Real-time 3D imaging of nuclear structural materials at high temperature Dr. Dong LIU EPSRC Postdoctoral Research Fellow 1851 Exhibition Brunel Research Fellow Junior Research Fellow at Mansfield College Department of Materials, University of Oxford, UK Research Affiliate Lawrence Berkeley Lab, UC Berkeley, USA
Content What is in situ x-ray computed tomography o Deformation and fracture o Examples for in situ mechanical testing with x-rays: o Porous graphite composites (nuclear application) o Ceramic-based composites (aero application) o Electronic devices (communications, radars…) o
What is x-ray computed tomography Contrast • Different absorption in different materials Higher atomic number more absorption • Phase contrast from • Tomography – Radiograph abrupt boundaries • X-rays are like light in that they are electromagnetic waves, but they are more (more complex) energetic, so they can penetrate many materials.
Tomography – “X-ray Vision” • CT completely eliminates the superimposition of images of structures outside the area of interest. • Inherent high-contrast resolution, differences between tissues that differ in physical density by less than 1% can be distinguished. https://commons.wikimedia.org/w https://commons.wikimedia.org/wiki/ iki/File:3d_CT_scan_animation.gif File:UPMCEast_CTscan.jpg
Tomography – Rotating Beam
Tomography – Rotating Sample
Tomography – Reconstruction Back-Projection Method Slice-by-slice
Tomography – Reconstruction Back-Projection Method
Tomography – Reconstruction
• Scan an object when it is static to obtain its 3D structure only • Take a scan when an event is happening: • Chemical reaction • Physical loading • … In situ XCT
How things break: deformation and fracture Cracks may not be visible to a the human eye… • Too small • Hidden deep in material They can propagate catastrophically … ‘Fracture mechanics’
The Liberty Ships • Ductile to brittle transition of metals • Square hatch corners increase stress concentration • Steel sheet were welded rather than riveted • Local defects and discontinuities in the welds • … The Liberty ship S.S. Schenectady, which, in 1943, failed before leaving the shipyard. (Reprinted with permission of Earl R. Parker, Brittle Behavior of Engineering Structures, National Academy of Sciences, National Research Council, John Wiley & Sons, New York, 1957.)
DeHavilland Comet Disasters Design flaws, including dangerous stresses at the corners of the square avionics windows and installation methods, were ultimately identified. Full-scale cyclic internal pressurisation test of the fuselage in a water tank of the aircraft G-ALYU removed from service
• In addition to design improvement, ‘better’ materials (higher strength and toughness, lighter in weight..) have been developed, e.g. composite materials have seen an significant increase in various applications, e.g. nuclear and aero • There is a need to understand the 3D microstructure and defects in a material prior to its application
• Where can we do such experiments? • Lab-based x-ray machines (x-ray tubes)
Synchrotron radiation sources • An electron gun – 90 keV • A 100 MeV linear accelerator • A 100 MeV – 3 GeV booster synchrotron (158 m in circumference). • Electrons then travel at 3 GeV (near the speed of light) around a storage ‘ring’ (~561 m) • 48 sided polygon • Sudden change of direction causes the electrons to emit an bright beam (electro-magnetic radiation) to be used for experiments • X-ray to far infrared 10 billion times brighter than the sun.
Synchrotron radiation sources • US: • SSRL and LCLS at SLAC National Accelerator Laboratory • APS at Argonne National Laboratory • ALS at Lawrence Berkeley National Laboratory • NSLS at Brookhaven National Laboratory • … • UK: • Diamond Light Source , Rutherford Appleton Laboratory • … • Europe: • European Synchrotron Radiation Facility, France • Swiss Light source, Switzerland • …
Diamond Light Source I12 Beamline Storage ring
“Where does this bit go?”
Cast Iron
Limpet Shell
Limpet Shell
Limpet Shell - Cracked
What to do after the experiment? 5 days of experiments generated 8TB of data! • Reconstruction • Comparison with Models • Deformation Analysis (3D image tracking algorithms)
Nuclear-grade Graphite The UK has 15 operational nuclear fission reactors at seven plants (14 advanced gas- cooled reactors (AGR) and one pressurised water reactor (PWR)), as well as a nuclear reprocessing plant at Sellafield.
Nuclear-grade Graphite o Graphite has been widely used as a moderator, reflector and fuel matrix in various types of nuclear reactors, such as gas cooled reactor (e.g. AGR, MAGNOX), Russian RBMK reactors, high temperature gas cooled reactor (Dragon, Peach Bottom, AVR, THTR-300, Fort St. Vain, HTTR, HTR-10 ) etc. o Gilsocarbon graphite is used as moderators and structural components in operating Advanced Gas-cooled Reactors (AGRs) in the UK; Life-limiting as it is not replaceable.
Microstructure • • Micro- and Nano- scale Macro-scale • Manufacture route Filler particle Threshold image Gilsonite coke Filler Calcination (~1300°) Milled and sized Coal Filler and flour tar pitch Hot mixed 100 µm Cooled Micro-scale Mrozowski cracks Moulded Green article Baking at ~800° Baked article Re-impregnated with pitch Baking Binder Graphitisation (~3000°C) Nuclear 500 µm 500 µm graphite
Multi-scale Characterisation: RT & HT Macro-scale deformation 3D microstructure Lattice strain Crystal bonding 10 µm Room temperature Elevated temperature
In situ high temperature tomography High temperature mechanical tests • Heating type: laser, lamp, induction, current… • Furnace (controlled environment + loading cell) • Microscopy chamber based (combined with laser heating or hot stage) • Indentation kit with temperature option… Challenges • Temperature control / measurement; • Beamline 8.3.2, Advanced Light Source (LBNL); Hot cell with displacement measurement; strain capability of heating up to ~2300°C; Vacuum: up to 10 -3 torr; distribution. • Gas environment: inert - Ar or N 2 , oxidizing - air • Need to be able to ‘see’ the sample during • Maximum tensile load: 2 kN; LVDT extension measurements; deformation and fracture. test volume: 0.5 cm 3 • …
In situ high temperature tomography Schematic of the setup and operation Hotcell Alignment and in situ control of crack growth Graphite Loading jig rollers Graphite sample
In situ high temperature tomography 1500 • Flexural strength and fracture toughness 40 J max Flexural strength (MPa) 30 1000 2 ) J ( J/m 20 a max 500 10 1000 C Flexural strength Average values 650 C 0 20 C 0 400 800 1200 0 Temperature ( C ) 0.0 0.5 1.0 1.5 2.0 a (mm) • Flexural strength increases with temperature • Failure strain is larger at high temperature Fracture toughness increases with temperature between ambient and 1000 C • D. Liu & R. O. Ritchie et al. Nature Communications, 2017
• In situ crack growth: rising J-R curve 1500 IV 1000 2 ) III J Q (J/m 500 II I 0 0.0 0.5 1.0 1.5 2.0 a (mm)
In situ high temperature tomography • 3D maximum principal strain overlay (DVC) • Interaction between filler particles and strain field • 3D segmentation of a crack at 1000°C D. Liu & R. O. Ritchie et al. Nature Communications, 2017
In situ high temperature tomography • Toughening mechanisms Crack deflection Constraint micro-cracking Microcracks\ unmicrocracked material Uncracked-Ligament Bridging uncracked ligament uncracked ligament crack tip crack tip bridges bridges • Less micro-cracking at HT • More bifurcation at HT
In situ high temperature Raman spectroscopy • Raman spectra provide the ‘ figure print ’ of the various forms of carbon G band: crystalline; D band: disorder G G Intensity (a.u.) 800°C D* Intensity (a.u.) 600°C 400°C D 200°C Wavenumber (cm -1 ) 500 1000 1500 2000 2500 3000 -1 ) Wavenumber (cm • G band shift changes with strain/temperature D. Liu & R. O. Ritchie et al. Nature Communications, 2017
In situ high temperature Raman Spectroscopy • In situ Raman spectroscopy at high temperature indicate that there is residual stress relaxation in this material 60 800 C G peak_centre position change with temperature Slope = -0.0246 0.00037 Linear Fit of peaks I 1585 1580 1581cm -1 1575 1570 40 ΔG I 1565 1560 Counts 1555 1551cm -1 1550 ΔT 20°C 1400°C 0 500 1000 1500 H 20 20 C • 121 measurements in each map; four maps in total. The same area was measured at RT and 800 ° C 0 • 1550 1560 1570 1580 1590 • The histogram on the right shows that at RT there is large -1 ) variation of the G peak shift (strain) and at 800 ° C this G peak position (cm variation is reduced D. Liu & R. O. Ritchie et al. Nature Communications, 2017
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