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Title: Influence of a Cerium Surface Treatment on the Oxidation Behavior of Cr2O3-Forming Alloys (title on slides varies: Oxidation Behavior of Cerium Surface Treated Chromia Forming Alloys)

Abstract

Current goals of the U.S. Department of Energy’s Advanced Power Systems Initiatives include coal generation at 60% efficiency, which would require steam temperatures of up to 760°C. This temperature will require the construction of boiler and turbine components from austenitic stainless steels and nickel alloys. Many of the alloys being considered for use are primarily Cr2O3 forming alloys [1-4]. It is well known that the addition of a small amount of reactive elements, such as the rare earths elements Ce, La, and Y, can significantly improve the high temperature oxidation resistance of both iron- and nickel- base alloys. A list of the benefits of the reactive element effect include: (i) slowing scale growth, (ii) enhancing scale adhesion; and (iii) stabilizing Cr2O3 formation at lower Cr levels. The incorporation of the reactive element can be made in the melt or through a surface infusion or surface coating. Surface modifications allow for the concentration of the reactive element at the surface where it can provide the most benefit. This paper will detail a Ce surface treatment developed at NETL that improves the high temperature oxidation resistance of Cr2O3 forming alloys. The treatment consists of painting, dip coating, or spraying the alloy surfacemore » with a slurry containing CeO2 and a halide activator followed by a thermal treatment in a mild (x10-3 Torr) vacuum. During treatment the CeO2 reacts with the alloy to for a thin CrCeO3-type scale on the alloy surface. Upon subsequent oxidation, scale growth occurs at a reduced rate on alloys in the surface treated condition compared to those in the untreated condition.« less

Authors:
; ; ;
Publication Date:
Research Org.:
National Energy Technology Laboratory (NETL), Pittsburgh, PA, and Morgantown, WV
Sponsoring Org.:
USDOE - Office of Fossil Energy (FE)
OSTI Identifier:
916963
Report Number(s):
DOE/NETL-IR-2007-236
TRN: US0804396
DOE Contract Number:
None cited
Resource Type:
Conference
Resource Relation:
Conference: 21st Annual Conference on Fossil Energy Materials, Knoxville, TN, Apr. 30-May 1, 2007
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 24 POWER TRANSMISSION AND DISTRIBUTION; ALLOYS; CERIUM; DIP COATING; NICKEL ALLOYS; OXIDATION; POWER SYSTEMS; RARE EARTHS; STAINLESS STEELS; SURFACE COATING; SURFACE TREATMENTS

Citation Formats

Alman, D.E., Holcomb, G.R., Adler, T.A., and Jablonski, P.D.. Influence of a Cerium Surface Treatment on the Oxidation Behavior of Cr2O3-Forming Alloys (title on slides varies: Oxidation Behavior of Cerium Surface Treated Chromia Forming Alloys). United States: N. p., 2007. Web.
Alman, D.E., Holcomb, G.R., Adler, T.A., & Jablonski, P.D.. Influence of a Cerium Surface Treatment on the Oxidation Behavior of Cr2O3-Forming Alloys (title on slides varies: Oxidation Behavior of Cerium Surface Treated Chromia Forming Alloys). United States.
Alman, D.E., Holcomb, G.R., Adler, T.A., and Jablonski, P.D.. 2007. "Influence of a Cerium Surface Treatment on the Oxidation Behavior of Cr2O3-Forming Alloys (title on slides varies: Oxidation Behavior of Cerium Surface Treated Chromia Forming Alloys)". United States. doi:. https://www.osti.gov/servlets/purl/916963.
@article{osti_916963,
title = {Influence of a Cerium Surface Treatment on the Oxidation Behavior of Cr2O3-Forming Alloys (title on slides varies: Oxidation Behavior of Cerium Surface Treated Chromia Forming Alloys)},
author = {Alman, D.E. and Holcomb, G.R. and Adler, T.A. and Jablonski, P.D.},
abstractNote = {Current goals of the U.S. Department of Energy’s Advanced Power Systems Initiatives include coal generation at 60% efficiency, which would require steam temperatures of up to 760°C. This temperature will require the construction of boiler and turbine components from austenitic stainless steels and nickel alloys. Many of the alloys being considered for use are primarily Cr2O3 forming alloys [1-4]. It is well known that the addition of a small amount of reactive elements, such as the rare earths elements Ce, La, and Y, can significantly improve the high temperature oxidation resistance of both iron- and nickel- base alloys. A list of the benefits of the reactive element effect include: (i) slowing scale growth, (ii) enhancing scale adhesion; and (iii) stabilizing Cr2O3 formation at lower Cr levels. The incorporation of the reactive element can be made in the melt or through a surface infusion or surface coating. Surface modifications allow for the concentration of the reactive element at the surface where it can provide the most benefit. This paper will detail a Ce surface treatment developed at NETL that improves the high temperature oxidation resistance of Cr2O3 forming alloys. The treatment consists of painting, dip coating, or spraying the alloy surface with a slurry containing CeO2 and a halide activator followed by a thermal treatment in a mild (x10-3 Torr) vacuum. During treatment the CeO2 reacts with the alloy to for a thin CrCeO3-type scale on the alloy surface. Upon subsequent oxidation, scale growth occurs at a reduced rate on alloys in the surface treated condition compared to those in the untreated condition.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2007,
month = 4
}

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  • In order to study the effects on oxidation behavior of changing the composition of oxide scales without changing the composition of the underlying alloys, thin films, which contained various amounts of Y{sub 2}O{sub 3}, Cr{sub 2}O{sub 3}, or Al{sub 2}O{sub 3} have been deposited on Fe-25%Cr and Fe-25%Cr-5%Al prior to oxidation. There were major differences between the (Fe-25%Cr)-(Cr{sub 2}O{sub 3}-Y{sub 2}O{sub 3}) and (Fe-25%Cr-5%Al)-(Al{sub 2}O{sub 3}-Y{sub 2}O{sub 3}) systems. A film of Cr{sub 2}O{sub 3} on Fe-25%Cr reduced the oxidation rate and Cr{sub 2}O{sub 3}-Y{sub 2}O{sub 3} films reduced it still further. A film of Al{sub 2}O{sub 3} on Fe-25%Cr-5%Almore » reduced the rate considerably, but Al{sub 2}O{sub 3}-Y{sub 2}O{sub 3} films exhibited rates that were greater than those for Al{sub 2}O{sub 3} alone. A film, which consisted entirely of Y{sub 2}O{sub 3}, greatly decreased the oxidation rate of Fe-25%Cr, but increased that of Fe-25%Cr-5%Al. The changes in oxidation rate produced by Y{sub 2}O{sub 3} in the (Fe-25%Cr)-(Cr{sub 2}O{sub 3}-Y{sub 2}O{sub 3}) system were much greater than those produced in the (Fe-25%Cr-5%Al)-(Al{sub 2}O{sub 3}-Y{sub 2}O{sub 3}) system. As far as oxidation rate is concerned, the optimum amount of Y{sub 2}O{sub 3} in the (Fe-25%Cr)-(Cr{sub 2}O{sub 3}-Y{sub 2}O{sub 3}) system was found to be greater than or equal to 40% and less than 100%; in the Fe-25%Cr-5%Al-(Al{sub 2}O{sub 3}-Y{sub 2}O{sub 3}) system it was approximately 10%. In thermal-cycling tests, the results for the (Fe-25%Cr)-(Cr{sub 2}O{sub 3}-Y{sub 2}O{sub 3}) system followed the same pattern as that for the isothermal tests; a film of Y{sub 2}O{sub 3} reduced the oxidation rate and a film of Cr{sub 2}O{sub 3}-33%Y{sub 2}O{sub 3} reduced it still further.« less
  • The cost of solid oxide fuel cells (SOFC) can be significantly reduced by using interconnects made from ferritic stainless steels. In fact, several alloys have been developed specifically for this application (Crofer 22APU and Hitachi ZMG323). However, these steels lack environmental stability in SOFC environments, and as a result, degrade the performance of the SOFC. A steel interconnect can contribute to performance degradation through: (i) Cr poisoning of electrochemically active sites within the cathode; (ii) formation of non-conductive oxides, such as SiO2 or Al2O3 from residual or minor alloying elements, at the base metal-oxide scale interface; and/or (iii) excessive oxidemore » scale growth, which may also retard electrical conductivity. Consequently, there has been considerable attention on developing coatings to protect steel interconnects in SOFC environments and controlling trace elements during alloy production. Recently, we have reported on the development of a Cerium surface treatment that improves the oxidation behavior of a variety alloys, including Crofer 22APU [1-5]. Initial results indicated that the treatment may improve the performance of Crofer 22APU for SOFC application by: (i) retarding scale growth resulting in a thinner oxide scale; and (ii) suppressing the formation of a deleterious continuous SiO2 layer that can form at the metal-oxide scale interface in materials with high residual Si content [5]. Crofer 22 APU contains Fe-22Cr-0.5Mn-0.1Ti (weight percent). Depending on current market prices and the purity of raw materials utilized for ingot production, Cr can contribute upwards of 90 percent of the raw materials cost. The present research was undertaken to determine the influence of Cr content and minor element additions, especially Ti, on the effectiveness of the Ce surface treatment. Particular emphasis is placed on the behavior of low Cr alloys.« less
  • A surface treatment was applied to the surface of Type 347 stainless steel to enhance oxidation resistance. The treatment consisted of dip coating coupons in a CeO2 and halide activator slurry, followed by a thermal treatment at 900C in an inert atmosphere for 12 hours. Cyclical oxidation tests were conducted at 800C in either dry air or air+3%H2O. In dry air, the treatment reduced the oxidation rate (reduced the magnitude of weight gain) of the alloy by a factor of three. Protective chromium based oxide and spinel ((Mn,Cr)3O4 and (Cr,Fe)2O3) phases formed on the surface of the untreated and treatedmore » alloy. More significantly, the treatment suppressed the oxide scale spallation that occurred upon cyclical exposure of this alloy to moist air. In moist air, less protective chromite (FeCr2O4), magnetite (Fe+2Fe2+3O4), and hematite (Fe2O3) formed as oxide products on the surface of the base alloy. The treated alloy did not spall during exposure to moist air, and interestingly, the treated alloy possessed similar oxidation rates (magnitude of weight gain) in both moist and dry air. The same protective chromium based oxide and spinel ((Mn,Cr)3O4 and (Cr,Fe)2O3) phases formed on the surface of the treated alloy exposed to both moist and dry air. In the aggressive moist environment, the Ce surface treatment suppressed the formation of less protective iron-oxides, and concomitant oxide scale spallation during thermal cycling.« less
  • Long-term, cyclic-oxidation testing in still air for about 2 years (720 days) at 982 C and 1 year (360 days) at 1093, 1149, and 1204 C has been conducted on the commercial, high-temperature chromia-forming HR-120, HR-160, and 230 alloys (all trademarks of Haynes International, Inc.). Each thermal cycle consisted of 30 days at temperature followed by about 4 hr at ambient. The results demonstrated the significant effects of alloy composition on long-term, cyclic-oxidation resistance. Each of the alloys exhibited scale spallation; however, the manner by which spallation occurred varied between the alloys. The 230 alloy, which contains 0.02 wt.% La,more » exhibited partial scale spallation, thus allowing for the easier formation of a protective or semiprotective Cr{sub 2}O{sub 3}-rich scale during subsequent oxidation. The HR-160 alloy exhibited complete spallation owing largely to its relatively high silicon content (2.75 wt.%). However, the silicon was also beneficial in promoting protective or semiprotective scale formation when the exposed alloy was subsequently oxidized. The HR-120 alloy showed the poorest cyclic-oxidation resistance, due in part to poor scale adhesion and the tendency of the iron in this alloy (33 wt.%) to eventually oxidize and result in the formation of a less-protective scale. All of the alloys underwent internal attack in the form of internal oxidation and void formation. In most cases, the extent of internal attack was significantly greater than that of metal loss.« less