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Though YB6 and LaB6 share the same crystal structure, atomic valence electron configuration, and phonon modes, they exhibit drastically different phonon-mediated superconductivity. YB6 superconducts below 8.4 K, giving it the second-highest critical temperature of known borides, second only to MgB2. LaB6 does not superconduct until near-absolute zero temperatures (below 0.45 K), however. Though previous studies have quantified the canonical superconductivity descriptors of YB6's greater Fermi-level (Ef) density of states and higher electron-phonon coupling (EPC), the root of this difference has not been assessed with full detail of the electronic structure. Through chemical bonding, we determine low-lying, unoccupied 4f atomic orbitals in lanthanum to be the key difference between these superconductors. These orbitals, which are not accessible in YB6, hybridize with π B-B bonds and bring this π-system lower in energy than the σ B-B bonds otherwise at Ef. This inversion of bands is crucial: the optical phonon modes we show responsible for superconductivity cause the σ-orbitals of YB6 to change drastically in overlap, but couple weakly to the π-orbitals of LaB6. These phonons in YB6 even access a crossing of electronic states, indicating strong EPC. No such crossing in LaB6 is observed. Finally, a supercell (the M k-point) is shown to undergo Peierls-like effects in YB6, introducing additional EPC from both softened acoustic phonons and the same electron-coupled optical modes as in the unit cell. Overall, we find that LaB6 and YB6 have fundamentally different mechanisms of superconductivity, despite their otherwise near-identity.

Borides are promising wear-resistant materials. The mechanical and tribological properties of ZrB 2 , (Ta, Zr)B 2 , (Ta, Zr, Ti)B 2 , (Ta, Zr, Ti, V)B 2 and (Ta, Zr, Ti, V, Hf)B 2 synthesized by spark plasma sintering were compared to examine the elemental dependence. The results indicated that the hardness and fracture toughness of borides increased with the increase of entropy. (Ta, Zr, Ti, V, Hf)B 2 obtained the highest hardness and fracture toughness of 23.14 GPa and 5.13 Mpa·m1/2 due to the pores and second phases that change the path of crack propagation. In terms of wear, all the Ta-contained borides have a lower wear rate than that of ZrB 2. It is almost one order of magnitude lower for (Ta, Zr, Ti, V, Hf)B 2 than that of ZrB 2. This is mainly due to the formation and action of tribofilm rich of amorphous Ta 2 O 5. Thermodynamic calculation indicates that the Ta atoms in borides are more prone to being oxidized resulting in the formation of a layer of Ta 2 O 5 on the surface, which is beneficial to wear resistance improvement. This work provides guidelines for the composition-design of high-entropy borides for wear-resistant material applications. [ABSTRACT FROM AUTHOR]

Revealing the hardening mechanisms is crucial for facilitating the design of superhard high‐entropy borides. Taking high‐entropy diborides (HEB2) as the prototype, the hardening mechanisms of high‐entropy borides are thoroughly investigated. Specifically, the equiatomic 4—9‐cation single‐phase HEB2 ceramics (4—9HEB2) are fabricated by an ultra‐fast high‐temperature sintering method. The experimental results show that the hardness of the as‐fabricated 4—9HEB2 samples has an increasing tendency with the increase of metal components. With a combination of first‐principles calculations, machine‐learning‐potential‐based molecular dynamics simulations, and scanning transmission electron microscopy characterizations, lattice distortion is explicitly identified to be essential in hardening HEB2 by increasing strain field fluctuation, enlarging atomic strain energy, and strengthening B─B bonds. The results unravel the hardening mechanisms of HEB2 by intensifying lattice distortion, providing fascinating guidance for developing superhard high‐entropy borides. [ABSTRACT FROM AUTHOR]

A facile and highly efficient chemoselective reduction of α,β‐unsaturated amides leading to saturated amide has been described. In situ generated nickel boride was found to act as an efficient reagent for the conjugate reduction. The reaction proceeds smoothly under an inert atmosphere at ambient temperature with a moderate to good yield. Both aliphatic and aromatic α,β‐unsaturated amides were found to be compatible with the reaction protocol. [ABSTRACT FROM AUTHOR]

Using a mixture of TiH 2 , Al, B 4 C, and graphite powders with a molar ratio of 3+2 m/1.2/m/2-m (where m ranges from 0 to 0.25, with increments of 0.05), porous Ti 3 AlC 2 -TiB 2 composite ceramics were successfully synthesized through activated reaction sintering. The effect of B 4 C content on the phase composition, volumetric expansion, microstructure, and pore structure parameters (including pore size, porosity, and permeability) was systematically studied. When the molar ratio of B 4 C was less than 0.1, the volumetric expansion rate, average pore size, and permeability increased with the addition of B 4 C, reaching maximum values of −5.46 %, 2.23 μm, and 92.4 m3 m−2·10 kPa−1 h−1, respectively. Conversely, when the B 4 C molar ratio exceeded 0.1, the parameters related to the pore structure of the porous Ti 3 AlC 2 -TiB 2 composite ceramics decreased, with minimum values of −10.40 %, 1.46 μm, and 68 m3 m−2·10 kPa−1 h−1, respectively. In addition, the pore formation mechanism of the porous Ti 3 AlC 2 -TiB 2 composite ceramics was systematically explored. The revolution tendency of pores is related to the decomposition of TiH 2 , Kirkendall partial diffusion, diffusion between B and C, and the transition process of the final phase Ti 3 AlC 2 -TiB 2. This research work could provide a reference for the preparation of the MAX phase composite porous materials. [ABSTRACT FROM AUTHOR]

A novel bimetallic CoMoB-coupled carbon nitride with dual moiety defects (CN-TH 3/3) Schottky junction photocatalyst (CoMoB/CN-TH 3/3) was designed for photocatalytic nitrogen fixation. [Display omitted] • A novel CoMoB/(CN-TH 3/3) Schottky junction photocatalyst was designed for photocatalytic NRR. • Both of the intralayer exciton characteristics and the visible light adsorption capacity were altered. • The synergistic effect of CoMoB and CN-TH 3/3 accelerated charge transfer and enhanced the N 2 adsorption and activation. • The photocatalytic NRR performance of optimum CoMoB/CN-TH 3/3 is 6.2 times higher than CN. The sustainable generation of ammonia by photocatalytic nitrogen fixation under mild conditions is fascinating compared to conventional industrial processes. Nevertheless, owing to the low charge transfer efficiency, the insufficient light absorption capacity and limited active sites of the photocatalyst cause the difficult adsorption and activation of N 2 molecules, thereby resulting in a low photocatalytic conversion efficiency. Herein, a novel bimetallic CoMoB nanosheets (CoMoB) co-catalyst modified carbon nitride with dual moiety defects (CN-TH 3/3) Schottky junction photocatalyst is designed for photocatalytic nitrogen reduction reaction (NRR). The photocatalytic nitrogen reduction rate of the optimized CoMoB/CN-TH 3/3 photocatalyst is 4.81 mM·g−1·h−1, which is 6.2 and 2.2 times higher than carbon nitride (CN) (0.78 mM·g−1·h−1) and CN-TH 3/3 (2.21 mM·g−1·h−1), respectively. The excellent photocatalytic NRR performance is ascribed not only to the introduction of dual moiety defects (cyano and cyanamide groups) that extends the visible light absorption range and promotes exciton polarization dissociation, but also to the formation of interfacial electric field between CoMoB and CN-TH 3/3 , which effectively facilitates the interfacial charge transfer. Thus, the synergistic interaction between CN-TH 3/3 and CoMoB further increases the electron numble of CoMoB active sites, which effectively strengthens the adsorption and activation of N 2 and weakens the N N triple bond, thereby enhancing the photocatalytic NRR activity. This work highlights the introduced dual moiety defects and bimetallic CoMoB co-catalyst to synergistically enhance the photocatalytic nitrogen reduction performance. [ABSTRACT FROM AUTHOR]

Sodium borohydride (NaBH 4) hydrolysis is considered as a promising hydrogen production strategy. The key to accelerating NaBH 4 hydrolysis is the development of efficient catalysts. Metal-modified cobalt boride has demonstrated superior catalytic activity for NaBH 4 hydrolysis compared to pure cobalt boride. However, the relationship between the high activity of metal-modified cobalt boride and the modifying metal has not been summarized. In this work, through extensive literature research, the mechanisms of metal modification on the catalytic activity improvement of metal-modified cobalt boride were clarified, the reaction mechanisms of NaBH 4 hydrolysis catalyzed by cobalt boride and metal-modified cobalt boride were compared and analyzed, the challenges metal-modified cobalt boride may encounter in the future study of NaBH 4 hydrolysis were discussed, and our recommendations were provided. This work can provide an important theoretical basis for the design and development of efficient and robust catalysts, as well as for the advancement of hydrogen production technology. • Metal-modified cobalt boride (Co-M-B) for NaBH 4 hydrolysis was overall reviewed. • The mechanism of catalytic activity enhancement of Co-M-B was clarified. • Challenges that Co-M-B may encounter in future development were proposed. [ABSTRACT FROM AUTHOR]

Nickel-base superalloys contain high amounts of solutes like Cr, Mo, W, Nb, Ti, etc. These solutes promote the formation of different types of carbide and boride phases that may contain multiple elements. Researchers have mostly discussed the roles of primary elements responsible for the formation of a given carbide/boride phase, often ignoring the role of other solutes on its stability. In the present work, thermodynamic stability of carbide and boride phases in seven commercial superalloys, namely, Alloy 625, Alloy 690, Alloy 718, MAR M246, Rene 100, Udimet 710 and Nimonic 80A, has been studied using the CALPHAD based Thermo-Calc software. The aim of the study was to understand the role of different alloying elements on temperature stability and chemical compositions of equilibrium phases in superalloys. As the accuracy of CALPHAD based predictions depends upon the database used, a detailed examination of its inadequacies has also been carried out to ascertain the limitations of the predicted data. From the calculated equilibrium chemical compositions, major and minor constituents promoting the formation of carbides and borides have been identified. The individual effect of a given solute as well as the synergistic effect of two solutes on the relative thermodynamic stability of carbide/boride phases has been identified using property diagrams and isothermal sections of the temperature-composition diagrams. Most of the simulated results have been found to be consistent with the experimental data available in the literature. From a comparison of the experimental literature and the simulated data of the stable carbide and boride phases in the studied alloys, the interplay of different solutes has been deduced to define conditions under which these phases form, within the limitations of the database used. This study has helped in better understanding of general tendencies of solutes to form different carbide and boride phases in nickel-based superalloys. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In order to further improve the density and properties of high-entropy boride ceramics, (Hf,Zr,W,Mo,Ti)B2 high-entropy boride ceramics were prepared by boro/carbothermal reduction combined with SPS. The phase composition, microstructure, and mechanical properties of the ceramics were studied, and the results showed that (Hf,Zr,W,Mo,Ti)B2 high-entropy boride powder contained a highentropy phase, an oxides impurities phase, a WB phase, and a HfB2 phase at 1600 °C. After sintering at 2000 °C, there was no oxide impurity in the (Hf,Zr,W,Mo,Ti)B2 high-entropy boride ceramics, which consisted of a high-entropy phase and a small amount of WB second phase. The hardness and fracture toughness were 29.9 ± 1.0 GPa and 3.36 ± 0.21 MPa·m1/2, respectively. The hardness was higher than the high-entropy boride ceramics with the same components prepared by in situ reactive sintering and borothermal reduction. The mechanical properties of the high-entropy ceramics obtained by boro/carbothermal reduction was excellent. and were higher than those reported in the literature of the same component. [ABSTRACT FROM AUTHOR]

One of the most fascinating 2D nanomaterials (NMs) ever found is various members of MXene family. Among them, the titanium‐based MXenes, with more than 70% of publication‐related investigations, are comparatively well studied, producing fundamental foundation for the 2D MXene family members with flexible properties, familiar with a variety of advanced novel technological applications. Nonetheless, there are still more candidates among transitional metals (TMs) that can function as MXene NMs in ways that go well beyond those that are now recognized. Systematized details of the preparations, characteristics, limitations, significant discoveries, and uses of the novel M‐based MXenes (M‐MXenes), where M stands for non‐Ti TMs (M = Sc, V, Cr, Y, Zr, Nb, Mo, Hf, Ta, W, and Lu), are given. The exceptional qualities of the 2D non‐Ti MXene outperform standard Ti‐MXene in several applications. There is many advancement in top‐down as well as bottom‐up production of MXenes family members, which allows for exact control of the M‐characteristics MXene NMs to contain cutting‐edge applications. This study offers a systematic evaluation of existing research, covering everything in producing complex M‐MXenes from primary limitations to the characterization and selection of their applications in accordance with their novel features. The development of double metal combinations, extension of additional metal candidates beyond group‐(III–VI)B family, and subsequent development of the 2D TM carbide/TMs nitride/TM carbonitrides to 2D metal boride family are also included in this overview. The possibilities and further recommendations for the way of non‐Ti MXene NMs are in the synthesis of NMs will discuss in detail in this critical evaluation. [ABSTRACT FROM AUTHOR]

We report the structure and physical properties of a new rare-earth (RE) high-entropy boride (HEB) (Dy 0.2 Ho 0.2 Er 0.2 Tm 0.2 Lu 0.2)(Rh 0.85 Ru 0.15) 4 B 4. The as-cast HEB consists of a highly crystallized, body-centered-tetragonal phase (I 4 1 / a c d , a = 7.460 Å and c = 14.860 Å); here, all the RE elements share the same crystallographic site and are distributed uniformly on both macroscopic and microscopic scales. At high temperature, the HEB shows a paramagnetic behavior with a large effective moment p eff yet it becomes a bulk superconductor upon cooling below 6.0 K. Remarkably, a peculiar cocktail effect of properties is observed: while the lattice parameters, T c and p eff of the HEB agree reasonably well with the compositional averages of the individual pseudo-ternary counterparts, the increased RE mixing entropy tends to suppress the superconductivity even without the magnetic exchange interactions, and a reentrant resistive transition is induced at magnetic fields above 0.8 T. Our results indicate that the high-entropy design of the RE sublattice is a viable way to tune the electrical and magnetic properties in RE intermetallics. [ABSTRACT FROM AUTHOR]

The oxidation resistance of Hf0.28B0.72 and Hf0.11Al0.20B0.69 thin films was investigated comparatively at 700 °C for up to 8 h. Single-phase solid solution thin films were co-sputtered from HfB2 and AlB2 compound targets. After oxidation at 700 °C for 8 h an oxide scale thickness of 31 ± 2 nm was formed on Hf0.11Al0.20B0.69 which corresponds to 14% of the scale thickness measured on Hf0.28B0.72. The improved oxidation resistance can be rationalized based on the chemical composition and the morphology of the formed oxide scales. On Hf0.28B0.72 the formation of a porous, O, Hf, and B-containing scale and the formation of crystalline HfO2 is observed. Whereas on Hf0.11Al0.20B0.69 a dense, primarily amorphous scale containing O, Al, B as well as approximately 3 at% of Hf forms, which reduces the oxidation kinetics significantly by passivation. Benchmarking Hf0.11Al0.20B0.69 with Ti–Al-based boride and nitride thin films with similar Al concentrations reveals superior oxidation behavior of the Hf-Al-based thin film. The incorporation of few at% of Hf in the oxide scale decelerates oxidation kinetics at 700 °C and leads to a reduction in oxide scale thickness of 21% and 47% compared to Ti0.12Al0.21B0.67 and Ti0.27Al0.21N0.52, respectively. Contrary to Ti–Al-based diborides, Hf0.11Al0.20B0.69 shows excellent oxidation behavior despite B-richness. [ABSTRACT FROM AUTHOR]

High-entropy borides are deemed robust candidates because of their complex combination of entropy-driven, multi-component disordered solid solutions. They are particularly remarkable for their unique single-crystal structures and significant bandgap. This structural adaptability positions them uniquely among materials, setting them apart from conventional transition metal diborides. Researchers have been fascinated by the appeal of high-entropy borides for a long time, driven by the groundbreaking idea of 'High entropy ceramics'. Nevertheless, the lack of thorough review papers in this field has hindered the progress of creating strong and durable high-entropy borides. This paper proposes adopting a collaborative strategy to properly negotiate this unexplored region. This perspective covers the up-to-date research on successfully synthesized high-entropy boride complexes. It examines compositional strategies, historical backgrounds, structural complexity, fabrication methods, mechanical, thermal, and oxidation properties, as well as emergent properties with potential uses, pathways, and future possibilities. This attempt challenges materials science traditions by introducing novel materials with superior performance. [ABSTRACT FROM AUTHOR]

Abstract The oxidation resistance of Hf0.28B0.72 and Hf0.11Al0.20B0.69 thin films was investigated comparatively at 700 °C for up to 8 h. Single-phase solid solution thin films were co-sputtered from HfB2 and AlB2 compound targets. After oxidation at 700 °C for 8 h an oxide scale thickness of 31 $$\pm$$ ± 2 nm was formed on Hf0.11Al0.20B0.69 which corresponds to 14% of the scale thickness measured on Hf0.28B0.72. The improved oxidation resistance can be rationalized based on the chemical composition and the morphology of the formed oxide scales. On Hf0.28B0.72 the formation of a porous, O, Hf, and B-containing scale and the formation of crystalline HfO2 is observed. Whereas on Hf0.11Al0.20B0.69 a dense, primarily amorphous scale containing O, Al, B as well as approximately 3 at% of Hf forms, which reduces the oxidation kinetics significantly by passivation. Benchmarking Hf0.11Al0.20B0.69 with Ti–Al-based boride and nitride thin films with similar Al concentrations reveals superior oxidation behavior of the Hf-Al-based thin film. The incorporation of few at% of Hf in the oxide scale decelerates oxidation kinetics at 700 °C and leads to a reduction in oxide scale thickness of 21% and 47% compared to Ti0.12Al0.21B0.67 and Ti0.27Al0.21N0.52, respectively. Contrary to Ti–Al-based diborides, Hf0.11Al0.20B0.69 shows excellent oxidation behavior despite B-richness.

This study investigated the synthesis mechanism of tantalum boride (TaB2) powder via the boron/carbothermal reduction method, based on thermodynamic calculations and experimental results. The insufficient presence of the intermediate product B2O3 leads to the emergence of TaC and Ta3B4, while in the presence of a sufficient boron source in the reaction system, the primary products formed include TaB2, TaC, and B2O3, with TaC subsequently reacting with B2O3 and carbon to yield TaB2. TaB2 powder was successfully synthesized at 1500°C with the addition of an excess of 20 wt% B4C. The particle size of the powder was approximately 298 nm, and the oxygen content and carbon content in the powder were 0.6 and 0.1 wt.%, respectively. [ABSTRACT FROM AUTHOR]

We have analyzed topological motifs of whole crystal structures and unconnected non-metal sublattices in 967 borides, 721 carbides, 899 nitrides and 927 silicides of metals within the periodic net model. In addition, we have classified the topological types of connected non-metal motifs in 333 carbides and 86 nitrides containing N–N or C–C bonds. The topology of the whole structure was found to be essentially predetermined by the sublattice motif; however, there were exceptions, which were caused by geometrical distortions of the structure. In contrast, sublattices of the same type can exist in different structural and topological types. We have proposed an integral criterion 〈G3〉 of the sublattice distortion, which can also be considered as a measure of the sublattice uniformity. In most cases, the sublattices of non-metal atoms possess high uniformity, which reflects the tendency of the negatively charged atoms to be placed as distant as possible from each other. The sublattices, which have high symmetry, simple topology, and high uniformity in the most symmetrical embedding, were found to be the most suitable for the realization in different structures. The low uniformity of a sublattice indicates either strong interatomic interactions in the sublattice or its subordinate structural role. [ABSTRACT FROM AUTHOR]

This study selected ZrB2–hBN ceramics as the matrix for low‐cost second‐generation SiC fibers, due to their low modulus and ability to be sintered at relatively low temperatures. The resulting composites, which contained up to 30 wt.% short‐chopped SiCf, were consolidated using reactive spark plasma sintering at 1550 and 1700°C under 50 MPa for 5 min. Without needing to prepare interfaces on the SiCf surfaces, fiber pullout, strengthening, and toughening during the fracture process were realized. By constructing the volatility phase diagram for the fiber, the microstructural changes that occurred on the fiber surfaces during sintering were successfully illustrated. Mechanical properties of ZrB2–hBN ceramics with 10 wt.% SiCf sintered at 1550°C still showed considerable improvements, including an elastic modulus of 187 GPa, a flexural strength of 337 ± 16 MPa, and a fracture toughness of 4.12 ± 0.25 MPa m1/2, increases of 12.6%, 61.2%, and 118%, respectively, compared to the counterparts without adding chopped fibers. Variations in these properties were linked to the matrix porosity and SiCf pullout behaviors, which were subsequently analyzed using the He–Hutchinson model. [ABSTRACT FROM AUTHOR]

Titanium diboride powders were synthesized from TiO2 following different reduction methods at temperatures range from 1000 to 1400°C for 1h under flowing argon gas. The reduction processes used in this study are classified as TiO2 + B (borothermal reduction), TiO2 + H3BO3 + C (carbothermal reduction) and TiO2 + B + C (combined reduction). XRD peaks of TiO2 phase are present for each sample below 1100°C. It was also observed that XRD peaks of TiO2 disappeared and TiB2 was formed in borothermal and combined reduction methods at temperature of 1100°C and above. In the carbothermal method, TiBO3 and TiC phases were present at these temperatures and TiB2 could only be obtained after heat treatment at 1400°C. However, this temperature also caused considerable particle growth and formation of the powders with hexagonal shape morphology. The powders synthesized by the carbon-containing reduction process contained residual carbon.

A novel approach was applied to synthesize B6O using CaB6 and B2O3 powders as reactants. CaB6 and B2O3 were reacted to generate B6O and CaB2O4 at 1573 K, and the by‐product CaB2O4 was removed by acid leaching. It was found that the samples prepared in this work were oxygen deficient (B6Ox, x ≈ .76–.77). The optimal molar ratio of CaB6 to B2O3 was determined to be 3:5, and excess B2O3 could not lead to a change in the value of oxygen occupancy. Scanning electron microscope images showed that regular holes similar to the morphologies of CaB6 particles were exhibited in the final samples, which could be explained by the diffusion of CaB6 during the reaction process. [ABSTRACT FROM AUTHOR]

Tribological characteristics of fine-grained dual-phase high-entropy carbide/boride ceramics were investigated using the ball-on-flat dry sliding method in air, applying linear reciprocation motion with SiC counterpart. Detailed fractographical analyses were used for the characterization of the deformation and damage mechanisms. The investigated system with composition (Ti 0.14 Zr 0.2 Nb 0.2 Hf 0.2 Ta 0.26)C + (Ti 0.38 Zr 0.18 Nb 0.22 Hf 0.115 Ta 0.105)B 2 showed density with value 8.72 g/cm3 and very high hardness of HV1 29.4 ± 2.0 GPa. The friction coefficient at the test with 5 N was 0.56 and during the test with 10 N and 25 N loads were 0.48 and 0.5, respectively. The effective wear rates at the loads of 5 N and 25 N were very similar with values of 7.93 × 10−7 mm3/Nm and 6.63 × 10−7 mm3/Nm. At load 50 N the effective wear rate is significantly higher with a value of 9.11 × 10−6 mm3/Nm. Detailed fractography revealed that the dominant wear mechanisms at loads of 5 N and 25 N were an oxidation-driven tribochemical reaction and tribo-layer formation in boride grains and mechanical wear in carbide grains and at the load of 50 N fracture of boride and carbide grains and formation of chemically complex tribolayers. [ABSTRACT FROM AUTHOR]

Transition metal diboride thin films are promising functional materials for their outstanding mechanical properties and thermal stability. By combining experiment and simulations, we discuss angular distribution of the sputtered species, their scattering in the gas phase, re-sputtering and potential evaporation from the grown films for the complex evolution of film compositions, as well as energetic preference for vacancy formation and competing phases as factors for governing the phase constitution. By co-sputtering from two compound targets, we developed phase-pure crystalline (Ta,Al)B2 solid solution thin films and correlate the stoichiometry changes with the evolution of their microstructure, hardness, and elastic modulus. [ABSTRACT FROM AUTHOR]

In this study, we have conducted a thorough investigation into the influence of the atomic radius of transition metals on the structural, electronic, and optical properties of nanolaminated borides MAlB (M = Cr , Mo, W) using first principles calculation. The validity and dependability of our calculation parameters are confirmed and compared with other available data sets. The calculated elastic constants reveal stronger resistance to deformation along the c direction as compared to the a- and b-directions. The mechanical properties of these borides increased in tandem with the atomic radius of transition metal. The chemical bonding within the borides is a mix of metallic and covalent bonds. Interestingly, there is a decrease in the boride metallicity concurrent with an increase in the atomic radius of the transition metal. Optical property analysis shows promise for these borides as absorbent materials. Furthermore, there is a correlation between the increase in the atomic nucleus of the transition metal and the increase in the maximum absorption coefficient. [ABSTRACT FROM AUTHOR]

Reactive Sintered Borides (RSBs) were fabricated to investigate the effects of carbon and chromium content producing a series of samples referred to as Gen 2 RSBs. These RSBs were tested and evaluated for various mechanical (bulk moduli, fracture toughness, nano and micro-hardness) and microstructural properties. It is the first time when the correlation between different RSB phases and mechanical properties are understood in detail, along with the CALPHAD assessment of RSBs. CALPHAD was used to investigate the effect of sintering pressure and composition on melting point and liquid volume at sintering temperature and was critical in understanding of phase differences in Gen 1 and Gen 2 RSBs. Effects of carbon and chromium addition on mechanical and microstructural properties of RSBs were also investigated. Optimal second generation RSBs have fracture toughness of 7–10.1 MPa m0.5 and hardness of 15.9–19.1 GPa. RSBs with relative sintered density >98 % were achieved in this work. Combined X-ray diffraction and EBSD-EDX techniques were used to determine and confirm phase presence in RSBs. This work has demonstrated tractability and reproducibility of RSB materials with suitable mechanical properties for potential applications in spherical tokamaks alongside existing cemented tungsten carbides. [ABSTRACT FROM AUTHOR]

Wear behavior of a fine‐grained dual‐phase high‐entropy carbide/boride ceramics was investigated using ball‐on‐flat dry sliding methods in air, applying rotational and linear reciprocation motion with SiC counterpart. The investigated system showed very high nanohardness of the carbide and boride grains with mean values of 37.4 ± 2.3 and 43.0 ± 2.9 GPa, respectively, with the microhardness of dual system HV1 29.4 ± 2.0 GPa. The stabilized friction coefficient values during the circular tests changing from.62 to.77. During the reciprocal test, the frictional coefficient values are very similar with an average value of.53. The specific wear rates during the circular motion were similar in the range from 4.65 × 10−7 to 1.68 × 10−7 mm3/N m. During the reciprocal test, the wear rates at 5 and 25 N were similar as in the case of circular motion, but at 50 N load, the wear rate increased significantly to the value of 9.11 × 10−6 mm3/N m. The dominant wear mechanisms in all cases were oxidation driven tribochemical reaction and tribolayer formation in boride grains and mechanical wear in carbide grains. During the linear reciprocation test, the loading mode created conditions resulted in relatively low coefficient of friction and very high specific wear rate. [ABSTRACT FROM AUTHOR]

Super‐hard (Hf,Mo,Ti,V,W)B2 was synthesized by boro‐carbothermal reduction and densified by spark plasma sintering. This composition was produced for the first time as a single‐phase ceramic in the present research. The optimized ceramic had a single hexagonal AlB2‐type crystalline phase with a grain size of 3.8 µm and homogeneous distribution of the constituent metals. The Vickers hardness exhibited the indentation size effect, increasing from 27 GPa at a load of 9.8 N to as high as 66 GPa at a load of 0.49 N. This is the highest hardness reported to date for high entropy boride ceramics. [ABSTRACT FROM AUTHOR]

This study systematically investigates the microstructure, martensitic phase transformation, crystal structure, and mechanical properties of (Ni43Mn47Sn9Gd1)100−xBx (x = 0, 0.8, 1.5 and 3 at%) shape memory alloys. Experimental results reveal that these alloys consist of a matrix phase and precipitated phases. The introduction of Gd elements leads to the formation of milky-white particles dispersed along grain boundaries, with the composition identified as GdNiSn. When the B element content reaches 1.5 at%, bright-white particles form and are uniformly distributed within the matrix. Their concentration increases with higher levels of B doping, and they are characterized as Mn2B. Simultaneously, the initially present Gd-rich milky-white particles distributed along grain boundaries, exhibit a diminishing trend with increasing B doping. B doping elevates the alloy's phase transition temperature, and the compressive strength of the alloy approximately follows a linear trend with increasing B content. At a B doping level of 3%, the annealed alloy demonstrates a compressive strength of up to 1313 MPa with a compressive fracture strain of 11.6%, marking a 110% improvement. For the as-cast alloy, a compressive strength of 1652 MPa is achieved, accompanied by a compressive fracture strain of 12.3%, representing a 130% enhancement. Transmission electron microscopy reveals pronounced twinning features on the alloy surface, resulting in the formation of numerous fine lines in the as-cast state, that are magnified into voids after heat treatment. This phenomenon is detrimental to the alloy's mechanical performance; hence, the as-cast compressive strength is favored over the annealed state. [ABSTRACT FROM AUTHOR]

Metal borides have received a lot of attention recently as a potentially useful material for a wide range of applications. In particular, molybdenum‐based borides and MBenes are of great significance, due to their remarkable properties like good electronic conductivity, considerable stability, high surface area, and environmental harmlessness. Therefore, in this article, the progress made in molybdenum‐based borides and MBenes in recent years is reviewed. The first step in understanding these materials is to begin with an overview of their structural and electronic properties. Then synthetic technologies for the production of molybdenum borides, such as high‐temperature/pressure methods, physical vapor deposition (PVD), chemical vapor deposition (CVD), element reaction route, molten salt‐assisted, and selective etching methods are surveyed. Then, the critical performance of these materials in numerous applications like energy storage, catalysis, biosensors, biomedical devices, surface‐enhanced Raman spectroscopy (SERS), and tribology and lubrication are summarized. The review concludes with an analysis of the current progress of these materials and provides perspectives for future research. Overall, this review will offer an insightful reference for the understanding molybdenum‐based borides and their development in the future. [ABSTRACT FROM AUTHOR]

Most modern catalysts are based on precious metals and rear-earth elements, making some of organic synthesis reactions economically insolvent. Density functional theory calculations are used here to describe several differently oriented surfaces of the higher tungsten boride WB5-x, together with their catalytic activity for the CO oxidation reaction. Based on our findings, WB5-x appears to be an efficient alternative catalyst for CO oxidation. Calculated surface energies allow the use of the Wulff construction to determine the equilibrium shape of WB5-x particles. It is found that the (010) and (101) facets terminated by boron and tungsten, respectively, are the most exposed surfaces for which the adsorption of different gaseous agents (CO, CO2, H2, N2, O2, NO, NO2, H2O, NH3, SO2) is evaluated to reveal promising prospects for applications. CO oxidation on B-rich (010) and W-rich (101) surfaces is further investigated by analyzing the charge redistribution during the adsorption of CO and O2 molecules. It is found that CO oxidation has relatively low energy barriers. The implications of the present results, the effects of WB5-x on CO oxidation and potential application in the automotive, chemical, and mining industries are discussed. [ABSTRACT FROM AUTHOR]

The oxidation performance of CoCrFe2Ni0.5 HEA borided through a powder-pack boriding process was investigated at 900 °C for 120 h. The boriding process at 900 °C for 6 h resulted in the formation of a two-zone structure: the outmost part contained a Ni2Si layer and the inner part consisted of a MB/M2B layer. The borided alloy displayed better oxidation resistance with the least oxidation rate constant value of 0.0383 (mgn cm−2n h−1). Moreover, this alloy rendered a continuous oxide layer that was denser, more compact, and contained fewer defects, which confirmed the improvement in oxidation resistance. The Ni2Si layer plus the boride layer was responsible for the enhanced oxidation performance of borided alloy. [ABSTRACT FROM AUTHOR]

The ternary TaIr2B2 boride was prepared by the reaction between iridium and TaB2 powders. It was shown that a choice in favor of any crystal structure of TaIr2B2 boride using only X-ray powder diffraction analysis and single-crystal XRD is rather difficult to make. The DFT calculations were carried out to predict the energetically preferred crystal structure of TaIr2B2. The 11B solid-state NMR spectrum of TaIr2B2 was recorded for the first time. A combination of diffraction and spectroscopic methods, as well as theoretical calculations, allowed us to make clear choice in favor of the triclinic space group for the crystal structure of TaIr2B2. The Vickers microhardness value for TaIr2B2 was found to be 17.9 ± 2.3 GPa, and the ternary TaIr2B2 boride can be considered a hard material. Therefore, the family of hard ternary boride phases got a new member. The coefficients of thermal expansion of TaIr2B2 measured by in situ high-temperature XRD analysis are independent of temperature along the a and b axes, but the CTE along the c axis deviates noticeably at elevated temperatures. The findings for the new ternary TaIr2B2 boride are of interest for the rational design of complex structural materials containing Ta–Ir–B-based components and prediction of their high-temperature behavior. Further research into this ternary boride as well as other iridium-containing ternary borides will provide a tool to solve the problems faced by high-temperature materials science. [ABSTRACT FROM AUTHOR]

The presence of boride precipitates has a detrimental impact on the mechanical properties of TLP bonding joints. This study investigated the effectiveness of the long-term post-bonded homogenization treatment (PBHT) in mitigating the adverse effects of boride precipitates and enhancing the overall performance of TLP joints formed with IN718/316LN. Within the diffusion affected zone on the side of 316LN (referred to as DAZ-316LN), the low concentrations of Cr, Mo, and Nb in boride precipitates, coupled with a significant lattice mismatch at the boundary between boride precipitates and the matrix, facilitate the dissolution of boride precipitates during the PBHT process. This contributes to the improvement of the metallurgical bonding strength at the interface between the isothermal solidification zone (ISZ) and DAZ-316LN (referred to as the ISZ/DAZ-316LN interface), consequently shifting the location of tensile fracture from the ISZ/DAZ-316LN interface towards ISZ. Moreover, the PBHT process induces a breakdown of needle-like or continuously distributed borides along grain boundaries, transforming them into small block or short acicular boride precipitates that are uniformly distributed in the joint. This optimization process not only enhances the precipitation-strengthening effect but also alleviates stress concentration, resulting in an overall improvement in the joint's strength and ductility. [ABSTRACT FROM AUTHOR]

Size, morphology and distribution of light and stiff, but inherently brittle particles are of critical importance for the property profile of high modulus steels. Powder atomisation can dramatically reduce the borides’ size to the nanoscale, but they typically coarsen substantially during annealing or compaction via hot isostatic pressing. This study investigated the effect of compaction parameters, namely temperature, pressure and time on the coarsening mechanism, porosity evolution and resultant mechanical properties of atomised Fe-Cr-B powder. Increasing annealing temperature and time from 950 to 1150 °C, respectively, 30 min to 8 h, resulted in a non-linear boride radius growth from 76 nm in the atomised state to 1.9 µm. Hot isostatic pressing, with additional pressures up to 140 MPa, decreased the pore size from about 5 to 0.2 µm. An optimised hot isostatic pressing processing window was defined at 1050 °C and 140 MPa, combining sufficiently reduced defects with a limited particle radius, and yielded in 730 MPa tensile strength at more than 20 % tensile elongation. Powder-metallurgical synthesis of Fe-Cr-B achieved similar properties to casted and hot-rolled material, by avoiding component size scaling effects of casting. The underlying phenomena and optimisation of high modulus steel production via powder metallurgy are discussed.

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.

To form in situ nano-borides in the solid-liquid two-phase region, Ti46 A l8Nb2·6C0.8Ta x B alloys were prepared under ultrasound to improve the microstructural and mechanical properties. The morphology and distribution of borides and the characteristics of lamellar colonies were observed with scanning and transmission electron microscopy and X-ray diffraction; these analyses revealed the influence of borides on microstructural evolution and improved strength and plasticity. The borides that form are elongated and spherical. As the B content increases, the borides gradually spheroidise, and nano-borides precipitate on the lamellar phase. There are a large number of dislocations around the borides to form stacking faults and dislocation walls. The average size of the lamellar colonies decreases from 26.9 to 19.3 μm. The increase in boride nucleation sites as the B content increases and ultrasound-mediate breaking of primary borides are the reasons for forming B27-type borides. The increase in nucleation particles refines the lamellar colony. The compressive strength increases from 2058 to 2299 MPa, and the strain increases from 25.2% to 32.3% when the addition of B increases from 0% to 1.2%. The significantly improved mechanical properties are due to uniformly distributed nano-borides that hinder the movement of dislocations to form stacking faults and dislocation walls and refinement of the lamellar colonies. [ABSTRACT FROM AUTHOR]

A method for obtaining composite surface-alloyed castings from gray cast iron SCh25 by cavityless casting with the use of master alloys containing chromium and ferroboron deposited as a paste layer on the surfaces of the casting molds is considered. The microstructure and the phase composition of the surface layer and the microhardness of the structural components are determined. Mechanical tests of the cast samples for compression and wear are carried out. Self-propagating high-temperature synthesis is shown to occur between the components of the master alloys deposited on the surfaces the molds during the production of the castings. The types and compositions of the borides and carboborides formed in the alloyed layer are determined. The effect of the parameters of the alloyed layer on the properties of the composite castings is analyzed. [ABSTRACT FROM AUTHOR]

Purpose: Modification of sintered iron with the addition of molybdenum and boron leads to the formation of boride phases that significantly impact the properties of the sintered materials. The paper aims to determine Fe-Mo-B phases that might be formed during the sintering of base powders. With EDS microanalysis, determining those phases in the microstructure is difficult since the B-Kα peak is extremely close to Mo-Mζ (only a 9.3 eV difference). Thus, diffraction techniques must be implemented to unambiguously define the phases occurring in the sintered samples (WDS and EBSD). Design/methodology/approach: The sintered samples were obtained from initial powders of Fe, Mo, and B that were mixed and compressed. The reducing hydrogen atmosphere was used to sinter green samples at 1200°C for 60 minutes. The obtained sinters were subjected to microstructural observations by scanning electron microscope, and some analyses (EDS/WDS and EBSD) were conducted, which led to the determination of phases present in the material. Findings: Based on the investigations conducted, iron, molybdenum, and molybdenumiron borides have been reported. It is confirmed with the EBSD method that Fe2B, MoB and FeMo2B2 phases are formed in particles' connection regions. Besides, the interparticle region, formed due to a liquid phase during sintering, is based on Fe-Fe2B eutectic. The microstructural observations prove that the amount of the liquid phase, and thus the size of the interparticle region, diminishes with increasing molybdenum content. It was also noted that the iron matrix (interior of former iron particles) is free from contributing elements coming from boron or molybdenum powders. Research limitations/implications: The application of the EDS method is limited in the case of measuring boron in Mo-containing alloys and phases. The EDS method does not have a sufficient energetic resolution to separate the B-Kα line from Mo-Mζ one. Thus, it must be complemented with WDS and EBSD in order to unambiguously determine the presence and localization of iron and molybdenum borides. Practical implications: It can be stated that WDS has sufficient energy resolution to separate B-Kα from Mo-Mζ emission lines. Therefore, WDS analysis is suitable for boride observation in sintered iron powders by constructing distribution maps of interparticle connection regions and precipitates. Besides, measurements by the EBSD method can be used to confirm the presence of Fe2B, MoB and FeMo2B2 phases. Originality/value: Determination of boron-containing phases in Fe-Mo-B sinters by means of diffraction methods. [ABSTRACT FROM AUTHOR]

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In this work, (Zr 0.5 Ta 0.5) B 2 and (Zr 0.5 Hf 0.5) B 2 solid solutions are produced in dense form by coupling the Self-propagating High-temperature (SHS) and Spark Plasma Sintering (SPS) routes. A single boride phase solid solution is formed in both cases by SPS (1850 °C, 20 min) from the multiphasic ceramic powders preliminarily obtained by SHS. The use of small amounts of graphite during SPS is highly beneficial to eliminate oxide contaminants (from 14.5–16.0 wt% to 2.1–2.8 wt%), improve powder consolidation (from 87-90 % to 97.5–98 %), and make the operating conditions milder. Better mechanical properties are exhibited by the binary ceramics with respect to ZrB 2 produced by SHS-SPS. The presence of Ta makes the performance of (Zr 0. 5 Ta 0.5)B 2 superior compared to the Hf-containing system, with hardness, Young's modulus, and fracture toughness equal to 22.1 GPa, 636.9 GPa, and 2.46 MPa m1/2, respectively. On the other hand, (Zr 0.5 Hf 0.5) B 2 shows higher oxidation resistance in flowing and stagnant air at elevated temperatures. [ABSTRACT FROM AUTHOR]

In this work, the Dybkov model was applied to simulate the boronizing kinetics of AISI 1045 steel and the subsequent phase homogenization (PH) by considering two fitting parameters and boride incubation times to reproduce the experimental thicknesses of FeB and (FeB + Fe2B) layers. The bilayer (FeB/Fe2B) was generated on AISI 1045 steel using the ultra fast boriding (UFB) process in the range of 1123 to 1223 K for 0.25–0.75 h. New expressions of analytical solutions of Dybkov model were then developed. As a main result, the boron activation energies in FeB and Fe2B were determined as 145.27 and 133.13 kJ mol–1 for FeB and Fe2B layers, respectively. The relations describing the evolution of layers thicknesses during the phase homogenization (PH) were derived. They were used to estimate the holding time required for dissolving completely the FeB layer. [ABSTRACT FROM AUTHOR]

A novel technique to simultaneously lower the synthesis temperature of highentropy carbides and maintain their high mechanical properties was proposed. Certain amount of carbon vacancies was first introduced to significantly lower the temperature down to 2000°C for uniform elemental distributions in highentropy carbides. Those carbon vacancies were then fully eliminated through the reaction between high-entropy carbides and certain amount of boron carbide. Concomitantly, the high-entropy boride phasewas formed. The elimination of carbon vacancies and the formation of high-entropy boride phase significantly improved the mechanical properties of the high-entropy carbides. A high mechanical strength over 500 MPa can be obtained by phase optimization. [ABSTRACT FROM AUTHOR]

Chromium boride, an advanced ceramic material, is commonly produced by powder metallurgy methods using elemental boron and chromium powder, borothermic reactions, or boron carbide reduction of Cr 2 O 3. In this study, a mechanochemical method for the production of chromium boride was developed, subsequent purification was performed, and the whole process was optimized. The amounts of Cr 2 O 3 , B 2 O 3, and Mg in the initial powder blends were determined by computational thermodynamic methods based on their equilibrium compositions. Firstly, stoichiometric starting-powder blends were milled at different durations (1, 2, 3, 4, 5, and 8 h). The optimum purification route was determined using acid leaching experiments carried out with different acids, at different temperatures, and concentrations. Secondly, powders prepared in excess amounts were synthesized at the optimum duration (5 h) and leaching condition (0.1 M HCl, 25 °C). For the 100 wt % excess B 2 O 3 , 25 wt % excess Mg and 0.8 moles of Cr 2 O 3 composition, annealing was conducted at 1100 °C. Characterization studies, X-ray diffractometry (XRD), scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS), transmission electron microscopy (TEM), and atomic absorption spectroscopy (AAS) were conducted on the milled and leached powders. After annealing, CrB, CrB 2 , Cr 3 B 4 and MgO phases were obtained in the XRD patterns. The particle sizes of the resulting materials were also analyzed, and it was found to be nearly 3.11 μm after annealing. Finally, the TEM analysis revealed that the MgO peak evident in the XRD patterns was MgO shell covering the Cr boride particles having submicron sizes; hence, a pure Cr boride@MgO core-shell structure was obtained. [ABSTRACT FROM AUTHOR]

Diffusion kinetics of boron in AISI 1050 steel is investigated. AISI 1050 steel samples are borided for 2, 4 and 6 h at 850, 900 and 950°C by the powder-pack boriding method using Ekabor-II boriding powder. After the powder-pack boriding, about 25.4 – 118.9 μm thick FeB/Fe2B boride layers are obtained on the surfaces of the samples. The boride layers have a typical tooth morphology and their hardness is 1071 – 1460 HV0.1. The growth rate constants for the boriding temperatures of 850, 900 and 950°C for the AISI 1050 steel are determined to be 1.522 × 10 –12, 2.964 × 10 –13 and 6.354 ×10 –12 m2 · sec –1, respectively. The boron diffusion activation energy in the AISI 1050 steel is 162.93 kJ · mol –1. [ABSTRACT FROM AUTHOR]

Transition meal and rare earth borides have been subjected to extensive investigations because of their unique structures, superior properties and diverse applications. Conventional methods for their syntheses suffer from various drawbacks. So several alternative approaches have been explored. Among them, the so-called 'molten salt synthesis (MSS)' technique has proved promising. Over the past 10–15 years, it has been used to prepare a range of transition metal and rare earth borides. In this paper, the main results from these studies are reviewed. Initially, the relevant background on metal borides and their conventional synthesis methods are introduced, followed by the main principles/mechanisms of MSS. The following three sections provide an overview of the main work on MSS of binary and ternary borides, boride solid solutions, and boride-based composite powders. Then, two newly modified MSS approaches are presented. Finally, the main issues covered in this paper are summarised, and future prospects considered. [ABSTRACT FROM AUTHOR]

The quinary members in the solid solution Hf2Fe1−δRu5−xIrx+δB2 (x=1–4, VE=63–66) have been investigated experimentally and computationally. They were synthesized via arc‐melting and analyzed by EDX and X‐ray diffraction. Density functional theory (DFT) calculations predicted a preference for magnetic ordering in all members, but with a strong competition between ferro‐ and antiferromagnetism arising from interchain Fe−Fe interactions. The spin exchange and magnetic anisotropy energies predicted the lowest magnetic hardness for x=1 and 3 and the highest for x=2. Magnetization measurements confirm the DFT predictions and demonstrate that the antiferromagnetic ordering (TN=55–70 K) found at low magnetic fields changed to ferromagnetic (TC=150–750 K) at higher fields, suggesting metamagnetic behavior for all samples. As predicted, Hf2FeRu3Ir2B2 has the highest intrinsic coercivity (Hc=74 kA/m) reported to date for Ti3Co5B2‐type phases. Furthermore, all coercivities outperform that of ferromagnetic Hf2FeIr5B2, indicating the importance of AFM interactions in enhancing magnetic anisotropy in these materials. Importantly, two members (x=1 and 4) maintain intrinsic coercivities in the semi‐hard range at room temperature. This study opens an avenue for controlling magnetic hardness by modulating antagonistic AFM and FM interactions in low‐dimensional rare‐earth‐free magnetic materials. [ABSTRACT FROM AUTHOR]

Prolonging the life of hot stamping dies in the automotive industry is challenging. Surface modification is an effective way to improve the durability of the dies. In this study, two tool steel grades, one cold work tool steel (V4E) and one high‐boron tool steel (HBS), are deposited on a tool steel substrate using directed energy deposition, followed by tempering. Softening behavior at high temperatures of 550 and 600 °C is investigated. In the key findings, it is revealed that both steels exhibit remarkable hardness, surpassing the substrate even after extended exposure to high temperatures. HBS shows excellent softening resistance in terms of hardness at 550 °C but experiences a significant drop at 600 °C. V4E demonstrates an overall superior softening resistance due to its thermal stable MC (M represents metal) carbides and the relatively stable dislocation density. Microstructural analysis highlights some unique features, such as borides in HBS and dendritic structures in V4E. In this study, the correlation between microstructure characteristics and hardness evolution is revealed, providing some insights into how these materials resist softening to enhance the longevity and performance of hot stamping dies. [ABSTRACT FROM AUTHOR]

This review presents a comprehensive overview of the special strategies employed to boost the electrochemical performances of TMBs in Li-S batteries. [Display omitted] Although the lithium-sulfur (Li-S) battery has a theoretical capacity of up to 1675 mA h g−1, its practical application is limited owing to some problems, such as the shuttle effect of soluble lithium polysulfides (LiPSs) and the growth of Li dendrites. It has been verified that some transition metal compounds exhibit strong polarity, good chemical adsorption and high electrocatalytic activities, which are beneficial for the rapid conversion of intermediate product in order to effectively inhibit the "shuttle effect". Remarkably, being different from other metal compounds, it is a significant characteristic that both metal and boron atoms of transition metal borides (TMBs) can bind to LiPSs, which have shown great potential in recent years. Here, for the first time, almost all existing studies on TMBs employed in Li-S cells are comprehensively summarized. We firstly clarify special structures and electronic features of metal borides to show their great potential, and then existing strategies to improve the electrochemical properties of TMBs are summarized and discussed in the focus sections, such as carbon-matrix construction, morphology control, heteroatomic doping, heterostructure formation, phase engineering, preparation techniques. Finally, the remaining challenges and perspectives are proposed to point out a direction for realizing high-energy and long-life Li-S batteries. [ABSTRACT FROM AUTHOR]

This work reviews the recent development of High Entropy Ceramics (HEC), which have five or more elements combined in equimolar or near equimolar quantities and have demonstrated unique properties. The comprehensive review is based on the general classifications of high entropy ceramics into carbides, borides, oxides, and other ceramic compounds. For each class of HECs, the synthesis processes, microstructure, and mechanical, thermal, and electrical properties are summarized in detail, with property data tables. Additionally, the fabrication and properties of HEC in the form of film, coatings, and composites are discussed. In addition to these material properties, this review article also highlights the utilization of computational studies and machine learning (ML) in the discovery of high entropy carbides. Finally, the overall conclusion of the current status and future research direction are discussed. [ABSTRACT FROM AUTHOR]

Artificial neural network approach was used to predict the thicknesses of total (FeB+Fe2B), FeB and Fe2B borides layers of AISI 1020, AISI 1060, and AISI 4140 steels. Boronizing heat treatment was conducted in a solid medium comprising of EKabor®2 powders at 840-960 °C at 40 °C intervals for 2, 4, 6, and 8 hours. Optical microscope analysis of the borided layer revealed the saw-tooth (columnar) and planar morphology. The depth of the total (FeB+Fe2B), FeB and Fe2B boride layers was accurately predicted. For total boride layers generated by the artificial neural network model, the average error varied between 0.04 and 7.64 µm. Micro hardness values increased by 423% in AISI 1020, 336% in AISI 1060, and 411% in AISI 4140 after the boronizing process. [ABSTRACT FROM AUTHOR]