Quaternary Al-Cu-Mg-Si Q Phase: Sample Preparation, Heat Capacity Measurement and First-Principles Calculations
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The quaternary Q phase is an important precipitate phase in the Al-Cu-Mg-Si alloy system and its accurate thermodynamic description is crucial for further tailoring this material class for light-weight structural applications. In order to achieve an improved thermochemical parameter set of this phase, we used a combination of experimental measurements and first-principles calculations, which was focussed on the heat capacity. Its accurate experimental determination required the preparation of pure samples of Q phase and sophisticated calorimetric measurements. On the theoretical side, a simultaneous treatment of lattice vibrations within the quasiharmonic approximation, electronic excitations, and configuration entropy within the compound energy formalism were required to achieve a complete description of the heat capacity. The evaluation demonstrates the high predictive power of the first-principles as well as the Calphad modeling.
Keywordsab initio methods CALPHAD approach heat capacity quaternary thermodynamic assessment
The funding of this work by the Deutsche Forschungsgemeinschaft (DFG) within the joint Project PAK 461 under Grant Nos. Re1261/7, Ne428/12, and Schm 588/35 is gratefully acknowledged.
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