CORROSION RESISTANCE AND COMPATIBILITY OF EUROFER STEEL COATINGS IN THE Pb-Li AT THE TEMPERATURE OF 550 C

Transcription

1 CORROSION RESISTANCE AND COMPATIBILITY OF EUROFER STEEL COATINGS IN THE P-Li AT THE TEMPERATURE OF 55 C Zuzn Skoumlová, Krel ŠPLÍCHAL, Lukáš KOŠEK, Jroslv BURDA Ústv jderného výzkumu, Řež.s., Husinec-Řež čp. 13, 5 Řež, sko@ujv.cz Centrum výzkumu, Řež s.r.o., Husinec-Řež čp. 13, 5 Řež, spl@cvrez.cz Astrct Structurl ferritic-mrtensitic EUROFER 97 steel will e used for the test lnket module (TBM) of the Interntionl Thermonucler Experimentl Rector (ITER). Due to the eutectic P-Li lloy environment, EUROFER 97 shll meet the corrosion resistnce requirements nd limit tritium penetrtion t the operting temperture rnging from 5 to 55 C. In this work the tests of cotings sed on prepred y Electrochemicl ssisted deposition of method (ECA) in Krlsruhe Institute of Technology (KIT) hve een crried out under conditions modeling the TBM operting conditions. The specimens were exposed in the P-Li melt t 55 C t flow rte of 1 cm/s for, 3 nd 5h. The tests were conducted with cotings the thickness of which in s-delivered condition ws 5 µm (E series) 57 µm (F series). The effects of experimentl conditions on thickness, microstructure nd chemistry of the melt interction with coted EUROFER steel specimens hve een evluted y mens of light opticl microscope equipped with imge nlysis nd scnning electron microscope. Keywords: EUROFER 97, eutectic P-Li lloy, corrosion resistnce, Electro-chemicl ssisted deposition of (ECA), -sed cotings 1. INTRODUCTION In recent yers, construction of the prototype of the ITER fusion rector hs egun s continution of previous work done under the Europen Fusion Development Agreement (EFDA) imed t the fusion rector development. At present, within the Fusion for Energy projects (FE), the reserch work on the development of components nd their verifiction under operting conditions continue long with the tests of operting nd uxiliry systems for the Europen vrint of the helium cooled fusion rector using Helium-Cooled Lithium Led (HCLL) melt s reeding mteril for tritium production. Within the reserch nd development of the HCLL fusion rector prticulr ttention hs een pid to the evlution of structurl nd functionl mterils of the TBM. For the operting conditions of the fusion rector lnket will e used construction ferritic-mrtensitic EUROFER 97 steel which, considering opertionl environment of P-Li eutectic lloy, shll fulfill the requirements of sufficient corrosion resistnce t 55 C. Another requirement from the point of view of opertionl reliility nd sfety is to decrese tritium penetrtion in the lnket systems. Tht is the reson why the use of cotings hs een recently tested with the im to ensure corrosion resistnce s well s reduce tritium penetrtion into the cooling medium nd/or other rector systems. As nti-permetion cotings the mterils sed on luminum, erium oxide, sndwich lyers of W- O 3 type nd oxidic lyers formed directly on EUROFER 97 steel hve een exmined. The im of this work is to crry out experimentl tests nd to evlute cotings prepred in KIT Krlsruhe.

2 . EXPERIMENT The tests of corrosion resistnce hve een performed in the Meliloo loop [1]. For the P-Li melt filling nd drining, 1 liter drin tnk ws used. The tests hve een crried out t 55 C t the verge flow rte of 1cm/s []. Argon hs een used s protective tmosphere [1]. For testing the cotings sed on luminum prepred in KIT Krlsruhe were used. cotings were generted y n Electro-Chemicl uminum deposition (ECA) on the Eurofer steel specimens followed y het tretment t 9 C nd 7 C for 3 min. nd min., respectively. The im of the first tretment is to remove rittle phses produced during coting deposition nd to form ductile phse; the second tretment ims to restore ferritic-mrtensitic structure of steel. The scle thickness fter using the ECA method ws 5 µm nd µm in E nd F series specimens, respectively. After het tretment the thickness will chnge [3]. The specimens were fixed to holder nd exposed in the P-Li melt for, 3 nd 5 h ccording to scheme given in T.1. Metllogrphic evlution nd micronlysis hs een crried out on cross section of the specimens. Tle1 Exposure time of specimens. Exposure time [h] Smple 3 5 coting 5 µm E 7 E E 5 E coting 57 µm F 7 F F 5 F 3. EXPERIMENTAL RESULTS AND DISCUSSION 3.1 Thickness nd microstructure of the lyer Delivered specimens cotings prepred y the ECA process consist of two sulyers (Fig. 1). The inner compct lyer (ICL) creted y ig columnr grins of - () phse is in direct contct with steel nd the outer porous lyer (OPL) is thinner nd includes mostly P-17Li melt residues. Close to the coting lyer surfce so clled Kirkendll pores could e oserved. On some prts of coting technologicl defects hve een oserved which developed lredy during the preprtion of lyers. The oserved defects hd form of pss-through pittings or voids in the cross section of the specimen, Fig.. The coting totl thickness fter het tretment ws 5 µm (E 7 specimen) nd 57 µm (F7 specimen). coting of E7 specimen ws uniform on the whole surfce (Fig. 1) nd technologicl defects occurred spordiclly. The F 7 ws not uniform (Fig 1) nd frequent technologicl defects occurred. Kirkendll pores Inner compct lyer (ICL) Outer porous lyer (OPL) Mtrix Fig. 1 Uniform (E7) nd non-uniform (F7) TL

3 Specimens fter exposure in P-Li Fig. Technologicl defects pss-through defect () nd voids () After the selected exposure time pssed, the specimens were removed from the specimen holder when the loop shut down. Their surfce documenttion, metllogrphic evlution nd micronlysis were performed without removing the P-Li residues on specimens fter h (E, F), 3 h (E5, F5) nd 5h (E, F) of exposure. P-Li corrosive effect mnifested y severl effects: the decrese of the su-lyers thickness nd in severl plces y prtil ttck or y totl ttck of the outer porous lyer nd/or compct lyer ttck. The thickness of lyers decreses depending on the exposure time. It cn e seen, from T., the totl decrese of lyer thickness ws 5 m for oth specimen series (E, F). The ttck of the steel mtrix hs een found in pss-through technologicl defects or in plces where during the exposure corrosion pittings penetrted through the outer porous nd inner compct lyers. Due to the fct tht this type of defects hs not een oserved in s-delivered condition it cn e ssumed tht the ttck took plce during the exposure. Corrosion ttck took plce long the grin oundries simultneously with the grdul dissolution of the mtrix (less distinct structure of steel) nd hs een oserved fter 3 h of exposure, Fig. 3 The steel corrosion rte hs een clculted from the ttck depth of se mteril in the re of technologicl defect nd pittings going through the coting lyer, respectively, where the dissolution of the steel mtrix took plce. Bse on the dt mesured from the ttck depth in F specimens fter 3 nd 5h (T. ) the corrosion rte ws 3 m/yer, which is sustntilly lower thn of Eurofer steel corrosion without coting t the temperture of 55 C. Tle Thickness of the totl lyer, the outer porous lyer nd the compct lyer Specimens Exposure time [h] E (ECA lyer- 5 m) F (ECA lyer - m) Prt of the lyer Prt of the lyer TL OPL CL TL OPL CL As-delivered condition

4 Corrosion pitting Fig. 3 Corrosion ttck of steel mtrix in pss-through technologicl defects or corrosion pittings 3. Micronlysis Micronlysis hs een performed on the cross section of the specimens nd included the P-Li lyer, the coting lyer nd the steel se mteril, viz. Fig. The contents in unexposed nd exposed specimens decreses grdully from the vlues t the specimen surfces towrds the interphse with steel grdully. In the cse of unexposed specimen E, content chnges from surfce vlues of % nd in cse F specimen from 1 to less thn.5% t interfce with steel mtrix. In the cse of exposed specimens E, content decreses from vlues of 5% nd in cse of F specimens from vlues of round 1% to out,5%. In contrst, the nd contents on the cross section of the coting lyer decrese in opposite direction from interphse of coting to steel mtrix. The content decreses from out 9 % to 1 % t the coting lyer surfce nd similrly, the content decreses from out 9 % to reltively low vlues., V nd W contents on the cross section of the coting lyer do not significntly vry nd the extent of determined vlues corresponds to the dt in the steel sic mtrix. On the coting surfce on the interphse with P-Li coting lyer luminum oxide in locl res is present. Distriution nd contents of elements in the defects re (technologicl defects nd pittings) show tht during the interction of P-Li with the coting lyer the dissolution of steel elements pssing into the melt tkes plce. The re of steel ttck is in cse of oth types of defects chrcterized y steel mtrix depleted zone with the content which vried in the rnge of to 7%. The P-Li melt in pss-through defects shows different contents of,, nd, which re products of its interction with coting nd steel mterils. The frequency nd extent of locl dmge indicte higher corrosion resistnce of E specimens which is chrcterized y smller totl coting thickness in s-delivered condition s well s y uniformly deposited lyer compred with specimens of F line. In cse of E specimens the numer of technologicl defects with corrosion ttck ws considerly lower compred with F specimens. so, vried higher nonuniform thickness of coting my result in vried surfce ttck of surfce lyers.

5 Weight percent of,, Weight percent of Weight percent of,, Weight percent of Weight percent of,, Weight percent of Weight percent of,, Weight percent of , Brno, Czech Repulic, EU E7 E lyer Steel mtrix Depth from surfce [ m] Depth from surfce [ m] F7 F Depth from surfce [ m] 75 c Depth from surfce [ m] Fig.,, nd concentrtion profiles on the cross section of the coting lyer in s-delivered condition (E7, F7) nd fter 5h of exposure (E, F) d

6 . CONCLUSIONS In this work the tests of cotings sed on prepred y Electro-chemicl ssisted deposition of (ECA) method in KIT Krlsruhe hve een crried out under conditions modeling the TBM operting conditions. The specimens were exposed in the P-Li melt t 55 C t flow rte of 1cm/s for, 3 nd 5h. The effects of experimentl conditions of the melt interction with coted EUROFER steel specimens on thickness, microstructure nd chemistry were evluted. In principle, cotings of specimens free of technologicl defects in s-delivered condition did not show ny significnt corrosion ttck. In some res the ttck of the outer porous nd the inner compct lyer nd consequently the steel se mteril hs locl chrcter. For the future development of luminium cotings it is therefore necessry: To prepre homogenous coting lyer free of technologicl defects. To limit nd/or remove the upper porous surfce lyer which compred with the compct lyer hs lower corrosion resistnce. To crry out tests of corrosion resistnce of improved coting lyers t long-term exposure times nd to follow up mechnism of the interction with P-Li with regrd to coting composition, compctness nd chrcter. ACKNOWLEDGMENT The presented work hs een supported y the Europen Fusion Development Agreement. REFERENCES [1] BERKA, J, FRÝBORT, O., HÁJEK, P., KOŠEK, L., ŠPLÍCHAL, K., MASAŘÍK, V., VŠOLÁK.,R., SKOUMALOVÁ Z., BURDA, J., KEILOVÁ, E. Components of the Helium Cooled P-Li Test Blnket Modeule, Report TLR Řež Z 9, 11. [] FRÝBORT, O., HÁJEK, P., ŠPLÍCHAL, K., MASAŘÍK, V., VŠOLÁK.,R., SKOUMALOVÁ Z, BURDA, J.,. Corrosion resistnce nd comptiility of Eurofer steel cotings in the P-Li t the temperture of 55 C. Report CVR Z, Octoer 11. [3] KRAUSS, W., KONYS, J., HOLSTEIN, N. Specimens with coting produced y n electrochemicl deposition process. Report 37, FZK Krlsruhe,.