Research project is (co) funded by the Slovenian Research Agency.
UL Member: Faculty of Mathematics and Physics
Project: High-Entropy Alloys
Period: 1.1.2016 - 31.12.2018
Range per year: 1,45 FTE, category D
Head: Dolinšek Janez
Research activity: Natural sciences and mathematics
Research Organisations: link on SICRIS
Researchers: link on SICRIS
Citations for bibliographic records: link on SICRIS
Within the past several years, a new approach to metallic alloy design with multiple principal elements in equimolar or near-equimolar ratios, termed high-entropy alloys (HEAs), has been proposed. According to this concept, high entropy of mixing can stabilize disordered solid solution phases with simple structures like a body-centred cubic (bcc) or a face-centred cubic (fcc) with small unit cells, in competition with ordered crystalline intermetallic phases that often contain structurally complex giant unit cells. The HEA structure is characterized by a topologically ordered lattice with an exceedingly high chemical (substitutional) disorder. In order to achieve high entropy of mixing, the alloys must be composed of five or more major elements in similar concentrations, ranging from 5 to 35 at. % for each element, but do not contain any element whose concentration exceeds 50 at. %. Examples of HEAs are alloys derived within the systems Al-Si-Co-Cr-Cu-Fe-Mn-Ni-Ti, W-Nb-Mo-Ta-V, and Ta-Nb-Hf-Zr-Ti. Since many different elements can be alloyed, and the concentration of each element can vary significantly, the number of possible HEAs is virtually unlimited. Astonishingly, only about ten different HEAs have been studied up to date, making the field practically empty. Most existing studies focus on the relationship between phase, microstructure and mechanical properties, where it was demonstrated that HEAs exhibit enhanced mechanical properties like high hardness and solid-solution strengthening. Physical properties of HEAs remain largely unexplored. In 2014, the group of prof. J. Dolinšek (the principal investigator of this project) has made a breakthrough in the field of physical properties of HEAs, by discovering the first superconducting HEA within the Ta-Nb-Hf-Zr-Ti system (P. Koželj et al., Phys. Rev. Lett. 113, 107001 (2014)).
The aims of this project are: (1) to synthesize, characterize and determine electrical, magnetic and thermal physical properties of new HEA systems with bcc structure within the systems Ta-Nb-Hf-Zr-Ti, transition-metals based Zr-Ti-V-Cr-Fe-Ni and aluminium-containing Al-Co-Cr-Cu-Fe-Ni; (2) to develop and investigate HEAs with hexagonal structure in systems containing rare-earths series of elements Ce-Ho-Dy-Y-Lu-Gd-Tb, which are expected to exhibit unconventional magnetism, a heavy-fermion-type conductivity and spin-fluctuation phenomena; (3) we shall also model theoretically the physical properties of a solid material possessing topologically ordered lattice with an exceedingly high degree of chemical (substitutional) disorder.
Since the field of physical properties of HEAs is still almost empty, our research announces opening of a new physical branch - the physics of solid state materials that possess an exceedingly high chemical disorder on an otherwise topologically well-ordered lattice. We expect to develop new original theoretical concepts for the understanding of HEA-type solid-state materials with regard to the phase stability and electronic, magnetic and thermal properties. A practical result of our research will be the development of new HEA materials with novel/enhanced physical properties for the application in electronic, magnetic and magnetocaloric applications. The execution of the project is done by the research and technical staff of three renowned Slovenian research/education institutions: (1) the Physics department of the Faculty of Mathematics and Physics of the Ljubljana University, (2) the Jožef Stefan Institute and (3) the Institute of Mathematics, Physics and Mechanics, in cooperation with the Juelich Research Center, Germany, ETH Zurich, Switzerland and Chalmers University, Sweden.
The work program is divided into four work packages:
- Work package I (WP I): Transition-metals-based bcc high-entropy alloys HEAs CoCrFeNiZrx (x = 0.40, 0.45, 0.50) and CrCuFeNi2Alx (x = 1.0, 1.2, 1.4).
- Work package II (WP II): Superconductivity in the Ta-Nb-Hf-Zr-Ti bcc HEAs.
- Work package III (WP III): Hexagonal high-entropy alloys from rare-earths elements.
- Work package IV (WP IV): Theoretical description of physical properties of high-entropy alloys.