Single-phase solid-solution refractory high-entropy alloys (RHEAs) have been receiving significant attention due to their excellent mechanical properties and phase stability at elevated temperatures. Recently, many studies have been reported regarding the precipitation-enhanced alloy design strategy to further improve the mechanical properties of RHEAs at elevated temperatures. In this study, we attempted to develop precipitation-hardened light-weight RHEAs via addition of Ni or Co into Al_0.8NbTiV HEA. The added elements were selected due to their smaller atomic radius and larger mixing enthalpy, which is known to stimulate the formation of precipitates. The addition of the Ni or Co leads to the formation of the sigma precipitates with homogeneous distribution. The formation and homogeneous distribution of sigma particles plays a critical role in improvement of yield strength. Furthermore, the Al_0.8NbTiVM_0.2 (M = Co, Ni) HEAs show excellent specific yield strength compared to single-phase AlNbTiV and NbTiVZr RHEA alloys and conventional Ni-based superalloy (Inconel 718) at elevated temperatures.

Developing inexpensive and rapid fabrication methods for high efficiency thermoelectric alloys is a crucial challenge for the thermoelectric industry, especially for energy conversion applications. Here, we fabricated large amounts of p-type Cu_0.07Bi_0.5Sb_1.5Te₃ alloys, using water atomization to control its microstructure and improve thermoelectric performance by optimizing its initial powder size. All the water atomized powders were sieved with different aperture sizes, of 32–75 μm, 75–125 μm, 125–200 μm, and <200 μm, and subsequently consolidated using hot pressing at 490 °C. The grain sizes were found to increase with increasing powder particle size, which also increased carrier mobility due to improved carrier transport. The maximum electrical conductivity of 1457.33 Ω⁻¹ cm⁻¹ was obtained for the 125–200 μm samples due to their large grain sizes and subsequent high mobility. The Seebeck coefficient slightly increased with decreasing particle size due to scattering of carriers at fine grain boundaries. The higher power factor values of 4.20, 4.22 × 10⁻³ W/mk² were, respectively, obtained for large powder specimens, such as 125–200 μm and 75–125 μm, due to their higher electrical conductivity. In addition, thermal conductivity increased with increasing particle size due to the improvement in carriers and phonons transport. The 75–125 μm powder specimen exhibited a relatively high thermoelectric figure of merit, ZT of 1.257 due to this higher electric conductivity.

Transition metal dichalcogenide-based quantum dots are promising materials for applications in diverse fields, such as sensors, electronics, catalysis, and biomedicine, because of their outstanding physicochemical properties. In this study, we propose bio-imaging characteristics through utilizing water-soluble MoS₂ quantum dots (MoS₂-QDs) with two different sizes (i.e., ~5 and ~10 nm). The structural and optical properties of the fabricated metallic phase MoS₂-QDs (m-MoS₂-QDs) were characterized by transmission electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, UV–vis absorption spectroscopy, and photoluminescence. The synthesized m-MoS₂-QDs showed clear photophysical characteristic peaks derived from the quantum confinement effect and defect sites, such as oxygen functional groups. When the diameter of the synthesized m-MoS₂-QD was decreased, the emission peak was blue-shifted from 436 to 486 nm under excitation by a He-Cd laser (325 nm). Density functional theory calculations confirmed that the size decrease of m-MoS₂-QDs led to an increase in the bandgap because of quantum confinement effects. In addition, when incorporated into the bio-imaging of HeLa cells, m-MoS₂-QDs were quite biocompatible with bright luminescence and exhibited low toxicity. Our results are commercially applicable for achieving high-performance bio-imaging probes.

In this study, Mo–Si–N coatings were deposited on Si wafers and tungsten carbide substrates using a reactive direct current magnetron sputtering system with a MoSi powder target. The influence of sputtering parameters, such as the N₂ gas flow ratio and working pressure, on the microstructure and mechanical properties (hardness (H), elastic modulus (E), and H/E ratio) of the Mo–Si–N coatings was systematically investigated using X-ray diffractometry (XRD), scanning electron microscopy (SEM), nanoindentation, and transmission electron microscopy (TEM). The gas flow rate was a significant parameter for determining the crystallinity and microstructure of the coatings. A Mo₂N crystalline coating could be obtained by a high N₂ gas flow ratio of more than 35% in the gas mixture, whereas an amorphous coating could be formed by a low N₂ gas flow ratio of less than 25%. Furthermore, the working pressure played an important role in controlling the smooth surface and densified structure of the Mo–Si–N coating. For the amorphous Mo–Si–N coating deposited with the lowest working pressure (1 mTorr), the hardness, elastic modulus, and H/E ratio reached from 9.9 GPa, 158.8 GPa, and 0.062 up to 17.9 GPa, 216.1 GPa, and 0.083, respectively.

The mechanical behavior and microstructural evolution of a BCC‐phase NbTaTiV refractory multi‐principal element alloy (RMPEA) is studied over a wide range of strain rates (10 ⁻³ to 10 ³ s ⁻¹ ) and temperatures (room temperature to 850 °C). The mechanical property of present RMPEA shows less strain‐rate dependence and strong resistance to softening at high temperatures. Under high strain‐rate loading, the formation of thin type‐I twins is observed, which could lead to an increase in strain‐hardening rates. However, this hardening mechanism competes with adiabatic heating effects, resulting in the deterrence of strain‐hardening behaviors. In contrast, substantial strain‐hardening occurs at cryogenic temperatures due to the formation of twins, which act as stronger barriers to dislocation motion and interact with each other. To further understand the different strain‐hardening behaviors, density functional theory (DFT) calculations predict relatively low stacking fault energies and high twinning stress for the NbTaTiV RMPEA.

High entropy alloys (HEAs) are defined as a multi-element alloy including more than 4 elements with near equi-atomic percentage. In general, the configurational entropy of the HEAs is known to be sufficient to stabilize a single solid solution, such as body-centered cubic (BCC), face-centered cubic (FCC) and hexagonal-closed pack (HCP). Compared to BCC single-phase alloys, FCC single-phase alloys draw extensive attention because they are advantageous in manufacturing and processing. FCC-based HEAs show excellent ductility but limited strength, so many research on improving strength has been conducted. Outstanding mechanical properties with a balance of strength and ductility are rarely achieved in single-phase FCC-based HEAs. This is why most alloys for structural applications exhibit a multi-phase microstructure. In this study, we aimed to develop multi-phase FCC-based HEA with superior mechanical properties than single-phase CoCrFeMnNi HEA, via Co substitution in CoCrFeMnNi HEA by Cu, which has a high mixing enthalpy. It was found that the CuCrFeMnNi HEA is composed of two FCC phases and one BCC phase. The CuCrFeMnNi HEA was cold-rolled, and subsequently aged at 500, 700, 900oC for 1 hour. As the annealing temperature increased, the volume fraction of the FCC phase (FCC1 + FCC2) increased and the residual stress was gradually relieved by recrystallization. Furthermore, small amount of sigma phase was formed at 900oC. The effect of the microstructural evolution on the mechanical properties, such as hardness and tensile properties at room temperature, will be discussed.