| 1. |
- Dong, Y. B., et al.
(författare)
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The growth of graphene on Ni–Cu alloy thin films at a low temperature and its carbon diffusion mechanism
- 2019
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Ingår i: Nanomaterials. - : MDPI AG. - 2079-4991. ; 9:11
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Tidskriftsartikel (refereegranskat)abstract
- Carbon solid solubility in metals is an important factor affecting uniform graphene growth by chemical vapor deposition (CVD) at high temperatures. At low temperatures, however, it was found that the carbon diffusion rate (CDR) on the metal catalyst surface has a greater impact on the number and uniformity of graphene layers compared with that of the carbon solid solubility. The CDR decreases rapidly with decreasing temperatures, resulting in inhomogeneous and multilayer graphene. In the present work, a Ni–Cu alloy sacrificial layer was used as the catalyst based on the following properties. Cu was selected to increase the CDR, while Ni was used to provide high catalytic activity. By plasma-enhanced CVD, graphene was grown on the surface of Ni–Cu alloy under low pressure using methane as the carbon source. The optimal composition of the Ni–Cu alloy, 1:2, was selected through experiments. In addition, the plasma power was optimized to improve the graphene quality. On the basis of the parameter optimization, together with our previously-reported, in-situ, sacrificial metal-layer etching technique, relatively homogeneous wafer-size patterned graphene was obtained directly on a 2-inch SiO2 /Si substrate at a low temperature (~600◦ C).
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| 2. |
- Abu-Odeh, A., et al.
(författare)
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Efficient exploration of the High Entropy Alloy composition-phase space
- 2018
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Ingår i: Acta Materialia. - : Acta Materialia Inc. - 1359-6454 .- 1873-2453. ; 152, s. 41-57
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Tidskriftsartikel (refereegranskat)abstract
- High Entropy Alloys (HEAs), Multi-principal Component Alloys (MCA), or Compositionally Complex Alloys (CCAs) are alloys that contain multiple principal alloying elements. While many HEAs have been shown to have unique properties, their discovery has been largely done through costly and time-consuming trial-and-error approaches, with only an infinitesimally small fraction of the entire possible composition space having been explored. In this work, the exploration of the HEA composition space is framed as a Continuous Constraint Satisfaction Problem (CCSP) and solved using a novel Constraint Satisfaction Algorithm (CSA) for the rapid and robust exploration of alloy thermodynamic spaces. The algorithm is used to discover regions in the HEA Composition-Temperature space that satisfy desired phase constitution requirements. The algorithm is demonstrated against a new (TCHEA1) CALPHAD HEA thermodynamic database. The database is first validated by comparing phase stability predictions against experiments and then the CSA is deployed and tested against design tasks consisting of identifying not only single phase solid solution regions in ternary, quaternary and quinary composition spaces but also the identification of regions that are likely to yield precipitation-strengthened HEAs.
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| 3. |
- Aripov, G. R., et al.
(författare)
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The Study of Structural Changes in Homogenized High-Entropy Alloys
- 2021
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Ingår i: Physical Mesomechanics. - : Pleiades Publishing Ltd. - 1029-9599 .- 1990-5424. ; 24:6, s. 663-673
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Tidskriftsartikel (refereegranskat)abstract
- This work investigates the effect of chemical composition on the microstructure and properties of cast high-entropy alloys, and optimal conditions for homogenization annealing. The investigation is performed on alloys of the following compositions: Fe22.5Ni22.5Cu22.5Co22.5Al10, Fe22.5Ni22.5Cu22.5Cr22.5Al10, and Fe22.5Ni22.5Cu22.5Mn22.5Al10 (shortly Fe22.5Ni22.5Cu22.5(Co, Cr or Mn)(22.5)Al-10), melted in an induction furnace with casting into a copper mold. The structural and phase changes in high-entropy alloys of different chemical composition are examined before and after homogenization annealing. The morphology of crystalline phases and microstructural evolution are analyzed experimentally. The strength characteristics of the alloys subjected to different homogenization annealing conditions are determined.
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| 4. |
- Bigdeli, Sedigheh
(författare)
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Developing the third generation of Calphad databases: what can ab-initio contribute?
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Developing the third generation of Calphad databases with more physical basis valid within a wider temperature range is the aim of the present work. Atomistic scale (ab-initio) methods, particularly techniques based on DFT theory, are used for modelling dierent phenomena, so as to gauge the capacity for use in Calphad modelling. Several systems are investigated in this work for studying dierent phenomena, such as magnetism and vibration of atoms. In the case of pure elements (unaries), thermodynamic properties of Mn, Al and C are optimized in the whole temperature range by the help of new models. In addition, DFT results and specic characteristics of these elements are also used to develop models for describing magnetic properties and atomic vibrations. With regards to coupling between DFT and Calphad, the EMTO technique is used for determining the magnetic ground state of the metastable hcp phase in Fe and Mn, and the TU-TILD technique is used for modelling solid phases above the melting point. TU-TILD is also used for calculating thermodynamic properties of bcc Mn at nite temperatures. The same phenomena are investigated in higher-order systems, i.e. the binaries Fe-Mn and Mn-C. Thermodynamic properties and phase diagrams of these systems are assessed against experimental data. Moreover, the revised magnetic model is used for modelling magnetic properties in these systems.It is shown through this investigation that although the DFT methods are powerful tools for model development and for resolving discrepancies between dierent experimental datasets, they should not be overly-trusted. Caution must be taken when using DFT results, since the approximations and assumptions for computational implementations may cause some errors in the results. Moreover, implementing them into Calphad software as a connected methodology is not currently accessible due to the computational limitations.It is concluded that coupling between the DFT and Calphad approaches can currently be achieved by using DFT results as an input in Calphad modelling. This will help to improve them until they can be integrated into the Calphad approach by the progress of computational possibilities.One of the advantages of developing the third generation Calphad databases is the possibility of using the 0 K DFT results in Calphad modelling, since the new databases are valid down to 0 K. This has not been possible in the past, and such potential opens a new door to bring more physics into the Calphad approach.
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| 5. |
- Brennhaugen, David D. E., et al.
(författare)
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Predictive modeling of glass forming ability in the Fe-Nb-B system using the CALPHAD approach
- 2017
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Ingår i: Journal of Alloys and Compounds. - : Elsevier. - 0925-8388 .- 1873-4669. ; 707, s. 120-125
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Tidskriftsartikel (refereegranskat)abstract
- Accurate values needed for the most commonly used indicators of good Glass Forming Ability (GFA) in alloys, i.e. the liquidus (T-l), crystallization (T-x) and glass transition (T-g) temperatures, are only available after successful production of the metallic glass of interest. This has traditionally made discovery of new metallic glasses an expensive and tedious procedure, based on trial-and-error methodology. The present study aims at testing the CALPHAD (Computer Coupling of Phase Diagrams and Thermochemistry) approach for predicting GFA in the Fe-Nb-B system by the use of the Thermo-Calc software and the thermodynamic database TCFE7. The melting temperatures and phase stabilities were calculated and combined with data for an atomic size mismatch factor, lambda, in order to identify and map potential high-GFA regions. Selected compositions in the identified regions were later produced by suction casting and melt spinning, and the potential success verified using X-Ray Diffraction (XRD). Differential Scanning Calorimetry (DSC) was also used to compare thermodynamic calculations for the model predictions, and evaluate standard GFA indicators. The model is found to fit well with literature data, as well as predict new bulk glassy compositions at and around Fe70.5Nb7B22.5. These results show promise in further predictive use of the model.
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| 6. |
- Chen, Hai-Lin, et al.
(författare)
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Database development and Calphad calculations for high entropy alloys : Challenges, strategies, and tips
- 2018
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Ingår i: Materials Chemistry and Physics. - : Elsevier. - 0254-0584 .- 1879-3312. ; 210, s. 279-290
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Tidskriftsartikel (refereegranskat)abstract
- The development of a reliable multicomponent thermodynamic database for high entropy alloys (HEAs) is a daunting task and it faces new challenges comparing to the development of databases for conventional single principal element alloys, such as the assessment of a large number of ternary systems, the proper estimation of phase stability within metastable compositional and temperature ranges, and the reasonable extrapolation into higher order systems. We have recently established a thermodynamic database (TCHEA1) especially for HEAs within a 15-element framework. This work highlights the usage of high throughput density functional theory (OFT) calculations for validating and refining the binary and ternary parameters of the solid solution phases, and having a more reliable extrapolation into metastable regions and higher order systems. TCHEA1 consists of 105 binaries and 200 ternaries and contains nearly all the stable solution phases and intermetallic compounds in each of the assessed systems. Together with Thermo-Calc, this database enables us to predict the stability of the desired multicomponent solid solution relative to intermetallic compounds and other solid solutions. Calculation examples are presented not only for case studies but also for bridging the knowledge gap between Calphadian and people who do not have a background of the Calphad approach.
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| 7. |
- Chen, Kaixuan, et al.
(författare)
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Mapping formation mechanisms and transformation regimes of multiple Fe precipitates in Cu-Fe-Co alloy during casting process
- 2024
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Ingår i: Scripta Materialia. - : Elsevier BV. - 1359-6462 .- 1872-8456. ; 246
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Tidskriftsartikel (refereegranskat)abstract
- Precipitate features including size, morphology, crystal structure, etc., are important parameters determining the performance of precipitate-strengthened alloys. Multiple Fe precipitates were identified in as-cast Cu alloys exhibiting the distinct features, which dramatically influence mechanical properties. However, a complete understanding of precipitation behaviors of Fe particles during casting, in terms of both microscopic kinetics and thermodynamics, remains experimentally challenging. Here, we report the combined implementation of transmission electron microscopy, Thermo-Calc calculations and First-principles calculations to map mechanisms and growth regimes of Fe precipitation in a Cu-Fe-Co system. Our analyses support the idea that to understand the microstructural evolution in the system, both thermodynamic and kinetic arguments must be taken into account. Then, using our multi-approach strategy, the complete picture of the formation and transformation of Fe precipitates is proposed. This work is vital to promote microstructural design for Cu-Fe(-Co) systems, and sheds new insights into understanding of intricate precipitation in alloys.
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| 8. |
- Chen, Kaixuan, et al.
(författare)
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Optimization of deformation properties in as-cast copper by microstructural engineering. Part I. microstructure
- 2018
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Ingår i: Journal of Alloys and Compounds. - : Elsevier. - 0925-8388 .- 1873-4669. ; 763, s. 592-605
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Tidskriftsartikel (refereegranskat)abstract
- The microstructural features required to optimize both the strength and ductility of copper are investigated by examining the as-cast pure Cu and Cu-(1.0e3.0)Fe-0.5Co and Cu-1.5Fe-0.1Sn (wt %) alloys. Uniaxial tensile tests show that (Fe, Co)- or (Fe, Sn)-doping improves both the strength and ductility of pure copper. The microstructure evolution with Fe, Co, or Sn doping is characterized by using optical and scanning and transmission electron microscopies. The effects of Fe, Co, and Sn doping on the microstructure clearly show that (i) iron-rich nanoparticles are dispersed inside the grains. The spherical nanoparticles grow in size with increasing Fe content, and when the Fe content exceeds 2.0 wt %, the particles transition into a petal-like morphology. (ii) The microstructure of the alloys (grain size and morphology) is notably influenced by the Fe and Co contents, and the grain size is reduced from an average of 603 mu m in pure Cu to an average of 26 mm in the Cu-3.0Fe-0.5Co alloy. (iii) The addition of 1.5wt % Fe and 0.1wt % Sn dramatically reduces the grain size to an average of 42 mu m, and this reduction is correlated with the appearance of smaller spherical iron-rich nanoparticles. The evolution mechanisms of the iron-rich nanoparticles and grain structure under the alloying effect are discussed.
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| 9. |
- Chen, K. X., et al.
(författare)
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3D morphology of the petal-like precipitates in Cu-Fe alloys: Experimental study and phase field modelling
- 2024
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Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 270
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Tidskriftsartikel (refereegranskat)abstract
- Precipitation hardening is a well-known phenomenon which is widely harnessed in alloy design strategy. In particular, the microstructural features such as shape, size, precipitate number density and volume fraction determine the mechanical behaviour of materials. During service, the morphology of precipitates sometimes achieves a complex 3D shape upon displaying branching and/or splitting patterns. Unfortunately, the detailed information about this intricate morphology cannot be retrieved through traditional experimental techniques based on 2D visualization. Here, we report the implementation of a 3D analysis technique combining Focused Ion Beam (FIB) and Scanning Electron Microscopy (SEM) tomography to visualize the atypical petal-like morphology of Fe-rich precipitates in a Cu-Fe alloy. Using Phase-Field modelling (PFM), we identify the mechanism responsible for the unusual morphologies of Fe-rich particles. Our work highlights the significance of 3D characterization of precipitates and provides a fascinating pathway for refining understanding of precipitation mechanisms in metals and alloys.
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| 10. |
- Churyumov, A. Yu., et al.
(författare)
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Effect of Nb Addition on Microstructure and Thermal and Mechanical Properties of Fe-Co-Ni-Cu-Cr Multiprincipal-Element (High-Entropy) Alloys in As-Cast and Heat-Treated State
- 2019
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Ingår i: JOM. - : SPRINGER. - 1047-4838 .- 1543-1851. ; 71:10, s. 3481-3489
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Tidskriftsartikel (refereegranskat)abstract
- The microstructure and thermal and mechanical properties of (FeCoNiCuCr)(100-x)-Nb-x multiprincipal-element alloys have been investigated in the as-cast and heat-treated state. The alloys were smelted by arc-melting in argon atmosphere. As-cast samples were produced by copper mold casting. The structure was studied by scanning electron microscopy (SEM) and x-ray diffraction (XRD) analysis. The calculated phase diagrams of the Fe-Co-Ni-Cu-Cr-Nb system were used to predict the phase composition. The predicted thermodynamic temperatures and phase areas were compared with those obtained using differential scanning calorimetry (DSC) and the results of SEM observation, respectively. Addition of 10 at.% Nb caused phase separation of the alloy in the liquid state. Addition of Nb caused an increase in the yield strength by solid-solution hardening and by the formation of intermetallic compounds. Heat treatment also affected the mechanical properties of the studied alloys.
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