Besides the excellent high-temperature mechanical properties, Si3N4 and SiC based ceramics containing insulating or electrically conductive phase are attractive for their tunable dielectric propert...

Electromagnetic properties of Si–C–N based ceramics and composites

The establishment of covalent junctions between carbon nanotubes (CNTs) and the modification of their straight tubular morphology are two strategies needed to successfully synthesize nanotube-based three-dimensional (3D) frameworks exhibiting superior material properties. Engineering such 3D structures in scalable synthetic processes still remains a challenge. This work pioneers the bulk synthesis of 3D macroscale nanotube elastic solids directly via a boron-doping strategy during chemical vapour deposition, which influences the formation of atomic-scale "elbowg" junctions and nanotube covalent interconnections. Detailed elemental analysis revealed that the "elbowg" junctions are preferred sites for excess boron atoms, indicating the role of boron and curvature in the junction formation mechanism, in agreement with our first principle theoretical calculations. Exploiting this materialĝ€™s ultra-light weight, super-hydrophobicity, high porosity, thermal stability, and mechanical flexibility, the strongly oleophilic sponge-like solids are demonstrated as unique reusable sorbent scaffolds able to efficiently remove oil from contaminated seawater even after repeated use.

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Covalently bonded three-dimensional carbon nanotube solids via boron induced nanojunctions

Stability of binary nanocrystalline alloys against grain growth and phase separation

In the last two decades, fibre-reinforced SiC ceramic-matrix composites (CMCs) have attracted extensive interests. Owing to the designable multi-scale microstructure feature and the tailorable processing methods such as chemical vapour infiltration and polymer derived ceramics, SiC matrix composites attain great potential as multifunctional composites. Through designing the fibre, interphase, matrix and coating, the composite exhibits a multitude of functionalities which are desirable for various technological applications. Besides strengthening and toughening design of CMCs, three inspiring issues of multifunctional CMCs are receiving increasing attention, including crack self-healing, friction self-lubrication, and electromagnetic shielding and absorption, which are the key mechanisms to promote the application of CMCs in hot structures of engines and aerospace vehicles, braking pads/discs, various electronic devices, etc. The present review covers the main mechanisms on strengthening and toughening, cr...

Fibre-reinforced multifunctional SiC matrix composite materials

Aluminum becomes the most popular nonferrous metal and is widely used in many fields such as packaging, building transportation and electrical materials due to its rich resource, light weight, good mechanical properties, suitable corrosion resistance and excellent electrical conductivity. Grain refinement, which is obtained by changing the size of grain structure by different techniques, is a preferred method to improve simultaneously the strength and plasticity of metallic materials. Therefore, grain refining of aluminum is regarded as a key technique in aluminum processing industry. Up to now, there have been a number of techniques for aluminum grain refining. All the techniques can be classified as four categories as follows: grain refining by vibration and stirring during solidification, rapid solidification, the addition of grain refiner and severe plastic deformation. Each of them has its own merits and demerits as well as applicable conditions, and there are still some arguments in the understanding of the mechanisms of these techniques. In this article, the research progresses and challenges encountered in the present techniques and the future research issues and directions are summarized.

A Review on Grain Refinement of Aluminum Alloys: Progresses, Challenges and Prospects

Preparation and oxidation protection of CVD SiC/a-BC/SiC coatings for 3D C/SiC composites

Introduction Particle reinforced silicon carbide and silicon nitride ceramic matrix composites were fabricated using designed particle agglomeration and chemical vapor infiltration (CVI) technique. Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) were employed to observe the microstructures of the preforms and as-infiltrated composites. In the preform, the inter-agglomeration and intra-agglomeration pores had an approximate size of 500–800 μm and 5–10 μm, respectively. After infiltrated, a large amount of silicon carbide and silicon nitride matrix were infiltrated in the preform, the sizes of inter-agglomeration and intra-agglomeration pores were 200–400 μm and 2–4 μm, respectively. The SiC and Si 3 N 4 whiskers were observed in the residual intra-agglomeration pores. The flexural strength of SiC (p) /SiC composites changed with first-step pressure and second-step pressure. The maximum of the strength was 284 MPa, and the ratio of the retained strength was 95.4% at 1600 °C. The fracture toughness of SiC (p) /SiC composites was around 7 Mpa m 1/2 . The Si 3 N 4(p) /Si 3 N 4 composite attained an acceptable strength, 113.4 MPa and low dielectric constant, about 4.2–4.3.

Microstructure and properties of particle reinforced silicon carbide and silicon nitride ceramic matrix composites prepared by chemical vapor infiltration

Effect of deposition temperature on boron-doped carbon coatings deposited from a BCl3–C3H6–H2 mixture using low pressure chemical vapor deposition

Tensile fracture behaviors and mechanisms of 2D C/SiC-BCx composite were investigated. Results showed that the 2D C/SiC-BCx composite exhibited similar tensile strength (about 250 MPa), but different fracture mode and damage evolution compared to that of 2D C/SiC composite under similar monotonic tensile stress condition at room temperature. The initial modulus and fracture modulus of 2D C/SiC-BCx composite obtained under tensile cyclic loading at RT were about 98.6 GPa and 54.5 GPa, respectively. At high temperatures, the tensile strengths were lower than that at room temperature and behaved as a step-like stress–strain curve.

Wenbin Yang

Papers

Preparation and oxidation protection of CVD SiC/a-BC/SiC coatings for 3D C/SiC composites

Microstructure and properties of particle reinforced silicon carbide and silicon nitride ceramic matrix composites prepared by chemical vapor infiltration

Effect of deposition temperature on boron-doped carbon coatings deposited from a BCl3–C3H6–H2 mixture using low pressure chemical vapor deposition

Fracture behaviors and mechanism of 2D C/SiC-BCx composite under tensile load

Microstructural evolution of coating-modified 3D C/SiC composites after annealing in wet oxygen at different temperatures