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The effect of LaB6 on the densification and microstructure of pressure‐less sintered 0.4B4C–0.4SiC–0.2ZrB2 ternary ceramic with eutectic composition was investigated. The Vickers hardness, bending strength, and fracture toughness of the quaternary ceramic were discussed based on the microstructural characteristics. The densification of the 0.4B4C–0.4SiC–0.2ZrB2 ceramic was enhanced with increasing LaB6 content from 0 to 70 mol% (the proportion to B4C–SiC–ZrB2). When the LaB6 content was 50 mol%, the densification rate of the composite ceramic reached a peak. The 0.27B4C–0.27SiC–0.13ZrB2–0.33LaB6 quaternary composite ceramic has reached a density of over 95% after being sintered at 2 100°C for 1 h. The B4C and SiC phases had refined grains of 1–3 µm with intragranular structures in the as‐sintered ceramics. The hardness and strength reached 17.9 ±.8 GPa and 307 ± 38 MPa, respectively. Crack deflection and branching were ascribed to the improved fracture toughness of 3.78 ±.26 MPa·m1/2. This study provides new ideas for fabricating dense non‐oxide ceramic composites with enhanced properties. [ABSTRACT FROM AUTHOR]

In this study, Si3N4−Si2N2O composite ceramics were prepared through a two‐step combination of the direct nitriding method and spark plasma sintering method with diamond‐wire saw silicon waste in the photovoltaic industry as raw material. The whole holding time at the constant temperature of the preparing process only lasts 35 min, in which the nitriding time only takes 30 min and the sintering time only takes 5 min. The effects of the Fe2O3 additive on the nitriding and sintering process were investigated in detail. The results show that the Fe2O3 additive accelerates the nitriding process by promoting the formation and diffusion of the gas phase and reducing the apparent activation energy of the reaction between the gas phase containing silicon and N2. Meanwhile, the Fe2O3 additive also promotes the sintering process by lowering the eutectic temperature of the SiO2−Al2O3 and the SiO2−Y2O3 binary system. The optimal technical parameters follow the nitriding temperature of 1400°C, the nitriding time of 30 min, the sintering temperature of 1800°C, and the sintering time of 5 min. The Si3N4−Si2N2O composite ceramic prepared under the above conditions exhibits good performance with an apparent porosity of 2.7%, Vickers hardness of 16.54 GPa, and fracture toughness of 4.1 MPa·m1/2. [ABSTRACT FROM AUTHOR]

Although the addition of other phases into TiB2 matrix to form ceramic composites has been widely used to improve the mechanical properties of monolithic TiB2 ceramics, it is still difficult to greatly enhance the flexural strength and fracture toughness simultaneously. In this work, TiB2–TiC–SiC composites were successfully prepared by reactive spark plasma sintering of Ti3SiC2–B4C–Ti powder mixtures. During the sintering process, TiB2 grains grew into an elongated morphology, endowing the composites with integrated high strength and high toughness. The growth mechanism of TiB2 grains was attributed to the evaporation–condensation kinetics induced by the presence of B2O3. These findings can accelerate the exploration of ceramic composites with excellent comprehensive properties. [ABSTRACT FROM AUTHOR]

B4C-45vol.% (TiZrHfNbTa) B2 composite was prepared by in-situ reactive spark plasma sintering at 2000°C using powders of transition metal carbides and amorphous boron as raw materials. The composite reached a relative density of over 97% Within 6 min. The simultaneously generated B4C and (TiZrHfNbTa) B2 phases had homogeneous microstructures with particle sizes ~ 1 μm, and Nb segregations in (TiZrHfNbTa) B2 grains were detected. The composite obtained a high three-point bending strength of 422 MPa, a Vickers hardness of 20.9 GPa and a fracture toughness of 5.48 MPa m1/2, respectively. The fine grain and solid solution effects are the main reasons for the improved properties. The crack deflection, branching, and bridging mechanisms observed are also helpful for an improved fracture toughness of the composite. This work provides a fast, convenient method of preparing novel B4C high-entropy boride composite ceramics with enhanced properties. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract: High electrical resistance and low fracture toughness of B4C ceramics are 2 of the primary challenges for further machining of B4C ceramics. This report illustrates that these 2 challenges can be overcome simultaneously using core‐shell B4C‐TiB2&TiC powder composites, which were prepared by molten‐salt method using B4C (10 ± 0.6 μm) and Ti powders as raw materials without co‐ball milling. Finally, the near completely dense (98%) B4C‐TiB2 interlayer ceramic composites were successfully fabricated by subsequent pulsed electric current sintering (PECS). The uniform conductive coating on the surface of B4C particles improved the mass transport by electro‐migration in PECS and thus enhanced the sinterability of the composites at a comparatively low temperature of 1700°C. The mechanical, electrical and thermal properties of the ceramic composites were investigated. The interconnected conductive TiB2 phase at the grain boundary of B4C significantly improved the properties of B4C‐TiB2 ceramic composites: in the case of B4C‐29.8 vol% TiB2 composite, the fracture toughness of 4.38 MPa·m1/2, the electrical conductivity of 4.06 × 105 S/m, and a high thermal conductivity of 33 W/mK were achieved. [ABSTRACT FROM AUTHOR]

Ternary B 4 C-SiC-ZrB 2 ceramics with eutectic compositions were prepared in situ by reactive spark plasma sintering at 1600–1800 °C. The two-step sintering, including an in situ reaction 2ZrSi 2 + 5B 4 C+ 3 C= 4B 4 C+ 4SiC+ 2ZrB 2 at 1600 °C and sintering at 1800 °C, is superior to combined one-step sintering at 1800 °C. The as-sintered 40B 4 C-40SiC-20ZrB 2 composites (sample 16R18) had grain sizes of microns with a density over 97%. The Vickers hardness, bending strength and fracture toughness of the ternary ceramic reached 28.6 GPa, 631 MPa and 5.50 MPa m1/2 respectively. Crack deflection and branching were ascribed to improved fracture toughness. The elongated plate-like ZrB 2 grains not only had toughening effects but also helped to lower the percolation threshold of the electrical conductivity. The 16R18 sample possessed an electrical conductivity of 5.38 × 104 S/m, owing to the tiny conductive ZrB 2 grains with aspect ratios of 3–4, which is beneficial for the electro-discharge machining of the B 4 C-SiC based composites. • The solid phase reaction at 1600 °C and densification at 1800 °C is advanced in obtaining B 4 C-SiC-ZrB 2 composites. • The two-step RSPS-ed B 4 C-SiC-ZrB 2 composite has grain sizes of 0.5–3 µm with an enhanced density of 97.6%. • The in situ elongated ZrB 2 grains are helpful to good comprehensive mechanical properties and electrical conductivity. [ABSTRACT FROM AUTHOR]

To reduce the negative effects of the long-time and B 2 O 3 phase on the traditional sintering process for B 4 C-based composite ceramics, nearly fully dense B 4 C–VB 2 composite ceramics were prepared by reactive spark plasma sintering (SPS) technology at 2000 °C with B and V 8 C 7 powders as raw materials in this paper. The effects of the degassing time during SPS on the microstructure and the mechanical properties of the final products were investigated in detail. The results revealed that the proper degassing time was beneficial for the vent of B 2 O 3 during the sintering process, which refined the grain size, promoted densification and improved the mechanical properties of the composite ceramic. However, the redundant degassing time increased the holding time at high temperature, resulting in abnormal grain growth and mechanical performance deterioration. In the present work, the optimal degassing time was 6 min, and the final product prepared under the above conditions exhibited excellent comprehensive performance with a relative density of 99.2%, Vickers hardness of 31.2 GPa, bending strength of 654 MPa and fracture toughness of 5.7 MPa m1/2. In addition, the strengthening and toughening mechanisms of the products were mainly attributed to the residual thermal stresses and bridging structure caused by the fine B 4 C and VB 2 grains distributed uniformly. [ABSTRACT FROM AUTHOR]

Intra/inter type super hard B 4 C-based composites were fabricated by two-step spark plasma sintering at 1600–1800°C with ZrSi 2 , B 4 C and C additives under 40 MPa. The ZrSi 2 transient liquid and in situ ternary (B 4 C-SiC-ZrB 2) eutectic composition assisted the densification of the B 4 C matrix. The as-sintered composites had a unique microstructure of inter- and intra- SiC (ZrB 2) secondary phases in the B 4 C matrix with strong bondings. The fully dense B 4 C-40 wt%(B 4 C-SiC-ZrB 2) composite possessed a Vickers hardness, flexural strength and fracture toughness of 31.2 GPa, 542 MPa and 5.08 MPa·m0.5 respectively, owing to the strengthening and toughening effect of both the inter- and intra- particles. The inter- elongated ZrB 2 phase also provided an enhanced electrical conductivity of 230.7 S/m. The composite was facilitated to wire electrical discharge machining with a material removal rate of 2.84 mm3/min, which is ten times that of the monolithic B 4 C ceramic. • ZrSi 2 transient liquid and in situ (B 4 C-SiC-ZrB 2) assist densification of B 4 C. • Inter- and intra- SiC (ZrB 2) particles disperse in fully dense B 4 C ceramic. • Inter- and intra- particles are helpful to good mechanical and WEDM properties. [ABSTRACT FROM AUTHOR]

Previous research have reported that B 4 C–TiB 2 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 B 4 C–TiB 2 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 B x C–TiB 2 (x > 4) composites were obtained. The increasing B content improved the hardness and fracture toughness but decreased the flexural strength of B x C–TiB 2 (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. [ABSTRACT FROM AUTHOR]