SEARCH · Engineering Papers

Results for “deformation”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 325 records · Page 18

All sources NASA NTRS DOE OSTI

DOE OSTI2023

Multiscale Imaging of Nuclear Deformation at the Electron-Ion Collider

We show within the Color Glass Condensate framework that exclusive vector meson production at high energy is sensitive to the geometric deformation of the target nucleus at multiple length scales. Studying e+U collisions and varying the deformation of the uranium target, we demonstrate that larger deformations result in enhanced incoherent vector meson production cross sections. Further, different multipole deformation parameters affect different regions of transverse momentum transfer. Employing JIMWLK evolution to study the Bjorken-x dependence of our results, we find that the ratio of incoherent to coherent cross sections decreases with decreasing x, largely independently of the quadrupole deformation of the target. Comparing results for the same process using 20 Ne targets with 16 O targets, we find that differences in deformation are clearly visible in the incoherent cross section. These findings show that certain observables at the Electron-Ion Collider are very sensitive to nuclear structure. Consequently, deformations need to be taken into account when interpreting experimental results. More importantly, this also means that |t|-differential diffractive vector meson production could become a powerful tool, enabling the most direct measurements of nuclear structure at different length scales, ranging from nuclear deformation at low |t| to nucleon and subnucleon-size scales at higher |t|.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2021

Measurement of Deformation Heterogeneity During Shale Swelling Using Digital Image Correlation

Abstract Rock-fluid interactions in shale formations are one of the main sources of wellbore instability issues and inadequate stimulation performance. For better planning of fracturing operations and optimizing production from these reservoirs, it is important to understand the mechanisms behind these interactions. These issues are especially prevalent in clay-rich shales, such as Tuscaloosa Marine Shale, which is the subject of this study. Conventional techniques to quantify these shale-fluid interactions comprise of measuring swelling in powdered rock grains or measurement of deformation in the whole pieces of the core using a linear variable differential transformer and strain gages. However, the contribution from individual laminae to overall deformation cannot be evaluated using these methods. In this study, we developed an experimental setup to evaluate the spatial deformation in shale during interaction with water using digital image correlation (DIC). Deformation of two shale samples, with 34 wt% to 51 wt% clay content, was studied. White paint was used to generate a random speckle pattern on the specimen and then immersed in deionized water. The deformation process was captured using a digital camera and images were analyzed using DIC to quantify the deformation. The implementation of the DIC technique enables the visualization and quantification of spatial deformation in the specimen during interacting with water. The results show the localization of large strains in select laminations. The results provide a better understanding of shale deformation when interacting with water in comparison to traditional measurements that can provide only an average strain value.

Energy & Fuels↗

DOE OSTI2014

SU-E-J-260: Dose Recomputation Versus Dose Deformation for Stereotactic Body Radiation Therapy in Lung Tumors: A Dosimetric Study

Purpose: To evaluate the dosimetric accuracy between recomputed dose and deformed dose for stereotactic body radiation therapy in lung tumors. Methods: Two non-small-cell lung cancer patients were analyzed in this study, both of whom underwent 4D-CT and breath-hold CT imaging. Treatment planning was performed using the breath-hold CT images for the dose calculation and the 4D-CT images for determining internal target volumes. 4D-CT images were reconstructed with ten breathing amplitude for each patient. Maximum tumor motion was 13 mm for patient 1, and 7 mm for patient 2. The delivered dose was calculated using the 4D-CT images and using the same planning parameters as for the breath-hold CT. The deformed dose was computed by deforming the planning dose using the deformable image registration between each binned CT and the breath-hold CT. Results: For patient 1, the difference between recomputed dose and deformed mean lung dose (MLD) ranged from 11.3%(0.5 Gy) to 1.1%(0.06 Gy), mean tumor dose (MTD) ranged from 0.4%(0.19 Gy) to −1.3%(−0.6 Gy), lung V20 ranged from +0.74% to −0.33%. The differences in all three dosimetric criteria remain relatively invariant to target motion. For patient 2, V20 ranged from +0.42% to −2.41%, MLD ranged from −0.2%(−0.05 Gy) to −10.4%(−2.12 Gy), and MTD ranged from −0.5%(−0.31 Gy) to −5.3%(−3.24 Gy). The difference between recomputed dose and deformed dose shows strong correlation with tumor motion in all three dosimetric measurements. Conclusion: The correlation between dosimetric criteria and tumor motion is patient-specific, depending on the tumor locations, motion pattern, and deformable image registration accuracy. Deformed dose can be a good approximation for recalculated dose when tumor motion is small. This research is supported by Siemens Medical Solutions USA, Inc and Iowa Center for Research By Undergraduates.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2014

Few-view cone-beam CT reconstruction with deformed prior image

Purpose: Prior images can be incorporated into the image reconstruction process to improve the quality of subsequent cone-beam CT (CBCT) images from sparse-view or low-dose projections. The purpose of this work is to develop a deformed prior image-based reconstruction (DPIR) strategy to mitigate the deformation between the prior image and the target image. Methods: The deformed prior image is obtained by a projection-based registration approach. Specifically, the deformation vector fields used to deform the prior image are estimated through iteratively matching the forward projection of the deformed prior image and the measured on-treatment projections. The deformed prior image is then used as the prior image in the standard prior image constrained compressed sensing (PICCS) algorithm. A simulation study on an XCAT phantom and a clinical study on a head-and-neck cancer patient were conducted to evaluate the performance of the proposed DPIR strategy. Results: The deformed prior image matches the geometry of the on-treatment CBCT more closely as compared to the original prior image. Consequently, the performance of the DPIR strategy from few-view projections is improved in comparison to the standard PICCS algorithm, based on both visual inspection and quantitative measures. In the XCAT phantom study using 20 projections, the average root mean squared error is reduced from 14% in PICCS to 10% in DPIR, and the average universal quality index increases from 0.88 in PICCS to 0.92 in DPIR. Conclusions: The present DPIR approach provides a practical solution to the mismatch problem between the prior image and target image, which improves the performance of the original PICCS algorithm for CBCT reconstruction from few-view or low-dose projections.

60 APPLIED LIFE SCIENCES↗

NASA NTRS2004

Associative Flow Rule Used to Include Hydrostatic Stress Effects in Analysis of Strain-Rate-Dependent Deformation of Polymer Matrix Composites

designing reliable composite engine cases that are lighter than the metal cases in current use. The types of polymer matrix composites that are likely to be used in such an application have a deformation response that is nonlinear and that varies with strain rate. The nonlinearity and the strain-rate dependence of the composite response are due primarily to the matrix constituent. Therefore, in developing material models to be used in the design of impact-resistant composite engine cases, the deformation of the polymer matrix must be correctly analyzed. However, unlike in metals, the nonlinear response of polymers depends on the hydrostatic stresses, which must be accounted for within an analytical model. By applying micromechanics techniques along with given fiber properties, one can also determine the effects of the hydrostatic stresses in the polymer on the overall composite deformation response. First efforts to account for the hydrostatic stress effects in the composite deformation applied purely empirical methods that relied on composite-level data. In later efforts, to allow polymer properties to be characterized solely on the basis of polymer data, researchers at the NASA Glenn Research Center developed equations to model the polymers that were based on a non-associative flow rule, and efforts to use these equations to simulate the deformation of representative polymer materials were reasonably successful. However, these equations were found to have difficulty in correctly analyzing the multiaxial stress states found in the polymer matrix constituent of a composite material. To correct these difficulties, and to allow for the accurate simulation of the nonlinear strain-rate-dependent deformation analysis of polymer matrix composites, in the efforts reported here Glenn researchers reformulated the polymer constitutive equations from basic principles using the concept of an associative flow rule. These revised equations were characterized and validated in an experimental program carried out through a university grant with the Ohio State University, wherein tensile and shear deformation data were obtained for a representative polymer for strain rates ranging from quasi-static to high rates of several hundred per second. Tensile deformation data also were obtained over a variety of strain rates and fiber orientation angles for a representative polymer matrix composite composed using the polymer.

Goldberg, Robert K.↗

NASA NTRS2015

Representing Matrix Cracks Through Decomposition of the Deformation Gradient Tensor in Continuum Damage Mechanics Methods

A method is presented to represent the large-deformation kinematics of intraply matrix cracks and delaminations in continuum damage mechanics (CDM) constitutive material models. The method involves the additive decomposition of the deformation gradient tensor into 'crack' and 'bulk material' components. The response of the intact bulk material is represented by a reduced deformation gradient tensor, and the opening of an embedded cohesive interface is represented by a normalized cohesive displacement-jump vector. The rotation of the embedded interface is tracked as the material deforms and as the crack opens. The distribution of the total local deformation between the bulk material and the cohesive interface components is determined by minimizing the difference between the cohesive stress and the bulk material stress projected onto the cohesive interface. The improvements to the accuracy of CDM models that incorporate the presented method over existing approaches are demonstrated for a single element subjected to simple shear deformation and for a finite element model of a unidirectional open-hole tension specimen. The material model is implemented as a VUMAT user subroutine for the Abaqus/Explicit finite element software. The presented deformation gradient decomposition method reduces the artificial load transfer across matrix cracks subjected to large shearing deformations, and avoids the spurious secondary failure modes that often occur in analyses based on conventional progressive damage models.

Leone, Frank A., Jr.↗

DOE OSTI2012

Halos in a deformed relativistic Hartree-Bogoliubov theory in continuum

In this contribution we present some recent results about neutron halos in deformed nuclei. A deformed relativistic Hartree-Bogoliubov theory in continuumhas been developed and the halo phenomenon in deformed weakly bound nuclei is investigated. These weakly bound quantum systems present interesting examples for the study of the interdependence between the deformation of the core and the particles in the halo. Magnesium and neon isotopes are studied and detailed results are presented for the deformed neutron-rich and weakly bound nuclei {sup 42}Mg. The core of this nucleus is prolate, but the halo has a slightly oblate shape. This indicates a decoupling of the halo orbitals from the deformation of the core. The generic conditions for the existence of halos in deformed nuclei and for the occurrence of this decoupling effect are discussed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2016

Workshop on Advancing Experimental Rock Deformation Research: Scientific and Technical Needs

A workshop for the experimental rock deformation community was held in Boston on August 16-19, 2012, following some similar but smaller preliminary meetings. It was sponsored primarily by the NSF, with additional support from the DOE, the SCEC, and in-kind support by the USGS. A white paper summarizing the active discussions at the workshop and the outcomes is available (https://brownbox.brown.edu/download.php?hash=0b854d11). Those attending included practitioners of experimental rock deformation, i.e., those who conduct laboratory experiments, as well as users of the data provided by practitioners, namely field geologists, seismologists, geodynamicists, earthquake modelers, and scientists from the oil and gas industry. A considerable fraction of those attending were early-career scientists. The discussion initially focused on identifying the most important unsolved scientific problems in all of the research areas represented by the users that experiments would help solve. This initial session was followed by wide-ranging discussions of the most critical problems faced by practitioners, particularly by early-career scientists. The discussion also focused on the need for designing and building the next generation of experimental rock deformation equipment required to meet the identified scientific challenges. The workshop participants concluded that creation of an experimental rock deformation community organization is needed to address many of the scientific, technical, and demographic problems faced by this community. A decision was made to hold an organizational meeting of this new organization in San Francisco on December 1-2, 2012, just prior to the Fall Meeting of the AGU. The community has decided to name this new organization “Deformation Experimentation at the Frontier Of Rock and Mineral research” or DEFORM. As of May 1, 2013, 64 institutions have asked to be members of DEFORM.

58 GEOSCIENCES↗

DOE OSTI2016

Deformation mechanisms of nanotwinned Al

The objective of this project is to investigate the role of different types of layer interfaces on the formation of high density stacking fault (SF) in Al in Al/fcc multilayers, and understand the corresponding deformation mechanisms of the films. Stacking faults or twins can be intentionally introduced (via growth) into certain fcc metals with low stacking fault energy (such as Cu, Ag and 330 stainless steels) to achieve high strength, high ductility, superior thermal stability and good electrical conductivity. However it is still a major challenge to synthesize these types of defects into metals with high stacking fault energy, such as Al. Although deformation twins have been observed in some nanocrystalline Al powders by low temperature, high strain rate cryomilling or in Al at the edge of crack tip or indentation (with the assistance of high stress intensity factor), these deformation techniques typically introduce twins sporadically and the control of deformation twin density in Al is still not feasible. This project is designed to test the following hypotheses: (1) Certain type of layer interfaces may assist the formation of SF in Al, (2) Al with high density SF may have deformation mechanisms drastically different from those of coarse-grained Al and nanotwinned Cu. To test these hypotheses, we have performed the following tasks: (i) Investigate the influence of layer interfaces, stresses and deposition parameters on the formation and density of SF in Al. (ii) Understand the role of SF on the deformation behavior of Al. In situ nanoindentation experiments will be performed to probe deformation mechanisms in Al. The major findings related to the formation mechanism of twins and mechanical behavior of nanotwinned metals include the followings: 1) Our studies show that nanotwins can be introduced into metals with high stacking fault energy, in drastic contrast to the general anticipation. 2) We show two strategies that can effectively introduce growth twins in high-stacking-energy metals: use Ag as a template to introduce high density growth twins in epitaxial Al; and the film thickness is important in determination of volume fraction of growth twins. 3) We prove that high density twin boundaries can lead to significant work hardening capability in nanotwinned Al. We have published 13 articles, including Nature Communications, Nano Letters, and two review articles, one in Annual Review of Materials Research; and one in MRS Bulletin. Two postdocs and three graduate students have worked on the project. Two of them have become postdoc at Sandia National Laboratory and Los Alamos National Laboratory. One of the postdoc has become a faculty at a University. One patent has been filed.

36 MATERIALS SCIENCE↗

DOE OSTI2016

Helium release during shale deformation: Experimental validation

This paper describes initial experimental results of helium tracer release monitoring during deformation of shale. Naturally occurring radiogenic 4 He is present in high concentration in most shales. During rock deformation, accumulated helium could be released as fractures are created and new transport pathways are created. We present the results of an experimental study in which confined reservoir shale samples, cored parallel and perpendicular to bedding, which were initially saturated with helium to simulate reservoir conditions, are subjected to triaxial compressive deformation. During the deformation experiment, differential stress, axial, and radial strains are systematically tracked. Release of helium is dynamically measured using a helium mass spectrometer leak detector. Helium released during deformation is observable at the laboratory scale and the release is tightly coupled to the shale deformation. These first measurements of dynamic helium release from rocks undergoing deformation show that helium provides information on the evolution of microstructure as a function of changes in stress and strain.

58 GEOSCIENCES↗

DOE OSTI2018

Stages of Mechanical Alloying in Systems with Different Solubility Cu–Zn and Au–Co in the Case of Cold and Low-Temperature Deformation by Torsion Under Pressure

Methods of X-ray structural analysis and durometry, as well as electron microscopy were used to identify the stages of mechanical alloying in the case of torsion under high quasi-hydrostatic pressure on Bridgman anvils in the Cu–Zn and Au–Co systems that have different mutual solubility and enthalpy of mixing. It was established that decrease in temperature of mechanical alloying from room temperature (cold deformation) to the boiling temperature of liquid nitrogen (80 К, low-temperature deformation) has a considerable impact on mechanical alloying at different processing stages and on characteristics of an alloy synthesized by deformation. In the Cu–Zn system, when the ratio of powder components corresponds to the solid solution of α-brass in equilibrium state, as deformation increased, one observed consecutive change of evolution stages of the powder mix to the state of copper-based solid solution. At the same time, when processing temperature decreases, larger deformation is required to achieve analogous structural changes. In the Au–Co system characterized by absence of solubility at room and lower temperatures, one also observes the stages of powder mix evolution with the increase in deformation. However, complete dissolution occurs in the case of processing at 80 К, while larger deformation is required in the case of increase in mechanical alloying temperature. The paper examines possible mechanisms of solid solution formation in the system of components that are mutually insoluble under equilibrium conditions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2018

Quantitative Studies of Machining-Induced Microstructure Alteration and Plastic Deformation in AISI 316 Stainless Steel Using EBSD

Surface machining can result in a heavily plastic deformed layer in the subsurface. The microstructure alterations and the extent of plastic deformation of a milled 316 austenitic stainless steel were investigated using electron backscatter diffraction (EBSD) technique in this study. The microstructure alteration of the deformed layer was characterized by the generation of grain and subgrain boundaries. The plastic deformation was evaluated by kernel average misorientation (KAM) and grain average misorientation (GAM). The local deformation within grains was assessed by the misorientation from adjacent point (MFAP). The EBSD results indicated gradients of microstructure and plastic deformation along the depth direction. High-angle grain boundaries were generated within the depth of 40 μm, and subgrain boundaries were produced up to the depth of 150 μm. Estimated by KAM and GAM, the plastic strain was about 0.7 at the depth of 25 μm and decreased to 0.1 at the depth of 115 μm The MFAP analysis revealed that the local deformation varied within individual grains. Additionally, the change of micro-hardness along the depth direction showed a strong correlation with KAM and GAM values.

36 MATERIALS SCIENCE↗

DOE OSTI2020

High-energy synchrotron x-ray study of deformation-induced martensitic transformation in a neutron-irradiated Type 316 stainless steel

An unusual tensile deformation behaviour in the form of a propagating band along the sample gauge was observed in two neutron-irradiated 316 stainless steel samples during room-temperature tests, leading to a combination of high strength and high ductility. These bands were not observed in an unirradiated counterpart. With the help of in situ high-energy synchrotron x-ray diffraction, the phase-specific crystal information was tracked at different deformation levels in each sample. Post-irradiation and post-deformation samples were examined using electron microscopy to characterize various microstructural features. All samples displayed a deformation-induced martensitic phase transformation, which was identified as a second strain-hardening mechanism accompanying the dislocation hardening. The deformation-induced martensitic transformation was rationalized by the effect of applied stress on the effective martensite start temperature. The results showed that the irradiation did not alter the dislocation hardening and the martensitic transformation mechanisms, but the increased yield strength in irradiated materials facilitated the localized phase transformation at the onset of plastic deformation, in contrast to the unirradiated material which required pre-straining. The hardening effect of the martensitic transformation reduced the tendency towards necking and mitigated the loss of ductility in the irradiated material by carrying the deformation in the form of a propagating band. Despite the beneficial effect from the martensitic transformation, this study indicates that this mechanism cannot not be activated at typical operating temperatures of nuclear reactors.

36 MATERIALS SCIENCE↗

DOE OSTI2023

Discrete element modeling of granular hopper flow of irregular-shaped deformable particles

Many natural and engineered granular materials have relatively deformable particles. Besides particle size and shape, particle deformability is another salient factor that significantly impacts the material’s flow behavior. Here, in this work, the flow of irregular-shaped deformable particles in a wedge-shaped hopper is investigated using discrete element simulations. A bonded-sphere model is developed to simultaneously capture irregular particle shapes and particle-wise deformations (e.g., compression, deflection, and distortion). Quantitative analysis of the effects of irregular shapes and particle deformations shows that the increase in particle stiffness tends to increase initial packing porosity and decrease the flow rate in the hopper. Rigid particles tend to have clogging issues, whereas deformable particles have less chance to, indicating particle deformation reduces the critical bridging width in the hopper flow. Detailed analysis of stress fields is also conducted to provide insights into the mechanism of particle flow and clogging. Stresses and discharge rates calculated from numerical simulations are compared and show good agreement with Walker’s theory and the extended Beverloo formula. Simulations with various particle shape combinations are also performed and show that the initial packing porosity decreases with an increasing percentage of fibers while the discharge rate has a complex dependency on particle shapes.

09 BIOMASS FUELS↗

DOE OSTI2019

Characterization of localized plastic deformation behaviors associated with dynamic strain aging in pipeline steels using digital image correlation

Localized deformation behavior in X52 and X70 pipeline steels during dynamic strain aging (or DSA, caused by interstitial atom-dislocation interactions during plastic deformation) were systematically assessed using digital image correlation with incremental strain analysis during elevated temperature tensile testing in the range of 25-350 °C. Similar to materials that use substitutional atoms for DSA, deformation band propagation and nucleation behaviors in the steels were directly related to the morphologies of flow curves from the tensile data. Comparisons between the steels and substitutional DSA systems were made. The type of localized deformation behavior was dependent on the temperature and strain rate conditions of the tensile test and the total amount of strain in the sample. Plastic flow was primarily dominated by deformation band propagation and nucleation at relatively low and high temperatures respectively within the DSA regime. It was theorized that the changing serration morphologies and deformation behaviors at different temperature-strain rate conditions were due to relative differences between the mobility of the solute atoms and the velocity of the mobile dislocations throughout the DSA regime. The dislocation density (which increases due to strain hardening during a tensile test) also influenced deformation behavior at relatively low and high strains.

36 MATERIALS SCIENCE↗

DOE OSTI2014

Feasibility of Multimodal Deformable Registration for Head and Neck Tumor Treatment Planning

Purpose: To investigate the feasibility of using deformable registration in clinical practice to fuse MR and CT images of the head and neck for treatment planning. Method and Materials: A state-of-the-art deformable registration algorithm was optimized, evaluated, and compared with rigid registration. The evaluation was based on manually annotated anatomic landmarks and regions of interest in both modalities. We also developed a multiparametric registration approach, which simultaneously aligns T1- and T2-weighted MR sequences to CT. This was evaluated and compared with single-parametric approaches. Results: Our results show that deformable registration yielded a better accuracy than rigid registration, without introducing unrealistic deformations. For deformable registration, an average landmark alignment of approximatively 1.7 mm was obtained. For all the regions of interest excluding the cerebellum and the parotids, deformable registration provided a median modified Hausdorff distance of approximatively 1 mm. Similar accuracies were obtained for the single-parameter and multiparameter approaches. Conclusions: This study demonstrates that deformable registration of head-and-neck CT and MR images is feasible, with overall a significanlty higher accuracy than for rigid registration.

62 RADIOLOGY AND NUCLEAR MEDICINE↗

DOE OSTI2014

Statistical Modeling of CTV Motion and Deformation for IMRT of Early-Stage Rectal Cancer

Purpose: To derive and validate a statistical model of motion and deformation for the clinical target volume (CTV) of early-stage rectal cancer patients. Methods and Materials: For 16 patients, 4 to 5 magnetic resonance images (MRI) were acquired before each fraction was administered. The CTV was delineated on each MRI. Using a leave-one-out methodology, we constructed a population-based principal component analysis (PCA) model of the CTV motion and deformation of 15 patients, and we tested the model on the left-out patient. The modeling error was calculated as the amount of the CTV motion-deformation of the left-out-patient that could not be explained by the PCA model. Next, the PCA model was used to construct a PCA target volume (PCA-TV) by accumulating motion-deformations simulated by the model. A PCA planning target volume (PTV) was generated by expanding the PCA-TV by uniform margins. The PCA-PTV was compared with uniform and nonuniform CTV-to-PTV margins. To allow comparison, geometric margins were determined to ensure adequate coverage, and the volume difference between the PTV and the daily CTV (CTV-to-PTV volume) was calculated. Results: The modeling error ranged from 0.9 ± 0.5 to 2.9 ± 2.1 mm, corresponding to a reduction of the CTV motion-deformation between 6% and 60% (average, 23% ± 11%). The reduction correlated with the magnitude of the CTV motion-deformation (P<.001, R=0.66). The PCA-TV and the CTV required 2-mm and 7-mm uniform margins, respectively. The nonuniform CTV-to-PTV margins were 4 mm in the left, right, inferior, superior, and posterior directions and 8 mm in the anterior direction. Compared to uniform and nonuniform CTV-to-PTV margins, the PCA-based PTV significantly decreased (P<.001) the average CTV-to-PTV volume by 128 ± 20 mL (49% ± 4%) and by 35 ± 6 mL (20% ± 3.5%), respectively. Conclusions: The CTV motion-deformation of a new patient can be explained by a population-based PCA model. A PCA model-generated PTV significantly improved sparing of organs at risk compared to uniform and nonuniform CTV-to-PTV margins.

62 RADIOLOGY AND NUCLEAR MEDICINE↗

DOE OSTI2015

Sessile dislocations by reactions in NiAl severely deformed at room temperature

B2 ordered NiAl is known for its poor room temperature (RT) ductility; failure occurs in a brittle like manner even in ductile single crystals deforming by single slip. In the present study NiAl was severely deformed at RT using the method of high pressure torsion (HPT) enabling the hitherto impossible investigation of multiple slip deformation. Methods of transmission electron microscopy were used to analyze the dislocations formed by the plastic deformation showing that as expected dislocations with Burgers vector a(100) carry the plasticity during HPT deformation at RT. In addition, we observe that they often form a(110) dislocations by dislocation reactions; the a(110) dislocations are considered to be sessile based on calculations found in the literature. It is therefore concluded that the frequently encountered 3D dislocation networks containing sessile a(110) dislocations are pinned and lead to deformation-induced embrittlement. In spite of the severe deformation, the chemical order remains unchanged.

36 MATERIALS SCIENCE↗