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SFB 1394:  Structural and Chemical Atomic Complexity: From Defect Phase Diagrams to Material Properties

Subject Area Materials Science and Engineering
Term since 2020
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Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 409476157
 
New metallic materials are essential for realising future key technologies, from efficient energy conversion over lightweight transport to safe medical devices. Two approaches have proven immensely successful for the design of new metallic materials. Firstly, thermodynamic models of crystal phases have enabled alloy tailoring and processing to obtain desired microscale structures. Secondly, understanding and manipulation of crystal defects, which govern strength, formability and corrosion resistance, has led to alloying and processing concepts that resulted in some of the most advanced high-performance alloys in operation today. However, these two approaches are essentially decoupled, employed by scientists and developers from different communities. This separation is deeply engrained in materials science and most textbooks discuss phases and defects separately. On the other hand, it seems blatantly obvious that phases and defects are not independent factors for the properties of a material. It is the vision of this CRC to join and integrate the two approaches into a new, unified framework that will consider defects and phases in a holistic, all-encompassing manner. This will enable new materials design concepts that originate from the atomic scale and jointly consider the local crystalline structure at defects (structural complexity), the distribution of chemical elements in phases and defects (chemical complexity) and the prevalent defects for given external conditions, such as chemical potentials, temperature, applied stress or electrode potential. The CRC will not only investigate and clarify the interrelation between structural complexity, chemical complexity and defect phases, but further support the development of novel materials design concepts by providing new quantitative descriptors of the local structure and chemistry of defect phases which govern a materials' bulk properties. Here a defect phase is defined as a structurally and chemically distinct atomic-scale defect configuration with properties that are smooth functions of intensive external variables. Defect phase diagrams display the observed defects for given external conditions and show the transition between and the coexistence of defect phases. In the first funding period, the CRC has successfully identified and described several defect phases in theory and experiment. Examples include planar defect phases that do not grow to form precipitates and chemically induced structural transitions of grain boundary defect phases in Mg, as well as mechanism transition of dislocation defect phases in the Ca(Mg,Al)2 Laves phases. Structural and chemical complexity at the atomic scale is ubiquitous in materials. We believe that by studying defect phases, we will lead a paradigm change in the physical description of metallic materials and provide a powerful toolbox for future design of engineering materials with tailored properties regarding both, mechanical and corrosion performance.
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