| 1. |
- Masood, Ansar, 1983-, et al.
(author)
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Distinct Plasticity of Biocompatible Ti-Zr-Cu-Pd-Sn Bulk Metallic Glass
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Other publication (other academic/artistic)abstract
- We have developed Ti-Zr-Cu-Pd-Sn bulk metallic glass without toxic elements which exhibits distinct plasticity (~12.6%) by revealing strain hardening before failure. Specimens performed under compression tests do not show any crystalline phases which usually enhance plasticity by branching or restricting the rapid propagation of shear bands. Along with excellent mechanical properties alloy exhibits appreciably high bulk forming ability, GFA, with large supercooled regime (~56K) and as a consequence cylindrical rods of at least 7mm were fabricated directly by Cu-mold casting. The combination of such mechanical properties and appreciably high bulk forming ability makes it a potential candidate for biomedical applications.
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| 2. |
- Granbom, Ylva
(author)
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Structure and mechanical properties of dual phase steels : An experimental and theoretical analysis
- 2010
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Doctoral thesis (other academic/artistic)abstract
- The key to the understanding of the mechanical behavior of dual phase (DP) steels is to a large extent to be found in the microstructure. The microstructure is in its turn a result of the chemical composition and the process parameters during its production. In this thesis the connection between microstructure and mechanical properties is studied, with focus on the microstructure development during annealing in a continuous annealing line. In-line trials as well as the lab simulations have been carried out in order to investigate the impact of alloying elements and process parameters on the microstructure. Further, a dislocation model has been developed in order to analyze the work hardening behavior of DP steels during plastic deformation. From the in-line trials it was concluded that there is an inheritance from the hot rolling process both on the microstructure and properties of the cold rolled and annealed product. Despite large cold rolling reductions, recrystallization and phase transformations, the final dual phase steel is still effected by process parameters far back in the production chain, such as the coiling temperature following the hot rolling. Lab simulations showed that the microstructure and consequently the mechanical properties are impacted not only by the chemical composition of the steel but also by a large number of process parameters such as soaking temperature, cooling rate prior to quenching, quench and temper annealing temperature.
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| 3. |
- Hillert, Mats, et al.
(author)
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Reply to comments on "On the definition of paraequilibrium and orthoequilibrium"
- 2005
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In: Scripta Materialia. - : Elsevier BV. - 1359-6462 .- 1872-8456. ; 52:1, s. 87-88
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Journal article (peer-reviewed)abstract
- In the equilibrium conditions called CPE the letters PE stand for paraequilibrium. However, paraequilibrium plays no important role in the process for which CPE was introduced. The essential feature is the equilibration of carbon between a and γ under the constraint that the interface is immobile. In order to avoid confusion regarding the nature of paraequilibrium, the term CCE (constrained carbon equilibrium) is proposed instead of CPE.
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| 4. |
- Larsson, Henrik, et al.
(author)
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Oxidation of iron at 600 degrees C - experiments and simulations
- 2016
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In: Materials and corrosion - Werkstoffe und Korrosion. - : Wiley-Blackwell. - 0947-5117 .- 1521-4176.
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Journal article (peer-reviewed)abstract
- Pure iron has been oxidized at 600°C and 1bar in dry O2 (oxygen partial pressure 0.05, bal. N2) and the mass gain as well as the thicknesses of the individual oxide phases have been measured. The oxidation process has been simulated using a modified version of the homogenization model as implemented in Dictra; this has helped to rationalize the kinetics of oxide scale formation and in particular the evolution of the hematite (Fe2O3), magnetite (Fe3O4), and wustite (FeO) which form. Independently assessed thermodynamic and kinetic Calphad databases are needed for the calculations; details of these are given. Reasonable agreement between simulation results and experimental data is obtained, though it is concluded that the large influence of grain boundary diffusion on the oxidation rate needs further consideration.
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| 5. |
- Odqvist, Joakim, et al.
(author)
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3D analysis of phase separation in ferritic stainless steels
- 2012
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In: Proceedings of the 1st International Conference on 3D Materials Science. - Cham : John Wiley & Sons. - 9781118470398 ; , s. 221-226
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Conference paper (peer-reviewed)abstract
- The embrittlement of ferritic stainless steels during low temperature aging is attributed to the phase separation with Fe and Cr demixing. The small scale of the decomposed structure with only minor compositional fluctuations and short distances between the enriched and depleted regions has been a challenge for quite some time. A wide selection of experimental and modeling tools have been used to quantify these types of structures. These analyses often focus on rather late stages of decomposition where the mechanical properties are already seriously affected. The recent advance in 3D tools like phase-field and atom probe tomography have created a need for good quantitative procedures of evaluating the structure and also to link results from the continuum approach to the individual atom measurements. This work aims at addressing this need.
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| 6. |
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| 7. |
- Safara, Nima, et al.
(author)
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Study of the mean size and fraction of the second-phase particles in a 13% chromium steel at high temperature
- 2020
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In: Philosophical Magazine. - : Taylor & Francis. - 1478-6435 .- 1478-6443. ; 100:2, s. 217-233
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Journal article (peer-reviewed)abstract
- The mean size and fraction of the second-phase particles in a 13% chromium steel are investigated, while no plastic deformation was applied. The results of the measurement are compared with the modelling results from a physicallybased model. The heating sequence is performed on samples using a Gleeble thermo-mechanical simulator over the temperature range of 850–1200°C. Using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), the size distribution and composition of the carbides were evaluated, respectively. For obtaining particle size distribution (PSD), an image-processing software was employed to analyse the SEM images. Additionally, the relation between the 2D shape factor and size of the particles is also studied at different temperatures and most of the particles turned out to have a shape factor close to two. In order to measure the carbide weight fraction, electrochemical phase isolation was employed. The Ms and fraction of the martensite phase after quenching of samples are calculated and the results were comparable with the measured hardness values at corresponding temperatures. The measured hardness of the samples is found to comply very well with the measured mean size of the precipitates. The calculated mean size of the particles from the model shows very good agreement with both hardness value and experimentally measured mean size, while the calculated volume fraction from simulation follows a slightly different trend.
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| 8. |
- Safara Nosar, Nima, 1982-
(author)
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Modeling the Microstructure Evolution During and After Hot Working in Martensitic Steel
- 2021
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Licentiate thesis (other academic/artistic)abstract
- In this study, the goal is to predict the microstructure evolution during and after the hot working of a martensitic stainless steel with 13% chromium using a physically-based model in the form of a MATLAB toolbox. This model is based on dislocation density theory and consists of coupled sets of evolution equations for dislocation, vacancies, recovery, recrystallization, and grain growth.The focus in this work is on the flow stress calculation and the effect of second phase particles on the strengthening mechanisms in the material at elevated temperatures. Recovery and recrystallization are also studied for this alloy during deformation and following stress relaxation.The experimental part of this work was performed with a Gleeble thermo-mechanical simulator over the temperature range of 850 to 1200°C. Samples were investigated later by a light optical microscope (LOM) and a scanning electron microscope (SEM) equipped with energy dispersive X-ray spectroscope (EDS). Hardness test and phase isolation were also performed on the samples and the results are compared with the modeling results.The model can satisfactorily predict the grain growth, recovery, recrystallization, and flow stress for this alloy. Further investigation on the second phase particles showed that the measured mean size of carbides has a good agreement with what is obtained from the model and the hardness values. On the other hand, the modeled volume fraction of the carbides followed a slightly different trend comparing to hardness values, and phase isolation results at temperatures higher than 1000°C. Additionally, the Ms temperature and fraction of the martensite phase are calculated for quenched samples where the results are following the measured hardness values.Finally, the Zener-Hollomon parameter (Z) and its relation to the flow stress and the activation energy for deformation are defined. The dynamic recrystallization (DRX) kinetic is modeled and the fraction DRX was calculated at various temperatures and strain rates for this alloy.
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| 9. |
- Yeddu, Hemantha Kumar, 1980-
(author)
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Martensitic Transformations in Steels : A 3D Phase-field Study
- 2012
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Doctoral thesis (other academic/artistic)abstract
- Martensite is considered to be the backbone of the high strength of many commercial steels. Martensite is formed by a rapid diffusionless phase transformation, which has been the subject of extensive research studies for more than a century. Despite such extensive studies, martensitic transformation is still considered to be intriguing due to its complex nature. Phase-field method, a computational technique used to simulate phase transformations, could be an aid in understanding the transformation. Moreover, due to the growing interest in the field of “Integrated computational materials engineering (ICME)”, the possibilities to couple the phase-field method with other computational techniques need to be explored. In the present work a three dimensional elastoplastic phase-field model, based on the works of Khachaturyan et al. and Yamanaka et al., is developed to study the athermal and the stress-assisted martensitic transformations occurring in single crystal and polycrystalline steels. The material parameters corresponding to the carbon steels and stainless steels are considered as input data for the simulations. The input data for the simulations is acquired from computational as well as from experimental works. Thus an attempt is made to create a multi-length scale model by coupling the ab-initio method, phase-field method, CALPHAD method, as well as experimental works. The model is used to simulate the microstructure evolution as well as to study various physical concepts associated with the martensitic transformation. The simulation results depict several experimentally observed aspects associated with the martensitic transformation, such as twinned microstructure and autocatalysis. The results indicate that plastic deformation and autocatalysis play a significant role in the martensitic microstructure evolution. The results indicate that the phase-field simulations can be used as tools to study some of the physical concepts associated with martensitic transformation, e.g. embryo potency, driving forces, plastic deformation as well as some aspects of crystallography. The results obtained are in agreement with the experimental results. The effect of stress-states on the stress-assisted martensitic microstructure evolution is studied by performing different simulations under different loading conditions. The results indicate that the microstructure is significantly affected by the loading conditions. The simulations are also used to study several important aspects, such as TRIP effect and Magee effect. The model is also used to predict some of the practically important parameters such as Ms temperature as well as the volume fraction of martensite formed. The results also indicate that it is feasible to build physically based multi-length scale model to study the martensitic transformation. Finally, it is concluded that the phase-field method can be used as a qualitative aid in understanding the complex, yet intriguing, martensitic transformations.
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| 10. |
- Zhou, Jing, et al.
(author)
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Direct atom probe tomography observations of concentration fluctuations in Fe-Cr solid solution
- 2015
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In: Scripta Materialia. - : Elsevier BV. - 1359-6462 .- 1872-8456. ; 98, s. 13-15
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Journal article (peer-reviewed)abstract
- The local concentration of atoms in an Fe-46.5 at.% Cr alloy, solution treated at four different temperatures above the miscibility gap, has been investigated using atom probe tomography. It is experimentally found that Cr atoms cluster in the solid solution and that the clustering tendency decreases with increasing temperature above the miscibility gap. These findings are corroborated by Monte Carlo simulations of the atomic short-range order, which show that clustering markedly decrease with increasing temperature from 800 to 1200 degrees C.
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