Quaternary Al-Cu-Mg-Si Q Phase: Sample Preparation, Heat Capacity Measurement and First-Principles Calculations


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.

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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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Correspondence to Tilmann Hickel.

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Löffler, A., Zendegani, A., Gröbner, J. et al. Quaternary Al-Cu-Mg-Si Q Phase: Sample Preparation, Heat Capacity Measurement and First-Principles Calculations. J. Phase Equilib. Diffus. 37, 119–126 (2016). https://doi.org/10.1007/s11669-015-0426-y

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  • ab initio methods
  • CALPHAD approach
  • heat capacity
  • quaternary
  • thermodynamic assessment