scholarly journals Historical Perspective on Diffraction Line-Profile Analyses for Crystals Containing Defect Clusters

Crystals ◽  
2019 ◽  
Vol 9 (5) ◽  
pp. 257 ◽  
Author(s):  
Bennett C. Larson
Keyword(s):  
Dynamical Theory ◽  
Diffraction Line ◽  
Experimental Investigations ◽  
Size Distributions ◽  
Line Profiles ◽  
Dislocation Loops ◽  
Defect Clusters ◽  
Diffraction Line Profile ◽  
Stacking Fault Tetrahedra ◽  
The 1960S

Deviations of crystal diffraction line profiles from those predicted by the dynamical theory of diffraction for perfect crystals provide a window into the microscopic distributions of defects within non-perfect crystals. This overview provides a perspective on key theoretical, computational, and experimental developments associated with the analysis of diffraction line profiles for crystals containing statistical distributions of point defect clusters, e.g., dislocation loops, precipitates, and stacking fault tetrahedra. Pivotal theoretical developments beginning in the 1940s are recalled and discussed in terms of their impact on the direction of theoretical and experimental investigations of lattice defects in the 1960s, the 1970s, and beyond, as both experimental and computational capabilities advanced. The evolution of experimental measurements and analysis techniques, as stimulated by theoretical and computational progress in understanding the distortion fields surrounding defect clusters, is discussed. In particular, consideration is given to determining dislocation loop densities and separate size distributions for vacancy and interstitial type loops, and to the internal strain and size distributions for coherent precipitates.

The evolution of the microstructure of 600 Mev proton irradiated materials

1990 ◽  
Vol 48 (4) ◽  
pp. 1002-1003
Author(s):  
R. Gotthardt ◽  
A. Horsewell ◽  
F. Paschoud ◽  
S. Proennecke ◽  
M. Victoria
Keyword(s):  
Nuclear Reactions ◽  
Dislocation Loops ◽  
Defect Clusters ◽  
Weak Beam ◽  
Stacking Fault Tetrahedra ◽  
Small Defect ◽  
Sufficient Intensity ◽  
Reactor Materials ◽  
Metallic Impurities ◽  
Beam Technique

Fusion reactor materials will be damaged by an intense field of energetic neutrons. There is no neutron source of sufficient intensity at these energies available at present, so the material properties are being correlated with those obtained in irradiation with other irradiation sorces. Irradiation with 600 MeV protons produces both displacement damage and impurities due to nuclear reactions. Helium and hydrogen are produced as gaseous impurities. Other metallic impurities are also created . The main elements of the microstructure observed after irradiation in the PIREX facility, are described in the following paragraphs.A. Defect clusters at low irradiation doses: In specimens irradiated to very low doses (1021-1024 protons.m-2), so that there is no superimposition of contrast, small defect clusters have been observed by the weak beam technique. Detailed analysis of the visible contrast (>0.5 nm diameter) revealed the presence of stacking fault tetrahedra, dislocation loops and a certain number of unidentified clusters . Typical results in Cu and Au are shown in Fig. 1.

Calculation of diffraction line profiles from specimens with dislocations. A comparison of analytical models with computer simulations

2000 ◽  
Vol 33 (4) ◽  
pp. 1122-1127 ◽  
Author(s):  
J.-D. Kamminga ◽  
R. Delhez
Keyword(s):  
Monte Carlo Simulation ◽  
Profile Analysis ◽  
Diffraction Line ◽  
Analytical Models ◽  
Line Profile Analysis ◽  
Line Profiles ◽  
Diffraction Line Profile ◽  
Analytical Expressions ◽  
Good Agreement ◽  
Made In

A method is presented for the calculation of diffraction line profiles using Monte Carlo simulation. The method is used to calculate diffraction line profiles for specimens with some idealized distributions of dislocations. The results have been compared with analytical expressions available for these special dislocation distributions. This comparison has been used to validate some essential assumptions made in the derivation of the analytical expressions. In general, very good agreement has been found. Thus, the proposed method is shown to be a valuable tool for diffraction line profile analysis.

Lorentz–polarization factor for correction of diffraction-line profiles

1987 ◽  
Vol 20 (3) ◽  
pp. 258-259 ◽  
Author(s):  
W. Yinghua
Keyword(s):  
Line Profile ◽  
Diffraction Line ◽  
Peak Shape ◽  
Line Profiles ◽  
Diffraction Line Profile ◽  
Polarization Factor ◽  
Integrated Intensity

The Lorentz–polarization factor (1 + cos22 θ)/sin2 θ cos θ for the integrated intensity of a diffraction line is different from the Lorentz–polarization factor (1 + cos2 2θ)/sin2 θ for a diffraction-line profile; nevertheless, in most of the literature it is being used to correct diffraction-line profiles. The errors introduced in the peak shape and position by use of the Lorentz–polarization factor (1 + cos2 2θ)/sin2 θ cos θ are discussed.

Characterization of Point Defect Clusters by 2-1/2-D TEM

1975 ◽  
Vol 33 ◽  
pp. 160-161
Author(s):  
B. Mitchell ◽  
W. L. Bell
Keyword(s):  
Point Defect ◽  
Structural Defects ◽  
Size Distributions ◽  
Dislocation Loops ◽  
Number Density ◽  
Crystalline Materials ◽  
Defect Clusters ◽  
Black Spots ◽  
Point Defect Clusters

Many of the TEM studies of radiation damage in crystalline materials have been directed toward illucidating the nature, number density, and size distributions of the primary structural defects resulting from the displacement of atoms from their normal lattice sites, i.e., "black spots." The "black spots" have been identified as either nonresolvable dislocation loops or planar clusters of self interstitials or vacancies by TEM techniques and diffraction contrast theories that are described in the book by Hirsch, et al. and the reviews by Ruhle and Eyre. An indispensable part of the studies of point defect clusters is the identification of their character (vacancy or interstitial).

Effect of a crystallite size distribution on X-ray diffraction line profiles and whole-powder-pattern fitting

2000 ◽  
Vol 33 (3) ◽  
pp. 964-974 ◽  
Author(s):  
J. I. Langford ◽  
D. Louër ◽  
P. Scardi
Keyword(s):  
Crystallite Size ◽  
Line Profile ◽  
Profile Analysis ◽  
Diffraction Line ◽  
Powder Pattern ◽  
Line Profile Analysis ◽  
Line Profiles ◽  
Diffraction Line Profile ◽  
Transmission Electron ◽  
Using Data

A distribution of crystallite size reduces the width of a powder diffraction line profile, relative to that for a single crystallite, and lengthens its tails. It is shown that estimates of size from the integral breadth or Fourier methods differ from the arithmetic mean of the distribution by an amount which depends on its dispersion. It is also shown that the form of `size' line profiles for a unimodal distribution is generally not Lorentzian. A powder pattern can be simulated for a given distribution of sizes, if it is assumed that on average the crystallites have a regular shape, and this can then be compared with experimental data to give refined parameters defining the distribution. Unlike `traditional' methods of line-profile analysis, this entirely physical approach can be applied to powder patterns with severe overlap of reflections, as is demonstrated by using data for nanocrystalline ceria. The procedure is compared with alternative powder-pattern fitting methods, by using pseudo-Voigt and Pearson VII functions to model individual line profiles, and with transmission electron microscopy (TEM) data.

Diffuse X-Ray Scattering for the Study of Defects in Silicon

1980 ◽  
Vol 2 ◽  
Author(s):  
BC Larson ◽  
JF Barhorst
Keyword(s):  
Diffuse Scattering ◽  
Analytical Models ◽  
Size Distributions ◽  
Dislocation Loops ◽  
Crystalline Materials ◽  
X Ray ◽  
Analysis Techniques ◽  
Defect Clusters ◽  
X Ray Scattering

ABSTRACTX-ray diffuse scattering can be used to study the size, concentration, and nature of lattice defects and defect clusters in crystalline materials. The availability of analytical models and detailed numerical calculations for the “Huang” diffuse scattering close to Bragg reflections and the “asymptotic” diffuse scattering at somewhat larger distances from Bragg reflections has made it possible to carry out detailed analyses of the intensity and angular distribution of the diffuse scattering in terms of specific defect parameters. Accordingly, diffuse scattering has been used to study point defects, dislocation loops, and precipitates in metals, semiconductors, and insulators and has provided information on defect geometries, size distributions, and concentrations. In this paper, the theoretical framework necessary for the interpretation of the “Huang” and “asymptotic” diffuse scattering from defect clusters is presented and examples of diffuse scattering calculations for defects in silicon are given. Diffuse scattering from clustered defects in silicon is discussed in terms of the type of information available from this scattering and the relative merits of diffuse scattering as an investigative tool for defect clusters. Diffuse scattering analysis techniques for the determination of separate size distributions for vacancy and interstitial dislocation loops in silicon are presented and applied to diffuse scattering measurements on neutron irradiated silicon. Dislocation loop densities and sizes determined in the as-irradiated state and after thermal anneals are compared with electron microscopy results.

Annealing Of Radiation Damage in Tungsten

1970 ◽  
Vol 28 ◽  
pp. 412-413
Author(s):  
Robert C. Rau ◽  
John Moteff
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Radiation Damage ◽  
Thermal Annealing ◽  
Neutron Fluence ◽  
Dislocation Loops ◽  
Defect Clusters ◽  
Polycrystalline Tungsten ◽  
Transmission Electron ◽  
Radiation Induced

Transmission electron microscopy has been used to study the thermal annealing of radiation induced defect clusters in polycrystalline tungsten. Specimens were taken from cylindrical tensile bars which had been irradiated to a fast (E > 1 MeV) neutron fluence of 4.2 × 1019 n/cm2 at 70°C, annealed for one hour at various temperatures in argon, and tensile tested at 240°C in helium. Foils from both the unstressed button heads and the reduced areas near the fracture were examined.Figure 1 shows typical microstructures in button head foils. In the unannealed condition, Fig. 1(a), a dispersion of fine dot clusters was present. Annealing at 435°C, Fig. 1(b), produced an apparent slight decrease in cluster concentration, but annealing at 740°C, Fig. 1(C), resulted in a noticeable densification of the clusters. Finally, annealing at 900°C and 1040°C, Figs. 1(d) and (e), caused a definite decrease in cluster concentration and led to the formation of resolvable dislocation loops.

Contrast From Point Defects in The Infinitesimal Approximation

1980 ◽  
Vol 38 ◽  
pp. 350-351
Author(s):  
L. J. Sykes ◽  
J. J. Hren
Keyword(s):  
Electron Microscope ◽  
Point Defects ◽  
Broad Class ◽  
Stacking Fault ◽  
Crystalline Solids ◽  
Dislocation Loops ◽  
Analytical Expression ◽  
Stacking Fault Tetrahedra

In electron microscope studies of crystalline solids there is a broad class of very small objects which are imaged primarily by strain contrast. Typical examples include: dislocation loops, precipitates, stacking fault tetrahedra and voids. Such objects are very difficult to identify and measure because of the sensitivity of their image to a host of variables and a similarity in their images. A number of attempts have been made to publish contrast rules to help the microscopist sort out certain subclasses of such defects. For example, Ashby and Brown (1963) described semi-quantitative rules to understand small precipitates. Eyre et al. (1979) published a catalog of images for BCC dislocation loops. Katerbau (1976) described an analytical expression to help understand contrast from small defects. There are other publications as well.

Radiation-Induced Precipitation in Ti-6A1-4V

1980 ◽  
Vol 38 ◽  
pp. 154-155
Author(s):  
J. E. O'Neal ◽  
S. M. L. Sastry ◽  
J. W. Davis
Keyword(s):  
Dark Field ◽  
Dislocation Loops ◽  
Beta Titanium Alloy ◽  
Defect Clusters ◽  
Weak Beam ◽  
Beta Titanium ◽  
Small Defect ◽  
Radiation Induced ◽  
Vector Orientation ◽  
Defect Microstructures

The radiation-induced defect structure and nonequilibrium phase precipitation were studied in T1-6A1-4V (an alpha-beta titanium alloy), irradiated at 450 ± 30°C in row VII of the EBR-II to a fluence of 3.0 × 1021 neutrons/cm2 (En > 0.1 MeV). The Irradiation-induced defect microstructures were examined using bright-field, conventional dark-field, and weak-beam dark-field techniques. The nature of dislocations and dislocation loops was determined by standard-contrast experiments under two-beam conditions, and the small defect clusters were identified using the line-of-contrast criterion and black-white vector orientation criterion.

scholarly journals A FEM-Based 2D Model for Simulation and Qualitative Assessment of Shot-Peening Processes

Materials ◽  
2021 ◽  
Vol 14 (11) ◽  
pp. 2784
Author(s):  
Georgios Maliaris ◽  
Christos Gakias ◽  
Michail Malikoutsakis ◽  
Georgios Savaidis
Keyword(s):  
Process Parameters ◽  
Material Properties ◽  
Shot Peening ◽  
Qualitative Assessment ◽  
Experimental Investigations ◽  
Elastoplastic Material ◽  
Size Distributions ◽  
User Friendly ◽  
The Impact ◽  
2D Model

Shot peening is one of the most favored surface treatment processes mostly applied on large-scale engineering components to enhance their fatigue performance. Due to the stochastic nature and the mutual interactions of process parameters and the partially contradictory effects caused on the component’s surface (increase in residual stress, work-hardening, and increase in roughness), there is demand for capable and user-friendly simulation models to support the responsible engineers in developing optimal shot-peening processes. The present paper contains a user-friendly Finite Element Method-based 2D model covering all major process parameters. Its novelty and scientific breakthrough lie in its capability to consider various size distributions and elastoplastic material properties of the shots. Therewith, the model is capable to provide insight into the influence of every individual process parameter and their interactions. Despite certain restrictions arising from its 2D nature, the model can be accurately applied for qualitative or comparative studies and processes’ assessments to select the most promising one(s) for the further experimental investigations. The model is applied to a high-strength steel grade used for automotive leaf springs considering real shot size distributions. The results reveal that the increase in shot velocity and the impact angle increase the extent of the residual stresses but also the surface roughness. The usage of elastoplastic material properties for the shots has been proved crucial to obtain physically reasonable results regarding the component’s behavior.

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