Sintering and fracture toughness of alumina-zirconia composites (original) (raw)
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Fracture toughness of alumina and ZTA ceramics: microstructural coarsening effects
Journal of Materials Processing Technology, 2003
The influence of zirconia particles addition and microstructural coarsening, as a result of different heat treatments, on the fracture toughness of a monolithic alumina and a zirconia-toughened-alumina (ZTA) composite is studied. It is observed that addition of zirconia particles results in an enhancement of fracture toughness with respect to that exhibited by the alumina matrix. Similarly, microstructural coarsening within ZTA is found to produce a fracture toughness increment, mainly associated with the effect of zirconia particle size on their phase transformability. The obtained mechanical properties and grain growth kinetics are discussed in terms of microstructural features and operative toughening mechanisms.
Materials, 2013
Alumina-zirconia (AZ) composites are attractive structural materials, which combine the high hardness and Young's modulus of the alumina matrix with additional toughening effects, due to the zirconia dispersion. In this study, AZ composites containing different amounts of zirconia (in the range 5-20 vol %) were prepared by a wet chemical method, consisting on the surface coating of alumina powders by mixing them with zirconium salt aqueous solutions. After spray-drying, powders were calcined at 600 °C for 1 h. Green bodies were then prepared by two methods: uniaxial pressing of spray-dried granules and slip casting of slurries, obtained by re-dispersing the spray dried granulates. After pressureless sintering at 1500 °C for 1 h, the slip cast samples gave rise to fully dense materials, characterized by a quite homogeneous distribution of ZrO 2 grains in the alumina matrix. The microstructure, phase composition, tetragonal to monoclinic transformation behavior and mechanical properties were investigated and are here discussed as a function of the ZrO 2 content. The material containing 10 vol % ZrO 2 presented a relevant hardness and exhibited the maximum value of K I0 , mainly imputable to the t → m transformation at the crack tip.
Fracture toughness of zirconia–alumina composites
International Journal of Refractory Metals and Hard Materials, 1999
The dependence of fracture toughness on microstructure coarsening, induced by thermal treatment at 1600°C, has been studied in zirconia±alumina composites with compositions 5%, 15% and 30% zirconia by volume. The fracture toughness has been evaluated using dierent methods based on producing small surface cracks by Vickers indenters, or on producing a large through the thickness crack. It is concluded that fracture toughness increases with the volume fraction of zirconia as well as with zirconia particle coarsening. This is explained by the eect of these microstructural parameters on the main operating toughening mechanism, which is found to be stress induced phase transformation.
Role of Microstructural Features in Toughness Improvement of Zirconia Toughened Alumina
Journal of Minerals and Materials Characterization and Engineering, 2016
Ceramics constitute an integral part of highly efficient armours due to their low density, high hardness, strength and stiffness. However, they lack toughness and multi-hit capability. Therefore, zirconia toughened alumina is investigated. The hardness is evaluated using Vickers, Knoop and instrumented indentations, while the fracture toughness is evaluated using the indentation technique and Charpy tests. The strength is evaluated using ring-on-ring, four point bend and drop weight tests. The Young's modulus is evaluated using the unloading instrumented indentation curves. Microstructure, porosity and density are characterised using ultrasonic scanning, Archimedes principle, optical and scanning electron microscopy. Results show an indentation size effect on all mechanical properties. A substantial improvement in toughness is achieved through retardation of crack initiation by tetragonal-to-monoclinic phase transformation in zirconia particles, crack deviation thanks to appropriate grain structure, as well as energy absorption by densification due to remaining porosity. This improved toughness is expected to promote multi-hit capability.
IJERT-Structural and Mechanical Properties of Zirconia Toughened Alumina (ZTA) Composites
International Journal of Engineering Research and Technology (IJERT), 2014
https://www.ijert.org/structural-and-mechanical-properties-of-zirconia-toughened-alumina-zta-composites https://www.ijert.org/research/structural-and-mechanical-properties-of-zirconia-toughened-alumina-zta-composites-IJERTV3IS20451.pdf The Zirconia toughened Alumina (ZTA) composites with 0-16 wt % of ZrO 2 were prepared by slurry method and sintered at temperature (T s) 1500°C and 1600°C for 2 hours. The density, porosity, structural properties and mechanical properties of Al 2 O 3-ZrO 2 composites with respect to ZrO 2 content as well as sintering temperature have been explored in the present work. About 2% higher density of 16 wt % ZTA has been achieved and the microstructures are highly homogeneous and finer with less porosity when compared to pure Al 2 O 3. The surface morphology of the samples was studied by using SEM. The effect of zirconia content on hardness and elastic modulus were investigated. At 1500°C, maximum hardness shows 15.79 GPa and at 1600°C, it is 19.76 GPa, which is observed for pure Alumina. However, at same temperatures, minimum hardness shows 11.24 GPa and 12.96 GPa, respectively, that is observed for 16 wt% ZrO 2. Elastic modulus also shows same behaviour as shown for hardness. Flexural strength increases with the increase of both zirconia content and sintering temperature. The approach adopted in the present study may provide an alternative to design Al 2 O 3-ZrO 2 composites with improved mechanical properties.
International Journal of Refractory Metals and Hard Materials, 2013
The aim of this research is to investigate the mode of crack propagation in zirconia toughened alumina (ZTA) added with MgO and CeO 2 , respectively. The mode of crack refers to the toughening mechanism of the materials. Different ZTA compositions containing MgO and CeO 2 as sintering additives were prepared using pressureless sintering at 1600°C. Each sample was subjected to Vickers indentation with 294 N load and the cracks that propagated were observed with SEM. The ZTA with an addition of 0.7 wt.% MgO showed a crack deflection with a fracture toughness value of 6.19 ± 0.26 MPa • √m. On the other hand, the ZTA with CeO 2 addition of 0.5 to 7 wt.% showed both crack bridging and deflection, and produced 5.78 ± 0.16 MPa • √m to 6.59 ± 0.23 MPa • √m fracture toughness values, respectively. The fracture toughness of the ZTA-MgO-CeO 2 compositions is higher due to crack bridging and crack deflection. The toughening mechanisms of crack deflection and bridging hinder crack propagation since more energy is required to make the crack propagate. However, the formation of CeAl 11 O 18 phase was observed; this consequently decreases the hardness and fracture toughness of the ZTA-MgO-CeO 2 compositions.
MECHANICAL PROPERTIES OF ZIRCONIA TOUGHENED ALUMINA PREPARED BY DIFFERENT METHODS
Le Journal de Physique Colloques, 1986
Resume -Des ceramiques alumineuses renforcees par de l a zircone ont Gte -preparees par deux procedes d i f f e r e n t~ a p a r t i r des memes matieres premieres (poudres). Le premier u t i l i s e l e broyage par a t t r i t i o n e t l a compression I chaud ; l e second, une dispersion 6lectrochimique, l e coulage en barbotine e t l e f r i ttage sans charge. L'influence des parametres d'elaboration sur les proprietes mecaniques des pieces denses e s t examinee. L'influence des teneurs en ZrOz e t Y203 e s t discutee.
Effect of sintering curves on the microstructure of alumina–zirconia nanocomposites
Ceramics International, 2014
Zirconia-toughened alumina (ZTA) ceramics of various compositions have high relevance in the field of mechanical engineering for cutting tools and wear parts as well as in biomedical applications for hip and knee implants. In this study a matrix of submicron size a-alumina is reinforced with 10 vol% unstabilized zirconia nanoparticles. The ZTA ceramics were consolidated by means of hot pressing at 1400-1550°C at 60 MPa axial pressure for 1 h in order to test the influence of the sintering conditions on the mechanical properties, microstructure and phase composition. Despite the conventional mixing and milling method used, ZTA nanocomposites of high homogeneity were obtained. Low sintering temperatures result in ultra-fine-grained materials with high hardness. High strength of 900-1050 MPa was observed over the whole sintering temperature range, while toughness rises with sintering temperature. A clear correlation between transformability of the tetragonal phase and toughness cannot be identified. Highest strength was found for ZTA with a low initial monoclinic content and high transformability. Increasing sintering temperatures led to only slight microstructural coarsening but to a migration of zirconia particles and rising monoclinic content. Associated with these effects, a gradual shift from transformation toughening to microcrack toughening was observed.
Microstructural Coarsening of Zirconia-Toughened Alumina Composites
Journal of the American Ceramic Society, 2005
H. M. Chan-contributing editor This work has been partly funded by the Spanish Ministerio de Ciencia y Tecnologı´a (MCYT) and the Generalitat de Catalunya under grants MAT2000-1014-C2-01 and 2001SGR00229, respectively. One of the authors (D. C.) is grateful to the Generalitat de Catalunya for financial support through an FI scholarship.
This paper reports an investigation on the impact of in-situ formation of CaAl 12 O 19 (hibonite) on the microstructure and mechanical properties of zirconia-toughened-alumina (ZTA). Various amounts of CaCO 3 (0–13 wt%) were added to ZTA to form CaAl 12 O 19. Samples were sintered at 800 1C for 4 h to obtain CaO from decomposition of CaCO 3 , and then at 1600 1C for 4 h to produce elongated CaAl 12 O 19 grains. Analyses of samples were done using XRD and FESEM. The higher the amount of CaCO 3 added, the higher the amounts of CaAl 12 O 19 and pores observed. The toughness value increased with the increase of CaAl 12 O 19 for a critical range, and subsequently decreased; the reverse trend was observed for the hardness and density results. The sample with 0.5 wt% CaCO 3 addition produced the highest toughness (6.3 MPa m 1/2), reasonable hardness (1568.6 HV), density (4.11 g/cm 3), and porosity (1.29%) values.