Boron Carbide Phase Research Articles

High pressure and high temperature synthesis of a new boron carbide phase

The dense boron carbide (B-C) phases with diamond structure are predicted to be superhard, with hardness close to that of a cubic boron nitride (c-BN). At ambient conditions, graphite-like BC3 is well characterized, firstly reported by Kouvetakis et al. In this work, we have synthesized a new B-C phase from the graphite-like BC3 in a laser-heated diamond anvil cell. Interestingly, this phase could be recoverable to ambient pressure due to dynamic stabilities. The Raman spectrum and X-ray diffraction patterns give the possible structure of this new phase.

Mechanical properties of AlMgB14-related boron carbide structures. A first principle study

We examine the effects produced by replacing B–B interlayer bonds by C–C bonds in AlMgB14-related boron network on its mechanical properties. The elastic constants, Vickers hardness and shear strength are evaluated by means of first principle computer simulations on the basis of density functional theory. The results of simulations suggest a possibility of existence of several orthorhombic boron carbide phases with strongly enhanced mechanical properties with the Young's modulus and Vickers hardness being within the range of 550–600 GPa and 43–50 GPa, respectively.

Preparation of fully dense boron carbide ceramics by Fused Filament Fabrication (FFF)

Boron carbide is the third hardest material known, with a high melting point (2450 °C) and poor sintering ability. Therefore, boron carbide is a challenging material for shaping by conventional processing routes and can still be considered as unsuitable for commercial production of ceramics parts by additive manufacturing technologies. This work reports the first successful preparation of boron carbide ceramics fabricated by fused filament fabrication from a newly developed composite filament containing 65 wt% of micron-sized boron carbide powder dispersed in a thermoplastic binder. A commercial FFF desktop printer with a 0.40 mm nozzle was used for manufacturing of complex-shaped green bodies. Almost fully dense boron carbide ceramics with printed parts sized up to 4 centimeters and relative density higher than 96% after sintering were prepared. The DTA/TG analysis of composite filament and heat microscopy technique were used to set the debinding temperature program with critical temperature at 140 °C, due to the thermal decomposition of the binder. Microstructure SEM images after sintering showed excellent material homogeneity, while micro-CT images showed very well retained experimental shapes of collimator-like printed grids. The x-ray diffraction proved the presence of boron carbide phase with the free carbon phase at the level of about 1 wt% without significant influence on the measured hardness value of 29.88 ± 1.27 GPa.

Comparison of tribological behaviors of polycrystalline diamonds synthesized by titanium- and boron-coated diamond particles

In this study, the influence of the coating of diamond particles on the tribological behaviors of polycrystalline diamond (PCD) was investigated. Titanium- (Ti)- and Boron- (B)-coated diamond particles were sintered under high pressure-high temperature condition to obtain Ti-PCD and B-PCD, respectively. The Ti and B coatings were deposited via magnetic sputtering. The PCD specimens were characterized through scanning electron microscopy, X-ray diffraction, impact tests, thermal gravimetric analysis-differential scanning calorimetry and tribological tests. The results indicate that uniform titanium carbide (TiC) and boron carbide (B4C) phases are generated during the sintering processes of Ti-PCD and B-PCD, respectively. The as-obtained TiC phase promotes the tribological behaviors of Ti-PCD in vacuum, including a considerable enhancement of wear resistance. The TiC phase inhibits diamond exfoliation by strengthening interface bonding, which involved transforming the mechanical interaction between the diamond grains and cobalt binder to chemical bonding. However, massive pores are formed during sintering that weakens the interface bonding in B-PCD, and thus the induced wear resistance is low. Therefore, the Ti coating of diamond particles promotes the tribological behaviors of PCD, whereas B coating deteriorates it. This study lays a foundation for the development of suitable technology for the fabrication of PCD.

Reactive Sintering of Boron Carbide Based Ceramics by SPS

Boron carbide is a highly covalent non-oxide ceramic with a high melting temperature. Therefore, the densification of boron carbide via a thermally activated process is extremely hard and requires additional driving forces. In addition to searching alternative production techniques for boron carbide, the production of boron carbide composites is one of the most interested subjects. In this study, BxC-TiB2-SiC ceramic was produced through an in-situ reaction between B4C and Ti3SiC2 and excess amorphous boron using spark plasma sintering method at 1600°C-1800°C. XRD and microstructure analysis of the sintered sample show that boron rich boron carbide phase is present in the sintered specimen, which did not develop a continuous matrix through the sample. The three phases present in ceramics formed agglomerate throughout the microstructure and did not show homogeneous distribution.

Synthesis of Submicron Boron Carbide by the Non-Vacuum Method with Indirect Supply of the Thermal Energy of a DC Arc Discharge

The results of experimental studies demonstrating the possibility of obtaining boron-carbide powder by treating a mixture of carbon and amorphous boron containing a small amount of boron oxide with DC arc discharge plasma are presented. A feature of the applied nonvacuum electric-arc method for the synthesis of boron carbide is its implementation in an open air environment due to achievement of the effect of screening the reaction zone with gaseous oxide and carbon dioxide. In this case, the initial reagents are heated to the required temperatures by a DC arc discharge plasma burning in the immediate vicinity of the initial-material mixture in the cavity of the graphite crucible. The resulting material contains particles of boron carbide with a size in the submicron range, which are characterized by the “shell–core” type structure. The scheme of the discharge circuit of a laboratory reactor with horizontal arrangement of electrodes and an indirect supply of thermal energy to the initial reagents described in the paper makes it possible to significantly increase the content of the boron-carbide phase and reduce the content of the graphite impurity phase.

Effect of temperature on static fatigue behavior of self-healing CMC in humid air

Static fatigue tests at 100 MPa with unload-reload cycles were performed at 500, 550, 650 and 800 °C in air + 10 %vol·H2O on a self-healing ceramic matrix composite (SH-CMC) with a pyrocarbon interphase. The self-healing matrix was multi-layered and deposited by chemical vapor infiltration (CVI) based on the Si-B-C system. During static fatigue tests, damage was monitored during the tests with acoustic emission (AE) and electrical resistance (ER). AE demonstrated that crack initiation primarily takes place during loading for all test conditions. Evolution of ER, strain and modulus demonstrated that failure was primarily driven by interphase degradation at constant load due to unsealed cracks at temperatures below 550 °C. In these conditions, crack sealing is prevented by boria volatilization and interphase degradation takes place due to both interphase oxidation and recession of the boron carbide phase surrounding the interphase.

Products Investigation of Contact Interaction of Diamond and a Matrix of Diamond-Metal Composites

Since the strength of the filler-matrix boundaries largely determines the properties of composite materials, the study of the interaction between the filler and the matrix is an urgent task for the development of high-performance composites. The purpose of this work is to study the products of contact interaction between the diamond and the matrix material of wear-resistant diamond-metal composites obtained by explosive pressing with subsequent heat treatment. Composites structure: natural diamond powder in a two-component iron-carbon matrix. Structural and phase studies of the diamond-matrix interface were performed using optical microscopy, scanning electron microscopy, and x-ray analysis. It is revealed that a significant factor contributing to the improvement of the performance properties of experimental diamond composites is the formation of a boron-carbide phase at the interfacial boundary with high values of strength and wear resistance. The scientific novelty of the work is due to the fact that the problems connected with a formation and a state of matrix-filler zones of various composite materials are one of the main ones in the field of fundamental research of the crystalline multiphase state of matter. The obtained data can be used in the engineering practice in the development of new composite materials.

Pressureless sintering and properties of boron carbide composite materials

AbstractBoron carbide and Tantalum boride composites were prepared by pressureless sintering of B4C with addition of TaC powder. The effect of TaC addition on the sinterability of boron carbide was studied. High densified ceramic with a relative density of 98.7% was obtained at sintering temperature of 2250°C. The composition and the microstructure of the dense composites are characterized by means of x‐ray diffraction (XRD), scanning electron microscopy (SEM), and energy‐dispersive x‐ray spectroscopy (EDX). The studies show that the composites contain boron carbide, TaB2, and carbon phases with a homogeneous structure. In addition, the correlation between the composition and the electrical conductivity was investigated. The electrical conductivity of the composite increased with increasing addition of TaC, and a change in conduction behavior from semiconducting to metallic was observed. High hardness value of 28.49 ± 1.33 GPa was obtained by the sample with 30 wt% TaC addition.

Preparation of submicron boron carbide powder through gas-solid reaction method

Abstract Boron carbide submicron powder was synthesized with boron oxide and graphene as starting materials by gas-solid reaction method using two different apparatuses. The effects of calcination temperature and holding time, apparatus type and B 2 O 3 /C ratio of the starting materials on the phase composition and morphology of the synthesized powders were evaluated. A newly formed residual carbon morphology distinct from original graphene were present in samples synthesized at a higher B 2 O 3 /C ratio or temperature. The synthesis temperature of ∼1500 °C was found to be more suitable to obtain boron carbide powder without the existence of residual carbon. The new type of apparatus enabled the synthesis of boron carbide phase at a relatively lower temperature, due to its more efficient use of B 2 O 3 vapor.

Kinetics of Nonisothermal Pressure Sintering of Zirconium Diboride Powder with Additives of Boron and Chromium Carbides in Vacuum

The analysis of the experimental data on the kinetics of nonisothermal pressure sintering of zirconium diboride-based powder mixtures with the addition of boron and chromium carbides in vacuum showed a division of the sintering temperature mode into low-temperature and hightemperature areas. The division is clearly observed when the temperature increases at a rate of 20°C/min. In low-temperature area, the densification occurs slowly and hardly depends on the temperature. In high-temperature area, the viscous flow of the matrix of the porous material is controlled by the power-law creep of the matrix forming the porous body with an activation energy of 394 kJ/mol. Twofold increase in heating rate leads to acceleration of low- and high-temperature strain of the matrix and increase in the apparent activation energy to 581 kJ/mol, indicating the series engagement of additional mechanisms of material flow. The investigation of structure and properties of materials has showed that the formation of new boron–carbide phases and eutectic that disappears during sintering activates the densification of the porous material. It is found out that under low pressure nonisothermal sintering, a superplasticity phenomenon can occur, which results in the densification of the porous body to the virtually non-porous state.

Effect of TiB2 nano-inclusions on the thermoelectric properties of boron rich boron carbide

Boron carbide has exceptional thermoelectric properties due to its unique crystal structure. The effects of nano-TiB2 inclusions on the thermoelectric properties of boron rich boron carbide is presented here. Boron rich boron carbide-TiB2 composites were prepared in-situ by sintering of wet ball milled B, B4C and nano-TiO2 powders through Spark Plasma Sintering (SPS) at 1900 °C under 50 MPa pressure. Five different compositions of the composite were prepared- with 1, 2.5, 5, 7.5 and 10 wt.% TiO2. The dependence of densification and thermoelectric properties on TiO2 content were studied. The microstructure was observed through Field Emission Scanning Electron Microscope (FESEM) and phases were analyzed using X-ray diffraction (XRD). Relative densities of 94.8% to 99. 3% were obtained and an almost homogeneous distribution of TiB2 was observed. The electrical property was found to be high for sample with 1 wt% TiO2 and reduced subsequently with higher wt% of TiO2. The overall dimensionless figure of merit was found to be higher than B4C-TiB2 composites, due to the formation of boron rich phase but the effect of TiO2 was not significant. The increase in lattice parameter of boron carbide phase for different TiO2 amounts added showed that the final composition of the composite depends on the amount of TiO2 added.

Elucidation of the role of rotation speed and stirring direction on AA 7075-B4C surface composites formulated by friction stir processing

In the present research investigation, aluminum–boron carbide surface composites were fabricated using friction stir processing technique. Boron carbide powder particles were incorporated into AA 7075 substrate by the thermomechanical mixing generated through multiple passes of friction stir processing. A parametric investigation was conducted to encounter homogeneous boron carbide powder particles distribution in the substrate matrix by employing various parameter combination sets like tool rotational speed and alteration in tool travel direction. Microstructural characterizations were performed by means of optical microscopy, scanning electron microscopy and X-ray diffraction analysis to investigate on boron carbide powder particles distribution, phases present, and grain morphologies in the substrate matrix. Homogeneous distribution of boron carbide powder particles was observed for surface composites processed at lowest tool rotational speed. Uniform boron carbide powder particles distribution in the processed zone along with various strengthening mechanisms brought about two-fold increase in microhardness and wear resistance of the prepared composites.

Unveiling polytype transformation assisted growth mechanism in boron carbide nanowires

We demonstrate direct evidence that the lattice distortion, induced by boron carbide (BxCy) stoichiometry, assists the growth of boron carbide nanowires. The transformation between different polytypic boron carbide phases lowers the energy barrier for boron diffusion, promoting boron migration in the nanowire growth. An atomistic mass transport model has been established to explain such volume-diffusion-induced nanowire growth which cannot be explained by the conventional surface diffusion model alone. These findings significantly advance our understanding of nanowire growth processes and mass transport mechanisms and provide new guidelines for the design of nanowire-structured devices.

Prediction of superstrong τ -boron carbide phase from quantum mechanics

Prediction of superstrong <i>τ</i> -boron carbide phase from quantum mechanics

Synthesis of boron carbide nanoparticles via spray pyrolysis

Abstract

Room and high temperature flexural failure of spark plasma sintered boron carbide

Dense (95–98.6%) bulk boron carbide prepared by Spark Plasma Sintering (SPS) in Ar or N2 atmospheres were subject to three-point flexural tests at room and at 1600°C. Eight different consolidation conditions were used via SPS of commercially available B4C powder. Resulting specimens had similar grain size not exceeding 4µm and room-temperature bending strength (σ25°C) of 300–600MPa, suggesting that difference in σ25°C is due to development of secondary phases in monolithic boron carbide ceramics during SPS processing. To explain such difference the composition of boron carbide and secondary phases observed by XRD and Raman spectroscopy. The variation in intensity of the Raman peak at 490cm−1 of boron carbide suggests modification of the boron carbide composition and a higher intensity correlates with a higher room-temperature bending strength (σ25°C) and Vickers hardness (HV). Secondary phases can modify the level of mechanical characteristics within some general trends that are not dependent on additives (with some exceptions) or technologies. Namely, HV increases, σ25°C decreases, and the ratio σ1600°C/σ25°C (σ1600°C – bending strength at 1600°C) is lower when fracture toughness (KIC) is higher. The ratio σ1600°C/σ25°C shows two regions of low and high KIC delimited by KIC=4.1MPam0.5: in the low KIC region, boron carbide specimens are produced in nitrogen.

Priority compositions of boron carbide crystals obtained by self-propagating high-temperature synthesis

Splitting of reflections from boron carbide has been found for the first time by an X-ray diffraction study of polycrystalline mixture of boron carbide В15–хСх, (1.5 ≤ x ≤ 3) and its magnesium derivative C4B25Mg1.42. An analysis of reflection profiles shows that this splitting is due to the presence of boron carbide phases of different compositions in the sample, which are formed during crystal growth. The composition changes from В12.9С2.1 to В12.4С2.6.

Raman spectroscopic characterization of the core-rim structure in reaction bonded boron carbide ceramics

Raman spectroscopy was used to characterize the microstructure of reaction bonded boron carbide ceramics. Compositional and structural gradation in the silicon-doped boron carbide phase (rim), which develops around the parent boron carbide region (core) due to the reaction between silicon and boron carbide, was evaluated using changes in Raman peak position and intensity. Peak shifting and intensity variation from the core to the rim region was attributed to changes in the boron carbide crystal structure based on experimental Raman observations and ab initio calculations reported in literature. The results were consistent with compositional analysis determined by energy dispersive spectroscopy. The Raman analysis revealed the substitution of silicon atoms first into the linear 3-atom chain, and then into icosahedral units of the boron carbide structure. Thus, micro-Raman spectroscopy provided a non-destructive means of identifying the preferential positions of Si atoms in the boron carbide lattice.

Polymer-derived SiC ceramics from polycarbosilane/boron mixtures densified by SPS

Spark plasma sintering (SPS) is considered as an efficient method for the densification of advanced ceramics. Since commercially available prepyrolized polycarbosilane could not be densified by SPS even at 2050°C, the addition of amorphous boron was investigated. Aiming to control dispersion of boron in the powder mixture, the preceramic polymer was mixed either before or after pyrolysis. Boron worked as a sintering additive resulting in dense monoliths, with a good combination of Vickers hardness and indentation fracture toughness. Toughening mechanisms were mainly attributed to crack deflection of finely distributed boron carbide phase. The boron mixing before pyrolysis resulted in optimum dispersion of B-rich secondary phase which resulted in Vickers hardness as high as 25.8GPa and fracture toughness of 4.7MPam0.5