Bonk, Simon

Hoffmann, Andreas

Hoffmann, Jan

Reiser, Jens

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KIT – University of the State of Baden-Wuerttemberg andNational Research Center of the Helmholtz Association 6 μmGB climbdislocationsGB glidedislocationsLatticedislocations0.0 0.5 1.0 1.5 2.005001000150020002500 0.50 0.75 1.00 1.252000210022002300   true stress (MPa) true strain (%)   true stress (MPa) true strain (%)Simon Bonk1, Jan Hoffmann1, Andreas Hoffmann2, Jens Reiser11: KIT2: PLANSEE SE Simon Bonksimon.bonk@kit.eduKarlsruhe Institute of TechnologyInstitute for Applied Materials- Applied Materials Physics (IAM-AWP)www.kit.eduAcknowledgement: DFG (RE 3551-2/1), PLANSEE SE, University of Oxford,Erich Schmid Institute of Materials Science and all involved colleagues at IAM (KIT)Further presentations given by our team:J. Reiser, Walter Schwarzkopf Hall, Tue 15:20, RM9 C. Bonnekoh, poster, RM 631000 µmIPF [001] 1000 500 300 200 10001002003004005006007008009001000 nc   grain size (nm) thickness (µm)coarse grainedfine grainedUFG0 1 2 3 4 505001000150020002500   true stress (MPa) true strain (%)εU ≈  0.75    1.4x 0 200 400 600 8000100020003000   flow stress σ 0.2 (MPa) temperature T (°C)    100 µm   200 µm   300 µm   500 µm 1000 µm hot-rolled W recryst. W x m  ∆∗∆	 ,	Strain rate sensitivity:Δσ grainsize grainsizeScrew dislocation Grain boundarymediated plasticitycontrolled by kink pairnucleation & propagation↓thermally activated↓T↑  m↓d↓  m↓100 µmS-Directioncoarse grained Wbrittle fracture (εU ≈ 0)at room temperature Tensile strain rate jump tests:Temperature range: 20 °C – 800 °CStrain rates: 10-3  ⁄ ↔  10-4  ⁄Strain-controlled testing 0.0 0.5 1.0 1.5 2.005001000150020002500   W1000 - 800 °CW500 - 400 °Ctrue stress (MPa) true strain (%)W100 - 20 °Creduction of pile-up by absorbing GBs↓controlled by dislocation climb (diffusion process)↓T↑  m↑d↓  m↑ W-foil: application inlaminates:Controlling  mechanismsworkinghypothesisfabrication of W-foils with microstructural evolutioncharacterizationmicrostructure mechanicaltestingverification by electron microscopySEMEBSD Tensile TestsNanoindentationSRJ TestsTEM  /  High Resolution EBSDPROJECTMOTIVATIONINTRODUCTIONThe aim of this project is to investigate cold-rolled,ultrafine-grained (UFG) tungsten, a material interesting forfuture high-temperature applications.The focus is set on the analysis and correlation of themicrostructure and mechanical properties to illuminate themechanisms responsible for plastic deformation.Tests are performed at different microstructures andtemperatures between 20 °C and 800 °C, showing anevolution of deformation mechanisms . WHY ARE TUNGSTEN FOILS DUCTILE ?increasedcold rollingEvolving εU(RT – ductility)(II) 20 °C, 100 μm20 °C, 300 μm800 °C, 100 μm800 °C, Ref (cg)800 °C, 300 μm20 °C, Ref (cg)Cold rolling: Increased strengthat high and lowtemperatures(I) Plateau formationfor 100 μm foil:plastic deformation without hardening(III)Hint to change in deformation mechanism in 100 μm foilIV)Cold rolling:Increased flow stress increased degree of deformation V)(IV)(V)T ↑: Flow stress ↓steady decrease with asymptotic behaviourScrew dislocationstill dominant Screw dislocation still dominant  (V),but propagation eased for smaller grain sizes (II, III) RepeatabilityELECTRON MICROSCOPY Working hypothesisstrain rate jump↓stress response↓Exclusive batch of tungsten sheets5 sheets with increasing degree of deformation φ:1000 μm  – 500 μm – 300 μm  – 200 μm  – 100 μm(φ = 1.7)        (2.4)           (2.9)           (3.3)           (4.0) Produced by „cold-rolling“ (Trolling  << 1200°C) One single sintered compact (> 99.97 wt.-% W)Working hypothesis TEM: Imaging dislocations HR-EBSD GND density [m-2]Working hypothesisLow temperatures: Confined plastic slip →Compare sub-structure (focus on dislocations):                    Before and after tensile tests at low THigh temperatures:GBs change from blocking to absorbing→Analyse sub-structure after tensile tests at high T: Decreased pile up in UFG-W? 100 nm = (110) confinedplastic slip? 1015.510151014.510141013.51013rollingdirectionS LT(001)<110> texture grain size (S-Dir)IPF-Maps 240 nmMATERIALTENSILE TESTS STRAIN RATE JUMP TEST10 mmtungstenfoil:Ductilisation of tungsten (W) through cold-rolling:correlation of microstructure and mechanical properties[Ahmed, Hartmaier,Acta Mat. 59 (2011)]6 μm 1015.510151014.510141013.51013100 μm foil 1000 μm sheet

Ductilisation of tungsten (W) through cold-rolling: correlation of microstructure and mechanical properties

https://publikationen.bibliothek.kit.edu/1000077016/5124345

Ductilisation of tungsten (W) through cold-rolling: correlation of microstructure and mechanical properties

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