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The carbon fiber (T300-6K) with a three-dimensional four-way braiding structure was selected as the reinforcement, and the 3D-Cf/6061Al composites at different braiding angles (10°, 20° and 30°) were prepared by the pressure infiltration method, and the effects of different braiding angles on the mechanical properties of the composites were discussed. It is found that the pressure infiltration avoids the weak bonding force between the carbon fiber and the aluminum matrix to a certain extent, so that a better infiltration effect can be obtained. The bending performance of the composites become worse with the increase of braiding angle. With the increase of braiding angle, the strain force of the composites also increases, and the greater the elongation is, the better the toughness is. When the braiding angle was larger, the transverse component force of the fiber was larger, the unevenness of the fiber fracture surface increases, the pulling phenomenon was obvious.

A ZrSi2-SiC/SiC gradient coating system was designed to reduce the thermal stress of anti-oxidation coatings for C/C composites and prolong their anti-oxidation time at a high temperature. The SiC transition layer was prepared by pack cementation and the gradient ZrSi2-SiC outer coatings with different ZrSi2 contents added were deposited by supersonic air plasma spraying (SAPS). The micro-morphologies and phase compositions of the coatings were studied by SEM, EDS, XRD, and TG/DSC, and their anti-oxidation performances were tested by a static oxidation experiment. The findings suggested that the gradient coating with 30 wt.% ZrSi2 content displayed the optimum and dense microstructure without obvious pores and microcracks, compared with the other three proportional coatings. During the oxidation test, because of the oxidation reaction of ZrSi2 and SiC phases, a large amount of silica was formed in the coating to fill the pores and microcracks and densify the coating further. Oxidation products ZrO2 and ZrSiO4, having a high melting point and outstanding anti-oxidation property, were embedded in the SiO2 glass layer to reduce the layer volatilization rate and improve the ability to block oxygen. Therefore, the specimen with 30 wt.% ZrSi2 still kept mass gain after 188 h oxidation time at 1500 °C. However, when the oxidation time was increased to 198 h, it had a mass loss of 0.1%, because the coating compactness was destroyed by the escape of the oxidation gases. [ABSTRACT FROM AUTHOR]

-doped nanopowders have been prepared via combustion synthesis of the silicon and carbon system in a 0.1 MPa nitrogen atmosphere under different reaction time, using copper as the dopant and PTFE as the chemical activator, respectively. X-ray diffraction, scanning electronic microscope and Raman spectra have been used to characterize the phase and morphology of prepared nanopowders. Results indicate that the lattice constant of prepared -doped nanopowder decreases with extending reaction time. The prepared nanopowders have fine spherical particles and narrow particle size distribution and the particle size increases with increasing reaction time. The electric permittivities of prepared -doped nanopowders in the frequency range of 8.2-12.4 GHz have been determined. The real part ε′, imaginary part ε′′ and dielectric loss tgδ of complex permittivity decrease with increasing reaction time. All prepared -doped nanopowder exhibits good microwave absorption property in the frequency range of 8.2-12.4 GHz. Cu-doped SiC nanopowders have been prepared via combustion synthesis of the silicon and carbon system in 0.1 MPa nitrogen atmosphere under different reaction time, using copper as the dopant and PTFE as the chemical activator, respectively. All the prepared Cu-doped SiC nanopowder exhibits good microwave absorption property in the frequency range of 8.2-12.4 GHz. [ABSTRACT FROM AUTHOR]

In this work, Ti3SiC2/nano-Cu powders were synthesized by two different routes: mechanical ball-milling and electroless-plating process. The phase composition was identified by XRD and the microstructure was observed by SEM. Both the real and imaginary parts of complex permittivity for Ti3SiC2/nano-Cu powders prepared by electroless-plating process are higher because of the uniformly dispersing nano-Cu particles. In addition, the influences of concentration on the dielectric and microwave absorption properties were also investigated. As the content of Ti3SiC2/nano-Cu rises from 40 to 70 wt%, the real part of complex permittivity increases from 8.81 to 7.37 to 24.73-20.24, while the imaginary part enhances from 0.78-1.65 to 8.02-7.71 in the frequency range of 8.2-12.4 GHz. The most favorable absorption performance is obtained for the Ti3SiC2/nano-Cu/paraffin mixture containing 60 wt% filler with a thickness of 1.8 mm. The effective absorption bandwidth below − 10 dB is obtained in 9.2-12.2 GHz with a minimum reflection loss of − 20.42 dB at 10.88 GHz. [ABSTRACT FROM AUTHOR]

Dense SiO 2 -coated Ti 3 SiC 2 powders were prepared by the representative Stober route and heat treated process. The phase composition, microstructure, dielectric and microwave absorbing properties of the powders were characterized. XRD pattern reveals the existence of amorphous SiO 2 and SEM image shows the SiO 2 layer uniformly coated on Ti 3 SiC 2 powders. Both the real and imaginary part of complex permittivity for the SiO 2 -coated Ti 3 SiC 2 powders decrease due to the insulating SiO 2 coating hiders the polarization and electric conductance loss effect. The oxidation resistance of the dense SiO 2 -coated Ti 3 SiC 2 powders at high temperature was improved. Although the complex permittivity of the powders decrease after oxidized at 600 °C, the dense SiO 2 -coated Ti 3 SiC 2 powders have larger dielectric constant compared with the bare Ti 3 SiC 2 powders. In addition, the dense SiO 2 -coated Ti 3 SiC 2 presents better microwave absorption performance after oxidation. The results indicate the dense SiO 2 coating can improve oxidation resistance as well as microwave absorption performance of the Ti 3 SiC 2 powders. [ABSTRACT FROM AUTHOR]