High-throughput experimental and Calphad screening of CCAs (Hi-TeCC) - towards new alloys with exceptional mechanical properties

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During the past 13 years a new window of opportunity for the design of novel materials was opened by the development of alloys with multi principal elements (MPEAs). MPEAs can be subdivided into single-phase high-entropy alloys (HEAs) and multi-phase compositionally complex alloys (CCAs). Instead of constituting one base element, MPEAs contain five or more principal elements. Hence, a vast space of possible chemical compositions and properties became available, which stimulated intensive research in this field. However, due to the very high number of possible alloy systems, only a small fraction could be investigated so far. Even more alarming, most single-phase, disordered HEAs potentially suitable for structural applications have mechanical properties that cannot compete with established steels and Ni-base alloys. Therefore, precipitation/multi-phase hardening by advancing from single-phase HEAs to multi-phase CCAs is a promising path to improve the mechanical properties of these alloys. This opens a vast field of hitherto unexplored opportunities. In order to explore and make optimal use of HEAs and CCAs, an extensive alloy screening approach, combining high-throughput thermodynamic simulations and experiments is inevitable. This proposal describes a research strategy that meets the issues mentioned above. It also fits and contributes very well to the objectives of the SPP 2006 "Compositionally Complex Alloys - High Entropy Alloys". We will use a methodology that allows high-throughput computational and experimental screening of HEAs/CCAs and facilitates easier design of new alloy systems. Thermodynamic modeling will include development of databases and evaluation of individual ternary systems as a basis for reliable Calphad calculations. Suitable chemical compositions will be determined from Calphad data in order to develop promising multi-phase CCAs. High-throughput production of bulk material with high chemical homogeneity will be performed by rapid alloy development using laser metal deposition (LMD) of elemental powder blends. Promising alloys identified by the first screening step will be subjected to deep screening by thorough characterization of the microstructure evolution and mechanical properties. Finally, the most promising alloy will also be produced following conventional processing by casting, rolling, and annealing to prove producibility in large quantities. We will focus on the Co-Cr-Fe-Mn-Ni system with additions of Al and/or C to extend this alloy system and allow for advancing from single-phase HEAs to multi-phase CCAs. On the one hand, this approach will allow us to develop a better fundamental thermodynamic description and gain a basic understanding of the microstructural features that influence the mechanical properties of HEAs and CCAs. On the other hand, the extension of HEAs towards CCAs enables an application-oriented assessment of design criteria for new advanced structural materials based on the concepts of HEAs.