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Low symmetry of hexagonal crystal allows control of deformation modes

alana-joyner
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Low symmetry of hexagonal crystal allows control of deformation modes

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  1. Microstructure Evolution of Beryllium Subjected to Shear-Compression Investigated Using Synchrotron X-ray Diffraction T.A. Sisneros1, D. W. Brown1, B. Clausen1, C.M. Cady1, G.T. Gray III1, E. Tulk1 and J. Almer21Los Alamos National Laboratory, Los Alamos, New Mexico2Argonne National Laboratory, Argonne, Illinois

  2. Low symmetry of hexagonal crystal allows control of deformation modes • Compressive strain transverse to the basal pole. • Basal slip is off, Prismatic slip and tensile twinning are active. • Balance between slip and twin modes affected by strain rate. • High strain rate favors twinning

  3. Crystallography of (10.2)<10.1> twinning in beryllium • Discrete crystal reorientation • Near one-to-one switching of 00.2 and 10.0 poles • Monitor with X-Ray diffraction

  4. Texture signature is distinctive feature of twinning deformation 5000/sec 1/sec As-Rolled 0.0001/sec

  5. The mechanical properties of beryllium can be very anisotropic As-Rolled

  6. Rolling of beryllium results in strong crystallographic texture A B As-Rolled • Sample A Shear is 45 degrees from basal pole • May be parallel to twin plane • Sample B Shear is normal to basal pole RN RD

  7. (10.0) (11.0) (002) Orientation of crystals with respect to load axis is critical A B

  8. Beryllium is brittle at room temperature in tension, ductility was observed in shear

  9. Measurements on 1-ID at Advanced Photon Source Slits Sample 200 Diffracted beam Beam from monochromator 110 Diffracted beam 2q h 0.1x0.1mm beam • X-ray energy = 65KeV. • Beam cross section: 100mm X 100mm • Collection time: seconds. • Precision translation and rotation stages for mapping. • 15kN load frame. • ~1200C furnace.

  10. We use in-situ diffraction to learn about deformation

  11. Basal peak intensity begins to increase markedly from the initial value, signaling the detection of deformation twins Normalized basal pole intensities (002) along the loading direction (Long.) 0.2mm,1/sec 0.4mm, 0.001/sec Deformation twins Deformation twins Pre-deformation Deformed Fast Post -deformation Deformed Slow Post -deformation

  12. Evolution of microstructure dependent upon orientation of load WRT texture Post- deformation Pre- deformation B A

  13. Evolution of microstructure dependent upon orientation of load WRT texture Post- deformation Pre- deformation B A

  14. Conclusions • X-raydiffraction can be used to monitor evolution of microstructure during deformation. • Deformation twinning in hexagonals has a strong signal in X-ray diffraction. • Data is being used to develop and validate rate dependent polycrystalline plasticity models.

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