scholarly journals Location and distribution of micro-inclusions in the EDML and NEEM ice cores using optical microscopy and in-situ Raman spectroscopy

2016 ◽  
Author(s):  
Jan Eichler ◽  
Ina Kleitz ◽  
Maddalena Bayer ◽  
Daniela Jansen ◽  
Sepp Kipfstuhl ◽  
...  
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Large Scale ◽  
Flow Behavior ◽  
Ice Cores ◽  
Second Phase ◽  
Impurity Effect ◽  
Polar Ice

Abstract. Impurities control a variety of physical properties of polar ice. Their impact can be observed at all scales – from the microstructure (e.g., grain size and orientation) to the ice sheet flow behavior (e.g., borehole tilting and closure). Most impurities are likely to form micrometer-sized second phase inclusions. It has been suggested that these particles control the grain size of polycrystalline ice by the pinning of grain boundaries (Zener pinning), which should be reflected in the distribution of the inclusions in relation to the grain boundary network. We used an optical microscope to generate high-resolution large-scale maps (3 μm pix−1, 8 × 2 cm2) of the distribution of micro-inclusions in four samples from the EDML (Antarctica) and NEEM (Greenland) polar ice cores. The in-situ positions of more than 5000 μ-inclusions have been determined. A Raman microscope was used to confirm the extrinsic nature of a sample proportion of the mapped inclusions. A superposition of the 2D grain boundary network and μ-inclusion distributions show no significant correlations between grain boundaries and μ-inclusions. In particular, no signs could be found of grain boundaries harvesting μ-inclusions, no evidence of μ-inclusions inhibiting grain boundary migration by slow mode pinning could be detected. Consequences for our understanding of the impurity effect on ice microstructure and rheology are discussed.

scholarly journals Location and distribution of micro-inclusions in the EDML and NEEM ice cores using optical microscopy and in situ Raman spectroscopy

2017 ◽  
Vol 11 (3) ◽  
pp. 1075-1090 ◽  
Author(s):  
Jan Eichler ◽  
Ina Kleitz ◽  
Maddalena Bayer-Giraldi ◽  
Daniela Jansen ◽  
Sepp Kipfstuhl ◽  
...  
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Large Scale ◽  
Flow Behavior ◽  
Boundary Migration ◽  
Ice Cores ◽  
Impurity Effect ◽  
Polar Ice

Abstract. Impurities control a variety of physical properties of polar ice. Their impact can be observed at all scales – from the microstructure (e.g., grain size and orientation) to the ice sheet flow behavior (e.g., borehole tilting and closure). Most impurities in ice form micrometer-sized inclusions. It has been suggested that these µ inclusions control the grain size of polycrystalline ice by pinning of grain boundaries (Zener pinning), which should be reflected in their distribution with respect to the grain boundary network. We used an optical microscope to generate high-resolution large-scale maps (3 µm pix−1, 8 × 2 cm2) of the distribution of micro-inclusions in four polar ice samples: two from Antarctica (EDML, MIS 5.5) and two from Greenland (NEEM, Holocene). The in situ positions of more than 5000 µ inclusions have been determined. A Raman microscope was used to confirm the extrinsic nature of a sample proportion of the mapped inclusions. A superposition of the 2-D grain boundary network and µ-inclusion distributions shows no significant correlations between grain boundaries and µ inclusions. In particular, no signs of grain boundaries harvesting µ inclusions could be found and no evidence of µ inclusions inhibiting grain boundary migration by slow-mode pinning could be detected. Consequences for our understanding of the impurity effect on ice microstructure and rheology are discussed.

scholarly journals Dual Beam In Situ Radiation Studies of Nanocrystalline Cu

Materials ◽  
2019 ◽  
Vol 12 (17) ◽  
pp. 2721 ◽  
Author(s):  
Cuncai Fan ◽  
Zhongxia Shang ◽  
Tongjun Niu ◽  
Jin Li ◽  
Haiyan Wang ◽  
...  
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Ion Beam ◽  
Heavy Ion ◽  
Radiation Response ◽  
Nanocrystalline Metals ◽  
Grain Coarsening ◽  
Dual Beam

Nanocrystalline metals have shown enhanced radiation tolerance as grain boundaries serve as effective defect sinks for removing radiation-induced defects. However, the thermal and radiation stability of nanograins are of concerns since radiation may induce grain boundary migration and grain coarsening in nanocrystalline metals when the grain size falls in the range of several to tens of nanometers. In addition, prior in situ radiation studies on nanocrystalline metals have focused primarily on single heavy ion beam radiations, with little consideration of the helium effect on damage evolution. In this work, we utilized in situ single-beam (1 MeV Kr++) and dual-beam (1 MeV Kr++ and 12 keV He+) irradiations to investigate the influence of helium on the radiation response and grain coarsening in nanocrystalline Cu at 300 °C. The grain size, orientation, and individual grain boundary character were quantitatively examined before and after irradiations. Statistic results suggest that helium bubbles at grain boundaries and grain interiors may retard the grain coarsening. These findings provide new perspective on the radiation response of nanocrystalline metals.

Micromechanical testing of olivine grain boundaries

2021 ◽  
Author(s):  
Diana Avadanii ◽  
Lars Hansen ◽  
Ed Darnbrough ◽  
Katharina Marquardt ◽  
David Armstrong ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Large Scale ◽  
Boundary Migration ◽  
Small Scale ◽  
High Angle ◽  
In Situ Tests ◽  
Tidal Forces ◽  
In Situ Experiments

<p>The mechanics of olivine deformation play a key role in large-scale, long-term planetary processes, such as the response of the lithosphere to tectonic loading or the response of the solid Earth to tidal forces, and in short-term processes, such as the evolution of roughness on oceanic fault surfaces or postseismic creep within the upper mantle. Many previous studies have emphasized the importance of grain-size effects in the deformation of olivine. However, most of our understanding of the role of grain boundaries in deformation of olivine is inferred from comparison of experiments on single crystals to experiments on polycrystalline samples.</p><p>To directly observe and quantify the mechanical properties of olivine grain boundaries, we use high-precision mechanical testing of synthetic forsterite bicrystals with well characterised interfaces. We conduct nanoindentation tests at room temperature on low-angle (13<sup>o</sup> tilt about [100] on (015)) and high-angle (60<sup>o</sup> tilt about [100] on (011)) grain boundaries. We observe that plasticity is easier to initiate if the grain boundary is within the volume tested. This observation agrees with the interpretation that certain grain-boundary configurations can act as sites for initiating microplasticity.</p><p>As part of continuing efforts, we are also conducting in-situ micropillar compression tests at high-temperature (above 600<sup>o</sup> C) within similar bicrystals. In these experiments, the boundary is contained within the micropillar and oriented at 45<sup>o</sup> to the loading direction to promote shear along the boundary. In these in-situ tests, our hypothesis is that the low-angle grain boundary displays a higher viscosity relative to the high-angle interface. Key advantages of performing in-situ experiments are the direct observation of grain-boundary migration or sliding, simplified kinematics of a single boundary segment, and  potentially changes in style of deformation with different grain-boundary character.</p><p>These small deformation volume experiments allow us to qualitatively explore the differences between the crystal interior and regions containing grain boundaries. Overall, the variation in strain and temperature in our small scale experiments allows the fundamental investigation of the response of well characterised forsterite grain boundaries to deformation. </p>

Microstructure, Mechanical and Electrical Properties of CuO Doped 8YSZ

2013 ◽  
Vol 32 (6) ◽  
pp. 551-556 ◽  
Author(s):  
Bülent Aktaş
Keyword(s):  
Electrical Conductivity ◽  
Fracture Toughness ◽  
Grain Size ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Second Phase ◽  
Phase Layer ◽  
Boundary Conductivity ◽  
Mechanical And Electrical Properties ◽  
Frequency Response Analyzer

AbstractThe effect of the addition of a small amount of CuO on the microstructure, hardness, fracture toughness and electrical conductivity properties of 8YSZ were investigated using 8 mol% yttria-stabilized cubic zirconia (8YSZ). The addition of 1 wt% CuO to 8YSZ powders were doped using a colloidal process. Undoped and CuO doped 8YSZ specimens were pressureless sintered at 1400 °C for 10 h. The grain size measurement results showed that the presence of CuO as a intergranular second phase at the grain boundaries of the 8YSZ gave rise to a decrease in the grain size. The fracture toughness values for undoped and 1 wt% CuO-doped 8YSZ specimens were obtained as 1.79 and 2.20 MPa.m1/2, respectively. The decrease in the grain size of the 8YSZ with CuO addition caused an increase in the fracture toughness. The electrical conductivity of the undoped and 1 wt% CuO-doped 8YSZ specimens was measured using a frequency response analyzer in the frequency range of 100 mHz–13 MHz and at the temperature range of 300–800 °C. The electrical conductivity results showed that there was a decrease in the grain interior, and specific grain boundary conductivity, with the addition of a small amount of CuO to 8YSZ. The presence of a second phase layer with high resistance at the grain boundaries of the 8YSZ caused a decrease in the specific grain boundary conductivity.

Morphology of Σ3{/70.53°} grain boundaries in a C15 intermetallic compound

1994 ◽  
Vol 52 ◽  
pp. 684-685
Author(s):  
Fuming Chu ◽  
D. P. Pope ◽  
D. S. Zhou ◽  
T. E. Mitchell
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Crystallographic Analysis ◽  
Laves Phase ◽  
Second Phase ◽  
Bright Field Image ◽  
Boundary Edge ◽  
Arc Melting ◽  
Fcc Lattice ◽  
Diffraction Patterns

A C15 Laves phase, HfV2+Nb, shows promising mechanical properties and here we describe the structure of its grain boundaries. The C15 Laves phase has a fcc lattice with a=7.4Å. An alloy of composition Hf14V64Nb22 (including a C15 matrix and a second phase of V-rich bcc solution) was made by arc-melting. The alloy was homogenized at 1200°C for 120h. Preliminary study concentrated on Σ3{<110>/70.53°} grain boundaries in the C15 phase using Philips 400T and CM 30 microscopes.The most-commonly observed morphology of Σ3{<110>/70.53°} grain boundaries in the C15 phase is a faceted boundary. A bright field image (BFI) of the faceted boundary and the corresponding diffraction patterns with the grain boundary edge-on are shown in Fig. 1(a). From the diffraction patterns using a <110> zone axis for both grains, it is obvious that this is a Σ3{<110>/70.53°} grain boundary. Crystallographic analysis shows that the Σ3{<110>/70.53°} grain boundaries selectively facet with the following relationships between the two grains: {111}1//{111}2, {112}1//{112}2, {111}1//{115}2, and {001}1//{221}2.

EFFECT OF SMALL BULK SULFUR CONTENT AND ANNEALING TEMPERATURE ON THE INTERGRANULAR FRACTURING SUSCEPTIBILITY OF METALLIC NICKEL

2016 ◽  
Vol 23 (06) ◽  
pp. 1650050 ◽  
Author(s):  
BOUTASSOUNA DJAMAL ◽  
RENÉ LE GALL ◽  
IBEN KHALDOUN LEFKAIER
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Sulfur Content ◽  
Auger Spectroscopy ◽  
Metallic Nickel ◽  
Boundary Equilibrium ◽  
Influence Of Temperature On ◽  
Sulfide Compound ◽  
Equilibrium Segregation

In this paper, we investigate the influence of temperature on the nickel grain boundary equilibrium segregation of sulfur and the resulting intergranular fracturing susceptibility. Auger electron spectroscopy has been used to study equilibrium segregation of sulfur to the grain boundaries of a metallic nickel, with a mass bulk content of 3.6[Formula: see text]ppm in sulfur. Samples were first annealed at adequate temperatures for sufficiently large equilibrium time, and then quenched in water at room temperature. The analysis carried out shows a significant increase of sulfur concentration in the grain boundary with decreasing temperature. However, the sulfur content in the grain boundary shows a drastic shrink at 700[Formula: see text]C. This can be interpreted by the formation of an aggregate sulfide compound in the area of the grain boundaries. At 650[Formula: see text]C, in situ brittle fracture becomes unworkable and only intragranular fractures are observed. Using the results obtained through the investigation of the grain boundaries by Auger spectroscopy, the standard segregation energy is estimated as [Formula: see text].

Effect of mass transport along interfaces and grain boundaries on copper interconnect degradation

2004 ◽  
Vol 812 ◽  
Author(s):  
Ehrenfried Zschech ◽  
Moritz A. Meyer ◽  
Eckhard Langer
Keyword(s):  
Mass Transport ◽  
Grain Boundaries ◽  
Void Formation ◽  
Degradation Process ◽  
Copper Interconnects ◽  
Second Phase ◽  
Copper Interconnect ◽  
Void Evolution ◽  
Two Phases

AbstractIn-situ SEM electromigration studies were performed at fully embedded via/line interconnect structures to visualize the time-dependent void evolution in inlaid copper interconnects. Void formation, growth and movement, and consequently interconnect degradation, depend on both interface bonding and copper microstructure. Two phases are distinguished for the electromigration-induced interconnect degradation process: In the first phase, agglomerations of vacancies and voids are formed at interfaces and grain boundaries, and voids move along weak interfaces. In the second phase of the degradation process, they merge into a larger void which subsequently grows into the via and eventually causes the interconnect failure. Void movement along the copper line and void growth in the via are discontinuous processes, whereas their step-like behavior is caused by the copper microstructure. Directed mass transport along inner surfaces depends strongly on the crystallographic orientation of the copper grains. Electromigration lifetime can be drastically increased by changing the copper/capping layer interface. Both an additional CoWP coating and a local copper alloying with aluminum increase the bonding strength of the top interface of the copper interconnect line, and consequently, electromigration-induced mass transport and degradation processes are reduced significantly.

Research on Micro-Mechanism of Nanocomposite Ceramic in Two-Dimensional Ultrasound Grinding

2007 ◽  
Vol 359-360 ◽  
pp. 344-348 ◽  
Author(s):  
Bo Zhao ◽  
Yan Wu ◽  
Guo Fu Gao ◽  
Feng Jiao
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Deformation Mechanism ◽  
Ground Surface ◽  
Grain Boundary Sliding ◽  
Second Phase ◽  
Two Dimensional ◽  
Composite Ceramics ◽  
Nano Composite ◽  
Boundary Sliding

Surface microstructure of nano-composite ceramics prepared by mixed coherence system and machined by two-dimensional ultrasonic precision grinding was researched using TEM, SEM, XRD detector and other equipments. Structure, formation mechanism and characteristic of metamorphic layer of ground surface of nano-composite ceramics were researched. The experiment shows micro deformation mechanism of ceramic material in two-dimensional ultrasound grinding is twin grain boundary and grain-boundary sliding for Al2O3, and it is crystal dislocation of enhanced phase, matrix grain boundary sliding, coordination deformation of intergranular second phase as well as its deformation mechanism for nano-composite ceramics. The fracture surfaces of nano-composite materials with different microscopic structure were observed using TEM and SEM. Research shows that ZrO2 plays an important influence on the generation and expansion of crack, and enhances the strength of grain boundaries. When grain boundaries is rich in the ZrO2 particles, the crack produced in grinding process will be prevented, and the surface with plastic deformation will be smooth. The results shows nanoparticles dispersed in grain boundary prevents crack propagation and makes materials fracture transgranularly which makes the processed surface fine.

Simulation of the interaction of plastic zone dislocations with the grain boundary at brittle-plastic transition temperatures in molybdenum

2021 ◽  
Vol 2021 (3) ◽  
pp. 77-85
Author(s):  
K. M. Borysovska ◽  
◽  
N. M. Marchenko ◽  
Yu. M. Podrezov ◽  
S. O. Firstov ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Grain Size ◽  
Grain Boundary ◽  
Plastic Zone ◽  
Grain Boundaries ◽  
Crack Tip ◽  
Dynamics Simulation ◽  
Density Of Dislocations ◽  
Grain Sizes ◽  
Pile Up

The (DD) method was used to model the formation of the plastic zone of the top of the cracks in polycrystalline molybdenum. Special attention was paid to take into account the interaction of dislocations in the plastic zone with grain boundaries. Structural sensitivity of fracture toughness was analyzed under brittle-ductile condition. Simulations were performed for a range of grain sizes from 400 to 100 μm, at which a sudden increase in fracture toughness with a decrease of grain size was experimentally shown. We calculated the value of K1c taking into account the shielding action of dislocations. The position of all dislocations in the plastic zone at fracture moment was calculated. Based on these data, we obtained the dependences of dislocation density on the distance from the crack tip thereby confirming significant influence of the grain boundaries on plastic zone formation. At large grain sizes, when the plastic zone does not touch the boundary, the distribution of dislocations remained unchanged. As grains reduce their size to size of the plastic zone, they start formating a dislocation pile – up near the boundaries. Dislocations on plastic zone move slightly toward the crack tip, but the density of dislocations in the middle of the grain remains unchanged, and fracture toughness remains almost unchanged. Further reduction of the grain size leads to the Frank-Reed source activation on the grain boundary Forming dislocation pile-up of the neighbor grains. Its stress concentration acts on dislocations of the first grain and causes redistribution of plastic zone dislocations. If the reduction in grain size is not enough to form a strong pile-up, density of dislocations on plastic zone increases slightly and crack resistance increases a few percent. Further reduction of grains promotes strong pile-up, dislocations move to crack tip, and its density on plastic zone increases. Crack is shielded and fracture toughness increases sharply. The calculation showed that the fracture toughness jump is observed at grain sizes of 100—150 μm, in good agreement with the experiment. Keywords: dislocation dynamics simulation, molybdenum, fracture toughness, grain size, plastic zone, brittle-ductile transition.

Mechanical Behaviour of Nanocrystalline Copper Related to Grain-boundary Structure

2002 ◽  
Vol 727 ◽  
Author(s):  
Y. Champion ◽  
P. Langlois ◽  
S. Guérin-Mailly ◽  
C. Langlois ◽  
M. J. Hÿtch
Keyword(s):  
Plastic Deformation ◽  
Grain Size ◽  
Structural Analysis ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Mechanical Behaviour ◽  
Tensile Testing ◽  
Metallic Nanostructures ◽  
Nanocrystalline Powders ◽  
Clear Understanding

AbstractUnderstanding the mechanical behaviour of metallic nanostructures is a key issue for their development. On the one hand, knowledge of the plastic behaviour at various temperatures is essential to control the synthesis, forming, and machining of such materials. Equally, a clear understanding of atomic and mesoscopic mechanisms, involving defects and their interactions, is essential for the control of ageing and functional properties. Regarding plastic deformation at room temperature, there is now evidence for unusual behaviour in nanostructured metals. In addition to high resistance and ductility, tensile testing reveals peculiar elasto-plastic deformation. Such behaviour was initially attributed to grain-boundary sliding. However, intergranular areas (including triple junctions) may possess special properties compared to their microcrystalline counterparts. For example, low activation energies have been measured for grain-boundary diffusion and it has been observed that grain-boundaries may act as dislocation sources and nucleation sites for deformation twinning.In this paper, we report on analysis on bulk copper nanostructures. Grain-boundaries are studied, by cross-correlating information from mechanical tensile testing and structural analysis, including X-ray diffraction (XRD) and transmission electron microscopy (TEM). Macroscopic bulk specimens (with grain size of about 80 nm) are prepared by powder metallurgy techniques, modified to fit to the special properties of nanocrystalline powders. Processing includes coldisostatic pressing, sintering and differential extrusion. The powders used (grain size of 40 nm) are synthesised by evaporation and cryo-condensation of a metallic vapour within liquid nitrogen. Results on mechanical testing and structural analysis will be reported. Emphasis will be placed on the structure of grain-boundaries (type of grain-boundary, grain-boundary thickness) studied by TEM and high resolution TEM image analysed using the geometric phase technique. The nanostructure was revealed to be consist in agglomerate of nano-size grains separated by low angle grain-boundaries. Agglomerates are themselves separerated by general high angle boundaries. These observations will then be related to the unusual mechanical true stress-true strain curves of the metallic nanostructures.

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