Search Results (296)

High-entropy ceramics (HECs) represent an emerging class of materials composed of at least five different cations or anions in near-equiatomic proportions, garnering significant attention due to their extraordinary functional and structural properties. While multi-component ceramics have played a crucial role for many years, the concept of high-entropy materials was first introduced eighteen years ago with the synthesis of high-entropy alloys, and the first high-entropy nitride films were reported in 2014. These newly developed materials exhibit superior properties over traditional ceramics, such as enhanced thermal stability, hardness, and chemical resistance, making them suitable for a wide range of applications. High-entropy carbides, borides, oxides, oxi-carbides, oxi-borides, and other systems fall within the HEC category, typically occupying unique positions within phase diagrams that lead to novel properties. HECs are particularly well suited for high-temperature coatings, for tribological applications where low thermal conductivity and similar heat coefficients are critical, as well as for energy storage and dielectric uses. Computational tools like CALPHAD streamline the element selection process for designing HECs, while innovative, energy-efficient synthesis methods are being explored for producing dense specimens. This paper provides an in-depth analysis of the current state of the compositional design, the fabrication techniques, and the diverse applications of HECs, emphasizing their transformative potential in various industrial domains. Full article

Pack boriding with CeO₂ was performed on the powder metallurgical (PM) near-α type titanium alloy at a temperature of 1273–1373 K for 5–15 h followed by air cooling. The microstructure analysis showed that the boride layer on the surface of the alloy was mainly composed of a monolithic TiB₂ outer layer, inner whisker TiB and sub-micron sized flake-like TiB layer. The growth kinetics of the TiB₂ and TiB layers obeyed the parabolic diffusion model. The diffusion coefficient of boron in the boride layers obtained in the present study was well within the ranges reported in the literature. The activation energies of boron in the TiB₂ and TiB layers during the pack boriding were estimated to be 166.4 kJ/mol and 122.8 kJ/mol, respectively. Friction tests showed that alloys borided at moderate temperatures and times had lower friction coefficients, which may have been due to the fine grain strengthening effect of TiB whiskers. The alloy borided at 1273 K for 10 h had a minimum friction coefficient of 0.73. Full article

To improve the wear resistance of the Ti60 alloy, laser cladding was used to obtain a composite coating containing a high-entropy (Ti_0.2Zr_0.2Mo_0.2Ta_0.2Nb_0.2)B₂ boride phase, with Ti, Zr, Mo, Ta, Nb, and B powders as the raw materials. The microstructure and wear characteristics of the coating were studied using XRD, SEM, EDS, and the pin-on-disc friction wear technique. The results show that the coating mainly consists of six phases: (Ti_0.2Zr_0.2Mo_0.2Ta_0.2Nb_0.2)B₂, ZrB₂, TiB, TiZr, Ti_1.83 Zr_0.17, and Ti_0.67Zr_0.67Nb_0.67. The average microhardness of the coating was 1062.9 HV_0.1 due to the occurrence of the high-entropy, high-hardness (Ti_0.2Zr_0.2Mo_0.2Ta_0.2Nb_0.2)B₂ boride phase, which was about 2.9 times that of the Ti60 alloy substrate. The coating significantly improved the wear resistance of the Ti60 alloy substrate, and the mass wear rate was about 1/11 that of the Ti60 alloy substrate. The main types of wear affecting the coating were abrasive, adhesive, and oxidation wear, while the main wear affecting the Ti60 alloy matrix was abrasive wear, accompanied by a small amount of adhesive and oxidation wear. Full article

Hydrogen boride (HB) sheets are emerging as a promising two-dimensional (2D) boron material, with potential applications as unique electrodes, substrates, and hydrogen storage materials. The 2D layered structure of HB was successfully synthesized using an ion-exchange method. The chemical bonding and structure of the HB sheets were investigated using Fourier Transform Infrared (FT–IR) spectroscopy and Transmission Electron Microscopy (TEM), respectively. X-ray photoelectron spectroscopy (XPS) was employed to study the chemical states and transformation of the components before and after atomic hydrogen adsorption, thereby elucidating the atomic hydrogen adsorption process on HB sheets. Our results indicate that, upon atomic hydrogen adsorption onto the HB sheets, the B-H-B bonds were broken and converted into B-H bonds. This research highlights and demonstrates the changes in chemical states and component transformations of the boron element on the HB sheets’ surface before and after atomic hydrogen adsorption, thus providing a clearer understanding of the unique bonding and structural characteristics of the HB sheets. Full article

Transition metal borides have emerged as pivotal players in various fields. In addition to their exceptional properties such as high hardness, a high melting point, and corrosion resistance, certain compounds exhibit remarkable characteristics including superconductivity, magnetism, electrical conductivity, and catalytic activity. Among these compounds, ZrB₁₂ has garnered significant attention due to its unique physicochemical properties. However, previous research on ZrB₁₂ has predominantly focused on its mechanical behavior while overlooking the electron-electron interactions of the superconducting state. In this paper, resistance characterization of ZrB₁₂ under high-pressure conditions was conducted to further investigate its superconductivity. Our research findings indicate that ZrB₁₂ maintains its superconductivity within a pressure range of 0 to 1.5 GPa and is classified as a type 2 superconductor. Additionally, the results confirm the anisotropic nature of ZrB₁₂’s superconductivity. As the pressure increases, the superconducting transition temperature undergoes a gradual decrease. Remarkably, ZrB₁₂ exhibits metallic behavior under pressures up to 31.4 GPa. The observed decline in superconductivity in ZrB₁₂ can be ascribed to the intensified influence of Zr’s movement on phonon dispersion, ultimately leading to a reduction in carrier concentration. Full article

Increasing demand for functional materials crucial for advancing new technologies has motivated significant scientific and industrial research efforts. High-entropy materials (HEMs), with tunable properties, are gaining attention for their use in high-frequency transformers, microwave devices, multiferroics, and high-density magnetic memory components. The initial exploration of HEMs started with high-entropy alloys (HASs), such as CrMnFeCoNi, CuCoNiCrAlxFe, and AlCoCrTiZn and paved the way for a multitude of HEM variations, including oxides, oxyfluorides, borides, carbides, nitrides, sulfides, and phosphides. In this study, we fabricated the high-entropy oxide (HEO) compound ${\mathrm{B}\mathrm{i}}_{0.5}{\mathrm{L}\mathrm{a}}_{0.1}{\mathrm{I}\mathrm{n}}_{0.1}{\mathrm{Y}}_{0.1}{\mathrm{N}\mathrm{d}}_{0.1}{\mathrm{G}\mathrm{d}}_{0.1}\mathrm{F}\mathrm{e}{\mathrm{O}}_3$ through the solid-state synthesis method. Magnetic measurements at 300 K show ferromagnetic behavior with significant coercivity. At the same time, this novel composition exhibits excellent dielectric properties and shows potential for electronic applications demonstrating that a high-entropy approach can expand the compositional range of rare earth multiferroics and improve the multifunctional properties in multiferroic applications. Full article

Molten salt electrophoretic deposition is a novel method for preparing coatings of transition metal borides such as TiB₂, which has emerged in recent years. To broaden the applications of transition metal boride coatings prepared by this method, this paper investigates the corrosion resistance of TiB₂ coatings, produced through molten salt electrophoretic deposition, to liquid zinc. By applying a cell voltage of 1.2 V (corresponding to an electric field of 0.6 V/cm) for 1 h in molten NaF-AlF₃, the nanoscale TiB₂ particles migrated to the cathode and were deposited on the graphite substrate, forming a smooth and dense TiB₂ coating with a thickness of 43 μm. Subsequently, after subjecting the TiB₂-coated graphite to corrosion resistance tested in molten zinc for 120 h of continuous immersion, no cracks were observed on the surface or within the coating. The produced TiB₂ coating demonstrated excellent corrosion resistance. These research results suggest that the fully dense TiB₂ coating on the graphite substrate, produced through molten salt electrophoretic deposition, exhibits excellent corrosion resistance to liquid zinc. Full article

Commercially pure titanium was plasma paste borided using various temperatures of the process. An increase in the boriding temperature resulted in an increase in the thickness of the borided layer. All the layers produced consisted of an outer compact TiB₂ zone and an inner TiB zone in the form of whiskers penetrating into the substrate. The presence of hard titanium borides resulted in a significant increase in wear resistance compared to non-borided pure titanium. However, the thickness of the layer produced strongly influenced the wear behavior, in respect of the time required for complete destruction of the layer. Higher wear resistance was characteristic of the TiB₂ layer due to its compact nature, whereas the specific morphology of TiB whiskers resulted in their lower wear resistance compared to the outer TiB₂ layer. Plasma paste boriding of pure titanium also had an advantageous effect on corrosion resistance compared to non-borided pure titanium. Simultaneously, due to the higher thickness of TiB₂ layer, the specimen borided at a higher temperature showed higher corrosion resistance. Full article

The ternary transition metal boride Fe₂AlB₂ is a unique ferromagnetic “MAB” phase that demonstrates a sizable magnetocaloric effect near room temperature—a feature that renders this material suitable for magnetic heat pump devices (MHP), a promising alternative to conventional vapor compression technology. Here, we provide a comprehensive review of the material properties of Fe₂AlB₂ (magnetofunctional response, transport properties, and mechanical stability) and discuss alloy synthesis from the perspective of shaping these materials as porous active magnetic regenerators in MHPs. Salient aspects of the coupled magnetic and structural phase transitions are critically assessed to elucidate the fundamental origin of the functional response. The goal is to provide insight into strategies to tune the magnetofunctional response via elemental substitution and microstructure optimization. Finally, outstanding challenges that reduce the commercial viability of Fe₂AlB₂ are discussed, and opportunities for further developments in this field are identified. Full article

As a Pt-group element, Pd has been regarded as one of the alternatives to Pt-based catalysts for the hydrogen evolution reaction (HER). Herein, we performed density functional theory (DFT) computations to explore the most stable structures of Pd_xB_y (x = 6, 19, 44), revealed the in situ structural reconstruction of these clusters under acidic conditions, and evaluated their HER activity. We found that the presence of B can prevent underpotential hydrogen adsorption and activate the H atoms on the cluster surface for the HER. The theoretical calculations show that the reaction barrier for the HER on ~1 nm sized Pd₄₄B₄ can be as low as 0.36 eV, which is even lower than for the same-sized Pt and Pd₂B nanoparticles. The ultra-high HER activity of sub-nanosized Pd_xB_y clusters makes them a potential new and efficient HER electro-catalyst. This study provides new ideas for evaluating and designing novel nanocatalysts based on the structural reconstruction of small-sized nanoparticles in the future. Full article

This work studies the mechanical behavior of microalloyed steels (API X60 and API X70) with boride layers using a boriding process and immersion in diesel. First, the microalloyed steels were borided using dehydrated boron paste at a temperature of 1273 K for 6 h, and then the borided microalloyed steels were immersed in diesel for one year. The characterization of the layers on the specimens subjected to diesel used scanning electron microscopy (SEM), energy dispersive spectroscopy, and X-ray diffraction (XRD). The evaluation of the mechanical properties was performed with tensile tests according to ASTM E8, and then the fracture surface was observed by SEM. This work contributes to the understanding of the changes in the mechanical properties of borided microalloyed steel immersed in diesel for possible potential applications in the storage of fuels, oils, hydrogen, and biofuels. Full article

In this paper, quantitative two-dimensional (2-D) phase-field simulations were performed to gain insight into the effects of B and Nb for Al-Ti-Nb balanced-ratio GH4742 alloys. The microstructure evolution during the precipitation process was simulated using the MICRESS (MICRostructure Evolution Simulation Software) package developed in the formalism of the multi-phase field model. The coupling to CALPHAD (CALculation of PHAse Diagram) thermodynamic databases was realized via the TQ interface. The morphological evolution, concentration distribution, and thermodynamic properties were extensively analyzed. It is indicated that a higher Nb content contributes to a faster precipitation rate and higher amounts and the smaller precipitate size of the γ′ phase, contributing to better mechanical properties. The segregation of the W element in γ′ precipitate due to its sluggish diffusion effect has also been observed. Higher temperatures and lower B contents accelerate the dissolution of boride and reduce the precipitation of borides. With the increased addition of B, the formation of borides may have a pinning effect on the grain boundary to hinder the kinetic process. In addition, borides are prone to precipitate around the interface rather than in the bulk phase. Once the M₃B₂ borides nucleate, they grow in the consumption of γ′ phases. Full article

DIN 16MnCr5 is commonly used in mechanical engineering contact applications such as gears, joint parts, shafts, gear wheels, camshafts, bolts, pins, and cardan joints, among others. This study examined the microstructural and mechanical properties and tribological behavior of different surface treatments applied to DIN 16MnCr5 steel. The samples were hardened at 870 °C for 15 min and then quenched in water. The surface conditions evaluated were as follows: quenched and tempered DIN 16MnCr5 steel samples without surface treatments (control group), quenched and tempered DIN 16MnCr5 steel samples with gas-nitriding at 560 °C for 6 h, quenched and tempered DIN 16MnCr5 steel samples with pack boriding at 950 °C for 4 h, and quenched and tempered DIN 16MnCr5 steel samples with duplex gas-nitriding and pack boriding. Microstructure characterization was carried out using metallographic techniques, optical microscopy, scanning electron microscopy with energy-dispersive spectroscopy, and X-ray diffraction. The mechanical properties were assessed through microhardness and elastic modulus tests using nanoindentation. The tribological behavior was evaluated using pin-on-disc tests following the ASTM G99-17 standard procedure under dry sliding conditions. The results indicated that the surface treated with duplex gas-nitriding and pack boriding exhibited the highest wear resistance and a reduced coefficient of friction due to improved mechanical properties, leading to increased hardness and elastic modulus. Full article

One of the primary challenges in the automotive industry is the wear of engine components, such as the crankshaft and camshaft, which is the most pronounced during the engine’s startup phase, when the amount of lubricant fluid is at its lowest. This study aims to enhance the surface wear resistance of automotive crankshaft steel by applying a boriding thermochemical process. This process forms a hard surface layer on the steel, improving its mechanical properties and bolstering its wear resistance, especially under dry conditions. Boride layers were achieved using the powder-pack boriding process in a conventional furnace, with meticulous treatment times of 2, 4, and 6 h at a constant temperature of 950 °C. The nature of the layers was analyzed using X-ray diffraction, and their tribological behavior was evaluated using the pin-on-disk test. The growth of the layers was directly proportional to the treatment time and was estimated at 145 µm and 48 µm for the 6 and 2 h of treatment, respectively. The surface hardness increased from 320 HV for the non-treated steel to 2034 HV for the sample exposed to 950 °C for 6 h. The results indicate a significant reduction in the coefficient of friction from 0.43 for the non-treated steel to 0.12 for the samples exposed to 950 °C for 6 h, suggesting potential wear protection during the engine starting period. Full article

The short-term (5 min) exposure to the supersonic flow of carbon dioxide plasma on ultrahigh-temperature ceramics of HfB₂-30vol.%SiC composition has been studied. It was shown that, when established on the surface at a temperature of 1615–1655 °C, the beginning of the formation of an oxidized layer takes place. Raman spectroscopy and scanning electron microscopy studies showed that the formation of a porous SiC-depleted region is not possible under the HfO₂-SiO₂ surface oxide layer. Numerical modeling based on the Navier–Stokes equations and experimental probe measurements of the test conditions were performed. The desirability of continuing systematic studies on the behavior of ultrahigh-temperature ZrB₂/HfB₂-SiC ceramics, including those doped with various components under the influence of high-enthalpy gas flows, was noted. Full article