In this study, we investigate the scandium-containing Sc-Hf-Nb-Ta-Ti-Zr system of refractory high-entropy alloys (HEAs). Using the arc-melting method, we synthesized nine equimolar alloys (five 4-, three 5- and one 6-component), with all of them containing Sc. The alloys were characterized by XRD, electron microscopy and EDS, while superconductivity was investigated via electrical resistivity, specific heat and the Meissner effect. The results were compared to the parent Hf-Nb-Ta-Ti-Zr refractory HEAs, forming a single-phase body-centered cubic (bcc) structure and quite homogeneous microstructure. The addition of Sc produces a two-phase structure in the Sc-Hf-Nb-Ta-Ti-Zr alloys, with one phase being bcc and the other hexagonal close-packed (hcp). The hcp phase absorbs practically all Sc, whereas the Sc-poor bcc phase is identical to the bcc phase in the Hf-Nb-Ta-Ti-Zr parent system. Upon the Sc addition, the microstructure becomes very inhomogeneous. Large bcc dendrites (10–100 µm) are homogeneous in the central parts, but become a fine dispersion of sub-micron precipitates of the bcc and hcp phases close to the edges. The interdendritic regions are also a fine dispersion of the two phases. Superconductivity of the Sc-Hf-Nb-Ta-Ti-Zr alloys originates from the bcc phase fraction, which demonstrates identical superconducting parameters as the bcc Hf-Nb-Ta-Ti-Zr parent alloys, while the Sc-containing hcp phase fraction is non-superconducting.

Purpose: To introduce an analytical method for a quantitative determination of magnetic force on a coronary stent in the magnetic resonance imaging (MRI) magnet that is generally applicable to metallic implants. Magnetic forces on metallic implants in the MRI magnets are traditionally determined empirically by measuring deflection from the vertical plane at the central axis of the magnet and at the point of the largest force along the longitudinal axis of the magnet. Materials and Methods: Magnetic and chemical characterization of the stents was performed by a commercial magnetometer and energy‐dispersive X‐ray spectroscopy. Magnetic force on the stents fabricated of paramagnetic alloys (surgical stainless steel and cobalt–chromium) was determined by measuring the stent's magnetic dipole moment and employing the on‐axis magnetic field profile of an MRI magnet. Results: The maximum force on the stainless steel stent was found to be F_S,max = 0.18 mN, whereas on the cobalt–chromium stent it was F_C,max = 0.06 mN. Conclusion: The magnetic force on the investigated paramagnetic stents is even smaller than the gravitational force acting on the stents in the Earth's gravity field, so that it has no physiological impact on the stented vessels. J. Magn. Reson. Imaging 2013;37:391–397.

In an attempt to incorporate tin (Sn) into high-entropy alloys composed of refractory metals Hf, Nb, Ti and Zr with the addition of 3d transition metals Cu, Fe, and Ni, we synthesized a series of alloys in the system HfTiZrSnM (M = Cu, Fe, Nb, Ni). The alloys were characterized crystallographically, microstructurally, and compositionally, and their physical properties were determined, with the emphasis on superconductivity. All Sn-containing alloys are multi-phase mixtures of intermetallic compounds (in most cases four). A common feature of the alloys is a microstructure of large crystalline grains of a hexagonal (Hf, Ti, Zr)₅Sn₃ partially ordered phase embedded in a matrix that also contains many small inclusions. In the HfTiZrSnCu alloy, some Cu is also incorporated into the grains. Based on the electrical resistivity, specific heat, and magnetization measurements, a superconducting (SC) state was observed in the HfTiZr, HfTiZrSn, HfTiZrSnNi, and HfTiZrSnNb alloys. The HfTiZrSnFe alloy shows a partial SC transition, whereas the HfTiZrSnCu alloy is non-superconducting. All SC alloys are type II superconductors and belong to the Anderson class of “dirty” superconductors.

In the search for electronic phenomena in high-entropy alloys (HEAs) that go beyond the independent-electron description, we have synthesized a series of hexagonal rare earth (RE)-based HEAs: Ce_xLaLuScY (x = 0.05–1.0). The measurements of electrical resistivity, magnetic susceptibility and specific heat have shown that the Ce_xLaLuScY HEAs exhibit the Kondo effect, which is of a single impurity type in the entire range of employed Ce concentrations despite the alloys being classified as dense (concentrated) Kondo systems. A comparison to other known dense Kondo systems has revealed that the Kondo effect in the Ce_xLaLuScY HEAs behaves quite differently from the chemically ordered Kondo lattices but quite similar to the RE-containing magnetic metallic glasses and randomly chemically disordered Kondo lattices of the chemical formula RE1_xRE2_1−xM (with RE1 being magnetic and RE2 being nonmagnetic). The main reason for the similarity between HEAs and the metallic glasses and chemically disordered Kondo lattices appears to be the absence of a periodic 4f sublattice in these systems, which prevents the formation of a coherent state between the 4f-scattering sites in the $T\to$ 0 limit. The crystal-glass duality of HEAs does not bring conceptually new features to the Kondo effect that would not be already present in other disordered dense Kondo systems. This study broadens the classification of HEAs to correlated electron systems.

High-entropy alloys (HEAs) introduce a new concept of developing advanced metallic materials with properties that conventional alloys, based on one principal element, cannot achieve [1]. Other multi-component metallic systems are quasicrystals (QCs), complex metallic alloys (CMAs) and bulk metallic glasses (BMGs). HEAs are multicomponent mixtures of 4 to 9, and occasionally up to 20 chemical elements, in similar concentrations, ranging from 5 to 35 at.% each, where the high entropy of mixing can stabilize disordered solid-solution phases with simple crystal structures like a body-centered cubic (bcc), a face-centered cubic (fcc) and a hexagonal close-packed (hcp), in competition with ordered intermetallic phases and phase-segregated mixtures [2]. Though the average crystal structure of a HEA is generally simple, microstructure might be highly complex, as will be shown later in this presentation. In our research, the HEA series CoCrFeNiZr_x (x = 0.40, 0.45, and 0.50) has been investigated. Various SEM techniques were employed, including backscattered-electron (BSE) imaging, EDS point analysis, chemical mapping and EBSD. The results reveal high complexity of the HEAs' microstructure and helped us to determine the grains' composition. Brief outline is presented in the four figures shown below. Figs. 1 and 2 show BSE SEM images. The coarsest interpretation is that the samples are composed of two different types of microstructures: (1) rounded dark phases and (2) fine interweaving of the light and dark phases. Higher magnification of the image in Fig. 2 shows the “invisible borders”, where the fine microstructure changes its character. EBSD investigations at lower magnification (2.000x) revealed that the “invisible borders” correspond to grain boundaries of larger grains (see Fig. 3 – showing different area than Figs. 1 and 2.), whereas more detailed EBSD results at higher magnification of 10.000x (Fig. 4) explained the fine grain structure inside the main grains. Therefore, grains' sizes at two different scales are present in these samples. The effect of Zr content on the HEA microstructure was thus traceable in great detail.