Nathalie Dupin

Thermodynamic assessment of the AlNi system

The sub-lattice model is used to describe the thermodynamic behaviour of the ordered phases existing in the AlNi system. The model parameters are derived from an optimisation procedure using all available experimental data. The order-disorder transformation f.c.c.-Al:Ll2 phase is modelled using either two or four sub-lattices which are mathematically equivalent.

Reply to the paper: “When is a compound energy not a compound energy? A critique of the 2-sublattice order/disorder model”: Of Nigel Saunders, Calphad 20 (1996) 491–499

Abstract An attempt is made to present in a more didactic manner the treatment of the order/disorder transformation expressed in the compound energy formalism. Some statements made in the article by Saunders are analysed and corrected.

On the compound energy formalism applied to fcc ordering.

The influence on the phase diagram and thermodynamic properties of some parameters in the Compound Energy Formalism (CEF) is studied for different simple binary and ternary cases showing fcc ordering. It is shown that the flexibility of this formalism should enable to model most real cases. Recommendations for the ternary parameters that should be set from the binary systems are made.

Thermodynamic assessment of the SiZr system

Abstract The binary Si-Zr system was thermodynamically assessed using the available experimental information: enthalpies of formation of the liquid and compound phases, and phase diagram data. A set of thermodynamic parameters consistent with phase diagram data was obtained.

Using first-principles results to calculate finite-temperature thermodynamic properties of the Nb-Ni μ phase in the Bragg-Williams approximation

Results of first-principles (FP) total energy calculations for 32 different configurations of the μ phase in the binary system Nb–Ni are used in the compound energy formalism (CEF) to model finite-temperature thermodynamic properties. A comparison with Cluster Expansion Hamiltonian–Cluster Variation Method (CEH-CVM) calculations indicates that the CEF describes temperature-dependent site occupancies as well as the CEH-CVM within the temperature range of interest for applications. This suggests that the Bragg–Williams–Gorsky approximation (BWGA) used in the CEF is sufficient to describe site occupancies and thermodynamics of the μ phase. A phase diagram is calculated using the μ phase description derived in the present work together with a previous Calphad description for the other phases of this system. The FP-CEF approach significantly improves the description of the thermodynamic properties as a function of composition compared to the Calphad procedure generally used up to now.

IV.6 – Microstructure of a five-component Ni-base superalloy: experiments and simulation

Publisher Summary The ever-increasing demand for high-performance alloys for high-temperature applications has led to the development of the present Ni-base superalloys. These alloys are routinely used as turbine blades in gas turbine engines. Their development was based on experimental observation and metallurgical intuition. Numerical simulations providing indication of trends, correlation between measurable quantities and determination of detrimental effects, even when qualitative, are welcome, allowing time and costs to be saved as well as the efficiency to be improved when compared with the usual trial-and-error methods. Many steps in the design and production of these alloys cannot be quantitatively simulated. Solidification simulations have been achieved, which enabled a revision of the empirical methods to be made, bringing more understanding and thereby implying an improvement in the entire alloy development process. This chapter presents the work that was performed within the frame of the Collaborative Research Center SFB 370, “ Integrated modeling of materials ” which aimed at understanding, controlling, and optimizing the microstructure evolution during solidification, heat treatment, coating, and operational service.