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Continuous silicon carbide fiber–reinforced silicon carbide matrix composites (SiC f /SiC) are promising candidate materials for nuclear applications. In this paper, three–dimensional SiC f /SiC composites were fabricated using polymer infiltration and pyrolysis method. Interface properties of SiC f /SiC composites that were irradiated with 3 MeV Si ions to 1 dpa and 5 dpa at room temperature were studied using single-fiber push–out test, Raman spectroscopy, and transmission electron microscopy. Results indicate that, after being irradiated with different doses of Si ions, SiC f /SiC composites have weaker interfacial shear strength compared to that of samples before irradiation. The greater that the ion irradiation damage is, the lower that the interfacial shear strength is. With an increase in ion irradiation dose, the strength of the disordered (D) and graphitic (G) characteristic peaks in Raman spectra of SiC f /SiC composite decreases, and full width at half–maximum broadens. TEM micrographs show that ion irradiation damaged the continuity of SiC f /SiC composites, and microcracks appeared at pyrocarbon interface between the fiber and matrix. The crystallinity of SiC was lowered, the grain size shrank, and the ordered C phase became amorphous noncrystalline structure. [ABSTRACT FROM AUTHOR]

Continuous silicon carbide fiber reinforced silicon carbide matrix composites (SiC f /SiC) are promising candidate materials for nuclear applications. In this paper, three–dimensional (3D) SiC f /SiC composites were fabricated using the polymer infiltration and pyrolysis (PIP) process at different pyrolysis temperatures (i.e. 1100, 1300 and 1500 °C). The effect of the pyrolysis temperature on the thermal and mechanical properties of the SiC f /SiC composites was investigated with a laser flash method, a three–point bending test and a single–edged notch beam method. The results indicated that the thermal diffusivity of the SiC f /SiC composites improved considerably with increasing pyrolysis temperatures, due to a higher degree of crystallization in the matrix. Additionally, as the testing temperature increased, the thermal diffusivity of the SiC f /SiC composites gradually decreased. With increasing pyrolysis temperatures, the mechanical properties of the SiC f /SiC composites first increased and later decreased. The SiC f /SiC composites fabricated at 1300 °C had the highest average flexural strength and fracture toughness, i.e. 535.6 MPa and 17.3 MPa m 1/2 , respectively. [ABSTRACT FROM AUTHOR]

Continuous silicon carbide fiber–reinforced silicon carbide matrix (SiC f /SiC) composites have developed into a promising candidate for structural materials for high–temperature applications in aerospace engine systems. This is due to their advantageous properties, such as low density, high hardness and strength, and excellent high temperature and oxidation resistance. In this study, SiC f /SiC composites were fabricated via polymer infiltration and pyrolysis (PIP) with the lower–oxygen–content KD–II SiC fiber as the reinforcement; a mixture of 2,4,6,8–tetravinyl–2,4,6,8–tetramethylcyclotetrasiloxane (V4) and liquid polycarbosilane (LPCS), known as LPVCS, was used as the precursor; while pyrolytic carbon (PyC) was used as the interface. The effects of oxidation treatment at different temperatures on morphology, structure, composition, and mechanical properties of the KD–II SiC fibers, SiC matrix from LPVCS precursor conversion, and SiC f /SiC composites were comprehensively investigated. The results revealed that the oxidation treatment greatly impacted the mechanical properties of the SiC fiber, thereby significantly influencing the mechanical properties of the SiC f /SiC composite. After oxidation at 1300 °C for 1 h, the strength retention rates of the fiber and composite were 41% and 49%, respectively. In terms of the phase structure, oxidation treatment had little effect on the SiC fiber, while greatly influencing the SiC matrix. A weak peak corresponding to silica (SiO 2 ) appeared after high–temperature treatment of the fiber; however, oxidation treatment of the matrix led to the appearance of a very strong diffraction peak that corresponds to SiO 2 . The analysis of the morphology and composition indicated cracking of the fiber surface after oxidation treatment, which was increasingly obvious with the increase in the oxidation treatment temperature. The elemental composition of the fiber surface changed significantly, with drastically decreased carbon element content and sharply increased oxygen element content. [ABSTRACT FROM AUTHOR]

Silicon-containing hyperbranched polymers (Si-HBPs) have drawn much attention due to their promising applications. However, the construction of Si-HBPs, especially those containing functional aromatic units in the branched backbones by the simple and efficient Piers-Rubinsztajn (P–R) reaction, has been rarely developed. Herein, a series of novel hyperbranched polycarbosiloxanes were prepared by the P–R reactions of methyl-, or phenyl-triethoxylsilane and three Si–H containing aromatic monomers, including 1,4-bis(dimethylsilyl)benzene, 4,4′-bis(dimethylsilyl)-1,1′-biphenyl and 1,1′-bis(dimethylsilyl)ferrocene, using B(C6F5)3 as the catalyst for 0.5 h at room temperature. Their structures were fully characterized by Fourier transform infrared spectroscopy, 1H NMR, 13C NMR, and 29Si NMR. The molecular weights were determined by gel permeation chromatography. The degrees of branching of these polymers were 0.69–0.89, which were calculated based on the quantitative 29Si NMR spectroscopy. For applications, the ferrocene-linked Si-HBP can be used as precursors to produce functional ceramics with good magnetizability after pyrolysis at elevated temperature. [ABSTRACT FROM AUTHOR]