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Behavior of Copper‐Containing High‐Entropy Alloys in Harsh Metal‐Dusting Environments

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Behavior of Copper‐Containing High‐Entropy Alloys in Harsh Metal‐Dusting Environments Ames Laboratory Accepted Manuscripts Ames Laboratory 2-12-2021 Behavior of copper‐containing high‐entropy alloys in harsh metal‐dusting environments Mathias C. Galetz Dechema Forschungsinstitut Clara Schlereth Dechema Forschungsinstitut Emma M. H. White Ames Laboratory, [email protected] Follow this and additional works at: https://lib.dr.iastate.edu/ameslab_manuscripts Part of the Metallurgy Commons Recommended Citation Galetz, Mathias C.; Schlereth, Clara; and White, Emma M. H., "Behavior of copper‐containing high‐entropy alloys in harsh metal‐dusting environments" (2021). Ames Laboratory Accepted Manuscripts. 853. https://lib.dr.iastate.edu/ameslab_manuscripts/853 This Article is brought to you for free and open access by the Ames Laboratory at Iowa State University Digital Repository. It has been accepted for inclusion in Ames Laboratory Accepted Manuscripts by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. Behavior of copper‐containing high‐entropy alloys in harsh metal‐dusting environments Abstract Metal dusting is still an unresolved issue at high temperatures. Currently, two material‐related strategies to mitigate metal dusting are described in the literature. On the one hand, highly alloyed materials are used, which contain large amounts of protective oxide‐forming elements, such as Cr, Al, and Si. The second mitigation strategy is based on inhibiting the catalytic effect of Fe, Ni, and Co. These elements all strongly catalyze the formation of solid carbon from the gas phase. Combining the catalytic protection of Cu alloying for metal dusting with protection by a classical alumina/chromia barrier is a native feature that high‐entropy alloys (HEAs) can offer. In this study, the behavior of different equiatomic HEAs with and without Al and/or Cu are studied when exposed at 620°C in a highly aggressive metal‐dusting environment. Keywords high‐entropy alloys, metal dusting Disciplines Materials Science and Engineering | Metallurgy This article is available at Iowa State University Digital Repository: https://lib.dr.iastate.edu/ameslab_manuscripts/ 853 Received: 12 September 2020 | Revised: 10 January 2021 | Accepted: 15 January 2021 DOI: 10.1002/maco.202012075 ARTICLE Behavior of copper‐containing high‐entropy alloys in harsh metal‐dusting environments Mathias C. Galetz1 | Clara Schlereth1 | Emma M. H. White2 1Dechema‐Forschungsinstitut— High‐Temperature Materials, Abstract Frankfurt, Germany Metal dusting is still an unresolved issue at high temperatures. Currently, two 2 Ames Laboratory Ringgold Standard material‐related strategies to mitigate metal dusting are described in the literature. Institution—Materials Sciences and Engineering, Ames, Iowa, USA On the one hand, highly alloyed materials are used, which contain large amounts of protective oxide‐forming elements, such as Cr, Al, and Si. The second Correspondence mitigation strategy is based on inhibiting the catalytic effect of Fe, Ni, and Co. Mathias Galetz, Dechema Forschungsinstitut—High‐Temperature These elements all strongly catalyze the formation of solid carbon from the gas Materials, Theodor‐Heuss‐Allee 25, phase. Combining the catalytic protection of Cu alloying for metal dusting with 60486 Frankfurt, Germany. protection by a classical alumina/chromia barrier is a native feature that Email: [email protected] and [email protected] high‐entropy alloys (HEAs) can offer. In this study, the behavior of different equiatomic HEAs with and without Al and/or Cu are studied when exposed at Funding information 620°C in a highly aggressive metal‐dusting environment. Office of Energy Efficiency and Renewable Energy, KEYWORDS Grant/Award Number: DE‐AC02‐ high‐entropy alloys, metal dusting 07CH11358 1 | INTRODUCTION usually manifests as local, extremely fast‐growing damage in the form of “pits” outofwhichthedust(“metal dust”)from The processing and storage of energy through the turnover metal particles, oxides, cementite, graphite, and amorphous of carbon‐containing gases suffer from one of the most carbon grows, which gave this corrosion issue its name. In critical material corrosion problems at high temperatures. addition, it is difficult to predict because it often affects only The carbon‐rich, thermodynamically unstable gases of such small areas of components, which see the most critical processes induce the extremely aggressive high‐temperature conditions, especially in heat exchangers, as well as on – corrosion form of “metal dusting.”[1 3] It occurs in conven- intakes, outlets, transition pieces, and cooler flanges. tional processes of energy technologies and the chemical Currently, two material‐related strategies to mitigate engineering and petrochemical industry, as well as in- metal dusting are described in the literature. On the one novative and new efficient processes, such as dry reforming hand, highly alloyed materials are used, which contain or co‐electrolysis. Metal dusting appears at temperatures large amounts of protective oxide‐forming elements, such ranging from about 400°C to 850°C, with the greatest risk in as Cr, Al, and Si. The durability of these materials under the range of 600–650°C.[3,4] It is characterized by high highly carburizing conditions relies on the formation of carbon ingress into the material followed by carbide and dense and slow‐growing oxide barriers, which protect the graphite formation within the microstructure. The graphite base material from the corrosive environment. Examples formation leads to a strong volume increase and ultimately of such materials include Alloy 602 CA, Alloy 690, Alloy – to disintegrating stresses in the material. The corrosion 699 XA, or Alloy 693.[5 8] In addition, from the class of This is an open access article under the terms of the Creative Commons Attribution‐NonCommercial‐NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non‐commercial and no modifications or adaptations are made. © 2021 The Authors. Materials and Corrosion published by Wiley‐VCH GmbH Materials and Corrosion. 2021;1–11. www.matcorr.com | 1 2 | GALETZ ET AL. high‐alloyed steels, the Al2O3‐forming Kanthal APMT studied HEA. The oxidation behavior of this alloy at in- (Fe‐21Cr‐5Al‐3Mo),[9] as well as aluminide coatings,[10] termediate temperatures was studied by Holcomb should be mentioned. The second mitigation strategy is et al.[33] They reported the long‐term oxidation behavior based on inhibiting the catalytic effect of Fe, Ni, and Co, in the air at 650°C and 750°C, which is dominated by the which all strongly catalyze the formation of solid carbon formation of an Mn/Cr oxide scale. Substituting Al and from the gas phase.[1] The alloying elements Sn, Ge, and Cu for Mn makes this alloy an ideal candidate for car- Cu have the demonstrated capability to catalytically burizing environments; as discussed earlier, alloying suppress carburization in metal‐dusting environ- with Al, Cu, and Cr is key to metal‐dusting protection. – ments.[11 13] On the basis of this concept, coatings with Initial work on the AlCu‐CoCrFeNi system with an Ge and Sn were developed,[11,14,15] as well as alloys with overlay welding process[34] showed that Cu modification – Cu.[16 20] Cu was shown to decrease the metal‐dusting promoted spallation of the oxide scales at high tem- attack significantly, an effect ascribed to the low solubi- peratures, compared to a Cu‐free variation. To date, there lity for carbon in Cu as well as the inhibition of graphite is no literature data for this system in the metal‐dusting formation within the alloy. In a study on the metal environment and temperature range, even though the dusting of binary Ni‐Cu alloys, Nishiyama et al.[19] mechanical properties of such alloys at metal‐dusting showed that with a Cu concentration of 20 wt%, the temperatures are likely more in line than at higher surface reaction is inactivated within the CO‐containing temperatures. In this study, the behavior of different synthesis gas and the material is protected from metal equiatomic HEAs with and without Al and/or Cu are dusting. The impact of different Cu levels in austenitic studied when exposed at 620°C in a highly aggressive steels was investigated by Zhang and Young,[16,20] and metal‐dusting environment for potential application in was shown to improve the alloys' resistance up to a the area of energy processing and storage through the certain content, for example, up to 10 wt% Cu for 310 turnover of carbon‐containing gases. steel. Above a certain level, depending on the steel grade, aCu‐solid solution phase is precipitated, which leads to deleterious behavior. This is in contrast to binary Ni‐Cu 2 | MATERIALS AND METHODS alloys, in which the higher the Cu content, the better the performance,[19] as the binary system shows solubility Equiatomic alloy (16.67 or 20 at% for each alloying ele- over the full range of compositions. Two commercial ment) buttons were prepared by vacuum arc melting on a high‐temperature materials that have adapted the Cu water‐cooled Cu hearth with a nonconsumable tungsten alloying concept are the Ni‐base materials HR‐235 and electrode. Each button was flipped and remelted three alloy 696 with Cu contents between 2 and 4 wt%. The times, by which a homogeneous distribution of each alloying content is rather low due to the limited alloying element was achieved. The overview and the nomen- capability of Cu in classical multielement, high Cr‐ clature of the compositions in wt% for a better compar- containing Ni‐base alloys. Unwanted phase formation, ison with classical alloys are given in Table 1. Cubic embrittlement, and hot cracking can occur, especially samples with a few millimeters edge length were arc wire during welding with a Cu content of above ~4 wt%.[21,22] cut from these buttons and ground to 800 grit. Mn is another element that is believed to strongly affect For comparison, a reference sample of alloy 800 was metal dusting, as— in contrast to Fe, Cu, Co, or Ni—it also exposed with the nominal composition given in oxidizes in metal‐dusting environments and, therefore, Table 2 in wt%.
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