Subsurface Depletion and Enrichment Processes During Oxidation of a High Chromium, Laves-Phase Strengthened Ferritic Steel

Asensio, C.; Chyrkin, A.; Niewolak, L.; Konoval, V. P.; Hattendorf, Heike; Kuhn, Bernd; Singheiser, L.; Quadakkers, W. J.

doi:10.1149/1.3590258

Cited by 20 publications

(2 citation statements)

References 16 publications

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“…Enrichment-depletion of Laves-phase in the subsurface zone of Crofer 22H has been previously reported by Asensio et al and was attributed to Nb uphill diffusion in the subscale Cr-depletion profile as well as to preferential nucleation at the scaleealloy interface [29,34,35].…”

Section: Crofer 22hsupporting

confidence: 69%

Long-term behaviour of solid oxide fuel cell interconnect materials in contact with Ni-mesh during exposure in simulated anode gas at 700 and 800 °C

Garcia-Fresnillo

Shemet

Chyrkin

et al. 2014

Journal of Power Sources

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Section: Crofer 22hsupporting

confidence: 69%

Long-term behaviour of solid oxide fuel cell interconnect materials in contact with Ni-mesh during exposure in simulated anode gas at 700 and 800 °C

Garcia-Fresnillo

Shemet

Chyrkin

et al. 2014

Journal of Power Sources

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“…This can be seen in the crosssectional images in Figure 105 The effects in the Ni-based alloy are more severe than would occur in a ferritic or austenitic steel due to a greater effect of the Cr content on Nb activity. [89] There were not significant amounts of degradation with the aged OCS and OCT specimens, and the large build-up of Laves phase and NbC at the surface as well as the correlation seen previously between higher volume fractions of these phases increasing corrosion resistance indicates that these phases are effecting the corrosion mechanism in some way. It could possibly be that with a larger amount of Nb tied up in these phases, there is less in the austenite matrix, producing a locally increased amount of chromium in the matrix available to form the protective oxide scale.…”

Section: Ocs and Oct Scm Resultsmentioning

confidence: 56%

Determination of the Initiation and Propagation Mechanism of Fireside Corrosion

2015

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A variety of deposit compositions were examined in short-term laboratory tests with the aim of determining the corrosion mechanisms of fireside corrosion for a range of chromiaforming alloys in various combustion systems. The deposits formed in boilers are complex, and despite decades of study, the propagation mechanism of fireside corrosion is not well understood. Alkali iron trisulfates, which are stabilized by SO 3 in the gas atmosphere, have been believed to be the major corrosive species for many years. The propagation mechanism for fireside corrosion was investigated using T92 (a typical ferritic boiler steel) and a model austenitic Fe-Ni-Cr alloy and synthetic coal ash deposits. The metal loss, corrosion product morphologies, and compositions were carefully characterized in order to define a propagation mechanism. The corrosive species responsible for degradation was a (Na,K) 2 SO 4 -Fe 2 (SO 4 ) 3 solution and not alkali iron trisulfates, which is contrary to what has been believed for decades.The formation of the liquid deposit is similar to Type II hot corrosion of gas turbine engines.The mechanism is a synergistic dissolution process similar to that which can occur for hot corrosion as well. Simultaneous basic and acidic dissolution of protective Cr 2 O 3 and Fe 2 O 3 disrupts protective oxide formation and locally produces negative solubility gradients at the oxide/salt interface. The dissolved Fe 2 O 3 and Cr 2 O 3 reprecipitate where there is lower solubility, creating the observed corrosion products. The effect of the deposit composition, gas atmosphere iii composition, alloy composition, temperature, and deposit thickness were examined with respect to the proposed fireside corrosion mechanism. These measurements were found to be consistent with the proposed mechanism based on synergistic fluxing.iv Oxy-fuel firing is one of three ways in which CCS can be accomplished. The other two ways are post-combustion capture, where the CO 2 is removed from the flue gas after combustion, and pre-combustion capture, where the CO 2 is removed from the fuel before combustion. Oxy-1 fuel firing is carrying out the combustion in an environment consisting of recirculated flue gases containing primarily CO 2 , steam and pure oxygen instead of air in order to create a flue gas with minimal amounts of N 2 . A schematic diagram of the oxy-fuel process is shown below in Figure 1. Figure 1: Schematic diagram of oxy-fuel combustionOxy-fuel combustion produces flue gases containing approximately 60%CO 2 -30%H 2 O-4%O 2 -5%N 2 , whereas traditional air-fired combustion produces flue gases containing 74%N 2 -[2] The flue gases in oxy-fuel systems are able to be recycled through the fuel burners leading to decreased CO 2 emissions. However, with the reduced amounts of nitrogen, the products of the oxy-fuel combustion process have increased amounts of CO 2 , steam and corrosive gases, such as SO 2 that can cause significant corrosion in superheater and reheater 2 tubes when compared to air-fired combustion. Bu...

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Oxide scale formation and subsurface phase transformations during long‐term steam exposure of the cobalt base alloy 25

Fresnillo

Chyrkin

Hüttel

et al. 2012

Materials & Corrosion

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High chromium nickel and cobalt base alloys are presently being considered as construction materials for various components in high efficiency steam turbines with envisaged operating temperatures around 700 °C. In the present study, the steam oxidation behavior of the cobalt base alloy 25 in the temperature range 650–800 °C was investigated whereby exposures up to 10 000 were carried out. Post exposure analyses of the oxidation products and alloy microstructures included optical microscopy, scanning and transmission electron microscopy, X‐ray diffraction analysis and secondary neutrals mass spectrometry. The experiments showed in all cases formation of oxide scales mainly consisting of chromia with minor amounts of outer Cr/Mn spinel and internal silica. The oxidation induced chromium depletion resulted in a number of microstructural changes in the subsurface depletion layer. First, the intermetallic phase Co3W became enriched at the scale alloy interface. Additionally, the chromium rich M23C6 and the tungsten rich M6C dissolved in the depletion layer. The mechanisms for occurrence of these effects are discussed on the basis of phase equilibria in the binary Co–W and the ternary Co–Cr–W system.

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Subsurface Depletion and Enrichment Processes During Oxidation of a High Chromium, Laves-Phase Strengthened Ferritic Steel

Cited by 20 publications

References 16 publications

Long-term behaviour of solid oxide fuel cell interconnect materials in contact with Ni-mesh during exposure in simulated anode gas at 700 and 800 °C

Long-term behaviour of solid oxide fuel cell interconnect materials in contact with Ni-mesh during exposure in simulated anode gas at 700 and 800 °C

Determination of the Initiation and Propagation Mechanism of Fireside Corrosion

Oxide scale formation and subsurface phase transformations during long‐term steam exposure of the cobalt base alloy 25

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