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High-entropy alloys are alloys containing at least five main metallic elements in equiatomic proportions from 5 to 35 at. %. The main feature of high-entropy alloys is the formation of a single-phase thermodynamically stable solid solution mainly with bcc and fcc lattices. Stabilization of the solid solution and prevention of the intermetallic phases formation during the solidification is ensured by the high entropy of mixing of the components. The highest value of entropy is achieved with an equiatomic ratio of components, and, according to the Boltzmann hypothesis, the configurational entropy increases with an increase in the number of elements. Along with the characteristics typical of metal alloys, such materials have unique and unusual properties inherent, for example, in metal ceramics: high hardness and resistance at high temperatures, positive temperature hardening coefficient, resistance to corrosion and oxidation, good wear resistance and a number of other properties. The continuous expansion of practical applications of high-entropy alloys shows that the deviation of one or more elements from equiatomic proportions can even improve some specific properties. The main experimental difficulties in extreme thermodynamic conditions of the liquid state are related to the high melting temperatures of the elements. Therefore, it is helpful to study similar multicomponent alloys with lower melting points of the elements. Information about the properties of such low-temperature systems, as well as their subsystems with a smaller number of components, which can be considered as model systems, is necessary for further study of the high-temperature alloys' characteristics and for their industrial production. In this work, temperature dependence of viscosity for Cu-Bi, Cu-Ga, Cu-Pb and Cu-Sn binary alloys with chemical compositions deviating from equiatomic ones was investigated. These alloys are subsystems of the high-entropy five-component Bi-Cu-Ga-Sn-Pb system. Based on the obtained results, the activation energy of the viscous flow and the configurational entropy of mixing were calculated. The obtained negative values of entropy of mixing indicate structural ordering in the system. [ABSTRACT FROM AUTHOR]

Conventional alloys are mainly based on one principal element with different kinds of alloying elements added to improve their properties. These alloys form an alloy family based on the chosen principal element. However, the number of elements in the periodic table is limited, thus the alloy families which can be developed are also limited. The new concept has been named a high-entropy alloy (HEAs). According to the proposed definition, any multi-component alloy consisting of five or more principal elements which have a concentration between 5 and 35 at.%, belongs to HEA. Besides principal elements, HEAs could contain also minor elements with concentrations below 5 at.%. Compared to conventional alloys, these alloys have significantly higher mixing entropies, which lead to the formation of liquid or random solid solution states. Thus, the effect of entropy is much more pronounced in high-entropy alloys than in conventional alloys. The high entropy of mixing in these alloys facilitates the formation of solid solution phases with simple structures. Thus, it reduces the number of phases formed in HEAs during solidification process. Such unique structural features caused by the effect of higher entropy are of paramount importance for further industrial application of these alloys. Due to the unique multi-principal element composition, the high-entropy alloys can have extraordinary properties, including high strength/hardness, outstanding wear resistance, exceptional high-temperature strength, good structural stability, good corrosion and oxidation resistance. Some of these properties are not seen in conventional alloys, making HEAs attractive in many fields. The fact that they can be used at high temperatures broadens their spectrum of applications even further. Moreover, the fabrication of HEAs does not require special processing techniques or equipment, which indicates that the mass production of HEAs can be easily implemented with existing equipment and technologies. The development of new advanced materials with predicted properties requires a clear and thorough understanding of their structural properties on the basis of sufficient and reliable thermophysical data. The increasing influence of computational modeling in all technological processes generates an increased demand for accurate values of the physical properties of the materials involved, which are used as fundamental inputs for each model. The solidification process of a liquid alloy has a profound impact on the structure and properties of the solid material. Therefore, knowledge of the thermophysical properties of molten alloys becomes very important for understanding the structural transformations in alloys in the liquid-solid temperature range and modeling the solidification process, so that materials with required characteristics can be developed. In this study, experimental measurements of electrical conductivity and thermoelectric power of the liquid HEAs of equiatomic concentrations Al16:6Co16:6Cr16:6Cu16:6Fe16:6Ni16:6, Al20Co20Cu20Fe20Ni20, Al25Co25Cu25Fe25, Al25Co25Cr25Ni25 and Co20Cr20Cu20Fe20Ni20 were carried out in a wide temperature range from their melting points to 1750 K. [ABSTRACT FROM AUTHOR]

The increasing scientific interest in Sn-based nanocomposite alloys with minor additions of oxides, metals and carbon in nanosized form is explained by the possible application of these materials as an alternative to commercial lead-free solders. As pointed out in recent literature reviews, the improved mechanical properties and reinforced microstructure of solder joints using nanocomposite Sn-Ag-Cu (SAC) alloys, compared to those without nanoinclusions, revealed new possibilities for the development of the currently used commercial lead-free solders. The main benefit of the nanosized additions is related to the suppression of the extensive growth of the Cu6Sn5 intermetallic compound (IMC) at the solder/Cu interface towards the solder side. This is achieved due to the spreading of nanoparticles over the IMC's surface, thereby suppressing the growth of Cu6Sn5 on the interface as well as in the bulk solder. In particular, the adsorbed nanoparticles on the IMC layer interface hinder the diffusion of Sn atoms from the bulk solder towards the interface and thereby suppress the IMC growth. Compared to the solid state, there is a limited number of papers dealing with experimental investigations of nanocomposite SAC solders in the liquid state after melting as well as in the semi-solid state. It has been shown that minor metal nanoadditions have an impact on the microstructure of solidified SAC solders, but practically without any significant change of the melting temperatures. The effect of small nanosized (up to 3 wt.%) nickel impurities on the electrical conductivity of Sn95.5Ag3.8Cu0.7 (SAC387) alloy has been investigated. It has been shown that the electrical conductivity gradually decreases with an increase in the impurity content of Ni. Conductivity, as a structure-sensitive transport characteristic of the liquid state of a substance, is important for modeling the processes of melting and solidification. The conductivity data provide additional information on the influence of admixtures on the structure and physicochemical properties of the metal matrix, which is important for understanding the microstructural transformations in a liquid state. Morphology of the samples was examined using REMMA-102-02 Scanning Electron Microscope- Analyzer (JCS SELMI, Sumy, Ukraine). [ABSTRACT FROM AUTHOR]

The increasing scientific interest in Sn-based nanocomposite alloys with minor additions of oxides, metals and carbon in nanosized form is explained by the possible application of these materials as an alternative to commercial lead-free solders. As pointed out in recent literature reviews, the improved mechanical properties and reinforced microstructure of solder joints using nanocomposite Sn-Ag-Cu (SAC) alloys, compared to those without nanoinclusions, revealed new possibilities for the development of the currently used commercial lead-free solders. The main benefit of the nanosized additions is related to the suppression of the extensive growth of the Cu6Sn5 intermetallic compound (IMC) at the solder/Cu interface towards the solder side. This is achieved due to the spreading of nanoparticles over the IMC's surface, thereby suppressing the growth of Cu6Sn5 on the interface as well as in the bulk solder. In particular, the adsorbed nanoparticles on the IMC layer interface hinder the diffusion of Sn atoms from the bulk solder towards the interface and thereby suppress the IMC growth. Compared to the solid state, there is a limited number of papers dealing with experimental investigations of nanocomposite SAC solders in the liquid state after melting as well as in the semi-solid state. It has been shown that minor metal nanoadditions have an impact on the microstructure of solidified SAC solders, but practically without any significant change of the melting temperatures. The effect of small nanosized (up to 3 wt.%) nickel impurities on the electrical conductivity of Sn95.5Ag3.8Cu0.7 (SAC387) alloy has been investigated. It has been shown that the electrical conductivity gradually decreases with an increase in the impurity content of Ni. Conductivity, as a structure-sensitive transport characteristic of the liquid state of a substance, is important for modeling the processes of melting and solidification. The conductivity data provide additional information on the influence of admixtures on the structure and physicochemical properties of the metal matrix, which is important for understanding the microstructural transformations in a liquid state. Morphology of the samples was examined using REMMA-102-02 Scanning Electron Microscope- Analyzer (JCS SELMI, Sumy, Ukraine). [ABSTRACT FROM AUTHOR]

Thin-film solar cells based on chalcopyrite are promising for terrestrial and space applications. The CuInSe2 semiconductor (CIS) has a band gap of about 1.04 eV, which is somewhat smaller than the ideal value for photovoltaic solar cells. Adding Ga to CIS in order to form the CuIn1−xGaxSe2 compound (CIGS) increases the band gap width, bringing it closer to the “ideal”; increases the idle voltage but reduces the short-circuit current. However, until now the effects of Ga admixtures remain unknown. It was reported that acceptor levels in crystals CIS and CIGS are identical and donor levels in CIGS are deeper than in CIS. Therefore, doping with CIGS crystals is more difficult than with CIS crystals. Obviously, further progress in the implementation of such devices can be achieved using new technologies for producing thin films with reproducible and controllable physical parameters. In this study, crystal films CuIn0.5Ga0.5Se2 were obtained by laser deposition on dielectric substrates from presynthesized crystals. The size of the crystallites based on SEM images does not exceed 50 nm. The parameters of the tetragonal cell of the solid solution were determined and the linear increase of the tetragonal parameter was recorded. The p-type conductivity of the material was determined by the method of measuring the photodiffusion current. In the case of intensive zone-zone excitation, an emission of bound excitons from nanosized crystallites has been registered. The origin of the features of the thin-film photoluminescence spectra has been analyzed. [ABSTRACT FROM AUTHOR]