Dynamic observations of dislocation generation at grain boundaries in ice

Liu, Fuping; Baker, Ian; Dudley, Michael

doi:10.1080/01418619308224770

Cited by 55 publications

(19 citation statements)

References 21 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…One way to explain these data is that the modification of grain boundary topology via grain boundary migration (GBM) could be more widespread at a warmer temperature, which could obscure evidence of the additional process responsible for a weaker CPO in smaller grains. The interaction of GBS with dislocation processes and GBM is developed a little in the ice literature (Hondoh and Higashi, 1983;Liu et al, 1993Liu et al, , 1995Duval, 1985;Faria et al, 2014), and experiments that show offsets of grain boundaries whilst GBM occurs (Drury and Humphreys, 1988;Ree, 1994) suggest that GBS may not leave a clear microstructural signal when GBS and GBM coexist. There are two candidate processes that may explain weakening of CPO in smaller grains and the lack of rational crys-tallographic misorientation axes of small grains relative to each other or to larger grains.…”

Section: Cpo Development: Differences Related To Grain Sizementioning

confidence: 99%

Temperature and strain controls on ice deformation mechanisms: insights from the microstructures of samples deformed to progressively higher strains at −10, −20 and −30 °C

et al. 2020

View full text Add to dashboard Cite

Abstract. In order to better understand ice deformation mechanisms, we document the microstructural evolution of ice with increasing strain. We include data from experiments at relatively low temperatures (−20 and −30 ∘C), where the microstructural evolution with axial strain has never before been documented. Polycrystalline pure water ice was deformed under a constant displacement rate (strain rate ∼1.0×10-5 s−1) to progressively higher strains (∼ 3 %, 5 %, 8 %, 12 % and 20 %) at temperatures of −10, −20 and −30 ∘C. Microstructural data were generated from cryogenic electron backscattered diffraction (cryo-EBSD) analyses. All deformed samples contain subgrain (low-angle misorientations) structures with misorientation axes that lie dominantly in the basal plane, suggesting the activity of dislocation creep (glide primarily on the basal plane), recovery and subgrain rotation. Grain boundaries are lobate in all experiments, suggesting the operation of strain-induced grain boundary migration (GBM). Deformed ice samples are characterized by interlocking big and small grains and are, on average, finer grained than undeformed samples. Misorientation analyses between nearby grains in 2-D EBSD maps are consistent with some 2-D grains being different limbs of the same irregular grain in the 3-D volume. The proportion of repeated (i.e. interconnected) grains is greater in the higher-temperature experiments suggesting that grains have more irregular shapes, probably because GBM is more widespread at higher temperatures. The number of grains per unit area (accounting for multiple occurrences of the same 3-D grain) is higher in deformed samples than undeformed samples, and it increases with strain, suggesting that nucleation is involved in recrystallization. “Core-and-mantle” structures (rings of small grains surrounding big grains) occur in −20 and −30 ∘C experiments, suggesting that subgrain rotation recrystallization is active. At temperatures warmer than −20 ∘C, c axes develop a crystallographic preferred orientation (CPO) characterized by a cone (i.e. small circle) around the compression axis. We suggest the c-axis cone forms via the selective growth of grains in easy slip orientations (i.e. ∼ 45∘ to shortening direction) by GBM. The opening angle of the c-axis cone decreases with strain, suggesting strain-induced GBM is balanced by grain rotation. Furthermore, the opening angle of the c-axis cone decreases with temperature. At −30 ∘C, the c-axis CPO changes from a narrow cone to a cluster, parallel to compression, with increasing strain. This closure of the c-axis cone is interpreted as the result of a more active grain rotation together with a less effective GBM. We suggest that lattice rotation, facilitated by intracrystalline dislocation glide on the basal plane, is the dominant mechanism controlling grain rotation. Low-angle neighbour-pair misorientations, relating to subgrain boundaries, are more extensive and extend to higher misorientation angles at lower temperatures and higher strains supporting a relative increase in the importance of dislocation activity. As the temperature decreases, the overall CPO intensity decreases, primarily because the CPO of small grains is weaker. High-angle grain boundaries between small grains have misorientation axes that have distributed crystallographic orientations. This implies that, in contrast to subgrain boundaries, grain boundary misorientation is not controlled by crystallography. Nucleation during recrystallization cannot be explained by subgrain rotation recrystallization alone. Grain boundary sliding of finer grains or a different nucleation mechanism that generates grains with random orientations could explain the weaker CPO of the fine-grained fraction and the lack of crystallographic control on high-angle grain boundaries.

show abstract

Section: Cpo Development: Differences Related To Grain Sizementioning

confidence: 99%

Temperature and strain controls on ice deformation mechanisms: insights from the microstructures of samples deformed to progressively higher strains at −10, −20 and −30 °C

et al. 2020

View full text Add to dashboard Cite

show abstract

“…The strain localization features observed in our experiments can be explained by the fact that only dislocation glide in the basal plane contributes to the deformation [3, 191. The lattice dislocations generated at the grain boundary [20] move under the resolved shear stress parallel to the basal plane. Dislocations of the same sign move in a direction which depends on the sign of the resolved shear stress, whereas under the same resolved shear stress dislocations of opposite signs move in opposite directions (see Fig.…”

Section: Discussionmentioning

confidence: 99%

Localization of deformation in polycrystalline ice

2001

View full text Add to dashboard Cite

Since ice deforms mainly by dislocation glide on the basal planes, very strong incompatibilities exist between the grains of a polycrystal. Specially designed two-dimensional compression creep tests on different types of ice multicrystals embedded in a matrix of fine-grained isotropic ice allow to observe the strain heterogeneities which arise during the deformation of polycrystalline ice, and which ace the consequence of inter-granular strain incompatibilities. The main features observed were bending and kink bands initiated at triple junctions or at geometric defects of the grain boundaries. These bands developed perpendicularly to the observed basal slip lines and provided additional degrees of freedom for the accommodation of intergranular deformation. Mechanisms related to dislocations motion and dynamic recrystallization are proposed for the initiation and for possible development of the observed localization features.

show abstract

“…Grain boundary dislocation emission occurs before the dislocation multiplication mechanisms observed in single crystal ice can operate. Liu and colleagues (Jia et al, 1996;Liu et al, 1992bLiu et al, , 1993Liu et al, , 1995b showed three different deformation situations are possible in polycrystals. First, for grains and grain boundaries that are not oriented in any special relationships with respect to the loading direction, screw and 60°F ig.…”

Section: Synchrotron X-ray Topographymentioning

confidence: 97%

“…Liu and co-workers (Jia et al, 1996;Liu et al, 1992bLiu et al, , 1993Liu et al, , 1995a are the only researchers to have used SWBXT to study polycrystalline ice. They used in-situ straining to demonstrate that grain boundary regions always deform before the grain interiors.…”

Section: Synchrotron X-ray Topographymentioning

confidence: 99%

Imaging dislocations in ice

Baker

2003

Microscopy Res & Technique

View full text Add to dashboard Cite

Three techniques have been used to study dislocations in ice: etch pitting-replication, transmission electron microscopy, and X-ray topography (XT). It is shown that, because ice is a weak absorber of X-rays and can be produced with a low dislocation density, allowing relatively thick specimens to be studied, the most useful technique is XT. The observations that have been made with conventional XT are briefly outlined. However, the introduction of high-intensity synchrotron radiation, with its concomitant short exposure times, showed that images obtained through conventional XT observations were of dislocations that had undergone recovery. The important dynamic observations and measurements that have been made using synchrotron X-ray topography are presented. Dynamic synchrotron X-ray topography observations of ice single crystals undergoing deformation in situ have shown that slip mainly occurs by the movement of screw and 60 degrees (1/3) [1120] dislocations on the basal plane, although non-basal slip by edge dislocations can also occur. The operation of Frank-Read and other dislocation multiplication sources have been clearly demonstrated and dislocation velocities have been measured. In contrast, in polycrystals, dislocation generation occurred at grain boundaries where there are stress concentrations before lattice dislocation generation mechanisms operate. Faulted dislocation loops have been determined to be mainly interstitial in both polycrystals and single crystals.

show abstract

Dynamic observations of dislocation generation at grain boundaries in ice

Cited by 55 publications

References 21 publications

Temperature and strain controls on ice deformation mechanisms: insights from the microstructures of samples deformed to progressively higher strains at −10, −20 and −30 °C

Temperature and strain controls on ice deformation mechanisms: insights from the microstructures of samples deformed to progressively higher strains at −10, −20 and −30 °C

Localization of deformation in polycrystalline ice

Imaging dislocations in ice

Contact Info

Product

Resources

About