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In order to control the pore characteristics and macroscopical performance of porous ceramics, roles of the freeze casting parameters are the key points. Herein, aligned dendritic porous SiC was fabricated by freeze casting of PCS-camphene solutions with different solid loading, freeze front velocity, temperature gradient, and freezing temperature. Influence of these parameters on the microstructure and compressive strength of porous SiC was investigated. With increasing the PCS content, freeze temperature, freeze front velocity or temperature gradient, degree of undercooling of the camphene was increased, resulting in the formation of smaller pore size, decreased porosity and increased compressive strength. Compared to variables of freeze temperature and temperature gradient, increased freeze front velocity was more efficiency in improving the compressive strength of porous SiC, owing to the formation of smaller pore size and longer secondary dendritic crystals. Promising micron-sized porous SiC with high porosity (79.93 vol%) and satisfactory strength (15.84 MPa) was achieved for 10% PCS-camphene solution under optimized freezing conditions.

Improving the flexoelectric coefficients of materials is of great significance and challenge in physics and material sciences. Herein, graphite was roughly added into a paraelectric SrTiO3 (STO) ceramic, in order to increase the dielectric permittivity and electrical conductivity, which brings minimized variations to crystal, both structure and microstructure. More importantly, the flexoelectric coefficient of the doped STO with 20 wt% C was found to experience a jump increase by an order of magnitude relative with the pure STO, which could be well interpreted by the occurrence of an interface layer between the semiconductor surface and the electrodes, whereby under bending, a large macroscopic polarization in the paraelectric ferroelectrics was generated. The facile strategy in this paper introduces a general way to probing the semiconductor flexoelectricity in the paraelectric ferroelectrics.

The preparation of porous SiC ceramics is the key process for co-continuous SiC/Al composites, which are promising materials for electronic packaging and precision instrument. Porous ceramics prepared by mould pressing and freeze casting are the most widely used preforms. However, the former preforms own high solid loading, raising the machining difficulty of composites. The latter preforms possess nonuniform microstructure, which is inappropriate for precision instruments. In this work, SiC preforms with low solid loading and uniform microstructure were prepared by non-aqueous gelcasting. Moreover, the pore size of the preforms could be controlled easily (1.03–22.82 μm) by changing the raw powder size. The effects of preform pore size on the mechanical properties and thermal expansion coefficient of the composites were researched. When the preform with a proper pore size of 7.14 μm was applied, the flexural strength and thermal expansion coefficient of the composite were 986.8 MPa and 8.11 × 10−6/K (50 °C), respectively.

Abrupt change of acoustic impedance at the interfaces of step gradient composites is the main reason which hinder their further improving of bulletproof performance. Eliminating these interfaces is an effective method to fundamentally solve this problem. In this study, continuous gradient Ti/TiB–TiB2 composite was fabricated by spark plasma sintering (SPS) combined with tape casting. Interfaces between the different thin tape layers were successfully eliminated through the growth of rod-like TiB crystals during SPS sintering. High speed impact test indicates the continuous gradient Ti/TiB–TiB2 composite not only possesses excellent anti-penetration performance, but also has the ability to resist a second strike.

Near-net-shape mullite ceramics with high porosity were prepared from ultra-low cost natural aluminosilicate mineral kaolin as raw material and polystyrene micro-sphere (PS) as pore-forming agent. Microstructure, flexural strength, thermal conductivity and dielectric properties of the ceramics were systematically researched. Results show that the porous mullite ceramics possess fibrous skeleton structure formed by a large quantity of interlocked mullite whiskers, which results in good mechanical properties and low-to-zero sintering shrinkage. Flexural strength of the porous mullite ceramics can be up to 41.01 ± 1.12 MPa, even if the porosity is as high as 62.44%. The dielectric constant and loss tangent of the porous mullite ceramics at room temperature are lower than 2.61 and 5.9 × 10−3, respectively. Besides, dielectric constant is very stable with the rising of temperature, and the dielectric loss can be consistently lower than 10−2 when the temperature is not higher than 800 °C. In addition, thermal conductivity at room temperature is as low as 0.163 W/m/K when the porosity of mullite ceramics is 80.05%. The infiltration of SiO2 aerogels (SiO2 AGs) can further decrease the thermal conductivity to 0.075 W/m/K, while has just little effects on the dielectric properties. Excellent mechanical, thermal and dielectric properties show that the porous mullite ceramics have potential applications in radome fields. The porous mullite ceramics prepared from kaolin not only have low cost, but also can achieve near-net-shape.

The micro-scale effect of Al 2 O 3 particle on the deformation behaviors of the copper matrix was investigated using nanoindentation. Moderate strengthening effects were produced by the Al 2 O 3 as indicated from the mechanical deformation evolutions. Specifically, the displacement recovery ratio and elastic work ratio is 6% and 9% higher for the Cu-5 wt% Al 2 O 3 (C5A) composite material compared with that of the pure copper (PC) material, respectively. While for the indentation hardness and indentation modulus, the increment is 36% and 75%, respectively. Notably, the moderate strengthening effects were quantitatively illuminated from the power law index m for the C5A indent (1.2) and PC indent (1.1–1.3). In addition, synergetic strengthening effects were proposed from the microstructure evolutions in the C5A composite material. Specifically, the increment in yield strength deduced from the grain refinement is 120 MPa, which is 67% higher than that of the Al 2 O 3 particle dispersion strengthening. The synergetic strengthening effects revealed from the microstructure evolutions are expected to provide new strengthening approaches for the ceramic particle reinforced metal matrix composite materials.

Dense silicon nitride (Si3N4) ceramics were prepared using Y2O3 and MgF2 as sintering aids by spark plasma sintering (SPS) at 1650 °C for 5 min and post-sintering annealing at 1900 °C for 4 h. Effects of MgF2 contents on densification, phase transformation, microstructure, mechanical properties, and thermal conductivity of the Si3N4 ceramics before and after heat treatment were investigated. Results indicated that the initial temperature of liquid phase was effectively decreased, whereas phase transformation was improved as increasing the content of MgF2. For optimized mechanical properties and thermal conductivity of Si3N4, optimum value for MgF2 content existed. Sample with 3 mol.% Y2O3 and 2 mol.% MgF2 obtained optimum flexural strength, fracture toughness and thermal conductivity (857 MPa, 7.4 MPa m1/2 and 76 W m−1 K−1, respectively). It was observed that excessive MgF2 reduced the performance of the ceramic, which was caused by the presence of excessive volatiles.

An experimental investigation was performed to study the fatigue behavior of plain-weave fiber fabrics reinforced C/C-SiC composites (2D C/C-SiC composites) prepared by liquid silicon infiltration (LSI) under dynamic flexural stresses at room temperature. The results indicate that the fatigue limit (105 cycles) of 2D C/C-SiC composites subjected to flexural fatigue stresses is 95 MPa, corresponding to approximately 78% of flexural strength of virgin specimens. Moreover, as the fatigue loading/unloading proceeds, both strength enhancement and strength degradation are successively observed in the post-fatigue specimens under quasi-static flexural tests. Maximum residual flexural strength (RFS) of post-fatigue specimens increases to 135.7 MPa when the 2D C/C-SiC specimens are exposed to maximum fatigue stress of 95 MPa for 5000 cycles. The microstructures and fractured surfaces indicate that evolution of RFS is determined by the interaction of matrix cracking and interfacial degradation. The interfacial debonding and relief of residual thermal stresses induced by matrix cracking are mainly responsible for the enhanced strength in the post-fatigue specimens.

CaCu3Ti4O12 ceramics have been prepared by the spark plasma sintering method. Our results indicate that facile fabrication process control can lead to an obvious microstructure change, and thus modulate the nonlinear current-voltage properties such as the breakdown electric field Eb (0.33–9.28 kV/cm) and nonlinear coefficient α (2.4–21.5). The SPS ceramics sintered at 900 °C for 5 min possess the largest Eb and α values, which are much higher than those of previous pure CaCu3Ti4O12 ceramics without dopants. It is suggested that the synergistic effects of enhanced barrier height, large activation energy at grain boundaries, and the evolution of microstructure lead to the superior J-E performance in present samples. These results reveal that the CaCu3Ti4O12 material has a promising prospect in the application as a varistor.

Single phase hexagonal α-Ta 2 C ceramics were synthesized by spark plasma sintering and using TaC and Ta as the starting powders. Effects of sintering temperatures and holding times on the densification process, phase formation, microstructure development, and mechanical properties of the α-Ta 2 C ceramics were investigated. Densification occurred in the temperature range of 1520–1675 °C in less than 2.5 min. But completion of the Ta 2 C formation took about 40 min at 1500 °C, and 5 min at 1900 °C. The materials sintered at 1500 °C consisted of fine equiaxed grains. The Ta 2 C grains grew anisotropic to form an elongated self-toughening microstructure at 1700 °C. At 1900 °C, the neighboring Ta 2 C individual crystals coalesced to form large Ta 2 C blocks to entrap the residual pores. Although higher flexural strength and fracture toughness were reached at 1700 °C, the unstable microstructures of the Ta 2 C materials indicated limited applications at high temperatures.

A gravity-electrophoretic deposition method (GD-EPD) was developed for depositing yttria-stabilized zirconia (YSZ) films on porous NiO-YSZ anode substrates. GD-EPD was the method that deposited an additional layer of YSZ by electrophoretic deposition (EPD) technique on the YSZ film prepared by gravity deposition method (GD). The microstructure of the YSZ film, the performance and impedance spectra of fuel cell prepared by GD-EPD were investigated and compared with that of the YSZ film prepared by only GD method. The SEM photos showed that the size and quantity of the pin-holes in YSZ film has been reduced down by the subsequent EPD process after GD. The output properties of the fuel cell with YSZ film deposited by GD-EPD were obviously improved. The most apparent improvement was the fuel cell's power density of GD-EPD sample that increased seven times from 20 to 144 mW cm −2 at intermediate-temperature of 700 °C than that of GD ones.