The effect of grain boundary sliding on curvature-driven boundary migration in Zn bicrystals

2007 ◽  
Vol 56 (12) ◽  
pp. 1043-1046 ◽  
Author(s):  
A.D. Sheikh-Ali
Keyword(s):  
Grain Boundary ◽  
Boundary Migration ◽  
Grain Boundary Sliding ◽  
Boundary Sliding ◽  
Curvature Driven

Atomistic simulation of sliding of [1010] tilt grain boundaries in Mg

2009 ◽  
Vol 24 (11) ◽  
pp. 3446-3453 ◽  
Author(s):  
Hao Zhang
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Twin Boundary ◽  
Boundary Migration ◽  
Rigid Motion ◽  
Grain Boundary Sliding ◽  
Normal Displacement ◽  
Tangential Displacement ◽  
Boundary Sliding ◽  
Shear Motion

A series of molecular dynamics simulations was performed to study grain boundary sliding of three types of [101¯0] tilt grain boundaries in a magnesium bicrystal. In particular, a near Σ11 twin boundary, an asymmetric near Σ11 twin boundary, and a θ = 40.3° general [101¯0] tilt grain boundary were studied. Simulations showed that grain boundary sliding (a rigid motion of two grains relative to each other along boundary plane) did not occur over the stress range applied; instead, coupled shear motion (grain boundary sliding induced boundary migration) was dominant. Although the measured coupling coefficient, the ratio of boundary tangential displacement to boundary normal displacement, was in good agreement with theoretical prediction, the detailed shear behavior was different, depending on types of grain boundary, magnitude of applied shear stress, and temperature. It was also noted that grain boundary twining was the predominant mechanism that allowed the coupled shear motion to occur in hexagonal close-packed (HCP) magnesium.

Development of interconnected fine-grained polyphase networks during progressive exhumation of a shear zone

2020 ◽  
Author(s):  
Alexander Lusk ◽  
John Platt
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Shear Zone ◽  
Strain Localization ◽  
Cooling System ◽  
Boundary Migration ◽  
Grain Boundary Sliding ◽  
Fine Grained ◽  
Subgrain Rotation ◽  
Boundary Sliding

<p>Present exposure of the ductile Caledonian retrowedge in northwestern Scotland records the evolution of a shear zone that was exhuming while actively deforming, providing a natural laboratory to study strain localization in a progressively cooling system. Examination of rocks from two detailed transects across this region consistently show a transition from microstructures that are dominated by interconnected phyllosilicate networks in a quartz-rich matrix with feldspar porphyroclasts, to interconnected fine-grained regions of mixed quartz + phyllosilicate + feldspar. These polyphase regions are demonstrably weaker than surrounding quartz layers and likely deform by grain-size sensitive mechanisms including diffusion-accommodated grain boundary sliding.</p><p>Microstructures characterized by a quartz-rich matrix and interconnected phyllosilicates undergo quartz recrystallization by high temperature grain boundary migration and are dominated by prism <em>a</em> slip. In contrast, fine-grained polyphase microstructures record quartz recrystallization dominated by subgrain rotation and activation of rhomb <em>a</em> and basal <em>a</em> slip systems. We propose transient hardening occurs in quartz-dominated regions as quartz with a strong Y-axis maximum undergoes the switch from prism <em>a</em> easy slip to basal <em>a</em> easy slip during cooling, and thus partitions strain into interconnected phyllosilicate layers. In response, interconnected phyllosilicate layers undergo mechanical comminution, becoming increasingly mixed by grain-size sensitive creep processes to form polyphase layers as they accommodate an increased proportion of strain. This transition from quartz-rich matrix with phyllosilicate interconnected weak layers to fine-grained, polyphase weak layers could be of first-order importance in strain localization within polyphase mylonitic and ultramylonitic rocks.</p>

Shear coupled grain boundary migration as a deformation mechanism in minerals.

2020 ◽  
Author(s):  
Gill Pennock ◽  
Martyn Drury
Keyword(s):  
Grain Boundary ◽  
Deformation Mechanism ◽  
Boundary Migration ◽  
Critical Shear Stress ◽  
Grain Boundary Sliding ◽  
Grain Boundary Migration ◽  
Extensive Literature ◽  
Literature Study ◽  
Wide Range ◽  
Boundary Sliding

<p>A grain boundary can move under stress by a mechanism called shear coupled grain boundary migration (SC GBM) and contribute to strain. SC GBM is considered to be a general property of all grain boundaries over a wide range of misorientation angles, although higher deformation temperatures favour grain boundary sliding. Apart from a structured boundary interface, SC also requires a critical shear stress. We examine evidence for SC GBM in ice. An extensive literature study showed that SC GBM of high angle boundaries does occur in ice bicrystals that were probably deformed under conditions close to those found in nature. We conclude that SC GBM is likely to be an important deformation mechanism for geological materials, where extensive GBM occurs and also in nano sized materials, such as fault gauges.</p>

Quartz deformation and the recognition of recrystallization regimes in the Flinton Group conglomerates, Ontario

1982 ◽  
Vol 19 (1) ◽  
pp. 81-93 ◽  
Author(s):  
Joseph C. White
Keyword(s):  
Grain Boundary ◽  
Boundary Migration ◽  
Grain Boundary Sliding ◽  
Dislocation Creep ◽  
Subgrain Structure ◽  
Stress Regime ◽  
Metasedimentary Rocks ◽  
Metamorphic Temperature ◽  
Boundary Sliding ◽  
Compositional Control

The clastic metasedimentary rocks that form the Flinton Group occur as arcuate belts within the Grenville Structural Province, southeastern Ontario. Metamorphic isotherms transect these rocks and allow comparison of deformation over an approximate temperature range of 550–650 °C. Two geometrically discrete but temporally continuous deformation phases contribute significantly to pebble deformation within the conglomeratic units. There is a general increase in both finite strain, over which there is a strong compositional control, and the frequency of D2 minor structures with increasing metamorphic temperature. D1 is characterized by the creation of a subgrain structure and progressive misorientation of the subgrains as strain accumulates. Ultimately this leads to formation of high-angle boundaries defining recrystallized grains of a size similar to that of the precursor subgrains. D2 produces a new, finer subgrain structure, elongated grains, grain boundary migration (bulging), and small recrystallized grains. Empirical relationships between stress and subgrain diameter suggest that D1 is a low stress (5–6 MPa) deformation and D2 is a higher stress (12–80 MPa) deformation. This emphasizes that rotation recrystallization defines a low-temperature, low-stress regime, whereas migration recrystallization is typical of higher temperatures and stresses. Although dislocation creep predominates in most pebble types, evaluation of the deformation in terms of non-uniform flow laws can explain the compositional control of strain in the quartzite pebbles and suggests that significant grain boundary sliding occurred.

The Influence of Grain Boundary Structure on Strain-Induced Grain Growth During Superplastic Deformation

1990 ◽  
Vol 196 ◽  
Author(s):  
H. J. Frost ◽  
R. Raj
Keyword(s):  
Grain Boundary ◽  
Grain Growth ◽  
Superplastic Deformation ◽  
Boundary Migration ◽  
Forced Migration ◽  
Grain Boundary Sliding ◽  
Boundary Structure ◽  
Grain Boundary Structure ◽  
Diffusional Flow ◽  
Boundary Sliding

ABSTRACTA model is presented to explain the grain growth that is often observed during superplastic deformation. The atomic structure of grain boundaries leads to a coupling between boundary sliding and boundary migration. There is a similar coupling between the absorption or emission of vacancies from a boundary and boundary migration. Because of these couplings, the grain boundary sliding and diffusional flow of superplastic deformation produce extensive boundary migration. We propose that this forced migration leads to random changes in the sizes of grains, and that this evolution of the grain size distribution leads to grain growth.

Examination of Fracture Interfaces in Silicon Nitride

1975 ◽  
Vol 33 ◽  
pp. 60-61
Author(s):  
Nancy J. Tighe
Keyword(s):  
Silicon Nitride ◽  
Grain Boundary ◽  
Crack Growth ◽  
Subcritical Crack Growth ◽  
Slow Crack Growth ◽  
Ceramic Materials ◽  
Grain Boundary Sliding ◽  
Boundary Phase ◽  
Turbine Engines ◽  
Boundary Sliding

Silicon nitride is one of the ceramic materials being considered for the components in gas turbine engines which will be exposed to temperatures of 1000 to 1400°C. Test specimens from hot-pressed billets exhibit flexural strengths of approximately 50 MN/m2 at 1000°C. However, the strength degrades rapidly to less than 20 MN/m2 at 1400°C. The strength degradition is attributed to subcritical crack growth phenomena evidenced by a stress rate dependence of the flexural strength and the stress intensity factor. This phenomena is termed slow crack growth and is associated with the onset of plastic deformation at the crack tip. Lange attributed the subcritical crack growth tb a glassy silicate grain boundary phase which decreased in viscosity with increased temperature and permitted a form of grain boundary sliding to occur.

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