| 1. |
- Palumbo, M., et al.
(författare)
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Thermodynamic modelling of crystalline unary phases
- 2014
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Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 251:1, s. 14-32
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Tidskriftsartikel (refereegranskat)abstract
- Progress in materials science through thermodynamic modelling may rest crucially on access to a database, such as that developed by Scientific Group Thermodata Europe (SGTE) around 1990. It gives the Gibbs energy G(T) of the elements in the form of series as a function of temperature, i.e. essentially a curve fitting to experimental data. In the light of progress in theoretical understanding and first-principles calculation methods, the possibility for an improved database description of the thermodynamics of the elements has become evident. It is the purpose of this paper to provide a framework for such work. Lattice vibrations, which usually give the major contribution to G(T), are treated in some detail with a discussion of neutron scattering studies of anharmonicity in aluminium, first-principles calculations including ab initio molecular dynamics (AIMD), and the strength and weakness of analytic model representations of data. Similarly, electronic contributions to G(T) are treated on the basis of the density of states N(E) for metals, with emphasis on effects at high T. Further, we consider G(T) below 300K, which is not covered by SGTE. Other parts in the paper discuss metastable and dynamically unstable lattices, G(T) in the region of superheated solids and the requirement on a database in the calculation of phase diagrams.
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| 2. |
- Hallstedt, B., et al.
(författare)
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PrecHiMn-4—A thermodynamic database for high-Mn steels
- 2017
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Ingår i: Calphad. - : Elsevier. - 0364-5916 .- 1873-2984. ; 56, s. 49-57
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Tidskriftsartikel (refereegranskat)abstract
- This paper concerns a Calphad database that was developed to describe precipitation of cubic carbides and nitrides (V, Nb and Ti) in high manganese steels and to describe phase equilibria in high manganese steels with high aluminium content. The database has also been shown to be useful for calculations on medium manganese steels and low-density steels with varying aluminium additions. Thus the database covers a significant fraction of the steels that are termed advanced high strength steels (AHSS) of the second and third generation. A number of systems were assessed (or reassessed) for the database, namely Fe–Mn–Al, Fe–Mn–C, Fe–Nb, Mn–Nb, Fe–Mn–Nb, Fe–Nb–V, Fe–Nb–C, Mn–Nb–C, Fe–Mn–Nb–C, Nb–N, Fe–Mn–Nb–N. The remaining systems were taken from published assessments. The database covers the elements Fe, Mn, Al, Si, V, Nb, Ti, C and N.
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| 3. |
- Lindahl, Bonnie B., et al.
(författare)
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Ordering in ternary BCC alloys applied to the Al-Fe-Mn system
- 2015
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Ingår i: Calphad. - : Elsevier. - 0364-5916 .- 1873-2984. ; 51, s. 211-219
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Tidskriftsartikel (refereegranskat)abstract
- TWIP (TWinning Induced Plasticity) steels are attracting a lot of attention due to their combination of strength and ductility. In a previous work [1] (B. Lindahl, M. Selleby, Calphad 43 (2013) 86-93) a thermodynamic assessment of the Al-Fe-Mn system, which forms the basis of TWIP steels, was presented. The previous assessment treated the A2/B2 order-disorder transformation in the bcc phase using a two-sublattice model. In the present work a four-sublattice model has been used in order to also be able to describe the transition into the ordered DO3 compound that occurs at lower temperatures. pair interaction energies for the Fe-Mn system are evaluated which prove crucial to the extrapolations into the Al-Fe-Mn system. Along with this various aspects of modeling chemical ordering using the Calphad approach are discussed. Equations for determining the ternary compound energies from binary pair interactions energies are presented and equations for determining the parameter values from the ordered parameters are derived.
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| 4. |
- Liu, Xuan L., et al.
(författare)
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First-Principles Calculations, Experimental Study, and Thermodynamic Modeling of the Al-Co-Cr System
- 2015
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 10:4
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Tidskriftsartikel (refereegranskat)abstract
- The phase relations and thermodynamic properties of the condensed Al-Co-Cr ternary alloy system are investigated using first-principles calculations based on density functional theory (DFT) and phase-equilibria experiments that led to X-ray diffraction (XRD) and electron probe micro-analysis (EPMA) measurements. A thermodynamic description is developed by means of the calculations of phase diagrams (CALPHAD) method using experimental and computational data from the present work and the literature. Emphasis is placed on modeling the bcc-A2, B2, fcc-gamma, and tetragonal-sigma phases in the temperature range of 1173 to 1623 K. Liquid, bcc-A2 and fcc-gamma phases are modeled using substitutional solution descriptions. First-principles special quasirandom structures (SQS) calculations predict a large bcc-A2 (disordered)/B2 (ordered) miscibility gap, in agreement with experiments. A partitioning model is then used for the A2/B2 phase to effectively describe the order-disorder transitions. The critically assessed thermodynamic description describes all phase equilibria data well. A2/B2 transitions are also shown to agree well with previous experimental findings.
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| 5. |
- Zuazo, I., et al.
(författare)
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Low-Density Steels : Complex Metallurgy for Automotive Applications
- 2014
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Ingår i: JOM. - : Springer Science and Business Media LLC. - 1047-4838 .- 1543-1851. ; 66:9, s. 1747-1758
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Tidskriftsartikel (refereegranskat)abstract
- The current aim in the development of third-generation steels for lightweighting automotive applications is to increase strength keeping at least the same formability as current steel concepts. In this philosophy, an optimal concept would be one that brings, in addition, a lower density. For this purpose, low-density steels have been designed with important aluminum additions obtaining density reductions of 8-10% or higher in comparison with low-carbon steels. At the levels required for lightweighting, aluminum introduces complex phenomena in steels. Here, some of the effects of aluminum in phase stability, CALPHAD-type modeling, and microstructure development are described, the latter in relation with mechanical properties. Finally, the potential of two families of lightweight steels for automotive applications is assessed by comparison with a steel currently present in automotive structures.
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