Pure B4C Research Articles

Exceptional strength-toughness-hardness integrated B4C ceramics with synergistic reinforcement of nano-BN and in-situ ceramic phases

Boron carbide (B4C) ceramics with enhanced mechanical properties were fabricated by incorporating nano boron nitride (nano-BN), obtained through high-energy ball milling (HEBM) using ZrO2 balls as the medium, and utilizing the spark plasma sintering (SPS) technique. During the densification process of B4C/nano-BN composite powders, an in-situ reaction between the B4C matrix and ZrO2 resulted in the formation of ZrB2 ceramic phases at 1200–1300 °C. Additionally, the rapid sintering densification temperature of composites is reduced to 1500–1700 °C, approximately 80 °C lower than that required for pure B4C ceramics. Notably, while maintaining a high relative density (99.5 %), the Vickers hardness, flexural strength, and fracture toughness of B4C ceramics reinforced with synergistic effects of nano-BN and ZrB2 fabricated at 1750 °C are significantly improved to reach values of 36.8 ± 0.15 GPa, 701 ± 12 MPa, and 5.01 ± 0.13 MPa m1/2 respectively; representing an increase of 3.5 GPa (10.5 %), 225 MPa (47.3 %), and 1.72 MPa m1/2 (52.3 %) compared to pure B4C ceramics alone. The multiple reinforcement mechanisms including pinning effects provided by nano-BN and in-situ formed ZrB2 ceramic phases, B4C/ZrB2 grain boundary pressure and intracrystalline pressure within B4C, interlayer dislocations of nano-BN and turbulent layer of B4C/BN boundaries contribute to energy dissipation during fracture processes, such as crack deflection, bridging, propagation hindrance and branching effect; ultimately resulting in exceptional strength-toughness-hardness integrated B4C-based ceramics.

Nanoindentation of B4C-HfB2 particulate ceramic composite doped with Cr–B compounds

Mechanical behavior of B4C - HfB2 particulate ceramic composite doped with CrB + Cr3B4 chromium boride compounds were studied by nanoindentation. Hardness, Young's modulus, and indentation stress - indentation strain behavior of B4C and HfB2 phases was computed. It was found that hardness and Young's modulus of B4C matrix phase in B4C - HfB2 doped with Cr - B was increased as compared to those hardness and Young's modulus of pure B4C. It was also found that indentation stress was relieved by “pop-in” events in some of the B4C grains, however, the “pop-in” discontinuous events were always observed upon indentation of HfB2 grains, that lead to a decrease in hardness of HfB2 from 40 to 50 GPa before “pop-ins” to 28–32 GPa after “pop-ins”. The obtained results can be further used in calculations of thermal residual stresses in B4C and HfB2 phases of B4C - HfB2 particulate ceramic composite.

Enhanced mechanical properties of boron carbide ceramics prepared by spark plasma sintering with boron nitride nanosheets addition

Boron carbide (B4C) ceramics with enhanced mechanical properties have been fabricated with boron nitride nanosheets (BNNSs, 1.5–5 wt%) as reinforcement via spark plasma sintering. The densification temperature of the B4C ceramic containing 3 wt% BNNSs (B4C-3 %BNNSs) was reduced to 1480–1700 °C, approximately 100 ℃ lower than the pure B4C ceramic. The B4C-3 %BNNSs composites with a density of 98.9 % and associated Vickers hardness of 34.4 GPa, flexural strength of 654 MPa, and fracture toughness of 4.86 MPa·m1/2 that represent a respective increased by 1.1 GPa (3.3 %), 178 MPa (37.4 %) and 1.57 MPa·m1/2 (47.7 %) relative to pure B4C. The reinforcement mechanisms due to BNNSs combined with B4C involves a synergistic effect of the decrease in densification temperature where the BNNSs promote B4C grain rearrangement, B4C twin grain boundaries, and BNNSs pull-out, crack branching and crack deflection effects.

Spark plasma sintering of boron carbide (B4C): From characterisation to finite element modeling of sintering

Boron carbide (B4C), known for its unique properties, presents challenges in reaching its full density with sintering process due to low diffusion coefficients. This study explores the application of Spark Plasma Sintering (SPS) to overcome these challenges and enhance the understanding of its impact on pure B4C ceramics. The study outlines a comprehensive methodology for developing an SPS sintering model. Starting with a summary of conducted studies, powder oxidation analysis, characterization methods, and dilatometry curves processing, the article details the derivation of constitutive parameters based on the Skorohod-Olevsky theory. Isothermal profiles at different temperatures, variation in heating regimes, and a stepwise approach for SPS pressure application form the basis of the derivation methods. A grain growth model is developed for a comprehensive simulation of sintering, incorporating microstructural analysis and parameter derivation. Finally, the article addresses the integration of this mechanical sintering model with thermal and electrical considerations into a finite element method (FEM) software for a holistic SPS modeling. Thermo-electrical considerations, including the Peltier effect, are also computed, providing a well-rounded understanding of the SPS process for B4C ceramics. This study contributes valuable insights to optimizing the SPS parameters to achieve enhanced densification and microstructure control in B4C ceramics.

Densification of low‐density boron carbide by Li doping and its microstructural characterization

AbstractLithium (Li)‐doped boron carbide (B4C) has generated widespread attention for its potential to enhance mechanical properties. Nevertheless, the influence of the Li solid solution on the microstructure and mechanical properties of B4C ceramics remain unclear. In this research, the microstructure of Li‐doped B4C was investigated in meticulous detail. Through X‐ray diffraction, X‐ray photoelectron spectroscopy, and Raman spectroscopy analysis, it was confirmed that Li successfully solubilized in B4C at 1 500°C under 50 MPa for an 8 min, resulting in lattice expansion. Further insights from electron energy loss spectroscopy revealed the integration of Li into the crystal lattice and alterations in the C–B–C chains. Furthermore, the Li2O content significantly affected the densification and microstructure of B4C. Relative density increased from 91.2% (B4C) to 99.2% (9 wt.% Li2O–B4C), accompanied by a transition from a few intragranular planar defects to high‐density twins. Mechanical property tests demonstrated that 9 wt.% Li2O–B4C exhibited optimal comprehensive mechanical performance, with a flexural strength of 533 ± 27 MPa, fracture toughness of 3.71 ± 0.29 MPa∙m1/2, hardness of 33.3 ± 0.6 GPa, and a density of just 2.45 g/cm3, surpassing that of pure B4C.

Fabricating ultrahard boron carbide–silicon carbide–zirconium diboride composites by spark plasma sintering from B4C with ZrSi2 aids

Triplex-particulate ceramic composites with varying proportions of boron carbide plus SiC and ZrB2 second phases were fabricated by transient liquid-phase assisted spark plasma sintering (SPS) from B4C with 5–30 vol% ZrSi2 aids, optimising the SPS temperatures and identifying the so far elusive carbon source for the in situ formation of most of the SiC in these composites and in their boron carbide–SiC–metal diboride counterparts. Firstly, it is shown that ZrSi2 is a suitable sintering additive that significantly reduces the SPS temperatures of B4C, making densification possible at temperatures in the range 1500–1750 °C (the more ZrSi2 aid, the lower the SPS temperature) at which pure B4C is unsinterable. Secondly, it is shown that ZrSi2 is a reactive sintering additive that reacts with part of the starting B4C to form SiC, ZrB2, and Si, the latter being a transient phase that first contributes to densification by liquid phase sintering and then disappears upon reaction with the remaining B4C to form more SiC and a Si-doped B-rich boron carbide. Carbon exsolution from B4C is thus the carbon source for the formation of most of the SiC. Thirdly, it is shown that the thus-fabricated triplex-particulate composites are ultrahard (>30 GPa) when B4C is SPS-ed with 20 vol% ZrSi2 or less, and that the one SPS-ed from B4C with 20 vol% ZrSi2 has the best trade-off between sinterability (SPS at 1600 °C) and super-hardness (∼32.4 GPa). Finally, a comparison is made between these and other existing triplex-particulate boron carbide–SiC–metal diboride composites.

Enhanced toughness of boron carbide by single-wall carbon nanotube bundles

Breaking the contradictory of hardness and toughness in B4C is still a challenge to fabricate robust materials. Although compositing B4C with carbon nanotubes (CNTs) is an effective way to improve the toughness, the toughness has the limitation about 6 MPa·m1/2 or hardness below 30 GPa. The limitation of toughness in B4C-CNTs composites is caused by the weak interaction between B4C and CNTs, which impair the strength of composite. So, in this work, the inner compressive stress is introduced in B4C composite with the single-walled carbon nanotube bundles (B4C-SWNTb) by high pressure and high temperature (HPHT). The optimal hardness and fracture toughness are 30 GPa and 8.27 MPa·m1/2 in B4C-2 vol% SWNTb composites, which is 3.3 times higher than that of pure B4C. The high hardness and excellent toughness of B4C-SWNTb composite come from grain refinement of B4C particles, strong combination and inner compressive stress between B4C and SWNTb. This work holds much significance for improving hardness and toughness simultaneously in robust matrix composites.

Synthesis of Boron Carbide Powder via Rapid Carbothermal Reduction Using Boric Acid and Carbonizing Binder

Raw material is one of the most decisive factors for the quality of sintered boron carbide (B4C) products, in the past, there were relatively successful efforts for the synthesis of B4C powders via carbothermal reduction approaches. To prepare high-quality powder, a deeper understanding of the relationship between technological manufacturing parameters and resulting powder properties is required. In this paper, pure B4C powders were synthesized by rapid carbothermal reduction (RCR) under B2O3 excess conditions using boric acid and a carbonizing binder as B2O3 and carbon source, respectively. The molar ratio of B2O3/C of starting mixtures was varied from 0.75:1 to 4:1. The effects of heat-treating temperature and starting composition on phase constitution, morphology as well as stoichiometry of the prepared powders were investigated. The studies show that the starting composition has no effect on the stoichiometry of the powders, all boron carbides synthesized at 1900 °C have a stoichiometric composition of B4C. With increasing heating temperature and B2O3 content in the starting composition, the particle size of B4C was reduced. Uniform B4C powders with an average grain size of 300 nm were synthesized at 1900 °C from a starting powder mixture with a molar ratio of B2O3/C = 4. A formation mechanism is proposed under large B2O3 excess conditions. For the starting powder mixtures with a molar ratio of B2O3/C < 2, the formation of boron carbide occurs through both liquid–solid reaction and gas–solid reaction. Accordingly, the synthesized powders exhibit a morphology with mixed elongated platelets and small polyhedral particles. For the starting powder mixtures with a molar ratio of B2O3/C ≥ 2, fine-sized B4C particles were formed by a liquid–solid reaction.

The effect of Ti and B4C on the microstructure and properties of the laser clad FeCoCrNiMn based high entropy alloy coating

FeCoCrNiMnTix(B4C)y high entropy alloys (HEAs) coatings were laser cladded on Q355 steel using coaxial powder feeding laser 3D printing system by adjusting the additive ratio of pure Ti powder and B4C powder into the pre-alloyed spherical equi-atomic FeCoCrNiMn powder. Hardness, X-Ray Diffraction (XRD) phase composition, Scanning Electron Microscope (SEM) morphology, Energy Dispersive X-ray Spectroscopy (EDS) and wear resistance of the HEAs coatings were examined. The FeCoCrNiMnTix HEAs coatings (x = 0.5, 0.6, 0.8, 1.0) composed of fcc, bcc1 and bcc2 phase, The hardness increased as the Ti adding content increased, which may be attributed to the solution strengthening effect and promoting effect to the formation of bcc1 and bcc2 phase. The addition of B4C induced the formation of compound borides and carbides, and the decreasing of Ti solution in fcc and bcc phases. The phase composition of the FeCoCrNiMnTi0.6(B4C) y coating was mainly fcc, bcc2, borides and carbides. The increase of B4C improved the hardness and bcc2 content in FeCoCrNiMnTi0.6(B4C) y HEAs coating, and the wear resistance increased also to some extent. Among four FeCoCrNiMnTi0.6(B4C)y HEAs coatings (y = 0, 0.2, 0.4 and 0.6), FeCoCrNiMnTi0.6(B4C)0.4 HEAs coatings had the best wear resistance.

Mechanochemical synthesis investigations on the ternary and quaternary B2O3/TiO2/Mg/C systems

In this study, mechanochemical synthesis (MCS) was performed on the ternary and quaternary B2O3/TiO2/Mg/C system in order to investigate the probable reaction products. As being a high-energy ball milling (HEBM) technique, MCS was conducted on the B2O3–TiO2–Mg, B2O3–Mg–C and B2O3–TiO2–Mg–C powder blends. Various milling times were applied for MCS optimization. Besides, the effect of excess amount of Mg on the MCS process was investigated. Subsequently, a purification step was carried out on the milled powders to remove MgO by-product. The MgO content in the as-synthesized powders was leached out using 6 M HCl solution. Thermodynamic evaluations were made utilizing both the FactSage 7.1 and HSC thermochemical software to predict the reactions and products for each system. The as-synthesized and purified powders were characterized by using X-ray diffractometry (XRD), scanning electron microscopy/energy dispersive spectrometry (SEM/EDS), transmission electron microscopy (TEM), particle size analysis (PSA) and differential scanning calorimetry (DSC) techniques. Pure TiB2, B4C and TiC–TiB2 powders were synthesized from stoichiometric B2O3–TiO2–Mg, B2O3–Mg–C and B2O3–TiO2–Mg–C powder blends after MCS for 4 h, 10 h and 6 h, respectively. High purity TiB2, B4C and TiC–TiB2 powders were obtained with an average particle size of 50.20 nm, 330 nm and 17 nm, respectively.

Texture evolution in rhombohedral boron carbide films grown on 4H-SiC(0001̄) and 4H-SiC(0001) substrates by chemical vapor deposition.

Boron carbide in its rhombohedral form (r-BxC), commonly denoted B4C or B13C2, is a well-known hard material, but it is also a potential semiconductor material. We deposited r-BxC by chemical vapor deposition between 1100 °C and 1500 °C from triethylboron in H2 on 4H-SiC(0001) and 4H-SiC(0001̄). We show, using ToF-ERDA, that pure B4C was grown at 1300 °C, furthermore, using XRD that graphite forms above 1400 °C. The films deposited above 1300 °C on 4H-SiC(0001̄) were found to be epitaxial, with the epitaxial relationships B4C(0001)[101̄0]‖4H-SiC(0001̄)[101̄0] obtained from pole figure measurements. In contrast, the films deposited on 4H-SiC(0001) were polycrystalline. We suggest that the difference in growth mode is explained by the difference in the ability of the different surfaces of 4H-SiC to act as carbon sources in the initial stages of the film growth.

Electrical discharge machining of boron carbide-graphene nanoplatelets composites

Boron carbide (B4C) composites containing 0–10 wt.% graphene nanoplatelets (GNPs) were consolidated using hot pressing at 1950 °C for 60 min under 30 MPa in an argon atmosphere. Their electrical discharge machining (EDM) characteristics were evaluated for the first time. Additionally, the effects of GNPs on the microstructure, electrical conductivity, material removal rate (MRR), and surface roughness (Ra) of B4C composites were investigated. The results show that the B4C composite containing 10 wt.% GNPs exhibited the highest electrical conductivity of 4997 S·m−1 because of the formation of GNPs conductive networks. Under a fine machining condition, the MRR of the B4C composite was enhanced by 43.5 % (from 6.55 to 9.40 mm3 min−1) compared with that of monolithic B4C. Furthermore, the Ra decreased to 1.12 μm, which was significantly lower than that of pure B4C (2.44 μm). Scanning electron microscope and energy disperse spectroscopy analysis of the EDM surfaces were used to determine that the main material removal mechanisms for B4C composites with less than 2 wt.% GNPs were spalling and melting. As the GNPs content increased, B4C grain fallout, melting, and evaporation became more dominant. The other mechanisms, including thermal shock and oxidation, are also discussed in detail.

Rigid three-dimensional networks of hafnium diboride for improving mechanical and wear properties of boron carbide

Being one of the hardest materials known in nature, boron carbide (B4C) suffers from severe degradation of mechanical properties when subjected to external pressure or shear stress, which hinders its application in metal forming and machining industries. Herein, based on the phase diagrams, a new strengthening strategy consisting of constructing three-dimensional hafnium diboride (HfB2) networks was proposed to reinforce B4C using the molten-salts method followed by spark plasma sintering (SPS). It was found that the surface amorphization and subsequent decarburization were the main wear regime of pure B4C. Incorporating hard HfB2 networks in B4C resulted in enhanced mechanical properties and reduced wear rates, as the deformation and decarburization of B4C grains were effectively restrained. The excessively high Hf contents, however, made the composites prone to severe adhesive wear following the material transfer from mating materials during the inception of sliding contact, which led to deteriorated wear performances. Thus, the optimal molar ratio of Hf to B4C was determined with the underlying wear mechanisms delineated. The presented results not only show the feasibility of B4C-HfB2 composites as tool materials but also provide a novel designing strategy employing hard networks rather than conventional compliant binders to fabricate wear-resistant composite materials.

Reactive spark plasma sintering of B4C composite at low temperature using mechanically milled B4C–Ti–B mixtures

Sintering of pure B4C requires extremely high temperatures of more than 1800 °C, even with techniques such as spark plasma sintering (SPS). In this study, sintering of B4C was achieved at low temperature using reactive Ti–B mixture as a sintering additive. Ti and B powders (1:2 atom ratio) were milled for 8 h and added to B4C powder in proportions of 5, 10, and 20 wt% and milled for 4 h to achieve good dispersion. Dense B4C composite compacts were obtained using SPS at 1400 °C. A pore free microstructure consisting of B4C grains surrounded with fine grains of (Ti0·9W0.1)B2 and W2B5 was obtained due to WC contamination. The activation energy for sintering reduced from 234 to 155 kJ/mol with the increase in the amount of Ti–B mixture from 5 to 20 wt%. The B4C composite with 5 wt% Ti–B mixture had the maximum hardness of 3225 ± 218 H V.

EXAMINATION OF B4C–FeCrC COMPOSITE LAYER DURING DRY SLIDING USING STATISTICAL METHOD

In this work, the surface of AISI 430 stainless steel was coated with a hyper-eutectic FeCrC and pure B4C powders using the plasma transferred arc (PTA) welding method. Further, the microstructure, microhardness, and abrasive wear resistance of the coated layer were evaluated in this work. Hard coating layers were formed between 750[Formula: see text]HV and 1000[Formula: see text]HV from the PTA melting coating process with high energy input (due to PTA). Due to the addition of FeCrC and B4C, the martensite, austenite, M7(C-B)3, M[Formula: see text](C-B)6, Cr(C-B), FeCr, Fe2B, Fe3C, Fe2C, SiC, and Fe3(C-B) phases were formed in the coating layer which makes the layer very hard. The abrasive wear resistance of the coated layer was evaluated using the Taguchi method with L[Formula: see text] mixed-level orthogonal index. Samples, wear distance (m), applied load (N), and abrasive grain size (grid) were chosen as input parameters. The mass loss due to wearing was evaluated based on “the smaller the better”. All input parameters significantly influence the wear, but the highest effect was found with the wear (slip) distance. Also, a linear regression equation was obtained to estimate the mass loss between the parameters and the levels used.

Microstructure and mechanical properties of bilayer B4C/Si-B4C composite

Bilayer B4C based composites, B4C/Si-B4C, consisting of B4C and B4C/Si two-layer, were obtained using hot pressing method. Effect of Si content on microstructure and mechanical properties of the B4C based layered composites was investigated. The B4C/Si-B4C samples showed good interfacial bonding with different Si additions (x = 4, 8, 12 and 16 wt.%) in the B4C/Si layer. Secondary phases SiC and/or TiB2 dispersed randomly in B4C matrices for both layers of the composite by SEM observation. Vickers hardness data for both layers were in a range from 33.1 to 35.2 GPa. Flexural strength and fracture toughness both first increased and then slightly decreased as Si content increased from 4 to 16 wt.%. The fracture toughness of the B4C/Si-B4C composite was significantly improved compared with that of pure B4C material.

Spark plasma sintering of B4C and B4C-TiB2 composites: Deformation and failure mechanisms under quasistatic and dynamic loading

Spark plasma sintering (SPS) was employed to consolidate powder specimens consisting of B4C and various B4C-TiB2 compositions. SPS allowed for consolidation of pure B4C, B4C-13 vol.%TiB2, and B4C-23 vol.%TiB2 composites achieving ≥99 % theoretical density without sintering additives, residual phases (e.g., graphite), and excessive grain growth due to long sintering times. Electron and x-ray microscopies determined homogeneous microstructures along with excellent distribution of TiB2 phase in both small and larger-scaled composites. An optimized B4C-23 vol.%TiB2 composite with a targeted low density of ∼3.0 g/cm3 exhibited 30–35 % increased hardness, fracture toughness, and flexural bend strength compared to several commercial armor-grade ceramics, with the flexural strength being strain rate insensitive under quasistatic and dynamic loading. Mechanistic studies determined that the improvements are a result of a) no residual graphitic carbon in the composites, b) interfacial microcrack toughening due to thermal expansion coefficient differences placing the B4C matrix in compression and TiB2 phase in tension, and c) TiB2 phase aids in crack deflection thereby increasing the amount of intergranular fracture. Collectively, the addition of TiB2 serves as a toughening and strengthening phase, and scaling of SPS samples show promise for the manufacture of ceramic composites for body armor.

Effect of Additive Ti3SiC2 Content on the Mechanical Properties of B4C-TiB2 Composites Ceramics Sintered by Spark Plasma Sintering.

B4C–TiB2 composite ceramics with ultra-high fracture toughness were successfully prepared via spark plasma sintering (SPS) at 1900 °C using B4C and Ti3SiC2 as raw materials. The results showed that compared with pure B4C ceramics sintered by SPS, the hardness of B4C–TiB2 composite ceramics was decreased, but the flexural strength and fracture toughness were significantly improved; the fracture toughness especially was greatly improved. When the content of Ti3SiC2 was 30 vol.%, the B4C–TiB2 composite ceramic had the best comprehensive mechanical properties: hardness, bending strength and fracture toughness were 27.28 GPa, 405.11 MPa and 18.94 MPa·m1/2, respectively. The fracture mode of the B4C–TiB2 composite ceramics was a mixture of transgranular fracture and intergranular fracture. Two main reasons for the ultra-high fracture toughness were the existence of lamellar graphite at the grain boundary, and the formation of a three-dimensional interpenetrating network covering the whole composite.

Enhanced toughness and strength of boron carbide ceramics with reduced graphene oxide fabricated by hot pressing

Boron carbide (B4C) hybrids with different contents of graphene oxide (GO) were prepared by a heterogeneous co-precipitation method using cetyltrimethyl ammonium bromide (CTAB) as the cationic surfactant. The as-obtained mixtures were further hot-pressed at 1950 °C for 60 min under 30 MPa, by which B4C–reduced GO (rGO) composites were fabricated. It was found that the addition of only 0.5 wt% rGO could alter the predominance of trans-granular fracture in monolithic B4C ceramic material to mixed trans-granular and inter-granular modes in B4C–rGO composites. The flexural strength and fracture toughness of the B4C–2 wt% rGO were increased by 31% (from 350 to 455 MPa) and 83% (from 3.20 to 5.85 MPa·m1/2), respectively, compared with those of pure B4C. The improved mechanical properties are attributed to the mechanisms of pull-out and bridging of rGO and crack deflection, as evidenced by microstructural observations. The energy dissipation in the present B4C–rGO composites was further verified using two micromechanical models.

Initial investigation of B4C–TiB2 composites as neutron absorption material for nuclear reactors

In this study, a specifically designed B4C–TiB2 composite with the typical microstructural feature of a TiB2 network (cages) that encapsulates a B4C matrix was fabricated by the molten-salt and spark plasma sintering (SPS) method. The finite-element (FE) calculation results show that the connected TiB2 cages constitute a thermally conductive network, which effectively improves the overall thermal conductivity of the composite; these results agree well with the experimental results. Moreover, the Vickers indentation results reveal that the TiB2 network (cages) can effectively impinge/block the propagation of cracks, which increases the composite toughness. The composite was subjected to helium (He) ion irradiation to simulate the situation in which the B4C–TiB2 composites serve as neutron absorption material, and for which case a high quantity of He atoms is produced by the B10 (n, α) Li7 nuclear reaction. According to the transmission electron microscopy (TEM) results, the interfaces between TiB2 and B4C act as effective sinks for He atoms, and are preferential nucleation sites for He bubbles. The theoretical and experimental results show that when the B4C–TiB2 composites serve as neutron absorption pellets in nuclear reactors, they exhibit a better resistance to their disintegration than pure B4C pellets. Consequently, the performance of the control rods of nuclear reactors can be improved.