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Alloying and solid‐solution formation is a powerful technique that enhances and adds properties through elemental mixing, but unfortunately, some elements simply cannot mix as their chemical nature prevents a thermodynamically stable structure. For example, the inherent nobility of platinum group metals does not favor bond formation and precludes their incorporation into higher (boron‐rich) metal borides. However, we demonstrate that when using five or more constituents, the higher mixing entropy will overcome these chemical limitations and form a stable high‐entropy alloy, demonstrating the formation of new compounds with substituents that are seemingly impossible with a traditional metal alloying approach. The high‐entropy boride (HEB) Al0.2Nb0.2Pt0.2Ta0.2Ti0.2B2 was synthesized, where platinum was forced to occupy a 12‐coordinate site, sandwiched between honeycomb borophene sheets. In addition to the unusual coordination, the boron serves as a poison panacea. Pure platinum is strongly susceptible to sulfur poisoning by adsorption, rendering a platinum catalyst ineffective. Boron is known to be resistant to sulfur poisoning. The boron sheets present in the HEB shield the platinum from sulfur while maintaining high catalytic activity. This is confirmed with the facile hydrogenation of thiol‐containing nitro compounds, where the HEB resists sulfur poisoning while retaining its high catalytic activity. [ABSTRACT FROM AUTHOR]

Despite their superior material properties at high temperatures, the poor oxidation resistance of borides such as TiB2 above 1000°C limits their applications. Herein, we demonstrate the liquid-phase impregnation of Al or Si into the sintered compact of TiB2 and study their effect on the oxidation behavior at 1300°C. The thermogravimetric curves obtained under oxidation and subsequent crystal phase identification suggest that Al impregnation can prevent the evaporation of boron oxide by forming aluminum borate, which is an unstable protective layer, resulting in a slight increase in the oxidation resistance. By contrast, the Si-impregnated specimens showed lesser mass change due to oxidation than that in the unimpregnated specimens, owing to the formation of a stable protective SiO2 phase on the sample surface. Hence, molten Si impregnation of sintered borides is a promising new approach for improving high-temperature oxidation resistance. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The improved microstructure and enhanced elevated temperature mechanical properties of Ti-44Al-5Nb-(Mo, V, B) alloys were obtained by vacuum arc re-melting (VAR) and primary annealing heat treatment (HT) of 1 260 °C/6 h/Furnace cooling (FC). The phase transformation, microstructure evolution and tensile properties for as-cast and HTed alloys were investigated. Results indicate that three main phase transformation points are determined, Teut=1 164.3 °C, Tγ solv = 1 268.3 °C and Tβ trans = 1 382.8 °C. There are coarse lamellar colonies (300 µm in length) and neighbor reticular B2 and γ grain (3–5 µm) in as-cast alloy, while lamellar colonies are markedly refined and multi-oriented (20–50 µm) as well as the volume fraction and grain sizes of equiaxed γ and B2 phases (about 15 µm) significantly increase in as-HTed alloy. Phase transformations involving α+γ→α+γ+β/B2 and discontinuous γ coarsening contribute to the above characteristics. Borides (1–3 µm) act as nucleation sites for βeutectic and produce massive β grains with different orientations, thus effectively refining the lamellar colonies and forming homogeneous multi-phase microstructure. Tensile curves show both the alloys exhibit suitable performance at 800 °C. As-cast alloy shows a higher ultimate tensile stress of 647 MPa, while a better total elongation of more than 41% is obtained for as-HTed alloy. The mechanical properties improvement is mainly attributed to fine, multi-oriented lamellar colonies, coordinated deformation of homogeneous multi-phase microstructure and borides within lamellar interface preventing crack propagation. [ABSTRACT FROM AUTHOR]

In this work, FeCrB-based composites modified by in-situ ceramic particles (TiB2 and TiC) were synthesized, and the effects of ceramic particles on their microstructure evolution and the corrosion-resistant behavior in liquid aluminum were systematically investigated. Results indicate that the introduction of in-situ ceramic particles can significantly improve the size, morphology and distribution of borides, thus leading to a remarkable enhancement of the corrosion resistance. Based on the growth-dissolution kinetic relationship of intermetallic compounds (IMCs) at the corrosion interface, a theoretical numerical model was established to quantitatively describe the corrosion behavior of ferrous alloys in liquid aluminum, and the multi-scale corrosion-resistance mechanism is proposed to elucidate the excellent performance of FeCrB-based composites in liquid aluminum.

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Boron has almost null solubility in iron, and its addition to stainless steels leads to the formation of hard borides, beneficial for increasing the wear resistance. However, these boron-containing steels have poor printability, with the occurrence of pronounced cracking, high porosity and risk of delamination. In this work, Box-Behnken design coupled with analysis of variance (ANOVA) was used to optimize the LPBF (Laser Powder Bed Fusion) processing parameters of a highly boron-alloyed stainless steel reinforced with a boride network. The proposed models demonstrated to be accurate in determine the porosity percentage for the studied alloys, in which the laser power and scanning speed play the main role in the alloys’ densification, and absence of extensive defects. These results indicate that the use of design of experiments tools is essential to produce defect-free boron-modified stainless steel specimens with a relatively low number of experiments, identifying a narrow optimized processing window to build bulk composite materials.

The structural parameters of yttrium chromium tetraboride YCrB4 were refined based on single-crystal X-ray diffraction data. YCrB4 is orthorhombic, having a space group of type Pbam (No. 55) and with lattice parameters of a = 5.9425 (2), b = 11.4831 (4), c = 3.4643 (1) Å. The Y and Cr atoms are located at Wyckoff 4h sites (x, y, 0) and B atoms at the Wyckoff 4g sites (x, y, 1/2). The first structural investigation of YCrB4 was performed using a single crystalline sample [Kuz'ma, (1970). Kristallografiya. 15, 372–374]. The present study successfully refined all the positional and atomic displacement parameters of the Y, Cr, and B atoms.

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.

The structural parameters of yttrium chromium tetraboride YCrB4 were refined based on single-crystal X-ray diffraction data. YCrB4 is orthorhombic, having a space group of type Pbam (No. 55) and with lattice parameters of a = 5.9425 (2), b = 11.4831 (4), c = 3.4643 (1) Å. The Yand Cr atoms are located at Wyckoff 4h sites (x, y, 0) and B atoms at the Wyckoff 4g sites (x, y, 1/2). The first structural investigation of YCrB4 was performed using a single crystalline sample [Kuz'ma, (1970). Kristallografiya. 15, 372-374]. The present study successfully refined all the positional and atomic displacement parameters of the Y, Cr, and B atoms. [ABSTRACT FROM AUTHOR]

The effect of Mo addition on microstructure, impact property, and wear resistance of high boron Fe-4.5 wt% B surfacing alloy, which was developed by the three-arc double-wire welding method was investigated in this work. The phase structure and microstructure of the surfacing alloy were studied by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and Electron Backscattered Diffraction (EBSD). Besides, a two-body abrasive wear test and impact fracture test was carried out to study the wear behavior and fracture mechanism of the surfacing alloy. The results show, hypereutectic Fe-4.5 wt% B surfacing alloys with different Mo additions are mainly composed of primary (Fe, Mo)2B boride, eutectic matrix, and FeMo2B2. With the increase of Mo content in Fe-4.5 wt% B surfacing alloy, the continuous growth of the eutectic structure is blocked, which can inhibit the formation and expansion of cracks in the surfacing layer. With the increase of Mo, the wear resistance of Fe-4.5 wt% B alloy increases from 16.70 g-1 to 22.72 g-1. In the impact fracture experiment, Fe-4.5 wt% B surfacing alloy has high brittleness, the primary Fe2B is a transgranular fracture, and the interface between primary Fe2B boride and eutectic structure is an intergranular fracture. With the addition of Mo, the fracture mechanism of the surfacing alloy changes from transgranular fracture to transgranular fracture + ductile fracture, which reduces the fragmentation and spalling during the wear process, thereby improving its wear resistance.

To achieve efficient connectivity of dissimilar γ'-strengthened superalloy, transient liquid-phase (TLP) diffusion bonding of 718Plus and Ni3Al-based superalloys is carried out using BNi-2 interlayer at a constant temperature of 1100 °C with holding times of 3, 15, 30, and 60 min. It is shown in the results that when the holding time is insufficient, isothermal solidification transforms into athermal solidification. Due to the enrichment of B and Cr elements in liquid phase, ternary eutectic consisting of γ, Ni3B, and CrB is formed at the joint center. Ternary eutectic with higher hardness (≈600 Hv) is poorly bonded to the matrix, which can easily become crack initiation location and significantly deteriorated the tensile properties. In addition, microhardness of the joint becomes more uniform and tensile strength gradually increases due to the reduction of eutectic with holding time increasing. Isothermal solidification completes and a joint without eutectic structure is formed at 1100 °C for 60 min. Diffusion of Al atoms leads to the formation of γ' with gradient size and tensile strength is comparable to that of base metal which is about 690.93 MPa. [ABSTRACT FROM AUTHOR]

[Display omitted] • The content of the active sites over borides can be quantified by the temperature-programmed desorption of ammonia. • The TOF of catalysts, except for BP, exhibit negative linear regularity with the electronegativity of non-boron elements. • The non-boron elements affect the ability of B–OH groups to activate oxygen or propane and further change the relative energies of the rate-determining step. Boron-based catalysts are active and selective in the oxidative dehydrogenation reaction of propane (ODHP) to propylene. Herein, the binary boron-based compounds (boron nitride, boron phosphide, boron carbide, and silicon boride) composed of boron elements and one type of other non-boron elements, and the elemental boron were systematically compared to elucidate how the non-boron elements of binary borides influence their catalytic activity in ODHP. By combined experimental and computational studies, we demonstrated that the non-boron elements can modulate the performance of catalysts by altering the ability of the B-OH site to activate dioxygen and the subsequent activation of propane. In particular, the turnover frequency (TOF) of the catalyst exhibited a high negative linear correlation with the electronegativity of the non-boron element, except for the boron phosphide. This study highlights the importance of the chemical environment around the active boron sites and provides insight into the design of efficient ODHP catalysts. [ABSTRACT FROM AUTHOR]

Dense and light B4C–(Ti0.9Cr0.1)B2 composites with excellent mechanical properties were designed and reactively densified from boron, TiC, and Cr3C2 powder mixtures by spark plasma sintering in this work. Due to solid solution effects, the as‐obtained B4C–(Ti0.9Cr0.1)B2 composite exhibited obviously enhanced hardness (43.2 ± 3.0 GPa at 9.8 N) and higher specific hardness (12.82 GPa cm3 g−1) together with improved flexural strength (663 ± 39 MPa) and fracture toughness (KIC, 5.40 ± 0.25 MPa m1/2), compared to the counterparts such as B4C–TiB2 composite and B4C. Toughening contributions in the as‐sintered ceramics were quantitatively analyzed, and higher KIC in B4C–(Ti0.9Cr0.1)B2 was mainly due to their larger initial fracture toughness and compressive stress toughening. The combination of these properties makes B4C–(Ti0.9Cr0.1)B2 composites exhibit great potentials in the application as lightweight structural materials. This work provided an inspiration to achieve lightweight materials with high performance through doping minor‐amount atoms into the matrix. [ABSTRACT FROM AUTHOR]

Multi-phase ceramics based on ZrB2, TiB2 and doped with CrB2 and SiC were prepared by powder metallurgy and hot pressing to explore the possibility of obtaining multi-scale microstructures by super-saturation of complex (Zr,Ti,Cr)B2 solid solutions. Core–shell structures formed in TiB2 grains, whereas ZrB2 appeared to form a homogeneous solid solution with the other metals. Precipitation of nano-inclusions within both micron-sized borides was assessed by transmission electron microscopy and thermodynamics elucidated the preferential formation of boride inclusions due to the specific sintering atmosphere. In addition, atomic size factors explicated the precipitation of CrB2 nano-particles into ZrB2-rich grains and of ZrB2 nano-particles into TiB2-rich grains. The hardness of the constituent phases measured by nanoindentation ranged from 36 to 43 GPa.

The present work is focused on analyzing the thermodynamically equilibrium path of structure formation in a multi-component Fe-W-Mo-Cr-Ti-Mn-Si alloy of tribotechnical purpose, containing 0.72 wt. % C and 2.75 wt. % B is analyzed. Computer simulation of the crystallization process was performed using the program “Thermo-Calc Software”. It was found that the alloy belongs to the hyper-eutectic compositions, since its crystallization begins at 1472 oC with the formation of primary boride WB and carbide TiC. After a series of subsequent eutectic reactions (in the range of 1126-923 oC) and solid-phase transformations, a set of equilibrium phases is formed in the alloy, which at room temperature consists of borides WB, MoV, Fe2B, Cr4B, Mn4B, carbides TiC, M7C3, and ferrite. The total volume fraction of borides and carbides is 45.05 vol. %. A comparison of the obtained data with the results of the study of the manufactured alloy showed that the simulation with “Thermo-Calc Software” provides satisfactory adequacy in predicting the structure in the alloys of the selected alloying system.

All‐solid‐state batteries are promising candidates for safe energy‐storage systems due to non‐flammable solid electrolytes and the possibility to use metallic lithium as an anode. Thus, there is a challenge to design new solid electrolytes and to understand the principles of ion conduction on an atomic scale. We report on a new concept for compounds with high lithium ion mobility based on a rigid open‐framework boron structure. The host–guest structure Li6B18(Li3N) comprises large hexagonal pores filled with ∞1[ ${{}_{{\rm { \infty }}}{}^{{\rm { 1}}}{\rm { [}}}$ Li7N] strands that represent a perfect cutout from the structure of α‐Li3N. Variable‐temperature 7Li NMR spectroscopy reveals a very high Li mobility in the template phase with a remarkably low activation energy below 19 kJ mol−1 and thus much lower than pristine Li3N. The formation of the solid solution of Li6B18(Li3N) and Li6B18(Li2O) over the complete compositional range allows the tuning of lithium defects in the template structure that is not possible for pristine Li3N and Li2O. [ABSTRACT FROM AUTHOR]

All‐solid‐state batteries are promising candidates for safe energy‐storage systems due to non‐flammable solid electrolytes and the possibility to use metallic lithium as an anode. Thus, there is a challenge to design new solid electrolytes and to understand the principles of ion conduction on an atomic scale. We report on a new concept for compounds with high lithium ion mobility based on a rigid open‐framework boron structure. The host–guest structure Li6B18(Li3N) comprises large hexagonal pores filled with ∞1[ ${{}_{{\rm { \infty }}}{}^{{\rm { 1}}}{\rm { [}}}$ Li7N] strands that represent a perfect cutout from the structure of α‐Li3N. Variable‐temperature 7Li NMR spectroscopy reveals a very high Li mobility in the template phase with a remarkably low activation energy below 19 kJ mol−1 and thus much lower than pristine Li3N. The formation of the solid solution of Li6B18(Li3N) and Li6B18(Li2O) over the complete compositional range allows the tuning of lithium defects in the template structure that is not possible for pristine Li3N and Li2O. [ABSTRACT FROM AUTHOR]

All‐solid‐state batteries are promising candidates for safe energy‐storage systems due to non‐flammable solid electrolytes and the possibility to use metallic lithium as an anode. Thus, there is a challenge to design new solid electrolytes and to understand the principles of ion conduction on an atomic scale. We report on a new concept for compounds with high lithium ion mobility based on a rigid open‐framework boron structure. The host–guest structure Li6B18(Li3N) comprises large hexagonal pores filled with ∞1[ ${{}_{{\rm { \infty }}}{}^{{\rm { 1}}}{\rm { [}}}$ Li7N] strands that represent a perfect cutout from the structure of α‐Li3N. Variable‐temperature 7Li NMR spectroscopy reveals a very high Li mobility in the template phase with a remarkably low activation energy below 19 kJ mol−1 and thus much lower than pristine Li3N. The formation of the solid solution of Li6B18(Li3N) and Li6B18(Li2O) over the complete compositional range allows the tuning of lithium defects in the template structure that is not possible for pristine Li3N and Li2O. [ABSTRACT FROM AUTHOR]

All‐solid‐state batteries are promising candidates for safe energy‐storage systems due to non‐flammable solid electrolytes and the possibility to use metallic lithium as an anode. Thus, there is a challenge to design new solid electrolytes and to understand the principles of ion conduction on an atomic scale. We report on a new concept for compounds with high lithium ion mobility based on a rigid open‐framework boron structure. The host–guest structure Li6B18(Li3N) comprises large hexagonal pores filled with ∞1[ ${{}_{{\rm { \infty }}}{}^{{\rm { 1}}}{\rm { [}}}$ Li7N] strands that represent a perfect cutout from the structure of α‐Li3N. Variable‐temperature 7Li NMR spectroscopy reveals a very high Li mobility in the template phase with a remarkably low activation energy below 19 kJ mol−1 and thus much lower than pristine Li3N. The formation of the solid solution of Li6B18(Li3N) and Li6B18(Li2O) over the complete compositional range allows the tuning of lithium defects in the template structure that is not possible for pristine Li3N and Li2O. [ABSTRACT FROM AUTHOR]

Borides with varied morphologies and structures obtained by changing B content in as-cast Ti-45Al-2Mn-2Nb alloys are investigated. With the increase of B content, morphologies of borides change from curved to straight, and flake shape, ribbon shape, needle/rod shape, and blocky appear in turn. Curved boride particles have a lamellar structure composed of TiB2 and B2 layers, accompanied by the random appearance and distribution of Ti3B4 and Bf-TiB layers. Except for the absence of the B2 layer, straight needle-like and blocky boride particles have roughly the same structure as curved boride particles, revealing that the formation of curved boride particles is accompanied by divorced eutectic with the matrix and internal irregular eutectic, while no eutectics occurs in straight boride particles. The lack of B atoms during solidification in alloys with lower B content results in a less regular structure and higher stacking fault density of curved boride particles compared to straight boride particles in alloys with higher B content. In addition, some needle-like boride particles are observed to have pure B27-TiB structure without intergrowth. The difference in morphologies and structures can be attributed to the difference in formation mechanism and crystallographic structures of the borides.

The influence of certain factors on the kinetics of the process of obtaining aluminum borides (burning rate, ingot formation, and phase separation) was investigated. In this study, we report the registration of diboride using the SHS protocol. The synthesis of aluminum diboride from boric anhydride occurred by the aluminothermic method. The initial components were boron trioxide and aluminum in the form of powders. Researchers paid special attention to the degree of grinding of the charge fluxing substances. The influence this had on the rate of development of the degree of charge concentration was studied. To calculate the degree of charge, a composition was chosen according to the speed obtained from a number of experiments where melting was carried out with the following charge densities in g/cm3: 0.80; 1.08; 1.18; 1.74. The method of melting was ignition from above. The experimental results allowed us to conclude that the nature of the change in the combustion rate of the system, where there was an excess of the reducing agent in the charge, is the same. An increase in the combustion rate, where there was an excess of aluminum of up to 20%, was likely due to the fact that the reaction area of the charge components increased. In addition, an increase in speed can be explained by a decrease in heat losses due to a reduction in the melting time. With an increase in excess aluminum above 20% of the stoichiometry, the observed decrease in the combustion rate can be explained by a decrease in the specific heat of the process due to the melting of the excess aluminum, which played the role of a ballast.

In this paper, a Fe, Cr-rich multiphase Ni3Al-based alloy is joined through transient liquid phase bonding (TLP) technique. Different from typical γ+γ′ dual phase Ni3Al-based alloys, the joint can be divided into three distinct zones: isothermal solidification zone (ISZ), gamma prime zone (GPZ) and diffusion affected zone (DAZ). Interestingly, the massive fine grains with γ+γ′ dual phase are observed inside the ISZ, and the GPZ consists of blocky γ′ phase. The precipitation of Cr-rich borides in DAZ provides an advantageous compositional condition for the local coarsening of γ′ phase. In addition, hardness value of the bonded samples fluctuates from the centerline to the BM and reaches the peak at the DAZ. The bonded specimens share equivalent room-temperature tensile strength and elongation to failure with the parent metal after the weld thermal cycle. Moreover, the fracture path propagates along the base metal (BM), which indicates excellent tensile properties of the joint.

In the present work, a novel method was first proposed to realise direct powder forging of high borated stainless steel on Gleeble through hot compression tests performed at 1150°C and 0.01–10 s−1 with strains of 32% and 50%. Particle deformation and microstructural evolution of high borated stainless steel powder during direct forging were investigated. Backscattered electron (BSE) and electron backscatter diffraction (EBSD) were employed for microstructure examination. Microstructure reveals that large deformation zones were easily distinguished by boride and grain features. Enhanced boride coarsening in the contact area of powders was attributed to the combined action of strain, dislocation, stress and temperature rising. Strain rates had no obvious influence on densification but significantly affected the deformation of particles. Furthermore, the mechanism of particle deformation enhanced by a higher strain rate was discussed. [ABSTRACT FROM AUTHOR]

Medium and High entropy borides with high hardness and corrosion resistance are promising wear resistant materials. High temperature (>2000 °C) is always necessary for the densification of medium and high entropy borides. Using a mixture of 10 vol% metallic cobalt and 20 vol% SiC as additives, medium entropy (Ti,Zr,Ta)B 2 ceramics were prepared at a relatively low temperature of 1600 °C by SPS. The reduced sintering temperature is attributed to the synergistic effect of Co and SiC that wet the grain boundary and promote the interdiffusion. The prepared (Ti,Zr,Ta)B 2 obtains the microhardness of 22.54 ± 0.92 GPa, comparable with other medium entropy boride ceramics prepared at 2000 °C. The tribo-tests results of (Ti,Zr,Ta)B 2 sliding against steel suggests that the tribological performance are load dependent. As the load increases, the friction coefficient first rises and then falls at a load of 10 N, which is associated with the chemical differences of the tribofilm. The tribofilm is primarily composed of O and Fe, along with Zr, Ti and Ta oxides. The iron oxide in the tribofilm will deteriorate the tribological performance. Abrasive wear is the main wear mechanism at lower load of 1 N, while adhesive wear is the predominant wear mechanism at 10 N. • The densification temperature of medium entropy diborides was significantly reduced by introducing Co and SiC as additives. • The microhardness of (Ta, Zr, Ti)B 2 prepared at 1600 °C is comparable with other medium entropy boride ceramics prepared at 2000 °C. • The tribological performance and wear mechanism of (Ta 1/3 Ti 1/3 Zr 1/3)B 2 ceramic was studied. • As the load increases, the friction coefficient first rises and then falls at a load of 10 N, which is associated with the chemical differences of the tribofilm. • From the viewpoint of its engineering applications, boride has the advantage of high hardness and can be applied in the field of wear resistant materials. [ABSTRACT FROM AUTHOR]

In this study, the effects of titanium addition on microstructure, hardness, and wear rate of Fe(13-x)TixB7 (x = 0, 1, 2, 3 and 5) based hard surface alloy layers formed by gas tungsten arc (GTA) welding method were investigated. As a result of the microstructure studies and phase analysis, it was determined that the structures of the coating layers consisted of α-Fe, αFe+Fe2B eutectic, α-Fe+Fe2Ti eutectic and hard TiB2 phases. In the hard surface alloy layer, as the amount of titanium was increased, the TiB2 phase density formed in the system increased and it was observed that rod-like and long sharpedged phases formed from the equiaxed structure. As a result of wear tests performed at different loads, it was determined that the addition of titanium reduces the wear rates in the coating layers. In addition, scanning electron microscopy (SEM) images of the worn surfaces showed that the wear mechanisms were adhesive and oxidative.

The crystal structures of the rare-earth (RE) trirhodium diborides praseodymium trirhodium diboride, PrRh3B2, neodymium trirhodium diboride, NdRh3B2, and samarium trirhodium diboride, SmRh3B2, were refined on the basis of single-crystal X-ray diffraction data. The crystal chemistry of RERh3B2 (RE: Pr, Nd, and Sm) compounds has previously been analyzed mainly on the basis of powder samples [Ku et al. (1980). Solid State Commun. 35, 91–96], and no structural investigation by single-crystal X-ray diffraction has been reported so far. The crystal structures of the three hexagonal RERh3B2 compounds are isotypic with that of CeRh3B2; RE, Rh and B sites are situated on special positions with site symmetry 6/mmm (Wyckoff position 1a), mmm (3g) and \overline{6}m2 (2c), respectively. In comparison with the previous powder X-ray study of hexagonal RERh3B2, the present redetermination against single-crystal X-ray data has allowed for the modeling of all atoms with anisotropic displacement parameters (ADPs). The ADPs of the Rh atom in each of the structures result in an elongated displacement ellipsoid in the direction of the stacking of the Rh kagomé-type layer. The features of obtained ADPs of atoms are discussed in relation to RERh3B2-type and analogous structures.

To strengthen the face-centered-cubic (FCC) type CoCrFeNi high-entropy alloy (HEA) by in-situ reinforced phase, (CoCrFeNi)100−x(NbB2)x (x=0, 2, 4, 6, 8, at.%) alloys were prepared. Phase constitution, microstructure, tensile mechanical properties of the alloys were studied, and the mechanisms were discussed. Results show that the microstructure of all the reinforced alloys consists of the matrix FCC phase, Laves phase, and (Cr3Fe)Bx phase. The eutectic structure and (Cr3Fe)Bx phases are formed in the interdendritic region, and the eutectic structure is composed of Laves and FCC phases. When x increases from 0 to 8, i.e., with increase of Nb and B elements, the volume fraction of Laves and (Cr3Fe)Bx phases increases gradually from 0 to 5.84% and 8.3%, respectively. Tensile testing results show that the ultimate strength of the alloys increases gradually from 409 MPa to 658 MPa, while the fracture strain decreases from 75% to 1.6%. Fracture analysis shows that the crack originates from the (Cr3Fe)Bx phase. The CoCrFeNi alloys are mainly strengthened by the second phase (Laves phase and boride phase). [ABSTRACT FROM AUTHOR]

To develop strong refractory high-entropy alloys for use at elevated temperatures as well as to overcome grain-boundary brittleness, an equimolar HfMoNbTaTiZr alloy was prepared, and a minor amount of boron (0.1 at.%) was added into the alloy. The microstructures of the alloys were characterized, and their macro-to-microscale mechanical properties were measured. The microstructural observations indicated that the matrices of both the alloys were composed of a body-centered cubic solid-solution structure, and the added boron induced the precipitation of hexagonal close-packed borides (most likely the (Hf, Zr)B2) at the grain boundaries. The modulus and hardness of differently oriented grains were about equivalent, suggesting a diminished anisotropy, and many small slips occurred on multiple {110} planes. While the hardness of the matrix was not increased, the intergranular precipitation of the borides markedly raised the hardness of the grain boundaries. Owing to the enhanced grain boundary cohesion, the work hardenability and ductility were effectively improved with the addition of boron. [ABSTRACT FROM AUTHOR]

The influence of certain factors on the kinetics of the process of obtaining aluminum borides (burning rate, ingot formation, and phase separation) was investigated. In this study, we report the registration of diboride using the SHS protocol. The synthesis of aluminum diboride from boric anhydride occurred by the aluminothermic method. The initial components were boron trioxide and aluminum in the form of powders. Researchers paid special attention to the degree of grinding of the charge fluxing substances. The influence this had on the rate of development of the degree of charge concentration was studied. To calculate the degree of charge, a composition was chosen according to the speed obtained from a number of experiments where melting was carried out with the following charge densities in g/cm3: 0.80; 1.08; 1.18; 1.74. The method of melting was ignition from above. The experimental results allowed us to conclude that the nature of the change in the combustion rate of the system, where there was an excess of the reducing agent in the charge, is the same. An increase in the combustion rate, where there was an excess of aluminum of up to 20%, was likely due to the fact that the reaction area of the charge components increased. In addition, an increase in speed can be explained by a decrease in heat losses due to a reduction in the melting time. With an increase in excess aluminum above 20% of the stoichiometry, the observed decrease in the combustion rate can be explained by a decrease in the specific heat of the process due to the melting of the excess aluminum, which played the role of a ballast. [ABSTRACT FROM AUTHOR]

Transition metal sulfides and their corresponding derivatives, such as MAX phases, have been widely studied because of their unique physical properties. However, due to the low melting/boiling point and volatile characteristics of sulfur, it is difficult to control the element ratio in their in-situ synthesis, and some impurities are introduced. Based on this, we first studied the reaction mechanism of sulfur-containing MAX phase Hf 2 SB. Previous studies generally believed that the mechanism of MAX phase synthesis is that elements M and X first form compounds and then react with elements A. Interestingly, Hf reacts with sulfur to form Hf 2 S firstly, and then boron enters the octahedral gap between the two layers of hafnium to form Hf 2 SB. Based on the reaction mechanism, Hf 2 SB with a purity of 91.99 wt% and its corresponding sulfide Hf 2 S with a purity of 96.75 wt% were successfully and rapidly synthesized by thermal explosion synthesis using a spark plasma sintering furnace. The microstructure of the sample fractured surface was observed by scanning electron microscopy, which confirmed that the Hf 2 SB grains were in lath shape, that is, the typical grain shape of MAX phases. The crystal structure and atomic positions of Hf 2 SB and Hf 2 S were obtained accurately, and the similar structure between them confirms our conclusion on the reaction mechanism. [ABSTRACT FROM AUTHOR]

A composite UN fuel containing 10wt% UB 2 has been manufactured via spark plasma sintering using different milling methods prior to sintering, and the resulting pellets characterised to understand the effects of UB 2 location and morphology on UN sintering behaviour and oxidation performance. Differences in microstructure and phases present were observed, with planetary ball milling leading to smaller UB 2 inclusions as well as the formation of a UBN phase on sintering. Composite pellets showed an increase in the steam oxidation onset temperature when compared to UN at similar density and manufactured from the same feedstock. Of particular note was the behaviour of one sample with a comparably low density (∼92 %) which had an onset temperature of 823 K and a significantly reduced rate of reaction compared to monolithic UN at similar density. This provides the first confirmatory evidence that UB 2 limits the UN-steam reaction by some other mechanism than simply promoting a high-density microstructure. This is supported by examination of post-oxidation composite material, which shows a varied and more complex morphology compared to reference UN samples, including large apparently-bound agglomerates and limited free fine particulate. [ABSTRACT FROM AUTHOR]

A novel approach is demonstrated for the synthesis of the high entropy transition metal boride (Ta, Mo, Hf, Zr, Ti)B2 using a single heating step enabled by microwave-induced plasma. The argon-rich plasma allows rapid boro-carbothermal reduction of a consolidated powder mixture containing the five metal oxides, blended with graphite and boron carbide (B4C) as reducing agents. For plasma exposure as low as 1800 °C for 1 h, a single-phase hexagonal AlB2-type structure forms, with an average particle size of 165 nm and with uniform distribution of the five metal cations in the microstructure. In contrast to primarily convection-based (e.g., vacuum furnace) methods that typically require a thermal reduction step followed by conversion to the single high-entropy phase at elevated temperature, the microwave approach enables rapid heating rates and reduced processing time in a single heating step. The high-entropy phase purity improves significantly with the increasing of the ball milling time of the oxide precursors from two to eight hours. However, further improvement in phase purity was not observed as a result of increasing the microwave processing temperature from 1800 to 2000 °C (for fixed ball milling time). The benefits of microwave plasma heating, in terms of allowing the combination of boro-carbothermal reduction and high entropy single-phase formation in a single heating step, are expected to accelerate progress in the field of high entropy ceramic materials.

In order to investigate the effect of boron element on liquefied wood carbon fibers and their composites, boric acid and boron carbide were utilized to modify liquefied wood resin through copolymerization and blending methods respectively. Then boric acid-modified liquefied wood carbon fiber (BA-WCF) and boron carbide-modified liquefied wood carbon fiber (BC-WCF) were produced via melt spinning, curing, and carbonization treatments. As expected, this modification approach effectively prevents the formation of skin-core structures and accelerates the evolution of a graphite microcrystalline structure, thereby enhancing the mechanical properties of the carbon fibers. Particularly, the tensile strength and elongation at break of BA-WCF increased to 331.57 MPa and 7.57 % respectively, representing increments of 117 % and 86 % compared to the conventional fibers. Furthermore, the as-fabricated carbon fiber/resin composites (CFPRs), composing of BA-WCF or BC-WCF as fillers and liquefied wood resin as matrix, exhibited excellent interlaminar shear strength, outstanding abrasion resistance, and well thermal conductivity, as well as electrical performance, significantly outperforming the conventional carbon fiber/phenolic resin composites. The friction rate of BC-WP/BA-WCF/CF was 2.37 %, while its thermal conductivity could reach 1.927 W/(m·K). These promising attributes lay the groundwork for the development of high-performance carbon fiber-based materials, fostering their widespread utilization across various industries. [ABSTRACT FROM AUTHOR]

Boron and its alloys have been explored a lot and it is expected that they can replace pure aluminum powder in the energetic formulation of active materials. MgB2 compounds were prepared and characterized by a combination of mechanical alloying and heat treatment. The ignition and combustion of boron–magnesium alloys were studied with the ignition wire method and laser ignition infrared temperature measurement. The results show that MgB2 has good ignition characteristics with maximum ignition temperatures obtained by the two various methods of 1292 K and 1293 K, respectively. Compared with boron, the ignition temperature of MgB2 is greatly reduced after alloying. The ignition reaction of MgB2 mainly occurs on the surface and the ignition process has two stages. In the initial stage of ignition, the large flame morphology and combustion state are close to the combustion with gaseous Mg, whereas the subsequent combustion process is close to the combustion process of B. Compared with boron, the ignition temperature of MgB2 is greatly reduced which suggests that MgB2 may be used in gunpowder, propellant, explosives, and pyrotechnics due to its improved ignition performance. [ABSTRACT FROM AUTHOR]

A comparative analysis of the structural-phase state, microhardness, wear resistance and wear mechanisms is carried out during tests on fixed abrasive and non-rigid fixed abrasive particles, as well as in sliding friction conditions, arc-deposited coatings with a composite material (CM) based on the powder material of the Ni–Cr–B–Si system, modified with a material containing titanium and chromium borides and obtained using the selfpropagating high temperature synthesis. It is found that under wear conditions for fixed abrasive particles, the wear resistance of CM (10% modifying composite material (MCM) + 90% ПГ-10Н-01) is 1.5 times higher, and CM (20% microns + 80% ПГ-10Н-01) is 1.7 times higher than that of the ПГ- 10Н-01 alloy. This is due to the introduction of MCM, which contributes to the formation of new crystallization centres during surfacing and as a result leads to grinding of the structure. The ПГ-10Н-01 nickel-based plastic matrix redistributes stresses, providing conditions in which solid components occupy a favourable position. This eliminates the local increase in contact pressure and reduces the probability of separation of solid wear-resistant particles. It is found that under friction under the influence of non-rigid abrasive particles, the increased wear resistance (1.2 times at a content of 10% MCM and 1.4 times at 20% MCM more compared to the ПГ-10Н-01 alloy) is due to the higher ability of CM to resist micro-cutting processes due to the formation of a structure based on a nickel matrix, which contains evenly distributed solid inclusions in the form of titanium diboride (TiB2), nickel borides (Ni3B) and chromium (CrB), titanium (TiO) and iron (Fe3O4) oxides. Based on the obtained experimental results, it is concluded that the presence of titanium diboride (TiB2), chromium borides (CrB) and nickel (Ni3B), titanium oxides (TiO) and iron (Fe3O4) in the deposited coating leads to a decrease in the intensity of wear under various friction conditions. [ABSTRACT FROM AUTHOR]

In this study, the effects of titanium addition on microstructure, hardness, and wear rate of Fe(13-x)TixB7 (x = 0, 1, 2, 3 and 5) based hard surface alloy layers formed by gas tungsten arc (GTA) welding method were investigated. As a result of the microstructure studies and phase analysis, it was determined that the structures of the coating layers consisted of α-Fe, αFe+Fe2B eutectic, α-Fe+Fe2Ti eutectic and hard TiB2 phases. In the hard surface alloy layer, as the amount of titanium was increased, the TiB2 phase density formed in the system increased and it was observed that rod-like and long sharpedged phases formed from the equiaxed structure. As a result of wear tests performed at different loads, it was determined that the addition of titanium reduces the wear rates in the coating layers. In addition, scanning electron microscopy (SEM) images of the worn surfaces showed that the wear mechanisms were adhesive and oxidative. [ABSTRACT FROM AUTHOR]

Boronising is a thermochemical treatment which enhances the resistivity of metals used as component in applications dominated by wear and corrosion. In this study, boronising was performed on a gamma-TiAl intermetallic alloy with the pack cementation method. The experiments took place at temperatures 1173–1323 K for 8–14 h and a compact hard boride layer was formed. Its thickness varied between 6 and 25 μm. An 80 μm wide boron diffusion zone with elevated hardness was detected via micro-hardness measurements. The measured thickness values were applied to a mathematical model based on Fick's second law of diffusion to extract the kinetic parameters of the process. Additionally, the presence of the ΤiΒ2 and the total absence of the TiB phase were confirmed via XRD measurements. The hardness of the coating and the substrate was evaluated using Vickers micro-hardness tester (above 1100 HV at the coating layer). [ABSTRACT FROM AUTHOR]

The crystal structures of the rare-earth (RE) trirhodium diborides praseodymium trirhodium diboride, PrRh3B2, neodymium trirhodium diboride, NdRh3B2, and samarium trirhodium diboride, SmRh3B2, were refined on the basis of single-crystal X-ray diffraction data. The crystal chemistry of RERh3B2 (RE: Pr, Nd, and Sm) compounds has previously been analyzed mainly on the basis of powder samples [Ku et al. (1980). Solid State Commun. 35, 91-96], and no structural investigation by single-crystal X-ray diffraction has been reported so far. The crystal structures of the three hexagonal RERh3B2 compounds are isotypic with that of CeRh3B2; RE, Rh and B sites are situated on special positions with site symmetry 6/mmm (Wyckoff position 1a), mmm (3g) and 6m2 (2c), respectively. In comparison with the previous powder X-ray study of hexagonal RERh3B2, the present redetermination against single-crystal X-ray data has allowed for the modeling of all atoms with anisotropic displacement parameters (ADPs). The ADPs of the Rh atom in each of the structures result in an elongated displacement ellipsoid in the direction of the stacking of the Rh kagome' -type layer. The features of obtained ADPs of atoms are discussed in relation to RERh3B2-type and analogous structures. [ABSTRACT FROM AUTHOR]

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To develop strong refractory high-entropy alloys for use at elevated temperatures as well as to overcome grain-boundary brittleness, an equimolar HfMoNbTaTiZr alloy was prepared, and a minor amount of boron (0.1 at.%) was added into the alloy. The microstructures of the alloys were characterized, and their macro-to-microscale mechanical properties were measured. The microstructural observations indicated that the matrices of both the alloys were composed of a body-centered cubic solid-solution structure, and the added boron induced the precipitation of hexagonal close-packed borides (most likely the (Hf, Zr)B2) at the grain boundaries. The modulus and hardness of differently oriented grains were about equivalent, suggesting a diminished anisotropy, and many small slips occurred on multiple {110} planes. While the hardness of the matrix was not increased, the intergranular precipitation of the borides markedly raised the hardness of the grain boundaries. Owing to the enhanced grain boundary cohesion, the work hardenability and ductility were effectively improved with the addition of boron.

The present study investigates experimentally phase equilibria relations in the B-Fe-W ternary system. For the experimental study, B-Fe-W alloys were produced by arc-melting. These alloys were equilibrated using long-term annealing for 2000 h and 4224 h at temperatures of 1050 and 677 °C, respectively. The alloys were characterized by scanning electron microscopy coupled with energy dispersive x-ray spectroscopy, x-ray powder diffraction analysis, and differential scanning calorimetry. Based on the experimental results, the B-Fe-W system was modeled using the CALPHAD method. Herein, boron was modeled interstitially in the solid solutions of iron and tungsten. Also, in this study, the volume phase fractions for selected B-Fe-W alloys were determined using an image analysis technique. [ABSTRACT FROM AUTHOR]

We analyze the specific features of the structure and elastic characteristics of powder titanium-matrix composites reinforced with titanium carbide and titanium boride. The difference between the characters of dependence of the modulus of elasticity on the content of high-modulus component is analyzed for sintered and hot-forged composites. It is discovered that the modulus of sintered materials is determined both by the content of reinforcing admixtures and by the porosity of the alloy. At the same time, for hot-forged specimens, the modulus monotonically increases with the content of the high-modulus components. It is shown that, for sintered composites of all compositions and for hot-forged composites reinforced by titanium carbide, anisotropy is practically absent, whereas for hot-forged composites reinforced by titanium boride, an insignificant (up to 10%) anisotropy of the structure and elastic characteristics is caused by the reorientation of acicular titanium monoboride particles in the direction perpendicular to the direction of application of the active force in course of hot forging. [ABSTRACT FROM AUTHOR]

The effects of Cr or V substitution on the crystal structure and mechanical properties of Mo2NiB2 were investigated by experiments and first principles calculation. Mo2Ni1-xCrxB2 and Mo2Ni1-xVxB2 samples were synthesized via the powder metallurgy method. The XRD analysis revealed that the tetragonal Mo2NiB2 phase appeared with the addition of the Cr or V in both Mo2Ni1-xCrxB2 and Mo2Ni1-xVxB2 samples, and increased with the increase of the Cr or V content x. Orthorhombic Mo2NiB2 phase decreased with the increase of the Cr or V content x, and completely disappeared at x = 0.75. The Vickers hardness of Mo2Ni1-xCrxB2 and Mo2Ni1-xVxB2 samples improved with increasing Cr or V additions, and the maximum values of 20.4 GPa and 19.8 GPa for x = 0.75 samples, respectively. The calculated shear modulus of the tetragonal Mo2Ni1-xCrxB2 and tetragonal Mo2Ni1-xVxB2 increase with increasing Cr or V content x. The calculated Vickers hardness of orthorhombic Mo2NiB2, tetragonal Mo2CrB2 and tetragonal Mo2VB2 are 21.915 GPa, 22.492 GPa and 24.656 GPa, respectively. The Crystal Orbital Hamilton Population (COHP) analysis indicates the excellent mechanical properties of tetragonal Mo2CrB2 and tetragonal Mo2VB2 are due to the strong bonding between Mo-(Cr or V) and (Cr or V)-B atoms. [ABSTRACT FROM AUTHOR]

In this study, titanium matrix composites (TMCs) were prepared by plasma activated sintering. The microstructure and mechanical properties of the composites were studied, and the strengthening mechanism was determined. The results showed that the main phases of Ti-rich samples are TiB, α-Ti and β-Ti, while the primary phases of TiB 2 -rich samples are TiB 2 and TiB. The composites containing 70 wt%TC4-30 wt%TiB 2 demonstrated the best performance which achieved a balance of high strength and ductility, with a yield strength of 1800 ± 28 MPa and compressive strength of 2215 ± 39 MPa. The key reinforcing and toughening mechanisms were due to the dislocation defects and stacking faults in the samples, which consume more fracture energy during crack propagation and comprehensively improve the strength and toughness of the composites. Furthermore, crack deflection and whisker pull-out caused by TiB can toughen the composites. [ABSTRACT FROM AUTHOR]

Titanium diboride exhibits outstanding properties for hard and wear resistant coatings. However, efficient physical vapor deposition (PVD) processing through DC vacuum arc, with a deposition rate unreachable for any other PVD technique, is comparatively unexplored for TiB 2 thin films due to challenges associated with the film synthesis process. In this work, we used an industrial scale arc plasma source having a plane cathode of 100 mm in diameter and a permanent magnet on its back side. We present analysis of the cathode surface, plasma generation/composition, as well as analysis of collected macroparticles. The cathode weight loss and the amount of generated macroparticles were measured as a function of process parameters (arc current and pressure, in both Ar and N 2 gas). Plasma analysis shows average ion energies around 120 and 25 eV for Ti and B, respectively, and plasma ion composition of approximately 50 % Ti and 50 % B. The cathode weight loss was around 0.3–0.5 g/min, of which at least 25 % is estimated to be macroparticles. Notably, the intensity of the macroparticle generation was reduced with an increase in N 2 pressure. Altogether, the results show a stable and reproducible plasma generation process and a high potential for the use of the cathodic arc as an efficient and useful method for deposition of metal borides. • Stable arc plasma production from industrial-scale TiB 2 cathodes (100 mm diameter). • Around 25 % of the cathode weight loss is due to macroparticle generation. • The plasma flux along the cathode normal shows depletion of B ions. [ABSTRACT FROM AUTHOR]

Electron-beam powder bed fusion (EPBF) has been demonstrated to enable crack-free additive manufacturing of the traditionally non-weldable IN738 Ni-based superalloy. This is related to grain boundary (GB) segregation and precipitation phenomena during EPBF thermal cycling. We investigate such GB microstructures around typical interphase boundaries in IN738. Cyclic reheating results in γʹ dissolution, reprecipitation, and formation of layers enriched in refractory elements at γʹ-γʹ interfaces. Interfacial excess shows that >10 atomic layers of Cr and 3.5 of Co at the GB suppress the segregation of W, B, and C. GBs around heterogeneously nucleated γ grains are decorated with less Cr and Co. This is linked to microsegregation of carbide and boride-forming elements, facilitating diffusion of minor elements during cooling. A heterogeneous interfacial excess profile at a γʹ-γʹ interface is reported. These findings improve the current understanding of interphase boundaries and segregation in EPBF-manufactured IN738, possibly contributing to crack-free additive manufacturing. [Display omitted] [ABSTRACT FROM AUTHOR]

Seawater electrocatalysis holds significant promise as a technology for sustainable energy production, but the challenge of electrode corrosion by chloride ions is urgently needed to be addressed. Herein, a Ce-B-containing electrode was found to activate an in-situ evolutionary oxide (CeO 2)-anion (B(OH) 4 –) dual-layer during the electrocatalytic reconstruction process, effectively resisting the invasion of chloride ions. In detail, a Ni-Fe-Ce-B electrode exhibits high hydrogen and oxygen evolution activity with only 160 and 271 mV overpotentials at 100 mA cm–2 in 1 M KOH + 0.5 M NaCl, and superior stability with slight overpotential loss after over 100 h at industrial current density ∼ 0.5 A cm–2 at 1.817 V for alkaline natural seawater splitting. Comparative experiments indicating that existing alkaline electrocatalysts can be adjusted to withstand rigorous seawater conditions through straightforward modifications. This work reveals a novel evolutionary oxide-anion dual-layer protection mechanism to effectively prevent chloride ion corrosion in highly corrosive seawater splitting. [Display omitted] • A novel oxide-anion CeO 2 -B(OH) 4 – dual-layer protection mechanism. • Ni-Fe-Ce-B exhibits high hydrogen and oxygen evolution activity with 160 and 271 mV overpotential at 100 mA cm–2. • Excellent stability under industrial current density. • Improving existing electrocatalysts. [ABSTRACT FROM AUTHOR]