Effects of water vapor on high temperature oxidation of cryomilled NiCoCrAlY coatings in air and low-SO2 environments

Kaplin, Cory; Brochu, Mathieu

doi:10.1016/j.surfcoat.2011.03.026

Cited by 30 publications

(17 citation statements)

References 18 publications

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“…The effect of water vapor addition on the residual stress levels is ambiguous because of different oxide growth kinetics, which influences multiple opposing effects. The presence of water vapor during thermal cycling leads to an increase of the oxidation rate of HVOF NiCoCrAlY BCs and promotes the formation of spinel phases [27]. Moreover, the rate of scale spallation from bare BC surfaces is increased [14].…”

Section: Discussionmentioning

confidence: 99%

Effects of thermal cycling parameters on residual stresses in alumina scales of CoNiCrAlY and NiCoCrAlY bond coats

Nordhorn

Mücke

Unocic

et al. 2014

Surface and Coatings Technology

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Furnace cycling experiments were performed on free-standing high-velocity oxygen-fuel bond coat samples to investigate the effect of material composition, surface texture, and cycling conditions on the average stresses in the formed oxide scales after cooling. The oxide scale thicknesses were determined by SEM image analyses and information about the stresses were acquired by photo-stimulated luminescence-spectroscopy. Additionally, the scale thickness dependent stress fields were calculated in finite-element analyses including approximation functions for the surface roughness derived on the basis of profilometry data. The evolution of the average residual stress as a function of oxide scale thickness was subject to stochastic fluctuations predominantly caused by local scale spallations. In comparison to the supplementing modeling results, thermal stresses due to mismatch of thermal expansion coefficients are identified as the main contribution to the residual stresses. The theoretical results emphasize that analyses of spectroscopic data acquired for average stress investigations of alumina scales rely on detailed information about microstructural features.

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Section: Discussionmentioning

confidence: 99%

Effects of thermal cycling parameters on residual stresses in alumina scales of CoNiCrAlY and NiCoCrAlY bond coats

Nordhorn

Mücke

Unocic

et al. 2014

Surface and Coatings Technology

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“…Therefore, evaluating thickness -or mass gain, correlatively -as a function of environment, as is often done in TGO studies, does not fully capture relevant behavior. It may not even elucidate the most important mechanistic aspects of the TGO development: while understanding the effect of the exposure environment on overall oxide growth kinetics is important (as has been addressed elsewhere [22]), when one considers that TGO-YSZ interfacial weakness is a known mode of TBC failure, it is also critically important to quantify the amount of interface that is compromised by the presence of spinel. Having provided spatial context to plan view BSE data in this section -both in terms of TGO thickness and alloy-to-oxide phase relationships -even lower magnification BSE images (400 μm HFW vs. the 150 μm HFW images in Fig.…”

Section: Microstructural Observationmentioning

confidence: 99%

“…Could it be solely responsible for all spinel growth, even the most copious amounts? If the answer is yes, environmental conditions may be the key, specifically water vapor, which has been shown to increase the amount of spinel at the TGO surface of both NiCoCrAlY [19][20][21][22] and the analogous aluminaformer, FeCrAlY [23]. Enhanced oxidation kinetics have been observed in the transient stage, when less dense metastable aluminas (e.g.…”

Section: Introductionmentioning

confidence: 99%

“…δ-, γ-and θ-alumina phases) develop before later transforming into stable α-alumina, a more robust diffusion barrier. One study attempted to connect these concepts for MCrAlY, postulating that water vapor extends the transient stage, thus allowing more diffusion of spinel-forming cations to the TGO surface [22]. The conclusions were drawn from limited exposures (24 h, 0-8% H 2 O) that do not narrowly target the transient stage, and on only one sample type (thermally sprayed NiCoCrAlY); additional study is needed to validate the claim and elaborate upon the mechanistic connections.…”

Section: Introductionmentioning

confidence: 99%

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Transient stage oxidation of MCrAlY bond coat alloys in high temperature, high water vapor content environments

Sullivan

Mumm

2014

Surface and Coatings Technology

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a b s t r a c tIn order to evaluate the effect of water vapor on transient stage oxidation of MCrAlY (M_Ni and Co) bond coats, short-term exposures were carried out on thermally sprayed and cast alloy specimens at 1125°C in a range of N 2 -O 2 -H 2 O environments, and resultant thermally grown oxide (TGO) development was evaluated. On cast metal specimens, for which the three-phase alloy dispersion is coarse, growth of unwanted (Ni,Co)(Al,Cr) 2 O 4 spinel was primarily correlated spatially to the Al-poor phases, namely γ, while the preferred TGO product, α-alumina, correlated to the Al-rich β phase. At higher water vapor contents, spinel nucleated and grew out past the γ boundaries to develop above β, too. By thresholding plan view BSE images of TGO surfaces, the amount of spinel vs. alumina surface area coverage was quantified. Spinel coverage was correlated to increasing P H2O , increasing P O2 and, for the highest surface coverage observed, a combination of high P H2O and low P O2 . When a worst case spinel-creating environment of 30 vol.% H 2 O and 10 vol.% O 2 was presented to the more commercially relevant (i.e. sprayed) version of CoNiCrAlY, complete spinel coverage was achieved, indicating that what is often thought of as a long-term spinel growth problem related to Al-depletion of the bond coat, can be created in several hours. Water vapor may enhance transient spinel growth by extending the lifetime of the metastable γ-and δ-alumina phases, the defect spinel structure of which promotes the diffusion of Cr, Co and Ni cations to the TGO surface, whereupon they participate in the development of non-ideal oxides such as spinel. All exposures were carried out without a yttria-stabilized zirconia (YSZ) top coat present.

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“…Its influence on hot oxidation, when present in air or in other gases, was examined in many earlier studies. This was notably done in the cases of pure metals [5,6], intermetallic compounds [7,8], metallic coatings [9], alloys based on heavy refractory metals [10] and even ceramic materials [11].…”

Section: Introductionmentioning

confidence: 99%

Kinetic and metallographic study of oxidation at high temperature of cast Ni 25Cr alloy in water vapour rich air

Aranda¹,

Schweitzer²,

Mouton³

et al. 2015

Materials at High Temperatures

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International audienceThe high temperature oxidation behaviour of a Ni-25 wt-% Cr alloy in air enriched with water vapour (180 mbars H2O) was studied at 1000, 1100, 1200 and 1300 degrees C. The oxidised samples were characterised by X-ray diffraction, electron microscopy and wavelength dispersion spectroscopy. The obtained data were compared to the ones earlier obtained for the same alloy oxidised in dry air. Water vapour globally induced at all temperatures a decrease of the parabolic constant Kp and an increase in the chromia volatilisation constant Kv. The oxide scales do not present morphologic difference between the two atmospheres. After oxidation in humidified air the scale thickness is thinner and the Cr depleted depth is lower than in dry air

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Effects of water vapor on high temperature oxidation of cryomilled NiCoCrAlY coatings in air and low-SO2 environments

Cited by 30 publications

References 18 publications

Effects of thermal cycling parameters on residual stresses in alumina scales of CoNiCrAlY and NiCoCrAlY bond coats

Effects of thermal cycling parameters on residual stresses in alumina scales of CoNiCrAlY and NiCoCrAlY bond coats

Transient stage oxidation of MCrAlY bond coat alloys in high temperature, high water vapor content environments

Kinetic and metallographic study of oxidation at high temperature of cast Ni 25Cr alloy in water vapour rich air

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