B4C TiB2 Composites Research Articles

Improving properties of boron carbide (B4C) with silicon doping and titanium diboride addition

In this research, B4C-TiB2 composites were successfully fabricated via the spark plasma sintering method. First, the TiB2 source effect on the B4C-TiB2 composites was investigated using commercially available TiB2 and in-house synthesized TiB2. Subsequently, the effect of Si/B co-doped B4C on composite ceramics was studied, followed by examining the samples' microstructure and elastic and mechanical properties. The results showed that B4C-TiB2 composites made with in-house TiB2 powder obtained higher relative density and more desirable elastic and mechanical properties than samples made with commercial TiB2. In-house TiB2 and Si/B-B4C composites provided more properties improvement overall. The elastic modulus, Vickers hardness, and fracture toughness values of Si/B co-doped samples were 493 GPa, 30.09 ± 1.97 GPa, and 4.31 ± 0.74 MPa m1/2, respectively. Additionally, the amorphization of the TiB2-B4C composite decreased with Si/B co-doping.

Novel B4C[sbnd]TiB2 composites with high electrical and low thermal conductivity by selective grain growth in reactive sintering

High electrical conductivity and low thermal conductivity are beneficial for the electrical discharge machining performance of ceramics. In this work, B4C–TiB2 composites were prepared by spark plasma sintering of B4C–TiC–B powder mixture. The chemical reaction between TiC and B, together with subsequent selective matrix grain growth, expelled small in-situ generated TiB2 grains to form conductive interlayers around large B4C grains. The unique microstructure significantly enhances the electrical conductivity of B4C–TiB2 composites, especially at low TiB2 content, while the ultrafine in-situ formed TiB2 grains endow the composites with low thermal conductivity. The effects of TiB2 content on the microstructure, mechanical properties, thermal & electrical conductivity of the composites were investigated. B4C–20 vol% TiB2 composite exhibits excellent comprehensive performance, including a relative density, Vickers hardness, flexural strength, fracture toughness, room electrical and thermal conductivity of 98.6%, 28.15 GPa, 656 MPa, 5.46 MPa⋅m1/2, 1.08 × 105 S/m and 19.37 W/m⋅K, respectively.

B4C‒TiB2 composite with modified microstructure and enhanced properties from optimal size coupling of raw powders

AbstractB4C‒15 vol% TiB2 composites were fabricated by in situ reactive spark plasma sintering with B4C, TiC, and amorphous B powders as the raw materials. The size coupling of initial B4C and TiC particles was optimized based on the reaction mechanism to derive B4C‒TiB2 composites with enhanced microstructure and properties. During the reactive sintering, fine B4C–TiB2 particles were firstly formed by an in situ reaction between TiC and B. Then, large B4C particles tended to grow at the cost of small B4C particles. The in situ TiB2 grains gradually grew up and interconnect, distributing around the large B4C grains to form an intergranular TiB2 network. The results showed that the B4C‒15 vol% TiB2 composite prepared from 3.12 μm B4C powder and 0.80 μm TiC powder had the optimal comprehensive properties, with a relative density of 99.50%, a Vickers hardness of 31.84 GPa, a flexural strength of 780 MPa, a fracture toughness of 5.77 MPa·m1/2, as well as an electrical resistivity of 3.01 × 10−2 Ω·cm.

Properties and ballistic tests of strong B4C-TiB2 composites densified by gas pressure sintering

B4C-TiB2 composites with classical 75/25 vol ratio were sintered by pressureless sintering with and without gas pressure application in the final stage of densification, using a novel prototypal furnace. A small fraction of WC was introduced through high energy milling of the starting powders with WC-Co spheres. High energy milling facilitated the densification thanks to incorporation of WC impurities acting as sintering aid, and size reduction of the starting powders. Strength, stiffness and toughness of the ceramic densified at 2050 °C via gas pressure sintering were even better than hot pressed composites at 1900 °C. Depth of Penetration tests on plates with 3–5 mm thickness demonstrated that the gas pressure sintered material had a superior performance compared to the hot pressed one. This work also revealed that hardness was not the property spotting the best ballistic performance.

Reactively sintered B4C-TiB2 composites: Effects of nanolayer films and secondary phase size on mechanical and fracture properties

High theoretical density (>99%) B4C-TiB2 composites containing either well dispersed, fine TiB2 or coarser agglomerated TiB2 were processed by spark plasma sintering in argon or reactive nitrogen environments. Two types of nanoscopic grain boundary films during reactive sintering were determined with STEM, EFTEM and EELS, namely amorphous titanium oxynitride and hexagonal boron nitride that provide weak interphase boundaries as preferential paths for crack propagation resulting in increased fracture toughness up to 9.4 MPa√m for the coarser agglomerated TiB2 composites. Conversely, the fine TiB2 composite is beneficial for increasing the flexural strength up to 460 MPa. The strengthening and toughening mechanisms responsible for the tradeoff in properties were determined with microscopy of the fracture surfaces.

Micromechanics-based simulation of B4C-TiB2 composite fracture under tensile load

Micromechanics modeling was performed to study the effects of thermal residual stress, weak interphases, TiB2 volume fraction and particle size on the mechanical responses and fracture behaviors of B4C-TiB2 composites. Experimentally observed fracture behaviors including micro-cracking and crack deflection were successfully captured. The weak interphases at B4C-TiB2 boundaries and the thermal residual stress induced during cooling by the large CTE mismatch between B4C and TiB2 were identified as two major factors to promote micro-cracking that caused the enhanced progressive failure behavior. Micro-cracking was enhanced with higher TiB2 volume fraction due to higher fraction of weak interphase and material affected by thermal residual stress. Meanwhile, micro-cracking behaviors exhibited limited change with varying TiB2 particle sizes. This modeling study successfully captured the main fracture behaviors and their trends by varying micro-structures of B4C-TiB2 composites and can potentially aid microstructure design of tougher B4C-TiB2 composites in the future.

B4C–TiB2 composites fabricated by hot pressing TiC–B mixtures: The effect of B excess

Previous research have reported that B4C–TiB2 composites could be prepared by the reactive sintering of TiC–B powder mixtures. However, due to spontaneous oxidation of raw powders, using TiC–B powder mixtures with a B/TiC molar ratio of 6: 1 introduced an intermediate phase of C during the sintering process, which deteriorated the hardness of the composites. In this report, the effects of B excess on the phase composition, microstructure, and mechanical properties of B4C–TiB2 composites fabricated by reactive hot pressing TiC–B powder mixtures were investigated. XRD and Raman spectra confirmed that lattice expansion occurred in B-rich boron carbide and BxC–TiB2 (x > 4) composites were obtained. The increasing B content improved the hardness and fracture toughness but decreased the flexural strength of BxC–TiB2 (x > 4) composites. When the molar ratio of B/TiC increased from 6.6:1 to 7.8:1, the Vickers hardness and the fracture toughness of the composites were enhanced from 26.7 GPa and 4.53 MPa m1/2 to 30.4 GPa and 5.78 MPa m1/2, respectively. The improved hardness was attributed to the microstructural improvement, while the toughening mechanism was crack deflection, crack bridging and crack branching.

Microstructure and mechanical properties of b4c-tib2 composites reactive sintered from B4C + TiO2 precursors

Ceramic composites consisting of a boron carbide (B4C) matrix and titanium diboride (TiB2) secondary phase were obtained by reactive sintering from boron carbide powder with 40 and 50wt.% of titanium dioxide (TiO2) additive. The same sintering temperature of 1850?C and pressure of 35MPa, but different sintering times from 15 to 60min, were applied during reactive hot pressing of the composites in vacuum. The effects of TiO2 content and sintering time on phase compositions, microstructures and mechanical properties of the composites were studied. The TiO2 additive enhanced densification of the B4C-TiB2 ceramic composites. Both Vickers hardness and the fracture toughness of the composites increased with prolongation of sintering time. The highest hardness of 29.8GPa was achieved for the composite with 29.6 vol.% of TiB2 obtained by sintering of the precursor with 40wt.% of TiO2 additive for 60min. The fracture toughness reached a maximum value of 7.5MPa?m1/2 for the composite containing 40.2 vol.% of TiB2, which was fabricated by reactive sintering of the precursor with 50wt.% of TiO2 additive for 60min.

Mechanical Properties of Hot-Pressed B<sub>4</sub>C-TiB<sub>2</sub> Composites Synthesized from B<sub>4</sub>C-TiO<sub>2</sub> and B<sub>4</sub>C-TiC

In this study, B4C-TiB2 ceramic composites were manufactured by hot pressing method. The raw materials for the in-situ synthesis of TiB2 were TiO2 and TiC. After being sintered at 1900°C for 60min under a pressure of 30MPa, compact composites samples with a TiB2 volume fraction range from 0 to 11.05% were prepared. The relative density, fracture toughness and flexural strength of different sample were tested. Microstructures on the fracture surface were studied by SEM. The result shows that B4C-TiB2 ceramic composites sintered from B4C-TiC had a better mechanical property than the one sintered from B4C-TiO2. When the content of TiB2 (reacted from TiC) was 11.05vol.%, the strength and toughness of B4C-TiB2 ceramics can reach 598MPa and 6.45MPa·m1/2. The toughening mechanisms of B4C-TiB2 composites include micro-crack toughening and energy consumption by the pulling out process of second phase.

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.

Microstructure and properties of hot pressed TiB2 and SiC reinforced B4C–based composites

B4C ceramics were strengthened by introducing the hard second–phase particles TiB2 and SiC, and the effects of TiB2 and SiC contents on the microstructure and properties of the composites were investigated. B4C–TiB2 binary composites with TiB2 contents of 10, 20, 30, and 40 vol% were prepared by hot pressing. The microstructure, mechanical properties, and electrical properties of the composites with different TiB2 contents were investigated and compared. The results showed that the B4C–30 vol%TiB2 composite obtained the best comprehensive properties, with a relative density, hardness, bending strength, fracture toughness, and conductivity of 97.9 %, 29.5 GPa, 590 MPa, 6.41 MPa m1/2, and 7.6 × 104 S/m. The compressive stress generated on B4C, crack deflection induced by TiB2, and conductive network formed by TiB2 are of great significance in the context of the properties of the B4C–TiB2 composites. In addition, B4C–TiB2–SiC ternary composites with SiC contents of 0, 10, and 20 vol% were also fabricated by hot pressing. The effect of SiC content on the microstructure and mechanical properties, and the effect of SiC on the antioxidant properties of the composites were investigated. The results showed that the B4C–30 vol%TiB2–10 vol%SiC composite had the best comprehensive properties, with a relative density, hardness, flexural strength, fracture toughness, and residual flexural strength (1600 ℃) of 98.8 %, 29.5 GPa, 621 MPa, 6.80 MPa m1/2, and 465 MPa. The inhibition of the growth of SiC to other grains, removal of oxide impurities, and repair of damage by SiC oxidation products play an important role in the performance of the B4C–TiB2–SiC composites.

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.

Disclosing small scale length properties in core-shell structured B4C-TiB2 composites

This work explores the fine microstructural features of B4C-TiB2 composites and suggests an overall microstructure evolution from powder processing to sintering. In addition, small-scale grain structures are correlated to local properties measured by nanoindentation, thus providing trends in mechanical behavior. Dense ceramics were typified by development of a core/shell structure of the boride grains, with the shell comprising a (Ti,W)B2 solid solution with different assemblage and variable amount of W guest cation depending on the processing route. TEM analyses revealed chemical and morphological differences that were associated to the presumed densification mechanisms. Nanoindentation was used to extract the overall and single phase properties of TiB2 core, shell and B4C phase highlighting for the first time hardness and modulus variation as a function of the lattice perturbation, i.e. of nominally pure core boride and shells region.This work provides new experimental findings fundamental for the development and synthesis of high-performance structural materials starting from a small-length scale perspective.

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.

Fabrication and characterization of FAST sintered micro/nano boron carbide composites with enhanced fracture toughness

Toughening of boron carbide (B4C) without hardness degradation, was achieved by hierarchical structures consisting of B4C micro-grains, titanium diboride (TiB2) grains, and graphitic phases along B4C grain boundaries. Such hierarchical structures were uniquely achieved by co-sintering of B4C micro-powder and carbon-rich B4C nano-powder, in situ formation of TiB2, and by utilizing the short sintering time of field-assisted sintering technology. Toughening mechanisms observed after micro-indentation include crack deflection and delamination of graphite platelets, micro-crack toughening and crack deflection/bridging by TiB2 grains. Fracture toughness enhancement was achieved while maintaining hardness: 4.65 ± 0.49 MPa m1/2 fracture toughness and 31.88 ± 1.85 GPa hardness for a micro/nano B4C-TiB2 composite (15 vol% TiB2 and 15 vol% B4C nano-powders) vs. 2.98 ± 0.24 MPa m1/2 and 32.46 ± 1.67 GPa for a reference micro B4C sample. In future, macro-scale mechanical testing will be conducted to further evaluate how these micro-scale hierarchical structures can be translated to macro-scale mechanical properties.

Effects of TiC particle size on microstructures and mechanical properties of B4C–TiB2 composites prepared by reactive hot-press sintering of TiC–B mixtures

Effects of the starting TiC particle size on the phase compositions, microstructures and mechanical properties of B4C–TiB2 composites prepared by reactive hot-press sintering of TiC–B mixtures were investigated. B4C–TiB2 composites were prepared from a single grade amorphous B powder (0.9 μm) and three different TiC powders (50 nm, 0.8 μm and 3.0 μm), respectively. The composites prepared from 50 nm and 3.0 μm TiC powders exhibited finer microstructures and higher hardness (29–30 GPa). The composite prepared from 0.8 μm TiC powder showed the coarsest microstructure but possessed the highest strength of 659 MPa due to its homogenous phase distribution without C impurity and abnormal grain growth that presented in the other two composites. The results indicated that the mechanical properties of B4C–TiB2 composite could be controlled by the particle size matching between TiC and B powders.

Effect of sintering temperature and TiB2 content on the grain size of B4C-TiB2 composites

Boron carbide (B4C) is a ceramic with great properties such as low density, the third hardness after diamond and cubic BN. However, it is a limited use cause of its poor sinterability and low fracture toughness. Titanium diboride (TiB2) has been used as an ideal additive to get B4C ceramics with good properties. B4C-TiB2 composites were prepared by spark plasma sintering (SPS) at 1950℃ under a pressure of 50 MPa, using TiB2 and B4C powder mixture as starting materials. The effect of TiB2 content on the mechanical performance and grain size of B4C-TiB2 composites was investigated. The B4C-TiB2 composites with 20 mol% TiB2 addition show great comprehensive properties, the relative density of 97.91 %, a Vickers hardness of 29.82 ± 0.14 GPa, and fracture toughness of 3.70 ± 0.08 MPa·m1/2 respectively. The results indicated that as the TiB2 content increase, the hardness of the composite decreases and the fracture toughness increases. The main mechanism of the TiB2 phase toughening B4C ceramic is crack deflection as a result of the differences in their thermal expansion coefficients. The analysis of grain size distribution by electron backscattered diffraction (EBSD) shows that the pinning effect of TiB2 can refine B4C grain. The pinning effect is another reason for the high hardness and high toughness of the B4C-TiB2 composites. Dislocations are observed in the TEM image of the composite, which also improves the hardness and toughness of the material.

Effects of B4C particle size on the microstructures and mechanical properties of hot-pressed B4C–TiB2 composites

Full dense B4C–30 vol% TiB2 composites were prepared by hot pressing at 2000 °C under 35 MPa from four different starting B4C powders with their medium particle sizes ranging from 0.5 to 35.8 µm. The effects of B4C particle size on the microstructures and mechanical properties of composites were investigated. The results indicated that both B4C and TiB2 grains grew during sintering process, and each kind of grains had a pinning effect on the grain growth of the other. With coarse B4C powders as raw materials, TiB2 grains in obtained B4C–TiB2 composites tended to grow with the [001] zone axis parallel to the applied pressure direction, which possibly reinforced the composites. When the particle size of the starting B4C powder was 7.09 µm, the obtained B4C–TiB2 composite exhibited the optimized mechanical properties including a flexural strength of 754 MPa, a Vicker hardness of 30.01 GPa and a fracture toughness of 5.23 MPa m1/2, respectively, due to the most homogenous and finest microstructures.

Production and Properties of B4C–TiB2 Composites with Isotropic Eutectic Microstructure

Directionally reinforced B4C–TiB2 eutectic alloys were produced from green powder compacts by floating zone melting. Their mechanical properties were studied over a wide range of temperatures (25–1600°C). The high-temperature strength of the reinforced B4C–TiB2 composites hardly changes with increasing temperature and reaches about 200 MPa at 1600°C. Mechanical grinding and subsequent spark plasma sintering were used to produce reinforced B4C–TiB2 composites with an isotropic eutectic microstructure. The microstructure of the bulk-reinforced ceramic samples was examined. The developed ceramics meet the requirements imposed on high-temperature creepresistant and oxidation-resistant materials for reusable hypersonic vehicles.

Hard and easy sinterable B4C-TiB2-based composites doped with WC

B4C-TiB2 composites were contaminated with WC to study the effect on densification, microstructure and properties. WC was introduced through a mild or a high energy milling with WC-6 wt%Co spheres or directly as sintering aid to 50 vol% B4C / 50 vol%TiB2 mixtures. High energy milling was very effective in improving the densification thanks to the synergistic action of WC impurities, acting as sintering aid, and size reduction of the starting TiB2-B4C powders. As a result, the sintering temperature necessary for full densification decreased to 1860 °C and both strength and hardness benefited from the microstructure refinement, 860 ± 40 MPa and 28.5 ± 1.4 GPa respectively. High energy milling was then adopted for producing 75 vol% B4C/25 vol% TiB2 and 25 vol% B4C/ 75vol%TiB2 mixtures. The B4C-rich composition showed the highest hardness, 32.2 ± 1.8 GPa, whilst the TiB2-rich composition showed the highest value of toughness, 5.1 ± 0.1 MPa m0.5.