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In this article, we describe the characterization of a newly fabricated amorphous alloy system (TiZrNbCu)1−xCox covering a broad composition range from high-entropy (HEA) to Co-rich alloys (x ≤ 0.43). We investigated thermal stability, atomic and electronic structure, and magnetic and mechanical properties as a function of chemical composition x. One of the important findings is that all studied properties change their dependence on concentration x within the HEA range. In particular, it has been found that the average atomic volume deviates from Vegard's law for x > 0.2, the concentration for which the average atomic packing fraction suddenly changes. The valence band structure, studied with ultraviolet photoemission spectroscopy, shows a split-band shape with 3d-states of Co approaching the Fermi level on increasing x. Due to the onset of magnetic correlations, magnetic susceptibility rapidly increases for x > 0.25. Very high microhardness increases rapidly with x. The results are compared with those for similar binary and quinary metallic glasses and with those for Cantor type of crystalline alloys. [ABSTRACT FROM AUTHOR]

A study of a transition from conventional multicomponent alloys to high-entropy alloys (HEAs) is important both for understanding the formation of HEAs and for proper evaluation of their potential with respect to that of conventional alloys. We report the main result of such a study performed on (TiZrNbNi)1−xCux metallic glasses (MG) over a broad concentration range x ≤ 0.52 encompassing both high-entropy-MGs and Cu-based MGs. A comprehensive study of the composition, homogeneity, thermal stability, atomic structure, electronic structure, and magnetic susceptibility of 11 alloys has been performed. Thermal analysis revealed a rather weak variation of thermal parameters and glass forming ability with x. The study of the atomic structure showed a linear variation of average interatomic distances and atomic volumes close to those predicted by Vegard's law. The coordination numbers and atomic packing fractions were constant throughout the explored concentration range. The electronic density of states (DOS) showed a split-band structure with DOS close to the Fermi level dominated with d-states of Ti, Zr, and Nb. Accordingly, magnetic susceptibility decreased linearly with x and extrapolated to that of Cu. Thus, the studied alloys show ideal solution behavior similar to that of binary Cu-Ti, Zr, and Hf MGs. The results are compared with those for (TiZrNbCu)1−xNix MGs and (CrMnFeCo)1−xNix alloys and their impact on understanding the transition from high-entropy-MGs to conventional MGs with the same composition is briefly discussed. [ABSTRACT FROM AUTHOR]

Recent studies (J. Alloys Compd. 695 (2017) 2661) of the electronic structure and properties of (TiZrNbCu) 1-x Ni x ( x  ≤ 0.25) amorphous high entropy alloys (a-HEA) have been extended to x  = 0.5 in order to compare behaviours of a-HEA and conventional Ni-base metallic glasses (MG). The amorphous state of all samples was verified by thermal analysis and X-ray diffraction (XRD). XRD indicated a probable change in local atomic arrangements, i.e. short-range-order (SRO) for x  ≥ 0.35. Simultaneously, thermal parameters, such as the first crystallization temperature T x and the liquidus temperature showed a tendency to saturate for x  ≥ 0.35. The same tendency also appeared in the magnetic susceptibility χ exp and the linear term in the low temperature specific heat γ . The Debye temperatures and Young's moduli also tend to saturate for x  ≥ 0.35. These unusual changes in SRO and all properties within the amorphous phase seem correlated with the change of valence electron number ( VEC ) on increasing x . [ABSTRACT FROM AUTHOR]

Mechanical properties (Young's modulus and hardness) of TE-Ni,Cu (TE = Ti, Zr and Hf) amorphous alloys increase approximately linearly with Ni, Cu fraction, x, over a wide composition range (fraction of Ni, Cu atoms ≤ 66 %). This correlates with the observed increase of the Debye temperatures with x and shows that the strength of interatomic bonding increases with x in these alloys. The thermal stability (e.g. the crystallization temperatures) of these alloys also increases with x, thus with increasing interatomic bonding. Since in all these alloys the electronic density of states at the Fermi level, N(EF), decreases Ii- nearly with x within the same x-range, a very simple relationship exists between the electronic structure and mechanical and thermal properties. We also estimate the mechanical properties of amorphous TEs (by extrapolating the properties of alloys to x = 0) and compare them with those of crystalline TEs. [ABSTRACT FROM AUTHOR]

Abstract: The experimental results for the magnetic susceptibility and superconducting transition temperature of amorphous Zr–(Co,Ni,Cu) alloys extending over a wide composition range are analyzed in some detail. By combining the results of this analysis with the literature results for the electronic density of states at E F for the same alloy systems we obtained a set of parameters associated with the electronic structure of the amorphous Zr. The comparison of these parameters with the results of the band structure calculations for different crystalline phases of Zr and with the results of the atomic structure and crystallization studies of the same alloy systems indicates an fcc-like local atomic structure for amorphous Zr. [Copyright &y& Elsevier]

Abstract: Wide glass-forming range in Zr–TL alloys (TL, 3d metal) combined with a simple, often linear, variation of their properties with composition makes it possible to deduce the physical properties of a pure amorphous zirconium. We explore this possibility by using our results for the magnetic susceptibility (χ), superconducting transition temperature (T C), and Young''s modulus (E) of paramagnetic amorphous Zr–(Co,Ni,Cu) alloys. By combining our results with the literature results for the low temperature specific heat, we obtained set of parameters associated with the electronic structure and interatomic bonding of the amorphous Zr. The comparison of these parameters with the results of the electronic structure calculations for different crystalline phases of Zr and with the results of the atomic structure studies indicate an fcc-like local atomic structure for amorphous Zr. [Copyright &y& Elsevier]

The valence band (VB) structure of an Al0.5TiZrPdCuNi high-entropy alloy (HEA) obtained using x-ray photoelectron spectroscopy has been compared to that recently calculated by Odbadrakh et al. [J. Appl. Phys. 126, 095104 (2019)]. Both the experimental and theoretical VBs show a split-band structure, typical for alloys consisting of the early (TE) and late (TL) transition metals. Accordingly, several electronic structure (ES) properties of this alloy, both in the glassy and crystalline state, are compared with those of similar TE-TL alloys. The comparison shows a strong effect of alloying with Al on the density of states at the Fermi level, N(EF), and on the magnetic susceptibility of Al0.5TiZrPdCuNi HEA, similar to that in conventional glassy alloys, such as Zr-Cu-Al ones. Despite some similarity in the theoretical and experimental density of states of the VBs, there are significant differences between them, which should be taken into account in any future studies of ES in HEAs and other compositionally complex alloys. [ABSTRACT FROM AUTHOR]

A comprehensive study of selected properties of four (TiZrNbCu) 1-x Ni x (x ≤ 0.25) amorphous high entropy alloys (a-HEA) has been performed. The samples were ribbons about 20 μm thick and their fully amorphous state was verified by X-ray diffraction and thermal analysis. The surface morphology, precise composition and the distribution of components were studied with a Scanning electron microscope (SEM) with an energy dispersive spectroscopy (EDS) attachment. The properties selected were the melting temperature (T m ), the low temperature specific heat (LTSH), the magnetic susceptibility χ exp and the Young's modulus (E). Whereas LTSH and χ exp were measured for the as-cast samples, E was measured both for as-cast samples and relaxed samples (after a short anneal close to the glass transition temperature). The LTSH showed that the electronic density of states at the Fermi level, N 0 (E F ), decreases with increasing x, whereas the Debye temperature (θ D ) increases with x. This is similar to what is observed in binary and ternary amorphous alloys of early transition metals (TE) with late transition metals (TL) and indicates that N 0 (E F ) is dominated by the d-electrons of the TE. The LTSH also showed the absence of superconductivity down to 1.8 K and indicated the emergence of the Boson peak above 4 K in all alloys. The free-electron like paramagnetic contribution to χ exp also decreases with x, whereas E, like θ D , increases with x, indicating enhanced interatomic bonding on addition of Ni. The applicability of the rule of mixtures to these and other similar HEAs is briefly discussed. [ABSTRACT FROM AUTHOR]

The study of the transition from high-entropy alloys (HEAs) to conventional alloys (CAs) composed of the same alloying components is apparently important, both for understanding the formation of HEAs and for proper evaluation of their potential with respect to that of the corresponding CAs. However, this transition has thus far been studied in only two types of alloy systems: crystalline alloys of iron group metals (such as the Cantor alloy and its derivatives) and both amorphous (a-) and crystalline alloys, TE-TL, of early (TE = Ti, Zr, Nb, Hf) and late (TL = Co, Ni, Cu) transition metals. Here, we briefly overview the main results for the transition from HEAs to CAs in these alloy systems and then present new results for the electronic structure (ES), studied with photoemission spectroscopy and specific heat, atomic structure, thermal, magnetic and mechanical properties of a-TE-TL and Cantor-type alloys. A change in the properties of the alloys studied on crossing from the HEA to the CA concentration range mirrors that in the ES. The compositions of the alloys having the best properties depend on the alloy system and the property selected. This emphasizes the importance of knowing the ES for the design of new compositional complex alloys with the desired properties. [ABSTRACT FROM AUTHOR]

• Transition from high-entropy to Ni-rich metallic glasses (TiZrNbCu) 1 − x Ni x studied. • Transition is accompanied with a change in electronic properties for Ni-rich concentration range, x > 0.35. • Photoemission spectra reveal the split-band valence band in all alloys. • Superconducting transition temperatures follow the variation of density of states. • Temperature dependence of resistivity is dominated with quantum coherence effects. We present results of comprehensive study of electronic properties of (TiZrNbCu) 1 − x Ni x metallic glasses performed in broad composition range x encompassing both, high entropy (HE) range, and conventional Ni-base alloy concentration range, x ≥ 0.35. The electronic structure studied by photoemission spectroscopy and low temperature specific heat (LTSH) reveal a split-band structure of density of states inside valence band with d -electrons of Ti, Zr, Nb and also Ni present at Fermi level N (E F), whereas LTSH and magnetoresistivity results show that variation of N (E F) with x changes in Ni-base regime. The variation of superconducting transition temperatures with x closely follows that of N (E F). The electrical resistivities of all alloys are high and decrease with increasing temperature over most of explored temperature range, and their temperature dependence seems dominated by weak localization effects over a broad temperature range (10–300 K). The preliminary study of Hall effect shows positive Hall coefficient that decreases rapidly in Ni-base alloys. [ABSTRACT FROM AUTHOR]