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

• Published in: Journal of phase equilibria and diffusion 2016-04, Vol.37 (2), p.119-126
• Main Authors: Löffler, Andrea, Zendegani, Ali, Gröbner, Joachim, Hampl, Milan, Schmid-Fetzer, Rainer, Engelhardt, Hannes, Rettenmayr, Markus, Körmann, Fritz, Hickel, Tilmann, Neugebauer, Jörg
• Format: Article
• Language: English
• Subjects: Calorimetry; Ceramics; Composites; Computer simulation; Crystallography and Scattering Methods; Electronics; Engineering Thermodynamics; Entropy; Glass; Heat and Mass Transfer; Heat capacity; Mathematical models; Metallic Materials; Natural Materials; Phase transformations; Physics; Physics and Astronomy; Specific heat; Thermodynamics
• ISSN: 1547-7037; 1863-7345; 1934-7243
• DOI: 10.1007/s11669-015-0426-y

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.