Transition Metal Diborides Research Articles

The importance of the vibrational entropy in the mixing stabilization for complex ceramics

AbstractThe concept of high‐entropy materials has been introduced based on the idea that multiple principal components can be mixed through the increase in configurational entropy. Implicit in this idea is that the vibrational entropy, the other component of the mixing entropy, is small compared to the configurational entropy. To explore this relationship, we examined the mixing enthalpy, configurational entropy, and vibrational entropy of two binary ceramic systems—the transition metal carbides and transition metal diborides. We computed the vibrational entropy directly using the dynamical matrices obtained from density functional theory and the quasiharmonic approximation. The mixing vibrational entropy of the mixed diborides is at least as large as the configurational entropy while it is smaller for the carbides. Utilizing the phonon density of states, we further demonstrate the origin of the high mixing vibrational entropy arises because of a large number of new low‐frequency modes that appear in the diborides. Similar modes occur in the carbides but occur at larger frequencies. These differences ultimately arise because of the structural differences where metal atoms share nearest neighbors in the diborides, while they do not in the carbides. This increased vibrational mixing entropy dramatically enhances the mixing of the diborides and demonstrates that this type of entropy cannot be neglected when considering what stabilizes mixtures and provides a new perspective on what is considered high entropy.

Effects of irradiation damage on the hardness and elastic properties of quaternary and high entropy transition metal diborides

Effects of irradiation damage on the hardness and elastic properties of quaternary and high entropy transition metal diborides

First-principles study on pressure-induced superconductivity and structural design on transition metal diborides.

Recent experiments on α-MoB2 with MgB2-type structure achieved superconductivity at ∼32K under 90GPa, the highest among transition-metal diborides, rekindling interest in their superconducting properties. Our study systematically investigates the band structures of AlB2-type transition metal diborides. We found that the superior superconductivity of MoB2, WB2, and TcB2 correlates with their von Hove singularities near the Fermi level (EF), potentially linked to electron-phonon coupling. These three diborides exhibit similar critical temperature (Tc) trends under pressure: rising initially, peaking around 60GPa, and then declining. While unstable at ambient pressure, their thermodynamic and dynamical stability limits vary significantly, possibly explaining experimental discrepancies. To stabilize MoB2 at ambient pressure, we designed MoXB4 compounds (X = other transition metals) by substituting every other Mo layer in MoB2 with an X layer. This modification aims to stabilize the structure and enhance superconductivity by reducing d-electron concentration at EF. This principle extends to other potential superconducting diborides, such as WB2 and TcB2. Using Nb as an example, we found that Nb atoms in AlB2-type MoNbB4 may exhibit random occupancy, potentially explaining disparities between theoretical predictions and experimental results. Our study offers valuable insights into superconductivity in transition metal diborides, paving the way for future research and applications.

First-principles analysis of improved thermodynamic stability and mechanical properties in pseudo-binary Y[formula omitted]V[formula omitted]B2 alloys

This work explores a possibility of improving the mechanical behavior and thermodynamic stability of AlB2 -type YB2 through alloying with isostructural VB2 using first-principles calculations. The analysis derived from the cluster-expansion model suggests Y0.5V0.5B2, whose atomic configuration is represented by periodically alternating YB2/VB2 layers in the ¡0001¿ direction, is the only solution in the pseudo-binary YB2–VB2 system predicted to be stable from the thermodynamic viewpoint. By evaluating the influence of lattice dynamics on the Gibbs free energies of superlattice-structured Y0.5V0.5B2 and its constituent compounds within the quasiharmonic approximation, the thermodynamic stability, elastic properties, and hardness at a given pressure and temperature of the three diborides can be accessed. The results reveal, at a given temperature, isotropic compression of the diborides to high pressures enhances the stability of Y0.5V0.5B2 measured relative to YB2 and VB2, while raising the temperature at a given applied pressure can increasingly result in a driving force toward separation of Y0.5V0.5B2 into YB2 and VB2. The thermodynamic stabilization of superlattice-structured Y0.5V0.5B2, despite large distinctions in atomic radius and electronegativity between Y and V, can be explained in terms of band filling induced by introduction of V atoms in YB2. Within the range of temperatures (0–1200 K) and pressures (0–15 GPa) studied, the band-filling effect is found to result in significant positive deviations in the values of shear strength, stiffness, and hardness of superlattice-structured Y0.5V0.5B2 from those evaluated from its constituent compounds using the Vegard’s law, respectively, by ∼8%, ∼5%, and ∼25%, and the hardness of superlattice-structured Y0.5V0.5B2 is ∼40 GPa potentially indicating its superhard nature. These consequences strongly underline the essential impact of band filling on improvement in mechanical behavior and stability of YB2 through alloying with VB2, and also they can be served as guidance for further advancement of hard-coating technology based especially on transition-metal diborides.

A deep neural network potential model for transition metal diborides

Transition metal diborides (TMB2s) are renowned for their high melting point and exceptional wear, corrosion, and erosion resistance, making them promising candidate materials for applications in extreme environments. As such, there is an urgent need for reliable material design tools for TMB2s to improve efficiency in developing new materials. To address this need, we have developed a domain-specific medium-scale interatomic potential model for TMB2s that encompasses elements Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, and B. The prediction errors in energy and force of our model are 8.8 meV/atom and 387 meV/Å, respectively. Furthermore, the model demonstrates high accuracy in predicting various material properties, including lattice parameters, elastic constants, equations of states, and melting points, as well as grain boundary segregations. By providing a reliable and efficient tool for material design, this model will play a crucial role in the development of new, high-performance TMB2s for use in extreme environments.

First-principles explorations on 2D transition metal diborides featuring inverse sandwich structures and their gas sensing properties

First-principles calculations were carried out to investigate the stability of two dimensional (2D) MB2 monolayers (TiB2-I, VB2-I, MnB2-I, TiB2-II, ScB2-II, NiB2-II) with an inverse sandwich configuration and their potential as efficient gas sensors to detect toxic gas molecules. We first identified six stable 2D MB2 configurations, based on stability evaluation covering thermodynamical, dynamical, and thermal aspects. To investigate the performance of these novel structures as gas sensors, the adsorption behavior of five toxic gas molecules (CO, NO, NO2, NH3, SO2) on MB2 has been explored, and the charge transfer and magnetic changes of these adsorption systems were analyzed. It is found that five gases are all chemisorbed on 2D MB2. Particularly, when CO is adsorbed on TiB2-II, the magnetism of the system undergoes a significant change from non-magnetism to antiferromagnetism, showing selectivity for CO. Furthermore, the current−voltage characteristics obtained from simulations confirm gas sensing performance. The TiB2-II is expected to be a candidate material for CO gas sensor with short recovery time (7.50 × 10−10 s). Our theoretical study provides new ideas for designing gas sensor nanomaterials with magnetism alteration as the indicator featuring easy measurement and fast response.

Response of 11B enriched ZrB2 ultra-high temperature ceramic to neutron irradiation at elevated temperatures

ZrB2, an ultra-high temperature ceramic (UHTC) is being considered for use in fusion reactor first-wall structures, yet its response to irradiation remains poorly understood. This study employed scanning/transmission electron microscopy (S/TEM), synchrotron X-ray diffraction (XRD), finite element calculations, and thermal property measurements to thoroughly investigate the neutron-irradiation effects on 11B-enriched ZrB2. Neutron irradiations were conducted at 220 °C and 620 °C, with a neutron fluence of 2.2 × 1025 neutron/m2 (energy > 0.1 MeV), resulting in 3.9 dpa and 4200 appm He. The study revealed the unusual prevalence of prism loops and a > c anisotropic lattice swelling, likely linked to the low c/a ratio of ZrB2, leading to grain boundary microcracking. Reducing the grain sizes was effective in reducing intergranular cracking and macroscopic swelling. The observation of cavities in ZrB2 irradiated at 620 °C, as opposed to 220 °C, prompts questions about the temperature at which vacancies in ZrB2 become mobile, and the role of neutron absorption by 10B in elevating irradiation temperatures. Isotopic enrichment in 11B proves to be a viable strategy for mitigating helium production in transition-metal diborides, which is a critical consideration for nuclear applications. Irradiation-induced defects reduce the thermal diffusivity and conductivity of ZrB2 by a factor of 4–9, which has important implications for its role as a plasma-facing material in fusion reactors that drive high heat fluxes through first-wall materials. This comprehensive study lays the foundation for understanding ZrB2 behavior under neutron irradiation and highlights important phenomena to consider for various material applications.

Nontrivial d-electrons driven superconductivity of transition metal diborides

Leveraging the progress of first-principles modelings in understanding the mechanisms of superconductivity of materials, in this work we investigate the phonon-mediated superconducting properties of transition metal diborides. We report that TaB2 and NbB2 show superconducting transition temperatures as high as 27.0 and 26.0 K at ambient conditions, respectively, comparable with those obtained for CaB2 or MgB2. By mode-by-mode analysis of the electron-phonon-coupling, we reveal that the high superconducting temperature of transition metal diborides is due mainly to the strong coupling between d electrons of the transition metals and the acoustic phonon modes along out-of-plane vibrations. This fact is distinct from that of CaB2 or MgB2, where the superconductivity stems mainly from the boron px and py orbitals, which couple strongly to the optical phonon modes dominated by in-plane B atomic vibrations. Further, we find that transition metal diborides present only a superconducting gap at low temperatures, whereas CaB2 or MgB2 are double superconducting gap superconductors. In addition, we investigate the strain effect on the superconducting transition temperatures of diborides, predicting that Tc can be further enhanced by optimizing the phonon and electronic interactions. This study sheds some light on the exploring high Tc boron-based superconductor materials.

Vacancy Rich TiB2 Nanosheets Promote Electrochemical Ammonia Synthesis.

The ability to exfoliate transition metal diborides has led to a renewed interest in their prospect to be applied as catalysts for electrochemical reactions. This is due to an enhanced access to the unprecedented interfaces these nanomaterials offer. In this work, we show that nanosheets exfoliated from TiB2 exhibit vacancies that facilitate an excellent interface for catalyzing nitrogen reduction reaction (NRR). We found that these nanosheets demonstrate a high selectivity toward NH3 because of their abiity to preferentially chemisorb and activate N2. These nanosheets exhibit a superlative NH3 yield of 318 μg h-1 cm-2 at -0.2 V versus RHE with a faradaic efficiency of 57%. We also found how the relative ratios of Ti and B atoms in these nanosheets can affect the NH3 yield and faradaic efficiency. We supplement these results with DFT studies that indicate that it is the creation of frustrated Lewis pairs along with the Ti-B synergy that induces a push-and-pull effect; this in turn favors N2 activation and lowers the energy barrier for NRR. Furthermore, we explored B-exposed and Ti-exposed surfaces to understand how different surfaces affect the reaction yield and efficiency and found that Ti-exposed surfaces with boron divacancy have the highest propensity for NRR. The maiden insights presented in this study on the role of transition metal-boron synergy and interfaces present significant additions to the fast-expanding knowledge on nanoscaled metal borides.

Pressureless sintered high-entropy transition metal diboride ceramics doped with yttrium tetraboride

High entropy diborides (HEBs) are new candidates of ultra-high temperature ceramics. However, it is difficult to obtain dense HEB ceramics via pressureless sintering. In this study, yttrium tetraboride (YB4) was introduced to consolidate (Ti0.25Zr0.25Hf0.25Ta0.25)B2 (4TMB2) ceramics and its effects on the microstructures and mechanical properties were studied. YB4 addition facilitates the densification and grain elongation of 4TMB2 ceramics by forming eutectic liquid phases and eliminating oxide impurities. Relative density of 4TMB2 ceramics containing 5 vol% YB4 reaches to 94.4 % after pressureless sintered at 2000 °C for 3 h. The hardness and toughness determined by indention method are 26.9±1.5 GPa and 5.73±1.65 MPa∙m1/2. This ceramics also exhibit excellent four-point bending creep resistance with the strain rate of 1.48×10−7 s−1 at 1900 °C under 20 MPa. The observed creep behavior is attributed to grain boundary sliding, plastic deformation, grain refinement and enhanced atomic diffusion of Y element, all driven by high-temperature stresses.

Hardness and fracture toughness enhancement in transition metal diboride multilayer films with structural variations

The simultaneous enhancement of hardness (H) and fracture toughness (KIC) through the formation of superlattice structures challenges the conventional belief that these quantities are mutually exclusive. Here, this approach has been applied to the transition metal diborides, whose inherent brittleness severely restricts their application potential. The mechanical properties of TiB2/TaB2 systems as a function of bi-layer period Λ are investigated, combining theoretical and experimental approaches. Density Functional Theory is used to investigate the structural stability and mechanical properties of stoichiometric hexagonal TiB2/TaB2 superlattices for Λ = 3.9 – 11.9 nm. The calculations predict the highest H = 38 GPa and KIC (100) of 3.3 MPa.m1/2 at the value of Λ = 5.2 nm. Motivated by the theoretical results, multilayer films with Λ = 4–40 nm were prepared by direct current magnetron sputtering. Due to the sputtering effects, the deposited diboride films differ significantly from the view of stoichiometry and structure. A detailed structure investigation reveals TiB2/TaB2 in form of superlattices exhibiting coherent interfaces for Λ = 4 nm. For higher Λ, parts of TaB2 layers transform from the crystalline to the disordered phase. These transformations are reflected in the mechanical properties as measured by nanoindentation and micromechanical bending tests. The evolution of hardness follows Hall-Petch behavior, reaching a maximum of 42 GPa at Λ = 6 nm. Enhancing fracture toughness involves more complex mechanisms resulting in two KIC maxima: 3.8 MPa.m1/2 at Λ = 6 nm and 3.7 MPa.m1/2 at Λ = 40 nm.

Structural, mechanical, electronic and thermodynamic properties of YBC, YB2C, YB2C2, Y2B3C2 intermetallics

Transition metal diboride and transition metal boron-carbon intermetallics have attracted extensive attention. In this work, we adopted the first-principles method to reveal the structural stability, elastic behavior, anisotropy and electronic structures of transition metal boron-carbon intermetallics (YBC, YB2C, YB2C2, Y2B3C2). The formation enthalpy suggests that YB2, YBC, YB2C, YB2C2 and Y2B3C2 are thermodynamically stable. The calculated results of elastic constants indicates that all five intermetallics exhibit the mechanical stability. The band structures and density of states indicate that YB2, YBC, YB2C, YB2C2 and Y2B3C2 possess metallic properties. According to v and G/B, these intermetallics exhibit the brittleness. The 3D and 2D maps display the anisotropic properties. Moreover, the Debye temperature θD of YB2, YBC, YB2C, YB2C2 and Y2B3C2 at high temperatures obeys the order of YBC> YB2C2> YB2C > Y2B3C2 > YB2.

Effects of Mo target power on the structure and tribological properties of AlB2 Ta1-xMoxB films by magnetron sputtering

In this paper, magnetron sputtering from TaB2 and Mo stoichiometric targets is used to prepare AlB2 ternary Ta1-xMoxB films. The films with various Mo contents were obtained by adjusting the Mo target powers. It was discovered that the contents of Mo have an obvious impact on the crystallinity and phase structure stability of Ta1-xMoxB films. When x = 0.43, the (001) and (002) orientation is improved, while stabler AlB2 structure is maintained simultaneously. While increasing x to 0.59, the films show amorphous structure. Meanwhile, as Mo contents rise, the hardness of films first decreases and then increases, eventually drops a lot. The Ta1-xMoxB films with x = 0.44 exhibit the superhardness (H = 49.9 ± 1.5 GPa) and elastic modulus (E = 520 ± 4.7 GPa), which benefit from the structure of Transition-metal diboride (TMB2) and solid solution strengthening effect. Alloying Mo can increase the Valence electron concentration (VEC) of films and therefore enhanced films toughness, higher fracture toughness (KIC = 1.13 MPa·m1/2) and elasticity (85.805%) were achieved when x = 0.44, the films showed better ability to resist plastic deformation even in 500 gf load. In addition, the Ta0.56Mo0.44B films obtain higher wear resistance (4.5 × 10−7 mm3/Nm) in air, but excess Mo atoms lead to deterioration of mechanical properties (H = 25.0 GPa、E = 240.0 Gpa for Mo90). Ta1-xMoxB ternary films with appropriate Mo content show a good potential as a hard protective coating.

Diborides of Multielement Transition Metals: Methods for Calculating Physical and Mechanical Characteristics

From the first principles simulation (using the method of “a priori pseudopotential” and the “quasi-harmonic approximation” method- author’s developments), the basic characteristics of diborides and diborides of multielement transition metals (DMTMs) with an AlB2 type structure were calculated. For both diborides and DMTMs, the linear coefficients of thermal expansion (LCTE) along the axial axes differ little from each other, i.e., transition metal diborides and hexagonal lattice DMTMs are quasi-isotropic. Quasi-isotropy makes it possible to estimate the LCTE using an analytical formula that depends on the melting temperature. In the absence of experimental data on the melting point of DMTMs, a method for calculating it from first principles is presented. The theoretical hardness values of transition metal diborides and DMTMs with averaged parameters were calculated from the first principles. The hardness of both bulk and nano-sized DMTMs was assessed using a hybrid method. There is agreement between the calculated and available experimental data.

Oxidation properties of quaternary Zr-based diboride thin films grown by hybrid high-power impulse/DC magnetron co-sputtering

Sputter-deposited transition metal diborides are subject of increasing attention for protective hard coatings. However, they suffer from high brittleness and rapid oxidation. Alloying with Ta increases their toughness, but their oxidation resistance requires further enhancement. Here, the influence of adding Si on the microstructure, mechanical, and oxidation properties of quaternary Zr1−(x + y)TaxSiyBz thin films grown by hybrid high-power impulse/DC magnetron co-sputtering (ZrB2-DCMS/Ta-HiPIMS/Si-DCMS) is studied. The layers are deposited at two different conditions of Ta-target HiPIMS powers and frequencies (30 W/100 Hz and 60 W/200 Hz series) with Si-target DCMS powers PSi = 0, 10, 15, and 20 W, while the ZrB2-target DCMS power is maintained constant at 200 W. For the 30 W/100 Hz series, x decreases from 0.20 to 0.15, y increases from 0 to 0.22, and z decreases from 2.0 to 1.8 by increasing PSi. The Ta/metal ratio remains constant at x = 0.3 for the 60 W/200 Hz series, while y increases from 0 to 0.1, and z decreases from 1.7 to 1.4. All layers show columnar growth and crystallize in a hexagonal-diboride structure, but crystal orientations change by increasing PSi. The 60 W/200 Hz series have much denser microstructure than the 30 W/100 Hz series. The 60 W/200 Hz series have high hardness values (≥35 GPa), while the hardness of the 30 W/100 Hz series significantly decreases from ∼37 to ∼21 GPa as a function of PSi. Zr0.7Ta0.3B1.7 has markedly better high-temperature oxidation resistance than Zr0.8Ta0.2B2.0 due to the formation of protective B-containing oxide scales. Alloying with Si considerably decreases the oxidation rate of the 30 W/100 Hz series owing to the formation of oxide scales containing a ZrSiO4 phase with a thin Si oxide top layer; however, the oxidation rate increases for the 60 W/200 Hz series as these quaternary alloys do not contain sufficiently high B and Si to form oxidation protective barriers.

Reactively grown Al/Si-based top coatings protecting TM-diborides (TM = W, Ti, Hf) against high-temperature oxidation

Architectural designs involving Al- and/or Si-containing top coatings present an effective approach to protect oxidation-sensitive materials such as binary transition metal (TM) diborides against high-temperature oxidation. Using reactive arc evaporation, Al-Si-N, Al-Si-O, and Si-O top coatings were applied on sputter-deposited WB1.9, TiB2.7, and HfB2.4 thin films, respectively. A pure Si adhesion layer was introduced prior to the deposition of both oxide-based top coatings (Al-Si-O & Si-O) to prevent in-situ oxidation of the diboride base layers. During thermal annealing up to 1200 °C, Al-Si-O and Si-O provided outstanding oxidation resistance on top of TiB2.7 and HfB2.4, while limited adhesion was observed on WB1.9 at elevated temperatures. Contrary, Al-Si-N protected architectures suffered from accelerated oxidation beyond 800 to 1000 °C. Isothermal annealing in ambient air at 1200 °C for 30 h confirmed the long-term stability of the oxide-based top coatings, revealing no decohesion or oxygen inward diffusion beyond the Si interlayer. Complementary TEM analysis showed that the Si-O top coating forms a dense SiO2 scale above the columnar HfB2.4, while the formation of a mullite scale (3Al2O3·2SiO2) and pronounced recrystallization is recorded for the Al-Si-O protected HfB2.4. In summary, the Al-Si-O- and Si-O-based top coatings demonstrated exceptional high-temperature oxidation resistance, fully protecting the TM-diborides from oxidative attack.

The effect of chemical element on hardness in high-entropy transition metal diboride ceramics

The relationship between the chemical elements of high-entropy boride (HEB) ceramics and their hardness is important for the prediction of high-hardness HEB ceramics. In this work, by designing four HEB ceramics with different chemical elements, the effect of lattice parameter difference factor (δ, represents the difference-degree in lattice parameters among the five individual constitute diborides) on phase composition and lattice-distortion, and the effect of rule of mixture (ROM) average hardness and lattice-distortion on HEB ceramics hardness were studied. The results indicated that, as δ value increases, more severe lattice-distortion occurs inside the HEB ceramics, and a single solid-solution is difficult to be formed. Furthermore, lattice-distortion and the ROM average hardness codetermine the HEB ceramics hardness. The greater lattice-distortion brings about significantly higher hardness for HEB ceramics than their ROM average hardness. Among the four HEBs, (Hf0.2Zr0.2Ta0.2V0.2Nb0.2)B2 exhibits the high hardness of 26 GPa measured using a load of 9.8 N.

Macroscale ultradurable superlubricity on passivated transition-metal diborides

Superlubricity is a sliding regime with almost vanishing friction sustained under stringent material conditions. This remarkable phenomenon was first found between surfaces with incommensurate lattice structures, and later extended to materials with weak shear, as in many two-dimensional layered materials. Such materials, however, face great challenges that limit their applications, including the difficulty to scale up to meet the needs of many practical implementations and low durability stemming from the intrinsic structural weakness. Overcoming these limitations hinges on new design and fabrication of advanced superlubricating materials. Here, we report on the realization of macroscale ultradurable superlubricity on passivated transition-metal diborides (TMB2) following an unconventional design principle that first construct materials with strong anti-wear ability then create superlubricity via effective surface passivation. TMB2 possess superior mechanical strength and durability, along with the ability to activate in-situ load-induced passivation layers via tribochemical actions at the surface. The resultant passivated TMB2 exhibits characteristic superlubricating and ultradurable friction coefficient (0.002) and wear rate (10−19 m3/N·m). These findings introduce a fresh approach toward rational design and implementation of superlubricating materials, opening a new avenue for versatile applications at large (up to industrial) scales.

Core Electron Count as a Versatile and Accurate New Descriptor for Sorting Mechanical Properties of Diverse Transition Metal Compounds.

Transition-metal light-element compounds show superb mechanical, chemical, and thermal properties, and accurate descriptors are important to sorting targeted properties among this vast class of materials. Valence electron concentration (VEC) can track broad trends of mechanical properties, but this widely used descriptor suffers low accuracy with sorted data strongly scattered along trendlines, necessitating an improved sorting strategy. Here, elastic parameters from first-principles calculations are examined for 81 ternary transition-metal nitrides (TMN) in cubic structure and 81 ternary transition-metal diborides (TMB2 ) in hexagonal structure and identify core electron count (CEC) of the solvent atoms as a new descriptor. Combined with VEC, the composite VEC-CEC descriptor exhibits greatly improved ability to sort elastic parameters of distinct TMN and TMB2 compounds. Unregulated property variations under the VEC description are well-captured by CEC, which tends to enhance ductility and reduce strength at fixed VEC and rising CEC. By invoking a full-electron consideration, the VEC-CEC descriptor accounts for the impact on bonding behaviors by both core and valence electrons with much-improved accuracy and versatility in sorting mechanical properties of diverse TM compounds compared to many other commonly used descriptors, opening a fresh path for rational design and optimization of TM compounds with tailored performance benchmarks.

Ceramic eutectic composites based on B4C directionally reinforced by high-entropy (TiZrHfNbTa)B2 boride

Directionally solidified B4C/(Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)B2 eutectic high-entropy ceramics were prepared by the floating zone method based on the crucibleless zone melting of compacted powders using B4C and transition metal diboride (TiB2, ZrB2, HfB2, NbB2, TaB2) powders as initial materials. The structure of as-prepared composites consists of a B4C matrix uniformly reinforced by a single-phase high-entropy (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)B2 diboride. The XRD analysis of the composites confirmed the presence of the following phases in their compositions: B4C and (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)B2. The effect of the solidification rate on structural and mechanical characteristics of the B4C/(Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)B2 ceramics was revealed. It was found that an increase in the solidification rate leads to a decrease in the size of the reinforcing phase and an increase in hardness and fracture toughness from 36 to 39 GPa and 5.9–7.3 MPa·m1/2, respectively.