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Laminated Si3N4/SiCw ceramics were successfully prepared by tape casting and hot-pressing. Its mechanical properties were measured and the impact resistance was discussed. The toughness of the laminated Si3N4/SiCw ceramics was 13.5 MPa m1/2, which was almost 1.6 times that of Si3N4/SiCw composite ceramics, namely 8.5 MPa m1/2. Moreover, the indentation strength of laminated Si3N4/SiCw ceramics was not sensitive to increasing indentation loads and exhibited a rising R-curve behaviour, indicating that the laminated Si3N4/SiCw ceramics had excellent impact resistance. The improved toughness and impact resistance of laminated Si3N4/SiCw ceramics was attributed to the residual stress caused by a thermal expansion coefficient mismatch between the different layers, resulting in crack deflection and bridging of SiC whiskers in the interface layer, thus consuming a large amount of fracture work.

To achieve the densification of tough tantalum carbide ceramics at low sintering temperature, we reported a preparation of TaC ceramics by spark plasma sintering with SiC as the sintering aid and graphene platelet (GPL) as the reinforcement. The effects of GPL contents on the densification, grain growth and mechanical properties of the TaC–SiC/GPL composites were evaluated. Due to the surface reactions between SiC and TaC particles, relative density of the composite increased to 99.3% at GPL content of 1.0 wt%. The GPLs wrapped around the grains and acted as barriers for mass diffusion, therefore inhibiting grain growth. The flexural strength of the composite increased at first and reached maximum value of 570 MPa at the GPL content of 1.0 wt%; the fracture toughness reached the peak value of 5.8 MPa m1/2 at the GPL content of 1.5 wt%. Bending, bridging and pullout of GPLs were considered as the main toughening mechanisms. Thus, this work provides a new guide for the fabrication of TaC ceramics with high density and high fracture strength.

Zirconia ceramics were prepared by oscillatory pressure sintering (OPS) with zirconia whisker as the reinforcement. The effects of whisker fraction on the microstructure, densification and mechanical properties of the ceramics were investigated. By applying an oscillatory pressure ranging from 25 to 35 MPa to the powder mixtures, the relative density of the OPS zirconia reached approximately 99.7% at whisker fraction of 15 wt%. Because of the accelerated densification by grain boundary sliding and diffusional creep, the average grain size of the OPS zirconia was 0.9 μm, which was much finer than that of the pressure-less sintered zirconia (1.5 μm). The peak values of flexural strength and fracture toughness of the OPS zirconia corresponded to 1376 MPa and 6.7 MPa m1/2, respectively. Whisker bridging, crack deflections were considered as the primary toughening mechanisms. This study provides an approach to prepare zirconia ceramics with uniform, fine grains and excellent fracture strength and toughness.

This study reports the preparation of silicon carbide ceramic membranes with pure silicon carbide particles without sintering aids. The effects of sintering temperature on the microstructure, mechanical and filtration properties were investigated. The porosity of the substrate layer increased from 37% to 41% when the sintering temperature ranged from 2150 to 2300 °C, whereas the flexural strength increased from 14.5 to 18.2 MPa. The separation layer was coated on the substrate layer using a spray process. When sintered at 1850 °C, a smooth and defect-free layer was formed with an average pore size and layer thickness of 1.2 and 60 μm, respectively. With the increase of average pore size, the filtration flux increased from 2650 to 2800 L/(m2 h bar). Such ceramic membranes can be used to separate corrosive wastewater and high-temperature wastewaters owing to the exclusion of sintering aids, unlike the conventional ceramic membranes.

Oscillatory pressure sintering (OPS) technique is considered as a promising approach in the preparation of structural ceramics. In this study, the influence of oscillatory pressure on the grain growth, grain boundary characters and mechanical behaviors of silicon nitride ceramics was investigated. The TEM analysis indicated fringes in the grains and Moire' patterns at the grain boundaries of the OPS specimen. In addition, the OPS specimen presented a coarse structure resulted from the accelerated diffusion of atoms in liquid phase at high temperature. Based on these microstructure evolutions, the fracture work of the OPS specimen increased from 835 to 1240 J/m2 and the Weibull modulus of flexural strength increased from 23.9 to 35.9 when compared with that of the hot-pressed specimen.

We proposed a novel method consisting in the combination of oscillatory pressure sintering (OPS) followed by carburization in the vacuum, to prepare zirconia ceramics with high fracture strength and Weibull modulus. In this study, the zirconia particles were densified by an oscillatory pressure ranging from 27.5 to 32.5 MPa at 1450 °C, and then were carburized in the vacuum at 1300 °C. The result showed that the oscillatory pressure achieved several densification mechanisms, such as rearrangement of particles, plastic deformation of grains and sliding of grain boundaries. Consequently, the OPS specimen exhibited an increase in flexural strength from 998 MPa to 1556 MPa, and grain size reduction from 460 nm to 283 nm. The subsequent carburization of OPS zirconia induced high concentration of oxygen ion vacancies, and then high content and stability of the tetragonal phase. Thus, the carburized zirconia exhibited excellent comprehensive behaviors, demonstrating a flexural strength of 1646 MPa, fracture toughness of 8.8 MPa m1/2 and Weibull modulus of 25.8. The combination of OPS and consequent carburization in the vacuum is considered as an effective technique for preparing high-quality zirconia ceramics.

Laminated Graphite/ZrB2-SiC ceramics were fabricated by tape casting and hot pressing. The ablation properties of the ceramics in the parallel and the perpendicular directions were studied using an oxyacetylene torch. The mass ablation rates were 8.1 ± 0.4 mg/s in the parallel direction and 0.2 ± 0.1 mg/s in the perpendicular direction. The linear ablation rates were 3.1 ± 0.2 µm/s in the parallel direction and 1.2 ± 0.1 µm/s in the perpendicular direction. Thus, the ablation resistance of the laminated Graphite/ZrB2-SiC ceramics in the perpendicular direction was higher than that in the parallel direction. This anisotropy was mainly attributed to the lower surface temperature in the perpendicular direction resulted from higher thermal conductivity, as well as the orientation of the weak graphite interface layer perpendicular to the ablation surface.

Laminated BN/ZrB 2 –SiC ceramics were successfully fabricated by tape casting and hot-pressing. The oxidation behaviour of the ceramics at 1300, 1500 and 1600 °C in air was investigated. The results indicated their flexural strength and fracture toughness reached up to 583 ± 27 MPa and 16.1 ± 0.4 MPa m 1/2 , respectively, after oxidation at 1300 °C for 0.5 h. These values were higher than those obtained at room temperature (381 ± 31 MPa and 11.8 ± 0.5 MPa m 1/2 ). The improved mechanical properties could be attributed to the slight oxidation and healing effect to the defects of the SiO 2 glassy layer produced during oxidation. At 1600 °C, the mechanical properties decreased constantly, which was attributed to the substantive oxidation and formation of a thick, porous ZrO 2 layer under the thin, dense SiO 2 layer.

With BN and graphite as weak interfacial phases, ZrB2-SiC/BN (LZrB) and ZrB2-SiC/graphite (LZrG) laminated ceramics were prepared by tape casting and hot pressing. The fracture behaviors of the above two laminated ceramics were investigated at room temperature and high temperature. At room temperature, the flexural strengths of LZrB and LZrG ceramics were 381 ± 21 MPa and 414 ± 17 MPa, respectively. When heated at 1300 °C and 1500 °C, the flexural strength of LZrG ceramic was higher than that of the LZrB ceramic. When heated at 1500 °C for 2 h, flexural strength of the LZrG ceramic was as high as 352 MPa, suggesting typical multiple fractures. Such excellent high temperature flexural strength of LZrG ceramic was attributed to the healing of surface flaws by the glassy phase SiO2 after oxidation, the viscous bridging of ZrO2 and SiO2, as well as the transgranular fracture mode of ZrB2 grains in ZrB2-SiC layers.