THE EFFECT OF THE REACTIVE ELEMENT ON THE CHROMOXmE AND ALUMINmE LAYERS IN THEHIGH TEMPERATURE CONDITION. Oxide layers at high temperature condition, as Cr203' A12O3. growing act not only ascorrosion barrier, but also as a diffusion barrier of agressive components. MA956 and Ni75Cr25 alloy were studied to observethe effect of yttrium coating on their oxidation behavior. The influence of these coatings on the oxidation behaviour of the alloywas studied. Thin coatings of Yttrium have been applied to the surface of those alloys by vacuum coating. The growth of theoxide layers under controlled has been investigated in this work by Analytical Transmission Electron Microscope (ATEM) andScanning Electron Microscopy (SEM). It was found that addition of small amounts of elements such as Yttrium to these alloysgreatly increase their oxidation resistance

Dani, Mohammad

Effendi, Nurdin

English

Jurnal MIKROSKOPI dan MIKROANALISIS

J: Mikroskopi dan Mikroanalisis Vol 3 No.1 2000 ISSN 1410-5594THE EFFECT OF THE REACTIVE ELEMENTON THE CHROMOXIDE AND ALUM IN IDE LAYERSIN THE HIGH TEMPERATURE CONDITIONMohammad Dani and Nurdin EffendiP3IB-BATAN. Kawasan Puspiptek, Serpong -Tangerang 15314, INDONESIAABSTRACTTHE EFFECT OF THE REACTIVE ELEMENT ON THE CHROMOXmE AND ALUMINmE LAYERS IN THEHIGH TEMPERATURE CONDITION. Oxide layers at high temperature condition, as Cr203' A12O3. growing act not only ascorrosion barrier, but also as a diffusion barrier of agressive components. MA956 and Ni75Cr25 alloy were studied to observethe effect of yttrium coating on their oxidation behavior. The influence of these coatings on the oxidation behaviour of the alloywas studied. Thin coatings of Yttrium have been applied to the surface of those alloys by vacuum coating. The growth of theoxide layers under controlled has been investigated in this work by Analytical Transmission Electron Microscope (ATEM) andScanning Electron Microscopy (SEM). It was found that addition of small amounts of elements such as Yttrium to these alloysgreatly increase their oxidation resistance.ABSTRAKEFEK ELEMENREAKTIF PADA LAPISAN KROMOKSmADAN ALUMINmAPADA KONDISITEMPERATURTINGGL Lapisan oksida pada kondisi temperatur tinggi, seperti Cr20y A1203' tumbuh tidak hanya sebagai penahan korosi,tetapi juga sebagai penahan difusi daTi komponen-komponen agresif. Paduan MA956 daD Ni75Cr25 dipelajari untuk mengamatitrek daTi lapisan Yttrium pada sifat oksidasinya. Pengaruh daTi lapisan ini pada sifat oksidasi daTi paduan telah diteliti. Lapisantipis daTi Yttrium telah dibuat pada permukaan daTi paduan melalui pelapisan secara vakum. Pertumbuhan daTi lapisan oksidayang terkontrol telah diteliti dalam pekerjaan ini menggunakan Mikroskop Elektron Transmisi Analistik (ATEM) daD MikroskopElektron Sapuan (SEM). Telah ditemukan bahwa penambahan sejumlah kecil unsur seperti Yttrium terhadap paduan meningkatkansecara siginifikan daya tahan oksidasinya.1. INTRODUCTIONA research and developing program has beenfounded in order to reduce the oxidation rate by cover-ing the surface with oxidic protective layers, which oftenconsist of Cr2°:l and/or Al2°:l' One major limiting factorin the protection is extensive oxide loss from the surface,or oxide spalling under thermal cycling conditions. Ox-ide layers such as Cr2°:l' A12°:l in high temperature con-dition act not only as corrosion barrier, but also as adiffusion barrier of agressive components such as S, C,and N. Oxide layers in high temperature reactors (HTR),acts as radioactive permeation barrier of tritium (H:I) andhidrogen (HI), that pernleate through heat exchanger wall.It can be used as corrosion barrier in reactor core fuelelement [1-3]. Compact chromia and alumina layers thatform on high temperature alloys grow very slowly. Ox-ide layers preoxidized or in-situ grown in oxidizing atmo-spheres on high temperature alloys, act as corrosionbarrier to protect the base material. Most investigatorshave studied the effect of reactive element (RE) addi-tions in alloys on various types of Cr2OJ- formers andverified the first results. It was found that the coatingsdid not affect the amount of Cr2OJ scale, but the alloyhad enough chromium. However for Al2OJ- formers, theinfluence of this type of coating has never been re-ported.The grQwth of the oxide layers under controlledhas been investigated in this work by Analytical Trans-mission Electron Microscope,(ATEM) and ScanningElectron Microscopy (SEM). It was found that additionof small amounts of elements such as Yttrium to thesealloys greatly increase their oxidation resistance.2. MATERIALS AND METHODSThe current research was undertaken also to ex-tend the oxidation behaviour of alumina and chromia9The Effed of The Readive Element on The Chromoxide and Aluminide Layers in The High Temperature C'()ndition(Mohammad Dani 9-12)former on MA956 and Ni75Cr25 alloy with ytrium coat-ing. The investigated ODS alloy of the type MA 956were supplied by INCa Alloy International (Hereford,UK) and Ni75Cr25 from powder metalurgy. Specimenswere machined to disc geometry in 45 ~x 2 mm andgrounded with SiC-320 grid. The chemical compositionof the material are listed in Table I.Tabell. Nominal composition of the alloysNominal Composition in Mass-%Alloys Fe Ni Cr Al Ti Y 203MA 956 Base -20 4.5 0.3 0.5Ni75Cr25 -75 25 ---The growth of the oxide layers under controlledconditions is studied using an Analytical TransmissionElectron Microscope (ATEM) mOL mM-2000 FX II andScanning Electron Microscopy (SEM) mOL 840C. Thebehaviour of the oxide layers formed an alloys are inves-tigated with a new technique for preparing the speci-mens, especially by cross sectional preparation. Thespecimen should be bounded each other with a specialM-Bond6l0 on the Messingring (N. = 3mm) [4-5].The MA956 and Ni75Cr25 alloy are, in a specialoxidizing procedure, protected by an oxide layer. Hereonly a short survey of the standard oxidation by lnstitutfi.ir Angewandte Werkstofforschung Jiilich. [6-7].:-Glowing the samples in H2 atmospheres at thetemperatur 950 °C.-Oxidation in Ar~O mixing atmospheres at thetempercltur650 °C.-Oxidation in Ar/H2/H2O mixing atmospheres at thetemperatur 950 °C.-Cooling down untill the room temperatur3. RESULTS AND DISCUSSIONFig la and lb presents the TEM cross sectionalpreparation investigation on Yttrium uncoated MA 956after standard oxidation process. The Photograph wasfound at the interface position among the Aluminiumoxide layers (Al2O3) and basic metals. At the interfacethe void ist found. By EDX analysis, were found Ti2O3grain and also some sulfur elements, at the interface. Atthis condition H2S molecules flown to the oxide layersthrough the narrow crack inserted to the interface. Theoxide layers consist of A12O3' At the surface, the gasphase H2S were flown so that the sulfur element insertedto the oxide layer through grainboundary, as atoms andions [8].Figure 2: Analytical Transmission Electron MicroscopyMicrographs on Yttrium uncoated Ni75Cr25 alloyFig. 2 present TEM-cross section investigationon Yttrium uncoated Ni7 5Cr25 alloys after standard oxi-dation process. The photograph was found at the inter-face, under the interface were found voids forn1ed the1. Aluminium oxide layer2. Void3. Interface between oxide layers and the matrix10J: lJ,fi/(r()skopi dan Mikr()anaIL\"L\" Vol3 No.1 20001.\'SN 1.J/"-5_ilJ.Jno significant effect in the oxidationlAW-standard process [IS].b\4. CONCLUSIONFrom the microstructure investigation it can be concludedthat:2.After standard oxidation on Yttrium uncoated MA 956and Ni75Cr25 were found the voids at interface bc-tween the oxide layer and the matrix, that decreasetheir oxidation resistance. Contrary to alloying addi-tion of reactive elements in the foml of a Yttrium showedcompact chronua and a.lurnina oxide layer.The cross sectiona.l microstructural was investigatedby TEM, can be given more infoffilation for character-ization corrosion layer at high temperature alloys, es-pecially at the grain boundary, at the meta.l-oxide inter-face.5. ACKNOWLEDGEMENTSI would like to thallk to Prof. Dr. R. Hecker al1d DrD. Stoever from Institutrur Werkstoffe der Energietechl1ik,Forschungszentrunl Jiilich-Gernlany, Dr. P. Untoro fromNuclear Component Development and Engineering Cel1-tre, National Atomic Energy Agency, Indol1esia and Prof.Dr. Klaar from Central Laboratory for Electrol1 Microscopy.Aachen University of Technology, as their discussions.Figure 3a and 3b: Cross section SEM micrographs ofoxides !ornled after standard oxidation on Yttriumuncoated Ni75Cr25 alloy6. REFERENCESchannel like. By EDX analysis, at the interface werefound some sulfur elements. According to Smialek [9]and Lees [10], at high temperature the sulfur was ableto destroy the oxide layer stick from the matrix, due tosulfur segregation at the interface layer.Fig. 3 presentSEM.cross section investigationon Yttrium uncoated Ni75Cr25 alloys after standardoxidation process at the the oxide layer (Fig 3a) andinterface position (Fig. 3 b). The defects were found atthe oxide layer and at the interface as voids.If there metal cation like Mn2+, Fe2+ and CrJ+transport over, the holes will be formed and condensto form the voids [11-13]. It can be concluded that byincrease the oxidation rate and so will increase themetal cation diffusion or transportation. The void easierto transport the sulfur inserted to the matrix. Andecreasse in the oxidation rate with reactive elementcoating (Yttrium) was observed by HUSSEY et.al. [14].Compact cllronlia ,md alumina scales tl1at foml on hightemperature alloys grow very slowly and generally pro-vide very good resistance to high temperature oxida-tion. With reactive element coating (Yttrium) so willdecreasse the metal cation diffusion and greatly im-proves the oxidation resistance of the alloys. The Yt-trium content on MA 956 side is lower than 10% wi.Yttrium coating on Y -containing MA 956 alloy had[1]. NIEDER, A., Chemie des Hochtemperatur reaktors,KFA Juelich. Juel-Conf-43. 1981.[2]. BUCHKREMER, H.P., etal., ObeIblick fiber die neuerenAIbeiten auf dem Gebiet des Wasserstolf und Tritiumverhaltens in Hochtemperatur-reaktoren. KF~-Bericht,Juel-Nr.1497,1978.[3]. QUADAKKERS, W.J., Werk~to.IJe und Korrosion IYY().41, 659-668[4]. DANI M., Dissertation RWTH-Aachen, Germany(19%)[5]. DANIM.,UNTOROP.,andKLAARH.-J.. TEMandHRTEM investigation of Oxide Layers on High Tem-perature Alloys with New Technique Preparation. ThcAsian Science Senunar on New Direction in Transmis-sion Electron Microscopy and Nanocharacterizationof Materials, March 17-26, 1997, Fukuoka. Osaka andKyoto, Japan.[6]. ANDRITSCHKY M., Beitraege zur AufklarungdcsMechanismus der Wasserstolf-permeation durchoxidbeschichtete Metallegierungen, KF:4-Report.Juel-2074(1986).[7]. UNTORO, P., Di,\'.~ertation, RWTH-Aachen (IYY3)[8]. RAHMEL A., SCHWENK W : Korrosion undIIThe Effect of The Reactive Element on The Chromoxide and Aluminide Layer,~ in The High Temperature Clmdition(Mohammad Dani 9-12)[13]. GRUENLING H. W., ILSCHNER B., LEISTIKOWS., RAHMEL A., und SCHMID M.,Wechselwirkung zwischen Kriechverformung undHeissgaskorrosion. Werkst. U. Korr. 29 (1978) 691[14]. HUSSEY R.J., PAPAIACOVOU P., SHEN J..MICHELL D.F., and GRAHAM M.J., The Effect ofCeria Coating on the Hightemperature Oxidation ofIron-Chromium Alloys, Material Science Engineer-ingAI20 (1989) 147-151[15]. UNTORO P., DANI M., and KLAAR H.J., Micro-structural Investigation of Reactive Element Effectin Alumina and Chromia-Forming Alloys, XVI Na-tional Symposium on Physics and ASEANIP Re-gional Seminar on The Physics of Metal and AI-10ys,Bandung, December 12-14,1996[7). UNTORO, P., Dissertation, RWfH-Aachen (1993).[8). RAHMEL A., SCHWENK W.: Korrosion undKorrosionsschutz von Staehlen, Verlag Chemie,Weinheim 1977[9]. SMIALEK J .L., Adherent Al2O3 Scales Formed onUndoped NiCrAI Alloys, Met. Trans. A., 18,(January 1987) 164[10]. LEES D.G., On the Reasons for the Effects ofDis-persions of Stable Oxides and Additions ofReac-live Elements on the Adhesion and Growth-Mecha-nisms of Chronria and Alumina Scales-The "SulfurEffect", Oxidation of Metals, Vol 27, Nos. Y2 (1987)75[II]. KUENZLY J.D. and DOUGLASS D.L., TheOxida-lion Mechanism ofNi3Al Containing Yttrium, Oxi-dation of Metal, 8, (1974) 139[12]. STRINGER J.: Proceedings "Behaviour of HighTemperature Alloys" The MetaL\" Society, (1980)26612

THE EFFECT OF THE REACTIVE ELEMENT ON THE CHROMOXIDE AND ALUM IN IDE LAYERS IN THE HIGH TEMPERATURE CONDITION

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THE EFFECT OF THE REACTIVE ELEMENT ON THE CHROMOXIDE AND ALUM IN IDE LAYERS IN THE HIGH TEMPERATURE CONDITION

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