In the previous decade, a considerable amount of work has been done on the alumina-zirconia ceramic composite system with a particular emphasis on improving the mechanical properties utilizing the recognized toughening mechanisms. Zirconia-toughened aluminas (ZTA) can be regarded as a new generation of toughened ceramics; for example, a toughness of >12 MPa m0.5 has been obtained, compared with 3 MPa m0.5 for commercial alumina ceramics. The fracture strength of ZTA is also greatly in excess of that for alumina. The mechanical properties of ZTA are critically dependent on their microstructures, which can be designed in terms of specific applications and controlled by means of powder preparation and densification processes. This review also includes details of the possible future development of ZTA; these are expected to involve the development and measurement of the mechanical properties for high-temperature engineering applications.

Zirconia-toughened alumina (ZTA) ceramics

High temperature hermetic seal is essential for utilizing the full potentials of planar solid oxide fuel/electrolyzer cells. A seal glass needs to have excellent thermal and chemical stabilities, mechanical integrity, and sealing ability in stringent oxidizing and reducing environments and for hundreds of thermal cycles. Comprehensive analysis and understanding are needed in the design of a seal glass in order to meet the demanding requirements. In this review, seal requirements and the advantages of glass-based seals are first discussed. Different glass compositions are reviewed from thermal, chemical, mechanical, and electrical property point of view. Based on these considerations, glass composition design approaches are provided that aid in search of the best seal glass that can offer all the desired properties and stabilities. Required thermal properties such as thermal expansion coefficient, glass transition temperature, and softening temperature have been achieved in several alkaline earth borosilicate glass systems. Interfacial compatibility with other cell components has also been obtained for several alkaline earth borosilicate glass systems. However, long-term thermal and chemical stabilities are yet to be achieved. Among all the glass systems studied, a boron-free SrO–La2O3–Al2O3–SiO2 seal glass has been specifically discussed because it has met all the thermal and chemical properties along with high thermal and chemical stabilities. For future endeavors, the relationships between seal glass constituents, glass network structures, required thermal, chemical, mechanical, and electrical properties need to be established in order to improve sealing performance while maintaining design flexibility and low fabrication cost.

Glass-based seals for solid oxide fuel and electrolyzer cells - A review

The objective of this article is to provide an up-to-date overview of zirconia-toughened alumina (ZTA) components used in total hip arthroplasties. The structure, mechanical properties, and available data regarding the clinical performance of ZTA are summarized. The advancements that have been made in understanding the in vivo performance of ZTA are investigated. This article concludes with a discussion of gaps in the literature related to ceramic biomaterials and avenues for future research.

Advances in zirconia toughened alumina biomaterials for total joint replacement.

A review on laser deposition-additive manufacturing of ceramics and ceramic reinforced metal matrix composites

The need for new materials to substitute injured or damaged parts of the human body has led scientists of different areas to investigate bioceramics since the 70's, when other materials in use started to show rejection problems. Ceramics show some advantages like being the material that best mimics the bone tissue, although present low toughness when compared with the metallic materials. As patients have become more and more demanding regarding esthetic and biocompatibility aspects of their dental restorations, ceramic material has become a main object of scientific interest especially from the material point of view. The alumina-zirconia composites are one of the relatively good and promising candidate for biomaterials application, due to biocompatibility and their mechanical properties that combines high flexural strength with a high toughness. The aim of the present work is to analyze the mechanical properties of these composites, where Y-TZP zirconia content was varied from 5 to 80 wt.% These systems can achieve a flexural strength 93 % and fracture toughness 29 % superior when compared to the pure alumina ceramics. These results showed that ceramic abutments components can be prepared for prosthetic rehabilitations with dental implants.

/pdf/mechanical-properties-of-alumina-zirconia-composites-for-2bwkj1miho.pdf

Mechanical properties of alumina-zirconia composites for ceramic abutments

A series of Al2O3-ZrO2 ceramics has been fabricated using both conventional sintering and a hot-pressing route, which results in various microstructures including (i) Al2O3 with well-dispersed ZrO2 single crystals; (ii) Al2O3 With TZP (tetragonal zirconia polycrystals) agglomerates (20 to 50μm); and (iii) Al2O3-ZrO2 duplex structures, in which both well-dispersed ZrO2 single crystals and TZP agglomerates are dispersed. The fracture strength of the composites has been measured by means of three-point bending and the fracture toughness by means of the micro-indentation technique. The microstructural characterization was carried out using scanning and transmission electron microscopy, and phase analysis of the zirconia by means of X-ray diffraction. The high toughness values of ≈ 12 M Pa m1/2 measured for the duplex structure have been correlated with the toughening mechanisms operative and the fracture strength with the matrix grain size and with larger defects present in the structure. A combined toughening process is proposed to account for the improved properties, including transformation toughening, microcrack toughening and crack deflection, which are discussed in context with the property measurements and the microstructural observations.

Toughening mechanisms in duplex alumina−zirconia ceramics

The detrimental effect of water on the Y1Ba2Cu3O7-δ superconducting ceramics has been studied using X-ray diffraction, infrared spectroscopy and transmission electron microscopy. It has been shown that barium carbonate is the major reaction product after reaction. From the viewpoint of the process, the reaction is shown to occur in three stages, e.g. (I) microcrack formation along the layers perpendicular to the c-axis; (II) lattice dissolution which is a consequence of the increasing microcrack density and their subsequent propagation; (III) the formation of the corrosion product.

A study of the reaction of Y1Ba2Cu3O7-? superconducting ceramics with water

Mixed zirconia-hafnia (Hf0.25Zr0.75O2) powders of fine particle size and narrow particle-size distribution can be prepared via co-precipitation routes using mixed zirconium and hafnium salts as the starting materials. The characteristics of the resultant zirconia-hafnia powders are dependent strongly on the dehydration route by which the co-precipitated hydroxide gels are dried. Zirconium-hafnium hydroxide gels are formed when zirconium and hafnium oxynitrates are co-precipitated in an ammonia solution of pH 10.5. The co-precipitated hydrous gels were dried by three very different routes including organic solvent dehydration, microwave drying, and conventional infrared heating lamp drying. The dried hydroxides were then calcined at various temperatures in the temperature range 550–1150 °C, followed by ball milling to remove large soft-particle agglomerates. The resultant zirconia-hafnia powders were characterized for crystallite size, particle size, particle-size distribution, particle morphology, and the degree of powder agglomeration, using experimental techniques such as X-ray diffraction, BET surface area, differential thermal analysis, thermo-gravimetric analysis, sedigraph, scanning and transmission electron microscopy. Hard particle aggregates, which cannot be effectively eliminated using ball milling, occur in the zirconia-hafnia powders processed via either the microwave drying or conventional infrared heating lamp drying routes. In contrast, the organic solvent dehydration route resulted in an almost aggregate-free powder of fine crystallite and particle sizes. Therefore, the zirconia-hafnia powder processed via the organic solvent dehydration route exhibited high sinterability on sintering at 1300 °C.

The effects of hydroxide gel drying on the characteristics of co-precipitated zirconia-hafnia powders

Zirconia-cordierite ceramic composites were fabricated by the hot pressing of cordierite and zirconia powders at 1400 ° C/20 MPa for 10 min. Both the fracture toughness and fracture strength have been enhanced by the addition of zirconia. Such improvements are due to stress-induced transformation toughening and to the generation of residual stresses. Micro-crack toughening has been found not to occur in the composite as a consequence of the large thermal expansion mismatch. The transformability of zirconia inclusions in the cordierite matrix is higher than in the case of an alumina matrix, although the inclusions have a rounded morphology, resulting from the presence of a liquid phase at the hot-pressing temperature.

Zirconia toughened cordierite

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