Electro-chemical processing for tungsten fabrication and joining by layer deposition

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1 Challenges to Developing W-Based Materials for Fusion Applications UCSB, Santa Barbara, CA, USA, February 13 15, 2012 Electro-chemical processing for tungsten fabrication and joining by layer deposition W. Krauss, J. Konys, N. Holstein, J. Lorenz INSTITUTE FOR APPLIED MATERIALS MATERIAL PROCESS TECHNOLOGY CORROSION DEPARTMENT Outline: Motivation Challenges in W handling Machining by electro-chemical dissolution (ECM) Layer deposition / joining from aqueous systems Innovative deposition from aprotic electrolytes Conclusions KIT University of the State of Baden-Württemberg and National Research Center of the Helmholtz Association

2 Motivation for Electro-Chemical Processing Divertor development Eurofer Tungsten Application: Machining Joining Composites W, Cu Steel, SS Castellation Activation control Cleaning of EDM processed BU s Blanket development T-permeation and corrosion barriers Al, Er, W-based FW coating W-scales Oxidation protection Al, Si, Y 2 Developing W-based materials, Santa Barbara, USA, Feb. 2012

3 Motivation for Electro-Chemical Processing of W Typical defects and failures of W parts Primary machining defects Secondary failures, growing under HHF load Crack growth at machining defect HHF results defined needs for development in W-processing and joining Smooth surfaces No defects from machining No sharp edges Adapted fillers for brazing 3 Developing W-based materials, Santa Barbara, USA, Feb Filler behavior Mock up # 4 Post HHF analyses of mock-up. Machining defect caused failure KIT-Efremov coop.

4 Electro-Chemical Reactions 1000 ph = 12,4 ph = ph = 11 ph = 10 ph = 9 10 ph = 9 i / macm-2 ph = 8 ph = 7 ph = 7 1 ph = 6 ph = 5 ph = 3 0,1 ph = 1 i = f(ph) System: W / TCEE / Pt v = 1 mv/s, 1000 U/min, d = 16 mm 0,01 0,001 0,0001-0,75 Anodic reaction W-dissolution -0,5-0,25 0 0,25 0,5 0,75 1 1,25 1,5 E / V (Hg/HgSO4) 1,75 2 2,25 2,5 2,75 3 Basic investigation 3,25 Cathodic reaction Deposition Application Surface treatment Electro-polishing S-ECM Machining ECM C-ECM, M-ECM 4 Developing W-based materials, Santa Barbara, USA, Feb Layer deposition brazing e.g. by Ni, Cu, Pd protic Deposition aprotic e.g. W or Ta

5 ECM for 3-D structuring M-ECM C-ECM Cathode = ECM working tool h n 365 nm + Mask processing UV - lithography Electro-chemical Etching Structured workpiece - ECM Requirements Electrolyte development M-ECM: anode mask process C-ECM: cathode tool ECM Advantages No cracks by ECM process Surface polishing residue-free metal removal M-ECM for Slot array : UV-mask Novolak agitation by microstep-motor 2 H + + 2e - H 2 + Anode = workpiece Me Me e Processed workpiece framework - cathode guiding MAIN DIFFERING FEATURES M-ECM 5 Developing W-based materials, Santa Barbara, USA, Feb C-ECM Technique Conventional installation Complex facility Parameters Current x time = charge Charge + distance + steprate + convection Cathode passive counter electrode active shaping component (by step motor) Tool design 2-dim. mask (positive) 3-dim. electrode (negative) Transformation +2-dim g +3-dim -3-dim g +3-dim C-ECM scheme electrolyte + cathode = ECM working tool, negative image vertically mobile anode = workpiece

6 W machining impact on quality i [macm -2 ] E / mv (Hg/HgSO 4) Parameter dependencies Smaller distance tool work piece E = d(ae-ge) System: W / SL1 / Pt i = 200 ma/cm 2, 1500 U/min, d0 = 3 mm ma/cm2 100 ma/cm2 150 ma/cm2 50 ma/cm Abstand AE-GE / mm Higher frequency of pulsed DC power Desired flank profile Hz: C-ECM: Edge steepness as Function of pulse frequency n 1000 ph = ph = 11 ph = 10 ph = 9 10 ph = 8 ph = 7 1 ph = 6 ph = 3 0,1 ph = 1 0,01 Linear Scanning Voltametry (LSV) 0,001 Sytem: W / TCEE / Pt Scan rate: 1 mv/sec 0,0001-0,5-0,25 0 0,25 0,5 0,75 1 1,25 1,5 1,75 2 2,25 2,5 Potential E [V vs. NHE] Mobility control / reduction Conductivity of electrolyte 6 Developing W-based materials, Santa Barbara, USA, Feb J. Konys Electro-chemical IMF III/KOR processing for tungsten fabrication and joining

7 Tungsten by C-ECM (Anodic dissolution) C-ECM demonstrator cathodes Parallel grooved structure Angled structure Generated W-structures 7 Developing W-based materials, Santa Barbara, USA, Feb. 2012

8 Functional layers by cathodic deposition Requirements: Example for not adjusted filler matrix combination Cu-layer W thimble 50 cm (1/2 plate length) UCSD Malang et al. Steel W steel W-W joining Brazing lacks in the past No wetting Incomplete wetting Not adapted filler composition Embrittlement Development paths in EC: 20.8 cm Oxidation protection by scales e.g. Ta, Si, Cr, Y, Zr, La, Al, Eu Diffusion barriers e.g. W, Ta, V, Cr, (Ni), Fe Fillers based on e.g. Ti, V, Pd, Zr, (Ni), Cu, Fe 8 Developing W-based materials, Santa Barbara, USA, Feb. 2012

9 Electro-chemistry for coating development EC measurements of protic and aprotic metal deposition systems Organic electrolytes: EMIM-Cl (Ethyl-Methyl-Imidazolium-Cl) PC (Propylencarbonat) Elements with relevance to joining and electro-chemical deposition 9 Developing W-based materials, Santa Barbara, USA, Feb. 2012

10 Coatings from aqueous systems Surface activation EDM Turning Turning Interference Raw material EDM - worked Surface activation by K 3 [Fe(CN) 6 ] * KOH small roughing Turning etched Defects from working emphasized Cracks HNO 3 (conc.) * HF high temp. EDM etched KOH polishing, low adherence NaOH * KMnO 4 HCl cleaning HCl * H 3 C-COOH roughing NH 3 * NaNO 3 polishing, current Turning etched Clean, oxide free surface for coating 10 Developing W-based materials, Santa Barbara, USA, Feb. 2012

11 Coatings from aqueous systems Advantage of homogeneous layers EDM worked part Parts by turning Ni interlocking in interface layer Constant thickness on edge Tungsten EDM initiated cracks contrasted after heat treatment, 700 C, vacuum Electrolyte: 1.3 M Nickel sulfamate Ni(SO 3 NH 2 ) 2 T = 52 C, ph = 3.5, i = 10 ma/cm²,d = 12 µm/h 11 Developing W-based materials, Santa Barbara, USA, Feb. 2012

12 Resin Counts N [arb. units] W steel joining with Ni and Cu coatings from aqueous systems Functions: W Ni interlayer as alloying support Ni Eurofer surface activation Cu filler metal Brazing by Ni Cu alloying Cr (Eurofer) Fe (Eurofer) Ni (Functional scale) Cu (Brazing alloy) W Testing distance x [µm] Cu Tungsten Ni Copper Eurofer Eurofer Tungsten Ni Brazed at 1100 C W steel joint 12 Developing W-based materials, Santa Barbara, USA, Feb. 2012

13 Resin Counts N [arb. units] W W brazing with Ni and Cu coatings 800 Tungsten Ni Functional scale Cu Filler metal W Work pieces Ni Cu Ni scales Brazed at 1100 C W-W-Cu 10M Testing distance x [µm] Tungsten Tungsten Ni W W Cu Ni Cu filler W W joint 13 Developing W-based materials, Santa Barbara, USA, Feb. 2012

14 Coatings from aqueous systems Joining of W-W by Cu and Pd Cu+W Pd-W Pd-Cu No miscibility Direct reactive joining of W-W not possible by Cu Functional layer Pd required Cu is appropriate as filler metal due to fully miscibility with Pd W - Pd - Cu 14 Developing W-based materials, Santa Barbara, USA, Feb. 2012

15 Coatings from aqueous electrolyte systems Pd on W as reactive interlayer for Cu brazing Electrolyte testing Cu substrate Pd deposited on Cu W after chemical conditioning W coated by Pd + Cu W - Pd - Cu + W - Pd Pd layer Cu + Pd layers As deposited on W T = 1100 C, t = 10 min in Ar + cooling in air Pd layer Cu layer After brazing 15 Developing W-based materials, Santa Barbara, USA, Feb. 2012

16 uniaxial forcing Mechanical characterization of joints from aqueous electrolytes Shearing strength tests of brazed specimen 1100 C First shear tests show applicability of test method, but further development and optimization is needed 16 Developing W-based materials, Santa Barbara, USA, Feb Introduction Conclusion

17 Mechanical characterization of joints from aqueous electrolytes Shearing strength tests of brazed specimen Planned: Eurofer-Pd-Cu-Pd-Eurofer Preliminary specimen as model system steel-ni-cu-ni-steel for test qualification SEM SEM Specimen after test, optical overview Brazing material breaks amongst the brazed Cu bulk 17 Developing W-based materials, Santa Barbara, USA, Feb Introduction Conclusion

18 Deposition from aprotic systems Properties of organic aprotic electrolyte systems WCl 6 Only Al Al K F K Al N + N X - R Al Cl - or W Cl - EMIM-AlCl 4 or EMIM-WCl 6 18 Developing W-based materials, Santa Barbara, USA, Feb. 2012

19 Ionic liquids as electrolyte for W deposition - Ethylmethylimidazolium-chloride + WCl 6 EMIM-Cl, RT EMIM-Cl + Salt Scale Deposition IL melting Mixing IL + salt Deposited metal EMIM-Cl, 80 C EMIM-Cl + Salt + DC 19 Developing W-based materials, Santa Barbara, USA, Feb. 2012

20 Coatings from organic electrolytes (IL) W on Eurofer resin Tungsten layer on Eurofer steel W scale 15 μm Deposited at 120 C Electrolyte (IL) EMIN-Cl + WCl 6 W layer in vertical SEM view Eurofer Development needs for W, Ta.. Evaluation of solvent / salt compatibility Analyses of current modes Analyses of electrolyte composition Adhesion Morphology W layer in SEM cross section 20 Developing W-based materials, Santa Barbara, USA, Feb. 2012

21 Conclusions Electro-Chemical Machining (ECM) of tungsten ECM is a tool to machine W successfully without chemical passivation Quality improvement realized by short DC pulses and gap control Demonstrators fabricated by C-ECM with 10 khz pulse generator Electro-chemical deposition for joining and functional scales Aqueous systems: Successfully performed W W and W-steel joining by deposited Cu, Ni Multilayer deposition on W parts under execution to increase operation temperature Substitution of model metal Ni successfully demonstrated by Pd plating Mechanical shear tests showed well adherence of filler at bulk Organic systems: IL systems applicable for deposition of refractory metals 21 Developing W-based materials, Santa Barbara, USA, Feb. 2012