Dislocation Density Measurements Research Articles

Dislocation Density Measurements from x-ray Diffraction of Austenite and Ferrite Phases in Superduplex UNS S39274

Dislocation Density Measurements from x-ray Diffraction of Austenite and Ferrite Phases in Superduplex UNS S39274

Effect of Dislocation Density on the Dynamic Strength of Aluminium

AbstractThe effects of cold work on dynamic flow strength is studied through measurements of dislocation density and elastic precursor attenuation in shocked aluminium. High-purity aluminium and Al 6082 alloy samples are subjected to up to three passes of rotary swaging, a severe plastic deformation (SPD) technique, in order to produce large variations in starting material conditions. Detailed material characterisation is performed using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) to determine the initial dislocation density, texture, grain boundary density and misorientation distribution. Variations in dynamic strength are studied through the evolution of the elastic precursor amplitude with propagation distance in specimens with thicknesses between 0.2 and 1 mm, shock loaded to impact stresses of about 4.6 GPa. It is shown that dynamic strength decreases with increasing initial dislocation density in both materials, demonstrating rare, quantified measurements of a reversal in the effect of dislocation density on yield strength at strain rates around 10$$^{4}$$ 4 s$$^{-1}$$ - 1 and above.

Evolution of Microstructure During Stress Relieving Heat Treatment of 1S Aluminium

Aluminium and its alloys are extensively used in nuclear research reactors due to its low neutron absorption coefficient, good heat transfer properties, excellent corrosion and oxidation resistance in air and water environment combined with desirable mechanical properties along with considerable radiation stability. The thin walled tubes are normally manufactured through port hole die extrusion route and used in 'O' tempered condition. The thin tubes in 'O' tempered condition are undergone canning operation which may alter the microstructural features to some extent which may affect mechanical properties. The paper describes the extent to which microstructural and subsequently mechanical properties are altered due to the simulated canning process and further requirements of stress relieving heat treatment to restore the microstructural features and mechanical properties. The following studies are carried out with 1S aluminum tube in 'O' tempered state, simulated canning condition and stress relieved at different temperature, - hardness measurement, X ray line profile analysis for dislocation density measurement, tensile properties measurement using ring tensile testing, electron back scattered diffraction (EBSD) analysis for recrystallization fraction determination and changes in texture components. It is found that the canning operation changes dislocation density, micro-strain, coherent domain size which are well reflected in hardness and ring tensile testing. Subsequent stress relieving at 350°C for 2 hrs. leads to improvement of mechanical properties appreciably.

Effect of dynamic strain ageing on flow stress and critical strain for jerky flow in Al-Mg alloys

A comprehensive approach addressing the flow behavior and the critical strain for the initiation of serrations in Al-Mg alloys is developed in the present work. The basic premise of the approach is that the solute atmosphere influences the friction as well as the strain hardening component of the flow stress. The friction effect of the solute cloud is modeled by considering the interplay between the characteristic solute migration time and the dislocation waiting time according to the cross-core diffusion mechanism. The impact on strain hardening is modeled by considering the apparent strengthening of the forest dislocations because of formation of solute aggregates near the vicinity of dislocation junctions. The apparent forest strengthening effect scales as the square root of the ratio of solute concentration in vicinity of the dislocation junctions and the bulk solute concentration. The modified constitutive model is validated against experimental flow curves obtained for strain rates varying over several orders of magnitude. It was observed that the modified constitutive model outperforms the standard constitutive model (considers only the friction effect of solute atmosphere) in predicting the flow curves in the dynamic strain aging domain. Furthermore, the modified constitutive model also accurately predicts the critical strain for the initiation of the jerky flow in both the normal and inverse regimes of the critical strain versus strain rate curve. Additional validation of the modified constitutive model is provided by dislocation character and density measurements via X-ray diffractograms, dislocation structure investigation via transmission electron microscopy along with fracture surface analysis.

Investigating Influential Parameters for High-Purity Germanium Crystal Growth

This paper focuses on the research and development of high-purity germanium (HPGe) crystals for detector fabrication, specifically targeting applications in rare-event physics searches. The primary objective was to produce large-scale germanium crystals weighing >1 kg with a controlled diameter of ∼10 cm and an impurity range of approximately 1010/cm 3. Ensuring structural integrity and excellent crystalline quality requires a thorough assessment of dislocation density, a critical aspect of the crystal development process. Dislocation density measurements play a crucial role in maximizing the sensitivity of HPGe detectors, and our findings confirmed that the dislocation density fell within acceptable ranges for detector fabrication. Additionally, this paper examines the segregation coefficient of various contaminants during the crystal development process. Comprehensive analysis of impurity segregation is essential for reducing contaminant quantities in the crystal lattice and customizing purification processes. This, in turn, minimizes undesired background noise, enhancing signal-to-noise ratios for rare-event physics searches and overall detector performance. The investigation included the segregation coefficients of three major acceptors and one donor in crystals grown at the University of South Dakota, providing valuable insights for optimizing crystal purity and detector efficiency.

A large strain thermoplasticity model including recovery, recrystallisation and grain size effects

AbstractIn manufacturing, thermomechanical processes such as static annealing and hot working are commonly used to tailor the microstructure of metals to achieve favourable macroscopic material properties that meet specific application requirements. To improve sequential manufacturing processes and to accurately predict the microstructural changes of the material along the process chain, physically motivated constitutive models are required that simultaneously account for the effects of recovery and recrystallisation, as well as grain size dependencies. To this end, Cho et al. [Int. J. Plasticity 112, 123–157 (2019)] proposed a macroscopic hypo‐elasticity based large strain thermoplasticity model that aims at the unification of the effects of static and dynamic recovery and recrystallisation, as well as grain growth and refinement. In the present contribution, the hypo‐elasticity based large strain recrystallisation formulation proposed by Cho et al. is transferred to a hyper‐elasticity based large strain thermoplasticity framework to overcome the limitations typically accompanied with hypo‐elasticity based formulations. For this purpose, an isotropic temperature dependent hyper‐elastic Hencky type formulation defined in logarithmic strains is combined with a temperature dependent von Mises yield criterion. The recrystallisation modelling approach by Cho et al. is adopted, assuming a non‐associated temperature dependent proportional hardening rate in the form of an Armstrong‐Frederick type hardening minus recovery format, wherein the proportional hardening related internal variable is interpreted as a measure of dislocation density. It is shown that the hyper‐elasticity based format results in a thermodynamical consistency condition that effectively constrains the physically motivated evolutions of recrystallised volume fraction and average grain size. To investigate the capability of the model to predict the material response of unified recrystallisation thermodynamically consistently, representative thermomechanical sequential loading conditions including static annealing and hot working are studied.

A multi-method approach to the study of hydrogen trapping in a maraging stainless steel: the impact of B2-NiAl precipitates and austenite

The trapping behavior of hydrogen in a Fe-Cr-Ni-Al-Mo alloy (PH13–8Mo martensitic stainless steel) was investigated. Three different metallurgical states of the same alloy were obtained by heat treatment in an attempt to separate the impact of different microstructural features on the hydrogen trapping behavior. Microstructure analysis including dislocation density measurements and characterization of B2-NiAl precipitates and reverted austenite was conducted, using mainly X-ray Diffraction and Transmission Electron Microscopy. From electrochemical permeation conducted under varying hydrogen fugacity, the trapping characteristics (binding energy, trap density) of the three metallurgical states studied were first determined using the analytical one trap model of Kumnick and Johnson. Another more sophisticated numerical model was then developed in order to introduce two different types of traps. This model was used to simulate the permeation curves and the trapping characteristics were identified using an inverse approach. In a separate approach, Thermal Desorption Spectroscopy was also used to determine the trapping energies and the amount of hydrogen stored in different traps. Combination of these different experimental and modelling approaches have produced consistent results. It is shown that low-misfit coherent B2-NiAl precipitates have a very limited trapping capability. The high dislocation density, including dislocation walls (martensite lath boundaries), significantly traps hydrogen, at an intermediate energy of about 35 kJ/mol. Filmy reverted austenite has a double impact: hydrogen is trapped both at the martensite-austenite interfaces (∼35 kJ/mol) and in the austenite bulk (∼20 kJ/mol).

A robust phenomenological modeling framework based on cross-slip propensity factor for capturing the effect of dynamic strain aging on work hardening behavior of an Al-Mg alloy

In the present work, a new modeling framework for analyzing flow behavior of Al-Mg alloys is proposed by considering both direct and indirect effect of solutes on flow stress. While direct effect addresses the increased slip resistance due to dynamic strain aging (DSA), the indirect effect represents the role of solutes on cross-slip probability. This affects the dislocation annihilation propensity and consequently the work hardening behavior. The dislocation density evolution equation is suitably modified by including a factor based on activation volume and DSA-induced strengthening (σdsa) to account for the effect of solutes on dislocation annihilation propensity and develop a new phenomenological modeling framework for predicting flow curves spanning over a wide range of strain rate (0.00002–0.2 s−1). The proposed modeling framework is shown to be performing better than the existing models which consider only the direct effect of solutes on flow stress. Experimental validation of the proposed concept is shown via dislocation density measurements using X-ray line profile analysis, dislocation substructure analysis via transmission electron microscopy and fractography studies. The new modeling framework is also extended to predict flow curves of several Al-Mg alloys with varying Mg concentration to establish the robustness of the proposed concept.

Quantifying X-ray diffractometer precision for measurement of dislocation density and the evolution of defect structures during solidification of additive manufacturing powders

In this work, the Phillips PW 3020 X’Pert Diffractometer and PANalytical X’Pert Pro MPD X-ray Diffractometer were used to perform in-situ monitoring of quenched microstructures to define the defect evolution of Inconel 718 additive manufacturing powder. Dislocation density analysis based on X-ray Diffraction (XRD) measurement is sensitive to XRD peak broadening. The X-ray line profile is affected by the instrumental effects of the diffractometer, so quantifying and analyzing XRD instrument performance is important for accurate dislocation density analysis. The average measurement bias of the Phillips diffractometer was found to be -1.5490·10−3 Å while the precision was found to be 6.1000·10−5 Å. The average measurement bias of the PANalytical diffractometer was found to be -1.7633·10−4 Å while the precision was found to be 7.6917·10−5 Å. The average dislocation density calculated from the data was 3.93·1014 m−2 for the smaller particle size range and 2.58·1014 m−2 for the larger particle size range. The number of diffraction peaks utilized in dislocation density analysis was found to be a more significant factor than the instrumental differences. This work confirmed that differences in defect structure density can be observed across differently sized particles sourced from additive manufacturing powder.

Experimental measurement of dislocation density in metallic materials: A quantitative comparison between measurements techniques (XRD, R-ECCI, HR-EBSD, TEM)

Experimental measurement of dislocation density in metallic materials: A quantitative comparison between measurements techniques (XRD, R-ECCI, HR-EBSD, TEM)

Ultrasonic methods for the detection of near surface fatigue damage

Fatigue zones in a material can be identified using ultrasonic waves, as it has been shown that their propagation speed will reduce when travelling through such a zone. However, as fatigue damage is usually concentrated in a thin near-surface layer, through-thickness measurements result in very small changes of the average propagation speed across the full thickness, which are potentially difficult to reliably correlate to specific fatigue states. In this study, we have completed fatigue state assessments using Rayleigh waves, which travel on the surface of a material, to maximise those changes. We found that the use of Rayleigh waves amplifies the changes in speed, after propagation in the damaged region, by a factor of up to ten. The monotonic nature of the reduction in wave speed was verified against the theory using dislocation density measurements. Finally, a stiffness-reducing finite-element modelling technique, able to capture the effects of fatigue on the time of flight of longitudinal bulk and Rayleigh waves, was also derived and verified against the experimental measurements.

微小部XRDによる湾曲試料のX線ラインプロファイル解析の適用限界

X-ray Line Profile Analysis (XLPA) is a powerful and convenient method to investigate dislocation density, crystallite size and nature (screw or edge) and arrangement of dislocation in a material. However, few studies have been done concerning the application limit of dislocation density measurements for localized regions or curved materials. In this study, X-ray Diffraction measurements of iron powders formed into flat plates and cylinders were performed using the micro-focus method, and XLPA was performed. As a result, it was found that almost the same dislocation density as that of the Bragg-Brentano method could be derived for the flat specimen by micro-focus method, and that the dislocation density of the cylindrical specimen was almost the same as that of the flat specimen up to a radius in 10 mm.

About the automatic measurement of the dislocation density obtained by R-ECCI

A proof of concept of a new method for automatic characterization of the dislocation density from scanning electron microscopy images is presented. A series of backscattered electron images are acquired while the sample is rotated. For each pixel of the region of interest, the variation of the grey-level intensity as a function of the rotation angle, called the intensity profile, is calculated. This profile can be used to determine the nature of each pixel (dislocation, matrix or noise), such that an automatic dislocation density can be determined within the region of interest. The method is well adapted for dislocation densities ranging from 10 12 to 10 14 m −2 . The simulation of a volume containing dislocations enabled the determination of the maximum and minimum densities attainable as well as the theoretical and experimental measurement errors related to the projection of this volume on a two-dimensional image. The theoretical measurement error due to the projection of dislocation on a surface, is 3% for low dislocation densities (10 12 m −2 ) and 20% for higher dislocation densities (10 14 m −2 ). Experimentally, measurement errors are limited by image analysis conditions, which leads to total measurement errors of 15% for 10 12 m −2 and 34% error for 10 14 m −2 . These uncertainties were obtained considering a given analyzed depth value, that could not be experimentally verified. This uncertainty on the depth value leads to large errors bars in the final measurement, which can reach an order of magnitude. • A new method for automatic characterization of the dislocation density by SEM is presented. • The R-ECCI method and clustering are discussed. • The measurement error of the dislocation density measurement by the R-ECCI method and clustering is estimated.

Preparation of high purity germanium single crystal and analysis of dislocation density

High purity germanium detector plays an important role in the field of radiation detection. High purity germanium with 13N purity and dislocation density between 100 ~ 10 000 cm^-2 was successfully prepared through zone melting purification and single crystal growth. In the zone melting experiment, the self-made horizontal zone furnace is used to achieve the purification requirements through 20 ~ 50 times of zone melting in the environment of high-purity hydrogen. The single crystal is grown by Czochralski method along the [100] direction in high-purity hydrogen environment with effective length > 50 mm and effective diameter > 30 mm. The dislocation density measurement adopts the etching method. The acid etching solution is used to etch the crystal (100) surface and the number of the etch pits is counted. The results show that the dislocation densities at 25, 50 and 72 mm from the head of the single crystal are 2 537, 3 425 and 4 075 cm^-2 respectively. These results indicate that the dislocation density before 72 mm meets the requirements for the preparation of high-purity germanium detectors. The research can provide reference for the preparation of high purity germanium single crystal.

Influence of pulse duration on mechanical properties and dislocation density of dry laser peened aluminum alloy using ultrashort pulsed laser-driven shock wave

This study aims to investigate the influence of the pulse duration on the mechanical properties and dislocation density of an aluminum alloy treated using dry laser peening (DLP), which is a laser peening technique that uses ultrashort pulsed laser-driven shock wave to eliminate the need for a sacrificial overlay under atmospheric conditions. The results of the micro-Vickers hardness test, residual stress measurement, and dislocation density measurement demonstrate that over a pulse duration range of 180 fs to 10 ps, the maximum peening effects are achieved with a pulse duration of 1 ps. Moreover, the most significant DLP effects are obtained by choosing a pulse duration that achieves a laser intensity that simultaneously generates the strongest shock pressure, suppresses optical nonlinear effects, and realizes the least thermal effects, which weaken the shock effects. Shock temperature calculations based on thermodynamic equations also suggest that a laser intensity driving a shock pressure less than 80 GPa, as in the case of a pulse duration of 1 ps in this study, maintains the solid state of the material throughout the process, resulting in significant DLP effects.

Measurement of Dislocation Density in SiC Wafers Using Production XRT

X-ray topography (XRT) presents itself as an attractive non-destructive method to replace industry-standard destructive KOH etching used to measure dislocation density. However, a production-line-compatible XRT has to employ a low scan speed in order to work well with automated image analysis, which makes it impractical for a high-volume manufacturing to scan an entire wafer. We introduce the “radial band” approach to sampling the entire wafer’s area with a single-pass 16 mm tall scan band. Such a band spans the entire range of radii and thus captures the typically strong radial dependence of dislocation density over the entire range, while mostly ignoring the typically weak angular dependence of dislocation density and averaging the inevitable noise over the 16 mm band height. The XRT scan time savings for this approach are roughly 15-fold and 20-fold for 150mm and 200mm wafers respectively.

Ultrasonic nonlinear evaluation of tensile plastic damage in Nickel based single crystal superalloy

The tensile interruption tests of Nickel-based single crystal (NBSX) superalloys at room temperature were carried out to artificially introduce controllable levels of plastic damage, and linear and nonlinear ultrasonic nondestructive methods were used to evaluate it. The results indicate that ultrasonic nonlinear parameter β shows hypersensitivity to early tensile plastic damage compared with traditional linear parameters. Transmission electron microscope (TEM) and X-ray diffraction (XRD) measurements of dislocation string length and dislocation density were conducted to calculate the theoretical predicted values of β by ultrasonic nonlinearity dislocation monopole model, and they are in well agreement with experimental results. In addition, the actuation of slip systems and evolution of dislocation configuration were observed under optical microscope (OM) and TEM. From the perspective of element distribution and energy, it is revealed that the plastic deformation mechanism of the NBSX superalloys at room temperature is anti-phase boundary (APB) dislocation pairs shear γ′ phase. The measurement results of macro mechanical properties manifested that accumulative tensile plastic deformation lead to increase of strength and decrease of plasticity.

Experimental Measurement of Dislocation Density in Metallic Materials: A Quantitative Comparison between Measurements Techniques (Xrd, R-Ecci, Hr-Ebsd, Tem)

Experimental Measurement of Dislocation Density in Metallic Materials: A Quantitative Comparison between Measurements Techniques (Xrd, R-Ecci, Hr-Ebsd, Tem)

Architectured lightweight steel composite: evaluation of the effect of geometrical parameters and annealing treatments on deformation behavior

Architectured lightweight steel composites were designed and fabricated through the cold roll bonding (CRB) of stacked steel-aluminum sheet layers. The effects of geometrical parameters including thickness ratio (TR) and the number of constituent layers on bond strength and tensile properties of the composites were evaluated using peeling and tensile tests. It was found that by decreasing the TR of aluminum to steel from 0.5 to 0.2, the bond strength increased in the as-rolled specimen. However, it led to a decrease in the bond strength of the annealed sample by the facilitation of the formation of Fe–Al intermetallics along the interfaces. In order to obtain a more in-depth understanding of deformation behavior at the interface of steel/aluminum layers, strain gradient at these regions was evaluated through the measurement of dislocation density using the XRD analysis. Macrotexture measurement and anisotropy analysis were also carried out to evaluate the formability of the optimized sample. Moreover, it was found that by increasing the number of layers, the bond strength decreased due to the insufficient extrusion of the virgin metals to the interface of the layers. Higher steel/aluminum interfaces as effective microstructural heterogeneities improved the elongation in five-layered and seven-layered composites by arresting the propagating cracks. Employing the concept of laminated composite led to the production of a lightweight architectured steel with density of 5.6 g.cm−3, which can be a promising structural material for automotive applications.

Low cycle fatigue response of differently aged AA6063 alloy: Statistical analysis and microstructural evolution

Understanding the dynamic structural changes during cyclic deformation of Al-alloys is a discipline of great interest to material technologists. The primary objective of this report is to assess the low cycle fatigue (LCF) behaviour of AA6063 alloy in under-aged (UA), peak-aged (PA) and over-aged (OA) states and to understand the energetic aspects of cyclic plastic behaviour in the background of the nature and density of the dislocations. Two parameters Weibull distribution analyses, for the first time, establish that despite inferior monotonic strength, LCF life of UA alloy is twice compared to PA alloy at higher (≥0.5%) strain amplitudes. This corroborates well with the fact that the cumulative dissipated plastic strain energy density (CPSED) values exhibit reverse variation with applied strain amplitude in the case of UA alloy as compared to PA and OA alloys. TEM analyses confirm that strain-induced vacancy-driven dynamic precipitation causes dramatic cyclic hardening in UA alloy resulting in improved fatigue life. One can also evidence this from the fivefold increase in the plastic strain energy dissipation and 2-times increased of post-fatigue hardness. In contrast, fracture surface analyses and XRD-based dislocation density measurements coupled with TEM examinations reveal that the shearing or by-passing of precipitates by the dislocations in the PA or OA alloys, respectively, lead to strain localization and cyclic softening, and consequently, reduce the plastic strain energy dissipation and lower fatigue life. The study provides important guidelines for the development of high strength Al-alloys with improved fatigue performance.