Bridging the gap between atomic scale and thermodynamics for structurally complex multiphase multi-element systems: Metallic borides in Al-based metal–matrix composites as a case study
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Abstract
Intense researches on new kinds of materials, especially those with marked multi-principal-element character, currently give rise to all-intricate multiphase environments, for which reliably predicting structure and stability becomes extremely difficult to achieve with macroscopic phenomenological modellings. The purpose of this work is to demonstrate how this issue can be overcome by sticking down to the atomic scale, through ab initio-based thermodynamics within the Independent-Point-Defect Approximation (IPDA), which offers an efficient framework to investigate systems involving various chemistries and crystallographies. As a case study of significant intricacy, we consider ternary AlBTi viewed as an approximant for Al-based alloys reinforced with TiB particles and including AlB and AlTi additional compounds. Firstly, our IPDA investigations reveal unexpected discrepancies among neighbouring metallic borides, and predict point defect structures at odds with earlier pictures commonly employed hitherto, which suggests that many complex compounds may suffer from inadequate phenomenological modellings. Furthermore, we show that far-reaching conclusions on phase stability can be drawn only if the scope of analysis is broadened up to encompass global multiphase IPDA-based thermodynamics, a task which constitutes the core and the methodological originality of this work. Our approach thus provides reliable arguments to interpret the occurrence of various kinds of poorly known compounds, as illustrated by the controversial behaviour of AlTi and AlB in TiB-reinforced Al-based composites. Finally, our work allows to conclude that the robust and handsome IPDA approach can be extended to highly intricate multiphase situations, e.g. to investigate other classes of multiphase multi-principal-element materials, which due to the presence of complex crystal structures can hardly be explored by alternative methods.
期刊介绍:
The design of industrial processes requires reliable thermodynamic data. CALPHAD (Computer Coupling of Phase Diagrams and Thermochemistry) aims to promote computational thermodynamics through development of models to represent thermodynamic properties for various phases which permit prediction of properties of multicomponent systems from those of binary and ternary subsystems, critical assessment of data and their incorporation into self-consistent databases, development of software to optimize and derive thermodynamic parameters and the development and use of databanks for calculations to improve understanding of various industrial and technological processes. This work is disseminated through the CALPHAD journal and its annual conference.