Search Results (142)

Mixing enthalpy (ΔH_mix), mixing entropy (ΔS_mix), atomic-size difference (δ), and valence electron concentration (VEC) are the indicators determining the phase structures of multi-principal element alloys. Exploring the relationships between the structures and properties of multi-principal element films is a fundamental study. TiZrHf films with a ΔH_mix of 0.00 kJ/mol, ΔS_mix of 9.11 J/mol·K (1.10R), δ of 3.79%, and VEC of 4.00 formed a hexagonal close-packed (HCP) solid solution. Exploring the characterization of TiZrHf films after solving Ta, Y, and Cr atoms with distinct atomic radii is crucial for realizing multi-principal element alloys. This study fabricated TiZrHf, TiZrHfTa, TiZrHfY, and TiZrHfCr films through co-sputtering. The results indicated that TiZrHfTa films formed a single body-centered cubic (BCC) solid solution. In contrast, TiZrHfY films formed a single HCP solid solution, and TiZrHfCr films formed a nanocrystalline BCC solid solution. The crystallization of TiZrHf(Ta, Y, Cr) films and the four indicators mentioned above for multi-principal element alloy structures were correlated. The mechanical properties and thermal stability of the TiZrHf(Ta, Y, Cr) films were investigated. Full article

The cobalt crystalline islands (Co_cryst) were electrochemically deposited onto a glassy carbon (GC) support and then modified by a facile spontaneous deposition of platinum. The electrocatalytic activity of the resulting Co_cryst-Pt core-shell catalyst was evaluated for the oxygen reduction reaction (ORR) in an alkaline medium. The XRD characterization of the Co_cryst-Pt islands revealed that the cobalt core had a hexagonal close-packed (hcp) crystalline structure, and that the platinum shell exhibited a crystalline structure with a preferential (111) orientation. SEM images showed that the average lateral size of the Co_cryst islands was 1.17 μm, which increased to 1.32 μm after adding platinum. The XPS analysis indicated that the outer layer of the bulk metallic Co_cryst islands was fully oxidized. During the spontaneous deposition of platinum, the outer Co(OH)₂ layer was dissolved, leaving the cobalt core in a metallic state, while the platinum shell remained only partially oxidized. The high electrochemically active surface area of the Co_cryst-Pt/GC electrode, along with a suitable crystalline structure of the Co_cryst-Pt islands, contributes to enhancing its ORR activity by providing a greater number of surface active sites for oxygen adsorption and subsequent reduction. The ORR on the Co_cryst-Pt catalyst occurs via a four-electron reaction pathway, with onset and half-wave potentials of 1.07 V and 0.87 V, respectively, which exceed those of polycrystalline platinum and a commercial benchmark Pt/C. Full article

The mechanical response of monolithic CuZr metallic glass (MG) and MG/Cu composite substrates under high-velocity impact was investigated using molecular dynamics simulations, with variations in impact velocity and initial temperature. Higher impact velocities resulted in deeper penetration and increased plastic deformation, with the monolithic MG exhibiting greater energy absorption and slightly more extensive projectile fragmentation. The MG/Cu composite displayed enhanced plastic deformation, attributed to the higher stiffness of the crystalline Cu phase, which promoted plasticity in the amorphous matrix. Temperature effects were more pronounced in the composite, where elevated temperatures enhanced strain localization and atomic mobility in the glassy phase. This was supported by a decrease in dislocation density and the population of hexagonal close-packed (HCP) atoms with increasing temperature, indicating a shift in plastic activity toward the amorphous matrix. These findings provide insights into the interplay between impact velocity, temperature, and material composition, contributing to a deeper understanding of MG-based composite behavior under extreme loading conditions. Full article

Magnesium alloys are essential lightweight materials for engineering applications. However, conventional single-phase hexagonal close-packed (HCP) magnesium alloys exhibit poor cold workability and insufficient strength at room temperature, which limits their engineering applications. Compared to HCP structures with limited slip systems at room temperature, body-centered cubic (BCC) structures possess 12 independent slip systems, enabling better plasticity. Therefore, Mg–Sc alloys with a dual-phase structure (HCP + BCC) exhibit superior plasticity compared to single-phase HCP magnesium alloys. In this study, the deformation behavior of dual-phase Mg-19.2 at.% Sc alloy was investigated, revealing its deformation characteristics and multiscale strengthening mechanisms. Experimental findings indicate that with the rise in annealing temperature, the volume fraction of the α phase progressively declines, while that of the β phase expands. Moreover, the grain size of the α phase first grows and then reduces, whereas the β phase grain size consistently enlarges. When the annealing temperature reaches 600 °C, the alloy exhibits an optimal strength–ductility combination, with an ultimate tensile strength of 329 MPa and an elongation of 20.5%. At this condition, the α phase volume fraction is 20%, while the β phase volume fraction is 80%, with corresponding grain sizes of 5.9 µm and 30.1 µm, respectively. Microstructural analysis indicates that the plastic incompatibility between the α and β phases induces significant heterogeneous deformation-induced (HDI) strengthening. Moreover, the unique bimodal grain size distribution, where the α phase grains are significantly smaller than the β phase grains, enhances the “hard phase harder, soft phase softer” heterogeneous structural effect, further amplifying the HDI strengthening contribution. This study provides new theoretical insights into multiphase interface engineering for designing high-performance dual-phase magnesium alloys. Full article

Copper interconnect technology faces limitations due to the electron’s mean free path and electromigration, driving the adoption of cobalt alternatives. This study proposes a novel mechanism to achieve superfilling by tuning the adsorption energy of additive molecules on cobalt surfaces. The adsorption energies of additives are tailored by changing molecular structures with different functional groups. Computational results reveal that carbon–carbon triple bonds critically strengthen adsorption, while ether bonds further enhance binding on distinct cobalt crystallographic planes. Specifically, 1,4-bis(2-hydroxyethoxy)-2-butyne (BEO) containing both triple bonds and ether groups exhibits the highest adsorption energy (−22.62 eV). Replacing ether with hydroxyl groups in 2-butyne-1,4-diol (BOZ) reduces the adsorption energy to −10.39 eV, while eliminating triple bonds in 1,4-butanediol diglycidyl ether (BDE) further decreases it to −8.43 eV. Experimental studies demonstrate that BOZ and BEO preferentially adsorb on the (101) and (110) planes of hexagonal close-packed cobalt (HCP-Co) due to their differential adsorption energies. This selective suppression promotes preferential growth along the densely packed (002) orientation. This leads to a trench-filling process dominated by the most densely packed plane, resulting in better electrical performance. Superfilling is achieved when molecular adsorption energies are in the range of 5–8 eV. The work establishes a functional group design strategy to regulate additive adsorption, enabling crystallographic control for advanced cobalt electrodeposition processes. Full article

AlCrN and AlCrSiN coatings were deposited via reactive magnetron sputtering. This study investigates the effects of radio frequency (RF) substrate bias, ranging from 0 V to 200 V, on the chemical composition, microstructure, and mechanical properties of the coatings. All crystalline coatings exhibited a single wurtzite-type hexagonal close-packed (hcp) structure. At a 0 V substrate bias, the AlCrN coating consisted of porous V-shaped columnar crystallites, while the AlCrSiN coating exhibited a porous, fiber-like amorphous structure. As the substrate bias increased, crystal growth was promoted, void density decreased, and the surface morphology transitioned from a textured to a more rounded appearance. Additionally, the preferred orientation shifted toward the (101) direction. However, at excessively high substrate bias, re-nucleation occurred, leading to grain refinement and increased film densification, which in turn caused a further shift in the preferred orientation toward the (002) plane. Due to its multi-element composition and the low solubility of Si in nitrides, AlCrSiN coatings tend to exhibit an amorphous growth tendency during sputtering. As a result, their microstructure is more sensitive to substrate bias. This sensitivity results in the formation of a highly dense structure with an optimal crystallite size at a substrate bias of 100 V, leading to a hardness of 22.6 GPa—surpassing that of the AlCrN coating. Full article

The anisotropic strain development and releasing process in materials is largely related to their intrinsic mechanical properties and mesoscale grain interactions. Uniaxial compression can induce a large amount activation energy in a system, which builds up anisotropic elastic strain. This is especially common in a hexagonal close-packed (HCP) system. Utilizing the X-ray diffraction technique, we investigated the double-dome shaped evolution of its anomalous anisotropic strain when compressing a polycrystalline HCP–silver–aluminum (Ag₇₅Al₂₅) alloy up to 40 GPa. Analysis of the pressure-dependent grain size showed that the anisotropic strain relaxation was accompanied with grain-size refinement. This was a strong indication of microscopic structural anisotropy impacting both the mesoscopic mechanical properties and the macroscopic fracture behavior under uniaxial compression. Our findings provide valuable novel insights for further studies on materials with anisotropic mechanical properties. Full article

This study investigates how Zr doping influences the deformation behavior of Cu-Zr/Al₂Cu/Al composites through molecular dynamics simulations. The impact of Zr content (ranging from 0 to 0.8 wt%) and strain rate on phase evolution, dislocation dynamics, and fracture mechanisms under vertical and horizontal tensile loading was examined. The results indicate that Zr doping achieves a balance between strength and plasticity by means of solute drag, amorphization, and phase competition. At a Zr concentration of 0.2 wt%, the formation of the body-centered cubic (BCC) phase reached a peak (22.04% at ε = 0.11), resulting in a maximum tensile strength of 9.369 GPa while maintaining plasticity due to limited face-centered cubic (FCC) decomposition. A moderate Zr content of 0.6 wt% maximizes strength through amorphization but significantly diminishes plasticity due to excessive FCC-to-BCC transitions. Higher Zr concentrations (0.8 wt%) lead to solute supersaturation, which suppresses phase transitions and slightly reduces toughness by causing hexagonal close-packed (HCP) phase accumulation. The strain rate markedly enhances both strength and plasticity in vertical loading by accelerating dislocation interactions. Vertical tensile deformation initiates brittle fracture, whereas horizontal loading results in ductile failure through sequential load transfer from Al₂Cu layers to Al/Cu interfaces, ultimately causing interfacial decohesion. These findings underscore the essential roles of Zr content and strain rate in modulating phase transformations and interface responses. The research offers a framework for creating gradient Zr-doped or multi-scale composites with optimized strength, plasticity, and damage tolerance suitable for aerospace and electronics applications, where trace Zr additions can reinforce Cu matrices. Full article

Equation of state (EoS) parameters of hexagonal close-packed iron (hcp-Fe), the dominant core component in large terrestrial planets, is crucial for studying interior structures of super-Earths. However, EoS parameters at interior conditions of super-Earths remain poorly constrained, and extrapolating from Earth’s core conditions introduces significant uncertainties at TPa pressures. Here, we compiled experimental static and dynamic compression data and theoretical data up to 1374 GPa and 12,000 K from the literature to refine the EoS of hcp-Fe. Using the third-order Birch–Murnaghan and Mie–Grüneisen–Debye equations, we obtained V₀ (unit-cell volume) = 6.756 (10) cm³/mol, K_T0 (isothermal bulk modulus) = 174.7 (17) GPa, $K_{T0}^{\prime }$ (pressure derivative of K_T0) = 4.790 (14), θ₀ (Debye temperature) = 1209 (73) K, γ₀ (Grüneisen parameters) = 2.86 (10), and q (volume-independent constant) = 0.84 (5) at ambient conditions. These parameters were then incorporated into an interior model of CoRoT-7b and Kepler-10b, which includes four solid compositional layers (forsterite, MgSiO₃ perovskite, post-perovskite, and hcp-Fe). The model yields the core mass fractions (CMF) of 0.1709 in CoRoT-7b and 0.2216 in Kepler-10b, suggesting a Mars-like interior structure. Extrapolation uncertainties (±10–20% in density) can change CMF by −12.6 to 21.2%, highlighting the necessity of precise EoS constraints at the super-Earth interior conditions. Full article

In order to improve the room temperature yield strength of X and enhance its engineering applicability, a series of CoCr_1.7NiY_x (x = 0, 0.01, 0.02, 0.03, 0.04, and 0.1 at.%) medium-entropy alloys were synthesized to investigate the effect of Y addition on the microstructures and mechanical properties of the CoCr_1.7Ni-based alloy. The X-ray diffraction results show that the alloys exhibit face-centered cubic (FCC) + body-centered cubic (BCC) + hexagonal close packing (HCP) triphasic structure when the Y is adopted, whereas the CoCr_1.7Ni-based alloy has a FCC+BCC biphasic structure. The volume fraction of BCC and HCP phase increased with increasing Y content, which led to alloy grain refinement. As a result, the microhardness and strength of alloys were both enhanced. The addition of Y resulted in dispersion strengthening and solid solution strengthening of CoCr_1.7Ni alloy, the appearance of HCP, and an increase in BCC, which improved the room temperature yield strength and hardness of CoCr_1.7Ni alloy. In particular, for CoCr_1.7NiY_0.1 alloy, its microhardness and yield strength, respectively, increased by 98.18% and 260.59% as compared with those of CoCr_1.7Ni alloy. Full article

After the thermal-mechanical processing of Mg alloys, extensive 30°⟨0001⟩ grain boundaries (GBs) are present in the recrystallized structure, which strongly affects the mechanical properties via interactions with lattice dislocations. In this work, we systematically investigate how the 30°⟨0001⟩ GBs influence the slip transmission during plastic deformation. We reveal that basal dislocations can be transmuted into its neighboring grain and continue gliding on the basal plane. The prismatic dislocation can transmit the GB remaining on the same Burgers vector. However, a mobile pyramidal $⟨c+a⟩$ dislocation can be absorbed at GBs, initiating the formation of new grain. These findings provide a comprehensive understanding on GB-dislocation interaction in hexagonal close-packed (HCP) metals. Full article

Nickel–aluminum (NiAl) alloys appear to be remarkably resistant to heat and corrosion, and are used in heat-treatment furnaces. This study utilizes molecular dynamics simulations to explore the structural characteristics of a nickel–aluminum (NiAl) alloy at varying heating rates during the heating process. During the heating process, the temperature increases from 300 K to 4000 K, surpassing the melting point. The effect of the heating rate is varied at 93, 62, 46, and 37 K/ps. The findings indicate that both the potential energy and volume of the NiAl system rise as it undergoes heating. Moreover, at the temperature 4000 K, the local face-centered cubic (fcc) and hexagonal close-packed (hcp) structures in the NiAl exhibit variations depending on the heating rates. The results highlight the importance of accounting for heating rates in the structural evolution of NiAl showing their thermal behavior for high-temperature applications. Full article

In this study, nickel–cobalt (Ni–Co) coatings were fabricated via electrodeposition using a 2² central composite factorial design with two central and two axial points, totaling ten experiments. The effects of pH and current density on the coatings’ chemical composition and properties were evaluated. Coatings were characterized by microstructure, morphology, magnetic properties, and corrosion resistance. The results showed that pH significantly influenced chemical composition, while current density had no notable effect. Acidic pH produced cobalt-rich coatings (43–81 at.%), with uniform morphology, higher saturation magnetization, and lower corrosion resistance. Maximum cobalt content (81 at.%) resulted in a mixed face-centered cubic (fcc) + hexagonal close-packed (hcp) phase. Alkaline pH yielded nickel-rich coatings (89–95 at.%), featuring nodular morphology, lower magnetization, higher corrosion resistance, and, exclusively, the fcc phase. The highest polarization resistance (66.1 kΩ) occurred at pH 8.83 and 60 mA/cm², while resistance decreased with increasing cobalt content. The pH effect on deposition was linked to the formation of citrate complexes: ammonia and citrate complexes promoted nickel deposition under alkaline conditions, while stable cobalt complexes dominated in an acidic pH. These findings highlight the potential to tailor Ni–Co coatings for applications such as corrosion-resistant coatings (nickel-rich) or magnetic devices (cobalt-rich). Full article

This research explores the physical properties of refractory high-entropy alloys Ti₃Zr_yNbV_x (0.5 ≤ x ≤ 3.5; 1 ≤ y ≤ 2), utilizing the first-principles exact muffin-tin orbitals method, in addition to the coherent potential approximation. We examine the atomic size difference (δ), the valence electron concentration (VEC) and the total energy of the body-centered cubic (bcc), the face-centered cubic (fcc) and the hexagonal close-packed (hcp) lattices, revealing a disordered solid solution with a bcc lattice as the stable phase of these alloys. The stability of the bcc Ti₃Zr_yNbV_x alloys increases with the addition of vanadium, and slightly decreases with increasing Zr concentration. All the investigated RHEAs have densities less than 6.2 g/cm³. Adding V to the Ti-Zr-Nb-V system reduces the volume and slightly enhances the density of the studied alloys. Our results show that increasing V content increases the tetragonal shear modulus C′, which assures that V enhances the mechanical stability of the bcc phase, and also increases the elastic moduli. Moreover, all the examined alloys are ductile. Vickers hardness and bond strength increase as V concentration increases. In contrast, decreasing Zr content reduces the density and increases the hardness and the bond strength of the present RHEAs, potentially resulting in systems with desirable mechanical properties and lower densities. These findings provide theoretical insights into the behavior of RHEAs, and emphasize the necessity for additional experimental investigations. Full article

Platinum is widely used as a reduction promoter in transition metal heterogeneous catalysts, while its effects on the catalyst’s properties and CO hydrogenation behavior remain unclear. In this study, an improvement in the reducibility of platinum-promoted catalysts is observed. Notably, platinum suppresses the aggregation of cobalt nanoparticles (CoNPs) during catalyst preparation, as evidenced by STEM/TEM and XRD analyses, which reveal the presence of smaller CoNPs and weakened cobalt diffraction in platinum-promoted catalysts. In addition, platinum also promotes the formation of more active hexagonal close-packed (hcp) cobalt but inhibits metal-support interaction (MSI). Therefore, the cobalt-time yield (CTY) for CO hydrogenation in the promoted catalyst is strongly improved, and, furthermore, its intrinsic activity (turnover frequency, TOF) is also slightly increased. However, the product distribution seems unchanged except for the CO₂ for the platinum-promoted catalysts. Full article