scholarly journals Fabrication of nanoceramic hin-wall tubes by magnetic pulsed compaction and thermal sintering

2005 ◽  
Vol 37 (1) ◽  
pp. 55-60 ◽  
Author(s):  
V.V. Ivanov ◽  
S.Y. Ivin ◽  
V.R. Khrustov ◽  
Y.A. Kotov ◽  
A.M. Murzakaev ◽  
...  
Keyword(s):  
Grain Size ◽  
Wall Thickness ◽  
Thin Wall ◽  
Fine Grained ◽  
Mean Grain Size ◽  
Electrolytic Properties ◽  
Thermal Sintering

Gasproof thin-wall tubes of fine-grained ceramics based on zirconia and gadolinia have been produced by magnetic pulsed compaction and thermal sintering. Data on their structures and electric characteristics are presented. The tubes with a diameter of ~ 15 mm, wall thickness of ~ 0.7 mm, and length up to 80 mm are characterized by an uniform porous-free structure with a mean grain size in the range of 100 - 300 nm. The obtained ceramics possess high electrolytic properties.

scholarly journals Microstructural evolution in the fine-grained region of the Siple Dome (Antarctica) ice core

2011 ◽  
Vol 57 (206) ◽  
pp. 1046-1056 ◽  
Author(s):  
R.W. Obbard ◽  
K.E. Sieg ◽  
I. Baker ◽  
D. Meese ◽  
G.A. Catania
Keyword(s):  
Grain Size ◽  
Size Distribution ◽  
Grain Size Distribution ◽  
Electron Backscatter Diffraction ◽  
Ice Core ◽  
Axis Orientation ◽  
Fine Grained ◽  
Depth Analysis ◽  
Siple Dome ◽  
Mean Grain Size

AbstractAn in-depth analysis of seven samples from the Siple Dome (Antarctica) ice core, using optical microscopy and electron backscatter diffraction, illustrates rotational recrystallization or polygonization in the fine-grained region of the core between 700 and 800 m. Between 640 and 700 m, the microstructure is characterized by a bimodal grain-size distribution and a broken girdle fabric with evidence of polygonization. From 727 to 770 m, mean grain size decreases and a single-maximum fabric is found, and, by 790 m, mean grain size has again increased and a multiple-maxima fabric manifests itself. We compare grain-size distribution, c- and a-axis orientation, and misorientation between adjacent grains. We found that misorientations between adjacent grains in the 727–770 m region were predominantly low-angle and typically around a common a-axis, suggesting polygonization. This conclusion is supported by radar evidence of a physical disturbance at 757 m, which may be correlated with higher than usual strain in the 700–800 m range. Below 770 m, larger less regular misorientations and textural evidence show that migration recrystallization is the primary recrystallization mechanism.

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.

scholarly journals Effect of Multidirectional Forging on the Grain Structure and Mechanical Properties of the Al–Mg–Mn Alloy

Materials ◽  
2018 ◽  
Vol 11 (11) ◽  
pp. 2166 ◽  
Author(s):  
Mikhail Kishchik ◽  
Anastasia Mikhaylovskaya ◽  
Anton Kotov ◽  
Ahmed Mosleh ◽  
Waheed AbuShanab ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Thermomechanical Treatment ◽  
Strain Range ◽  
Grain Structure ◽  
Near Surface ◽  
Fine Grained ◽  
Multidirectional Forging ◽  
Cumulative Strain ◽  
Mean Grain Size

The effect of isothermal multidirectional forging (IMF) on the microstructure evolution of a conventional Al–Mg-based alloy was studied in the strain range of 1.5 to 6.0, and in the temperature range of 200 to 500 °C. A mean grain size in the near-surface layer decreased with increasing cumulative strain after IMF at 400 °C and 500 °C; the grain structure was inhomogeneous, and consisted of coarse and fine recrystallized grains. There was no evidence of recrystallization when the micro-shear bands were observed after IMF at 200 and 300 °C. Thermomechanical treatment, including IMF followed by 50% cold rolling and annealing at 450 °C for 30 min, produced a homogeneous equiaxed grain structure with a mean grain size of 5 µm. As a result, the fine-grained sheets exhibited a yield strength and an elongation to failure 30% higher than that of the sheets processed with simple thermomechanical treatment. The IMF technique can be successfully used to produce fine-grained materials with improved mechanical properties.

Fracture Processes in Fully Crystallized Co84Nb10B6 Metallic Glass

1985 ◽  
Vol 58 ◽  
Author(s):  
Janez Megusar ◽  
Tina Vargas ◽  
Nicholas J. Grant
Keyword(s):  
Grain Size ◽  
Fracture Surface ◽  
Fracture Process ◽  
Mean Free Path ◽  
Ductile Dimple ◽  
Fine Grained ◽  
Dimple Fracture ◽  
Mean Grain Size ◽  
The Mean ◽  
Fracture Processes

ABSTRACTFracture processes have been studied in a fully crystallized Co84Nb10B6 glass, with the mean grain size ranging from 43 nm to 0.65 μm. Tensile tested specimens with a mean grain size≥ 0.3 μm showed a ductile (dimple) fracture with microvoids initiated at the boride-cobalt matrix interfaces. As the mean grain size (more correctly, the corresponding mean free path of the deforming cobalt phase) was ≤ 0.1 μm, the fracture process may be similarly initiated by the microvoid formation at the boride-cobalt interface. However, one-to-one correspondence between dimples and boride particles may not be preserved. As a result, dimples become more shallow and may include several boride particles instead. Although the fracture surface of the brittle fine grained Co84Nb10B6 alloy gives an appearance of a cleavage fracture on a macroscale, it is distinctly different, by allowing for the microvoid formation on a microscale.

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.

Sedimentological and Biological Changes Associated with the Construction of the Oil Terminal of Antifer, France

1984 ◽  
Vol 16 (3-4) ◽  
pp. 399-406
Author(s):  
Y Monbet
Keyword(s):  
Grain Size ◽  
Environmental Changes ◽  
Biological Effects ◽  
Standing Stock ◽  
Natural Populations ◽  
Benthic Fauna ◽  
Field Investigations ◽  
Mean Grain Size ◽  
To Receive ◽  
Principal Species

A study was conducted to gain insight on actual sedimentological and biological effects associated with the construction of an oil Terminal designed to receive 500 000 d.w.t. tankers. Field investigations and subsequent laboratory analyses were organized to evaluate the nature and magnitude of environmental changes on benthic macrofauna, three years after the end of the construction. Sediments were found to decrease dramatically in medium grain size in area sheltered by the newly built breakwater. Increase of percentage of silt and clays (90 % against 20 %) was observed leeward of the jetty. The benthic fauna showed significant modifications. Although the same community (Pectinaria kareni Abra alba) recolonized the bottom after the dredging of up to 30 × 106 m3 of sediments, increase in abundance occured. Biomass remained at a constant level and decrease of diversity was observed. Considering the rate of siltation, and assuming a constant siltation rate equal to the rate observed from 1975 to 1978, a simple regressive model relating biomass to mean grain size of sediments has been developped. This model allowed the prediction of biomass and production of the two principal species for the period 1978 – 1981. Continuous siltation within the harbor leads to a maximum of biomass from years after the end of the construction, followed by a decrease of standing stock. This process may be explained by the respective tolerance of the two principal species to increase silt contant and also probably by the accumulation of organic matter which may impede the development of natural populations.

scholarly journals Preparation of high-entropy carbides by different sintering techniques

2021 ◽  
Vol 56 (19) ◽  
pp. 11237-11247 ◽  
Author(s):  
Johannes Pötschke ◽  
Manisha Dahal ◽  
Mathias Herrmann ◽  
Anne Vornberger ◽  
Björn Matthey ◽  
...  
Keyword(s):  
Grain Size ◽  
Single Phase ◽  
X Ray Diffraction ◽  
Vacuum Sintering ◽  
X Ray ◽  
High Entropy ◽  
Mean Grain Size ◽  
The Mean ◽  
Gas Pressure Sintering ◽  
Hardness Values

AbstractDense (Hf, Ta, Nb, Ti, V)C- and (Ta, Nb, Ti, V, W)C-based high-entropy carbides (HEC) were produced by three different sintering techniques: gas pressure sintering/sinter–HIP at 1900 °C and 100 bar Ar, vacuum sintering at 2250 °C and 0.001 bar as well as SPS/FAST at 2000 °C and 60 MPa pressure. The relative density varied from 97.9 to 100%, with SPS producing 100% dense samples with both compositions. Grain size measurements showed that the substitution of Hf with W leads to an increase in the mean grain size of 5–10 times the size of the (Hf, Ta, Nb, Ti, V,)C samples. Vacuum-sintered samples showed uniform grain size distribution regardless of composition. EDS mapping revealed the formation of a solid solution with no intermetallic phases or element clustering. X-ray diffraction analysis showed the structure of mostly single-phase cubic high-entropy carbides. Hardness measurements revealed that (Hf, Ta, Nb, Ti, V)C samples possess higher hardness values than (Ta, Nb, Ti, V, W)C samples.

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.

scholarly journals Ce-Bearing FeSi Alloy Inoculation of Electrically Melted, Low Sulphur Grey Cast Irons for Thin Wall Castings

Metals ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 1122
Author(s):  
Irina Varvara Balkan ◽  
Iulian Riposan
Keyword(s):  
Wall Thickness ◽  
Structural Characteristics ◽  
Cooling Curve ◽  
Thin Wall ◽  
Cast Irons ◽  
Iron Castings ◽  
Grey Cast ◽  
The Difference ◽  
Thermal Cooling ◽  
Fesi Alloy

Electrically melted and over-heated (>1500 °C) grey cast iron at less than 0.04%S, as commonly used, solidifies large amounts of carbides and/or undercooled graphite, especially in thin wall castings; this is necessary to achieve a stronger inoculation. The efficiency of Ce-bearing FeSi alloy is tested for lower ladle addition rates (0.15 and 0.25 wt.%), compared to the base and conventional inoculated iron (Ba,Ca-bearing FeSi alloy). The present work explores chill and associated structures in hypoeutectic grey iron (3.6–3.8%CE, 0.02%S, (%Mn) × (%S) = 0.013–0.016, Alres < 0.002%), in wedge castings W1, W2 and W3 (ASTM A 367, furan resin sand mould), at a lower cooling modulus (1.1–3.5 mm) that is typically used to control the quality of thin wall iron castings. Relatively clear and total chill well correlated with the standard thermal (cooling curve) analysis parameters and structural characteristics in wedge castings, at different wall thickness, displayed as the carbides/graphite ratio and presence of undercooled graphite morphologies. The difference in effects of the two inoculants addition is seen as the ability to decrease the amount of carbides and undercooled graphite, with Ce-bearing FeSi alloy outperforming the conventional inoculant, especially as the wall thickness decreased. It appears that Ce-bearing FeSi alloy could be a solution for low sulphur, electric melt, thin wall iron castings production.

Holocene sedimentation in the Hupo Trough of the southwestern East Sea (Japan Sea) and development of the East Korea Warm Current

The Holocene ◽  
2021 ◽  
pp. 095968362110032
Author(s):  
Boo-Keun Khim ◽  
Sunghan Kim ◽  
Yu-Hyeon Park ◽  
Jongmin Lee ◽  
Sangbeom Ha ◽  
...  
Keyword(s):  
Grain Size ◽  
Japan Sea ◽  
East Sea ◽  
Eastern Coast ◽  
Size Change ◽  
Sediment Properties ◽  
Warm Current ◽  
The Holocene ◽  
Mean Grain Size ◽  
East Korea Warm Current

Various sediment properties, such as mean grain size, total organic carbon, total nitrogen, C/N ratio, CaCO3, and biogenic opal content, were analyzed for a box core (BC02; 45 cm long) and a gravity core (GC02; 628 cm long), which were collected from the western margin of the Hupo Trough located off the eastern coast of Korea. The study area has been affected by the East Korea Warm Current (EKWC), a branch of the Tsushima Warm Current (TWC). The analytical results obtained for BC02 and the upper part of GC02 were in agreement, affirming the core-top preservation of GC02. Based on the corrected calibrated AMS 14C dates, the sedimentation rate of GC02 changed abruptly at ~8.2 ka from ~4.0–10.2 cm/kyr in the lower part to ~56.6–91.0 cm/kyr in the middle to upper part. This corresponds to the lithologic change from sandy mud to mud sediments showing the mean grain size change from 6.9 to 46.0 μm. Diverse paleoceanographic proxies representing the surface water condition exhibited varying degree of change at ~8.2 ka, after which all the properties remain almost unchanged, implying stable and continuous depositional conditions following the complete development of the EKWC. Furthermore, it indicated that the sediment depositional conditions in the Hupo Trough in response to the EKWC might have stabilized at ~8.2 ka since the opening of the Korea Strait during the Holocene sea level rise. Moreover, microfossil data from previous studies on the establishment of the TWC in the East Sea (Japan Sea) support our interpretation that the sediment properties revealed the Holocene development of the EKWC in the Hupo Trough.

Sign in / Sign up

Export Citation Format

Share Document