Holstein, N.

Konys, J.

Krauss, W.

Wulf, S.E.

Fusion Engineering and Design

Wulf, S. E.

KITopen

KIT – University of the State of Baden-Wuerttemberg andNational Research Center of the Helmholtz AssociationInstitute for Applied MaterialsMaterial Process Technology (IAM-WPT)Heat treatment behaviorConclusionsElectrodeposition of Al by ECXResults► Quality depends on surface morphology of Al-layers on Eurofer after electroplating► Pulse plated samples by ECX: uniform formation of Al-based scales, comparable to scales produced by ECA (see [1])► Rough and jagged surface structure (in this case DC plated): formation of relatively thick porous, oxygen containing layer on top of the sample► Al amount in the reacting zone of ca. 20 at.% (decreasing with distance from surface) Influence of deposition conditions on the microstructure  of Al-based coatings for applications as corrosion and anti-permeation barrierECX process show industrial relevance and deposit Al scales on Eurofer steel samples with controllable and reproducible thicknessMorphologies of Al coatings made by ECX process depend on deposition parametersAl layers have to be converted into protective scales by heat treatments (HT)HT behavior depends on the morphology of the coating produced by ECXFormation of Fe-Al scales during HT is influenced by morphologyRough and jagged surface structures cannot be recommended for further HTEven, dense and homogeneous morphologies are recommended for HTHeat treated samples with recommended morphology (pulse plated) werecomparable to known ECA or HDA produced Al-based scalesThe more flexible ECX process has proven to be a promising alternative to ECAElectrodeposition of AluminumS.-E. Wulf, N. Holstein, W. Krauss, J. KonysMotivationPrevious research revealed that the application of aluminum-based barriers is suitable to minimize corrosion rates of Eurofer steel in Pb-15.7Li (picture to the right) and tritium-permeation from the liquid breeder into the cooling system (HCLL) in an envisaged future fusion reactor. Developed deposition techniques to electroplate aluminum are based on water-free electrolytes. Either ECA or ECX process can provide several advantages compared to the established Hot-Dip Aluminization (HDA) process:► Better thickness distribution► Controllable coating thicknesses ► Reduced amounts of aluminum applicable (low activation)However, the main challenge is to convert the electroplated Al-coatings during a subsequent heat treatment, to enable the formation of protective scales on Eurofer for applications as corrosion and anti-permeation barriers in Pb-15.7Li.Aluminum is highly electronegative (E0= -1,6 V vs. NHE) ► Al cannot be deposited from aqueous electrolytes►Water-free / aprotic electrolytes are neededPrinciple types of electrolytes to electrodepositAl at moderate temperatures (RT-100°C)1. Toluene-based electrolytes  ECA process2. Ionic liquids  ECX processElectrochemical processes have in common► No reaction with the substrate material► Adjustable Al thickness (time, current density)► Good adherence to the substrate► Industrial relevance is givenWhy ECX?► Process is more flexible than ECA process Deposition parameters adjustable in a wider range (T, j, pulse plating,…)► Electrolytes not oxygen sensitive  non-inflammableAl-Surface ECA-plated 10 mA/cm², 1 h, 100°CExperimental  Heat treatment (HT) procedure according to [1] 640°C, 4 h  980°C, 0.5 h  760°C, 1.5 h In flowing argon atmosphere Reduction of oxidation effects Samples cooled down under flowing ArScheme: Pulse plating Electrodeposition of Al on Eurofer steel samples by ECX► From an imidazolium-based ionic liquid Direct current (DC) plated samples were compared topulse plated (P) samples  jmean and t were held constant Theoretical Al thickness should be about 12.5 µm [Emim]Cl:AlCl3;T=100°C; AgitationParameter DC P1 P2jmean 20 mA/cm²jpeak - 80 mA/cm² 25 mA/cm²Duty Cycle 100% 25% 80%t 30 minutesInfluence of deposition parametersSurface morphology is strongly influenced by deposition conditions ► DC plated sample : Jagged and rough surface; crystallites not grown together► Pulse plated samples: Dense, even and homogeneous morphologyDirect current Pulsed DC; P1 Pulsed DC; P2SurfaceasdepositedCross sectionsAlEuroferResinResinResinAlAl EuroferEuroferAl-Surface ECX-plated 20 mA/cm², 0.5 h, 100°CScheme: Heat treatmentReferences: [1] Konys, J. et al.: Impact of heat treatment on surface chemistry of Al-coated Eurofer for application as anti-corrosion and T permeation barriers in flowing Pb-15.7 environment, Fus. Eng. Des., 87 (2012), 1483.DC plated sample after HT Pulse plated samples after HTporous layerEuroferResin Resin ResinEurofer EuroferP1 P2Pulse plated (P2) sample after HTEDX linescan ResinEurofer-Fe(Al)For comparison: heat treated ECA sample(similar HT procedure)picture taken from [1]FeAl-Fe(Al)RAFM steelKirkendall pores 240270HV 320Reference scale made byHDA after heat treatment(1040°C/0.5 h + 750°C /1 h) HDA coated sample after exposure in flowingPb-15.7Li, taken from [1] 

Influence of deposition conditions on the microstructure of Al-based coatings for applications as corrosion and anti-permeation barrier

Sven-Erik Wulf

Nils Holstein

Wolfgang Krauss

Jürgen Konys

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https://publikationen.bibliothek.kit.edu/220088379/3816166

Influence of deposition conditions on the microstructure of Al-based coatings for applications as corrosion and anti-permeation barrier

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