Zhou Zhijun ¹, Yu Huang ^{1, 2}, Xiao Zhuohao ¹, Shen Ziqiang ³, Yang Guangyuan ³, Wang Ximeng ⁴,

Kong Lingbing ⁴, Dong Zhili ⁵

(1. Jingdezhen Ceramic University, Jingdezhen 333403, Jiangxi, China; 2. Jingdezhen University, Jingdezhen 333032,

Jiangxi, China; 3. Jiangxi New Electric Co., Ltd., Pingxiang 337200, Jiangxi, China; 4. Zhongshan Institute of Changchun University of Science and Technology, Zhongshan 528437, Guangdong, China;

5. Nanyang Technological University, Singapore 639798)

Extended abstract:

[Significance] Alumina ceramics exhibit high hardness, excellent wear resistance and high chemical stability, but their relatively low fracture toughness and high susceptibility to brittle failure limit their applications under complex stress states and high-reliability service conditions. Zirconia-toughened alumina (ZTA) composite ceramics, in which zirconia is introduced as a toughening phase into an alumina matrix, have significantly improved fracture toughness and damage tolerance, while retaining the high hardness and wear resistance of alumina, making it an important research focus in the field of advanced structural ceramics. In recent years, remarkable progress has been made in the composition design, microstructure regulation and application extension of ZTA ceramics through optimization of stabilizer systems, introduction of third phases and advances in processing and sintering technologies. However, the intrinsic relationships between regulation strategies, microstructural evolution and overall performance have not yet been systematically clarified. Therefore, it is necessary to provide a comprehensive review of the recent progress in ZTA ceramics from the perspective of composition-process-structure-property relationships, thus offering guidance for the design, fabrication and application of high-performance ZTA ceramics.

[Progress] This paper was aimed to systematically review the toughening mechanisms, processing routes, composition design, structure-property relationships and applications of high-toughness ZTA composite ceramics. First, the major toughening mechanisms of ZTA ceramics are summarized, including transformation toughening, microcrack toughening, crack deflection, crack bridging, pull-out and nano-scale toughening. It is emphasized that the superior toughness of ZTA ceramics originates from the cooperative action of multiple energy-dissipation mechanisms during crack propagation. Second, the processing route of ZTA ceramics, including powder preparation, forming technologies and sintering methods, is discussed, with particular attention given to the effects of powder homogeneity, green-body quality and sintering techniques on densification behavior, grain evolution, phase constitution and final properties. In terms of composition design, the effects of composition, stabilizer systems and third-phase introduction on performance of the ZTA ceramics are analyzed in detail, while the differences among MgO, Y₂O₃ and CeO₂-stabilized systems in phase stability, microstructural evolution and overall properties are compared. On this basis, various third-phase strengthening strategies, including in-situ formed reinforcing phases, hard particles, high-aspect-ratio reinforcements and two-dimensional platelet-like phases, are comprehensively summarized, while their influences on interface characteristics, crack propagation behavior, microstructural integrity and the synergy between strength and toughness are elucidated. Finally, combined with literature data and information on commercialized products, the application progress of ZTA ceramics in biomedical devices, wear-resistant and cutting fields, electronic packaging and lightweight protective structures is reviewed. It is pointed out that different application scenarios place distinct demands on material properties.

[Conclusions and prospects] Overall, substantial progress has been achieved in the understanding of toughening mechanisms, optimization of processing technologies, compositional regulation and engineering applications of ZTA ceramics, while a relatively clear performance-design strategy for different service environments has gradually been established. It is indicated that the improvement of the overall performance of ZTA ceramics does not rely on the optimization of a single factor, but is closely associated with the coordinated matching among composition design, processing routes, microstructure regulation and service conditions. Future studies should focus on the following aspects: strengthening multicomponent synergistic design to achieve balance among strength, toughness, hardness and service stability; enhancing the precise regulation of interfacial structures, phase stability and crack-evolution behavior to promote the transition of toughening design from empirical optimization to targeted control; developing advanced forming and sintering technologies suitable for complex components so as to improve microstructural uniformity and manufacturing capability and paying greater attention to the reliability evaluation of ZTA ceramics under hydrothermal environments, impact loading and complex friction and wear conditions for long-term service. Establishing clearer composition-process-structure-property relationships will provide a more systematic theoretical and practical basis for the design, fabrication and application of high-performance ZTA ceramics.
Key words: zirconia-toughened alumina composite ceramics; toughening mechanism; microstructure; mechanical properties; application progress