Reaction Bonded Boron Carbide Research Articles

The reinforcement of reaction-bonded boron carbide via adjusting SiC morphology controlled by carbon sources

Reaction-bonded boron carbide (RBBC) composites have great potential for large-scale industrial production owing to their low cost and flexible product size. In this work, RBBC composites with various carbon additions were fabricated by liquid Si infiltration. The morphology of carbon sources is decisive for the morphology of reaction-formed SiC grains at 1550 °C. The effects of carbon sources on the microstructure and mechanical properties of the composites were studied. The as-prepared composites achieve a flexural strength of up to 575 MPa and a fracture toughness of up to 5.1 MPa/m2. The enhancement of the strength and toughness was attributed to the formation of defects-containing nano-SiC grains and continuous ceramic skeletons composed of boron carbide and nano-SiC. In addition, high aspect ratio plate-like SiC grains also allow a considerable improvement in the mechanical properties, even if they are not uniformly distributed.

Diamond reinforced reaction-bonded boron carbide composites: Fabrication, microstructure, mechanical and tribological properties

Reaction-bonded boron carbide composites were fabricated by molten silicon infiltration of diamond-containing boron carbide preforms. The effects of diamond particle size on the microstructure, mechanical and tribological properties of reaction-bonded boron carbide composites were investigated. Fine diamond particles (≤7.7 µm) completely reacted with silicon generating nano silicon carbide particles, which bonded the boron carbide particles forming a 3-D ceramic skeleton and improving the flexural strength of the composites. Coarser diamond (≥24 µm) particles were retained protected by a dense SiC layer generated from the reaction of diamond and molten silicon. A “core-shell” structure with the retained diamond as the “core” and with the reaction formed silicon carbide as the “shell” formed. Relief structures were established on the composites’ surface during the wear process, greatly reducing the friction coefficient and improving the wear resistance.

Coextrusion of Reaction‐Bonded Carbides by Robocasting

Coextrusion by robocasting is a suitable process for fabricating multimaterial ceramic structures. Herein, the robocasting process is used to fabricate core–shell structures, combined with subsequent liquid silicon infiltration (LSI). Thus, reaction‐bonded silicon carbide (RBSC), reaction‐bonded boron carbide (RBBC), and reaction‐bonded silicon–boron carbide composites are produced. The LSI process offers the possibility to circumvent high temperatures and pressures used in traditional fabrication. Pastes with high solid loading and necessary carbon content are used in order to combine the robocasting with the subsequent LSI process. The influence of the paste rheology on the sample fabrication of multimaterial core–shell structures of reaction‐bonded carbides is investigated. The key rheological data, such as the viscosities of the combined pastes, are correlated with the observations from the microstructural investigation using scanning electron microscopy. A correlation between the difference in viscosity and the core geometry can be established. Crack formation in the material combination of RBSC and RBBC is found and compared with layered multimaterial structures of reaction‐bonded carbides. Residual stresses, which can be used to explain the crack formation, are investigated using Raman spectroscopy.

Continuous SiC Skeleton-Reinforced Reaction-Bonded Boron Carbide Composites with High Flexural Strength.

Reaction-bonded boron carbide (RBBC) composites have broad application prospects due to their low cost and net size sintering. The microstructure, reaction mechanism of boron carbide with molten silicon (Si), and mechanical properties have been substantially studied. However, the mechanical properties strengthening mechanism of reaction-bonded boron carbide composites are still pending question. In this study, dense boron carbide ceramics were fabricated by liquid Si infiltration of B4C-C preforms with dispersed carbon black (CB) as the carbon source. Polyethyleneimine (PEI) with a molecular weight of 1800 was used as the dispersant. CB powders uniformly distributed around boron carbide particles and efficiently protected them from reacting with molten Si. The uniformly distributed CB powders in situ reacted with molten Si and formed uniformly distributed SiC grains, thus forming a continuous boron carbide-SiC ceramic skeleton. Meanwhile, the Si content of the composites was reduced. Using PEI-dispersed CB powders as additional carbon source, the composites' flexural strength, fracture toughness, and Vickers hardness reach up to 470 MPa, 4.6 MPa·m1/2, and 22 GPa, which were increased by 44%, 15%, and 10%, respectively. The mechanisms of mechanical properties strengthening were also discussed.

Ceramics Based on Reaction-Bonded Boron Carbide for Heat Protection Coatings of Space Aircraft

Ceramics Based on Reaction-Bonded Boron Carbide for Heat Protection Coatings of Space Aircraft

Mixed Particle Size Effect on Improvement of Mechanical Properties of Reaction Bonded B4C

The research was aimed for improving the mechanical properties of reaction bonded boron carbide (RBBC) through use of two boron carbide (B4C) powders in the initial preform. Experimental results show that the Young’s modulus, Knoop hardness, and flexural strength of RBBC, produced with the combination of two powders, are greater by ∼15.2%, ∼33.8% and ∼15.5%, respectively, compared to that produced with single, i.e. fine B4C powder. The increase in ceramic phase (B4C and B4C +SiC) and reduction in residual Si content in the RBBC produced with mixed powders lead to an enhancement in its mechanical properties. Both RBBC exhibit indentation size effect and such characteristics are corroborated by their respective brittleness index.

Fabrication of Reaction-Bonded Boron Carbide-Based Composites by Binder Jetting 3D Printing

In this work, the binder jetting 3D printing of boron carbide was combined with a subsequent liquid silicon infiltration procedure to produce reaction-bonded boron carbide (RBBC)-based structures. After printing, the samples were isostatically pressed to obtain more homogeneous and denser microstructures while maintaining their complex shapes. The RBBC bodies were successfully fabricated, and the influence of the binder content on the amount of residual silicon was studied. By increasing the binder content from 10 to 22.5 vol.%, the Si content decreased from ~28 to ~12 vol.%. The mechanical properties dependent on the Si content were additionally investigated. The measured average values for the bending strength (~355 MPa), Young’s modulus (~348 GPa), and hardness (~20 GPa) are comparable to those reported in the literature for RBBC-based materials.

Residual-stress-induced crack formation in robocasted multi-material ceramics: Stress considerations and crack prevention

Layered multi-material ceramics are natural candidates for modern engineering applications due to their attractive mechanical properties. Residual stresses caused, for example, by a thermal mismatch during the processing of these materials can significantly affect their mechanical properties. In this work, Raman investigations were performed to estimate these residual stresses in layered reaction-bonded silicon carbide (RBSC) and reaction-bonded boron carbide (RBBC) composites fabricated by robocasting. The Raman measurements show that the residual stress in the silicon phase of RBSC and RBBC composites has a different sign, which can explain the crack formation that occurred after Si infiltration. To adjust the stresses and prevent this cracking, a new paste composition was investigated. SEM micrographs and Raman measurements showed that almost crack-free layered composites with similar stresses in the different layers could be realized. In addition, well-known analytical approaches were used to calculate these residual stresses.

Effect of Carbon Content on Mechanical Properties of Boron Carbide Ceramics Composites Prepared by Reaction Sintering.

In this study, different reaction-bonded boron carbide (RBBC) composites with a free carbon addition from 0 to 15 wt% were prepared, and the effect of the carbon content on the mechanical properties was discussed. With the free carbon addition increase from 0 to 15 wt%, the residual silicon content in the RBBC composite decreased first and then increased. Meanwhile, the strength of the RBBC composite improved first and then worsened. In the RBBC composite without free carbon, the B4C grains are obviously dissolved, the grains become facet-shape, and the grain boundary becomes straight. The microstructure of the composite was tested by SEM, and the phase composition of the composite was tested by XRD. The RBBC composite with the addition of 10 wt% free carbon has the highest flexural strength (444 MPa) and elastic modulus (329 GPa). In the composite with a 10 wt% carbon addition, the phase distribution is uniform and the structure is compact.

Laser powder bed fusion as a net-shaping method for reaction bonded SiC and B4C

ABSTRACT Additive manufacturing (AM) technologies for technical ceramics are rapidly emerging. Many of these processes rely on a polymer binder-assisted printing approach followed by de-binding and furnace sintering for densification. However, the required de-binding step is long and sensitive, and the presence of densification shrinkage requires a compensation in design. This study explores laser powder bed fusion (LPBF) as an additive manufacturing method for full net-shaping of reaction bonded silicon carbide (RBSC) and reaction bonded boron carbide (RBBC). During LPBF, silicon is used as a structural binder instead of traditional sacrificial polymer binders. By combining this with liquid silicon infiltration (LSI) as a densification method, long de-binding times and densification shrinkage are avoided. This leads to a net-shaping, additive manufacturing process for RBSC and RBBC ceramics with high Young’s modulus (285 and 308 GPa respectively), flexural strength (220 and 168 MPa) and hardness (2045 and 2242 HV).

Performance evaluation of multilayered ceramic composite armors: New design and advanced predictive method

Novel body armors are designed to protect against ballistic threats in the most vulnerable organs within the thorax and abdomen. Decreasing the armor weight without affecting its total integrity after the impact is one of the most challenging tasks. In this study, we combine advanced numerical simulations and experimental tests to investigate the ballistic performance of multilayered armor systems (MAS) consisting of laminated alumina (Al2O3) ceramic plates with multi-curve form and a hybrid composite backing. The ballistic trauma absorption and ceramic fracturing morphology are considered evaluation criteria. The investigation provides enough data on the measured trauma and the results are compared to advanced monolithic ceramics. The ballistic tests showed that bonding three or two ceramic plates with polymeric interlayer decreases considerably the eroded ceramic mass in comparison to monolithic ceramic tiles. Furthermore, the layup of two thin Al2O3tiles with frontal confinement gives the same trauma-weight index as monolithic silicon carbide and reaction-bonded boron carbide plates. The combination of K129 and KM2 aramid weave fabrics decreases the composite backing weight by 33% and increases its ballistic performance in comparison to homogeneous aramid fabrics. Numerical simulations that involve the use of solid Lagrange and adaptive solid/smooth particles hydrodynamics (SPH) numerical approaches with detailed 3D models of the bullet and the MAS are presented in this work. Based on the statistical analysis, a better prediction of the back face deformation and bullet residual length is obtained by the adaptive solid/SPH method, which is found more suitable for the simulation of multilayered armor impact scenarios.

Effect of Boron Carbide Particle Size Distribution on the Microstructure and Properties of Reaction Bonded Boron Carbide Ceramic Composites by Silicon Infiltration

Effect of Boron Carbide Particle Size Distribution on the Microstructure and Properties of Reaction Bonded Boron Carbide Ceramic Composites by Silicon Infiltration

Multi-material printing of reaction bonded carbides by robocasting

In the present work, reaction bonded boron carbide (RBBC) and reaction bonded silicon carbide (RBSC) composites were fabricated using multi-material robocasting followed by liquid silicon infiltration (LSI). The fabrication of carbide based materials using LSI is of great technological interest because it avoids the need for the relatively high temperatures and pressures required in traditional fabrication. Multi-material robocasting offers the possibility of combining materials and thus their properties, as demonstrated in this work with silicon carbide (SiC) and boron carbide (B 4 C). The feasibility of combining RBSC and RBBC was demonstrated by printing multilayer bending bars and more complex structures. The microstructure of the samples was investigated and, in particular, the interface between the different layers at each processing step was studied. After LSI, cracks were observed in the B 4 C layers due to differences in thermal expansion, but the interfaces showed no delamination and good interfacial bonding between the layers was evident. Hardness measurements were performed to investigate the interfacial bonding and residual stresses in the materials used. The manufactured RBSC and RBBC samples with a relative density of 99% and 98%, showed a hardness of 18.3 GPa and 17.1 GPa, respectively, which are within the range of the reference data from the literature. The residual stresses in the layers were calculated theoretically and also based on the crack pattern generated by Vickers indentation. Tensile stresses in RBBC and compressive stresses in RBSC were determined and can explain the cracking in the laminated structures.

Fabrication of carbon-coated boron carbide particle and its role in the reaction bonding of boron carbide by silicon infiltration

To tackle the dissolution problem of boron carbide particles in silicon infiltration process, carbon-coated boron carbide particles were fabricated for the preparation of the reaction-bonded boron carbide composites. The carbon coating can effectively protect the boron carbide from reacting with liquid Si and their dissolution, thus maintaining the irregular shape of boron carbide particles and preventing the growth of boron carbide particles and reaction formed SiC regions. Furthermore, the nano-SiC particles, originated from the reaction of the carbon coating and the infiltrated Si, uniformly coated on the surfaces of boron carbide particles, thus forming a ceramic skeleton of the nano-SiC particles-coated and -bonded boron carbide particles. The Vickers hardness, flexural strength and fracture toughness of the composites can be increased by 26 %, 45 %, and 37 % respectively, by using carbon-coated boron carbide particles as raw materials.

The effect of carbon nanotubes introduction on the mechanical properties of reaction bonded boron carbide ceramics

The influence of carbon nanotubes (CNTs) on the mechanical properties and structure formation during reactive sintering of B4C materials with Si addition was studied. Upon infiltrating the B4C structure with molten silicon, a non-porous composite was formed with a density of 2.45-2.55 g/cm3 and a hardness of 22-27 GPa. The formation of highly dispersed B-C-Si phases was observed in the interphase of adjacent B4C particles due to the incorporation of Si into B4C structures. These phases increase the bonding strength between B4C particles. In spite of the fact that the addition of 1-5 wt% Multi-Walled Carbon Nanotubes decreases the green density of the compacts, the flexural strength of the infiltrated material significantly increased. The improvement of the strength of ceramics modified with MWCNTs was interpreted in terms of the formation of thin flattened SiC crystals at the interfaces between B4C and B-C-Si particles, which strengthen the interfaces between ceramic particles.

On the effects of particle size and preform porosity on the mechanical properties of reaction-bonded boron carbide infiltrated with Al-Si alloy at 950 °C

The infiltration of boron carbide preforms with Al alloys at relatively low temperature prevents the formation of the undesired Al4C3 phase. In the present study the effect of boron carbide powder particle size on the mechanical properties and phase composition of composites infiltrated with Al-20%Si alloys at 950 °C was investigated. According to XRD analysis, the infiltrated composites contain Al8C7B4, AlB2 and AlB12, as well as non-reacted Al and Si that originated from solidification of Al-Si alloy. The presence of small amounts of SiC was noted in specimens fabricated from fine boron carbide powder. No evidence for the formation of non-desired aluminum carbide phase was obtained. Infiltration of ceramic preforms with virtually the same green density generated composites with an elastic modulus and bending strength that continuously decreased from 270 GPa and 405 MPa to 195 GPa and 345 MPa for powder with 90% particles close to 3 μm and powder with 90% particles close to 180 μm, respectively. These results ambiguously confirm that boron carbide particle size strongly affects mechanical properties of reaction-bonded composites infiltrated with Al-Si alloy at 950 °C and reflect the amount of newly formed ceramic phases appearing during infiltration and the presence of defects at the metal-ceramic interface.

Controllability of the pore characteristics of B4C/C preform prepared by gel-casting and the properties of RBBC composites

A new type of pore structure of B4C/C preform was fabricated by a resorcinol-formaldehyde (RF) hydrogel gel-casting system. Pore structure controllability of the B4C/C preform was achieved by adjusting the content of the catalyst Na2CO3. Increasing the content of Na2CO3 could achieve accurate control of the B4C/C preform from a single macroporous or mesoporous structure to a hierarchical macroporous-mesoporous structure. The reaction bonded boron carbide (RBBC) composites were prepared by the infiltration of B4C/C preforms of different pore structures with liquid silicon. The residual silicon content and mechanical properties of the RBBC composites were studied. The residual silicon content was controlled by the modification of the open porosity and pore structure of the B4C/C preforms, and the lowest residual silicon content was 33 vol%. Sample S300, which was prepared through liquid silicon infiltration of a B4C/C preform with a single mesoporous structure (with the optimum aperture size of 49 nm), had the best mechanical properties, including a flexural strength and fracture toughness of 419 ± 17 MPa and 4.12 ± 0.12 MPa·m1/2, respectively.

Effect of boron carbide on the liquid silicon infiltration and performance enhancement of reaction-bonded silicon carbide composites

Reaction-bonded boron carbide (RBBC) is prepared through the process that liquid silicon infiltrating into porous B4C/resin preforms. The reaction between B4C and liquid silicon, structural evolution of RBBC composites and factors affecting the mechanical properties were analyzed. The results showed that the independently distributed B4C particles and newly-formed coarse SiC grains surrounded by banded silicon phase were the main reasons for the performance degradation of RBBC composites. On this basis, we studied the effect of B4C on the liquid silicon infiltration and performance enhancement of reaction-bonded silicon carbide (RBSC) composites. It is an effective and easy method to improve the performance of RBSC composites sharply using refined B4C particle as the reinforcement. The main reasons for the performance enhancement are the reduction of the content and dimensions of residual silicon, increase of the fracture energy and grain refinement.

Microstructure and ballistic performance of hot pressed & reaction bonded boron carbides against an armour piercing projectile

ABSTRACTA comparative study on ballistic performance of hot pressed boron carbide (HPBC) and reaction bonded boron carbide (RBBC) tiles were performed using depth of penetration (DOP) configuration against 7.62 mm AP ammunition. Both HPBC and RBBC tiles were characterised for their phase contents and properties. Ballistic efficiency was calculated using the newly developed normalised ballistic efficiencies, normalised differential efficiency factor & normalised ballistic efficiency, in order to eliminate the influence of backing material on ballistic efficiency. It was found that for similar tile thickness, the residual shot weight and residual DOP of HPBC tiles were lesser than that of RBBC tiles. Normalised ballistic efficiencies, for both HPBC and RBBC ceramics, showed a higher ballistic performance for HPBC than RBBC tiles.

Strength of ceramic–metal joints measured in planar impact experiments

SPS-processed alumina and reaction-bonded boron carbide ceramic composite (RBBC) were joined with Al10SiMg alloy by spark plasma sintering and tested in a series of planar impact experiments designed to measure dynamic tensile (spall) strength of the joints. The results of the impact testing, together with postmortem inspection of the fractured samples, confirmed the applicability of this approach for testing joint strength. The measurements show that in the case of an RBBC/metal joint, the dynamic tensile strength of the joint exceeds that of the ceramic part, and that fracture of the shock-loaded ceramic–metal pair occurred in the ceramic portion. The dynamic tensile strength of the interface between alumina and Al10SiMg alloy virtually coincides with that of the metal part, with the fracture occurring exactly at the interface. The coincidence may be explained based on the recently published results of atomistic calculations of the structure of an alumina–aluminum interface.