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Hexagonal BN particles (BNp) reinforced fused SiO2 matrix composite (BNp/SiO2) was regarded as a very important candidate material for potential applications on wave transparent thermal protection parts. In this study, pressurelessly sintered 15 vol% BNp/SiO2 composites were prepared by cold isostatic pressing (CIP) and gel-casting routes, respectively, using two kinds of fused silica powders with different particle sizes (5.82 and 3.24 μm in d50, respectively) as starting SiO2. It was demonstrated that the microstructure and mechanical properties of the composites were well dependent on the preforming techniques of green compacts. Gel-casting preforming route has an overwhelming superiority over CIP route on the thermal stability of fused SiO2 matrix against α-cristobalite crystallization, sinterability, and thus the mechanical properties. Using the finer fused silica (3.24 μm in d50) as the starting SiO2, the 15 vol% BNp/SiO2 composite sintered at 1375°C get a density of 2.05 g/cm3, the silica matrix primarily keep amorphous phase with uniformly dispersed nanosized α-cristobalite crystallites (<5 nm in diameter). The bending strength, fracture toughness and Young's modulus all reach the highest values, 101.5 ± 4.3 MPa, 1.57 ± 0.04 MPa·m1/2 and 61.3 ± 2.4 GPa, respectively. Microstructure characteristics, chemical bond information and mechanical properties of the as-prepared composites are correlated with their preforming routes, starting fused SiO2 particle size, sintering temperature, etc. based on X-ray diffractometry, scanning electron microscope, transmission electron microscope, high resolution transmission electron microscope, and FT-IR analysis. [ABSTRACT FROM AUTHOR]

Abstract: Yb- and Y-doped α-SiAlON ceramics were effectively bonded by spark plasma sintering in less than 20min without using any interlayer materials at 1650–1700°C. The microstructures and mechanical properties of the joints were investigated by means of SEM, STEM, EDX, and three-point bending tests. The results showed that α-SiAlON joint formation was accompanied by fundamental rare earth diffusion. The intergranular liquids in the α-SiAlON ceramics at the bonding temperatures provided the diffusion paths for the species. α-SiAlON grain growth across the joining interfaces modified the joint microstructures to secure high bonding strength. [Copyright &y& Elsevier]

Monolithic α-SiC particles and in situ β-Si3N4-reinforced barium aluminosilicate (BAS) glass ceramic matrix composites with good mechanical properties were obtained by spark plasma sintering. However, attempts at the synthesis of ternary phase composites in order to maximize the reinforcing effects by co-adding α-SiC and β-Si3N4 were only partly successful. β-Si3N4 grain growth was remarkably hindered by the coexistent α-SiC, thus the resultant composite suffered a loss of reinforcement efficiency. [Copyright &y& Elsevier]

Abstract: A 20vol.% ZrCp/W composite is fabricated by hot-pressing, and its mechanical properties can be significantly improved by the addition of ZrC particles. On the other side, the residual pores within ZrC particles clustering regions which are some latent microcrack sources are mainly caused by the relative low sinterability of ZrC particles. In order to eliminate the pores within the particle clusters, the as-sintered composite is annealed at 2300°C for 1h. The microstructure of the annealed composite becomes more uniform and densified. Components of the as-sintered and annealed composites are composed of a dilute solid solution tungsten-matrix, (Zr, W)C solid solution particles and a new W2C phase, but the content of W2C phase in the annealed composite increases. After annealing, the strength properties of the composite decrease, but its plasticity increases. [Copyright &y& Elsevier]

Abstract: A detailed microstructural and mechanical characterization of a PM processed 20vol.% ZrCp/W composite disk indicates that the composite from the edge to the center of the disk has different phase compositions and mechanical properties. The difference is caused by a temperature gradient in the disk during heating and cooling. [Copyright &y& Elsevier]

In this study, amorphous SiBCN powders were mechanical milled and consolidated by low-temperature sintering at different pressure to provide an insight into the densification and mechanical behavior of dense amorphous SiBCN monoliths. Results show that the mechanical properties undergo a gradual variation closely related to the microstructural evolution. The increased degree of densification with few defects and free volume results in significantly improving Young’s modulus and nano hardness in case of high pressure application. The consolidation at relatively low pressure (3 GPa) occurs by heavy deformation with the support of limited short-range diffusion, whereas the densification at higher pressure (5 GPa) is mostly diffusion controlled showing a classic sintering mechanism. At 1000 °C, higher pressure (5 GPa) suppresses crystallization leading to an effective solid-state reaction, while SiBCN monoliths consolidated by lower pressure (3–4 GPa) show a hybrid structure of dominant amorphous phases and few nanocrystals. [ABSTRACT FROM AUTHOR]

Abstract: TaC/SiC composites with 5–40vol.% 6H–SiC were fabricated by spark plasma sintering at 1800°C for 5min. Effects of SiC concentrations on the densification, microstructure, and mechanical properties of the materials were investigated. The results showed the densification process of the TaC/SiC composites was composed of six sequent stages. SiC addition was effective in eliminating the closed porosities in the final stage to yield fully dense TaC/SiC composites at 20vol.% SiC concentrations and above. TaC grain sizes decreased with SiC concentration increase. The 40vol.% SiC composition had the highest flexure strength and fracture toughness up to 703MPa and 6.8MPam1/2 due to the reinforcement of the SiC agent. The TaC/SiC composites with 20 and 40vol.% SiC showed good flexural strength at 1400°C. [Copyright &y& Elsevier]

Abstract: Nano-sized Si–B–C–N powders nearly amorphous with different mole ratio of Si/C were prepared by mechanical alloying (MA) technique using cubic silicon (c-Si), hexagonal boron nitride (h-BN) and graphite powder (Cp) as starting materials, then consolidated at 1800°C under a pressure of 40MPa for 3min by spark plasma sintering (SPS). Sub-micrometer sized β-SiC and nano-sized BCN phase were formed as the final components in the ceramics. The grain size of the β-SiC tend to be a little coarser with the increase of the Si/C ratio as well as their total content, but no changes are observed for the fine sub-micrometer structure characteristics of β-SiC and BCN grains. Mechanical properties of the Si–B–C–N ceramics were found remarkably increased with the increase of the mole ratio of Si/C and their total relative content. Thermal physical properties, including thermal diffusivity, heat capacity, thermal conductivity, as well as thermal expansion coefficient were also studied. [Copyright &y& Elsevier]

Abstract: cBN/β-SiAlON composites with different cBN contents were fabricated by spark plasma sintering (SPS) process. The densification, thermal stability of cBN, microstructure and mechanical properties of the resultant composites were investigated. The addition of cBN particles to β-SiAlON could increase the Vickers hardness, flexural strength and fracture toughness of β-SiAlON. It is attributed to the high density, no obvious cBN to hBN transformation and good interface bonding between cBN grains and β-SiAlON matrix. [Copyright &y& Elsevier]

Abstract: Short-carbon-fiber-reinforced silicon carbide composites were prepared by hot-pressing with SiC powder, Polycarbosilane as precursor polymer and MgO–Al2O3–Y2O3 as sintering additives. The phase composition, microstructure and mechanical properties of the composites with different Polycarbosilane content were investigated. The results showed that, dense composites could be prepared at a relatively low temperature of 1800°C via the liquid-phase-sintering mechanism and the highest mechanical property was obtained for the composites with 20wt.% PCS and 8wt.% sintering additives. The amorphous interphase formed during sintering process in the composites not only contributed to the densification of the composites, but also improved the fiber–matrix bonding. The nano-silicon carbide derived from Polycarbosilane, could also play a role of improving the relative density of the composites. [Copyright &y& Elsevier]

Abstract: Y-α-SiAlON (Y1/3Si10Al2ON15) ceramics with 5wt.%BaAl2Si2O8 (BAS) as an additive were synthesized by spark plasma sintering (SPS). The kinetic of densification, phase transformation sequences and grain growth during sintering process were investigated. Full densification could be achieved by 1600°C without holding and using a heating rate of 100°Cmin−1, but the transformation from α-Si3N4 to α-SiAlON is not completed simultaneously with the densification process. The equilibrium phase assemblage could be reached after SPS at 1800°C for 5min and the resultant material possesses self-reinforced microstructure with high hardness of 19.2GPa and fracture toughness of 6.8MPam1/2. The complete crystallization of BAS is beneficial to the high temperature mechanical properties. The obtained could maintain the room strength up to 1300°C. [Copyright &y& Elsevier]