The Calphad Method and Its Role in Material and Process Development

Kattner, Ursula R.

doi:10.4322/2176-1523.1059

Cited by 115 publications

(36 citation statements)

References 88 publications

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“…The excess Gibbs free-energies for the liquid and the solid phases as a function of temperature used in the above thermodynamic equilibrium calculations were obtained using the CALPHAD approach in the form of Redlich-Kister polynomials [18] that contain the binary and ternary interaction coefficients for Nb, Ni, and Fe in the ternary system. The equilibrium interface Nb and Fe concentrations obtained using the Gibbs energy functions are fitted to polynomials as shown in Figure 1.…”

Section: Surrogate Alloy and Calphad Integrationmentioning

confidence: 99%

Phase Field Simulations of Microstructure Evolution in IN718 Using a Surrogate Ni–Fe–Nb Alloy during Laser Powder Bed Fusion

Radhakrishnan

Gorti

Turner

et al. 2018

Metals

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The solidification microstructure in IN718 during additive manufacturing was modeled using phase field simulations. The novelty of the research includes the use of a surrogate Ni-Fe-Nb alloy that has the same equilibrium solidification range as IN718 as the model system for phase field simulations, the integration of the model alloy thermodynamics with the phase field simulations, and the use of high-performance computing tools to perform the simulations with a high enough spatial resolution for realistically capturing the dendrite morphology and the level of microsegregation seen under additive manufacturing conditions. Heat transfer and fluid flow models were used to compute the steady state temperature gradient and an average value of the solid-liquid (s-l) interface velocity that were used as input for the phase field simulations. The simulations show that the solidification morphology is sensitive to the spacing between the columnar structures. Spacing narrower than a critical value results in continued growth of a columnar microstructure, while above a critical value the columnar structure evolves into a columnar dendritic structure through the formation of secondary arms. These results are discussed in terms of the existing columnar to dendritic transition (CDT) theories. The measured interdendritic Nb concentration, the primary and secondary arm spacing is in reasonable agreement with experimental measurements performed on the nickel-base superalloy IN718. and solidification of a powder bed using moving heat sources based on electron beam or laser. Part of the previously solidified layer is re-melted during a subsequent pass. The solidification microstructure that develops during the process is influenced both by the thermal history as well as the underlying structure in the previously solidified layer. The characteristics of the solidification microstructure including primary and secondary dendrite arms spacing, solute distribution within the dendrites and the dendrite orientations have a direct bearing on the mechanical properties of the as-processed component. Also, during post-processing heat treatment, evolution of the microstructure depends on the primary solidification structure due to potential solid-state transformations. Therefore, it is important to quantitatively predict the solidification microstructure in a given alloy, under a given set of processing parameters. An excellent review of the processing-structure relationships during AM of structural alloys is available in a recent publication [1].A key feature of the powder bed fusion processes is the extremely high cooling rate experienced by the melt pool. Typical cooling rates are of the order of 10 6 K/s. Under extreme conditions, the velocity of the solid-liquid (s-l) interface can approach several meters per second, especially along the heat source travel direction. This could cause significant deviation from thermodynamic equilibrium at the moving s-l interface. Non-equilibrium solute-partitioning could lead to a reduction in the solute...

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Section: Surrogate Alloy and Calphad Integrationmentioning

confidence: 99%

Phase Field Simulations of Microstructure Evolution in IN718 Using a Surrogate Ni–Fe–Nb Alloy during Laser Powder Bed Fusion

Radhakrishnan

Gorti

Turner

et al. 2018

Metals

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“…(Lukas et al, 2007;Zhang et al, 2014). Therefore, phase field model combined with convincible CALPHAD-type data are expected to quantitatively simulate the thermodynamics for phase transitions in even multicomponent systems (Kitashima 2008;Nestler and Choudhury, 2011;Kattner 2016).…”

Section: Introductionmentioning

confidence: 99%

Development of a Phase Field Tool Coupling With Thermodynamic Data for Microstructure Evolution Simulation of Alloys in Nuclear Reactors

Guo

Liu

et al. 2021

Front. Mater.

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We have developed a new phase field tool PHAFIS to automatically incorporate the thermodynamic data for both of WBM and KKS phase field simulations, which are widely used in the simulation of microstructure evolution of nuclear materials. Based on the generic C/C++ programming language, PHAFIS is capable of automatically parsing the standard TDB files, extracting the free energy and diffusion potential varying with the composition in an analytical way. Based on the two diffrerent TDB files of Fe-Cr binary system and the interpolated data, the phase morphologies during spinodal decomposition at 700 K and liquid-solid transition at high temperatures above 1800 K are reproduced and compared with each other by WBM and KKS model, respectively. Specifically, both of interface-controlled and diffusion-controlled phase transition mechanisms are successfully revealed for solidification through our KKS simulation, consistent with classic phase transition theories. It can be concluded that even slight differences in thermodynamic data will cause significant changes in the microstructure evolution. The integrity of our software tool will facilitate the coupling of phase field methods with thermodynamic data for other materials, paving a fundamental step for coupling more factors required in microstructure simulation.

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“…Superalloys are multi-component alloys, which makes the experimental determination of phase boundaries challenging. The CALPHAD (CALculation of PHAse Diagrams) method is widely accepted as one of the most effective tools for materials design because it can be used for quantitative prediction of the phase relations in multi-component alloys [2,3]. CALPHAD databases provide a set of self-consistent descriptions of the thermodynamic properties of multi-component systems obtained from critical assessments of the relevant elemental, binary and ternary systems [4].…”

Section: Introductionmentioning

confidence: 99%

Thermodynamic analysis of the topologically close packed σ phase in the Co Cr system

et al. 2019

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Density functional theory (DFT) calculations show that it is essential to consider the magnetic contribution to the total energy for the end-members of the σ phase. A more straightforward method to use the DFT results in a CALPHAD (Calculation of phase diagrams) description has been applied in the present work. It was found that only the results from DFT calculations considering spin-polarization are necessary to obtain a reliable description of the σ phase. The benefits of this method are: the DFT calculation work can be reduced and the CALPHAD description of the magnetic contribution is more reliable. A revised thermodynamic description of the Co–Cr system is presented which gives improved agreement with experimental phase boundary data for the σ phase.

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The Calphad Method and Its Role in Material and Process Development

Cited by 115 publications

References 88 publications

Phase Field Simulations of Microstructure Evolution in IN718 Using a Surrogate Ni–Fe–Nb Alloy during Laser Powder Bed Fusion

Phase Field Simulations of Microstructure Evolution in IN718 Using a Surrogate Ni–Fe–Nb Alloy during Laser Powder Bed Fusion

Development of a Phase Field Tool Coupling With Thermodynamic Data for Microstructure Evolution Simulation of Alloys in Nuclear Reactors

Thermodynamic analysis of the topologically close packed σ phase in the Co Cr system

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