scholarly journals Strain Effects on the Diffusion Properties of Near-Surface Self-Interstitial Atoms and Adatoms in Tungsten

2021 ◽  
Vol 8 ◽  
Author(s):  
Bochuan Sun ◽  
Dimitrios Maroudas ◽  
Brian D. Wirth ◽  
Enrique Martínez
Keyword(s):  
Thermal Stresses ◽  
Large Strain ◽  
Material Surface ◽  
Strain Effect ◽  
Dislocation Loops ◽  
Near Surface ◽  
Plasma Facing Components ◽  
Interstitial Atoms ◽  
Different Strains ◽  
Diffusion Properties

Tungsten (W) is a candidate for the plasma-facing components and divertor in future fusion applications. The material will be subject to a large particle influx (mainly helium and hydrogenic species) that will form bubbles. As bubbles grow, they compress the material, adding to thermal stresses, and eject self-interstitial atoms (SIAs—isolated or in clusters) to release internal pressure. These SIAs diffuse towards the surface in large stress/strain fields and on the surface are thought to act as precursors for nanotendril formation (also known as fuzz) that develops on the material surface modifying its morphology. In this work we analyze the effect of strain on the diffusion properties of both SIAs and adatoms. Relying on atomistic simulations, we compute the average time that a SIA created in the center of a tungsten slab takes to reach a (110) surface for different strains and temperatures. This time relates to the SIA diffusivity and allows to compute the activation energy and dipole tensor including surface effects. We observe a large strain effect that significantly modifies the propensity for SIAs to reach the surface and, hence, to cluster to form dislocation loops in the bulk crystal. Strain also alters the diffusivity of the adatom although to a lesser extent. Finally, we report on the resulting surface roughness evolution and its dependence on strain.

scholarly journals Elasto-thermoviscoplastic finite element analyses of cold upsetting and forging processes of S25C steel with dynamic strain aging considered

2021 ◽  
Vol 2047 (1) ◽  
pp. 012001
Author(s):  
S M Ji ◽  
M K Razali ◽  
K H Lee ◽  
W J Chung ◽  
M S Joun
Keyword(s):  
Finite Element ◽  
Flow Stress ◽  
Dynamic Strain Aging ◽  
Strain Aging ◽  
Large Strain ◽  
Flow Behavior ◽  
Cold Forging ◽  
Dynamic Strain ◽  
Strain Effect ◽  
Strain And Strain Rate

Abstract A practical methodology is presented to characterize the thermoviscoplastic flow stress at larger strain over the temperature range of cold metal forming using tensile and compression tests. Its importance is emphasized for non-isothermal finite element (FE) analysis of automatic multi-stage cold forging (AMSCF) process where maximum strain and strain rate exceed around 3.0 and 200/s, respectively. The experimental compressive flow stress is first characterized using traditional bilinear C-m model with high accuracy. It is employed for describing the closed-form function model to extrapolate the experimental flow stress over the experimentally uncovered ranges of state variables. The strain effect on the flow stress is then improved using the experimental tensile flow stress accurately calculated at large strain and room temperature. A complicated flow behavior of S25C characterized by its dynamic strain aging features is expressed by the presented methodology, which is utilized to analyze the test upsetting and AMSCF processes by the elasto-thermoviscoplastic finite element method for revealing the effects of flow stresses on the process.

scholarly journals The Usefulness of Seismic Surveys for Geotechnical Engineering in Karst: Some Practical Examples

Geosciences ◽  
2020 ◽  
Vol 10 (10) ◽  
pp. 406
Author(s):  
Mario Bačić ◽  
Lovorka Librić ◽  
Danijela Jurić Kaćunić ◽  
Meho Saša Kovačević
Keyword(s):  
Large Strain ◽  
Geotechnical Engineering ◽  
Geophysical Methods ◽  
Near Surface ◽  
Distinctive Features ◽  
Seismic Surveys ◽  
Karstic Features ◽  
Engineering Investigation ◽  
Control Campaign

Having in mind uncertainties linked with the nature of rock masses, it is a challenge for geotechnical engineers to characterize them in a credible manner, especially if the rock mass in question is a notoriously complex karst with its distinctive features such as voids and discontinuities. A large range of geophysical methods are useful tools in the characterization efforts and their utilization in karst environments nowadays is a non-negotiable requirement, even though near-surface scattering significantly affects the acquired data. This paper demonstrates the versatile applications of seismic geophysical methods for geotechnical engineering in karst, from mapping of near-surface karstic features to the application of elastic wave velocities in determination of small to large strain stiffness of karst. The highlighted practical examples offer a step forward from the traditional interpretation of seismic surveys, making them a prosperous tool in geotechnical engineering investigation works, design and quality control campaign.

scholarly journals Microstructure Evolution in ZrCx with Different Stoichiometries Irradiated by Four MeV Au Ions

Materials ◽  
2019 ◽  
Vol 12 (22) ◽  
pp. 3768
Author(s):  
Boxin Wei ◽  
Dong Wang ◽  
Yujin Wang ◽  
Haibin Zhang
Keyword(s):  
Radiation Damage ◽  
Microstructure Evolution ◽  
Vacancy Concentration ◽  
Ion Beam ◽  
Grazing Incidence ◽  
Dislocation Loops ◽  
Black Dot ◽  
X Ray Diffraction ◽  
Near Surface ◽  
Transmission Electron

ZrCx ceramics with different stoichiometries were irradiated under a four MeV Au ion beam in doses of 2 × 1016 ions/cm2 at room temperature, corresponding to ~130 dpa. Grazing incidence, X-ray diffraction and transmission electron microscopy were performed to study the radiation damage and microstructure evolution in ZrCx ceramics. With the decrease in C/Zr ratio, the expansion of ZrCx lattice became smaller after irradiation. Some long dislocation lines formed at the near-surface, while, in the area with the greatest damage (depth of ~400 nm), large amounts of dislocation loops formed in ZrC, ZrC0.9 and ZrC0.8. With the increase in carbon vacancy concentration, the size of the dislocation loops gradually decreased. Few dislocation loops were found in ZrC0.7 after irradiation, and only black-dot defects were found in the area with the greatest damage. For the non-stoichiometric ZrCx, with the increase of the intrinsic vacancies, the number of C interstitials caused by irradiation decreased, and the recombination barrier of C Frenkel pairs reduced. The above factors will reduce the total number of C interstitials after cascade cooling, suppressing the formation and growth of dislocation loops, which is significant for the enhancement of the tolerance of radiation damage.

scholarly journals Analyzing Near-Surface Regions of Hydrophobic and Long-Term Weathered Natural Stones at Microscopic Scale

Heritage ◽  
2020 ◽  
Vol 3 (2) ◽  
pp. 457-473
Author(s):  
Franziska Braun ◽  
Jeanette Orlowsky ◽  
Stefan Brüggerhoff
Keyword(s):  
Structural Changes ◽  
Color Difference ◽  
Outdoor Exposure ◽  
Material Surface ◽  
Building Structures ◽  
Near Surface ◽  
Visual Appearance ◽  
Microscopic Scale ◽  
Surface Damages

The visual appearance of building structures is an important attribute which reflects the character and identity of a region. Due to the influence of weathering, the surfaces of building stones alter, leading to aesthetic changes of the material surface such as discoloration or darkening. In this study, near-surface regions of weathered Baumberger (BST), Schleeriether (SST), and Obernkirchener Sandstones (OKS) have been analyzed at the microscopic scale in order to investigate the intensity and the extent of visual as well as structural changes and how both can be affected due to the presence of surface treatments with hydrophobing agents. It could be detected that aesthetic changes appeared already after 2 years of outdoor exposure, with the slightest variations on BST surfaces, followed by SST and OKS. The use of hydrophobing agents leads to a reduction in surface darkening in the short term. After long-term weathering, no significant changes are visible, as similar values in total color difference (ΔE*) were measured. Biogenic growth and the formation of black weathering crusts are the main reasons for color alterations in the case of the examined stones. The surface damages occur especially on calcareous (BST) followed by clayey (SST) and quartzitic (OKS) stone surfaces.

The Influence of the Initial Supersaturation of Si Interstitial Atoms on the Relative Thermal Stability of Dislocation Loops in Silicon

2000 ◽  
Vol 610 ◽  
Author(s):  
F. Cristiano ◽  
B. Colombeau ◽  
B. de Mauduit ◽  
F. Giles ◽  
M. Omri ◽  
...  
Keyword(s):  
Relative Stability ◽  
Thermal Evolution ◽  
Dislocation Loops ◽  
Transmission Electron Microscopy Analysis ◽  
Transmission Electron ◽  
Interstitial Atoms ◽  
Electron Microscopy Analysis ◽  
Microscopy Analysis ◽  
Implantation Process ◽  
Formation Energies

AbstractIn this work, we have studied the relative stability of perfect (PDLs) and faulted (FDLs) dislocation loops formed during annealing of preamorphised silicon. In particular, we have investigated the effect of the initial supersaturation of Si interstitial atoms (Si(int)s) created by the implantation process on their thermal evolution. Transmission Electron Microscopy analysis shows that in samples with a low Si interstitial supersaturation, FDLs are the dominant defects while PDLs appear as the most stable defects in highly supersaturated samples. We have calculated the formation energies of both types of dislocation loops and found that, for defects of the same size, FDLs are more energetically stable than PDLs, if their diameter is smaller than 80 nm and viceversa. The application of these calculations to the samples studied in this work indicates that a direct correspondence exists between the formation energy of the two defect families and the number of atoms bound to them. Moreover, we have shown that the relative stability of FDLs and PDLs depends on the initial supersaturation of Si(int)s created during the implantation process.

scholarly journals A Comprehensive Method for Accurate Strain Distribution Measurement of Cell Substrate Subjected to Large Deformation

2018 ◽  
Vol 2018 ◽  
pp. 1-10 ◽  
Author(s):  
Hong He ◽  
Rong Zhou ◽  
Yuanwen Zou ◽  
Xuejin Huang ◽  
Jinchuan Li
Keyword(s):  
Digital Image Correlation ◽  
Large Deformation ◽  
Digital Image ◽  
Strain Distribution ◽  
Large Strain ◽  
Image Correlation ◽  
Cell Substrate ◽  
Substrate Stretching ◽  
Different Strains

Cell mechanical stretching in vitro is a fundamental technique commonly used in cardiovascular mechanobiology research. Accordingly, it is crucial to measure the accurate strain field of cell substrate under different strains. Digital image correlation (DIC) is a widely used measurement technique, which is able to obtain the accurate displacement and strain distribution. However, the traditional DIC algorithm used in digital image correlation engine (DICe) cannot obtain accurate result when utilized in large strain measurement. In this paper, an improved method aiming to acquire accurate strain distribution of substrate in large deformation was proposed, to evaluate the effect and accuracy, based on numerical experiments. The results showed that this method was effective and highly accurate. Then, we carried out uniaxial substrate stretching experiments and applied our method to measure strain distribution of the substrate. The proposed method could obtain accurate strain distribution of substrate film during large stretching, which would allow researchers to adequately describe the response of cells to different strains of substrate.

scholarly journals Effects of the Surface on Displacement Cascades Produced by Heavy-Ion Irradiation of Ni3Al and Cu3Au

1996 ◽  
Vol 439 ◽  
Author(s):  
S. Müller ◽  
M. L. Jenkins ◽  
C. Abromeit ◽  
H. Wollenberger
Keyword(s):  
Ion Irradiation ◽  
Incident Angle ◽  
Ion Beam ◽  
Heavy Ion ◽  
Small Population ◽  
Dislocation Loops ◽  
Near Surface ◽  
Ion Energy ◽  
Heavy Ion Irradiation ◽  
Transmission Electron

AbstractStereo transmission electron microscopy has been used to characterise the distribution in depth of disordered zones and associated dislocation loops in the ordered alloys Ni3Al and Cu3Au after heavy ion irradiation, most extensively for Ni3Al irradiated with 50 keV Ta+ ions at a temperature of 573 K. The Cu3Au specimen was irradiated with 50 keV Ni+ ions at an incident angle of 45° at a temperature of 373 K. In Ni3Al the defect yield, i.e. the probability for a disordered zone to contain a loop was found to be strongly dependent on the depth of the zone in the foil, varying from about 0.7 for near-surface zones to about 0.2 in the bulk. The sizes and shapes of disordered zones were only weakly dependent on depth, except for a small population of zones very near the surface which were strongly elongated parallel to the incident ion beam. In Cu3Au the surface had a smaller but still significant effect on the defect yield. The dependence of the tranverse disordered zone diameter d on ion energy E for Ta+ irradiation of NiA was found to follow a relationship d = k1, E1/α with k, = 2.4 ± 0.4 and α = 3.3 ± 0.4. A similar relationship with the same value of α is valid for a wide variety of incident ion/target combinations found in the literature.

Microstructural Developments During Implantation of Metals

1983 ◽  
Vol 27 ◽  
Author(s):  
D. I. Potter ◽  
M. Ahmed ◽  
S. Lamond
Keyword(s):  
Chemical Composition ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
Auger Spectroscopy ◽  
Phase Region ◽  
Dislocation Loops ◽  
Two Phase ◽  
Model Calculations ◽  
Near Surface ◽  
Composition Profiles

ABSTRACTThe chemical and microstructural changes caused by the direct implantation of solutes into metals are examined. The particular case involving Al+-ion implantation into nickel is treated in detail. Chemical composition profiles measured using Auger spectroscopy and Rutherford backscattering, and average near-surface chemical composition measured using an analytical electron microscope, are compared with model calculations. The microstructures that develop during implantation are investigated using transmission electron microscopy. For low fluences implanted near room temperature, these microstructures contain dislocations and dislocation loops. Dislocation loops, dislocations, and voids result from implantations at temperatures near 500°C. Higher fluences at these elevated temperatures produce precipitates when the composition of implanted solute lies in a two-phase region of the phase diagram. Implanted concentrations corresponding to intermetallic compounds produce continuous layers of these compounds. Room temperature, as compared to elevated temperature, implantation may produce the same phases at the appropriate concentrations, e.g. β'-NiAl, or different phases, depending on the relative stability of the phases involved.

Strain Rate and Test Temperature Dependence on the Flow Properties of La2O3-Doped Tungsten

2008 ◽  
Vol 59 ◽  
pp. 319-325 ◽  
Author(s):  
I. Uytdenhouwen ◽  
R. Chaouadi ◽  
Jochen Linke ◽  
V. Massaut ◽  
G. Van Oost
Keyword(s):  
Strain Rate ◽  
Thermal Stresses ◽  
Large Strain ◽  
Oxide Dispersion Strengthened ◽  
Recrystallization Temperature ◽  
Flow Properties ◽  
Strain Rate Effects ◽  
Rate Effects ◽  
Subsurface Layers ◽  
Tungsten Material

Tungsten and tungsten alloys are promising metals as protective materials for the armour in future fusion reactors. These metals exhibit the highest melting point, superior thermo-mechanical properties, low erosion and moderate neutron activation properties. The main drawback is their intrinsic brittleness at room temperature and their low recrystallization temperature. During thermal shock events in ITER, tungsten materials will exhibit various crack formations and failure mechanisms. The extensive heat loads on the surface of the material will create high thermal stresses, huge temperature rises and therefore large strain rates in the subsurface layers. This paper deals with the flow properties combining both temperature and strain rate effects of a lanthanum oxide dispersion strengthened tungsten material and the influence of grain orientation on its ductility. Promising results were obtained using a yield strength model based on a thermally-activated slip process that rationalizes the data.

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