Towards long lasting zirconia-based composites for dental implants: Transformation induced plasticity and its consequence on ceramic reliability

Zirconia-based composites were developed through an innovative processing route able to tune compositional and microstructural features very precisely. Fully-dense ceria-stabilized zirconia ceramics (84 vol% Ce-TZP) containing equiaxed alumina (8 vol%Al2O3) and elongated strontium hexa-aluminate (8 vol% SrAl12O19) second phases were obtained by conventional sintering. This work deals with the effect of the zirconia stabilization degree (CeO2 in the range 10.0\u201311.5 mol%) on the transformability and mechanical properties of Ce-TZP-Al2O3-SrAl12O19 materials. Vickers hardness, biaxial flexural strength and Single-edge V-notched beam tests revealed a strong influence of ceria content on the mechanical properties. Composites with 11.0 mol% CeO2 or above exhibited the classical behaviour of brittle ceramics, with no apparent plasticity and very low strain to failure. On the contrary, composites with 10.5 mol% CeO2 or less showed large transformation-induced plasticity and almost no dispersion in strength data. Materials with 10.5 mol% of ceria showed the highest values in terms of biaxial bending strength (up to 1.1 GPa) and fracture toughness (>10 MPa 1am). In these ceramics, as zirconia transformation precedes failure, the Weibull modulus was exceptionally high and reached a value of 60, which is in the range typically reported for metals. The results achieved demonstrate the high potential of using these new strong, tough and stable zirconia-based composites in structural biomedical applications

Synthesis and thermal behaviour of nanostructured ZrO2 powders obtained under hydrothermal conditions

International audienc

Sintering behaviour of zirconia and ceria-doped zirconia powders crystallized under hydrothermal conditions

International audienceUndoped and ceria doped zirconia fine particles, obtained under hydrothermal conditions, were heated from 200 degreesC to 1000 degreesC to investigate the monoclinic-tetragonal phase transformation. The nanosized powders exhibit suitable sinterability and reduced grain size in the sintered product. The ZrO2 doped with 12 mol% CeO2 was sintered to a single phase 100% tetragonal structure at 900 degreesC with a grain size of similar to 35 n

Colloïdes de zircone cériée (synthèse et frittage à basse température)

LIMOGES-ENSCI (870852305) / SudocLIMOGES-BU Sciences (870852109) / SudocSudocFranceF

Elaboration de matériaux composites céramiques à faible coefficient de dilatation thermique pour des applications spatiales

Actuellement, la qualité de l imagerie provenant de systèmes optiques spatiaux est limitée par la taille de leurs miroirs et la masse des structures supportant le miroir. Le développement de systèmes athermiques légers (un seul matériau) constitue le principal challenge dans l amélioration de ces systèmes. De matériaux légers, résistants mécaniquement (E/ 3 > 10, f > 100 MPa) et stables thermiquement ( 10, f > 100 MPa) and thermal stability (< 2.0e-6/K) are required. Within this context, our project consists in processing new ceramic composites by combining positive thermal expansion coefficient (TEC) materials having good mechanical properties (alumina or ceria doped zirconia) and negative TEC materials (zirconium tungstate or b-eucryptite) The processing of zirconium tungstate-based materials showed several decomposition and chemical reactions with some oxide matrix leading to its giving up. In the case of b-eucryptite, vermicular phenomenon occurs during sintering leading to the formation of intragranular porosity. Sintering parameters optimization can limit this porosity. The study of the thermal behavior of pure b-eucryptite materials shows that the very negative TEC results from microcracking, generated by the TEC anisotropy of its crystal lattice. This microcracking depends on the grain size and the aggregate size in the case of powder materials. Despite the fact that the TEC of its lattice (called intrinsic TE C equals to -0.4e-6/K) is very low, its bulk (or extrinsic) TEC can reach values until -10.9e-6/K according to the processing conditions. In this work, two strategies for developing composites were studied. The first one consists in decreasing the matrix TEC using an uncracked b-eucryptite powder (-0.4e-6/K) while the second one consists in elaborating near zero TEC materials from a microcracked b-eucryptite powder (-3.0e-6/K). When ceria-doped zirconia is used, ceria content must be adjusted in order to limit zirconia phase transformation. This transformation is driven by tensile stresses induced by the b-eucryptite and modifies the composite thermal behavior linearity. In both studied cases, dense composites show a modification of the b-eucryptite intrinsic TEC from -0.4e-6/K to more than +3.2e-6/K as a consequence of compressive stresses applied by the oxide matrix. An uncompleted densification of composites is required to relax these stresses. Taking into account these observations, several very low TEC composites were elaborated. However, the uncompleted densification of composites and the b-eucryptite microcracking greatly decrease the mechanical properties of these materials.VILLEURBANNE-DOC'INSA-Bib. elec. (692669901) / SudocSudocFranceF

Elaboration et caractérisation des nanocomposites alumine-SiC

L élaboration des céramiques nanocomposites s impose dans l actualité comme une des voies la plus prometteuse pour l obtention des matériaux céramiques ayant des propriétés remarquables. Toutefois, il s agit d une voie compliquée puisque la nanostructure et la densification des matériaux sont en général contradictoires. En effet, les relativement hautes températures et longues périodes de temps requises pour bien densifier les matériaux céramiques nanocomposites produisent le phénomène de grossissement des grains : dans ces conditions les phases présentes dans le composite cessent d être nanostructurées. Dans ce contexte, l utilisation de nouvelles techniques de frittage, telles que le Spark Plasma Sintering (SPS), peuvent aider à la consolidation de ce type de matériaux tout en conservant une microstructure fine. Ce travail de recherche a été consacré à l élaboration des micro-nanocomposites alumine/5vol% SiC en utilisant trois techniques de frittage : conventionnelle ou naturelle (FN), le pressage à chaud ( Hot Pressing ou HP) et principalement le frittage par Spark Plasma Sintering . Dans un premier temps, l étape de dispersion des poudres d alumine et de SiC a été optimisée afin de préparer des barbotines stables et homogènes et des poudres composites. Puis, les meilleures performances de la technique SPS par rapport aux autres techniques de frittage ont été mises en évidence. Ainsi, l utilisation du frittage SPS permet une meilleure maîtrise de la microstructure : densité élevée, microstructure fine et la localisation des particules nanométriques principalement en position intergranulaire.The development of ceramic nanocomposites is needed in the news as one of the most promising ways to obtain ceramic materials with remarkable properties. However, this is a complicated way since the nanostructure materials and densification are usually contradictory. Indeed, the relatively high temperatures and long periods of time required to fully densify the ceramic nanocomposite materials produce the phenomenon of grain growth: in these conditions the phases present in the composite cease to be nanostructured. In this context, the use of new sintering techniques, such as "Spark Plasma Sintering" (SPS), may help to consolidate this type of material while maintaining a fine microstructure. This research has been devoted to developing micro-SiC nanocomposites alumine/5vol% using three sintering techniques: conventional or natural (FN), hot pressing ("Hot Dry" or HP) and mainly the sintering by "Spark Plasma Sintering." As a first step, the step of dispersing powders of alumina and SiC was optimized to prepare stable and homogeneous slurry and composite powders. Then, the best performances of the technique compared to other SPS sintering techniques have been demonstrated. Thus, the use of SPS sintering allows better control of the microstructure: high density, fine microstructure and localization of nanoparticles mainly intergranular position.VILLEURBANNE-DOC'INSA LYON (692662301) / SudocVILLEURBANNE-DOC'INSA-Bib. elec. (692669901) / SudocSudocFranceF

Preparation and Characterization of Pressureless Sintered Alumina/5 vol % SiC Micro-Nanocomposites

Alumina/5 vol % SiC micro-nanocomposites were produced by slip-casting and pressureless sintering. The dispersion of alumina and SiC particles in water using an electrosteric dispersant was studied for different solid contents. Although the rheological and granulometry measurements showed that the optimum amount of Darvan C for well-dispersing 50 wt % dry matter slurries was 0.20 vol %, this content was increased to 1.00 vol % in order to avoid the demixing of SiC nanoparticles during shaping. Well densified (&gt;99%) alumina–SiC pressureless sintered materials were obtained at 1800 °C-2 h in which SiC nanoparticles occupied inter/intragranular positions. The creep behaviour of these materials was examined at 1200 °C under stresses ranging from 70 to 140 MPa. A good creep resistance in alumina-SiC materials was obtained demonstrating that the use of less expensive conventional sintering methods is possible and highlighting the importance of the dispersion step

Surface Coating of Oxide Powders: A New Synthesis Method to Process Biomedical Grade Nano-Composites

Composite and nanocomposite ceramics have achieved special interest in recent years when used for biomedical applications. They have demonstrated, in some cases, increased performance, reliability, and stability in vivo, with respect to pure monolithic ceramics. Current research aims at developing new compositions and architectures to further increase their properties. However, the ability to tailor the microstructure requires the careful control of all steps of manufacturing, from the synthesis of composite nanopowders, to their processing and sintering. This review aims at deepening understanding of the critical issues associated with the manufacturing of nanocomposite ceramics, focusing on the key role of the synthesis methods to develop homogeneous and tailored microstructures. In this frame, the authors have developed an innovative method, named “surface-coating process”, in which matrix oxide powders are coated with inorganic precursors of the second phase. The method is illustrated into two case studies; the former, on Zirconia Toughened Alumina (ZTA) materials for orthopedic applications, and the latter, on Zirconia-based composites for dental implants, discussing the advances and the potential of the method, which can become a valuable alternative to the current synthesis process already used at a clinical and industrial scale

Effect of loading configuration on strength values in a highly transformable zirconia‐based composite

International audienceObjectives: The aim of this work was to determine mechanical properties of a highly transformable 10Ce-TZP/Al2O3/La2AlO3 composite, currently developed as a biomaterial for dental application, and to investigate the effect of loading configuration on its flexural strength.Methods: Fracture toughness is determined by the single-edge-V-notched beam (SEVNB) method. Strength measurements were conducted by four-point bending and biaxial bending tests (piston-on-three balls) according to ISO 6872, dedicated to ceramic materials in dentistry.Results: Strength obtained by either four-point or biaxial bending are very different, and take the values of 596MPa and 1470MPa respectively. It is demonstrated that the difference in measured strength cannot be attributed to the effect of volume on strength, generally predicted by the standard Weibull analysis, but to different transformation behaviors for the two bending configurations. More extensive transformation occurs in the biaxial configuration, with a lower autocatalytic transformation stress threshold, resulting to substantial compressive residual stresses.Significance: The significant influence of the loading configuration on the strength should be integrated when designing a component from a highly transformable ceramic

Intergranular alumina-SiC micro-nanocomposites sintered by spark plasma sintering

International audienceAlumina-5 vol% SiC micro-nanocomposites with almost completely intergranular microstructure were produced by spark plasma sintering (SPS). Before sintering, well dispersed slurries were obtained by ball-milling of powders using an electrosteric dispersant in aqueous media. High density composites could be achieved at lower sintering temperatures by SPS, as compared with hot pressing (HP) sintering process. Microstructure studies show that the nano-SiC particles were mainly located at the alumina grain boundaries