scholarly journals Electron backscatter diffraction (EBSD) based determination of crystallographic preferred orientation (CPO) in warm, coarse-grained ice: a case study, Storglaciären, Sweden

2020 ◽  
Author(s):  
Morgan E. Monz ◽  
Peter J. Hudleston ◽  
David J. Prior ◽  
Zachary Michels ◽  
Sheng Fan ◽  
...  
Keyword(s):  
Electron Backscatter Diffraction ◽  
Shear Plane ◽  
Preferred Orientation ◽  
Coarse Grained ◽  
Strain History ◽  
Shear Direction ◽  
Preparation Technique ◽  
Crystallographic Preferred Orientation ◽  
Electron Backscatter ◽  
Backscatter Diffraction

Abstract. Microstructures provide key insights into understanding the mechanical behavior of ice. Crystallographic preferred orientation (CPO) develops during plastic deformation as ice dynamically recrystallizes, with the dominance of intracrystalline glide on the basal plane. CPO patterns in fine-grained ice have been relatively well characterized and understood in experiments and nature, whereas CPO patterns in "warm" (T > −10 ºC), coarse-grained, natural ice remain enigmatic. Previous microstructural studies of coarse-grained ice have been limited to c-axis orientations using light optical measurements. We have developed a new sample preparation technique, by constructing composite sections, to allow us to use electron backscatter diffraction (EBSD) to obtain a representative, bulk CPO on coarse-grained ice. We suggest that a grain sampling bias of large, branching crystals that appear multiple times as island grains in thin section may result in the typical multiple maxima CPOs previously identified in warm, coarse-grained ice that has been subjected to prolonged shear. CPOs combined from multiple samples of highly sheared ice from Storglaciären provide a more comprehensive picture of the microstructure and yield a pronounced cluster of c-axes sub-normal to the shear plane and elongate or split in a plane normal to the shear direction, and a concomitant girdle of a-axes parallel to the shear plane with a maximum perpendicular to the shear direction. This pattern compares well with patterns produced by sub-sampling data sets from experimentally sheared ice at high homologous temperatures up to strains of ~ 1.5. Shear strains in the margin of Storglaciären are much higher than those in experimental work. At much lower natural strain rates, dynamic recrystallization, particularly grain boundary migration, may have been more effective so that the CPO has been continuously reset and represents a smaller, final fraction of the shear history, rather than the entire finite strain history.

scholarly journals Full crystallographic orientation (<i>c</i> and <i>a</i> axes) of warm, coarse-grained ice in a shear-dominated setting: a case study, Storglaciären, Sweden

2021 ◽  
Vol 15 (1) ◽  
pp. 303-324 ◽  
Author(s):  
Morgan E. Monz ◽  
Peter J. Hudleston ◽  
David J. Prior ◽  
Zachary Michels ◽  
Sheng Fan ◽  
...  
Keyword(s):  
Dynamic Recrystallization ◽  
Boundary Migration ◽  
Shear Plane ◽  
Sampling Bias ◽  
Optical Measurements ◽  
Coarse Grained ◽  
Shear Direction ◽  
Preparation Technique ◽  
Thin Sections ◽  
Crystallographic Preferred Orientation

Abstract. Microstructures provide key insights into understanding the mechanical behavior of ice. Crystallographic preferred orientation (CPO) develops during plastic deformation as ice deforms dominantly by dislocation glide on the basal plane, modified and often intensified by dynamic recrystallization. CPO patterns in fine-grained ice have been relatively well characterized and understood in experiments and nature, whereas CPO patterns in “warm” (T>-10∘C), coarse-grained, natural ice remain enigmatic. Previous microstructural studies of coarse-grained ice have been limited to c-axis orientations using light optical measurements. We present the first study of a axes as well as c axes in such ice by application of cryo-electron backscatter diffraction (EBSD) and do so in a shear-dominated setting. We have done this by developing a new sample preparation technique of constructing composite sections, to allow us to use EBSD to obtain a representative, bulk CPO on coarse-grained ice. We draw attention to the well-known issue of interlocking grains of complex shape and suggest that a grain sampling bias of large, branching crystals that appear multiple times as island grains in thin sections may result in the typical multimaxima CPOs previously identified in warm, coarse-grained ice that has been subjected to prolonged shear. CPOs combined from multiple samples of highly sheared ice from Storglaciären provide a more comprehensive picture of the microstructure and yield a pronounced cluster of c axes sub-normal to the shear plane and elongate or split in a plane normal to the shear direction as well as a concomitant girdle of a axes parallel to the shear plane with a maximum perpendicular to the shear direction. This pattern compares well with patterns produced by subsampling datasets from ice sheared in laboratory experiments at high homologous temperatures up to strains of ∼1.5. Shear strains in the margin of Storglaciären are much higher than those in experimental work. At much lower natural strain rates, dynamic recrystallization, particularly grain boundary migration, may have been more effective so that the CPO represents a small, final fraction of the shear history. A key result of this study is that multimaxima CPOs in coarse-grained ice reported in previous work may be due to limited sample sizes and a sampling bias related to the presence of island grains of a single host that appear several times in a thin section.

scholarly journals Using electron backscatter diffraction to measure full crystallographic orientation in Antarctic land-fast sea ice

2018 ◽  
Vol 64 (247) ◽  
pp. 771-780 ◽  
Author(s):  
PAT WONGPAN ◽  
DAVID J. PRIOR ◽  
PATRICIA J. LANGHORNE ◽  
KATHERINE LILLY ◽  
INGA J. SMITH
Keyword(s):  
Sea Ice ◽  
Crystallographic Orientation ◽  
Electron Backscatter Diffraction ◽  
Preferred Orientation ◽  
Angle Distribution ◽  
Crystal Preferred Orientation ◽  
Electron Backscatter ◽  
Backscatter Diffraction ◽  
First Time ◽  
Platelet Ice

ABSTRACTWe have mapped the full crystallographic orientation of sea ice using electron backscatter diffraction (EBSD). This is the first time EBSD has been used to study sea ice. Platelet ice is a feature of sea ice near ice shelves. Ice crystals accumulate as an unconsolidated sub-ice platelet layer beneath the columnar ice (CI), where they are subsumed by the advancing sea–ice interface to form incorporated platelet ice (PI). As is well known, in CI the crystal preferred orientation comprises dominantly horizontal c-axes, while PI has c-axes varying between horizontal and vertical. For the first time, this study shows the a-axes of CI and PI are not random. Misorientation analysis has been used to illuminate the possible drivers of these alignments. In CI the misorientation angle distribution from random pairs and neighbour pairs of grains are indistinguishable, indicating the distributions are a consequence of crystal preferred orientation. Geometric selection during growth will develop the a-axis alignment in CI if ice growth in water is fastest parallel to the a-axis, as has previously been hypothesised. In contrast, in PI random-pair and neighbour-pair misorientation distributions are significantly different, suggesting mechanical rotation of crystals at grain boundaries as the most likely explanation.

Inherited Fabric in an Omphacite Symplectite: Reconstruction of Plastic Deformation under Ultra-High Pressure Conditions

2013 ◽  
Vol 19 (4) ◽  
pp. 942-949 ◽  
Author(s):  
Florian Heidelbach ◽  
Michael P. Terry
Keyword(s):  
Orientation Relationship ◽  
Electron Backscatter Diffraction ◽  
Pure Shear ◽  
Additional Component ◽  
Western Gneiss Region ◽  
Crystallographic Preferred Orientation ◽  
Ultra High Pressure ◽  
Shear Component ◽  
Electron Backscatter ◽  
Backscatter Diffraction

AbstractWe investigated an eclogitic gneiss from the Western Gneiss Region in Norway, which underwent subduction as part of Baltica lithosphere beneath Laurentia during the Scandian orogeny. Petrologic data indicate that the eclogite was deformed plastically at about 4 GPa and 800°C producing a strong macroscopic foliation and lineation. Whereas garnet remained largely stable during the retrograde uplift, omphacite was transformed statically into a symplectite consisting of lamellar diopside and plagioclase with more equant grains of hornblende and orthopyroxene. Measurements of the crystallographic preferred orientation with electron backscatter diffraction show that diopside and hornblende, as well as orthopyroxene, have a systematic orientation relationship with the macroscopic fabric, as well as the (presumed) orientation of the host omphacite. The orientation relationship between the chain silicates is very sharp with the crystallographic forms {100}, {010}, and ⟨001⟩ being parallel. Their bulk texture shows a maximum of ⟨001⟩ parallel to the lineation and girdles of {010} and {110} perpendicular to the lineation with maxima subparallel to the foliation corresponding to an L-type texture of the original omphacite and indicating constrictional strain with an additional component of pure shear/simple shear component.

Transpressional deformation in the mantle below the North Anatolian fault system, Turkey

2020 ◽  
Author(s):  
Basil Tikoff ◽  
Vasili Chatzaras ◽  
Timothy Chapman ◽  
Naomi Barshi ◽  
Ercan Aldanmaz ◽  
...  
Keyword(s):  
Fault Zone ◽  
Electron Backscatter Diffraction ◽  
Preferred Orientation ◽  
North Anatolian Fault ◽  
Mantle Xenoliths ◽  
Fault System ◽  
Alkali Basalts ◽  
Crystallographic Preferred Orientation ◽  
The North ◽  
Backscatter Diffraction

&lt;p&gt;The North Anatolian Fault Zone (NAFZ) is a 1200-km-long, dextral intracontinental transform fault zone, and initiated ca. 13&amp;#8211;11 Ma ago.&amp;#160; The NAFZ formed in response to the N-S convergence of the Eurasian and Arabian plates, accommodated by the westward motion of the Anatolia plate relative to Eurasia plate.&amp;#160; Mantle xenoliths were sampled in late Miocene (11.68&amp;#177;0.25 to 6.47&amp;#177;0.47 Ma) alkali basalts and basanites, immediately N of the trace of the North Anatolian fault, and were previously interpreted to sample the mantle portion of the North Anatolian fault/shear zone at depth.&amp;#160; The studied xenoliths are mainly spinel lherzolites and harzburgites.&amp;#160; Equilibration temperatures estimated from two-pyroxene geothermometers range from 775 to 975 &amp;#176;C, while pressures estimated from the Cr in clinopyroxene geobarometer and pseudosection modelling range from 12 to 22 kbar, which correspond to depths of 40&amp;#8211;80 km.&amp;#160; We used high&amp;#8208;resolution X-ray computed tomography to quantify the xenolith fabric defined by the 3D shape preferred orientation of spinel grains.&amp;#160; Spinel displays dominantly oblate fabric ellispoids, consistent with flattening strain.&amp;#160; Olivine has two main crystallographic preferred orientation patterns, the axial-[010] and the A-type, determined with electron backscatter diffraction.&amp;#160; The axial-[010] pattern is consistent with the spinel fabric and other microstructures that show flattening strains.&amp;#160; To further constrain the strain path, we analyze the crystallographic vorticity axes in olivine, which show a complex pattern.&amp;#160; Our results are consistent with an interpretation of transpressional deformation in the upper mantle below the NAFZ, during the early stages of the development of the transform system.&amp;#160; Transpressional deformation is consistent with collision-induced, strike-slip extrusion of Anatolia.&lt;/p&gt;

scholarly journals Comparison of Impact Toughness in Simulated Coarse-Grained Heat-Affected Zone of Al-Deoxidized and Ti-Deoxidized Offshore Steels

Metals ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 1783
Author(s):  
Henri Tervo ◽  
Antti Kaijalainen ◽  
Vahid Javaheri ◽  
Mohammed Ali ◽  
Tuomas Alatarvas ◽  
...  
Keyword(s):  
Impact Toughness ◽  
Heat Affected Zone ◽  
Electron Backscatter Diffraction ◽  
Cooling Time ◽  
Coarse Grained ◽  
X Ray Diffraction ◽  
X Ray ◽  
Electron Backscatter ◽  
Backscatter Diffraction ◽  
The Impact

The presence of acicular ferrite (AF) in the heat-affected zone (HAZ) of steels used offshore is generally seen as beneficial for toughness. In this study, the effects of varying fractions of AF (0–49 vol.%) were assessed in the simulated, unaltered and coarse-grained heat-affected zones (CGHAZ) of three experimental steels. Two steels were deoxidized, with one using Ti and the other using Al. The characterization was carried out by using electron microscopy, energy-dispersive X-ray spectrometry, electron backscatter diffraction and X-ray diffraction. The fraction of AF varied with the heat input and cooling time applied in the Gleeble thermomechanical simulator. AF was present in one of the Ti-deoxidized steels with all the applied cooling times, and its fraction increased with increasing cooling time. However, in other materials, only a small fraction (13–22%) of AF was present and only when the longest cooling time was applied. The impact toughness of the simulated specimens was evaluated using instrumented Charpy V-notch testing. Contrary to the assumption, the highest impact toughness was obtained in the conventional Al-deoxidized steel with little or no AF in the microstructure, while the variants with the highest fraction of AF had the lowest impact toughness. It was concluded that the coarser microstructural and inclusion features of the steels with AF and also the fraction of AF may not have been great enough to improve the CGHAZ toughness of the steels investigated.

scholarly journals Evidence of new twinning modes in magnesium questioning the shear paradigm

2018 ◽  
Vol 51 (3) ◽  
pp. 809-817 ◽  
Author(s):  
Cyril Cayron ◽  
Roland Logé
Keyword(s):  
Habit Plane ◽  
Simple Shear ◽  
Electron Backscatter Diffraction ◽  
Shear Plane ◽  
Deformation Mode ◽  
Crystallographic Analysis ◽  
Hexagonal Close Packed ◽  
Electron Backscatter ◽  
Macroscopic Deformation ◽  
Backscatter Diffraction

Twinning is an important deformation mode of hexagonal close-packed metals. The crystallographic theory is based on the 150-year-old concept of simple shear. The habit plane of the twin is the shear plane; it is invariant. This article presents electron backscatter diffraction observations and crystallographic analysis of a millimetre-size twin in a magnesium single crystal whose habit plane, unambiguously determined both in the parent crystal and in its twin, is not an invariant plane. This experimental evidence demonstrates that macroscopic deformation twinning can be achieved by a mechanism that is not a simple shear. This unconventional twin is often co-formed with a new conventional twin that exhibits the lowest shear magnitude ever reported in metals. The existence of unconventional twinning introduces a shift of paradigm and calls for the development of new crystallographic theories of displacive transformations.

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