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CALPHAD est une méthode de calcul des diagrammes de phase, introduite par Larry Kaufman dans les années 1960. Le nom CALPHAD est l'acronyme de . Un diagramme de phase à l'équilibre est par exemple un diagramme binaire représentant la composition C d'un système chimique et la température T. Il montre les domaines (C,T) où les substances ou les solutions (c'est-à-dire les phases) sont stables et les domaines où deux ou plusieurs d'entre elles coexistent. Les diagrammes de phase sont un outil très puissant pour prédire l’état d’un système dans différentes conditions. Ils étaient à l’origine une méthode graphique permettant de rationaliser les informations expérimentales sur les états d’équilibre. Dans les systèmes complexes, des méthodes de calcul telles que CALPHAD sont utilisées pour modéliser les propriétés thermodynamiques de chaque phase et simuler le comportement de phase multicomposant. L'approche CALPHAD est fondée sur le fait qu'un diagramme de phase es

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Experimental investigation and thermodynamic modeling of the Au-Ge-Ni system

Shan Jin, Christian Leinenbach

Phase equilibria in the Au-Ge-Ni ternary system were studied by means of scanning electron microscopy, electron probe microanalysis, X-ray diffraction, and differential scanning calorimetry. The phase relations in the solid state at 600 A degrees C as well as a vertical section at Au72Ge28-Ni were established. No ternary compound was found at 600 A degrees C. On the basis of the experimental phase equilibria data, a thermodynamic model of the Au-Ge-Ni ternary system was developed using the CALPHAD method. Thermodynamically calculated phase diagrams are shown at 600 A degrees C, in two vertical sections and the liquidus projection. Reasonable agreement between the calculations and the experimental results was achieved.

Springer Wien2012

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Thermodynamic study and re-assessment of the Ge-Ni system

Shan Jin, Christian Leinenbach, Andrew Watson

The enthalpies of formation of the intermetallic compounds in the Ge-Ni binary system have been determined by calorimetric measurement and first-principles calculations. Based on the results obtained and information available in the literature, the phase diagram and thermodynamic properties of the Ge-Ni system have been re-assessed using the CALPHAD approach [L Kaufman, H. Bernstein, Computer Calculation of Phase Diagrams, Academic Press, New York (1970)], applying appropriate thermodynamic models for the phases. The liquid phase and the Ni-based solid solution (Ni) were modeled as substitutional solutions using the Redlich-Kister equation to represent the excess Gibbs energy. The B8-type intermediate phases epsilon Ni5Ge3, Ni19Ge12 and Ni3Ge2 were treated as a single phase, designated as Ni5Ge3. A three-sublattice model with stoichiometry (Ge)(Ni)(Va,Ni) was used to describe the B8-type Ni5Ge3-phase based on its crystal structure. The order-disorder transformation between disordered FCC_Al and the ordered L1(2)-type phase, beta Ni3Ge, was treated using a two-sublattice model. The other five intermetallic compounds were treated as stoichiometric compounds. The phase diagram and the thermodynamic properties calculated from the optimized model parameters are in good agreement with most of the experimental data. (C) 2012 Elsevier Ltd. All rights reserved.

Pergamon-Elsevier Science Ltd2012

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Influence of Hf on the heat treatment response of additively manufactured Ni-base superalloy CM247LC

Hossein Ghasemi Tabasi, Jamasp Jhabvala, Shreyas Sanjay Joglekar, Christian Leinenbach, Roland Logé

The influence of Hf on the heat treatment response of a Laser Powder Bed Fusion (L-PBF) fabricated Ni-base superalloy was investigated. A Hf-free version of CM247LC, CM247LC NHf, and CM247LC (similar to 1.4 wt% Hf) were subjected to identical thermal treatments and characterized. After solutionizing at 1260 degrees C for 2 h, both alloys displayed recrystallization and grain growth. The CM247LC NHf had numerous annealing twins suggesting that Hf inhibits twin formation. The CM247LC NHf alloy displayed a lower peak hardness than CM247LC (5000 MPa and 5200 MPa, respectively) and this was attributed to a similar to 6% point reduction (Calphad calculated) in gamma' phase fraction due to the removal of Hf. Despite the lower hardness values, the CM247LC NHf displayed a higher yield strength than CM247LC at 760 degrees C (969 MPa and 926 MPa, respectively). Elongation at fracture at 760 degrees C was similar (similar to 1%) for both CM247LC and CM247LC NHf. The removal of Hf was shown to be effective at mitigating the strain age cracking susceptibility of CM247LC, likely due to the decrease in y' phase fraction and lattice mismatch.

ELSEVIER SCIENCE INC2021

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