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This paper aims to study the effects of Si 3 N 4 whisker (β-Si 3 N 4 w) and MXene (Ta 3 C 4 T x) on the densification, microstructure and mechanical properties of Si 3 N 4 ceramics. In this research, Al 2 O 3 , Y 2 O 3 and CaF 2 are utilized as ternary composite sintering additives, and fast hot press sintering off 1750 °C and 30 MPa is conducted. The β-Si 3 N 4 w and Ta 3 C 4 T x are well dispersed in the ceramic matrix, resulting in the achievement of a high-density, high-toughness Si 3 N 4 ceramic. The microstructure observation shows that the uniform addition of whiskers leads to a significant increase in rod-shaped Si 3 N 4 grains. When 10 wt% of β-Si 3 N 4 w are added, the bending strength of 577.1 MPa and the fracture toughness of 7.6 MPa m1/2 are obtained. By introducing 0.5 wt% Ta 3 C 4 T x along with 10 wt% β-Si 3 N 4 w simultaneously, much higher bending strength and fracture toughness are achieved, with the bending strength being 743.9 MPa and the fracture toughness being 9.7 MPa m1/2. This demonstrates that the synergistic effect of β-Si 3 N 4 w and Ta 3 C 4 T x plays a significant role in enhancing the fracture toughness of Si 3 N 4 ceramics. This research paves a new way to prepare high-toughness Si 3 N 4 ceramics by fully utilizing of toughening agents and their coupling mechanisms. [ABSTRACT FROM AUTHOR]

Silica is one of the most widely used ceramics due to its excellent chemical stability and dielectric property. However, its destructive brittle nature inhabits it from wider application as a functional ceramic. An improvement in toughness is a challenging topic for silica ceramic, as well as other ceramics. In the paper, silica ceramic with different types of boron nitride powders and alumina platelets was fabricated by hot-pressing. Introduction of the additives had great influence on the composites' mechanical properties and microstructure. The silica matrix composite containing micro-sized boron nitride powders possessed the best mechanical properties, including the bending strength (134.5 MPa) and the fracture toughness (1.85 Mpa·m1/2). Meanwhile, the introduction of alumina platelets combined with boron nitride nanosheets achieved an effective enhancement of fracture toughness while maintaining the bending strength. Compared with the monolithic silica, the composite with simultaneous addition of alumina platelets and boron nitride nanosheets had a fracture toughness of 2.23 Mpa·m1/2, increased by approximately 27% (1.75 Mpa·m1/2). The crack deflection and platelet pullout were contributing to enhancement of the fracture toughness. The improved mechanical properties, combined with the intrinsic excellent dielectric and chemical properties, make the silica matrix composites promising wave transparent and thermal protection materials. [ABSTRACT FROM AUTHOR]

Alumina is one of the most commonly used and researched structural ceramic because of its excellent properties. However, its intrinsic brittleness is the fatal drawback, which hinders it from wider applications. How to improve its fracture toughness as well as the bending strength is always challenging for material researchers. In this paper, alumina matrix composites were fabricated by hot-pressing, in which some additives, including zirconia, alumina platelets, and MXene, were incorporated. The influence of the introduced additives on their microstructure and mechanical properties was investigated. Compare with the monolithic alumina, both bending strength and fracture toughness of all samples were improved greatly. Incorporation of zirconia was beneficial to the mechanical properties due to the phase-transformation strengthening and toughening mechanism. While alumina platelets resulted in high fracture toughness because of the self-toughening of elongated grains. The synergistic effect of alumina platelets and MXene enormously improved the fracture toughness from 2.9 ± 0.3 MPa·m1/2 for monolithic alumina to 7.5 ± 0.4 MPa·m1/2 for the composite, which was increased by 159%. This work will provide useful references for the fabrication of high-strength and high-toughness alumina ceramics by introducing additives properly. [ABSTRACT FROM AUTHOR]

Abstract Boron nitride nanosheets (BNNSs) have attracted increasing attention in the field of two-dimensional materials. In the paper, the BNNSs/alumina composites were fabricated by a flocculation method and hot pressing. It is found that the BNNSs were dispersed uniformly in the alumina matrix by the flocculation technique via pH adjustment. The experimental results showed that with the increasing BNNSs content, the density of the composites decreased. Compared with the monolithic alumina, bending strength of the composite with 1.0 wt% BNNSs was increased by 58.6%; while the fracture toughness was increased slightly. The addition of BNNSs changed the fracture pattern, refined the grains of composites and inhibited abnormal grain growth, which contributed to the improvement of mechanical properties of the composites. [ABSTRACT FROM AUTHOR]