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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]

In this study, the nacre-like alumina ceramics, with introduction of zirconia, are fabricated by freeze casting followed by hot pressing. The experimental results show that zirconia particles are uniformly distributed between the layered alumina 'brick' in the form of 'mortar'. Due to the incorporation of zirconia with proper particle size, both flexural strength and fracture toughness of the nacre-like alumina are greatly improved, much stronger and tougher than pure alumina. In regard to the sample containing 13.3 wt% zirconia, the flexural strength reaches 522 MPa, ∼47% increase in comparison with the monolith. Particularly, when zirconia content is 10 wt%, the fracture toughness is increased by ∼66%, from 6.1 MPa m1/2 to 10.1 MPa m1/2. Microstructure observation and fracture behavior analysis reveal that the coupling effects of bioinspired nacre-like structure and stress-induced transformation toughening are responsible for the enhanced mechanical properties. The results show that it is an effective method to increase the mechanical properties of layered alumina ceramics by introducing proper interlayer phase. [ABSTRACT FROM AUTHOR]

Microstructure–property relationships of pressureless-sintered multi-walled carbon nanotube (MWCNT)/alumina composites have been investigated using four types of MWCNTs having different mechanical characteristics as well as almost the same diameter and length; the influences of grain size, location of MWCNTs, fracture patterns, dispersion states of MWCNTs, and crack bridging characteristics of MWCNTs on the composites׳ mechanical properties have been explored. It has been found that the improvement in bending strength and fracture toughness observed for all types of the composites was primarily attributable to the grain refining effect by adding the MWCNTs and to the energy-dissipation by a MWCNT debonding and pullout, respectively. The number and size of clustered MWCNTs were increased in response to the increase in the MWCNT content, which resulted in the decrease in mechanical properties. The pressureless-sintered composites made with MWCNTs having larger load-bearing ability led to ~25% and ~45% improvement in bending strength (742.6±13.1 MPa) and fracture toughness (5.83±0.19 MPa m 1/2 ), respectively, than a MWCNT-free alumina. [ABSTRACT FROM AUTHOR]