scholarly journals TEM Observation of Loops Decorating Dislocations and Resulting Source Hardening of Neutron-Irradiated Fe-Cr Alloys

Metals ◽  
2020 ◽  
Vol 10 (1) ◽  
pp. 147
Author(s):  
Frank Bergner ◽  
Mercedes Hernández-Mayoral ◽  
Cornelia Heintze ◽  
Milan J. Konstantinović ◽  
Lorenzo Malerba ◽  
...  
Keyword(s):  
Dislocation Slip ◽  
Yield Drop ◽  
Irradiation Hardening ◽  
Hardening Model ◽  
Cr Content ◽  
Random Array ◽  
Quantitative Understanding ◽  
Neutron Exposure ◽  
Dislocation Sources ◽  
Open Issues

Several open issues remain concerning the quantitative understanding of irradiation hardening in high-Cr steels. One of these issues is addressed here by correlating yield points that are observed in stress-strain curves with dislocation decoration observed by TEM for neutron-irradiated Fe-Cr alloys. It is found that both higher neutron exposure and higher Cr content promote irradiation-induced loops to arrange preferentially along dislocation lines. Consequently, the activation of dislocation sources requires unlocking from the decorating loops, thus resulting in a yield drop. This process is considered within the source hardening model as opposed to the dispersed barrier hardening model, the latter aimed to describe dislocation slip through a random array of obstacles. Microstructure-informed estimates of the unlocking stress are compared with measured values of the upper yield stress. As functions of neutron exposure, a cross-over from the dominance of dispersed-barrier hardening accompanied by smooth elastic-plastic transitions to the dominance of source hardening accompanied by yield drops is observed for Fe-9% Cr and Fe-12% Cr.

Anomalous Strengthening Mechanism in NbSi2-Based Silicide Single Crystals

2000 ◽  
Vol 646 ◽  
Author(s):  
Yukichi Umakoshi ◽  
Takayoshi Nakano ◽  
Masafumi Azuma
Keyword(s):  
Single Crystals ◽  
Fracture Strain ◽  
Stress Amplitude ◽  
Strengthening Mechanism ◽  
Yield Drop ◽  
Dynamic Aging ◽  
Strain Change ◽  
Solute Atoms ◽  
Dislocation Sources ◽  
Rapid Drop

ABSTRACTAnomalous strengthening behavior of NbSi2-based silicide single crystals with C40 structure was examined focusing on the effect of substitutional alloying elements and the formation of a solute dragging atmosphere. After pre-straining to 1% at temperatures between 600 and 1600°C, single crystals were deformed at 400°C to examine the effects of dislocation sources and segregation of solute atoms around dislocations. The stress amplitude of yield drop was derived by the segregation of solute atoms at the superlattice intrinsic stacking fault (SISF) between two superpartials. Introduction of dislocation sources by pre-straining remarkably improved fracture strain, but the segregation of solute atoms around dislocations during pre-straining at higher temperatures induced a rapid drop of fracture strain. Change in the SISF energy by static and dynamic aging was observed to obtain evidence of segregation of solute atoms at the SISF between two superpartials.

Observations oh Nucleation and Growth of Voids in Nickel

1970 ◽  
Vol 28 ◽  
pp. 414-415
Author(s):  
J. L. Brimhall ◽  
H. E. Kissinger ◽  
B. Mastel
Keyword(s):  
High Purity ◽  
Growth Stage ◽  
Elevated Temperatures ◽  
Early Growth ◽  
Nucleation And Growth ◽  
Pure Nickel ◽  
Different Temperatures ◽  
Total Fluence ◽  
Neutron Exposure ◽  
Growth Of Voids

Some information on the size and density of voids that develop in several high purity metals and alloys during irradiation with neutrons at elevated temperatures has been reported as a function of irradiation parameters. An area of particular interest is the nucleation and early growth stage of voids. It is the purpose of this paper to describe the microstructure in high purity nickel after irradiation to a very low but constant neutron exposure at three different temperatures.Annealed specimens of 99-997% pure nickel in the form of foils 75μ thick were irradiated in a capsule to a total fluence of 2.2 × 1019 n/cm2 (E > 1.0 MeV). The capsule consisted of three temperature zones maintained by heaters and monitored by thermocouples at 350, 400, and 450°C, respectively. The temperature was automatically dropped to 60°C while the reactor was down.

DISLOCATION RELAXATION IN A RANDOM ARRAY OF SOLUTES

1981 ◽  
Vol 42 (C5) ◽  
pp. C5-319-C5-324 ◽  
Author(s):  
I. G. Ritchie ◽  
A. Atrens ◽  
C. B. So ◽  
K. W. Sprungmann
Keyword(s):  
Random Array

Highlights in the history of X-ray topography1

1995 ◽  
Vol 210 (6) ◽  
Author(s):  
A. R. Lang
Keyword(s):  
Magnetic Domain ◽  
Diffraction Theory ◽  
Dislocation Loops ◽  
X Ray Diffraction ◽  
X Ray ◽  
Domain Structures ◽  
Structure Factors ◽  
History Of ◽  
Dislocation Sources ◽  
Non Destructive

AbstractX-ray topography provides a non-destructive method of mapping point-by-point variations in orientation and reflecting power within crystals. The discovery, made by several workers independently, that in nearly perfect crystals it was possible to detect individual dislocations by X-ray diffraction contrast started an epoch of rapid exploitation of X-ray topography as a new, general method for assessing crystal perfection. Another discovery, that of X-ray Pendellösung, led to important theoretical developments in X-ray diffraction theory and to a new and precise method for measuring structure factors on an absolute scale. Other highlights picked out for mention are studies of Frank-Read dislocation sources, the discovery of long dislocation helices and lines of coaxial dislocation loops in aluminium, of internal magnetic domain structures in Fe-3 wt.% Si, and of stacking faults in silicon and natural diamonds.

Analysis of Voltage Contrast in Secondary Electron Images Using a High-Energy Electron Spectrometer

2019 ◽  
Author(s):  
Natsuko Asano ◽  
Shunsuke Asahina ◽  
Natasha Erdman
Keyword(s):  
Focused Ion Beam ◽  
Ion Beam ◽  
Sample Surface ◽  
High Energy ◽  
Secondary Electrons ◽  
Analysis Technique ◽  
Quantitative Understanding ◽  
Voltage Contrast ◽  
Acceleration Voltage ◽  
Failure Localization

Abstract Voltage contrast (VC) observation using a scanning electron microscope (SEM) or a focused ion beam (FIB) is a common failure analysis technique for semiconductor devices.[1] The VC information allows understanding of failure localization issues. In general, VC images are acquired using secondary electrons (SEs) from a sample surface at an acceleration voltage of 0.8–2.0 kV in SEM. In this study, we aimed to find an optimized electron energy range for VC acquisition using Auger electron spectroscopy (AES) for quantitative understanding.

A Comprehensive Analysis of Image Forensics Techniques: Challenges and future Direction

2019 ◽  
Vol 13 ◽  
Author(s):  
Mohd Dilshad Ansari ◽  
Ekbal Rashid ◽  
S Siva Skandha ◽  
Suneet Kumar Gupta
Keyword(s):  
Image Forensics ◽  
Digital Era ◽  
Current State ◽  
Benchmark Datasets ◽  
Passive Authentication ◽  
Prime Objective ◽  
Future Direction ◽  
Source Of Information ◽  
Research Domain ◽  
Open Issues

Background: image forensics deal with the problem of authentication of pictures or their origins. There are two types of forensics techniques namely active and passive. Passive forgery is also known as blind forensics technique. In passive forgery, copy-move (cloning) image forensics is most common forgery technique. In this approach, an object or region of a picture is copied and positioned somewhere else in the same image. Active method used watermarking to solve picture genuineness problem. It has limitations like human involvement or particularly equipped cameras. To overwhelm these limitations, numerous passive authentication approaches have been developed. Moreover, both approaches do not require any prior information about the picture. Objective: The prime objective of this survey is to provide an inclusive summary as well as recent advancement, challenges and future direction in image forensics. In Today’s digital era the digital pictures and videos are having great impact on our life as well as society, as they became the important source of information. Though earlier it was very difficult to doctor the picture, nowadays digital pictures can be doctored easily with the help of editing tools and internet. These practices make pictures as well as videos genuineness deceptive. Conclusion: This paper presents the current state-of- the-art of passive (cloning) image forensics techniques, challenges and future direction of this research domain. Further, the major open issues in developing a robust cloning image forensics detector with their performance are discussed. Lastly, the available benchmark datasets are also discussed

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