High entropy alloys, which are based on an equimolar concentration of 3 to 5 metals, represent a special group of materials which, in addition to their single-phase structure, also have relatively interesting properties. These usually relate to a wide range of temperature stability of the alloy, a favourable combination of strength and deformation properties, in some cases high corrosion resistance, etc. Judging from the high number of publications citing our papers, the workplace contributed to the development of knowledge in several areas:
(i) The possibility of producing HEA by mechanical alloying and subsequent spark plasma sintering was demonstrated, emphasising, in particular, the problems related to the possible contamination of the material.
(ii) The possibility of dispersion strengthening in these alloys, which can achieve a similar contribution to ODS steels, was demonstrated.
(iii) The possibility of interstitial strengthening of the HEA, which can be achieved for example by increasing the nitrogen content by 0.5 at% in the CoCrNi alloy, was demonstrated and that this effect can further optimise the yield strength/ductility trade-off.
(iv) The nitrogen-doped molten variant exhibits a stable single-phase face-centred cubic lattice without nitrides, even after different annealing, with a 24–33% higher yield strength at the same ductility compared to nitrogen-free HEA.
(v) The interstitial strengthening was explained (and quantified) by a simultaneous increase in lattice frictional stress and Hall–Petch coefficient.
(vi) In subsequent work including also ab-initio calculations, the nature of this behaviour was attributed to the influence of stacking fault energy on the evolution of the nano-twinning deformation mechanism.
(vii) Findings in the field of lightweight refractory HEAs (RHEAs) based on AlNbTaTiVZr alloy have shown some potential for applications.
In the field of advanced material design, the Department of Structure and Design of Materials also deals with the properties and optimisation of additively manufactured materials, whether based on titanium, aluminium, or nickel-chromium alloys, with a focus on their strength and fatigue properties under various loading conditions. In these areas, the department cooperates with the MPI für Eisenforschung Duesseldorf, Montanuniversität Leoben, and the Institute of Fundamental Technological Research, Polish Academy of Sciences. At the same time, we are focussing on possible applications of the results, e.g. in cooperation with the companies PBS Turbo Velká Bíteš or DT vyhybkárna a Strojírna, Prostějov.
Contact person:
Ivo Dlouhý, prof.