scholarly journals The microstructural record of porphyroclasts and matrix of serpentinite mylonites – from brittle and crystal-plastic deformation to dissolution-precipitation creep

2013 ◽  
Vol 5 (1) ◽  
pp. 365-390 ◽  
Author(s):  
J. Bial ◽  
C. A. Trepmann
Keyword(s):  
Plastic Deformation ◽  
High Pressure ◽  
Upper Mantle ◽  
High Stress ◽  
Oceanic Lithosphere ◽  
Dislocation Creep ◽  
Polarization Microscopy ◽  
Fine Grained ◽  
Dehydration Reactions ◽  
Deformation Features

Abstract. We examine the microfabric development in high-pressure, low-temperature metamorphic serpentinite mylonites exposed in the Erro-Tobbio Unit (Voltri Massif, Italy) using polarization microscopy and electron microscopy (SEM/EBSD, EMP). The mylonites are derived from mantle peridotites, were serpentinized at the ocean floor and underwent high pressure metamorphism during Alpine subduction. They contain diopside and olivine porphyroclasts embedded in a fine-grained matrix essentially consisting of antigorite. The porphyroclasts record brittle and crystal-plastic deformation of the original peridotites in the upper mantle at stresses of a few hundred MPa. After the peridotites became serpentinized, deformation occurred mainly by dissolution-precipitation creep resulting in a foliation with flattened olivine grains at phase boundaries with antigorite, crenulation cleavages and olivine and antigorite aggregates in strain shadows next to porphyroclasts. It is suggested that the fluid was provided by dehydration reactions of antigorite forming olivine and enstatite during subduction and prograde metamorphism. At sites of stress concentration around porphyroclasts antigorite reveals an associated SPO and CPO, characteristically varying grain sizes and sutured grain boundaries, indicating deformation by dislocation creep. Stresses were probably below a few tens of MPa in the serpentinites, which was not sufficiently high to allow for crystal-plastic deformation of olivine at conditions at which antigorite is stable. Accordingly, any intragranular deformation features of the newly precipitated olivine in strain shadows are absent. The porphyroclast microstructures are not associated with the microstructures of the mylonitic matrix, but are inherited from an independent earlier deformation. The porphyroclasts record a high-stress deformation in the upper mantle of the oceanic lithosphere probably related to rifting processes, whereas the antigorite matrix records deformation at low stresses during subduction and exhumation.

scholarly journals The microstructural record of porphyroclasts and matrix of partly serpentinized peridotite mylonites – from brittle and crystal-plastic deformation to dissolution–precipitation creep

Solid Earth ◽  
2013 ◽  
Vol 4 (2) ◽  
pp. 315-330 ◽  
Author(s):  
J. Bial ◽  
C. A. Trepmann
Keyword(s):  
Plastic Deformation ◽  
Upper Mantle ◽  
Boundary Migration ◽  
High Stress ◽  
Preferred Orientation ◽  
Dislocation Creep ◽  
Polarization Microscopy ◽  
Crystallographic Preferred Orientation ◽  
Fine Grained ◽  
Serpentinized Peridotite

Abstract. We present microfabrics in high-pressure, metamorphic, partly serpentinized peridotite mylonites from the Voltri Massif, in which porphyroclasts and matrix record independent deformation events. The microfabrics are analysed using polarization microscopy and electron microscopy (SEM/EBSD, EMP). The mylonites contain diopside and olivine porphyroclasts originating from the mantle protolith embedded in a fine-grained matrix consisting mainly of antigorite and minor olivine and pyroxene. The porphyroclasts record brittle and crystal-plastic deformation of the peridotite at upper-mantle conditions and differential stresses of a few hundred MPa. After the peridotites became serpentinized, deformation occurred mainly by dissolution–precipitation creep resulting in a pronounced foliation of the antigorite matrix, crenulation cleavages and newly precipitated olivine and pyroxene from the pore fluid at sites of dilation, i.e. in strain shadows next to porphyroclasts and folded fine-grained antigorite layers. Antigorite reveals a pronounced associated shape preferred orientation (SPO) and crystallographic preferred orientation (CPO) with the basal (001) cleavage plane oriented in the foliation plane. In monomineralic antigorite aggregates at sites of stress concentration around porphyroclasts, a characteristically reduced grain size and deflecting CPO as well as sutured grain boundaries indicate also some contribution of crystal-plastic deformation and grain-boundary migration of antigorite. In contrast, the absence of any intragranular deformation features in newly precipitated olivine in strain shadows reveals that stresses were not sufficiently high to allow for significant dislocation creep of olivine at conditions at which antigorite is stable. The porphyroclast microstructures are not associated with the microstructures of the mylonitic matrix, but are inherited from an independent earlier deformation. The porphyroclasts record a high-stress deformation of the peridotite with dislocation creep of olivine in the upper mantle probably related to rifting processes, whereas the serpentinite matrix records dominantly dissolution–precipitation creep and low stresses during subduction and exhumation.

scholarly journals Effect of confining pressure on the strength of wet quartzite revisited

2020 ◽  
Author(s):  
Lucille Nègre ◽  
Holger Stünitz ◽  
Hugues Raimbourg ◽  
Jacques Précigout ◽  
Petr Jeřábek ◽  
...  
Keyword(s):  
Plastic Deformation ◽  
High Pressure ◽  
Grain Boundaries ◽  
Solid Earth ◽  
Constant Strain Rate ◽  
Dislocation Creep ◽  
Temperature Deformation ◽  
Diffusion Creep ◽  
Fine Grained ◽  
Bulk Strain

<p>The ability of water to enhance plastic deformation of a quartz aggregate has been experimentally demonstrated during the sixties (e.g. Griggs and Blacic 1965), however the processes involved are still questioned. Notably the processes combining the effect of water and pressure during the deformation are still not completely understood. Pressure strongly influences the strength of fine-grained (3.6 - 4.9 µm) wet quartz aggregates (Kronenberg and Tullis 1984), where diffusion creep operates (Fukuda et al. 2018) but its effect on coarser-grained material expected to deform only by dislocation creep is not well constrained. To re-assess the effect of pressure on quartz crystal plastic deformation, natural wet quartzite samples from the Tana quarry in northern Norway (grain size ≈ 150 µm) have been deformed using a Griggs-type apparatus at varying confining pressures (from 0.6 to 2.0 GPa). All the samples with 0.1 wt. % H<sub>2</sub>O added were shortened coaxially up to 30% strain at constant strain rate (≈10<sup>-6</sup> s<sup>-1</sup>) and temperature (900°C).</p><p>All mechanical records show that quartzite flow stresses decrease systematically with increasing pressure. These results allow to determine the strength of quartzite as a function of water fugacity, such as introduced in the flow law by Kohlstedt et al. (1995) to account for both pressure and water effects. In our case, the fugacity coefficient is m≈1 when using a stress exponent of n=2.</p><p>Microstructure and image analyses of samples reveal that the bulk strain results mainly from crystal plastic deformation of original grains whereas the recrystallization processes are limited volumetrically (less than 5%) and restricted to the boundaries of original grains. Deformation is not strongly partitioned into recrystallized domains compared to flattened original grains. Optical and SEM-cathodoluminescence images revealed the presence of cracks in conjunction with recrystallization (even for high-pressure samples) and associated chemical/fluid interaction, but the cracks do not contribute significantly to the bulk strain of the samples.</p><p>In order to determine the amount of water used for the deformation and the redistribution of H<sub>2</sub>O during deformation, the H<sub>2</sub>O content of the quartzite has been calculated from FTIR (Fourier Transform InfraRed spectroscopy) measurements for both, grain interiors and grain boundaries. The H<sub>2</sub>O concentrations decrease inside grains with the onset of deformation with respect to the starting material. H<sub>2</sub>O is primarily stored in the grain boundary region. There is no systematic correlation with pressure. Thus, pressure dependence of H<sub>2</sub>O weakening is not restricted to fine-grained materials at high pressure and temperature. Deformation redistributes water from the grain interiors to their grain boundaries.</p><p>References:<br>Fukuda, J., Holyoke III, C.W., and Kronenberg, A.K. (2018). J. Geophysical Res.: Solid Earth, 123(6), 4676-4696.<br>Griggs, D. T., and Blacic J. D. (1965). Science, 147(3655), 292‑295.<br>Kohlstedt, D. L., Evans B., and Mackwell S. J. (1995). J. Geophysical Res.: Solid Earth, 100(B9), 17587-17602.<br>Kronenberg, A. K., and Tullis J. (1984). J. Geophysical Res.: Solid Earth, 89(B6), 4281‑4297.</p>

Deformation and reaction fabrics in eclogites from the Western Gneiss Region (Norway) - evidence of dehydration reactions attributed to episodic deformation

2021 ◽  
Author(s):  
Claudia A. Trepmann ◽  
Ane K. Engvik ◽  
Erick G. Prince Gutierrez
Keyword(s):  
Inner Core ◽  
White Mica ◽  
Coarse Grained ◽  
Dislocation Creep ◽  
Western Gneiss Region ◽  
Garnet Porphyroblasts ◽  
Boundary Area ◽  
Fine Grained ◽  
Dehydration Reactions

<p>The eclogites from Vårdalneset, Western Gneiss Region, Norway, show an exceptional large variety of reaction and deformation microfabrics that document the processes and conditions during burial and exhumation. Coarse grained eclogites comprise about 35% omphacite, 25% garnet and 20% amphibole with various amounts of white mica, zoisite, kyanite, rutile, zircon and pyrite. Their fabric is characterized by few mm long and several hundred µm wide amphibole and omphacite grains aligned in the foliation plane with zoned garnet porphyroblasts up to several mm in diameter. In contrast, finer-grained mylonitic eclogites with grain diameters of few hundred µm comprise systematically higher amounts of garnet (45%) and omphacite (35%) and generally less amphibole (< 5%) but similar amounts of zoisite, white mica, rutile and quartz. In the coarse-grained eclogite, amphibole shows evidence of dislocation creep as indicated by undulatory extinction, subgrains and recrystallized grains in necks of boudinaged coarse amphibole layers as well as in contact to garnet. The large garnet porphyroblasts generally show a complex zonation with an inclusion-rich Fe-poor and Mg-rich inner core surrounded by a zone with Fe- and Ca-rich patches and a broad Mg-rich, Ca- and Fe-poor rim. Only at contact to coarse amphibole an additional, a few tens of µm thin serrated rim further enriched in Mg can occur. At the direct contact to such serrated Mg-rich rims, amphibole is partly replaced by a fine-grained quartz-kyanite ± rutile aggregate, indicating dehydration reactions of amphibole. Quartz - kyanite ± rutile aggregates are surrounding garnet also in contact to omphacite, zoisite and to other garnet crystals. The microstructures suggest that deformation and dehydration of amphibole are coupled and played an important role during deformation of the eclogites finally leading to the mylonitic eclogites with higher amounts of garnet and omphacite. Deformation is suggested to have triggered the dehydration reaction by a slight and local increase in temperature. Furthermore, deformation provided additional pathways for the escaping fluids along the increased grain and phase boundary area, as indicated by commonly present quartz within interstitials between recrystallized amphibole grains. In all samples, few µm wide amphibole rims replacing garnets document restricted rehydration-reactions at a later stage. The large variety of the deformation and reaction microfabrics exemplarily show that both deformation and metamorphic reactions did not proceed at long-term continuous conditions, but that both are coupled and occurred episodically.</p>

Recrystallization and Grain Growth in Ultra Fine Grained Materials Produced by High Pressure Torsion

2012 ◽  
Vol 715-716 ◽  
pp. 373-373
Author(s):  
Anahita Khorashadizadeh ◽  
Myrjam Winning ◽  
Stefan Zaefferer ◽  
Dierk Raabe
Keyword(s):  
Mechanical Properties ◽  
Plastic Deformation ◽  
High Pressure ◽  
Severe Plastic Deformation ◽  
Grain Growth ◽  
High Pressure Torsion ◽  
Fine Grained ◽  
Fine Grained Material

Investigations of the microstructure of materials processed via severe plastic deformation methods such as high pressure torsion (HPT) and their recrystallization behaviour is of great interest as they are capable of producing ultra fine grained material (UFD) with good mechanical properties.

scholarly journals Dynamic High Pressure Torsion (DHPT)—A Novel Method for High Strain Rate Severe Plastic Deformation

Proceedings ◽  
2018 ◽  
Vol 2 (8) ◽  
pp. 493 ◽  
Author(s):  
Harishchandra Lanjewar ◽  
Leo Kestens ◽  
Patricia Verleysen
Keyword(s):  
Plastic Deformation ◽  
High Pressure ◽  
Severe Plastic Deformation ◽  
High Strain Rate ◽  
Strain Rate ◽  
High Strain ◽  
High Pressure Torsion ◽  
Pure Aluminum ◽  
High Deformation ◽  
Fine Grained

Metals with a fine-grained microstructure have exceptional mechanical properties. Severe plastic deformation (SPD) is one of the most successful ways to fabricate ultrafine-grained (UFG) and nanostructured (NC) materials. Most of the SPD techniques employ very low processing speeds. However, the lowest steady-state grain size which can be obtained by SPD is considered to be inversely proportional with the strain rate at which the severe deformation is imposed. In order to overcome this limitation, methods operating at higher rates have been envisaged and used to study the fragmentation process and the properties of the obtained materials. However, almost none of these methods, employ hydrostatic pressures which are needed to prevent the material from failing at high deformation strains. As such, their applicability is limited to materials with a high intrinsic ductility. Additionally, in some methods the microstructural changes are limited to the surface layers of the material. To circumvent these restrictions, a novel facility has been designed and developed which deforms the material at high strain rate under high hydrostatic pressures. Using the facility, commercially pure aluminum was processed and analysis of the deformed material was performed. The microstructure evolution in this material was compared with that observed in static high pressure torsion (HPT) processed material.

scholarly journals Achieving Superplasticity in Fine-Grained Al-Mg-Sc Alloys

2021 ◽  
Vol 1016 ◽  
pp. 11-17
Author(s):  
Pedro H.R. Pereira ◽  
Yi Huang ◽  
Megumi Kawasaki ◽  
Terence G. Langdon
Keyword(s):  
Plastic Deformation ◽  
High Pressure ◽  
High Pressure Torsion ◽  
Superplastic Forming ◽  
Superplastic Flow ◽  
Alternative Procedure ◽  
Flow Mechanism ◽  
Friction Stir ◽  
Fine Grained ◽  
Angular Pressing

Superplasticity denotes the ability of a limited number of materials to achieve exceptionally high tensile elongations of at least 400%. Experiments show that the Al-Mg-Sc alloys provide excellent capabilities for achieving superplastic flow and also they can be formed easily in biaxial superplastic forming operations. It is important, therefore, to examine the superplastic flow mechanism when the alloy is prepared using different procedures. This report examines the superplastic characteristics of these alloys after preparation without subjecting to any severe plastic deformation (SPD), after processing using the two SPD procedures of equal-channel angular pressing (ECAP) and high-pressure torsion (HPT) and after processing using the alternative procedure of friction stir processing (FSP). The results are compared using each technique and they are examined with reference to a theoretical model that was developed specifically for superplastic flow in conventional alloys.

Positron Annihilation Studies of Microstructure of Ultra Fine Grained Metals Prepared by Severe Plastic Deformation

2005 ◽  
Vol 482 ◽  
pp. 207-210 ◽  
Author(s):  
Jakub Čížek ◽  
Ivan Procházka ◽  
Bohumil Smola ◽  
Ivana Stulíková ◽  
Radomír Kužel ◽  
...  
Keyword(s):  
Plastic Deformation ◽  
High Pressure ◽  
Spatial Distribution ◽  
Severe Plastic Deformation ◽  
Positron Annihilation ◽  
Equal Channel Angular Pressing ◽  
High Pressure Torsion ◽  
Positron Annihilation Spectroscopy ◽  
Fine Grained ◽  
Angular Pressing

In the present work, positron annihilation spectroscopy (PAS) is employed for microstructure investigations of various ultra fine grained (UFG) metals (Cu, Ni, Fe) prepared by severe plastic deformation (SPD), namely high-pressure torsion (HPT) and equal channel angular pressing (ECAP). Generally, UFG metals prepared using both the techniques exhibit two kinds of defects introduced by SPD: dislocations and small microvoids. The size of the microvoids is determined from the PAS data. Significantly larger microvoids are found in HPT deformed Fe and Ni compared to HPT deformed Cu. The microstructure of UFG Cu prepared by HPT and ECAP is compared and the spatial distribution of defects in UFG Cu samples is characterized. In addition, the microstructure of a pure UFG Cu prepared by HPT and HPT deformed Cu+Al2O3 nanocomposite (GlidCop) is compared.

scholarly journals Pressure Dependence of Magnesite Creep

Geosciences ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 420
Author(s):  
Joseph W. Millard ◽  
Caleb W. Holyoke ◽  
Rachel K. Wells ◽  
Cole Blasko ◽  
Andreas K. Kronenberg ◽  
...  
Keyword(s):  
Oceanic Lithosphere ◽  
Coarse Grained ◽  
Dislocation Creep ◽  
Diffusion Creep ◽  
Flow Strength ◽  
Dislocation Glide ◽  
Fine Grained ◽  
Grain Sizes ◽  
And Diffusion ◽  
Flow Laws

We determined the activation volumes (V*) for polycrystalline magnesite with grain sizes of 2 and 80 µm deforming by low temperature plasticity (LTP) mechanisms (kinking and dislocation glide), diffusion creep, and dislocation creep at temperatures of 500, 750, and 900 °C, respectively, and a strain rate of 1–2 × 10−5 s−1 at effective pressures of 2.9–7.5 GPa in a D-DIA and 0.76 GPa in a Griggs apparatus. In each set of experiments performed at a given temperature, the strength of magnesite increases with increasing pressure. Microstructures of fine-grained magnesite deformed at 500 °C and 750 °C are consistent with deformation by LTP mechanisms and diffusion creep, respectively. Microstructures of coarse-grained magnesite deformed at 900 °C are consistent with deformation by dislocation creep. Pressure dependencies of magnesite flow laws for LTP, diffusion creep, and dislocation creep are given by activation volumes of 34 (± 7), 2 (± 1), and 10 (± 5) × 10−6 m3/mol, respectively. Addition of these activation volumes to previously determined flow laws predicts magnesite strength to be much lower than the flow strength of olivine at all subduction zone depths of the upper mantle. Thus, subducting oceanic lithosphere that has been partially carbonated by reaction with CO2-bearing fluids may deform at lowered stresses where magnesite is present, possibly resulting in strain localization and unstable run-away shear.

scholarly journals Application of the Composite Hardness Models in the Analysis of Mechanical Characteristics of Electrolytically Deposited Copper Coatings: The Effect of the Type of Substrate

Metals ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 111
Author(s):  
Ivana O. Mladenović ◽  
Nebojša D. Nikolić ◽  
Jelena S. Lamovec ◽  
Dana Vasiljević-Radović ◽  
Vesna Radojević
Keyword(s):  
Mechanical Characteristics ◽  
Dislocation Creep ◽  
Average Current Density ◽  
Fine Grained ◽  
Copper Coatings ◽  
Electrochemically Deposited ◽  
Composite Models ◽  
Average Current ◽  
Composite Hardness ◽  
Coating Hardness

The mechanical characteristics of electrochemically deposited copper coatings have been examined by application of two hardness composite models: the Chicot-Lesage (C-L) and the Cheng-Gao (C-G) models. The 10, 20, 40 and 60 µm thick fine-grained Cu coatings were electrodeposited on the brass by the regime of pulsating current (PC) at an average current density of 50 mA cm−2, and were characterized by scanning electron (SEM), atomic force (AFM) and optical (OM) microscopes. By application of the C-L model we determined a limiting relative indentation depth (RID) value that separates the area of the coating hardness from that with a strong effect of the substrate on the measured composite hardness. The coating hardness values in the 0.9418–1.1399 GPa range, obtained by the C-G model, confirmed the assumption that the Cu coatings on the brass belongs to the “soft film on hard substrate” composite hardness system. The obtained stress exponents in the 4.35–7.69 range at an applied load of 0.49 N indicated that the dominant creep mechanism is the dislocation creep and the dislocation climb. The obtained mechanical characteristics were compared with those recently obtained on the Si(111) substrate, and the effects of substrate characteristics such as hardness and roughness on the mechanical characteristics of the electrodeposited Cu coatings were discussed and explained.

Microstructure of Ultra Fine Grained Mg and Mg-10 wt.% Gd Prepared by High-Pressure Torsion

Magnesium ◽  
2005 ◽  
pp. 202-207
Author(s):  
J. Cizek ◽  
I. Prochazka ◽  
I. Stulikova ◽  
B. Smola ◽  
R. Kuzel ◽  
...  
Keyword(s):  
High Pressure ◽  
High Pressure Torsion ◽  
Fine Grained
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