interfacial and near interfacial crack propagation associated with the failure of sandwich specimens consisting of 99.5% pure polycrystalline alumina: 1) liquid state bonded with 99.999% pure aluminum layers and 2) partial transient liquid phase (PTLP) bonded using copper/niobium/copper interlayers.For the former system, the aluminum layer thickness was varied from 5 to 100 µm; it was found that the 3-point unnotched bending strength of the aluminum bonded joints increased, and the fracture toughness decreased, with decreasing layer thickness.Strength beams failed by ductile failure in the aluminum while fracture toughness samples failed by brittle fracture in the alumina. Under cyclic loading, crack growth occurred primarily by separating the aluminum from the alumina with evidence of ductile fatigue striations; cracks deviated into the alumina only for thin layered samples at high driving forces. Cyclic fatigue thresholds increased with decreasing layer thickness; however, the change to a brittle fatigue mechanism for thin layered samples at high driving forces was detrimental to the overall fatigue resistance. Under static loading in 2 moist air, interfacial separation was never observed at measurable rates (≥ 10 -9 m/sec); however, for 5 and 35 µm thick layered samples, cracks deviated off the interface and grew, sometimes stably, into the alumina resulting in time dependent failure.For alumina PTLP bonded with copper/niobium/copper interlayers, the mean interfacial fracture toughness was found to decrease from 39 J/m 2 to 21 J/m 2 as temperature was increased from 25 to 1000°C. At room temperature, cyclic fatigue crack propagation occurred at both the niobium/alumina interface and in the alumina, with higher fatigue thresholds resulting from a predominantly near interfacial (alumina) crack path. During both fracture and fatigue failure, residual copper at the interface deformed and remained adhered to both sides of the fracture surface, while separation of the niobium/alumina interface appeared essentially brittle in both cases. The observed behaviors of all samples are examined in terms of modulus mismatch effects, the level of plastic constraint, the relative crack propagation resistance of each observed crack path, the loading conditions, extrinsic toughening from ductile phase and/or alumina grain bridging, and environmental influences.i

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The influence of chromium addition on the toughness of γ-Niα-Al2O3 interfaces

Cited by 60 publications

References 22 publications

Delayed alumina scale spallation on Rene'N5+Y: moisture effects and acoustic emission

Delayed alumina scale spallation on Rene'N5+Y: moisture effects and acoustic emission

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

Interfacial and near interfacial crack growth phenomena in metal bonded alumina

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