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Abstract Graphene oxide (GO) is one of the most important ceramic-toughening candidates due to its outstanding physical and chemical properties. In this paper, nacre-like alumina ceramics reinforced with GO have been prepared by freeze casting followed by hot pressing. The experimental results showed that a laminated structure with homogeneous distribution of GO was obtained in the composites. Microstructural analysis, relative densities, flexural strength and fracture toughness of the samples were investigated to reveal the effect of GO. Higher flexural strength and fracture toughness (~380 MPa and ~7.5 MPa m1/2, respectively) were achieved and the multiple length-scale toughening mechanisms of composites contributed to the improved mechanical properties. The results show that it is a promising method to enhance the mechanical properties of nacre-like alumina by the addition of GO. [ABSTRACT FROM AUTHOR]

In order to overcome intrinsic brittleness and poor mechanical properties of fused silica (FS), boron nitride nanosheets (BNNSs) as a novel reinforcement were employed for fabrication of BNNSs/fused silica composites. BNNSs with micron lateral size were homogeneously dispersed with FS powder using a surfactant-free flocculation method and then consolidated by hot pressing. The flexural strength and fracture toughness of the composite with the addition of only 0.5 wt.% BNNSs increased by 53% and 32%, respectively, compared with those of pure FS. However, for higher BNNSs contents the improvement in mechanical properties was limited. Microstructural analyzes have shown that the toughening mechanisms are combinations of the pull-out, crack bridging, and crack deflection mechanisms. [ABSTRACT FROM AUTHOR]

BNNSs were prepared efficiently by magnesium borate nitridation. BNNSs/eutectic-composition Al 2 O 3 /YAG/YSZ ceramics were prepared by hot pressing sintering. The addition of BNNSs did not change the phase composition of BNNSs/eutectic-composition Al 2 O 3 /YAG/YSZ ceramics. The bending strength and fracture toughness of 1.5wt%BNNSs/ eutectic-composition Al 2 O 3 /YAG/YSZ ceramic were increased by 19.0% and 18.9% respectively. Doped BNNSs exist at the grain boundary between two or more different grains. The toughening mechanism of BNNSs contains mainly crack deflection, BNNSs pullout and BNNSs bridging. • BNNSs/eutectic-composition Al 2 O 3 /YAG/YSZ ceramics were originally prepared with excellent mechanical properties. • The toughening mechanism of BNNSs was discussed. • The effects of temperature and BNNSs doping amount on the mechanical properties of ceramics were explored. [ABSTRACT FROM AUTHOR]

The microstructure and mechanical properties of (Hf 0.2 Nb 0.2 Ta 0.2 Ti 0.2 Zr 0.2)B 2 high-entropy boride (HEB) were first predicted by first-principles calculations combined with virtual crystal approximation (VCA). The results verified the suitability of VCA scheme in HEB studying. Besides, single-phase (Hf 0.2 Nb 0.2 Ta 0.2 Ti 0.2 Zr 0.2)B 2 ceramics were successfully fabricated using boro/carbothermal reduction (BCTR) method and subsequent spark plasma sintering (SPS); furthermore, the effects of different amounts of B 4 C on microstructure and mechanical properties were evaluated. Due to the addition of B 4 C and C, all samples formed single-phase solid solutions after SPS. When the excess amount of B 4 C increased to 5 wt%, the sample with fine grains exhibited superior comprehensive properties with the hardness of 18.1 ± 1.0 GPa, flexural strength of 376 ± 25 MPa, and fracture toughness of 4.70 ± 0.27 MPa m1/2. Nonetheless, 10 wt% excess of B 4 C coarsened the grains and decreased the strength of the ceramic. Moreover, the nanohardness (34.5–36.9 GPa) and Young's modulus (519–571 GPa) values with different B 4 C contents just showed a slight difference and were within ranges commonly observed in high-entropy diboride ceramics. [ABSTRACT FROM AUTHOR]