Galioto, T. A.

Miller, R. L.

Whitlow, G. A.

Wilson, W. L.

UNT Digital Library

OBSERVATIONS ON THE IN-SODIUM CORROSION ANDTRI3OT CGY OF ALUMINIDE COATINGS ON INCONEL 718G. A. Whitlow, R. L. Miller, Y,r. L. Wilson, and T. A. GaliotoWsstinghouse Electric CorporationP. O. Box 158Madison, Pa. 15663ABSTRACTIn sodium cooled rast reactor systems, the ability of surfaces, whichare in contact under sodium to slide relative to one another is criticalto the successful operation of many components. Materials selectedfor application at these interfaces will be under load intermittently or con-tinuously in high temperature liquid sodium for many thousands of hours.During operation, reactor mechanical components such as the duct loadpads or core restraint mechanism* will be subject to movement resultingfrom normal operation, differential thermal expansion, and flow or msch-anically induced vibrations. Design requirements for these componentshave necessitated materials with adequate long term sodium stability at "^150°^ and thermal shock resistance coupled with good wear resistance•and low coefficients of friction. This paper describes initial experimentalinvestigations on the corrosion and tribological behavior of a nickel basealloy, Inconel 718, a material considered for use in these components.Subsequent studies have shown that the incorporation of an aluminide surfacelayer on Inconel 713, using a commercially available diffusion process,results in reductions in the corrosion rate and friction and wear coefficiants.Aftar 2000 hours exposure to l!00°F, low oxygen flowing sodium, theaverage corrosion r:*te for the diffusion treated alloy was significantly lowerthan the 0.06 mpy value recorded for the untreated Inconel 718. Structuralintegrity of the aluminide layer was maintained even though some aluminumloss was detected. Average dynamic friction coefficients of ^ 0.2 5 wereobtained for the treated material in 1000 F sodium pin on plate t es t s . Nor.aasureable wear of the aluminide coating against itself was observedin thesa tests. In contrast, Inconel 718 exhibited substantial adhesivetype wear. *INTRODUCTIONRelative motion of one surface with respect.to an adjacent contactingsurface is a common operating feature of many mechanisms in a reactordesign. In a sodium cooled system, materials selected for application atcertain component interfaces may be under load intermittently or continu-ously in a high tempsrature corrosive environment before being required toslide with respect to one another. In addition to the required motion duringnormal operation, movement may also result from differential thermal expan-sion and flow or mechanically induced vibrations. Nuclear componentdesign presently necessitates the inclusion of allowances for frictionalloads and wear between contacting surfaces, and intensive efforts areunderway with the objective of minimizing friction and wear.Design requirements for such components, e .g. , the core restraint.TSchanism, include materials with long term sodium stability at liuO F(523k C), thermal shock resistance, high wear resistance and low coe?£i-c'.zr.is of friction { __0.4). Some seising and galling has boon encounteredv.-;!:h the 300 series type stainless steels in sodium, with the result thatinterest has been stimulated in alternate structural materials such asIr.conel 713 for sliding contact applications. Current materials develop-ment prograr.s ha-e as one of their objectives the upgrading of Inconel713 and stainless steel by the use of chromium carbide coatings andaluxirude diffusion coatings for necessary low friction interfaces.In this paper, some of the metaliographic aspects of trie sodiumcompatibility and friction and wear studies on inconel 718 and on Inconai718 with an aluminide coating.performed as part of the above mentionedprogram are presented. •MATERIALS AND TECHNIQUESThe sodium compatibility testing was performed in a pumped sodiumloop system constructed of stainless steel and designed for the exposureof 4-1/4 in. x 5/8 in. x 0.180 in. plate and 1/8 in. diameter pin samples tohigh temperature sodium. This loop system, which is of a type described• in detail elsewhere, was operated non-isothermally at test sectiontemperatures of 1160 and 1100 F for 2128 hours at a sodium, flow velocityof n-5 fps, and an oxygen impurity level in the sodium in the range0.5 to 1. 0 ppm. Average corrosion rates for the period 0 to 2128 hourswere calculated from the change in weight of the test samples resultingfrom the sodium exposure.The friction and wear test machines permit prototypic testing insodium at temperatures up to 1200 F under controlled impurity contents(0.5-1.0 ppm, oxygen) and flow rates (^ 1 fps). The basic experimentalapproach is to press two diametrically opposed horizontal specimens ,(pins) against mating specimen surfaces (plates) mounted on a vertically(8)reciprocating rod. Tests are run under as prototypic-as-possible con-ditions of load and motion,simulating those anticipated in the reactorsystem. The contact loads {normal static loads), the force necessary tomove the plates (frictional load), and the displacement are continuouslymeasured and recorded on magnetic tape. Friction coefficients are cal-cuiated as the ratio of the frictional and the measured normal staticloads on the pin-plate specimens. Wear data are obtained from weightchanges and maasured height changes of the pin and from quantitativeanalysis of wear scars on the plate specimens using a surface profileinstrument.The heat analysis for the Inconei 718 used in these studies is as follows(all values in weight percent): 53.05 Ni, 18.35 Cr, 18.18 Fe, 5.29 Cb +la , 3.03 Mo, 0.95 Ti, 0=,59 Al. The aluminicio layer was applied byCY'omining Corporation and the prccoss entails the packing of the parttc i:a -coats-.'. ...i a mixture of alumina, aluminum and chromium.. Afterins 2rtiDn of amrr.onium fluoride into the mixture at a temperature of1300 F, aiuminurr. fluoride is formed and adsorbed on the metal surface.Dissociation t&l'.ss place with aluminum diffusing into the Inconel 718for—ing ?riAl and ICi Al, and typically results in a layer 2 mil thickafter 10 hours at temperature. Follo-ving the coating process, the partis pose heat troatad (1 h.' © 1750°?, quenched and aged 8 h. @ 1325°Fand 10 h. © 1150 F) to regain the desired Inconel 718 properties.Characterization of sodium exposed and friction and waar testsamples included optical and scanning electron microscopy and x-raydiffraction. Metallographic specimen preparation consisted of: nickelplacing for edge retention, conventional po.Hshing and etching. An etchconsisting of 1% chromic acid was used for the Inconoi 718, while -amixture of giycerol, hydrochloric and nitric acids (6:5:4) was the pre-ferred ctchant fcr tha aluminide layer.RESULTS AND DLOCUSSIQNIn the i;or!iu:r. compatibility section of this s':ady, samples of Inconal7l'-j ?.::d iilu-minisad Lnconal 713 wore exposed to sodium at 1160°F for 2123h.j..::s, '/.'hereupon uhy/ were cleaned of any ruji.dual sodium by rinsing inalcohol and water. Both materials lost weight as a result of exposure tosodium with average corrosion rates of 0.24 mpy for the Inconel 718 and0.03 mpy for the aiuminized material being recorded. These corrosionrates probably reflect the ease with which nickel is removed from thesurface. Previous work has shown that nickel alloys such as Inconel 718(7)lose weight during sodium exposure due to loss of nickel , but in thecssa of nickel aiurr.inides, nickel is more tenaciously fixed in the matrixas Ni~Al or :CL~I and therefore lower corrosion rates would be anticipated.Examination of the cross sectional microstructure of Inconel 718revealed only a very shallow affected depth (1-2 vm) in the sodium exposedsamples (see Figure 1). The matrix consists of uniform austenitic grainswith extensive grain boundary precipitation (gamma prime phase and a(9)JN^Nb phase). The micros true tural appearance of the aluminide layersimilarly appeared little changed in cross section, but in this case therewas no sign of an affected surface layer. Based on an optical metallo-graphic examination, it appeared that the measured weight losses must 'be attributable to surface or near surface (< 1 ym) changes and this waspartly confirmed in a scanning electron microscopical (SEM) examination.In Figure 2, some typical iov/ power surface views before and aftersodium exposure are depicted. The Inconel 718, as ground, unexposedsurface became somewhat smoother during exposure and at higher magni-fication (not shown) the surface ridges were less pronounced suggestingthat material rerr.ova'. co:t:3> stunt with th : wuirihi: lor;:- had occ.'.rrr.-I. Thr*ci;::-.:.n:d3 !-•/..*• m ui.ronoi 71.1-:; '.Tov/.ivor, exhibited a form of pitting typoi:..-c'.. rathe-r f.:.:±:: ;; general ron^ov::! with t:'-_» o'iyin-'.' :j!:rf:>c •; ndgoo aridp_-:;.;iy areas still in evidence a:car sjJium :y.-:uc.:v.re. Surxnc-' >:-r^yo.-^'y.iis usinj -i'*."> x-rays gsn^ratsci in t\ui 3EI/I rovoaled tr.at the t.> 'ter-rrost layer (• • - .- in dspih) of ;ho Inconai 718 sample- had lost nickel .vuchth-ii c'.-..-o-:_~ c5Tsme the major c:-.s:ituant in tha layor. For the sarnplauof Inconai "13 •vi:.i an aluminiis s.:r:2C3 layer, no major cheraga in surfaceche«.Tiijtry v/23 detected. Hov/a--er, from this work, there was a sugges-tion that tli9 aturcinun content o: tr.e s-jrfaco layer may have doc^asadslijhiiy. To corr.plament ths z'r.zr2z"orination studies, an x-ray diffrac-tion e:'?.rr.ir.a':ion usirg nickpl f LI tor .A, aoppsr ridi^tioi 'vaa conciuctojon both tr.z Incone! 71c,' -and ths r.tc::3i aiurr.imde lay^r. For tt-.o Ijiconal713, fchs major phase was austenito with minor indications for carbid-33and gamma prime phase. Figure 3 schematically depicts the structureof the aluminide layer obtained by x-ray diffraction. No change in com-position v/as detected as a result of sodium exposure for both ;r.aterl-:tlsv/hich is consistent with indications of shallow sffectcsd dapths dis-cussed previously.Friction results from pin on plato tests for Inconsl 713 and Inconal 713with an alurninida surface layer (each rubbing against itself) at a l'i, 000psi s-ress level arD compared in Figure 4. Ths data, which ere orassnt^d/z\ ..-;oyo dynamic iriction coefficients as a function of cumulative-i! distance, il'.u.strote the pronouacoJ enhancement in frictic ulivior r-ac-ulLiri'.j t:j.r the uluruinido dit'fcadLon coating. In all throeI2i3 than tiiosti for ~^zom\ 71B. In aiuiclon, the rang1; in friction ccafficior.ts, rcfloctir.g chrir.gas in friction v.-itr cumulative rubljir^g, is al-joicierabi/ s.TiaLyr for the alurrlnidj material. The highest friction_-os;flci'j:\L3 v/cre z'zl'-'.aeci at ths er.i of the initial 450 F period Tor theahirrilnid-j natoria'. b_: at the end o; tho final 450 F pariod for ti'.eI-Azonal 713. The reason for this differ3nce is not clear, but may bere-'-icod co speciT.en wetting behavior at 450 F coupled with the presenceof a sodiurr. chromlta lubrication filrr,.Th-j -•.lu.'ninide diffusion trsatnient was also found to greatly io.croasetha wear rssistaaca of Fnconel 718. Plate specimens -ware examined quantitativ^ly for wear using a surface profiling instrurr.^nt. Although lightwear scars wero visually evident on the plate specimens, no measurablewear could be detected. Tests involving Inconei 718 without an aluninidcdiffusion coatiny by coirpartson resulted in average wear coefficients (K)in the range of 12 invpsi-in x 10"^ and maximum wear depths of 1 to2 r.lls. (See Table 1). The typical surface appoaranca of the Incono] 7L°and the aluminido pin specimens tested under conditions shown in Figure 4are illustrated in Figura 5. Prior to testing tho Inconel 718 pin sample8had a ground finish a.id the aluRunidc pin was finished usini <n ubra^ivoto an 100 •_ incv. r .m.c. sirocco finish. The inconol 71!'. inaL.: t il Incurredrod-jrr-te to sa. :-ro surr'aco da.T.arja, character!:; tic of an adhesive ;••?!•»... ;.".roj<j3s. !..:-.c,j.'ial t r an^ . i ; " .me. j .v .ear i r .g v/.is ;?\.".doiit, '.vLth uj ' j : i .s-•uiidup on r^'jior.s of tho pin edg^s. In contiast, the dlummiclo ri'ct'riai,rested at the s ;̂r.-j conditions, incurred minimal surface damago v/ith•-.ear limited :D 5. sr.oothing ar.J polishing of surface asperities and unworn.":. jior.a (li:\\: ^rcy srsas) are r". i-i.-ly.2-/id3at on the pin surlaca. Noevidence of sx-.s^sivs r.aterial cir.s:2f across the interface could beSUM: "Â Y AND CONCLUSIONSRc-suitj frs.r. an e^psrlmsatai program have in.iicitad that nn ^di-fuslon. coating, consisting principally of an >uAI phase, on an Jncoml713 alloy substrate b.ss several advantages over uncoat-ad inconel 7iS forcertain sodium, cooled reactor applications. In compatibility er.d frictionand v/ear tssV.r.g, uncor sodium conditions typical of thon:> to bt> exyjrio::in reactor service, an aiuninide layer on mcortel 7 U ' has boen found toposj3ss a lov/er corrosion rate v.z HGO F, and a Jo>-/er friction and v/oarrate. I:o deterioration in the NiAl surface layer has been observed aftergreater than 2000 hours sodium exposure or 4000 inches cumulative rub-bing distance undar reciprocating conditions. Additional touting, pre-sently in progress at VvVjithiyhouse Hancord Company has as its objectivethj qualification o: co.-i^r^ surh as aiu-nlnidv.-ij for in-roactor service9and will supplement this vvor-k particularly in the* area of irradiation. . . (U»;.-•.: l o r . •This work was performed under USAEC Contract AT(11-1)-3Q45, withV.''3sti£*3lv;a3Q Electric Corporation. The authors wish to acknowledgez'-.? centr'.fcutions of S. L. Schrock, V.'estinghouse Advanced ReactorsDivision, anx; R. K. ."chnson, Westinghcuse Hanford Co. to the programc; v.-hich this v/ork is a part.(I) H. !•:. Johnson/ 3. L. Schrock and G.. A. Whitlow, "Wear ResistantC^utip.gs for Reactor Components in Liquid Sodium Environments,"to be published, J, Vac. Sci. Technol., Juiy/August (1974).e{2) W, J. Kurzaka, R. M. Oliva, and F. W. Poucher, in Atomics*Internai-.ional Rockv/etl International, Annual Technical ProgressReport, Sodium Technology and Cover Gas Seal DevelopmentPrograms Government Fiscal Year 1372, AI-AEC-13037, 59, (1972).(3) Liquid Metal Engineering Center (LMEC), Annual Technicalria Report, January-December 1972, LMEC-73-1, 1, (1973).10(•-.) '/.'^stir.gjiouoo Advanced Reactors Division, ood;.ur. Toc lvo ' c j /Pro;,Tcv-. 'Quarterly Progress Report IO'.- Period .indlny Jap.:..-"vy ?1,197-;, V/ARD-XA-3G45-9, (.1974).(5) N. J. Koffr.an and J. J. Droher, ''A Review of V.'ca: in Ccliur.:"presents;! ~: XACE Meriting, CORRO6ION/74, Chic.tgo, {•••[arch1274, Facer =15,' (1974).(5) G. A. V.'hiiiov/, R. L. Miller, .:. L. Sclirock and P. C. S. Y/u,"Sodium Compatibility Stadias of Low Friction Carbida Coating3fcr Reactor Application, " crasontod at NACE Mostin^, CORRCJIOri/74, Chicago, March 1974, Paper £17, (1974) co be published inCORROSION (1974).(7) G. A. \VhltIo-v, J. C. Cv/ynar, R. L. Miller, and S. ',. :i^rocx-.,"Sodium Corrosion of Alloys for Fast Reactor Applications, " Proc,Synp. Civamical Aspects of Corrosion and Mass Transfer in LiquidSodium, 1971 Mc-jting of AIME, Detroit, 1, (1973?.(8) W. L. "Wilson, B. Minuahkin and E. J, Cholon, "Friction andV/S?T Tosting in Support of FFTF Components - .(ntoriin Sum mar/Report, Westmghouse Electric Corporation Raport V/ARD-i\rA-'3O-';5-.l3,;•} H. J. W'a.ir.or and A. M. Anil, 'Physical Metallurgy of Alloy 718, "DMIC Koport-217, Juno (1955).0} G. L. Guth-rio, "Irradiation of Fuel Duct Load Pad Coatings"in Quarter// Progress Report, Irradiation Effects in ReactorStructural :.:aterials. May-July, 1973, HEDL-TME-73-67, 62,(1373).«;ozs: References 2, 3, 4, 8 and 10 may be obtained from:USAEC Technical Information CanterP.O. Jov:v2, Oak Ridge, Tenn. 37330-NOTICE-Thit report was prepared at an account of worksponsored by the United State* Government. Neitherthe United State* nor the United States EnergyResearch and Development Administration, nor any oftheir employee*, nor any of their contractors,subcontractors, or their employees, makes anywarranty, express or implied, or assumes any fegalliability or resporuibKty for the accuracy, completenessor usefulness of any information, apparatus, product orprocess disclosed, or represents that its use would satinfringe privately owned rights.12TABLE ITHE EFFECT OF AN ALUMINIDE DIFFUSION COATING?: THE CORROSION AND WEAR BEHAVIOR ON INCONEL 713 IN SODIUMMAT "RIAL CORROSION*RATEC~?y) .MAXIMUM WEAR COEFFICIENT**WEAR DEPTH K(mils) ( in 3 /ps i - in x 1013)Incoi: 1 718 0.24 2 .1 12.Aiuminide LayerOn Inconei 713 0.03 No measurable wear^Average rate over time period 0-2128 hr. in 1160 F, 0.5 - 1.0 ppm0 , 1 fps sodium.. • volume of mater ia l worn ay/ay * j v M -* U » r.- A**K = r~r. ; for details oi test cycle see Figure 4.contact stress x travel distance13INCONH 7 ISAluminized fiic. 718*~ - J • r:~:?X$a itAS RECEIVED SODIUM EXPOSED.OOI in.Figure 1. Effects of Sodium Exposure <2128 hrs. @ 1160°F) on the CrossSectional Microstructure of Inconel 718 and-Aluminized Inconel 718INCONEL 718' 1 * • V•MEXte'••~hZ*^" -"•'."' • if"- , • . •• " . • * , * *"-*-;« »* ; ^ /•j^u-*^4^Vji. . • .»- - • • - • . , - . • * . * « : • •- " * * * - ** -•'• * v : 5 |AS RECEIVED SODIUM EXPOSEDALUHINiZED INCONEL 718::•1 " ̂ ! >AS RECEIVED SODIUM EXPOSEDi'n.Figure 2. Scanning Electron Micrographs Showing Effects of Sodium Exposure(2128 hrs. @ 1160°F) OE the Surface Appearance of Inconel 718and Aluminized Inconel 718tHiOQ-1SURFACE1.2 MilMinor - CrFew % - HigTrace - Al0.6 Mil Minor - Fe, Crf Cr.Fe Minor - Al, Ni Possible - M23Cg° - 7 xM M Mo, Hb " 7 j 3f M3C2/ / / / / / , Inconel 718 Matrix / / / / ' //Xv/y///////////////////AFigure 3. Schematic Depiction of the Composition of the Aluminized Layeron Inconel 718 Obtained by X-Ray Diffraction6609-40.1 ipm Avg.Test VelocitylO.COCpsi StressStroke* 0.75 in Stroke = 0.125 in Stroke* 0.75 in.AluminizedInconel718I I I I I I I I I Ii l l0.020 60020 604000 8000 12000 16000TRAVEL CYCLESFigure 4. Effect of a Surface Aluminide Layer on the FrictionaX Behavior of Inconel 718 in Liquid Sodium£IKINCOMEI 718 ALUMINIZED IHCOHEL 7180.05 in.Figure S. Surface Appearance of Pin Specimens (0.125 in. diameter) of Inconel 718 and Aluminized Inconel'18 After Friction and Wear Test in Sodium

Observations on the in-sodium corrosion and tribology of aluminide coatings on Inconel 718

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Observations on the in-sodium corrosion and tribology of aluminide coatings on Inconel 718

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