Evaluation of the Corrosion Resistance of Fe–Al–Cr Alloys in Simulated Low NO x Environments

Deacon, Ryan M.; DuPont, J. N.; Kiely, Christopher J.; Marder, A. R.; Tortorelli, P.F.

doi:10.1007/s11085-009-9150-5

Cited by 7 publications

(6 citation statements)

References 31 publications

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“…Corrosion resistance experiments for Fe-Cr-Al alloys show Cr depletion in the Fe-10Al-5Cr alloy. 30 In the oxidation experiments of Fe 3 Al-͑0,2,4,6%͒Cr alloys a Cr-free region was observed. 31 In low Al or Si iron-chromium alloys the inward growth of Cr 2 O 3 was deduced to be initiated due to FIG.…”

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confidence: 97%

Third element effect in the surface zone of Fe-Cr-Al alloys

et al. 2010

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The third element effect to improve the high temperature corrosion resistance of the low-Al Fe-Cr-Al alloys is suggested to involve a mechanism that boosts the recovering of the Al concentration to the required level in the Al-depleted zone beneath the oxide layer. We propose that the key factor in this mechanism is the coexistent Cr depletion that helps to maintain a sufficient Al content in the depleted zone. Several previous experiments related to our study support that conditions for such a mechanism to be functional prevail in real oxidation processes of Fe-Cr-Al alloys.One of the best alloys regarding corrosion resistance at high temperature is Fe-Al. To maintain good oxidation resistance both the oxygen penetration through the oxide layer to the alloy and iron diffusion to the surface should be kept blocked. However, this blocking to be effective the Al concentration in bulk should be at least 10-15 at. %. 1 Unfortunately, this amount of Al makes the alloy very brittle consequently limiting the usability of Fe-Al in applications requiring ductile materials. However, the brittleness problem can be solved by adding, e.g., chromium to the alloy. Cr considerably improves the formation of the protective Al 2 O 3 scale so that the amount of Al can be reduced to an acceptable level ensuring reasonable mechanical properties for the alloy.Chromium addition to Fe-Al is an example of a more general so-called third element effect ͑TEE͒ frequently discussed in literature. 2 Adding 10 at. % Cr to Fe-Al, for instance, allows to reduce the Al concentration to 3 at. % without weakening the protecting layer at the surface. 2 Several phenomena have been proposed to be responsible for the observed TEE in Fe-Cr-Al alloys. 3 Early theories associated this effect to a transition from internal to external oxidation. 4Later, it was argued that Cr can inhibit the external oxidation of Fe. 2 Most recently, Cr 2 O 3 was considered as nucleation centers for the ␣-Al 2 O 3 , which may improve corrosion protection in contrast to the other transient aluminas. 5 At low temperatures Cr improves the oxidation resistance of FeCr-Al due to the fast formation of Cr 2 O 3 compared to that of ␣-Al 2 O 3 . 6,7 In this Brief Report, using a first-principles quantum-mechanical approach, we shed light on another possible mechanism responsible for the TEE in Fe-Cr-Al system. The proposed mechanism takes place under the surface through the interface between two different bulk regions. The first one is the deep bulk and the other one is the surface zone where the concentrations differ from those of the deep bulk due to, e.g., surface oxidation. However, it is worth to note that the proposed phenomenon is in principle quite general expected to appear in many ternary alloys whenever suitable conditions prevail.Our computer modeling is based on the density-functional theory 8 in combination with the generalized gradient approximation. 9 The Kohn-Sham equations were solved using the exact muffin-tin orbitals ͑EMTO͒ method. [10][11][12][13] The EMTO method ...

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confidence: 97%

Third element effect in the surface zone of Fe-Cr-Al alloys

et al. 2010

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“…Clearly, the addition of chromium was beneficial, but whether it was due to the formation of Cr 2 O 3 or to the chromium affecting the formation of Al 2 O 3 , for example, could not be determined in the present work. A more detailed description and analytical electron microscopy analysis of the role of chromium on the Fe-12.5Al alloy is presented in Part II of this work [23].…”

Section: Discussionmentioning

confidence: 99%

“…Considering the typical non-protective nature of iron sulfides on iron aluminum alloys, it is concluded that a more protective layer eventually formed underneath the iron sulfide film and acted as a sufficient diffusion barrier to inhibit the transport of either sulfur or iron ions through the scale. Further examination of the scale development on this alloy is presented in Part II [23].…”

Section: Discussionmentioning

confidence: 99%

Evaluation of the Corrosion Resistance of Fe–Al–Cr Alloys in Simulated Low NO x Environments

et al. 2009

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Due to their excellent corrosion resistance, iron aluminum alloys are currently being considered for use as weld claddings in fossil fuel fired power plants. The susceptibility to hydrogen cracking of these alloys at higher aluminum concentrations has led researchers to examine the effect of chromium additions on the corrosion resistance of lower aluminum alloys. In this work, three iron aluminum alloys were exposed to simulated coal combustion environments at 500 and 700°C for short (100 h) and long (5000 h) isothermal durations. Scanning electron microscopy was used to analyze the corrosion products. All alloys exhibited excellent corrosion resistance during short term exposures. For longer test times, increasing the aluminum concentration improved alloy corrosion resistance. The addition of chromium to the binary iron aluminum alloy prevented the formation iron sulfide and resulted in slower corrosion kinetics. A general classification of the scales developed on these alloys is presented.

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“…For instance, slurry aluminides have been exposed to steam for over 22,000 h in the bypass of a steam turbine at 640 °C and 180 bar without substrate degradation and under laboratory testing conditions (100% steam, 650 °C, 1 bar) the same coatings have reached 50,000 h of exposure (the test is still ongoing) . DuPont et al have also demonstrated that FeCrAl containing alloys exhibit an outstanding corrosion resistance in sulfidizing and oxidizing conditions due to the formation of a protective Al 2 O 3 scale stabilized by the presence of Cr .…”

Section: Introductionmentioning

confidence: 99%

“…Moreover, FeCrAl alloys are currently under study due to their low cost and excellent corrosion resistance. However there are still weldability issues that need to be addressed .…”

Section: Introductionmentioning

confidence: 99%

Laboratory corrosion testing of coatings and substrates simulating coal combustion under a low NO_x burner atmosphere

Agüero

Gutiérrez

Muelas

et al. 2013

Materials & Corrosion

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It is certainly a difficult task to evaluate new materials and coatings to be used for boilers in power plants, as conditions are extremely complex, comprising a highly erosive environment, high temperature, highly corrosive gases, and reactive deposits. In particular, early catastrophic failures, as well as higher degradation rates have been observed on different power plant boiler components when operating under atmospheres containing low levels of oxygen. These atmospheres are typical of low NO x burners, and can be more corrosive than normal oxidizing conditions. The presence of a sulfidizing atmosphere as well as ash deposits present in boilers, are in part responsible of this accelerated damage. In this work, testing under a low oxygen atmosphere has been carried out on T22 and P92 uncoated and coated specimens. The atmosphere was equal to that measured in a Spanish coal-fired power plant (ENDESA, Compostilla, León) and the test temperature was 580 8C. Tested coatings were slurry applied aluminides, as well as two HVOF sprayed coatings including a commercially deposited Cr 2 C 3 NiCr, and a newly developed Cr 2 O 3 -Cr composite coating. The specimens were covered with ash (taken from the plant) prior to testing. After testing, the uncoated substrates exhibited high thickness oxides with some sulfide inclusions whereas all tested coatings were very protective. Exposed samples of T22 tubes employed in the Compostilla power plants were analyzed and compared with the corresponding specimens tested in the laboratory. In both cases, the scales contained Fe 3 O 4 and FeS but the sulfide content was significantly higher in the scale formed in the plant. Moreover, ash particles were found embedded in the both scales.

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Evaluation of the Corrosion Resistance of Fe–Al–Cr Alloys in Simulated Low NO x Environments

Cited by 7 publications

References 31 publications

Third element effect in the surface zone of Fe-Cr-Al alloys

Third element effect in the surface zone of Fe-Cr-Al alloys

Evaluation of the Corrosion Resistance of Fe–Al–Cr Alloys in Simulated Low NO x Environments

Laboratory corrosion testing of coatings and substrates simulating coal combustion under a low NO_x burner atmosphere

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Evaluation of the Corrosion Resistance of Fe–Al–Cr Alloys in Simulated Low NO x Environments

Cited by 7 publications

References 31 publications

Third element effect in the surface zone of Fe-Cr-Al alloys

Third element effect in the surface zone of Fe-Cr-Al alloys

Evaluation of the Corrosion Resistance of Fe–Al–Cr Alloys in Simulated Low NO x Environments

Laboratory corrosion testing of coatings and substrates simulating coal combustion under a low NOx burner atmosphere

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Laboratory corrosion testing of coatings and substrates simulating coal combustion under a low NO_x burner atmosphere