In order to understand the influence of the mechanisms of ZrC nanoparticles on the high-temperature mechanical properties of C-SiC ceramic matrix composites, the mechanical properties were measured from room temperature (RT) to 1600 °C under vacuum. The microstructures features were characterized by scanning electron microscopy. In comparison with the composites without ZrC nanoparticles, the ZrC-modified composite presented better mechanical properties at all temperatures, indicating that the mechanical properties could be improved by the ZrC nanoparticles. The ZrC nanoparticles could reduce the residual silicon and improve the microstructure integrity of composite. Furthermore, the variation of flexural strength and the flexural modulus showed an asynchronous trend with the increase of temperature. The flexural strength reached the maximum value at 1200 °C, but the highest elastic modulus was obtained at 800 °C. The strength increase was ascribed to the decrease of the thermally-induced residual stresses. The degradation of mechanical properties was observed at 1600 °C because of the microstructure deterioration and the formation of strongly bonded fiber–matrix interface. Therefore, it is concluded that the high temperature mechanical properties under vacuum were related to the consisting phase, the matrix microstructure, and the thermally-induced residual stresses.

Thermally stable high-performance phenolic resin aerogels (PRAs) are of great interest for thermal insulation because of their light weight, fire retardancy and low thermal conductivity. However, the drawbacks of PRA synthesis, such as long processing time, inherent brittleness and significant shrinkage during drying, greatly restrict their wide applications. In this work, PRAs were synthesized at ambient pressure through a near-net shape manufacturing technique, where boron-containing thermosetting phenolic resin (BPR) was introduced into the conventional linear phenolic resin (LPR) to improve the pore characteristics, mechanical properties and thermal performances. Compared with the traditional LPR-synthesized aerogel, the processing time and the linear shrinkage rate during the drying of the PRAs could be significantly reduced, which was attributed to the enhanced rigidity and the unique bimodal pore size distribution. Furthermore, no catastrophic failure and almost no mechanical degradation were observed on the PRAs, even with a compressive strain of up to 60% at temperatures ranging from 25 to 200 °C, indicating low brittleness and excellent thermo-mechanical stability. The PRAs also showed outstanding fire retardancy. On the other hand, the PRAs with a density of 0.194 g/cm³ possessed a high Young’s modulus of 12.85 MPa and a low thermal conductivity of 0.038 W/(m·K).

In order to investigate the microstructure evolution and the degradation mechanism of SiC fiber in a high-temperature oxidative environment, the SiC fiber was thermally exposed at temperature up to 1600 °C in air. The morphologies of the surface and fracture surface were characterized by scanning electron microscopy. The consisting phase and crystallite size were analyzed by X-ray diffractometer. The mechanical properties of SiC fiber was characterized by a single-fiber tensile test technique. It was found that an obvious grain coarsening occurred at temperature above 1400 °C. A visible silica layer was formed at 1300 °C, and the morphology of silica layer was dependent on the exposure temperature. At 1400 °C, fiber surface formed a thick silica layer with cracks, while the silica layer exhibited a multilayered structure at 1600 °C. As for the tensile strength of fiber, it firstly decreased to about 1 GPa at 1200 °C, then the strength was maintained at 1400 °C. After thermal exposure at 1500 °C and 1600 °C, the strength decreased again. The degradation of mechanical properties was attributed to the grain coarsening and the decomposition of amorphous phase in fiber. Particularly, the decomposition of amorphous phase would damage the structure integrity of fiber. The current work would provide a valuable reference for research and application of SiC fiber.

Novel hierarchical SiC–SiO₂heterostructures were synthesized on a graphite paper substrateviaa catalyst free method.

High-entropy diboride-based (MeB₂-based) ceramics are promising high-temperature structural materials because of their excellent mechanical properties, high-temperature stability, and oxidation resistance. In order to achieve low-temperature sintering of the high-entropy ceramics, a novel preparation method of high-entropy (Ti,Zr,Nb,Mo,W)B₂-SiC ceramics based on reactive sintering of pre-alloyed solid-solution metals and nonmetals of Si, C, B₄C was conducted in the current work. Mechanical alloying behavior of the mixed metal powders, as well as the phase composition, microstructure, mechanical properties, and oxidation behavior of the as-sintered MeB₂-SiC ceramic were investigated. The XRD, SEM, and EPMA results indicated that the primary MeB₂ solid-solution and SiC phases could be successfully formed during reactive sintering at a relatively low temperature of 1650 °C. The as-sintered MeB₂-SiC ceramics had a high relative density of 97.8% and high mechanical properties (hardness of 19.74 ± 0.8 GPa, flexure strength of 533 ± 38 MPa, and fracture toughness of 6.01 ± 0.77 MPa·m^1/2). Combining the oxidation behavior and microstructure evolution of the oxidation layer, a continuous and relatively dense MeO_x-SiO₂ oxidation layer was gradually formed and covered on the external surface, leading to decelerating oxidation behavior after an oxidation exposure time of 10 min.