| 1. |
- Wadsö, Lars, et al.
(författare)
-
Effect of Alloying with Rare-Earth Metals on the Degradation of Magnesium Alloys Studied Using a Combination of Isothermal Calorimetry and Pressure Measurements
- 2019
-
Ingår i: Magnesium Technology, 2019. - Cham : Springer International Publishing. - 2367-1696 .- 2367-1181. - 9783030057886 ; , s. 121-126
-
Konferensbidrag (refereegranskat)abstract
- With all the versatility in structural performance and recent progress in developing magnesium alloys, their Achilles heel remains to be degradation or corrosion property. While applications in mobility demand corrosion protection by all means, bio-medical applications of Mg alloys require well-controlled degradation rates. Meeting these requirements is only possible through the understanding of phenomena on surface–environment interfaces and the characteristics of Mg alloys affecting them. In this study, in situ monitoring during immersion testing along with 3D-optical and scanning-electron microscopy were used for assessing structure-performance characteristics. The effect of alloying with rare-earth metals on the degradation of magnesium has been studied in three model alloys Mg–0.8Nd, Mg–0.2Zr and Mg–2.0Gd using a combination of isothermal calorimetry and pressure measurements. The combination appears to be a powerful method to study corrosion of magnesium. The degradation of the Gd-containing alloy is approximately 100 times that of the other two alloys studied and is associated with the release of heat and hydrogen gas in large quantities. Differences in the morphology of corrosion products on Mg–0.8Nd and Mg–0.2Zr alloy surfaces can be associated with minute variations in the degradation process detected by the developed method.
|
|
| 2. |
- Ameyama, Kei, et al.
(författare)
-
Harmonic structure, a promising microstructure design
- 2022
-
Ingår i: Materials Research Letters. - : Informa UK Limited. - 2166-3831. ; 10:7, s. 440-471
-
Tidskriftsartikel (refereegranskat)abstract
- The harmonic structure is a recently introduced concept paving the way for engineering metallic materials to achieve excellent mechanical performance. They consist of soft coarse-grained regions (Core) that are three-dimensionally surrounded by a connected network of hard ultra-fine grained regions (Shell). The interaction in these Core–Shell regions produces a synergistic effect, during plastic deformation, leading to superior mechanical properties that are extremely important in practical applications. The current review paper is aimed at providing a critical assessment on this novel concept of microstructure design. It also involves the identification and critical discussion of key issues which deserve additional studies.
|
|
| 3. |
- Backs, Alex, et al.
(författare)
-
Development and first results of a magnetic sample environment for polarized neutron imaging of thin metal sheets
- 2023
-
Ingår i: EPJ Web of Conferences. - 2100-014X. ; 286
-
Tidskriftsartikel (refereegranskat)abstract
- Polarized neutron imaging brings the great advantage of analyzing bulk magnetic properties with good spatial resolution. The technique is based on the interaction of the neutron spin with magnetic samples or free magnetic fields and observing the changes to a spin-polarized neutron beam. The high sensitivity to even small magnetic fields is a benefit in obtaining magnetization information but simultaneously a challenge in instrumentation, since magnetic environments for the polarized neutron beam and for the sample, as well as the fringe field from the magnetic sample itself all affect the measurement and can give rise to unwanted effects. We have used finite element simulations and ray tracing simulations, to design and analyze a magnetic sample environment devised for the measurement of ferromagnetic metal sheets. Here we show an analysis of performance of the experimental setup based on the simulation results and compare them to first experimental results on a grain oriented silicon steel sample.
|
|
| 4. |
- Chatellier, Joséphine, et al.
(författare)
-
Mechanics of accelerated strain hardening in harmonic-structure materials
- 2022
-
Ingår i: 42nd Risø International Symposium on Materials Science: Microstructural variability: Processing, analysis, mechanisms and properties : 5–9 September 2022, Department of Civil and Mechanical Engineering, Technical University of Denmark, Denmark - 5–9 September 2022, Department of Civil and Mechanical Engineering, Technical University of Denmark, Denmark. - : IOP Publishing. - 1757-899X. ; 1249
-
Konferensbidrag (refereegranskat)abstract
- Harmonic-structure (HS) design is one of the most efficient in the family of architected gradient-structure materials recently attracting increasing attention in global material science community due to leading structural performance characteristics. This work studies in situ the mechanics of plastic deformation in HS materials on the example of commercially pure nickel (Ni) during uniaxial tensile loading. It reveals that strain partitioning between ultrafine and coarse grain fractions in HS Ni commences already at early stages of plastic deformation. Slow accumulation of strain in the ultrafine-grain regions leads to the slow consumption of ductility resource, while accelerated accumulation of strain in the coarse-grain regions leads to an accelerated strain hardening. These effects combined with evolving variations of strain tensor components have synergetic effect leading to the unique plastic behaviour and excellent structural performance of HS materials.
|
|
| 5. |
- de Sousa, Theodor, et al.
(författare)
-
Peridynamic modelling of harmonic structured materials under high strain rate deformation
- 2021
-
Konferensbidrag (refereegranskat)abstract
- This paper applies the peridynamic continuum mechanics theory on a new type of material known as harmonic-structured materials. Using the Peridigm software, rapid uniaxial elongation is simulated on a peridynamic model of a thin bimodal harmonic-structured metal sheet. Mechanical wave initiation, propagation, and reflection, as well as fracture initiation and propagation are successfully simulated.
|
|
| 6. |
- Gardonio, Sandra, et al.
(författare)
-
Atomic-level mechanisms of magnesium oxidation
- 2016
-
Ingår i: Magnesium Technology 2016 - Held During TMS 2016: 145th Annual Meeting and Exhibition. - Hoboken, NJ, USA : John Wiley & Sons, Inc.. - 9781119225805 ; 2016-January, s. 73-76
-
Konferensbidrag (refereegranskat)abstract
- Magnesium has been recently becoming an increasingly popular material for various applications. However, excessive chemical reactivity, and oxidation rate in particular, is a major obstruction on the way of Mg to become widely adopted. A significant problem causing the lack of Mg reactivity control is insufficient understanding of mechanisms involved in the oxidation of magnesium surface. Herewith we present the investigation of atomic-level mechanisms of oxidation initiation and propagation in pure Mg. Namely, X-ray photoelectron spectroscopy at synchrotron Elettra was used as a surface sensitive direct method to determine the valence of Mg and O and the valence band states at the early stage of oxide formation over a principal, most densely packed, crystallographic plane (0001) in pure Mg. The mechanisms of oxygen adsorption on magnesium free surface followed by oxidation (i.e. initiation and kinetics of MgO formation) are clarified.
|
|
| 7. |
- Gunde, Miha, et al.
(författare)
-
First-principles characterization of Mg low-index surfaces : Structure, reconstructions, and surface core-level shifts
- 2019
-
Ingår i: Physical Review B. - 2469-9950. ; 100:7
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, first-principles calculations provide structural characterization of three low-index Mg surfaces - Mg(0001), Mg(1010), and Mg(1120) - and their respective surface core-level shifts (SCLSs). Inspired by the close similarities between Be and Mg surfaces, we also explore the reconstruction of Mg(1120). Through the calculation of surface energies and the use of the angular-component decomposed density of states, we show that reconstructions are likely to occur at the Mg(1120) surface, similarly to what was found earlier for Be(1120). Indeed, the surface energy of some of the explored reconstructions is slightly lower than that of the unreconstructed surface. In addition, because of lattice symmetry, the morphology of the unreconstructed surface (1120) results in a steplike zig-zag chain packing, with topmost chains supporting a resonant, quasi-one-dimensional (1D), partially filled electronic state. As the presence of partially filled quasi-1D bands is a necessary condition for Peierls-like dimerization, we verify that the undimerized surface chain remains stable with respect to it. Some of the reconstructions, namely, the 2×1 and 3×1 added row reconstructions, induce a stronger relaxation of the topmost chains, increasing the coupling with lower layers and thus significantly damping the quasi-1D character of this state. The original approach followed offers a common and general framework to identify quasi-1D bands - even in the case of resonant electronic surface states - and to meaningfully compare calculated and measured SCLSs even in the presence of multicomponent peak contributions.
|
|
| 8. |
- Joshi, Vineet V., et al.
(författare)
-
Preface
- 2019
-
Ingår i: Minerals, Metals and Materials Series. - 2367-1181.
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
|
|
| 9. |
- Lee, Wai Tung, et al.
(författare)
-
Polarisation Development at the European Spallation Source
- 2023
-
Ingår i: EPJ Web of Conferences. - 2100-014X. ; 286, s. 03004-03004
-
Tidskriftsartikel (refereegranskat)abstract
- To meet the ever-increasing user demand, eleven of the fifteen European Spallation Source (ESS) instruments under construction aim to offer polarised neutrons for user experiments. They include an imaging instrument, a SANS instruments, two reflectometers, three diffractometers, and four spectrometers. In conjunction with in-kind contributions and instrumentation grants, the ESS Polarisation Project will support the incorporation of polarisation analysis on eight of the eleven instruments. The project aims to deliver polarised neutrons for first-science experiments as instruments enter operation. Different polariser and polarisation analyser techniques will be available to accommodate the specifics of experiments on a given instrument. Polarised 3He neutron spin filter using either Metastable Optical Pumping (MEOP) or Spin-Exchange Optical Pumping (SEOP) techniques will provide shared-use equipment among many instruments, with SEOP’s main application being in situ beam-polarisation. Several instruments will also use polarising-supermirror devices. To provide wide-bandwidth spin-flipping capability to the time-of-flight instruments, Adiabatic Fast Passage (AFP) neutron spin flippers, also known as gradient-field radiofrequency spin flippers will be the main method of choice. Devices based on the same AFP principle will also be used to flip 3He nuclear spins. We are constructing our first 3He polariser setup, including field coils to produce highly uniform magnetic field. Monte Carlo simulations are being done for the supermirror polarisers. To ensure science-focused development, we are working with university partners in doing scientific experiments with polarised neutrons. These are some of the activities developing polarisation analysis for ESS instruments in our project.
|
|
| 10. |
- Long, Doudou, et al.
(författare)
-
Improving texture and microstructure homogeneity in high-purity ta sheets by warm cross rolling and annealing
- 2021
-
Ingår i: Metals. - : MDPI AG. - 2075-4701. ; 11:11
-
Tidskriftsartikel (refereegranskat)abstract
- The evolution of texture and microstructure uniformity in high-purity tantalum (Ta) sheets during 135◦ warm cross rolling (WCR) was analyzed in detail. X-ray diffraction suggested that relatively uniform ‘ideal’ deformation texture distribution across the thickness could be obtained from WCR, since more potential slip systems could be activated. Electron backscatter diffraction (EBSD) results indicated that the change in strain path in warm rolling could enhance dislocations mobility and increase the probability of dislocations rearrangement and annihilation. Thus, the proportion of low-angle grain boundaries was significantly reduced, and more sub-grain boundaries or sub-grains were formed via WCR. The calculation of geometrically necessary dislocation density based on the strain gradient model supports this result. The analysis of relative Schmid factor combined with the strain contouring map indicated that inhomogeneous orientation-dependent grain subdivision could be effectively weakened, and relatively uniform strain distribution could be formed in the WCR sample. Upon annealing, uniform fine grain size and more randomly oriented grains were obtained in the WCR sample after the completion of recrystallization because of relatively uniform grain subdivision and stored energy distribution.
|
|
| 11. |
- Maier, Petra, et al.
(författare)
-
Corrosion Rates by Immersion and Calorimetry on the Example of Extruded Mg10Gd(1Nd)1La
- 2024
-
Ingår i: Magnesium Technology 2024. - 2367-1181 .- 2367-1696. - 9783031502392 ; , s. 35-39
-
Konferensbidrag (refereegranskat)abstract
- This study is a follow-up investigation of the influence of the alloying elements Nd and La on the corrosionCorrosionby immersionImmersion of an extruded and heat-treated Mg10Gd. The previous study made clear that the age-hardened condition has the lowest corrosion rateCorrosion Rate but high pitting corrosionPitting corrosion susceptibility. The extruded Mg10Gd(1Nd)1La shows the lowest pitting factors based on severe corrosion. In this study, the corrosionCorrosion morphology and corrosion rates are discussed based on calorimetric data and 3D-analysis by µCT and compared to the results from the immersion tests. Thermal power and enthalpy readings from the isothermal calorimetryCalorimetry offer information on the reaction kinetics. The corrosion rateCorrosion Rate values are discussed based on the evaluation method—in general agreement alloying with Nd reduces the corrosion rateCorrosion Rate. The pitting factor is found to be very dependent on the reference average penetration: weight or volume loss, or evaluation by 3D volume or by 2D cross-sections.
|
|
| 12. |
- Mizelli-Ojdanic, Andrea, et al.
(författare)
-
Enhancing the Mechanical Properties of Biodegradable Mg Alloys Processed by Warm HPT and Thermal Treatments
- 2021
-
Ingår i: Materials. - : MDPI AG. - 1996-1944. ; 14:21
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, several biodegradable Mg alloys (Mg5Zn, Mg5Zn0.3Ca, Mg5Zn0.15Ca, and Mg5Zn0.15Ca0.15Zr, numbers in wt%) were investigated after thermomechanical processing via high-pressure torsion (HPT) at elevated temperature as well as after additional heat treatments. Indirect and direct analyses of microstructure revealed that the significant strength increases arise not only from dislocations and precipitates but also from vacancy agglomerates. By contrast with former low-temperature processing routes applied by the authors, a significant ductility was obtained because of temperature-induced dynamic recovery. The low initial values of Young's modulus were not significantly affected by warm HPT-processing. nor by heat treatments afterwards. Also, corrosion resistance did not change or even increase during those treatments. Altogether, the study reveals a viable processing route for the optimization of Mg alloys to provide enhanced mechanical properties while leaving the corrosion properties unaffected, suggesting it for the use as biodegradable implant material.
|
|
| 13. |
- Nawrocki, Robert A., et al.
(författare)
-
Fabrication of poly(3-hexylthiophene) nanowires for high-mobility transistors
- 2016
-
Ingår i: Organic Electronics. - : Elsevier BV. - 1566-1199. ; 30, s. 92-98
-
Tidskriftsartikel (refereegranskat)abstract
- Presented here is a novel and efficient method used to improve carrier mobilities of poly(3-hexylthiophene) (P3HT)-based organic field effect transistors by means of nanowire formation. The treatment, termed solvation, consists of depositing a small quantity of a solvent directly on top of a previously deposited semiconducting film, and allowing the solvent to evaporate slowly. Such treatment results in an increase of the saturation mobility by more than one order of magnitude, from 1.3 × 10-3 up to 3.4 × 10-2 cm2/Vs, while devices preserve their high ON/OFF ratio of ∼104. The atomic force and scanning electron microscopy studies show that solvated P3HT layers develop a network of nanowires, which exhibit increased degree of structural order, as demonstrated by micro Raman spectroscopy. The time-of-flight photoconductivity studies suggest that higher hole mobility stems from a reduced energy disorder of the transporting states in these structures.
|
|
| 14. |
- Neding, Benjamin, 1988-
(författare)
-
Stacking faults, deformation-induced martensite and micromechanics of metastable austenite in steels studied by high-energy synchrotron X-ray diffraction
- 2021
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Austenitic stainless steels are known for their remarkable corrosion resistance and exhibit a very high ductility and toughness. They posses the face centered cubic crystal structure. Depending on the chemical composition of the austenite, the austenite may be metastable and during plastic deformation may undergo a deformation-induced phase transformation into α′-martensite - and that α′-martensite is partly responsible for the steel’s remarkable mechanical properties. In order to predict and control the occurrence and extent of the deformation-induced transformation into α′-martensite, it is crucial to have a profound knowledge of that transformation. Such knowledge is important to further improve austenitic stainless steels but also to contribute to the development of third generation advanced high strength steels that possess a multi-phase microstructure since the deformation behavior of the austenitic phase crucially influences their bulk deformation properties. Accordingly, in order to improve the current knowledge about the micromechanical behavior of steels and to predict the deformationbehavior of metastable austenite reliably, parameters affecting the austenite’s deformation behavior need to be described and quantified. This work contributes to such knowledge by investigating experimentally the effect of temperature, chemical composition, and grain orientationon the deformation behavior of austenite. The investigations were performed mainly with the aid of high-energy X-ray diffraction(HEXRD). HEXRD is a measurement method that allows to examine the materials’ response to plastic deformation in a bulk specimen non destructively. With HEXRD phases and their fraction evolution, latticestrains and stresses, and the stacking fault energy (γSF) can be followed in situ as the sample is subjected to load. Moreover, the high spatial resolution of HEXRD allows line profile analysis, i.e. to study the shape of diffraction peaks in order to quantify the formation of dislocations and stacking faults as well as their evolution during the course of deformation. Also, high-energy X-ray diffraction microscopy (HEDM) measurementwere conducted in order to resolve and follow the deformation behavior of individual grains embedded within the polycrystalline bulk during deformation. This is important to understand the effect of grain orientation, grain neighborhood, and grain morphology on the deformation behavior of individual grains and consequently the deformationbehavior of the bulk as a whole.The temperature effect on γSF was studied both on powders of three austenitic model alloys with different alloy compositions using an in situ temperature HEXRD experiment and on a commercial 301LN bulk specimen with the aid of an in situ tensile loading experiment. It was found that the γSF increases significantly with increasing temperature. Moreover, the temperature induced increase of γSF significantly influences the predominantly active deformation mechanism. At low temperatures, large fractions of stacking faults, ε- and α′-martensite formed, which also reflects on the properties of the steel by a high work hardening rate. With increasing temperature, and consequently increasing γSF, the formation of stacking faults, ε- and α′-martensite becomes less predominant. As a result a significant decrease in work hardening with increasing temperature was observed. Moreover, it was found, that at elevated temperatures, the dissociation of dislocation into partial dislocation occurs at significantly higher strain. In addition to temperature, grain orientation was found to affect the deformation behavior of austenitic steels substantially. Grains deformed along [100] form predominantly stacking faults, whereas grains deformed along [111] mainly deform via dislocation glide. Grain orientation also played a key role in the formation of deformation-induced phases. Crystalline austenitic regions oriented with their {111} at 45° to external load were found to transform preferentially into ε-martensite before further transforming into α′-martensite, whereas crystalline austenitic regions oriented with their {111} at 0° and 90° to the load, transformed directly into α′-martensite, without transforming into ε-martensite first.The knowledge acquired by studying single phase austenitic steel was expanded to medium Mn steels (MMnS), possessing a multi-phase microstructure. It was found that the average bulk deformation behavior of medium Mn steels is crucially affected by the interdependencies between the micromechanical deformation behavior and the stability of the austenite, which can be controlled by tuning microstructure and austenite composition.The contribution of this work is to increase the knowledge of the deformation-induced martensitic phase transformations of metastable austenite, its dependence with γSF, temperature, and the correlation with parameters affecting the deformation behavior in the bulk which are not considered in the γSF.
|
|
| 15. |
- Ojdanic, Andrea, et al.
(författare)
-
The effects of severe plastic deformation and/or thermal treatment on the mechanical properties of biodegradable mg-alloys
- 2020
-
Ingår i: Metals. - : MDPI AG. - 2075-4701. ; 10:8, s. 1-33
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, five MgZnCa alloys with low alloy content and high biocorrosion resistance were investigated during thermomechanical processing. As documented by microhardness and tensile tests, high pressure torsion (HPT)-processing and subsequent heat treatments led to strength increases of up to 250%; as much as about 1/3 of this increase was due to the heat treatment. Microstructural analyses by electron microscopy revealed a significant density of precipitates, but estimates of the Orowan strength exhibited values much smaller than the strength increases observed. Calculations using Kirchner’s model of vacancy hardening, however, showed that vacancy concentrations of 10−⁵ could have accounted for the extensive hardening observed, at least when they formed vacancy agglomerates with sizes around 50‒100 nm. While such an effect has been suggested for a selected Mg-alloy already in a previous paper of the authors, in this study the effect was substantiated by combined quantitative evaluations from differential scanning calorimetry and X-ray line profile analysis. Those exhibited vacancy concentrations of up to about 10−3 with a marked percentage being part of vacancy agglomerates, which has been confirmed by evaluations of defect specific activation migration enthalpies. The variations of Young’s modulus during HPT-processing and during the subsequent thermal treatments were small. Additionally, the corrosion rate did not markedly change compared to that of the homogenized state.
|
|
| 16. |
- Orlov, Dmytro, et al.
(författare)
-
Advanced Immersion Testing of Model Mg-Alloys for Biomedical Applications
- 2020
-
Ingår i: Magnesium Technology 2020. - Cham : Springer International Publishing. - 2367-1696 .- 2367-1181. - 9783030366476 - 9783030366469 ; , s. 235-242
-
Konferensbidrag (refereegranskat)abstract
- The acceleration of developing magnesium alloys for biomedicine requires the advancement of experimental methods evaluating their performance. We have been developing an advanced immersion testing method for the assessment of biomedical Mg alloy degradation in aqueous environments. It is based on the combination of isothermal calorimetry with pressure measurement in the reaction cell. Such a combination allows in situ quantitative analysis of chemical reactions based on both the enthalpy (heat) of the process itself and hydrogen gas generated as one of the reaction products. Here, we analyze the evolution of the degradation rate of a ternary Mg–5.0Zn–0.3Ca intended for biomedical applications and two model binary Mg–5.0Zn and Mg–0.3Ca alloys (in as-cast and solutionized states) in 0.9% NaCl water solution and a simulated body fluid (SBF). The results obtained using the novel method are critically compared to more traditional immersion testing with hydrogen collection.
|
|
| 17. |
- Orlov, Dmytro, et al.
(författare)
-
Advantages of architectured harmonic structure in structural performance
- 2019
-
Ingår i: IOP Conference Series: Materials Science and Engineering. - 1757-8981. ; 580
-
Konferensbidrag (refereegranskat)abstract
- The concept of heterogenous materials with architectured harmonic structure (HS) has emerged recently with the aim of enhancing the structural performance of metals. This work presents critical microstructure characteristics contributing to the superior structural performance of harmonic-structured materials using as an example of commercially-pure nickel. Optical and scanning electron microscopy, along with nano-indentation and tensile testing, as well as digital image correlation analysis, were used for this purpose. A brief overview of the structural performance of several representative systems with HS is provided and interesting directions for future studies are discussed.
|
|
| 18. |
- Orlov, Dmytro, et al.
(författare)
-
Critical Assesment 37: Harmonic-structure materials - idea, status and perspectives
- 2020
-
Ingår i: Materials Science and Technology. - : Informa UK Limited. - 0267-0836 .- 1743-2847. ; 36:5, s. 517-526
-
Tidskriftsartikel (refereegranskat)abstract
- Recent efforts in engineering metals with high structural efficiency have resulted in developing a new category of artificial materials with heterogeneous microstructures architected across multiple scales. In this critical assessment, a relatively new concept of heterogeneous bimodal harmonic-structure (bHS) materials is introduced and analysed. It is shown that the bHS concept is applicable to a large variety of metallic materials and is most efficient in scenarios where changes in the chemical composition of materials are restricted for some reason. Basic principles, weaknesses and advantages along with present development status and perspectives are discussed. The overview of critical performance characteristics of various bHS materials is provided, and interesting directions for future research, development and applications are proposed.
|
|
| 19. |
- Orlov, Dmytro, et al.
(författare)
-
Novel Laboratory-Scale In Situ Methods for Studying Mg Alloy Degradation
- 2022
-
Ingår i: Magnesium Technology 2022. - Cham : Springer International Publishing. - 2367-1181 .- 2367-1696. - 9783030925321 - 9783030925338 ; , s. 253-254
-
Konferensbidrag (refereegranskat)abstract
- Magnesium metal and its alloys are lightweight and environment-friendly with tunable complex of structural and functional properties. However, significant gaps in understanding and assessing the degradation of these materials still remain, largely due to the limitations of existing experimental methods. Our novel laboratory-scale instrument combining isothermal calorimetry with pressure measurements allows quantitative in situ analysis of Mg degradation thermodynamics. Our latest achievements in studying model Mg alloys for biomedical applications are summarized below and discussed in respective lecture during the TMS2022 meeting.
|
|
| 20. |
- Orlov, Dmytro, et al.
(författare)
-
Preface
- 2018
-
Ingår i: Preface. - 2367-1181. ; Part F7
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
|
|
| 21. |
- Orlov, Dmytro, et al.
(författare)
-
Strain partitioning and back-stress evaluation in harmonic-structure materials
- 2020
-
Ingår i: Materials Letters. - : Elsevier BV. - 0167-577X. ; 275
-
Tidskriftsartikel (refereegranskat)abstract
- Heterogenous bimodal harmonic-structure (HS) materials are interesting because of excellent structural efficiency. In this work, we present a simple yet powerful analytical model allowing to evaluate strain partitioning between coarse- and ultrafine- grain (CG and UFG, respectively) structure components in HS materials and to estimate the magnitude of back-stress forming at their interphases. The analysis of experimental results on pure nickel using this model shows that HS promotes a favourable strain partitioning between CG and UFG components and the build-up of back-stress in the vicinity of their interfaces allowing the material performance to exceed expectations from the rule of mixtures.
|
|
| 22. |
- Ottenklev, Fredrik, et al.
(författare)
-
Non-monotonic evolution of surface roughness in a stainless steel during cold deformation
- 2021
-
Ingår i: Materials Science and Engineering A. - : Elsevier BV. - 0921-5093. ; 799
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, polished and unpolished sheet samples of austenitic stainless steel 316L were tensile strained to investigate the evolution of surface roughness based on Sa- and Ra characteristics. In polished steel sheets, surface roughness increases with the increase of true strain up to a maximum of e = 0.14. Thereafter, roughness decreases until e = 0.26 for approximately 25%, and then becomes independent on strain. The highest roughness levels are found to be localised primarily around surface grain boundaries. The roughness-strain correlation can be explained by grain rotation and cross-slip. Unpolished sheets demonstrate near-linear relationship between tensile strain and surface roughening due to the presence of an oxide layer. The layer has a thickness of approximately 1 μm with a morphology resembling the microstructure in the substrate. When strained, it appears to show two roughness components. First one is a shortwave component originating at the oxide grain boundaries, which is believed to be produced by the rotation of underlying grains. The second one is a longwave component, which is generated by the fracture of oxide layer due to lower ductility. The slope of roughness – true strain relationship is found to be also grain orientation-dependent.
|
|
| 23. |
- Peck, Philip, et al.
(författare)
-
Circular Economy - Sustainable Materials Management : A compendium by the International Institute for Industrial Environmental Economics (IIIEE) at Lund University
- 2020. - 2021
-
Rapport (populärvet., debatt m.m.)abstract
- The scope of the compendium covers many parts of theemerging circular economy. We choose to place considerablefocus on some of the substances that we extract from theground – in particular raw materials and critical materials.We focus on circularity in these areas, because presentlywe use too much, too fast, and we are not re-using nearlyenough. In turn, this approach demands that we look atthe technologies that rely on such materials, and howbusinesses are innovating to make circularity of materialsa reality.This document provides many concrete examples of whatwe mean by sustainable materials management. We presentcutting edge insights on a range of topics.• Why raw material supply chains are important to society?• How circularity can benefit us?• Where changes in our economies are required?• Who needs to be involved?• What businesses are doing to make the circular economya reality?• How governments and regulators can support the circulareconomy?
|
|
| 24. |
- Peruzzi, Niccolò, et al.
(författare)
-
Multimodal ex vivo methods reveal that Gd-rich corrosion byproducts remain at the implant site of biodegradable Mg-Gd screws
- 2021
-
Ingår i: Acta Biomaterialia. - : Elsevier. - 1742-7061 .- 1878-7568. ; 136, s. 582-591
-
Tidskriftsartikel (refereegranskat)abstract
- Extensive research is being conducted on magnesium (Mg) alloys for bone implant manufacturing, due to their biocompatibility, biodegradability and mechanical properties. Gadolinium (Gd) is among the most promising alloying elements for property control in Mg alloy implants; however, its toxicity is controversial. Investigating Gd behavior during implant corrosion is thus of utmost importance. In this study, we analyzed the degradation byproducts at the implant site of biodegradable Mg-5Gd and Mg-10Gd implants after 12 weeks healing time, using a combination of different imaging techniques: histology, energy-dispersive x-ray spectroscopy (EDX), x-ray microcomputed tomography (µCT) and neutron µCT. The main finding has been that, at the healing time in exam, the corrosion appears to have involved only the Mg component, which has been substituted by calcium and phosphorus, while the Gd remains localized at the implant site. This was observed in 2D by means of EDX maps and extended to 3D with a novel application of neutron tomography. X-ray fluorescence analysis of the main excretory organs also did not reveal any measurable accumulation of Gd, further reinforcing the conclusion that very limited or no removal at all of Gd-alloy happened during degradation.
|
|
| 25. |
- Pfaff, Sebastian, et al.
(författare)
-
A Polycrystalline Pd Surface Studied by Two-Dimensional Surface Optical Reflectance during CO Oxidation : Bridging the Materials Gap
-
Ingår i: ACS applied materials & interfaces. - 1944-8244.
-
Tidskriftsartikel (refereegranskat)abstract
- Industrial catalysts are complex materials systems operating in harsh environments. The active parts of the catalysts are nanoparticles that expose different facets with different surface orientations at which the catalytic reactions occur. However, these facets are close to impossible to study in detail under industrially relevant operating conditions. Instead, simpler model systems, such as single crystals with a well-defined surface orientation, have been successfully used to study gas-surface interactions such as adsorption and desorption, surface oxidation, and oxidation/reduction reactions. To more closely mimic the many facets exhibited by nanoparticles and thereby close the so-called materials gap, there has also been a recent move toward using polycrystalline surfaces and curved crystals. However, these studies are limited either by the pressure or spatial resolution at realistic pressures or by the number of surfaces studied simultaneously. In this work, we demonstrate the use of reflectance microscopy to study a vast number of catalytically active surfaces simultaneously under realistic and identical reaction conditions. As a proof of concept, we have conducted an operando experiment to study CO oxidation over a Pd polycrystal, where the polycrystalline surface acts as a collection of many single-crystal surfaces. Finally, we visualized the resulting data by plotting the reflectivity as a function of surface orientation. We think the techniques and visualization methods introduced in this work will be key toward bridging the materials gap in catalysis.
|
|
| 26. |
- Pfaff, Sebastian, et al.
(författare)
-
Operando Reflectance Microscopy on Polycrystalline Surfaces in Thermal Catalysis, Electrocatalysis, and Corrosion
- 2021
-
Ingår i: ACS applied materials & interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 13:16, s. 19530-19540
-
Tidskriftsartikel (refereegranskat)abstract
- We have developed a microscope with a spatial resolution of 5 μm, which can be used to image the two-dimensional surface optical reflectance (2D-SOR) of polycrystalline samples in operando conditions. Within the field of surface science, operando tools that give information about the surface structure or chemistry of a sample under realistic experimental conditions have proven to be very valuable to understand the intrinsic reaction mechanisms in thermal catalysis, electrocatalysis, and corrosion science. To study heterogeneous surfaces in situ, the experimental technique must both have spatial resolution and be able to probe through gas or electrolyte. Traditional electron-based surface science techniques are difficult to use under high gas pressure conditions or in an electrolyte due to the short mean free path of electrons. Since it uses visible light, SOR can easily be used under high gas pressure conditions and in the presence of an electrolyte. In this work, we use SOR in combination with a light microscope to gain information about the surface under realistic experimental conditions. We demonstrate this by studying the different grains of three polycrystalline samples: Pd during CO oxidation, Au in electrocatalysis, and duplex stainless steel in corrosion. Optical light-based techniques such as SOR could prove to be a good alternative or addition to more complicated techniques in improving our understanding of complex polycrystalline surfaces with operando measurements.
|
|
| 27. |
|
|
| 28. |
- Shokry, Abdallah, et al.
(författare)
-
Improvement of structural efficiency in metals by the control of topological arrangements in ultrafine and coarse grains
- 2021
-
Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 11:1
-
Tidskriftsartikel (refereegranskat)abstract
- Improvement of structural efficiency in various materials is critically important for sustainable society development and the efficient use of natural resources. Recently, a lot of attention in science and engineering has been attracted to heterogeneous-structure materials because of high structural efficiency. However, strategies for the efficient design of heterogenous structures are still in their infancy therefore demanding extensive exploration. In this work, two-dimensional finite-element models for pure nickel with bimodal distributions of grain sizes having ‘harmonic’ and ‘random’ spatial topological arrangements of coarse and ultrafine-grain areas are developed. The bimodal random-structure material shows heterogeneities in stress–strain distributions at all scale levels developing immediately upon loading, which leads to developing concentrations of strain and premature global plastic instability. The bimodal harmonic-structure material demonstrates strength and ductility significantly exceeding those in the bimodal random-structure as well as expectations from a rule of mixtures. The strain hardening rates also significantly exceed those in homogeneous materials while being primarily controlled by coarse-grain phase at the early, by ultrafine-grain at the later and by their compatible straining at the intermediate stages of loading. The study emphasises the importance of topological ultrafine-/coarse-grain distributions, and the continuity of the ultrafine-grain skeleton in particular.
|
|
| 29. |
- Shokry, Abdallah, et al.
(författare)
-
On the optimisation of phase fractions in harmonic structure materials
-
Ingår i: Journal of Materials Science. - 0022-2461.
-
Tidskriftsartikel (refereegranskat)abstract
- Materials with heterogeneous microstructures architected across several scales are becoming increasingly popular in structural applications due to unique strength–ductility balance. One of the most popular 3D-architected structure designs is harmonic structure (HS) where soft coarse-grain (CG) islands are embedded in a hard continuous 3D skeleton of ultrafine grains (UFGs). In this work, a series of HS with varying phase fractions and rheologies are studied based on several models. Model A focuses on a good fit with experimental data in the elastic–plastic transition region, model B focuses on a good fit at large-scale yielding, while in five intermediate models, phase rheology parameters are varied on a linear scale between the values for A and B. For each of the seven selected HS material models, structures with 19 different volumetric fractions of UFG were examined. It is found that the increase of UFG fraction leads to the monotonic increase of strength characteristics in HS material, while higher strain hardening rates in the phases lead to the enhancement of this effect. By contrast, the dependence of ductility characteristics on UFG fraction is non-monotonic having a local minimum at 30% UFG and a maximum at 60% UFG, while also significantly dependent on strain hardening in the phases. Namely, HS material with phases having significant strain hardening reveals the highest uniform elongation exceeding that in 100% CG material already at 40% UFG fraction. The fractions of UFG in a range of 58–62% form HS material with the highest possible uniform elongation.
|
|
| 30. |
- Singh, Digvijay, et al.
(författare)
-
Evolution of gradient structured layer on AZ91D magnesium alloy and its corrosion behaviour
- 2021
-
Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388. ; 882
-
Tidskriftsartikel (refereegranskat)abstract
- This article investigates the microstructure evolution and corrosion response of surface mechanical attrition treated (SMAT) AZ91D magnesium alloy. In-depth transmission electron microscopy and combined isothermal calorimetry and pressure measurement technique, a novel and powerful tool for in situ monitoring of the magnesium corrosion process, are explored in the present study. A gradient structured layer of ~ 500 µm thickness with improved (~2.5 times) surface hardness is successfully obtained on the AZ91D alloy surface. SMAT introduces compressive residual stress in the treated layer. TEM results confirmed nanoscale grains of ~125 nm in topmost region and multiple deformation twin-modes, including 101¯2 〈101¯1〉 dense twins and 101¯1 – 101¯2 double twinning in SMATed layer. Twining of secondary twins is established in the TEM analysis. Moreover, a twin density gradient is evident within the treated layer, where it decreases with an increase in depth. After 24 h of immersion in 0.9% NaCl solution, the average corrosion rate of SMATed and non-SMATed specimens is ~11.0 and ~3.8 mm/year, respectively. The corrosion product on non-SMATed specimens has densely packed nano-flakes morphology; however, the SMATed surface shows two different morphologies: sparse nanowires and porous honeycomb-like structure. The SMATed specimen's lower corrosion resistance is attributed to the combined effect of the high density of defects, rougher surface, and smaller volume fraction of β phase at the surface.
|
|
| 31. |
- Singh, Digvijay, et al.
(författare)
-
High-temperature oxidation behaviour of nanostructure surface layered austenitic stainless steel
- 2022
-
Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332. ; 581
-
Tidskriftsartikel (refereegranskat)abstract
- The present study investigates the high-temperature oxidation behaviour of nanostructure surface layered AISI 304L stainless steel. A severely deformed layer of ∼300 μm thickness, consisting of nanoscale grains (∼40 nm size) in the topmost region, is successfully developed using the surface mechanical attrition treatment (SMAT) process. The SMATed layer is substantially stable up to 700 °C; however, the surface hardness is reduced by ∼37% at 800 °C for 25 h oxidation duration. Glow discharge optical emission spectroscopy and X-ray photoelectron spectroscopy analysis revealed the considerable difference in the chemistry and elemental distribution across the oxide scale of SMATed and non-SMATed specimens. Adherent, denser, and thinner scale, dominated by nanocrystals of Cr- and Mn-rich oxides, is formed on the SMATed steel. However, the Fe-oxide dominated scale containing micro-crystals is found on the non-SMATed specimens, which shows noticeable exfoliation. A high density of grain boundaries and lattice defects in the SMATed layer display admirable reactive diffusion properties of Cr and Mn during oxidation of steel, instigating the formation of a protective oxide scale. The SMATed specimens exhibit multiple zones in the oxide scale: (i) Cr/Mn depleted outer layer, (ii) Cr-/Mn-rich inner layer, and (iii) gradually decreasing Cr/Mn region.
|
|
| 32. |
- Sjögren, Elis, et al.
(författare)
-
Separation of XRD peak profiles in single-phase metals with bimodal grain structure to analyze stress partitioning
- 2022
-
Ingår i: 42nd Risø International Symposium on Materials Science: Microstructural variability: Processing, analysis, mechanisms and properties : 5–9 September 2022, Department of Civil and Mechanical Engineering, Technical University of Denmark, Denmark - 5–9 September 2022, Department of Civil and Mechanical Engineering, Technical University of Denmark, Denmark. - : IOP Publishing. - 1757-899X. ; 1249
-
Konferensbidrag (refereegranskat)abstract
- Materials with bimodal grain size distributions have an attractive combination of strength and ductility. Harmonic structure materials are a category of bimodal-structure materials with a specific microstructure design. The deformation mechanisms of such novel materials during the early stages of deformation are not well understood. Thus, we deformed nickel with harmonic structure in tension until a true strain of 0.04 while recording powder diffraction patterns with high-energy synchrotron X-rays. Line profile analysis based on such data enables quantification of stress states and lattice defect densities in different phases in multi-phase materials. Bimodal size distributions in single-phase materials add extra complexity due to the absence of differences in composition and crystal structure causing the diffraction peaks from fine and coarse grains to appear at the same diffraction angles. Therefore, prior to any meaningful line profile analysis, the respective diffraction profiles need to be separated. A general method for automatically separating profiles originating from different grain fractions in bimodal materials is presented in this work.
|
|
| 33. |
- Sjögren-Levin, Elis, et al.
(författare)
-
Grain-level mechanism of plastic deformation in harmonic structure materials revealed by high resolution X-ray diffraction
- 2024
-
Ingår i: Acta Materialia. - 1359-6454. ; 265
-
Tidskriftsartikel (refereegranskat)abstract
- Materials with heterogeneous microstructures have been reported to have an attractive combination of strength and ductility. This is attributed to synergistic strengthening effects from the difference in strength of fine- and coarse-grained regions. Understanding the interaction of the regions is crucial for further optimization of the microstructures. In this work, we fabricated nickel of harmonic structure (HS) and a reference with homogenous coarse grains. The HS constitutes of an interconnected fine-grained network that surrounds regions of coarse grains. The interplay of the regions was studied by monitoring Bragg reflections from individual grains in situ during tensile deformation until approximately 2 % strain through synchrotron X-ray diffraction. The technique allows grain-level assessment of the degree of plastic deformation. Two grains were followed in the reference and two small grains (fine-grained region) and two large grains (coarse-grained region) in the HS. Three deformation regimes were identified: elastic deformation, onset of plastic deformation and significant plastic deformation. Our results reveal that the large grains in the harmonic structure onset plastic deformation during the macroscopic elastic stage. With increasing applied stress, the small grains yield plastically also and once a large fraction of the fine-grained network deforms plastically the large grains undergo significant plastic deformation. Notably, the onset of significant plastic deformation of large grains in the HS occurs at approximately 100 MPa higher applied stress than in the grains in the reference. This shows that fine grains constrain the large grains from deforming plastically in the HS.
|
|
| 34. |
- Sjögren-Levin, Elis, et al.
(författare)
-
Stress partitioning in harmonic structure materials at the early stages of tensile loading studied in situ by synchrotron X-ray diffraction
- 2023
-
Ingår i: Scripta Materialia. - : Elsevier BV. - 1359-6462. ; 226
-
Tidskriftsartikel (refereegranskat)abstract
- In situ X-ray diffraction was employed to gain insight into the tensile deformation behavior of harmonic structure (HS) nickel. HS consists of a continuous network of fine grains encompassing islands of coarse grains. With the aid of a newly developed separation algorithm, the X-ray diffraction signals from coarse and fine grains were analyzed separately. Using line profile analysis, the evolution of local stresses and microstrains in the respective grain fractions were examined. Several stages were identified during yielding and the onset of plastic deformation in HS nickel. The mechanical behavior of the individual fractions was related to the macroscopic behavior of the HS and compared to that of homogeneous counterparts with similar average grain sizes as the grain fractions. The analysis reveals that the stress partitions between the grain fractions and that the plastic deformation of coarse grains within the HS are constrained by the network of fine grains.
|
|
| 35. |
- Solanki, Kiran N., et al.
(författare)
-
Preface
- 2017
-
Ingår i: Minerals, Metals and Materials Series. - 2367-1181. ; Part F8
-
Tidskriftsartikel (refereegranskat)
|
|
| 36. |
- Steiner Petrovič, Darja, et al.
(författare)
-
Surface Analysis of Biodegradable Mg-Alloys after Immersion in Simulated Body Fluid
- 2020
-
Ingår i: Materials. - : MDPI AG. - 1996-1944. ; 13:7
-
Tidskriftsartikel (refereegranskat)abstract
- Two binary biodegradable Mg-alloys and one ternary biodegradable Mg-alloy (Mg-0.3Ca, Mg-5Zn and Mg-5Zn-0.3Ca, all in wt%) were investigated. Surface-sensitive X-ray photoelectron spectroscopy analyses (XPS) of the alloy surfaces before and after immersion in simulated body fluid (SBF) were performed. The XPS analysis of the samples before the immersion in SBF revealed that the top layer of the alloy might have a non-homogeneous composition relative to the bulk. Degradation during the SBF immersion testing was monitored by measuring the evolution of H2. It was possible to evaluate the thickness of the sample degradation layers after the SBF immersion based on scanning electron microscopy (SEM) of the tilted sample. The thickness was in the order of 10-100 µm. The typical bio-corrosion products of all of the investigated alloys consisted of Mg, Ca, P and O, which suggests the formation of apatite (calcium phosphate hydroxide), magnesium hydrogen phosphate hydrate and magnesium hydroxide. The bioapplicability of the analyzed alloys with regard to surface composition and degradation kinetics is discussed.
|
|
| 37. |
- Thamkaew, Grant, et al.
(författare)
-
Reversible Electroporation and Post-Electroporation Resting of Thai Basil Leaves Prior to Convective and Vacuum Drying
- 2022
-
Ingår i: Applied Sciences (Switzerland). - : MDPI AG. - 2076-3417. ; 12:5
-
Tidskriftsartikel (refereegranskat)abstract
- Pretreatment by reversible electroporation followed by resting (storage under saturated moisture at 21 ± 2 °C) was evaluated for modification of the properties of dried and rehydrated Thai basil leaves. The treated leaves were dried by convection at 40 °C or in a vacuum at room temperature. The results showed that vacuum drying provoked more cell damage and tissue collapse than convective air drying at a moisture ratio (MR) of 0.2 and 0.1. Under this level of MR, the pulsed electric field (PEF) and resting pretreatment exerts a protective effect of the tissue for both drying methods. However, under complete dehydration (water activity, aw = 0.05) damage seems to be similar for both drying methods despite the PEF pretreatment. Remarkably, reversible electroporation followed by resting resulted in higher trichome preservation. At MR of 0.05, the area of trichomes on the surface of convective-dried, PEF-rested and fresh samples were not statistically different at 2267 ± 89 µm2 and 2218 ± 65 µm2, respectively, showing that this pretreatment still exerts a protective effect on trichomes when complete dehydration is achieved.
|
|
| 38. |
- Wadsö, Lars, et al.
(författare)
-
Adding dimensions to the immersion testing of magnesium corrosion
- 2018
-
Ingår i: Magnesium Technology 2018. - Cham : Springer International Publishing. - 2367-1696 .- 2367-1181. - 9783319723310 ; Part F7, s. 31-36
-
Konferensbidrag (refereegranskat)abstract
- With the versatility of structural performance in magnesium alloys, Achilles hill remains to be their susceptibility to corrosion. The Mg community agrees that traditional methods are insufficient for revealing the root cause of difficulties in controlling Mg degradation rate. Therefore, developing new methods allowing simultaneous assessment of several characteristics is of great importance now. We designed an advanced cell for immersion testing allowing simultaneous assessment of two complementary characteristics of Mg corrosion in aqueous environments: isothermal calorimetry and pressure. Isothermal calorimetry monitors in situ heat production rate during chemical reactions, which can be recalculated to corrosion rate if the enthalpy of a process is known. Pressure monitoring allows alternative quantification of corrosion rate through hydrogen production. The proof-of-concept testing presented here reveals details of a corrosion process depending on electrolyte.
|
|
| 39. |
- Zeller-Plumhoff, Berit, et al.
(författare)
-
Nanotomographic evaluation of precipitate structure evolution in a Mg-Zn-Zr alloy during plastic deformation
- 2020
-
Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 10:1, s. 16101-16101
-
Tidskriftsartikel (refereegranskat)abstract
- Magnesium and its alloys attract increasingly wide attention in various fields, ranging from transport to medical solutions, due to their outstanding structural and degradation properties. These properties can be tailored through alloying and thermo-mechanical processing, which is often complex and multi-step, thus requiring in-depth analysis. In this work, we demonstrate the capability of synchrotron-based nanotomographic X-ray imaging methods, namely holotomography and transmission X-ray microscopy, for the quantitative 3D analysis of the evolution of intermetallic precipitate (particle) morphology and distribution in magnesium alloy Mg-5.78Zn-0.44Zr subjected to a complex multi-step processing. A rich history of variation of the intermetallic particle structure in the processed alloy provided a testbed for challenging the analytical capabilities of the imaging modalities studied. The main features of the evolving precipitate structure revealed earlier by traditional light and electron microscopy methods were confirmed by the 3D techniques of synchrotron-based X-ray imaging. We further demonstrated that synchrotron-based X-ray imaging enabled uncovering finer details of the variation of particle morphology and number density at various stages of processing-above and beyond the information provided by visible light and electron microscopy.
|
|
| 40. |
- Zeller-Plumhoff, Berit, et al.
(författare)
-
Oxygen-sensitive nanoparticles reveal the spatiotemporal dynamics of oxygen reduction during magnesium implant biodegradation
- 2022
-
Ingår i: npj Materials Degradation. - : Springer Science and Business Media LLC. - 2397-2106. ; 6:1
-
Tidskriftsartikel (refereegranskat)abstract
- Magnesium (Mg) alloys are becoming increasingly important in the biomedical field as temporary bone implants. However, the biodegradation process of Mg alloys is highly complex and recent findings suggest that oxygen (O2) consumption is non-negligible. In this study, we give experimental proof of O2 consumption during Mg degradation under physiological conditions. Specifically, we study pure Mg, Mg–6 wt%Ag and Mg–5 wt%Gd in Hanks’ balanced salt solution and Dulbecco’s modified Eagle’s medium. We show that O2 consumption and hydrogen evolution are inversely correlated and that O2 concentrations remain below 7.5% in certain cases, which could have significant implications for bone healing.
|
|
| 41. |
- Zhu, Jialin, et al.
(författare)
-
Asymmetric cross rolling : A new technique for alleviating orientation-dependent microstructure inhomogeneity in tantalum sheets
- 2020
-
Ingår i: Journal of Materials Research and Technology. - : Elsevier BV. - 2238-7854. ; 9:3, s. 4566-4577
-
Tidskriftsartikel (refereegranskat)abstract
- New rolling technique, i.e. asymmetric rolling combined with cross rolling is adopted to produce Ta sputtering targets in this study. Electron backscatter diffraction (EBSD) analysis suggests that (111) and (100) deformed grains distribute alternately along normal direction in cross rolling (CR) and asymmetric cross rolling (ACR) samples. Misorientation angle distribution indicates that severe orientation-dependent grain fragmentation exists in the CR sample, which is also confirmed by kernel average misorientation and grain reference orientation deviation-hyper. Grain average misorientation (GAM) and distribution of geometrically necessary dislocations (GNDs) suggest that the effect of increasing shear strain introduced by asymmetric rolling on deformation microstructure is mainly reflected in the (100) grains, which is further verified by orientation-dependent microhardness values. The computation of Schmid factor indicates that slip within (100) grains in the ACR sample is easier, and the system with higher Schmid factor can alone accommodate the majority of plastic strain. Transmission electron microscopy (TEM) reveals that dense dislocation walls (DDWs) are formed within the (100) deformed grains in the ACR sample, while only sparse dislocation lines can be observed in the CR sample. X-ray line profile analysis (XLPA) displays that ACR can significantly increase the stored energy of the (100) deformed grains and thus weaken the orientation-dependent stored energy distribution. The enhanced recrystallization ability of the (100) grains in the ACR sample facilitates homogenization of the annealing microstructure.
|
|
| 42. |
- Zhu, Jialin, et al.
(författare)
-
Enhancing the {100} grain subdivision in high-purity tantalum sheets by asymmetric cross rolling
- 2020
-
Ingår i: Materials Characterization. - : Elsevier BV. - 1044-5803. ; 166
-
Tidskriftsartikel (refereegranskat)abstract
- Weak subdivision or fragmentation ability of deformed {100} (<100> // ND, normal direction) grains by traditional unidirectional (symmetric) rolling results in uneven deformation during tantalum (Ta) processing. Thus, a recently developed asymmetric cross rolling (ACR) is adopted in this work to enhance the subdivision of {100} grain in Ta sheets. Electron backscatter diffraction (EBSD), transmission electron microscopy (TEM) and Vickers hardness (HV) were used for the characterisation of microstructure in deformed {100} grains. It is shown that added shear strain component in the ACR leads to heterogeneous deformation substructures within {100} grains. The increase of speed ratio in ACR further enhances the subdivision of deformed {100} grains and thus increases the density of geometrically necessary dislocations (GNDs) in them. The computation of the largest Schmid factor (SFrolling) along with Taylor model suggests that the ACR promotes easier slip within deformed {100} grains. Therefore, the necessary total shear strain contributing to the increase of GNDs density is small. By contrast, the shear strain accumulated after CR-1.0 is distributed more evenly in each slip system resulting in rather sparse distribution of dislocation lines.
|
|
| 43. |
- Zhu, Jialin, et al.
(författare)
-
Pass number dependence of through-thickness microstructure homogeneity in tantalum sheets under the change of strain path
- 2020
-
Ingår i: Materials Characterization. - : Elsevier BV. - 1044-5803. ; 160
-
Tidskriftsartikel (refereegranskat)abstract
- Microstructure and crystallographic texture are the key factors that determine the properties of sputtering target used in integrated circuit fabrication. Multi-pass clock-rolling has been used recently to produce Ta sputtering targets. However, the effect of strain per pass, or the number of passes to achieve desired thickness, in clock-rolling on the homogeneity of final microstructure has not been investigated yet. In this study, deformation and recrystallization behaviors of Ta sheets during 8-pass and 16-pass clock-rolling as well as subsequent annealing are investigated. X-ray diffraction reveal that 16-pass sample has relatively homogeneous {111} ⟨uvw⟩ {〈111〉//normal direction (ND)} and {100} ⟨uvw⟩ {〈100〉//ND} fibers along its thickness, whereas the distribution of texture in 8-pass sample is uneven. X-ray line profile analysis show that the distribution of stored energy is also more homogeneous in the 16-pass sample. Electron backscatter diffraction and transmission electron microscopy reveal numerous microshear bands and well-arranged microbands predominantly occurring in {111} deformed matrix. These prevail in the center of the 8-pass sample, whereas grain subdivision within {100} and {111} matrix in the 16-pass sample is more homogeneous through thickness. Average grain orientation spread (GOSaverage) within the {111} matrix in the center of the 8-pass sample is significantly higher than that at the surface and quarter-thickness, indicating enhanced grain subdivision. Schmid factor and Taylor model analysis demonstrate that a greater probability of activation of the primary slip system only in the 8-pass sample compared to larger number of active slip systems in the 16-pass sample. Upon annealing, uniform nucleation combined with a slower grain growth rate results in a finer and more uniform grain size in the 16-pass sample. By contrast, severe gradient in through-thickness recrystallization microstructure forms in the 8-pass sample. This is attributed to higher stored energy and preferential nucleation sites in the center leading to faster recrystallization compared to the surface. Overall, the increase of pass number improves the homogeneity of through-thickness recrystallization microstructure in Ta sheets under the change of strain path.
|
|
| 44. |
- Zhu, Jialin, et al.
(författare)
-
Strain dependence of deformation and recrystallization microstructure homogeneity in clock-rolled tantalum sheets
- 2020
-
Ingår i: Materials Characterization. - : Elsevier BV. - 1044-5803. ; 161
-
Tidskriftsartikel (refereegranskat)abstract
- Microstructure and crystallographic texture are the key factors that determine the sputtering target properties. Clock rolling plays an important role in improving the microstructure homogeneity, but the effect of strain during rolling on deformation and recrystallization behavior is not clear. Thus, high-purity tantalum (Ta) plates were 135° clock rolled to 70% and 87% reduction and then annealed at various temperatures to observe the microstructure evolution. Texture and microstructure in the center layer of the rolled and annealed Ta sheets were characterized via optical microscope (OM), X-ray diffraction (XRD), electron backscatter diffracting (EBSD) and transmission electron microscope (TEM). The results displayed that significant microstructure difference existed between 70% and 87% sample. Grain average misorientation value of {111} grains {〈111〉//normal direction (ND)} in the 70% sample was considerably higher than that in the 87% sample, suggesting a more heterogeneous grain fragmentation. Schmid factor (SFrolling) and Taylor model analysis of {111} grains in the 70% sample demonstrated that the slip was easier, and the system with higher SFrolling could alone accommodate the majority of plastic strain, contributing to the formation of micoshear bands. Upon annealing, the sample rolled 70% recrystallized more quickly, owing to strong {111} deformed texture, and severe microstructure subdivision and great stored energy within {111} grains. The {111} texture is very strong and grain size distribution was not uniform after the completion of recrystallization. However, after annealing of sample rolled 87%, smaller average grain size and variation, and relatively homogeneous texture distribution can be obtained.
|
|
| 45. |
- Zhu, Jialin, et al.
(författare)
-
The evolution of texture and microstructure uniformity in tantalum sheets during asymmetric cross rolling
- 2020
-
Ingår i: Materials Characterization. - : Elsevier BV. - 1044-5803. ; 168
-
Tidskriftsartikel (refereegranskat)abstract
- The evolution of texture and microstructure uniformity in tantalum (Ta) sheets for sputtering target applications is analyzed in detail across the thickness during asymmetric cross rolling (ACR). Three samples with different strains, i.e. 60%, 70% and 80% are obtained via ACR processing. X-ray diffraction suggests that the increase of strain during ACR results in the randomization of deformation texture across the sample thickness due to the penetration of shear strain into the center. Electron backscatter diffraction results indicate that the increasing strain in ACR can alleviate region-dependent microstructure inhomogeneity. This is also confirmed by the distributions of Vickers hardness and geometrically necessary dislocations. Taylor model analysis along with strain contouring maps suggest that relatively low and centralized number of active slip systems in the 80% sample effectively reduces strain concentrations and thus homogenizes the average shear strain of most active slip system in different grain orientations. Upon annealing, nuclei with random orientations can grow evenly from the deformed matrix in the 80% sample because of relatively homogeneous grain fragmentation and random deformation texture. These contribute to uniform and fine grain size combined with random crystallographic orientations after the completion of recrystallization.
|
|
