Microstructure Development and Ductility of Ultra-Fine Grained Mg-Gd Alloy Prepared by High Pressure Torsion

2009 ◽  
Vol 633-634 ◽  
pp. 353-363 ◽  
Author(s):  
Jakub Čížek ◽  
Ivan Procházka ◽  
Bohumil Smola ◽  
Ivana Stulíková ◽  
Vladivoj Očenášek ◽  
...  
Keyword(s):  
Grain Size ◽  
High Pressure ◽  
Elevated Temperatures ◽  
High Pressure Torsion ◽  
High Sensitivity ◽  
Tensile Tests ◽  
Lattice Defects ◽  
Coarse Grained ◽  
Fine Grained ◽  
Mean Grain Size

Microstructure of ultra fine grained (UFG) Mg-Gd alloy prepared by high-pressure torsion (HPT) was investigated in the present work. Lattice defects introduced by HPT were characterized at first. Subsequently thermal stability of UFG structure and its development with annealing temperature were studied and correlated with changes of hardness and ductility. Precipitation effects in the alloy with UFG structure were compared with those in a conventional coarse-grained alloy. Defect studies were performed by positron annihilation spectroscopy (PAS), which represents well established non-destructive technique with a high sensitivity to open volume lattice defects like vacancies, dislocations, misfit defects etc. PAS investigations were combined with transmission electron microscopy (TEM) and X-ray diffraction (XRD). Changes of mechanical properties were monitored by Vicker’s microhardness (HV) and deformation tensile tests. It was found that HPT deformed Mg-Gd alloy exhibits UFG structure with mean grain size of 100 nm and a dense network of dislocations distributed uniformly throughout the whole sample. Although recovery of dislocations takes place at relatively low temperatures, it is not accompanied by grain growth and the mean grain size remains around 100 nm up to 300oC. Tensile tests performed at elevated temperatures to examine ductility showed that HPT-deformed alloy exhibits a superplastic behavior at 400oC. Moreover, it was found that the precipitation sequence in HPT-deformed alloy differs from that in conventional coarse-grained material.

Microstructure and Thermal Stability of Ultra Fine Grained Mg-Based Alloys Prepared by High Pressure Torsion

2006 ◽  
Vol 503-504 ◽  
pp. 149-154 ◽  
Author(s):  
Jakub Čížek ◽  
Ivan Procházka ◽  
Bohumil Smola ◽  
Ivana Stulíková ◽  
Radomír Kužel ◽  
...  
Keyword(s):  
Grain Size ◽  
High Pressure ◽  
High Pressure Torsion ◽  
High Sensitivity ◽  
Complete Information ◽  
Positron Annihilation Spectroscopy ◽  
Coarse Grained ◽  
Fine Grained ◽  
Increasing Temperature ◽  
Distributed Dislocations

In the present work we studied microstructure of ultra fine grained (UFG) pure Mg and UFG Mg-based alloys. The initial coarse grained samples were deformed by high pressure torsion (HPT) using pressure of 6 GPa. Such deformation leads to formation of UFG structure in the samples. The severe plastic deformation results in creation of high number of lattice defects. Therefore, we used positron annihilation spectroscopy (PAS) for defect characterizations. PAS represents a well developed non-destructive technique with high sensitivity to open volume defects like vacancies, vacancy clusters, dislocations etc. In the present work we combined PAS with TEM and XRD to obtain complete information about microstructure of the UFG samples studied. We have found that microstructure of HPT-deformed Mg contains two kinds of regions: (a) ”deformed” regions with UFG structure (grain size 100-200 nm) and high number of randomly distributed dislocations, and (b) ”recrystallized” regions with low dislocation density and grain size of few microns. It indicates some kind of dynamic recovery of microstructure already during HPT processing. On the other hand, homogenous UFG structure with grain size around 100 nm and high density of homogeneously distributed dislocations was formed in HPT-deformed Mg-9.33 wt.%Gd alloy. After characterization of the as-deformed microstructure the samples were subsequently isochronally annealed and the development of microstructure with increasing temperature and recovery of defects were investigated.

Martensitic Transformations and Functional Stability in Ultra-Fine Grained NiTi Shape Memory Alloys

2008 ◽  
Vol 584-586 ◽  
pp. 852-857 ◽  
Author(s):  
Juri Burow ◽  
Egor Prokofiev ◽  
Christoph Somsen ◽  
Jan Frenzel ◽  
Ruslan Valiev ◽  
...  
Keyword(s):  
Grain Size ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Thermomechanical Processing ◽  
High Pressure Torsion ◽  
Martensitic Transformations ◽  
Coarse Grained ◽  
Functional Stability ◽  
Fine Grained ◽  
Niti Shape Memory Alloys

Martensitic transformations in NiTi shape memory alloys (SMAs) strongly depend on the microstructure. In the present work, we investigate how martensitic transformations are affected by various types of ultra-fine grained (UFG) microstructures resulting from various processing routes. NiTi SMAs with UFG microstructures were obtained by equal channel angular pressing, high pressure torsion, wire drawing and subsequent annealing treatments. The resulting material states were characterized by transmission electron microscopy and differential scanning calorimetry (DSC). The three thermomechanical processing routes yield microstructures which significantly differ in terms of grain size and related DSC chart features. While the initial coarse grained material shows a well defined one-step martensitic transformation on cooling, two-step transformations were found for all UFG material states. The functional stability of the various UFG microstructures was evaluated by thermal cycling. It was found that UFG NiTi alloys show a significantly higher stability. In the present work, we also provide preliminary results on the effect of grain size on the undercooling required to transform the material into B19’ and on the related heat of transformation.

Superplasticity of Ultra-Fine Grained 7075 Alloy Processed by High-Pressure Torsion

2014 ◽  
Vol 794-796 ◽  
pp. 807-810 ◽  
Author(s):  
Seungwon Lee ◽  
Zen Ji Horita
Keyword(s):  
High Pressure ◽  
Room Temperature ◽  
High Pressure Torsion ◽  
Applied Pressure ◽  
Tensile Tests ◽  
Initial Strain ◽  
Strain Rates ◽  
Fine Grained ◽  
Al 7075 ◽  
7075 Alloy

An Al 7075 alloy (5.63mass%Zn-2.56mass%Mg-1.68mass%Cu-0.21mass%Fe-0.19mass%Cr-0.14mass%Si-0.02mass%Ti with balance of Al) was processed by high-pressure torsion (HPT) under an applied pressure of 6 GPa for 1, 3 and 5 revolutions with a rotation speed of 1 rpm at room temperature. Vickers microhardness saturated to a level of 220 Hv after the HPT processing and the grain size was refined to 120 nm at the state of the hardness saturation. Tensile tests were conducted with initial strain rates from 2.0 × 10-4 to 2.0 × 10-2 s-1 at temperatures as 200 °C and 250 °C (equivalent to 0.52Tm and 0.57Tm, respectively, where Tm is the melting point of the alloy). The HPT-processed samples for 3 revolutions exhibited superplastic elongations of 640% and 510% at 250 °C with initial strain rates of 2.0 × 10-3 s-1 and 2.0 × 10-2 s-1, respectively.

Effect of Grain Size on Mechanical Properties of Mg-0.3at.%Y Dilute Alloy

2018 ◽  
Vol 941 ◽  
pp. 790-795
Author(s):  
Rui Xiao Zheng ◽  
Ichiro Kawarada ◽  
Wu Gong ◽  
Akinobu Shibata ◽  
Hidetoshi Somekawa ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Yield Strength ◽  
High Pressure Torsion ◽  
Tensile Elongation ◽  
Tensile Tests ◽  
Subsequent Annealing ◽  
High Yield ◽  
Grain Sizes ◽  
Mean Grain Size

In this study, a Mg-0.3at.%Y alloy was provided for a severe plastic deformation by high pressure torsion (HPT) and subsequent annealing. After the HPT by 5 rotations, nanocrystalline structures with a mean grain size of 0.23 μm having deformed characteristics were obtained. Fully recrystallized microstructures with mean grain sizes ranging from 0.66 μm to 32.7 μm were obtained by subsequent annealing at various temperatures. Room temperature tensile tests revealed that ultrafine grained (UFG; grain sizes smaller than 1 μm) specimen exhibited very high yield strength over 250 MPa but limited ductility. In contrast, good balance of strength and ductility was realized in fine grained specimens with grain sizes around 2~5 μm. Particularly, the yield strength and total tensile elongation of a specimen with a mean grain size of 2.13 μm were 184 MPa and 37.1%, respectively, which were much higher than those of pure Mg having a similar grain size. The significant effects of grain size and Y addition on the mechanical properties were discussed.

Microstructure and Mechanical Properties of Ultrafine-Grained Mg-Zn-Ca Alloy

2017 ◽  
Vol 381 ◽  
pp. 39-43 ◽  
Author(s):  
Olya B. Kulyasova ◽  
Rinat K. Islamgaliev ◽  
Ruslan Z. Valiev
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
High Pressure ◽  
Chemical Composition ◽  
High Pressure Torsion ◽  
Notable Effect ◽  
Ultrafine Grained ◽  
Mean Grain Size ◽  
High Microhardness ◽  
Mean Size

This paper studies the structure and mechanical properties of the Mg-1%Zn-xCa system subjected to high-pressure torsion (HPT) treatment. It was found that the chemical composition had a notable effect on the processes of grain refinement in the alloy. As is shown, HPT of Mg-1%Zn-0.005%Ca resulted in the formation of grains with a mean size of 250 nm, while HPT of the alloy with an increased content of Са up to 0.2% led to the formation of a nanostructure with a mean grain size of 90 nm. It is demonstrated that high microhardness is typical of all HPT-processed samples. The formation of fine Mg2Ca particles was established to increase the heat resistance of the alloy.

scholarly journals Effects of microparticles on deformation and microstructural evolution of fine-grained ice

2019 ◽  
Vol 65 (252) ◽  
pp. 531-541 ◽  
Author(s):  
TOMOTAKA SARUYA ◽  
KOKI NAKAJIMA ◽  
MORIMASA TAKATA ◽  
TOMOYUKI HOMMA ◽  
NOBUHIKO AZUMA ◽  
...  
Keyword(s):  
Grain Size ◽  
Particle Dispersion ◽  
Coarse Grained ◽  
Dislocation Creep ◽  
Compression Tests ◽  
Fine Grained ◽  
Mean Grain Size ◽  
Polycrystalline Ice ◽  
Order Of Magnitude ◽  
Deformation Processes

ABSTRACTWe investigated the effects of microparticles and grain size on the microstructural evolutions and mechanical properties of polycrystalline ice. Uniaxial compression tests were conducted using fine-grained pure ice and silica-dispersed ice under various conditions. Deformation behavior of fine-grained ice was found to be characterized by stress exponent n ≈ 2 and activation energy Q ≈ 60 kJ mol−1. The derived strain rates of fine-grained ice were ≈ 1 order of magnitude larger than those of coarse-grained ice obtained in previous studies, and they were found to be independent of particle dispersion and dependent on the mean grain size of ice, with grain size exponent p ≈ 1.4. Work hardening was observed in dislocation creep, while the strain rate continued to decrease. These results indicate that the deformation mechanism of fine-grained ice is different from typical dislocation creep, often associated with n = 3. Although microparticles restricted grain growth, there was little direct effect on the deformation of fine-grained ice. Microstructural observations of the ice samples indicated that the grain boundaries were straight and that the subgrain boundary densities increased after deformation. Our experiments suggest that grain size and boundaries play important roles in the deformation processes of polycrystalline ice.

The Enhanced Kinetics of Precipitation Effects in Ultra Fine Grained Mg Alloys Prepared by High Pressure Torsion

2008 ◽  
Vol 273-276 ◽  
pp. 75-80 ◽  
Author(s):  
Jakub Čížek ◽  
Ivan Procházka ◽  
Bohumil Smola ◽  
Ivana Stulíková ◽  
Vladivoj Očenášek ◽  
...  
Keyword(s):  
High Pressure ◽  
Grain Boundaries ◽  
Volume Fraction ◽  
High Pressure Torsion ◽  
Mg Alloys ◽  
Coarse Grained ◽  
Fine Grained ◽  
Transmission Electron ◽  
Positron Lifetime Spectroscopy ◽  
Kinetics Of

Precipitation effects in ultra fine grained (UFG) lightweight Mg-based alloys were studied in the present work by means of positron lifetime spectroscopy, transmission electron microscopy, and microhardness. The UFG samples with grain size around 100 nm were fabricated by high pressure torsion (HPT). The UFG structure contains a significant volume fraction of grain boundaries and exhibits a high number of lattice defects (mainly dislocations) introduced by severe plastic deformation during the HPT processing. A high dislocation density and volume fraction of grain boundaries enhance the long range diffusion of solute elements. Moreover, dislocations and grain boundaries act as nucleation centers for precipitates. As a consequence, the precipitation effects are facilitated in the UFG alloys compared to the conventional coarse-grained samples. This phenomenon was examined in this work by comparison of the precipitation sequence in Mg alloys with UFG structure and solution treated coarse-grained alloys.

Mechanical Behavior on Micro-compression Test in Ultra-low Carbon Steel Produced by High Pressure Torsion

2011 ◽  
Vol 1297 ◽  
Author(s):  
Takashi Nagoshi ◽  
Akinobu Shibata ◽  
Masato Sone ◽  
Yoshikazu Todaka
Keyword(s):  
Grain Size ◽  
High Pressure ◽  
Mechanical Behavior ◽  
Compression Test ◽  
High Pressure Torsion ◽  
Low Carbon Steel ◽  
Shear Direction ◽  
Low Carbon ◽  
Fine Grained ◽  
Ultra Low Carbon Steel

ABSTRACTMechanical behavior of ultra-fine grained (UFG) steel fabricated by high pressure torsion (HPT) was investigated by micro-sized compression test of a micro-sized pillar with uniform dimensions (non-tapered, non-filleted) carefully fabricated by FIB milling. After HPT process, grains were elongated to shear direction and its grain size was decreased down to 300 nm in diameter with increasing strain amount. Compression test confirmed that the uniform elongations of ultra-fine grained materials were lower than 3% and do not depend on the grain size.

Microstructure and Properties of Nanostructured Zirconium Processed by High Pressure Torsion

2010 ◽  
Vol 667-669 ◽  
pp. 433-438 ◽  
Author(s):  
Aleksey V. Podolskiy ◽  
Bartlomiej J. Bonarski ◽  
Daria Setman ◽  
Clemens Mangler ◽  
Erhard Schafler ◽  
...  
Keyword(s):  
Grain Size ◽  
High Pressure ◽  
High Pressure Torsion ◽  
Texture Evolution ◽  
Considerable Change ◽  
Prismatic Slip ◽  
Scanning Calorimetry ◽  
Fine Grained ◽  
Average Grain Size ◽  
Fine Grained Structure

Several structural states of nanostructured zirconium were achieved by high pressure torsion (HPT) at pressures of 2 and 4 GPa with and without subsequent low temperature annealing. The nanostructured Zr was studied by X-Ray Diffraction, Transmission Electron Microscopy and Differential Scanning Calorimetry to reveal the microstructure, phase composition and the thermal stability of this material. The fine grained structure being achieved by HPT had an average grain size of 100-200 nm. It was shown that HPT at 4 GPa leads to a phase transformation from α-Zr to ω-Zr, which has been demonstrated to be reversible by annealing at 300 °C without considerable change of the grain size. The evaluation of texture evolution in Zr during HPT exhibits activity of prismatic slip systems. DSC curves confirm the presence of HPT deformation induced lattice defects and the occurrence of the ω-α phase transition in Zr.

scholarly journals Submarine lava deltas of the 2018 eruption of Kīlauea volcano

2021 ◽  
Vol 83 (4) ◽  
Author(s):  
S. Adam Soule ◽  
Michael Zoeller ◽  
Carolyn Parcheta
Keyword(s):  
Grain Size ◽  
Pore Pressure ◽  
Mechanistic Model ◽  
Large Fraction ◽  
Volcanic Hazards ◽  
Lava Flows ◽  
Coarse Grained ◽  
Fine Grained ◽  
Fine Grain ◽  
Delta Formation

AbstractHawaiian and other ocean island lava flows that reach the coastline can deposit significant volumes of lava in submarine deltas. The catastrophic collapse of these deltas represents one of the most significant, but least predictable, volcanic hazards at ocean islands. The volume of lava deposited below sea level in delta-forming eruptions and the mechanisms of delta construction and destruction are rarely documented. Here, we report on bathymetric surveys and ROV observations following the Kīlauea 2018 eruption that, along with a comparison to the deltas formed at Pu‘u ‘Ō‘ō over the past decade, provide new insight into delta formation. Bathymetric differencing reveals that the 2018 deltas contain more than half of the total volume of lava erupted. In addition, we find that the 2018 deltas are comprised largely of coarse-grained volcanic breccias and intact lava flows, which contrast with those at Pu‘u ‘Ō‘ō that contain a large fraction of fine-grained hyaloclastite. We attribute this difference to less efficient fragmentation of the 2018 ‘a‘ā flows leading to fragmentation by collapse rather than hydrovolcanic explosion. We suggest a mechanistic model where the characteristic grain size influences the form and stability of the delta with fine grain size deltas (Pu‘u ‘Ō‘ō) experiencing larger landslides with greater run-out supported by increased pore pressure and with coarse grain size deltas (Kīlauea 2018) experiencing smaller landslides that quickly stop as the pore pressure rapidly dissipates. This difference, if validated for other lava deltas, would provide a means to assess potential delta stability in future eruptions.

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