scholarly journals Эволюция дефектной структуры при испытаниях в режиме ползучести ультрамелкозернистых металлов и сплавов, полученных методами интенсивной пластической деформации

2020 ◽  
Vol 62 (2) ◽  
pp. 267
Author(s):  
В.И. Бетехтин ◽  
А.Г. Кадомцев ◽  
М.В. Нарыкова
Keyword(s):  
Grain Boundaries ◽  
Elevated Temperatures ◽  
Mechanical Stability ◽  
Diffusion Mechanism ◽  
Metals And Alloys ◽  
Structural Factors ◽  
X Ray Scattering ◽  
Ultrafine Grained

Using small-angle X-ray scattering, electron microscopy, and density measurements, structural factors have been identified that lead to a decrease in the mechanical stability of ultrafine-grained (UFG) metals and alloys when tested in creep mode at elevated temperatures. It has been established that one of the important factors is nanopores formed during intense plastic deformation. The development of these nanopores in grain boundaries formed during creep is realized by the diffusion mechanism and leads to destruction. The role of dispersed inclusions and high-angle grain boundaries for the strength of UFG metals and alloys under their “short-term” and long-term loading is considered.

On Specific Phase Transitions to the Compound-Like Impurity Nanosegregation Structures at Dislocations and Grain Boundaries in Metals and their Influence on Diffusion-Assisted Processes

2008 ◽  
Vol 138 ◽  
pp. 91-118 ◽  
Author(s):  
Yuriy S. Nechaev
Keyword(s):  
Phase Transitions ◽  
Grain Boundaries ◽  
Elevated Temperatures ◽  
Physical And Mechanical Properties ◽  
Nanostructured Metals ◽  
Study Results ◽  
And Diffusion ◽  
Specific Phase Transitions ◽  
Specific Phase

Specific phase transitions to the compound-like impurity nanosegregation structures at dislocations and grain boundaries in metals and their influence on diffusion-assisted processes are considered, mainly, on the basis of the thermodynamic analysis of the related experimental data. The following systems and aspects are in detail considered: (1) the hydride-like nanosegregation of hydrogen at dislocations and grain boundaries in palladium and their influence on the apparent characteristics of hydrogen solubility and diffusivity in palladium; (2) the physics of the anomalous characteristics of diffusion of Fe and other transition impurities in crystalline Al at elevated temperatures, the role of the compound-like nanosegregation (CLNS) of Fe and the others at dislocations and grain boundaries in Al, analysis of the Mössbauer and diffusion data on CLNS of Fe at grain boundaries and dislocations in Al; (3) some new physical aspects of internal oxidation and nitridation of metals (for Cu-0.3%Fe alloy/Cu2O surface layer, and for (Ni-5%Cr) alloy / N2 gas), the role of the compound-like impurity nanosegregation at dislocations and grain boundaries, study results on the deviations from the classical theories predictions and their interpretation. The possibility is considered of nanotechnology applications of the study results for creation of nanostructured metals with compound-like nanosegregation structures at grain boundaries, in order to obtain specific physical and mechanical properties of such a cellural-type nanocomposites. In particular, it can be complex hydride-like, carbide-like, nitride-like, carbide-nitride-like, oxide-like or intermetallide-like nanosegregation structures at grain boundaries of nanostructured metals.

Yielding and Plastic Flow in Stainless Steel: A TEM Study of the Evolution of Microstructure Associated with the Stress-Strain Diagram

1980 ◽  
Vol 38 ◽  
pp. 386-387
Author(s):  
L.E. Murr ◽  
S-H. Wang
Keyword(s):  
Grain Boundaries ◽  
Elastic Stress ◽  
Metals And Alloys ◽  
Strain Diagram ◽  
Stress Concentrations ◽  
Polycrystalline Metals ◽  
Pile Up ◽  
Local Slip ◽  
Evolution Of Microstructure

In spite of the fascination with dislocation pile-ups and the description of flow in metals and alloys based upon pile-up models, evidence has existed for decades suggesting that slip often if not always starts at grain boundaries in polycrystalline metals and alloys. Hook and Hirth showed that elastic incompatibility could result in local slip at the boundary between bicrystals, and their contention that local elastic stress concentrations at grain boundaries would aid slip nucleation was confirmed by Carrington, etal. Ashby has also described polycrystalline metals and alloys as plastically non-homogeneous because gradients of plastic deformation are imposed by the grain boundaries, and Murr has discussed the role of grain boundary ledges as initial sources for dislocations when polycrystalline metals and alloys are deformed. Brentnall and Rostoker earlier concluded that grain boundaries are both sources of early dislocations and barriers limiting their movement at higher stresses, and that slip is confined to grains in which it was initiated until the yield point is reached.

Grain Boundary Design of Bulk Nanomaterials for Advanced Properties

2015 ◽  
Vol 5 ◽  
pp. 43-54 ◽  
Author(s):  
Ruslan Z. Valiev
Keyword(s):  
Plastic Deformation ◽  
Grain Boundary ◽  
Severe Plastic Deformation ◽  
Grain Boundaries ◽  
Metals And Alloys ◽  
New Approach ◽  
Petch Relation ◽  
Ultrafine Grained ◽  
Grain Boundary Segregations ◽  
Bulk Nanomaterials

Nanostructuring of metals and alloys by severe plastic deformation techniques is an effective way of enhancing their mechanical and functional properties. The features of the nanostructured materials produced by severe plastic deformation (SPD) are stipulated by forming of ultrafine-sized grains as well as by the state of grain boundaries. The concept of grain boundary (GB) design of ultrafine-grained metals and alloys is developed for enhancement of their properties by tailoring grain boundaries of different types (low-angle and high-angle ones, special and random, equilibrium and nonequilibrium) and formation of grain boundary segregations and precipitations by SPD processing. The paper presents experimental data demonstrating the super-strength and “positive” slope of the Hall-Petch relation when passing from micro-to nanostructured state in a number of metallic materials subjected to severe plastic deformation. The nature of the superior strength is associated with new strengthening mechanisms and the difficulty of generation of dislocations from grain boundaries with segregations. This new approach is used for achieving the enhanced strength in several commercial Al and Ti alloys as well as steels subjected to SPD processing.

The Role of Grain Boundaries and other Defects on Phase Transformations Induced by Severe Plastic Deformation

2015 ◽  
Vol 5 ◽  
pp. 77-92 ◽  
Author(s):  
Xavier Sauvage ◽  
Yana Nasedkina
Keyword(s):  
Plastic Deformation ◽  
Severe Plastic Deformation ◽  
Phase Transformations ◽  
Grain Boundaries ◽  
Mechanical Mixing ◽  
Ultrafine Grained ◽  
Ultrafine Grained Materials ◽  
Underlying Mechanisms ◽  
Scientific Questions

During the past two decades, processing of ultrafine grained materials using severe plastic deformation techniques has attracted great interest in the scientific community. Although the up-scaling of processes and the lack of ductility of ultrafine grained alloys are still some important challenges, these techniques look promising because they produce bulk materials free of porosities. More recently, some strategies to combine precipitation hardening and ultrafine grained structures have been proposed. It has also been shown that nanoscaled composite materials could be successfully processed. This experimental work rose however some very fundamental scientific questions about the influence of severe plastic deformation on the precipitation mechanisms or on the formation of supersaturated solid solution through mechanical mixing. The driving force and the thermodynamics of these phase transformations are of course affected by the high amount of energy stored in severely deformed alloys, especially as interfacial energy. But grain boundaries, with the help of dislocations and point defects, also play an important role in the kinetics. In this paper, it is proposed to shortly review these phenomena and the underlying mechanisms with a special emphasis on the contribution of grain boundaries.

Stacking of Bi2Te3 and FeSi2 for Thermoelectric Applications

2005 ◽  
Vol 492-493 ◽  
pp. 273-280 ◽  
Author(s):  
Cestmir Drasar ◽  
Eckhard Müller
Keyword(s):  
High Efficiency ◽  
Elevated Temperatures ◽  
Mechanical Stability ◽  
Negative Impact ◽  
Coefficient Of Thermal Expansion ◽  
Thermal Contact ◽  
Dissimilar Materials ◽  
Thermoelectric Device ◽  
High Electrical Resistivity

Recently, there is a strong interest in developing superior thermoelectric materials with the aim to improve the performance of a thermoelectric device. However, the performance of a thermoelectric generator (TEG) can be considerably improved also by applying a graded composition along the temperature gradient inside the thermoelectric device so that at each position the respective material achieves its maximum thermoelectric performance (TE FGM principle). Combining the high efficiency of Bi2Te3 (used at low temperatures) and general durability of FeSi2 (applied up to high temperatures) will result in a thermoelectric device with enhanced efficiency operating in air at a wide temperature range. The challenge is to contact these dissimilar materials without any negative impact on the performance of TEG. Besides providing a good electrical and thermal contact between Bi2Te3 and FeSi2 the junctions have to remain mechanically and chemically stable over long term. A Bi2Te3-SiO2 composite interlayer was used to adjust the different coefficient of thermal expansion (CTE) of FeSi2 (≈ 7·10-6 K-1) and Bi2Te3 (≈ 19·10-6 K-1). Due to low chemical stability of the Bi2Te3/FeSi2 contact at elevated temperatures (1000 h @ 300°C) a contacting material (diffusion barrier) based on Ni, Zn, Ti, and ZnTe was tested. Some contacts show excellent chemical and mechanical stability, though the electrical properties of the contacts do not meet the requirements (e.g. ZnTe is a wide gap semiconductor with high electrical resistivity). According to very recent studies at the Zn-based diffusion barriers a very thin layer of undoped ZnTe growing at the Bi2Te3/Zn interface causes the deterioration of the contact resistance. Ideas solving this problem are outlined and discussed.

scholarly journals Biophysical analysis of Plasmodium falciparum Hsp70-Hsp90 organizing protein (PfHop) reveals a monomer that is characterised by folded segments connected by flexible linkers

2019 ◽  
Author(s):  
Stanley Makumire ◽  
Tawanda Zininga ◽  
Juha Vahokoski ◽  
Inari Kursula ◽  
Addmore Shonhai
Keyword(s):  
Plasmodium Falciparum ◽  
Elevated Temperatures ◽  
Hsp 70 ◽  
X Ray ◽  
X Ray Scattering ◽  
Biophysical Analysis ◽  
Functional Complex ◽  
Inducible Protein ◽  
Tpr Domain

AbstractPlasmodium falciparum causes the most lethal form of malaria. The cooperation of heat shock protein (Hsp) 70 and 90 is important for folding of a select number of cellular proteins that are crucial for cyto-protection and development of the parasites. Hsp70 and Hsp90 are brought into a functional complex that allows substrate exchange by stress inducible protein 1 (STI1), also known as Hsp70-Hsp90 organizing protein (Hop). P. falciparum Hop (PfHop) co-localises and occurs in complex with the parasite cytosolic chaperones, PfHsp70-1 and PfHsp90. Here, we characterised the structure of recombinant PfHop using synchrotron radiation circular dichroism (SRCD) and small-angle X-ray scattering. Structurally, PfHop is a monomeric, elongated but folded protein, in agreement with its predicted TPR domain structure. Using SRCD, we established that PfHop is unstable at temperatures higher than 40 °C. This suggests that PfHop is less stable at elevated temperatures compared to its functional partner, PfHsp70-1, that is reportedly stable at temperatures as high as 80 °C. These findings contribute towards our understanding of the role of the Hop-mediated functional partnership between Hsp70 and Hsp90.

scholarly journals Structural Changes of the 21st Century and their Impact on the Gold Price

2019 ◽  
Vol 11 (3(J)) ◽  
pp. 72-83
Author(s):  
Roman Grynberg ◽  
Teresa Kaulihowa ◽  
Fwasa K Singogo
Keyword(s):  
Structural Changes ◽  
Gold Price ◽  
Economic Factors ◽  
Quantitative Easing ◽  
Structural Factors ◽  
Spot Prices ◽  
On Demand ◽  
Gold Market

Beginning in the trough of 2000 and culminating in the peak of 2012, gold prices have exhibited a spectacular and unparalleled increase. Based on annual averages, the price of gold did not decrease at all over this 12 year period. The paper considers the various factors that have shaped the surge of gold spot prices over the last two decades using quarterly data. The analysis considers the role of structural changes such as China’s liberalization of the domestic gold market post-2003 and its impact on demand as well as other important economic factors such as risk, the role of quantitative easing and other fundamental factors in the gold market. The study investigates which of the macroeconomic and structural factors are responsible for the long term bullish trend in the gold price, of which China, global economic risk assessments along with quantitative easing have been crucial to understanding the almost uninterrupted price increase over the period.

On the Mechanism of Oxidation Resistance of W-Cr-Pd Alloys

2018 ◽  
Vol 383 ◽  
pp. 133-141
Author(s):  
Alon Kafri ◽  
Alexandra Makonovitsky ◽  
Roni Z. Shneck
Keyword(s):  
Free Surface ◽  
Grain Boundaries ◽  
Oxidation Resistance ◽  
Intermediate Layer ◽  
Elevated Temperatures ◽  
Fast Diffusion ◽  
External Layer ◽  
Present Contribution ◽  
Mechanism Of Oxidation

While studying activation sintering of tungsten, Evans [5] and Ito and Furusawa [6] revealed that W-Cr-Pd alloys exhibit unexpected oxidation resistance at elevated temperatures. The role of palladium in stimulating oxidation resistance in W-Cr alloys is the main aim of the present contribution. As previously observed, at 800 °C these alloys form a relatively dense protective scale that consists of an inner layer of Cr2O3, an intermediate layer of Cr2WO6 and an external layer of WO3. At 1200 °C only Cr2WO6 layer is found, since the Cr2O3 and WO3 evaporate. To determine the role of paladium, W and W-Pd alloys were coated with Cr layers and undergone diffusion experiments. An extraordinary affinity between the Cr and Pd was revealed, manifested by extremely fast inward diffusion of Cr along grain boundaries. In a second experiment the dissolution of Cr into W grains at 1300°C was followed and found to take place preferentially along grain boundaries. These observations assess that the Pd segregated at grain boundaries provides fast diffusion channels for Cr to the free surface and it imparts the significant improvement of the oxidation resistance of W alloys, as suggested by Lee and Simkovitz [10-12].

The Effect of Long-Term Heating on Thermal Stability of Ultra-Fine Grained Titanium Alloy VT8M-1 Processed by Rotary Swaging

2021 ◽  
Vol 1016 ◽  
pp. 1398-1403
Author(s):  
Andrey Stotskiy ◽  
Tatyana Vitalyevna Yakovleva ◽  
Grigory Dyakonov ◽  
Alexander V. Polyakov ◽  
Irina Semenova
Keyword(s):  
Mechanical Properties ◽  
Thermal Stability ◽  
Ti Alloy ◽  
Fine Grained ◽  
Rotary Swaging ◽  
Ultrafine Grained ◽  
High Level ◽  
Thermal Stability Of

The paper focuses on the analysis of microstructure and mechanical properties of the Ti alloy VT8М-1 (Ti-5.3Al-4.0Mo-1.2Zr-1.3Sn-0.2Si) in an ultrafine-grained (UFG) state subjected to a long-term annealing at a service temperature of (≤ 450°С). A rotary swaging (RS) was used to process an UFG state in the material. The precipitation of disperse silicides of S2 was observed after the deformation by RS. It has been shown that the UFG alloy retained its high level of thermal stability and enhanced mechanical properties after long-term annealing up to 500 hours. The role of disperse silicides in both strengthening and stability of mechanical properties in the alloy after long-term annealing is discussed.

Sign in / Sign up

Export Citation Format

Share Document