Physico-Chemical Nanomaterials Science 

Formation of metal nanoclusters in Al-based high-entropy alloys with transition elements
Dufanets M., Plevachuk Yu., Sklyrchuk V., Kulyk Yu.
Department of Metal Physics, Ivan Franko National University of Lviv, Kyryla i Mefodiya Str. 8, 79005 Lviv, Ukraine.
E-mail: marta_dufanets@ukr.net

An increased practical interest to equiatomic multicomponent alloys, where entropy increases with increasing elements number and is close to ideal entropy of multicomponent solution, is due to their unique physico-chemical properties such as high hardness, wear resistance, thermal stability and corrosive resistance. 
In such alloys there is a decay with the release in the BCC - the matrix of a number of nanoscale multicomponent phases atomically ordered (B2, L12) and disordered (A2) with different chemical composition. They have periodic concentration fluctuations and segregation of chemical elements (clusters of nanometer scale), which contain different combinations of elements. All detected nanophases, as well as clusters, are multicomponent solid solutions, including atomically ordered and enriched with several elements based on systems Cu-Ni-Co-Al, Ni-Co-Fe-Al, Cr-Fe-Co, the spatial distribution of which is characterized by pronounced nanomodulation of the elemental phase composition over the volume of the alloy.
Phase formation processes in equiatomic AlCoCuFeNiCr high entropy alloys have been studied by means of XRD method, microstructure analysis and microhardness measurements. Thermodynamic and structural criteria for predicting the phase composition of alloy are considered. Temperature dependences of the electrical conductivity and thermoelectric power were measured in the solid and liquid states. Heating of the alloy above 300 K is accompanied by a decrease in the electrical conductivity with its saturation in the range of 600–700 K and further increase. It should be noted that  The temperature derivative of electrical conductivity in the range of 300–600 K  is higher than in the range of 600–700 K, reflecting the processes of atomic ordering (or possible phase separation). The absolute thermoelectric power is negative and quite high (30–40 μV / K) as for metal systems. It is suggested that the electronic properties of the studied systems are mainly determined by the diffusion mechanism of charge transfer.