scholarly journals Interactive comment on 'The grain size(s) of Black Hills Quartzite deformed in the dislocation creep regime'

2017 ◽  
Author(s):  
Anonymous
Keyword(s):  
Grain Size ◽  
Black Hills ◽  
Dislocation Creep ◽  
Creep Regime

scholarly journals The grain size(s) of Black Hills Quartzite deformed in the dislocation creep regime

2017 ◽  
Author(s):  
Renée Heilbronner ◽  
Rüdiger Kilian
Keyword(s):  
Grain Size ◽  
Black Hills ◽  
Dislocation Creep ◽  
Grain Size Analysis ◽  
Size Analysis ◽  
Cip Method ◽  
Axis Orientation ◽  
Creep Regime ◽  
Crystallographic Orientations ◽  
Shape And Size

Abstract. A number of general shear experiments on Black Hills Quartzite (BHQ) in the dislocation creep regime, 5 of which have been analyzed previously using the CIP method (Heilbronner & Tullis, 2002 and 2006), are (re-)examined using the higher spatial and orientational resolution of EBSD. Segmentations based on c-axis orientation and on full crystallographic orientations are compared. Texture domains of preferred c-axis orientation are extracted and analyzed separately. Subdomains are recognized and their shape and size is related the kinematic framework and the original grains in the BHQ. Grain size analysis using a segmentation based on c-axis orientations is carried out for all, high and low strain samples of all regimes, and for a number of texture domains. The results are compared to the recrystallized quartz piezometer of Stipp & Tullis (2003), returning consistently higher values for stress or grain size. Possible causes for the discrepancy are texture dependence, grain scale strain, and dependence on the kinematic framework (in axial versus general shear experiments).

scholarly journals The grain size(s) of Black Hills Quartzite deformed in the dislocation creep regime

Solid Earth ◽  
2017 ◽  
Vol 8 (5) ◽  
pp. 1071-1093 ◽  
Author(s):  
Renée Heilbronner ◽  
Rüdiger Kilian
Keyword(s):  
Grain Size ◽  
Black Hills ◽  
Dislocation Creep ◽  
Grain Size Analysis ◽  
Size Analysis ◽  
Axis Orientation ◽  
Grain Sizes ◽  
Deformation Intensity ◽  
Recrystallized Grain Size ◽  
Creep Regime

Abstract. General shear experiments on Black Hills Quartzite (BHQ) deformed in the dislocation creep regimes 1 to 3 have been previously analyzed using the CIP method (Heilbronner and Tullis, 2002, 2006). They are reexamined using the higher spatial and orientational resolution of EBSD. Criteria for coherent segmentations based on c-axis orientation and on full crystallographic orientations are determined. Texture domains of preferred c-axis orientation (Y and B domains) are extracted and analyzed separately. Subdomains are recognized, and their shape and size are related to the kinematic framework and the original grains in the BHQ. Grain size analysis is carried out for all samples, high- and low-strain samples, and separately for a number of texture domains. When comparing the results to the recrystallized quartz piezometer of Stipp and Tullis (2003), it is found that grain sizes are consistently larger for a given flow stress. It is therefore suggested that the recrystallized grain size also depends on texture, grain-scale deformation intensity, and the kinematic framework (of axial vs. general shear experiments).

scholarly journals Microstructural evolution during high-temperature tensile creep at 1,500°C of a MoSiBTiC alloy

2020 ◽  
Vol 39 (1) ◽  
pp. 136-145 ◽  
Author(s):  
Sojiro Uemura ◽  
Shiho Yamamoto Kamata ◽  
Kyosuke Yoshimi ◽  
Sadahiro Tsurekawa
Keyword(s):  
Grain Size ◽  
Grain Boundaries ◽  
Microstructural Evolution ◽  
Grain Boundary Sliding ◽  
Primary Creep ◽  
Tensile Creep ◽  
Tertiary Creep ◽  
Continuous Dynamic Recrystallization ◽  
Continuous Dynamic ◽  
Creep Regime

AbstractMicrostructural evolution in the TiC-reinforced Mo–Si–B-based alloy during tensile creep deformation at 1,500°C and 137 MPa was investigated via scanning electron microscope-backscattered electron diffraction (SEM-EBSD) observations. The creep curve of this alloy displayed no clear steady state but was dominated by the tertiary creep regime. The grain size of the Moss phase increased in the primary creep regime. However, the grain size of the Moss phase was found to remarkably decrease to <10 µm with increasing creep strain in the tertiary creep regime. The EBSD observations revealed that the refinement of the Moss phase occurred by continuous dynamic recrystallization including the transformation of low-angle grain boundaries to high-angle grain boundaries. Accordingly, the deformation of this alloy is most likely to be governed by the grain boundary sliding and the rearrangement of Moss grains such as superplasticity in the tertiary creep regime. In addition, the refinement of the Moss grains surrounding large plate-like T2 grains caused the rotation of their surfaces parallel to the loading axis and consequently the cavitation preferentially occurred at the interphases between the end of the rotated T2 grains and the Moss grains.

scholarly journals The role of grain size evolution in the rheology of ice: implications for reconciling laboratory creep data and the Glen flow law

2021 ◽  
Vol 15 (9) ◽  
pp. 4589-4605
Author(s):  
Mark D. Behn ◽  
David L. Goldsby ◽  
Greg Hirth
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Stress Exponent ◽  
Ice Sheets ◽  
Grain Boundary Sliding ◽  
Dislocation Creep ◽  
Ice Flow ◽  
Size Evolution ◽  
Boundary Sliding ◽  
Flow Law

Abstract. Viscous flow in ice is often described by the Glen flow law – a non-Newtonian, power-law relationship between stress and strain rate with a stress exponent n ∼ 3. The Glen law is attributed to grain-size-insensitive dislocation creep; however, laboratory and field studies demonstrate that deformation in ice can be strongly dependent on grain size. This has led to the hypothesis that at sufficiently low stresses, ice flow is controlled by grain boundary sliding, which explicitly incorporates the grain size dependence of ice rheology. Experimental studies find that neither dislocation creep (n ∼ 4) nor grain boundary sliding (n ∼ 1.8) have stress exponents that match the value of n ∼ 3 in the Glen law. Thus, although the Glen law provides an approximate description of ice flow in glaciers and ice sheets, its functional form is not explained by a single deformation mechanism. Here we seek to understand the origin of the n ∼ 3 dependence of the Glen law by using the “wattmeter” to model grain size evolution in ice. The wattmeter posits that grain size is controlled by a balance between the mechanical work required for grain growth and dynamic grain size reduction. Using the wattmeter, we calculate grain size evolution in two end-member cases: (1) a 1-D shear zone and (2) as a function of depth within an ice sheet. Calculated grain sizes match both laboratory data and ice core observations for the interior of ice sheets. Finally, we show that variations in grain size with deformation conditions result in an effective stress exponent intermediate between grain boundary sliding and dislocation creep, which is consistent with a value of n = 3 ± 0.5 over the range of strain rates found in most natural systems.

scholarly journals Recrystallization of ice enhances the creep and vulnerability to fracture of ice shelves 

2021 ◽  
Author(s):  
Meghana Ranganathan ◽  
Brent Minchew ◽  
Colin Meyer ◽  
Matej Pec
Keyword(s):  
Grain Size ◽  
Ice Sheet ◽  
Shear Zones ◽  
Dislocation Creep ◽  
Model Parameters ◽  
Localized Deformation ◽  
Ice Shelves ◽  
Fine Grained ◽  
Initiation And Propagation ◽  
Rapid Deformation

&lt;p&gt;The initiation and propagation of fractures in floating regions of Antarctica has the potential to destabilize large regions of the ice sheet, leading to significant sea-level rise. While observations have shown rapid, localized deformation and damage in the margins of fast-flowing glaciers, there remain gaps in our understanding of how rapid deformation affects the creep and toughness of ice. Here we derive a model for dynamic recrystallization in ice and other rocks that includes a novel representation of migration recrystallization, which is absent from existing models but is likely to be dominant in warm areas undergoing rapid deformation within the ice sheet. We show that, in regions of elevated strain rate, grain sizes in ice may be larger than expected (~15 mm) due to migration recrystallization, a significant deviation from solid earth studies which find fine-grained rock in shear zones. This may imply that ice in shear margins deforms primarily by dislocation creep, suggesting a flow-law exponent of n=4 in these regions. Further, we find from existing models that this increase in grain size results in a decrease in tensile strength of ice by ~75% in the margins of glaciers. Thus, we expect that this increase in grain size makes the margins of fast-flowing glaciers less viscous and more vulnerable to fracture than we may suppose from standard model parameters.&lt;/p&gt;

scholarly journals Relation between Sub-grain Size and Dislocation Density During Steady-State Dislocation Creep of Polycrystalline Cubic Metals

2018 ◽  
Vol 7 (4) ◽  
pp. 26 ◽  
Author(s):  
Manabu Tamura
Keyword(s):  
Grain Size ◽  
Steady State ◽  
Dislocation Density ◽  
Martensitic Steel ◽  
Empirical Relation ◽  
Dislocation Creep ◽  
Theoretical Relation ◽  
Cross Sectional ◽  
Cubic Metals ◽  
Polycrystalline Metals

The sub-grain size, d, during steady-state dislocation creep of polycrystalline metals is theoretically formulated to be inversely proportional to the dislocation density, ρ, which is defined as the number of dislocations swept out of a sub-grain divided by the cross-sectional area of the sub-grain. This dislocation density differs from the typically observed dislocation density inside a sub-grain after unloading, ρ_ob. In the current work, the ρ_ob values inside sub-grains in steadily crept specimens of Al, Cu, Fe, Fe–Mo alloy, austenitic stainless steel, and high-Cr martensitic steel reported in the literature were used to evaluate the relation ρ_ob=ηρ. It was confirmed that η≈1 for pure metals (regardless of the type of metal) crept at high temperatures and low stresses or for long durations and η&gt;1 for Mo-containing alloys and martensitic steel crept at low temperatures and/or high stresses. Moreover, it is suggested that the condition η&gt;1 corresponds to a state of excess immobile dislocations inside the sub-grain. The theoretical relation d_ob (≈d)∝η∙〖ρ_ob〗^(-1), where d_ob is the observed sub-grain size, essentially differs from the well-known empirical relation d_ob∝〖ρ_ob〗^(-0.5).

scholarly journals Myrmekite and strain weakening in granitoid mylonites

2018 ◽  
Author(s):  
Alberto Ceccato ◽  
Luca Menegon ◽  
Giorgio Pennacchioni ◽  
Luiz Fernando Grafulha Morales
Keyword(s):  
Grain Size ◽  
Heterogeneous Nucleation ◽  
Eastern Alps ◽  
Grain Boundary Sliding ◽  
Dislocation Creep ◽  
Diffusion Creep ◽  
Phase Mixing ◽  
Fine Grained ◽  
Fine Grain ◽  
Creep Cavitation

Abstract. At mid-crustal conditions, deformation of feldspar is mainly accomplished by a combination of fracturing, dissolution/precipitation and reaction-weakening mechanisms. In particular, K-feldspar is reaction-weakened by formation of strain-induced myrmekite – a fine-grained symplectite of plagioclase and quartz. Here we investigate with EBSD the microstructure of a granodiorite mylonite, developed at 420–460 °C during cooling of the Rieserferner pluton (Eastern Alps), to assess the microstructural processes and the role of weakening associated with myrmekite development. Our analysis shows that the crystallographic orientation of the plagioclase of pristine myrmekite was controlled by that of the replaced K-feldspar. Myrmekite nucleation resulted in both grain size reduction and ordered phase mixing by heterogeneous nucleation of quartz and plagioclase. The fine grain size of sheared myrmekite promoted grain size-sensitive creep mechanisms including fluid-assisted grain boundary sliding in plagioclase, coupled with heterogeneous nucleation of quartz within creep cavitation pores. Flow laws calculated for monomineralic quartz, feldspar, and quartz + plagioclase aggregates (sheared myrmekite), show that during mylonitization at 450 °C, grain-size-sensitive creep in sheared myrmekite accommodated strain rates several orders of magnitude higher than monomineralic quartz layers deforming by dislocation creep. Therefore, diffusion creep and grain size-sensitive processes contributed significantly to bulk rock weakening during mylonitization. Our results have implications for modelling the rheology of the mid-upper continental (felsic) crust.

Creep Processes in MAR-M247 Nickel-Base Superalloy

2016 ◽  
Vol 258 ◽  
pp. 603-606
Author(s):  
Marie Kvapilová ◽  
Květa Kuchařová ◽  
Karel Hrbáček ◽  
Vàclav Sklenička
Keyword(s):  
Creep Deformation ◽  
Elevated Temperatures ◽  
Dislocation Creep ◽  
Nickel Base Superalloy ◽  
Deformation And Fracture ◽  
Creep Life Prediction ◽  
Controlling Mechanism ◽  
Nickel Base ◽  
Creep Regime ◽  
Base Superalloy

Creep processes in MAR-M247 Nickel - Base Superalloy were studied at elevated temperatures. The stress exponents of creep rate n and time to fracture m indicate power-low (dislocation) creep regime and suggest the same controlling mechanism for the creep deformation and fracture. The variation of values of parameter n within the interval of applied stress may indicate changes in the rate-controlling creep deformation mechanism. The possibility of using of Monkman-Grant relationship for creep life prediction was demonstrated.

scholarly journals Texture analysis of experimentally deformed Black Hills Quartzite

2017 ◽  
Author(s):  
Rüdiger Kilian ◽  
Renée Heilbronner
Keyword(s):  
Black Hills ◽  
Dislocation Creep ◽  
Shear Stresses ◽  
Slip Systems ◽  
Dislocation Glide ◽  
Aspect Ratios ◽  
Deformation Intensity ◽  
Pole Figures ◽  
Three Samples ◽  
Texture Transition

Abstract. The textures of three samples of Black Hills quartzite (BHQ) deformed experimentally in the dislocation creep regime 1, 2 and 3 (according to Hirth and Tullis, 1992) have been analysed by EBSD. All samples were deformed to relatively high strain, within a temperature range of 65° and identical displacement rates and are almost entirely composed of dynamically recrystallized grains. A texture transition from peripheral c-axes in regime 1 to a central c-axis maximum in regime 3 is observed. Separate pole figures are calculated for different grain sizes, aspect ratios and long axis trend (θ) of grains, and high and low levels of intragranular deformation intensity as measured by the grain kernel average misorientation (gKAM). Misorientation relations are analysed for different texture components (named Y- B- R- and σ, with reference to previously published prism, basal, rhomb and σ1 – grains). Results show that regime 1 and 3 correspond to clear end member textures with regime 2 being transitional. Texture strength and the development of a central c-axis maximum from a girdle distribution depends on deformation intensity at the grain scale and on the contribution of dislocation creep which increases towards regime 3. Combined with calculations of resolved shear stresses and misorientation analysis, it becomes clear that the peripheral c-axis maximum in regime 1 is not due to deformation by basal –<a> slip. We interpret the texture transition as a result of different texture forming processes, one being more efficient at high stresses (formation of grains with peripheral c-axes), the other depending on strain (dislocation glide involving prism and rhomb slip systems), and not as a result of a temperature dependent activity of different slip systems.

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