TiB2 Grains Research Articles

Effect of temperature on the structure and mechanical properties of SiC–TiB2 composite ceramics by solid-phase spark plasma sintering

SiC composite ceramics have good mechanical properties. In this study, the effect of temperature on the microstructure and mechanical properties of SiC–TiB2 composite ceramics by solid-phase spark plasma sintering (SPS) was investigated. SiC–TiB2 composite ceramics were prepared by SPS method with graphite powder as sintering additive and kept at 1700 °C, 1750 °C, 1800 °C and 50 MPa for 10min.The experimental results show that the proper TiB2 addition can obviously increase the mechanical properties of SiC–TiB2 composite ceramics. Higher sintering temperature results in the aggregation and growth of second-phase TiB2 grains, which decreases the mechanical properties of SiC–TiB2 composite ceramics. Good mechanical properties were obtained at 1750 °C, with a density of 97.3%, Vickers hardness of 26.68 GPa, bending strength of 380 MPa and fracture toughness of 5.16 MPa m1/2.

The effect of B and Ti–Al intermetallics additions on the microstructure and mechanical properties of hot-pressed B4C

In this work, we studied the microstructure and mechanical properties of hot-pressed B4C, B4C + 5 wt% TiAl, and B4C + B + 5 wt% TiAl. The X-ray diffraction and Raman spectroscopy results showed that the addition of Ti–Al alone did not led to Al doping in B4C, and it did not reduce the degree of amorphization of B4C generated under high shear stresses. In contrast, the co-addition of Ti–Al and B resulted in both B and Al solid solutions in the B4C and effectively mitigated the amorphization of B4C. Electron probe microanalysis (EPMA) and energy dispersive X-ray spectroscopy (EDS) analyses suggested that the co-addition of Ti–Al and B promoted the interdiffusion of lightweight elements such as B, C, Al, Mg, and Si at high temperatures, resulting in a dense body with uniformly distributed second phase. The transmission electron microscopy (TEM) observations of the B4C + B + 5 wt% TiAl sample showed that a nano–core–shell structure with aggregated dislocations in the shells which was generated at TiB2 grains due to the segregation and dissolution-precipitation between TiB2 and B-rich boron carbide. The short-range ordered substitution of B and the disordered doping of Al in B4C led to lattice distortion and expansion, resulting in the formation of high-density defects, including stacking faults and nano-twins, improving the mechanical properties for B4C. The B4C + B + 5 wt% TiAl sample exhibits a combination of fascinating properties, including low density (2.52 g/cm3), high Vickers hardness (35.53 ± 0.83 GPa) and moderate fracture toughness (4.37 ± 0.35 MPa m1/2).

Microstructure of spark plasma sintered TiC–TiB2–SiCw composite

This research intends to implement a complementary study on the consolidation and microstructure of TiC-based ceramics incorporating 30 vol% TiB2 and 10 vol% SiC whiskers (SiCw). The spark plasma sintering was employed as the manufacturing tool to produce the designed composite under the sintering pressure of 40 MPa for 7 min at 1900 °C. The X-ray diffraction study and the microstructural observations revealed the formation of graphite as an in-situ phase during the sintering process, as a result of carbon deposition from the crystalline structure of the TiC matrix. Although the SiC introduced to the composite was needle-shaped, no SiC whiskers could be found in the final microstructure due to the nucleation and growth of new SiC grains. Additionally, it was suggested that the surface oxide impurities available on the starting powders could contribute to some reactions, resulting in the in-situ formation of SiC, TiB2, and TiC ingredients. Furthermore, the grain growth phenomenon led to the formation of intragranular TiB2 grains in the TiC matrix. The plastic deformation and the applied external pressure with an inconsistency among the thermal expansion coefficients of TiB2, TiC, and SiC over the cooling stage resulted in the generation of crystalline defects, e.g., dislocations and distorted atomic planes.

Effects of boron content on the microstructure and properties of B x C-TiB2 (x=4.5, 6.5 or 8.5) ceramic composites by the reactive spark plasma sintering

ABSTRACT B x C-TiB2 ceramic composites were fabricated via reactive spark plasma sintering using TiC and B as the raw materials. The impact of B/TiC mole ratios on the phase compositions, densification behaviors, microstructure, and mechanical properties of the ceramic composites were investigated. The results showed that the stoichiometry of ‘B x C’ could be tailored by changing initial boron content and the obtained B4.5C, B6.5C and B8.5C phases have the same crystal structure (R-3 m). The excess of B enhanced the reaction between TiC and B, which released a large amount of hot energy and promoted the densification of the composites. The TB8.5 composite sintered at 1900°C had the best comprehensive mechanical properties, with hardness and flexural strength of 40.36 GPa and 551 MPa, respectively. The formation of nano-sized TiB2 grains induced by reaction were beneficial for improving the mechanical properties of these composites.

Модифицирование наноразмерными частицами нитрида кремния материалов на основе системы Ti – B – Fe, полученных методом СВС-экструзии

Compact ceramic SHS-electrode materials based on titanium diboride modified with silicon nitride nanoparticles have been obtained by SHS-extrusion. The phase composition, structure, and physicomechanical properties of the obtained materials have been studied. The results of scanning electron microscopy showed that, in the modified samples, grain refinement of the main phase of titanium diboride is observed, as well as a change in the phase composition of the material. With the introduction of 5 wt. % nanosized particles of silicon nitride, in addition to the main wear-resistant phase TiB2, the formation of phases is observed: TiN, Fe2B and TiSi2 located in the FeTi intermetallic matrix. The average grain sizes of TiB2 and TiN are 0.5 – 2 mm and 2 mm, respectively. With the addition of 10 wt. % Si3N4, the structure of the material consists of TiB2 and TiN phases uniformly distributed in the FeTi intermetallic matrix, and a small amount of Si and B solid solutions. The TiB2 grain size does not exceed 0.5 – 1 mm, and the TiN phase has an average grain size about 0.5 – 1.5 mm. It is shown that the obtained modified ceramic SHS-electrode materials have higher microhardness and hardness compared to the material without Si3N4 additives.

Microstructure and Mechanical Properties of TiN-TiB2-hBN Composites Fabricated by Reactive Hot Pressing Using TiN-B Mixture.

In this study, TiN–TiB2–hBN composite ceramics were prepared via reactive hot pressing using TiN and amorphous B powders as raw materials. Different sintering temperatures and composition ratios were studied. The results show that the 70 vol% TiN–17.6 vol% TiB2–12.4 vol% hBN ceramic composites obtained ideal comprehensive properties at 1600 °C. The relative density, Vickers hardness, bending strength, and fracture toughness were 99%, 11 GPa, 521 MPa, and 4.22 MPa·m1/2, respectively. Densification was promoted by the highly active reaction product TiB2, and the structural defects formed in the grains. Meanwhile, the good interfacial bonding between TiN and TiB2 grains and the uniform dispersion of ultrafine hBN in the matrix contributed to the excellent bending strength. Moreover, the toughening mechanism of crack deflection and grain pull-out improved the fracture toughness.

Effects of ball milling on the densification behavior, microstructure, and mechanical properties of TiB2–SiC ceramics

High-performance and fine-grained TiB2–SiC composite ceramics were fabricated via hot pressing with ball-milled TiB2 powder doped with SiC. The final product was densified at a relatively low sintering temperature of 1850 °C and brief soaking time of 30 min. The effects of ball milling on TiB2 powder composition and densification behavior, mechanical properties, and microstructures of the ceramic composites were investigated. TiO2 and B2O3 in the raw material were converted to SiO2 via reactions with SiC and Si3N4, thereby forming liquid phases to promote densification. A longer milling time resulted in a small TiB2 grain size. The relative density, Vickers hardness, flexural strength, and fracture toughness of the fabricated TiB2–SiC composites reached 99.0% ± 0.3%, 24.25 ± 1.10 GPa, 647 ± 30 MPa, and 6.43 ± 0.15 MPa m1/2, respectively. The primary toughening mechanisms in the composites were crack deflection, partial crack branching, and crack bridging.

Microstructure and mechanical properties of B4C–TiB2 ceramic composites prepared via a two-step method

B4C–TiB2 ceramic composites were fabricated by a two-step method. First, B4C–TiB2 composite powders were synthesized from TiC–B powder mixtures at 1400 ℃, then mixed with commercial B4C powders by ball milling and the B4C–TiB2 ceramic composites were prepared by hot pressing at 1950 ℃. This two-step method not only effectively refined TiB2 grains, but also allowed the composition of the composites to be freely designed. The microstructure and mechanical properties of the composites were investigated. The results showed that the B4C–TiB2 ceramic composite with a 10 wt% TiB2 content obtained the ideal comprehensive performance, with a volume density, Vickers hardness, bending strength, and fracture toughness of 2.61 g/cm3, 35.3 GPa, 708 MPa, and 5.82 MPa m1/2, respectively. The advantages of the in-situ reaction process were fully exerted by the two-step method, which made a remarkable contribution to the excellent properties of B4C–TiB2 ceramic composites.

Influences of B4C content and particle size on the mechanical properties of hot pressed TiB2–B4C composites

ABSTRACT TiB2 ceramic has attracted many attentions due to its excellent performances both on mechanical and functional properties. However, it is still very difficult to obtain TiB2 bulks with full densification. Herein, TiB2–B4C composites were prepared via hot pressing at 1900°C under the pressure of 35 MPa with TiB2 and B4C as the raw materials. The influences of B4C content (0, 10 vol%, 20 vol% and 30 vol%) and particle size (0.50 µm, 3.12 µm and 7.09 µm) on the phase composition, relative density, microstructure and mechanical properties of TiB2–B4C composites were investigated. The using of 0.50 µm B4C brought more B2O3 which induced oriented growth of TiB2 grains and coarsened the obtained composites. When the raw B4C powders were 3.12 µm and 7.09 µm, the obtained composites with 20–30 vol% B4C could be fully densified. TiB2–30 vol% B4C composite prepared from 3.12 µm B4C powder resulted in the optimal mechanical properties. The bending strength, Vickers hardness, fracture toughness were 671 MPa, 27.93 GPa, and 3.91 MPa·m1/2, respectively. The excellent performance was attributed to its fine and homogenous microstructure.

In-situ graphene platelets formation and its suppression during reactive spark plasma sintering of boron carbide/titanium diboride composites

Boron carbide composites with 10 vol.% TiB2 were prepared by reactive sintering of B4C, TiO2, and carbon black powder mixture at the temperature of 1800 °C, under a pressure of 70 MPa in a vacuum. The combined effects of electric current and in-situ reactions led to a significant overheating of the central part of the sample, while no overheating was observed for hot press and non-reactive SPS processes. A lower electrical resistivity of TiB2 produced a significant Joule heating of boron carbide, leading to its partial decomposition to form gaseous boron and graphene platelets. Homogenous, fully dense and graphene-free samples were obtained when employing an insulating Al2O3 paper during reactive SPS. A short dwell time (30 s after a degassing step of 6 min) and the uniform distribution of fine TiB2 grains were the main advantages of isolated SPS over the reactive hot press and SPS processes, respectively.

The Interactions Between Oxide Film Inclusions and Inoculation Particles TiB2 in Aluminum Melt

In this work, a systematic study on the interactions between aluminum oxide films and TiB2 grain refiner particles and their effect on grain refinement behavior have been conducted. Oxide films were introduced into a commercial purity aluminum melt by adding AA 6061 alloy chips while the grain refiner particles were introduced by adding Al-3T-1B master alloy. Strong sedimentation of TiB2 grain refiner particles was observed in aluminum melt without chip addition during long-time settling. Most of the TiB2 particles were settled and accumulated at the bottom of crucible. In contrast, the sedimentation of TiB2 particles is much less in the melt with the addition of oxide films. A large fraction of TiB2 particles were found to be adhered to the oxide films located at the top part of the crucible, which inhibited the sedimentation of grain refiner particles. TP-1 type tests were also done to study the grain refinement efficiency of Al-3Ti-1B master alloy under different melt cleanliness and settling time. It is found that sedimentation of TiB2 particles greatly reduces the grain refinement efficiency. The introduction of oxide films seems to slightly alleviate the fading effect. This is owing to the strong adherence between the oxide films and TiB2 particles, which leads to a retardation of particle sedimentation.

Design and fabrication of TiB2–TiC–Al2O3 gradient composite ceramic tool materials reinforced by VC/Cr3C2 additives

In this study, TiB2–TiC–Al2O3 gradient composite ceramic tool materials reinforced by VC/Cr3C2 additives were prepared through vacuum hot-press sintering. The effects of gradient combination, thickness ratio and sintering process (sintering temperature and soaking time) on the mechanical properties and microstructures of the composites were investigated. The results showed that the high surface compressive stress produced by the adequate gradient combination and thickness ratios refined the grains and increased the crack growth path. By comparison, the sintering temperature and soaking time influenced the grain size and porosity. In addition, the effects of VC/Cr3C2 on the grain size were analysed, and it was found that VC/Cr3C2 inhibited TiC dissolution and accelerated Al2O3 re-precipitation, which in turn refined the TiC grains and coarsened the Al2O3 grains. Consequently, crack deflection and intergranular fracture occurred around the TiC grains, whereas trans-granular fracture occurred inside the TiB2 and Al2O3 grains because rapid Al2O3 precipitation facilitated TiB2 grain growth. The optimum mechanical properties were hardness of 23.59 GPa, fracture toughness of 7.45 MPa m1/2, and flexural strength of 764.11 MPa.

Preparation of TiB2-20 Wt Pct MoSi2 Composite Material by Mechanochemical Synthesis and Spark Plasma Sintering

The mechanosynthesis process of composite powders for the preparation of a TiB2-20 wt pct MoSi2 composite material from reaction mixtures Ti + B + Mo + Si and Ti + B + MoSi2 in an argon atmosphere has been investigated. Synthesis proceeds according to mechanically stimulated reactions, and, in both cases, ultradisperse composite powders, along with the main phases, contain traces of lower silicides. The mathematical modeling of the distribution of interparticle contacts in the mixtures during solid-phase interaction has revealed a good agreement between the calculated and experimental data of mechanosynthesis. Spark plasma sintering in nonlinear regimes with a sequential increase in the sintering pressure from 6 MPa up to 50 MPa, accompanied by a decrease in the heating rate from 150 °C/min down to 50 °C/min, enables us to reduce the sintering temperature down to 1550 °C and obtain a dense composite with a mean size of TiB2 grains of about 200 nm. The TiB2-20 wt pct MoSi2 composite sintered at 1550 °C surpasses the composite sintered at 1750 °C in Vickers hardness (27.5 ± 3.2 GPa and 24.6 ± 2.2 GPa, respectively) but ranks below it in bending strength (480 ± 32 MPa and 571 ± 24 MPa, respectively).

Dense and core‐rim structured B4C‐TiB2 ceramics with Mo‐Co‐WC additive

AbstractB4C‐TiB2 ceramics (TiB2 ranging 5~70 vol%) with Mo‐Co‐WC as the sintering additive were prepared by spark plasma sintering. In comparison with B4C‐TiB2 without additive, the enhanced densification was evident in the sintered specimen with Mo‐Co‐WC additive. Core‐rim structured grain was observed around TiB2 grains. The interface of the rim between TiB2 and B4C phases demonstrated different feature: the inner borderline of the rim exhibited a smooth feature, whereas a sharp curved grain boundary was observed between the rim and the B4C grain. The formation mechanism is discussed: the epitaxial growth of (Ti,Mo,W)B2 rim around the TiB2 core may occur as a result of the solid solution and dissolution‐precipitation between TiB2 phase and the sintering additive. It was revealed that the fracture toughness increased as the content of TiB2 content increased, alongside the decreased hardness. B4C‐30 vol% TiB2 specimen demonstrated the optimal combination of mechanical properties, reaching Vickers hardness of 24.3 GPa and fracture toughness of 3.33 MPa·m1/2.

Microstructure and mechanical property of (TiB2‐SiC) agglomerate‐toughened B4C‐TiB2‐SiC composites

AbstractB4C‐TiB2‐SiC composites toughened by (TiB2‐SiC) agglomerates were prepared via reactive hot pressing with B4C and TiSi2 as raw materials. Phase composition, microstructure, and mechanical properties of the fabricated composites were investigated. The function of (TiB2‐SiC) agglomerates was analyzed, and the strengthening and toughening mechanism were also discussed. Results indicated that some of the in situ formed TiB2 and SiC were interlocked to form special (TiB2‐SiC) agglomerates in the matrix. The good comprehensive performances of 510 MPa flexural strength, 5.84 MPa·m1/2 fracture toughness, and 31.93 GPa hardness were obtained in the composites fabricated with 30 wt% TiSi2. The in situ introduced fine TiB2 and SiC grains refined the grains of B4C due to the pinning effect, which enhanced the strength. The special (TiB2‐SiC) agglomerates and the existing toughening phenomena such as crack deflection, branching, and microcrack regions induced by the mismatch of thermal expansion coefficients, had cumulative effects on improving the fracture toughness.

Forming of the Ti6Al4V-60 %TiB2 metal-ceramic microcomponent under coupled multi-physical fields for improved microstructures and mechanical performances

Abstract In the presented study, a coupled multi-physical fields activation forming method was utilized to form the Ti6Al4V/TiB2 metal ceramic microcomponent with 60wt% TiB2 powders and the effects of the processing parameters on the microstructure, densification and mechanical performance of the formed sample were studied. The result shows that a relative density, 96.43 %, of the formed sample is achieved when the case of temperature 1500°C, heating rate 30°C /s, pressure 125MPa and dwell time 1 min, is used. Microstructures of the formed sample suggest the forming process involves the formation of TiB nanocrystalline in the Ti matrix due to the chemical reaction between the TiB2 and Ti phases and the formations of the defects in TiB2 grains and the liquid phase of Ti. Many stacking faults, lattice distortion and vacancy defects are produced in the TiB2 grain owing to the particles’ deformation during the forming process. The liquid Ti phase is formed in some local areas due to the Joule heat generated by the current. The variation tendency of Vickers hardness is in accordance with that of relative density, which initially shows a significant increase and then decreases with the forming time and a peak hardness of 1690 HV is achieved.

Tuning the combustion process during reactive sintering of high-performance ceramics by employing solid solutions as reactants

In this work, dense TiB2-B4C based ceramics with different amounts of hBN additions were spark plasma sintered at 1700−1850 °C through in-situ reactions involving with TiCxN1-x (x = 0.5 and 0.7) and boron. The molar Gibbs’ free energy of TiCN is lower than that of TiC and TiN, thereby the boronizing of TiCN is more favorable in multiple steps which suppressed the combustion process in the TiCN-B system. Taking advantage of this, the reaction rate in the TiCN-B system was dragged to accompany with that of densification, resulting that nanometric TiB2 grains were gradually produced and microstructures composed of B4C-hBN reinforcement and TiB2 –hBN(C) matrix were finally built. Although hBN additions reduce the Young’s modulus, TiB2-B4C composites with 17.4 vol% hBN additions densified at 1700 °C still exhibit excellent mechanical properties. The present study suggests solid solution powders are a class of promising reactants for achieving nanoceramics with better performance.

Nanoceramic composites with duplex microstructure break the strength-toughness tradeoff

There is a strength and fracture toughness tradeoff in nanoceramic composite. The strength varies reciprocally with the grain size whereas the toughness contributed by compressive residual stress increases with the dimension of the second phase. In this work, a novel duplex microstructure with reinforced clusters composing of nanosized grains was proposed and validated using a model system of B4C-TiB2 ceramics densified by carbide boronizing. As-obtained ceramics exhibit excellent combined mechanical properties at room temperature, including Vickers hardness, Young’s modulus, flexural strength and fracture toughness (by surface crack in flexure method) of 32.1 ± 2.7 GPa, 506.9 ± 2.0 GPa,1175 ± 71 MPa and 5.1 ± 0.4 MPa m0.5, respectively. Both strength and toughness are at least ∼30 % higher than the counterparts with similar composition but homogenously distributed TiB2 grains. Graphite onion was confirmed to be an intermediate product during reactive sintering, it facilitated the grain pullout during fracture and retained the nanometric TiB2 grain in the cluster, both of which also contribute the toughening and strengthening mechanisms in the B4C-TiB2 ceramics.

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.

Preparation of ultra-high temperature SiC–TiB2 nanocomposites from a single-source polymer precursor

SiC–TiB2 ceramic nanocomposites are valuable ultra-high temperature materials, which are rarely prepared from preceramic polymers. In this work, we synthesized SiC–TiB2 nanocomposites from a new preceramic polymer called titanium- and boron-modified polycarbosilane (TB–PCS). The polymer structure was characterized by Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance (NMR) spectroscopy. The structure, composition, and morphology of the resulting ceramic products were investigated by FT-IR, X-ray diffraction, and transmission electron microscopy. The elements of titanium and boron were incorporated into the preceramic polymer, and nanoscale TiB2 and β-SiC grains generated in situ were detected in the pyrolyzed ceramic products at temperatures higher than 1400 °C. The new preceramic polymer presents a novel approach to preparing SiC–TiB2 nanocomposites.