ESTUDO DO COMPORTAMENTO MECÂNICO EM TEMPERATURAS ELEVADAS DE LIGAS FeCr COM ADIÇÕES DE Al E Y
HIGH TEMPERATURE MECHANICAL BEHAVIOR OF FeCr ALLOYS CONTAINING Y AND/OR Al
Pillis, Marina Fuser; Ramanathan, Lalgudi Venkataraman; Couto, Antonio Augusto; Andrade, Arnaldo Homobono P. de; Castagnet, Danieli Aparecida P.
http://dx.doi.org/10.4322/tmm.00602006
Tecnol. Metal. Mater. Min., vol.6, n2, p.96-102, 2009
Resumo
Além de elevadas condutividades térmica e elétrica, e alta resistência à corrosão, o material utilizado como interconectores em células a combustível de óxido sólido (SOFC) deve ter propriedades mecânicas adequadas, tanto à temperatura ambiente, quanto em altas temperaturas. O objetivo deste estudo é avaliar o comportamento mecânico à temperatura ambiente e em temperaturas elevadas de ligas FeCr sem e com adição de ítrio e/ou alumínio. As ligas FeCr, FeCrY, FeCrAl e FeCrAlY foram obtidas por meio de fusão a vácuo em forno elétrico à indução. Os lingotes foram forjados e laminados. Foram preparados corpos-de-prova para ensaios de tração realizados nas temperaturas ambiente, 800°C e 900°C. A microestrutura e as superfícies de fratura foram observadas em microscópio eletrônico de varredura. Todas as ligas apresentaram um alto nível de inclusões. A liga FeCrAlY apresentou o melhor desempenho em relação ao comportamento mecânico, em todas as temperaturas investigadas. Todas as ligas apresentaram fratura dúctil, com mecanismo predominante de fratura por microcavidades.
Palavras-chave
Ligas FeCr, Comportamento mecânico, Célula a combustível, Interconectores
Abstract
Materials used as solid oxide fuel cell (SOFC) interconnects should have high electrical and thermal conductivities, high corrosion resistance and adequate mechanical strength at room as well as at high temperatures. In the light of this, the aim of this study is to determine the mechanical behavior of FeCr alloys without and with Y and/or Al additions at room and at high temperatures. Ingots of four alloys, FeCr, FeCrY, FeCrAl and FeCrAlY were prepared by induction vacuum melting and casting. These ingots were forged and rolled. Tensile test specimens were machined from the rolled sheets. The tensile tests were carried out at room temperature, 800°C and 900°C. Scanning electron microscopy was used to examine the microstructure of the alloys and the fractured surfaces after the tensile tests. The microstructure of all the alloys revealed a large number of inclusions. Among the alloys, FeCrAlY has the best mechanical behavior. The fracture surfaces of all the alloys tensile tested at the different temperatures revealed coalescence of micro-cavities (dimples) indicating ductile fracture.
Keywords
FeCr alloy, Mechanical behavior, Fuel cell, Interconnects
References
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14 FONTANA, S.; AMENDOLA, R.; CHEVALIER, S.; PICCARDO, P.; CABOCHE, G.; VIVIANI, M; MOLINS, R.;SENNOUR, M. Metallic interconnects for SOFC: Characterisation of corrosion resistance and conductivity evaluation at operating temperature of differently coated alloys. Journal of Power Sources, v. 171, n. 2, p. 652-62, Sep. 2007.
15 ALMAN, D.E.; JABLOUSKI, P.D. Effect of minor elements and a Ce surface treatment on the oxidation behavior of an Fe-22Cr-0.5Mn(Crofer22APU) ferritic stainless steel. International Journal of Hydrogen Energy, v. 32, n.
16, p.3743-53, Nov. 2007. 16 CABOURO, G.; CABOCHE, G.; CHEVALIER, S.; PICCARDO, P. Opportunity of metallic interconnects for ITSOFC: Reactivity and electrical property. Journal of Power Sources, v. 156, n. 1, p. 39-44, May 2006.
17 GOLIGHTLY, F. A.; STOTT, F. H.; WOOD, G. C. The relationship between oxide grain morphology and growth mechanisms for FeCrAl and FeCrAlY alloys. Journal of the Electrochemical Society, v. 126, n. 6, p. 1035-42, 1979.
2 QUADAKKERS, W. J.; GREINER, H.; KOCK, W. Metals and alloys for high temperature SOFC application. In: EUROPEAN SOLID OXIDE FUEL CELL FORUM, 1., 1994, Lucerne. Proceedings… Baden: European SOFC Forum, 1994. p. 522-41.
3 BADWAL, S. P. S.; DELLER, R.; FOGER, K.; RAMPRAKASH, Y.; ZHANG, J. P. Interaction between chromia forming alloy interconnects and air electrode of solid oxide fuel cells. Solid State Ionics, v. 99, n. 3-4, p. 297-310, Aug. 1997.
4 FONTANA, S.; CHEVALIER, S.; CABOCHE, G. Metallic interconnects for solid oxide fuel cell: Effect of water vapour on oxidation resitance of differently coated alloys. Journal of Power Sources, v. 193, n. 1, p. 136-45, Aug. 2009.
5 FERGUS, J. W. Metallic interconnects for solid oxide fuel cells. Materials Science and Engineering A, v. 397, n. 1-2, p.271‑83, Apr. 2005.
6 YANG, Z.; XIA, G.; SINGH, P.; STEVENSON, J. Effects of water vapor on oxidation behavior of ferritic stainless steels under solid oxide fuel cell interconnect exposure conditions. Solid State Ionics, v. 176, n. 17-8, p.1495-503, May 2005.
7 QUADAKKERS, W. J.; PIRON-ABELLAN, J.; FLESH, U.; SHEMET, V.; SINGHERSER, L. Metallic interconnects for solid oxide fuel cells: a review. Materials at High Temperature, v. 20, n. 2, p. 115-27, 2003.
8 HORITA, T.; XIONG, Y.; YAMAJI, K.; SAKAI, N.; YOKOKAWA,H. Evaluation of Fe-Cr alloys as interconnects for reduced operation temperature SOFCs. Journal of the Electrochemical Society, v. 150, n. 3, p. A243-8, Mar. 2003.
9 RHYS-JONES, T. N.; GRABKE, H. J.; KUDIELKA, H. The effects of various amounts of alloyed cerium and cerium oxide on the high temperature oxidation of Fe-10Cr and Fe-20Cr alloys. Corrosion Science, v. 27, n. 1, p.49-73, 1987.
10 MOON, D. P. Role of reactive elements in alloy protection. Materials Science and Technology, v. 5, n. 8, p. 754-64, Aug. 1989.
11 PILLING, N. B.; BEDWORTH, R. E. The oxidation of metals at high temperatures. Journal of the Institute of Metals, v. 29, p. 529-91, 1923.
12 WHITTLE, D. P.; STRINGER, J. Improvements in high temperature oxidation resistance by additions of reactive elements or oxide dispersions. Philosophical Transactions of the Royal Society of London, v. A295, n. 1413, p. 309-29, 1980.
13 PIERAGGI, B.; RAPP, R. A. Chromia scale growth in alloy oxidation and the reactive element effect. Journal of the Electrochemical Society, v. 140, n. 10, p. 2844-50, Oct. 1993.
14 FONTANA, S.; AMENDOLA, R.; CHEVALIER, S.; PICCARDO, P.; CABOCHE, G.; VIVIANI, M; MOLINS, R.;SENNOUR, M. Metallic interconnects for SOFC: Characterisation of corrosion resistance and conductivity evaluation at operating temperature of differently coated alloys. Journal of Power Sources, v. 171, n. 2, p. 652-62, Sep. 2007.
15 ALMAN, D.E.; JABLOUSKI, P.D. Effect of minor elements and a Ce surface treatment on the oxidation behavior of an Fe-22Cr-0.5Mn(Crofer22APU) ferritic stainless steel. International Journal of Hydrogen Energy, v. 32, n.
16, p.3743-53, Nov. 2007. 16 CABOURO, G.; CABOCHE, G.; CHEVALIER, S.; PICCARDO, P. Opportunity of metallic interconnects for ITSOFC: Reactivity and electrical property. Journal of Power Sources, v. 156, n. 1, p. 39-44, May 2006.
17 GOLIGHTLY, F. A.; STOTT, F. H.; WOOD, G. C. The relationship between oxide grain morphology and growth mechanisms for FeCrAl and FeCrAlY alloys. Journal of the Electrochemical Society, v. 126, n. 6, p. 1035-42, 1979.
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