Effect of Zr addition on the microstructure of the alumina scales on FeCrAlY-alloys

Wessel, E.; Kochubey, V.; Naumenko, D.; Niewolak, L.; Singheiser, L.; Quadakkers, W. J.

doi:10.1016/j.scriptamat.2004.07.023

Cited by 69 publications

(42 citation statements)

References 8 publications

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“…Or, if the diffusion of aluminium through the alumina layer is faster than the oxygen diffusion, the oxide grows outwards. The third possible oxide growth mechanism is based on the formation of a duplex oxide layer and occurs when the diffusion rates of aluminium and oxygen are almost equal [2][3][4]. Several papers have been published concerning the diffusion and growth mechanisms of alumina layers on FeCrAl alloys at high temperatures [3,[5][6][7][8][9][10].…”

Section: Introductionmentioning

confidence: 99%

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High temperature oxidation of FeCrAl‐alloys – influence of Al‐concentration on oxide layer characteristics

Engkvist

Bexell

Grehk

et al. 2009

Materials & Corrosion

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The superior high temperature oxidation resistance of FeCrAl alloys relies on the formation of a dense and continuous protective aluminium oxide layer on the alloy surface when exposed to high temperatures. Consequently, the aluminium content, i.e. the aluminium concentration at the alloy-oxide layer interface, must exceed a critical level in order to form a protective alumina layer. In the present study the oxidation behaviour of six different FeCrAl alloys with Al concentrations in the range of 1.2-5.0 wt% have been characterised after oxidation at 900 8C for 72 h with respect to oxide layer surface morphology, thickness and composition using scanning electron microscopy, energy dispersive X-ray spectroscopy and Auger electron spectroscopy. The results show that a minimum of 3.2 wt% Al in the FeCrAl alloy is necessary for the formation of a continuous alumina layer. For Al concentrations in the range of 2.0-3.0 wt% a three-layered oxide layer is formed, i.e. an oxide layer consisting of an inner alumina-based layer, an intermediate chromia-based layer and an outer iron oxide-based layer. In contrast, the 1.2 wt% Al FeCrAl alloy is not able to form a protective oxide layer inhibiting extensive oxidation.

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Section: Introductionmentioning

confidence: 99%

“…The AlN particles formed in the early stages of breakaway may also dissolve because Al 2 O 3 is thermodynamically more stable than AlN, causing further internal oxidation [4,11,15,16].…”

Section: Introductionmentioning

confidence: 99%

High temperature oxidation of FeCrAl‐alloys – influence of Al‐concentration on oxide layer characteristics

Engkvist

Bexell

Grehk

et al. 2009

Materials & Corrosion

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“…Specimens with a large Zr reservoir tend to exhibit "over-doping," here accompanied by extensive internal oxidation. The overdoping effect of RE-containing FeCrAl alloys was discussed by several authors; [5,[17][18][19][20] it was frequently found to result in increased oxidation rates sometimes accompanied by a decreased scale adhesion. [17] Excess RE's in the alloy may result in formation of intermetallic compounds with Al.…”

Section: Discussion Of the Oxidation Behaviormentioning

confidence: 99%

“…Wessel et al [20] showed the RE reservoir to be of great importance for scale formation on FeCrAlY type wrought alloys; later the significance of the reactive element reservoir for overall oxidation performance could also be demonstrated for NiCoCrAlY type coating systems. [21] The present studies confirm that the occurrence of over-doping substantially depends on specimen thickness, thus on the prevailing RE reservoir.…”

Section: Discussion Of the Oxidation Behaviormentioning

confidence: 99%

Effect of Zr Content on the Morphology and Emissivity of Surface Oxide Scales on FeCrAlY Alloys

et al. 2015

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The investigation aims at obtaining a life time extension of FeCrAlY heating elements by increasing the emissivity of the alumina surface scales. This approach will allow the use of a lower heating element temperature without decreasing the usable heat output. For this purpose, the oxidation mechanisms of Zr-doped FeCrAlY model alloys were investigated. For thick specimens a high Zr addition is accompanied by an undesired rapid increase of the oxidation rate adversely affecting the life time of the component. However, for thin foil heating elements (typically 50-200 mm thickness) an optimized high Zr content might be a suitable concept for obtaining a high emissivity, because apparently, a dark appearing, high emissivity oxide may be obtained without occurrence of dramatic internal oxidation.

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“…HfO 2 is known to be an excellent oxygen conductor that assists the oxygen diffusion through the TGO. Other mechanisms which are proposed to account for accelerated oxidation by Hf additions, like pores in the TGO, a higher grain boundary density, and hampered Y incorporation into the scale by Hf (or alternatively by Zr) [12] are less likely.…”

Section: Introductionmentioning

confidence: 99%

Lifetime‐determining spalling mechanisms of NiCoCrAlRE / EB‐PVD zirconia TBC systems

Fritscher

Schulz

Leyens

2007

Materialwissenschaft Werkst

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The mechanisms that control the lifetime of thermal barrier coating (TBC) systems have been traced by two particular overlay bondcoats serving as model systems: superalloy pins (IN100, CMSX-4) with two alternative NiCoCrAlRE (RE: Hf, Y) bond coat compositions (i) NiCoCrAlY without and (ii) with co-dopants of silicon and hafnium. On top an electron-beam physical-vapor deposited (EB-PVD) yttria partially stabilized zirconia (YPSZ) TBC commonly mixed with 2 wt.% hafnia, or, rarely with 10 wt.%, was applied. The test pins were thermo-cycled at 1100 and 1150 C until failure. Identical lifetimes in cyclic tests on YPSZ TBCs with 2 (relatively high sintering rate) and 10 wt.% hafnia (relatively low sintering rate) preclude an effect of diffusion mechanisms of the YPSZ TBC on lifetime. The fit of lifetimes and test temperatures to Arrhenius-type relationships gives activation energies for failure. These energies agree with the activation energies for anion and cation diffusion in alumina for the respective bondcoat variant:(i) for the NiCoCrAlY/TBC system for O 2-diffusion in alumina, (ii) for the NiCoCrAlYSiHf/TBC system for Al 3+ diffusion in alumina.SEM and EDS investigations of the thermally grown oxides (TGOs) confirm the mechanisms responsible for TBC failure as indicated by activation energies. Two categories of failure can be distinguished: (i) NiCoCrAlY coatings fail by an "adhesive mode of failure" along smooth bond coat/TGO interfaces driven by a critical TGO thickness. (ii) NiCoCrAlYSiHf coatings fail later and more reluctantly by a "cohesive" crack mode via de-cohesion at the TGO/TBC interface. In the latter case a quasi-integrity of the crack-affected TGO is lengthily maintained up to failure by a crack-pinning mechanism which runs via Al 3+ supply from the bondcoat.Keywords

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Effect of Zr addition on the microstructure of the alumina scales on FeCrAlY-alloys

Cited by 69 publications

References 8 publications

High temperature oxidation of FeCrAl‐alloys – influence of Al‐concentration on oxide layer characteristics

High temperature oxidation of FeCrAl‐alloys – influence of Al‐concentration on oxide layer characteristics

Effect of Zr Content on the Morphology and Emissivity of Surface Oxide Scales on FeCrAlY Alloys

Lifetime‐determining spalling mechanisms of NiCoCrAlRE / EB‐PVD zirconia TBC systems

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