Bürkle, U.

Gaganidze, E.

Mönig, R.

Rupp, D.

Walter, M.

Weygand, S.

English

KITopen

KIT – Universität des Landes Baden-Württemberg undnationales Forschungszentrum in der Helmholtz-GemeinschaftINSTITUT FÜR MATERIALFORSCHUNG IIwww.kit.eduFracture Mechanical Properties of Tungsten AlloysDaniel Rupp and Ermile GaganidzePresentation at: CRPP-EPFLFusion Technology Materials, ODGA/C110March 22, 5232 Villigen PSI, SwitzerlandContributors:S. WeygandR. MönigM. WalterU. BürkleD. Rupp and E. Gaganidze Institut für Materialforschung II2 22.03.2010CONTENTTungsten Alloys- Candidate Structural MaterialTest Method for Mode I Fracture Toughness Fracture Mechanical Properties of Tungsten Alloys Polycrystalline Rolled TungstenPolycrystalline Rolled ODS TungstenMA + Hipped ODS TungstenHipped TungstenSummary & OutlookD. Rupp and E. Gaganidze Institut für Materialforschung II3 22.03.2010Structural Materials for Fusion Applicationsgood thermo-physical (thermal conductivity, thermal expansion coefficient, …) &    mechanical properties (DBTT, toughness, ductility, strength, creep strength, …)resistance to high energy neutron flux (irradiation-induced damage)low neutron-induced activation (specific radioactivity, decay heat)fusion relevant joining technologies (heat affected zone, proper PWHT, …)compatibility with coolant, plasma (corrosion, erosion, oxidation)Key Issues:RAFM steelRAFM ODSW-alloyBlanket Box DivertorThermal Load: 2.5 MW/m2Operating Temperature: 250-550 °CIrradiation Dose: up to 150 dpaThermal Load: 10-15 MW/m2Operating Temperature: up to 1300 °CIrradiation Dose: up to 50 dpaBoccaccini et al., FZK-Nachrichten, 1/2004D. Rupp and E. Gaganidze Institut für Materialforschung II4 22.03.2010Tungsten Alloys - Candidate Structural MaterialsADVANTAGES:highest melting point of all metals Tm=3693Klowest vapour pressure Pv(Tm)=1.3 ×10−7Palow sputter yieldhigh thermal conductivitygood thermal shock resistancegood high temperature strengthlow-activating materialnearly zero tritium retentionDISADVANTAGES:high hardnessinherent low fracture toughnesshigh DBTTlow recrystallisation temperature (RCT)sensitivity to fabrication detailssensitivity to impurities and alloying element"not matched" thermal expansion coefficientD. Rupp and E. Gaganidze Institut für Materialforschung II5 22.03.2010MotivationFracture Mechanical (FM) properties of rolled polycrystalline tungsten alloys are expected to exhibit strong anisotropy due todifferent grain shape/orientation with respect to the rolling direction (RD) pronounced fiber textureObjective:Understanding of fracture behaviour of tungsten alloys by investigation of microstructure (grain size, texture etc.) and load rate dependence of the fracture toughness (KIC) Microstructure belongs to the main controlling factors for fracture toughness and DBTT of tungsten alloysD. Rupp and E. Gaganidze Institut für Materialforschung II6 22.03.2010Test Method for Mode I Fracture ToughnessBend Specimen SE (B)F/2 F/2FB2.1W 2.1WWa oASTM E399standard: B=0.5Walternative: B=0.25W÷WSpecimen LoadingDisplacement controlledSpecimen pre-crackingFatigue pre-crackingCompression fatigueComposite bendingRazor blade polishing25.2,, ⎟⎟⎠⎞⎜⎜⎝⎛σ>−yICooKaaWBsmMPaK /75.255.0 ≤≤ &Test RecordLoad - Load Line DisplacementLoad - Crack Opening DisplacementD. Rupp and E. Gaganidze Institut für Materialforschung II7 22.03.2010Three Point Bending Experimental Facility Universal Testing Machine INSTRON (RT-1600°C)high vacuum furnaceceramic rodsW -heaterbendfixtureD. Rupp and E. Gaganidze Institut für Materialforschung II8 22.03.2010Fracture mechanical investigation of polycrystalline rolled tungstenMaterial (Plansee)unalloyed 99.98% pure polycrystalline W rods break down rolling with a degree of deformation of 65%Anisotropy<110> fiber texture and elongated grains parallel to the rolling directionSpecimens6x4x27 mm with V shaped notch (3 mm)FM specimen preparationIntroduction of sharp crack starter notchesrazor blade polishingcompression fatigue composite bendingxEBSD pole figureySpecimens with three different orientations of the crack front with respect to the rolling directionD. Rupp and E. Gaganidze Institut für Materialforschung II9 22.03.2010Microstructure of polycrystalline rolled tungsten100 μmrollingdirectionHigh angle GB+ Low angle GBTEM samplesub-grain structureD. Rupp et al,   17th Plansee Seminar, 2009D. Rupp and E. Gaganidze Institut für Materialforschung II10 22.03.2010Temperature [°C]Brittle-to-Ductile Transition of polycrystalline rolled tungstendK/dt = 0.5 MPa m1/2/sStrong influence of the anisotropic microstructure on the fracture toughness and DBTTD. Rupp et al,   17th Plansee Seminar, 2009D. Rupp and E. Gaganidze Institut für Materialforschung II11 22.03.2010Fracture behavior of polycrystalline rolled tungstentype I type II type IIIType I & II: No significant change of the fracture morphology with increasing temperature up to 800°C. First local traces of ductile fracture at 950°C. Type III: Change of fracture behavior above 200°CRT RT RT350°CType I and II: Intergranular fracture, small amount of cleavage surfacesType III: Transgranular cleavage950°C 950°CD. Rupp and E. Gaganidze Institut für Materialforschung II12 22.03.2010Fracture behaviour of type III specimenbrittle fracture at RTstable crack growth above 275°C plastic yielding prior to stable crack growth at high TD. Rupp et al,   17th Plansee Seminar, 2009RT 275°CD. Rupp and E. Gaganidze Institut für Materialforschung II13 22.03.2010In situ Fracture ExperimentsIn-situ 3-point bending test were performed in SEM at elevated temperatures Insights into crack initiation and propagationFracture test at 350°C, type III specimenD. Rupp et al,   17th Plansee Seminar, 2009D. Rupp and E. Gaganidze Institut für Materialforschung II14 22.03.2010In situ Fracture Experiments100 µmcompetition between inter- and transgranular fracture elongated grain boundaries become preferred crack paths with increasing Tstable crack growthRDD. Rupp and E. Gaganidze Institut für Materialforschung II15 22.03.2010Loading rate dependencetype I type II0.05 MPa m1/2/s0.5 MPa m1/2/s 5 MPa m1/2/s0.05 MPa m1/2/s0.5 MPa m1/2/s 5 MPa m1/2/sD. Rupp and E. Gaganidze Institut für Materialforschung II16 22.03.2010⎟⎟⎠⎞⎜⎜⎝⎛−∂∂BDTBBDTTkEtK exp~Arrhenius-relationship:- Loading rate dependence follows Arrhenius-relationship- Activation energies in very good agreement with recently published results- Transition controlled by mobility of screw dislocationsActivation energytype Itype IID. Rupp and E. Gaganidze Institut für Materialforschung II17 22.03.20100.0 0.1 0.2 0.3 0.4 0.50100200300400500600  Load (N)Displacement (mm) RT 500°CPQ=184 NPQ=389 NFracture mechanical properties of    polycrystalline rolled W-1%La2O3transcrystallinecleavage at RT  transversal (II RD) cracking at 500°CRDSpecimens3x4x27mm with U shaped notch (1mm)razor blade polishingcompression fatigue pre-crackKIC=11 MPam1/2KQ=22 MPam1/2D. Rupp and E. Gaganidze Institut für Materialforschung II18 22.03.2010Fracture mechanical characterization of W-2%YMaterial (N. Baluc, CRPP-EPFL)- W powder (99.9%); particle sizes 1-5 μm- Y powder (99.99%), particle sizes below 40 μm- W-2.0Y (in wt.%) manufactured by MA and HIPping- Y2O3 particles formation during HIPpingSpecimen (N. Baluc, CRPP-EPFL)3x4x27 mm with V shaped notch (1mm)FM specimen preparation (KIT)Introduction of sharp crack starter notches by means    of a razor blade polishing - initial crack length 1040-1200 µm  - notch final radius 20-25 µmD. Rupp and E. Gaganidze Institut für Materialforschung II19 22.03.2010Fracture mechanical properties of W-2%YLoad (N)Displacement (mm)Displacement (mm)Load (N)RTloading rate 2µm/sPQ=108 NKIC=5.38 MPam1/21000°Cloading rate 2µm/sPQ=117 NKIC=5.28 MPam1/2Rapid drop of the load at PQ in the entire temperature range⇒ no indication of the ductile fractureD. Rupp and E. Gaganidze Institut für Materialforschung II20 22.03.2010Fractography of W-2%Y specimen (RT)D. Rupp and E. Gaganidze Institut für Materialforschung II21 22.03.2010Fractography of W-2%Y specimen (1000 °C)D. Rupp and E. Gaganidze Institut für Materialforschung II22 22.03.2010Fracture mechanical characterization of HIPped WMaterial (N. Baluc, CRPP-EPFL)- W powder (99.9%); particle sizes 1-5 μm- HIPped at 1320°CSpecimen (N. Baluc, CRPP-EPFL)specimens 3x4x27 mm with V shaped notch (1mm)FM specimen preparation (KIT)Introduction of sharp crack starter notches by means    of a razor blade polishing - initial crack length 1100 µm  - notch final radius 20-25 µmD. Rupp and E. Gaganidze Institut für Materialforschung II23 22.03.2010Fracture mechanical properties of Hipped W0.00 0.05 0.10 0.15050100150200  Force (N)Displacement (mm) RT 600°C 1000°Cunstable crack propagation below 600 °C ⇒ no indication of ductile behaviourcrack arrest events at 1000 °Cloading rate 1µm/sD. Rupp and E. Gaganidze Institut für Materialforschung II24 22.03.2010Fractography of HIPped W (RT)IIIIII I   necking between particles, open pore structureII  neck blunting, channel closureIII pore break down into discrete isolated poresE. Lassner and W.-D. Schubert, Kluwer Academic / Plenum Publishers, 1999D. Rupp and E. Gaganidze Institut für Materialforschung II25 22.03.2010Fractography of HIPped W (600°C)Fractography of HIPped W (1000°C)D. Rupp and E. Gaganidze Institut für Materialforschung II26 22.03.2010Fracture toughness of W and W-2%Y alloys0 200 400 600 800 10002345678  W   KIC (MPam1/2 )Temperature T (°C)W 2wt.%YMA & HIPped W-2%Y:low, temperature independent fracture toughness HIPped W:low, weakly temperature dependent fracture toughnessD. Rupp and E. Gaganidze Institut für Materialforschung II27 22.03.2010SummaryThe anisotropic microstructure of the polycrystalline rolled tungsten has a strong influence on the fracture behaviourthe largest fracture toughness and the lowest DBTT are observed for the longitudinal orientation when a crack propagates transverse to the RD through the elongated grains yielding a transgranular cleavagelower fracture toughnesses in the two transverse orientations are related to the propagation of a crack along weak GB yielding an intergranular fracturestrong loading rate dependence of the DBTT in the two transverse orientations. The apparent activation energies suggest that the brittle-to-ductile transition is controlled by the mobility of screw dislocations. The anisotropic microstructure of polycrystalline rolled W-1%La2O3 has a strong influence on the fracture behaviour. At 500°C the observed propagation of a crack along the RD indicates presence of weak GBLow, temperature independent fracture toughness for MA & HIPped W-2%Y isascribed to poorly consolidated matrix; islands of higher degree of consolidation Low, weakly temperature dependent fracture toughness for HIPped W is ascribed to poorly consolidated matrix; onset of isolated grain growthD. Rupp and E. Gaganidze Institut für Materialforschung II28 22.03.2010Fracture mechanical and microstructural characterization of novel tungsten alloysInvestigation of upper shelf fracture toughness of tungsten alloys by using J-Integral and/or COD methodsEquipping the high vacuum furnace with an optical system for in-situ observation of crack initiation and growth Development and validation of alternative procedure for controlled pre-cracking of notched bend-bar specimensOutlook

Fracture mechanical properties of tungsten alloys

https://publikationen.bibliothek.kit.edu/230078764/3815662

Fracture mechanical properties of tungsten alloys

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