Compositionally complex alloys (high-entropy alloys, HEAs)

Traditional metallic materials consist of one base element, with small additions of other elements that allow for better properties. Examples are Fe with C, Al with Cu and Mg, Ni with Al and Cr. Recently, a new class of materials has received considerable attention. These metallic materials contain several elements in equal concentrations (e.g. five elements with 20 atom percent each). These new materials are referred to as high-entropy alloys (HEAs). This name is based on the hypothesis that a high entropy of a mixture stabilizes a solid solution and makes it difficult for intermetallic compounds to form. This new class of materials opens a new compositional space with many interesting alloy compositions, with technical potential and intriguing properties. With the Otto paper from 2013, our group managed to contribute to a highly cited publication, which is on its way to becoming a citation classic. More importantly for our group, these alloys allow the study of a number of fundamental questions. How can one explain solid solution strengthening in these alloys? How do dislocations move in complex solid solutions? Can unusual deformation mechanisms be observed in HEAs? Do HEAs have better material properties than conventional alloys? Are they microstructurally stable? How does atomic diffusion proceed in these chemically complex materials? Guillaume Laplanche leads the HEA research group. Amongst other systems, he investigates Cr-Mn-Fe-Co-Ni (fcc) and Ti-Zr-Nb-Hf-Ta (bcc) alloys. Because of the importance of this particular research topic for our institute and because of the excellent research output from Guillaume Laplanche (several highly cited first author publications), he was given a permanent position after his Junior Professorship.
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