High Velocity Forming of Superconducting Structures with Bulk Nb and Cu Substrate - PowerPoint Presentation

1. High Velocity Forming of Superconducting Structures with Bulk Nb and Cu SubstrateFCC Week 2018, Amsterdam, NetherlandsPresented by: Jean-François Croteau (ESR 9), 12 April 2018

2. Project ObjectivesMechanical characterization of copper and niobium at high strain-ratesDesign of compensation die for the fabrication of niobium half-cellsFabrication of half-cells with large grain niobium sheetsMicrostructural studies of cavities formed by different processesInvestigation of the feasibility of forming seamless cavities2

3. Electrohydraulic FormingHigh strain-rate deformation of metal by a shock wave inside a water tankShock wave is generated using a high voltage discharge of capacitors3

4. Electrohydraulic FormingCurrently used with CERNto produce half-cellsAdvantagesHigh shape accuracyHigh reproducibilityThin affected layer on surfaceNo foreign particles embeddedNo intermediate heat treatmentstages required400 MHz cavity from EHF half-cells welded at CERN4

5. Project Timeline2018201920202021Project kick-offMid-termExpected completionEASITrainPhases1. Constitutive laws at high strain-rate2. Determination of forming limit diagram 3. Compensation die for 800 MHz half-cells5. Large grain Nb half-cells6. Investigate feasibility of seamless cavities4. Characterization of mechanical properties after forming5

6. Material Characterization at High Strain RatesConstitutive model for OFE Cu and NbTheoretical modelling of forming limit diagram with ENSTA Bretagne validated with experimental dataSplit-Hopkinson bar tests in compression and tension Adaptation of in-house testing device for large grain NbStrain rate Method Tensile test Split-Hopkinson6Large grain niobium sheets [1][1] P. Kneisel, et al., “Development of Large Grain/Single Crystal Niobium Cavity Technology at Jefferson Lab,” 2007, vol. 927, pp. 84–97.eet

7. Design of Compensation DieCompensation die for fabrication of Nb half-cells that fit within prescribed tolerances for 800 MHz cavitiesNew die to fit in the current die-splitter used for 400 MHz Cu half-cells7Old die-splitterCurrent die-splitterFuture compensation die

8. Expanded tubeDieTubeFluid12Comparison of Microstructures8HydroformingSpinningElectro-hydro formingHigh vs low strain rate deformation techniquesMicrostructural and mechanical characterizations (hardness, dislocation densities, deformation mechanisms, recrystallization, RRR)Electrode or explosive wireWaterStandoffWorkpieceHold-down ringDieVacuum lineTankWater levelBlankMandrelToolFigures: S. Kalpakjian and S. R. Schmid, Manufacturing engineering and technology, Seventh edition. Upper Saddle River, NJ: Pearson, 2014.

9. Investigation of Seamless CavitiesDefects at weld have negative effects on the heattransfer properties and for the formation ofsuperconducting thin filmsSignificant reduction of production costs and timeInvestigate the feasibility of the fabrication of seamless cavities96 GHz seamless cavity produced with EHF

10. Challenges and RisksReceiving Cu and Nb sheetsExperimental results of large grain Nb half-cellsProcurement of Cu and/or Nb tubes for seamless cavitiesSplit-Hopkinson tension testsModification of in-house setup for large grain Nb characterization at high strain-rates10

11. Project StatusProject started on March 1st 2018Currently cutting Cu samples for secondment at ENSTA Bretagne to test mechanical properties of OFE Cu at low and high strain ratesDesign of 800 MHz Nb compensation dieLiterature review, trainings on finite element modelling and more at I-Cube Research11

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