Line Profile Analysis Research Articles

Analysis of the dislocation activity of Mg-Zn-Y alloy using synchrotron radiation under tensile loading.

An understanding of deformation behavior and texture development is crucial for the formability improvement of Mg alloys. X-ray line profile analysis using the convolutional multiple whole profile (CMWP) fitting method allows the experimental determination of dislocation densities separately for different Burgers vectors up to a high deformation degree. A wider use of this technique still requires exploration and testing of various materials. In this regard, the reliability of the CMWP fitting method for Mg-Zn-Y alloys, in terms of the dislocation activity during tensile deformation, was verified in the present study by the combined analysis of electron backscatter diffraction (EBSD) investigation and visco-plastic self-consistent (VPSC) simulation. The predominant activity of non-basal 〈a〉 dislocation slip was revealed by CMWP analysis, and Schmid factor analysis from the EBSD results supported the higher potential of non-basal dislocation slip in comparison with basal 〈a〉 dislocation slip. Moreover, the relative slip activities obtained by the VPSC simulation also show a similar trend to those obtained from the CMWP evaluation.

Effects of intermediate annealing time on texture evolution during multi-pass cold-shear-straining of an Al–Mg–Si–Cu alloy

This study examines the effects of different intermediate annealing times during multi-pass cold-torsion tests on the microstructure in alloys of aluminum, magnesium, silicon, and copper (Al–Mg–Si–Cu). The mean flow stress, when the intermediate annealing time is shorter, increases until sufficient internal strain accumulates and then decreases rapidly. In contrast, the mean flow stress decreases continuously when the IA time is longer. X-ray line profile analysis revealed a rapid decrease in mean flow stress because of the high stored internal energy represented by the dislocation density. In addition, a short annealing time allows the B component to form in the initial stage of multi-pass torsion, and a random texture distribution occurs as the multi-pass torsion stage progresses. In contrast, a long annealing time can dissipate the texture distribution in a low-pass stage (low strain) and decreases the overall deformation resistance, despite the much stronger texture intensity in a high-strain area. Finally, the B texture component is consumed by the A component in the initial stages of the multi-pass cold torsion test. This is attributed to the different orientation relationships of the shear plane in the A and B components, which caused deviations in dislocation density.

Microstructure of Gear Steels Treated by Shot Peening by X-Ray Line Profile Analysis Method

Microstructure of Gear Steels Treated by Shot Peening by X-Ray Line Profile Analysis Method

Characterization of Bismuth Titanate by Line Profile Analysis

Bismuth Titanate (BIT), Bi4Ti3O12, was synthesized using the solid-state reaction process from the oxide mixture of Bi2O3CO3 and TiO2. The characterization analysis of the prepared sample was done by X-ray diffraction technique. The X-ray diffraction data revealed an orthorhombic perovskite phase that was clearly explained. The Scherrer method, modified W-H analysis, and the SSP studies were conducted to figure out the crystallite size and micro strain in Bi4Ti3O12. Morphological studies included SEM and TEM analysis. FTIR spectral investigation supports the M-O coordination of the synthesized Bi4Ti3O12 sample. The phase formation patterns of Bi4Ti3O12 determined by different methods are highly connected.

Modification of the Tensile Performance of an Extruded ZK60 Magnesium Alloy with the Addition of Rare Earth Elements.

The influence of rare earth (RE) elements on the microstructure and mechanical performance of an extruded ZK60 Mg alloy was studied. Two types of RE elements were added to a ZK60 material and then extruded at a ratio of 18:1. The first new alloy contained 2 wt% Y while the second one was produced using 2 wt% Ce-rich mischmetal. The microstructure, the texture, and the dislocation density in a base ZK60 alloy and two materials with RE additives were studied by scanning electron microscopy, electron backscattered diffraction, and X-ray line profile analysis, respectively. It was found that the addition of RE elements caused a finer grain size, the formation of new precipitates, and changes in the initial fiber texture. As a consequence, Y and Ce-rich RE elements increased the strength and reduced the ductility. The addition of these two types of RE elements to the ZK60 alloy decreased the work hardening capacity and the hardening exponent mainly due to grain refinement.

Optical characterization of point defects on internal quantum efficiency in AlGaN quantum wells grown on face-to-face-annealed sputtered AlN templates

The correlation between the internal quantum efficiency (IQE) and the effective diffusion length estimated by the cathodoluminescence intensity line profile near the dark spots, including the effect of non-radiative recombination due to point defects, was experimentally clarified for AlGaN multiple quantum wells (MQWs) on face-to-face annealed (FFA) sputter-deposited AlN templates with different IQEs and similar dislocation densities. The IQEs, which were determined by temperature- and excitation-power-dependent photoluminescence measurements, were independent of the dark spot densities and increased with increasing effective diffusion length (Leff) estimated from the cathodoluminescence line profile analysis. These results suggested that the IQEs of the MQW/FFA samples were governed by the point defect density. The fitting results for the relationship between IQE and Leff and for that between IQE and Cmax explained the experimental results qualitatively.

Statistical properties of fractal type dislocation cell structures

The dislocation microstructure developing during plastic deformation strongly influences the stress-strain properties of crystalline materials. Resent theoretical investigations based on the 2D continuum theory of straight parallel edge dislocations were able to predict a periodic dislocation microstructure. The results obtained, however, can only be considered as a very first step toward the understanding of the origin of dislocation patterning. One of the most challenging problems is the modeling of the formation of the fractal like dislocation microstructure. So, it is crucial to determine the statistical properties of such a structure developing at ideal multiple slip orientation. In the paper, by x-ray line profile analysis and the method of high resolution electron backscatter diffraction (HR-EBSD) a complex experimental characterization of dislocation microstructure developing in uniaxially compressed Cu single crystals is presented. With these methods, the maps of the internal stress, the Nye tensor, and the geometrically necessary dislocation (GND) density were determined at different load levels. It is found from the fractal analysis of the GND maps that the fractal dimension of the cell structure is decreasing with increasing average spatial dislocation density fluctuation. Moreover, it is shown that the evolution of different types of dislocations can be successfully monitored with the HR-EBSD-based technique.

Characterization of motion dependent magnetic field inhomogeneity for DWI in the kidneys

PurposeDiffusion-weighted imaging (DWI) of the abdomen has increased dramatically for both research and clinical purposes. Motion and static field inhomogeneity related challenges limit image quality of abdominopelvic imaging with the most conventional echo-planar imaging (EPI) pulse sequence. While reversed phase encoded imaging is increasingly used to facilitate distortion correction, it typically assumes one motion independent magnetic field distribution. In this study, we describe a more generalized workflow for the case of kidney DWI in which the field inhomogeneity at multiple respiratory phases is mapped and used to correct all images in a multi-contrast DWI series. MethodsIn this HIPAA-compliant and IRB-approved prospective study, 8 volunteers (6 M, ages 28–51) had abdominal imaging performed in a 3 T MRI system (MAGNETOM Prisma; Siemens Healthcare, Erlangen, Germany) with ECG gating. Coronal oblique T2-weighted HASTE images were collected for anatomical reference. Sagittal phase-contrast (PC) MRI images through the left renal artery were collected to determine systolic and diastolic phases. Cardiac triggered oblique coronal DWI were collected at 10 b-values between 0 and 800 s/mm2 and 12 directions. DWI series were distortion corrected using field maps generated by forward and reversed phase encoded b = 0 images collected over the full respiratory cycle and matched by respiratory phase. Morphologic accuracy, intraseries spatial variability, and diffusion tensor imaging (DTI) metrics mean diffusivity (MD) and fractional anisotropy (FA) were compared for results generated with no distortion correction, correction with only one respiratory bin, and correction with multiple respiratory bins across the breathing cycle. ResultsComputed field maps showed significant variation in static field with kidney laterality, region, and respiratory phase. Distortion corrected images showed significantly better registration to morphologic images than uncorrected images; for the left kidney, the multiple bin correction outperformed one bin correction. Line profile analysis showed significantly reduced spatial variation with multiple bins than one bin correction. DTI metrics were mostly similar between correction methods, with some differences observed in MD between uncorrected and corrected datasets. ConclusionsOur results indicate improved morphology of kidney DWI and derived parametric maps as well as reduced variability over the full image series using the motion-resolved distortion correction. This work highlights some morphologic and quantitative metric improvements can be obtained for kidney DWI when distortion correction is performed in a respiratory-resolved manner.

X-ray diffraction line profile analysis for the detection of the propensity to sensitize

Prior studies have revealed that the sensitization kinetics of 5xxx-series Al-Mg alloys are responsive to the dislocation content, with lower dislocation densities leading to higher rates of sensitization. In this work, X-ray line profile analysis (LPA) was employed to non-destructively assess the dislocation density in 5083 and 5456 alloys samples in various tempers and thermomechanical processing states. Using a conventional laboratory powder diffractometer with a Cu-Kα sealed tube source, it is shown that the approach has the ability to discriminate between samples of disparate tempers (H131, H116, and solutionized and water quenched). Destructive electron backscattered diffraction (EBSD) measurements on select samples confirm the variations, from the perspective of geometrically necessary dislocation density. Experiments were also performed using softer X-rays generated using a Cr Kα sealed tube source, which would render the approach more portable, due to lower shielding requirements. Unfortunately, Cr radiation was not successful due to the limited number of accessible diffraction peaks. Using the dislocations densities measured using LPA together with an established constitutive model permits accurate prediction of the mechanical strength of the alloys of the above disparate tempers. However, the technique does not appear capable of discriminating between samples within a given temper (e.g., H116). Use of a more highly monochromatic X-ray source could render the technique useful for a comprehensive structural health monitoring system for 5xxx alloys prone to sensitization.

Fractal characterizations of MeV ion treated CaF2 thin films.

We present the morphological evolution and fractal characterizations of CaF2 thin-film surfaces modified by bombardment with 100 MeV Au+8 ions at various fluences. Atomic force microscopy (AFM) combined with line profile and two-dimensional power spectral density (2D-PSD) analysis was utilized to investigate the evolution of surface morphology as a function of fluence. The AFM images were utilized to investigate the relationship between fractal dimension, roughness exponent, lateral correlation length, and ion fluence. The surface erosion owing to sputtering was depicted using Rutherford backscattering spectrometry. The structural characteristics' dependency on fluence was explored with the help of glancing angle x-ray diffraction measurements on virgin and irradiated samples. Tensile stress calculated using a peak shift in the glancing angle x-ray diffractogram showed an increase in tensile stress with fluence that caused the surface to crack after the fracture strength of the surface was crossed. 2D-PSD analysis signified the role of sputtering over surface diffusion for the observed surface modifications. Fractal dimensions first increased and then decreased with ion fluence. The lateral correlation length decreased, while the roughness exponent increased with fluence after the threshold value.

X-ray diffraction line profile analysis of defects in neutron-irradiated austenitic stainless steels at low displacement damage levels

Neutron irradiation-induced microstructural changes in variants of austenitic stainless steels were characterized using the Angle Dispersive X-Ray Diffraction (ADXRD) technique with a synchrotron X-ray source of energy 14.968 keV (wavelength ∼0.82833 Å). SS 304 L(N), SS 316 L(N), and SS 316 materials were neutron-irradiated to low displacement damage levels (1–6.75 dpa) in the Fast Breeder Test Reactor at Kalpakkam at temperatures in the range ∼380 °C-400 °C. The effect of the irradiation-induced defects on X-ray diffraction peak profile parameters such as peak broadening, peak shift, and asymmetry were quantified and related to dislocation density. Peak broadening is found to increase as a function of dpa in most of the cases. Considering the highest dpa sample, lattice contraction has been shown by SS 304 L(N) and SS 316 whereas lattice expansion is exhibited by SS 316 L(N). Asymmetry in peak broadening is found to decrease in case of the highest dpa sample. Ferrite volume percent is seen to have increased as a function of dpa in SS 304 L(N) and SS 316 L(N) but not observed in SS 316. SS 304 L(N) has shown a greater propensity towards the austenite to ferrite transformation and 5 dpa sample has about 18 vol% of α-ferrite. However, in case of 5 dpa SS 316 L(N), ferrite content has increased to ∼4 vol% . The increase in yield strength was also related to the dislocation density amongst all three grades of stainless steel. SS 304 L(N) showed saturation in dislocation density and yield strength around 2 dpa whereas SS 316 L(N) showed linear behaviour up to the highest dpa.

X-ray methods for strain energy evaluation of dislocated crystals

Two X-ray methods are applied to estimate the strain energy of crystals containing dislocations, a simpler method based on the full width at half-maximum (FWHM) of the diffraction peaks, and asymptotic line profile analysis (LPA), which exploits the functional form of the Fourier transform corresponding to small Fourier parameters. It is shown analytically that, in the single-defect approximation, the modified Williamson–Hall (mWH) plot of the FWHMs is linear and the slope of the line is directly related to the strain energy of the dislocation system. Evaluation of the numerically generated peaks for randomly arranged edge dislocation dipoles shows that the method based on the mWH plot gives accurate strain energy, while asymptotic LPA overestimates it by about 50%. The accurate result given by the mWH plot is explained by the long correlation distance associated with the FWHM, which better captures the dislocation arrangement over large distances. By contrast, asymptotic LPA is related to atomic correlations over distances smaller than the mean dislocation–dislocation spacing, where the displacement gradient is mainly determined by the field of single dislocations. Therefore, asymptotic LPA leads to a very accurate dislocation density (with error less than 1%) and the result is independent of the dislocation arrangement. However, these short-range correlations overestimate the outer cut-off radius by one order of magnitude.

X-ray line profile analysis on the deformation microstructure of Al-bearing high-Mn steels

X-ray line profile analysis on the deformation microstructure of Al-bearing high-Mn steels

A study of the rapid rotator ζ Aql: differential surface rotation?

ABSTRACT We report new, extremely precise photopolarimetry of the rapidly-rotating A0 main-sequence star ζ Aql, covering the wavelength range ∼400–900 nm, which reveals a rotationally-induced signal. We model the polarimetry, together with the flux distribution and line profiles, in the framework of Roche geometry with ω-model gravity darkening, to establish the stellar parameters. An additional constraint is provided by TESS photometry, which shows variability with a period, Pphot, of 11.1 h. Modelling based on solid-body surface rotation gives rotation periods, Prot, that are in only marginal agreement with this value. We compute new ester stellar-structure models to predict horizontal surface-velocity fields, which depart from solid-body rotation at only the ∼2 per cent level (consistent with a reasonably strong empirical upper limit on differential rotation derived from the line-profile analysis). These models bring the equatorial rotation period, Prot(e), into agreement with Pphot, without requiring any ‘fine tuning’ (for the Gaia parallax). We confirm that surface abundances are significantly subsolar ([M/H] ≃ −0.5). The star’s basic parameters are established with reasonably good precision: $M = 2.53\pm 0.16\, \mbox{M}_{\odot }$, log (L/L⊙) = 1.72± 0.02, $R_{\rm p}= 2.21\pm 0.02\, \mbox{R}_{\odot }$, Teff = 9693 ± 50 K, $i = 85{^{+5}_{-7}}^\circ$, and ωe/ωc = 0.95 ± 0.02. Comparison with single-star solar-abundance stellar-evolution models incorporating rotational effects shows excellent agreement (but somewhat poorer agreement for models at [M/H] ≃ −0.4).

Competitive strengthening between dislocation slip and twinning in cast-wrought and additively manufactured CrCoNi medium entropy alloys

In situ neutron diffraction experiments have been performed under loading in cast-wrought (CW) and additively manufactured (AM) equiatomic CoCrNi medium-entropy alloys. The diffraction line profile analysis correlated the faulting-embedded crystal structure to the dislocation density, stacking/twin fault probability, and stacking fault energy as a function of strain. The results showed the initial dislocation density of 1.8 × 1013m−2 in CW and 1.3 × 1014m−2 in AM. It significantly increased up to 1.3 × 1015m−2 in CW and 1.7 × 1015m−2 in AM near fracture. The dislocation density contributed to the flow stress of 470 MPa in CW and 600 MPa in AM, respectively. Meanwhile, the twin fault probability of CW (2.7%) was about two times higher than AM (1.3%) and the stacking fault probability showed the similar tendency. The twinning provided strengthening of 360 MPa in CW and 180 MPa in AM. Such a favorable strengthening via deformation twinning in CW and dislocation slip in AM was attributed to the stacking fault energy. It was estimated as 18.6 mJ/m2 in CW and 37.5 mJ/m2 in AM by the strain field of dislocations incorporated model. Dense dislocations, deformation twinning, and atomic-scale stacking structure were examined by using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM).

Formation and Microstructural Evolution of Ferritic ODS Steel Powders during Mechanical Alloying.

Ferritic ODS steel elemental powder compositions with various Zr content (0.3-1.0 wt.%), ground in a Pulverisette 6 planetary ball mill, were extensively studied by X-ray diffraction line profile analysis, microscopic observations, microhardness testing and particle size measurements. A characteristic three-stage process of flattening the soft powders, formation of convoluted lamellae and, finally, formation of nanocrystalline grains was observed. In order to quantify the microstructural properties, expressed mainly in terms of crystallite size and dislocation density, a methodology for detailed and accurate microstructure analysis of nanosized and severely deformed materials was proposed by the Whole Powder Pattern Modelling (WPPM) approach. In the case of the proposed ODS alloy composition, the overlapping of Fe and Cr Bragg reflections makes the microstructure analysis certainly more complicated. The results showed that the microstructure of powders evolved towards the nanocrystalline state consisting of fine (diameter of ~15 nm) and narrowly dispersed domains, with extensive dislocation density exceeding 1016 m-2.

Characterization of Dislocation Structure by Line Profile Analysis Using X-rays and Neutrons

Characterization of Dislocation Structure by Line Profile Analysis Using X-rays and Neutrons

ボールミリングによる純鉄粉末のミクロ構造変化~X線ラインプロファイル解析およびTEM観察~

X-ray Line Profile Analysis (XLPA) is a powerful and convenient method to investigate the dislocation density, crystallite size and nature (screw or edge) and arrangement of dislocation in a material. Microstructural observation by Scanning Transmission Electron Microscope (STEM) and XLPA were performed on low-energy ball milled iron powder. It was found that XLPA can be applied to low-energy and short-time ball milled iron powder. Dislocations were found to be concentrated on the surface of the particles by STEM observation, and XLPA was also evaluated on the surface of the particles.

Investigation of Quantitative Evaluation of Rolling Contact Fatigue Cracks in Rail Steel by X-Ray Diffraction Line Profile Analysis

Investigation of Quantitative Evaluation of Rolling Contact Fatigue Cracks in Rail Steel by X-Ray Diffraction Line Profile Analysis

High-Resolution Three-Axis Neutron Diffractometer for Microstructure Investigations of Polycrystalline Materials

Recently, focusing 3-axis diffractometer set-up equipped with the bent perfect crystal (BPC) monochromator and analyzer which has offered the sensitivity in determination of strains Δd/d < 10−4 in polycrystalline materials, has been introduced. The resolution determined by FWHM of the diffraction profiles is about one order of magnitude higher with respect to that of conventional 2-axis neutron strain/stress scanners. Therefore, the new set-up also offers possibility of line profile analysis for relatively large irradiated gauge volumes and reasonable counting times, because the 3-axis set-up exploits focusing in real and momentum space simultaneously. As it is demonstrated on several samples, the 3-axis diffractometer can be successfully used in the strain/stress measurements on samples exposed to an external load, studies of diffraction profile affected by plastic deformation, determination of phases having very close values of the lattice spacings etc. The analysis is carried out by rocking the BPC analyzer and the neutron signal is registered by a point detector.