New ZrO2/Al2O3 Nanocomposite Fabricated from Hybrid Nanoparticles Prepared by CO2 Laser Co-Vaporization.
ABSTRACT: Alumina toughened zirconia (ATZ) and zirconia toughened alumina (ZTA) are currently the materials of choice to meet the need for tough, strong, and bioinert ceramics for medical devices. However, the mechanical properties of ZrO2/Al2O3 dispersion ceramics could be considerably increased by reducing the corresponding grain sizes and by improving the homogeneity of the phase dispersion. Here, we prepare nanoparticles with an intraparticular phase distribution of Zr(1-x)Al(x)O(2-x/2) and (γ-, δ-)Al2O3 by the simultaneous gas phase condensation of laser co-vaporized zirconia and alumina raw powders. During subsequent spark plasma sintering the zirconia defect structures and transition alumina phases transform to a homogeneously distributed dispersion of tetragonal ZrO2 (52.4 vol%) and α-Al2O3 (47.6 vol%). Ceramics sintered by spark plasma sintering are completely dense with average grain sizes in the range around 250 nm. Outstanding mechanical properties (flexural strength σf = 1500 MPa, fracture toughness KIc = 6.8 MPa m(1/2)) together with a high resistance against low temperature degradation make these materials promising candidates for next generation bioceramics in total hip replacements and for dental implants.
Project description:Zirconia-toughened alumina (ZTA) using yttria-stabilised zirconia is a good option for ceramic-ceramic bearing couples for hip joint replacement. Gelcasting is a colloidal processing technique capable of producing complex products with a range of dimensions and materials by a relatively low-cost production process. Using gelcasting, ZTA samples were prepared, optimising the stages of fabrication, including slurry preparation with varying solid loadings, moulding and de-moulding, drying and sintering. Density, hardness, fracture toughness, flexural strength and grain size were observed relative to slurry solid loadings between 58 and 62 vol. %, as well as sintering temperatures of 1550 °C and 1650 °C. Optimal conditions found were plastic mould, 4000 g/mol PEG with 30 vol. % concentration, 61% solid loading and Ts = 1550 °C. ZTA samples of high density (maximum 99.1%), high hardness (maximum 1902 HV), high fracture toughness (maximum 5.43 MPa m1/2) and high flexural strength (maximum 618 MPa) were successfully prepared by gelcasting and pressureless sintering.
Project description:Developing high-radiation-tolerant inert matrix fuel (IMF) with a long lifetime is important for advanced fission nuclear systems. In this work, we combined zirconia (ZrO2) with magnesia (MgO) to form ultrafine-grained ZrO2-MgO composite ceramics. On the one hand, the formation of phase interfaces can stabilize the structure of ZrO2 as well as inhibiting excessive coarsening of grains. On the other hand, the grain refinement of the composite ceramics can increase the defect sinks. Two kinds of composite ceramics with different grain sizes were prepared by spark plasma sintering (SPS), and their radiation damage behaviors were evaluated by helium (He) and xenon (Xe) ion irradiation. It was found that these dual-phase composite ceramics had better radiation tolerance than the pure yttria-stabilized ZrO2 (YSZ) and MgO. Regarding He+ ion irradiation with low displacement damage, the ZrO2-MgO composite ceramic with smaller grain size had a better ability to manage He bubbles than the composite ceramic with larger grain size. However, the ZrO2-MgO composite ceramic with a larger grain size could withstand higher displacement damage in the phase transformation under heavy ion irradiation. Therefore, the balance in managing He bubbles and phase stability should be considered in choosing suitable grain sizes.
Project description: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.
Project description: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 ZrO₂ 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 ZrO₂ content. The material containing 10 vol % ZrO₂ presented a relevant hardness and exhibited the maximum value of KI0, mainly imputable to the t → m transformation at the crack tip.
Project description:Dense (>98 th%) and homogeneous ceramic/metal composites were obtained by spark plasma sintering (SPS) using ZrO2 and lamellar metallic powders of tantalum or niobium (20 vol.%) as starting materials. The present study has demonstrated the unique and unpredicted simultaneous enhancement in toughness and strength with very high flaw tolerance of zirconia/Ta composites. In addition to their excellent static mechanical properties, these composites also have exceptional resistance to fatigue loading. It has been shown that the major contributions to toughening are the resulting crack bridging and plastic deformation of the metallic particles, together with crack deflection and interfacial debonding, which is compatible with the coexistence in the composite of both, strong and weak ceramic/metal interfaces, in agreement with predictions of ab-initio calculations. Therefore, these materials are promising candidates for designing damage tolerance components for aerospace industry, cutting and drilling tools, biomedical implants, among many others.
Project description:Although ceramics have many advantages when compared to metals in specific applications, they could be more widely applied if their low properties (fracture toughness, strength, and electrical and thermal conductivities) are improved. Reinforcing ceramics by two nano-phases that have different morphologies and/or properties, called the hybrid microstructure design, has been implemented to develop hybrid ceramic nanocomposites with tailored nanostructures, improved mechanical properties, and enhanced functionalities. The use of the novel spark plasma sintering (SPS) process allowed for the sintering of hybrid ceramic nanocomposite materials to maintain high relative density while also preserving the small grain size of the matrix. As a result, hybrid nanocomposite materials that have better mechanical and functional properties than those of either conventional composites or nanocomposites were produced. The development of hybrid ceramic nanocomposites is in its early stage and it is expected to continue attracting the interest of the scientific community. In the present paper, the progress made in the development of alumina hybrid nanocomposites, using spark plasma sintering, and their properties are reviewed. In addition, the current challenges and potential applications are highlighted. Finally, future prospects for developing alumina hybrid nanocomposites that have better performance are set.
Project description:Although the thrombogenic nature of the surfaces of cardiovascular devices is an important aspect of blood biocompatibility, few studies have examined platelet deposition onto opaque materials used for these devices in real time. This is particularly true for the metallic surfaces used in current ventricular assist devices (VADs). Using hemoglobin depleted red blood cells (RBC ghosts) and long working distance optics to visualize platelet deposition, we sought to perform such an evaluation. Fluorescently labeled platelets mixed with human RBC ghosts were perfused across six opaque materials (a titanium alloy (Ti6Al4V), silicon carbide (SiC), alumina (Al2O3, 2-methacryloyloxyethyl phosphorylcholine polymer coated Ti6Al4V (MPC-Ti6Al4V), yttria partially stabilized zirconia (YZTP), and zirconia toughened alumina (ZTA)) for 5 min at wall shear rates of 400 and 1000 s(-1). Ti6Al4V had significantly increased platelet deposition relative to MPC-Ti6Al4V, Al2 O3 , YZTP, and ZTA at both wall shear rates (p < 0.01). For all test surfaces, increasing the wall shear rate produced a trend of decreased platelet adhesion. The described system can be a utilized as a tool for comparative analysis of candidate blood-contacting materials with acute blood contact.
Project description:This paper reports the improvement of microstructural and hardness properties of 3 mol% yttria-stabilized zirconia (3Y-TZP) ceramics with nano TiO2 powders (with 0, 0.9, 1.8, and 2.7 wt%) added using a low-temperature microwave-assisted sintering of 1250 °C. Even at such a low sintering temperature, all sintered samples had the main phase of tetragonal zirconia (t-ZrO2) without the appearance of the secondary monoclinic phase or TiO2 phase, and had high relative densities, larger than 95%. The grain growth was well developed, and the grain sizes were around 300-600 nm. The Ti and O elements appeared at the grain and grain boundary and increased with the increased nano TiO2 contents identified by the element analysis, although the TiO2 phase did not appear in the X-ray pattern. The Vickers hardness was in the range of 10.5 to 14.5 GPa, which first increased with increasing content till 0.9 wt% and then decreased. With citric acid corrosion treatment for 10 h, the Vickers hardness only decreased from 14.34 GPa to 13.55 GPa with the addition of 0.9 wt% nano TiO2 powder. The experiment results showed that 0.9 wt% nano TiO2 addition can improve the densification as well as the Vickers hardness under a low temperature of microwave-assisted sintering.
Project description:A new friction counterpart for carbon fiber-reinforced silicon carbide ceramic-matrix composites (C/SiCs) and zirconia (ZrO2) toughened by magnesia ceramics is proposed. The effects of the C/SiC surface processing parameters friction on the tribological performance are investigated under dry friction and ambient temperature conditions. The wear tests are carried out using the pin-on-disc friction method. Scanning electron microscopy (SEM) on an instrument equipped with an energy dispersive spectroscopy (EDS) is used to observe the surfaces of the pins and discs before and after the application of friction to reveal the wear mechanism. The results show that surface processing influenced the tribological properties of C/SiC significantly. When the pressure is 30?N, the speed is 0.5?m/s, and the C/SiC surface is ground using 1500# sandpaper, the counterpart tribological performance is the best among the samples considered herein. It is found that the retention ability of the counterparts influenced the tribology performance significantly.
Project description:In situ grown C0.3N0.7Ti and SiC, which derived from non-oxide additives Ti3SiC2, are proposed to densify silicon nitride (Si3N4) ceramics with enhanced mechanical performance via hot-press sintering. Remarkable increase of density from 79.20% to 95.48% could be achieved for Si3N4 ceramics with 5 vol.% Ti3SiC2 when sintered at 1600 °C. As expected, higher sintering temperature 1700 °C could further promote densification of Si3N4 ceramics filled with Ti3SiC2. The capillarity of decomposed Si from Ti3SiC2, and in situ reaction between nonstoichiometric TiCx and Si3N4 were believed to be responsible for densification of Si3N4 ceramics. An obvious enhancement of flexural strength and fracture toughness for Si3N4 with x vol.% Ti3SiC2 (x = 1~20) ceramics was observed. The maximum flexural strength of 795 MPa for Si3N4 composites with 5 vol.% Ti3SiC2 and maximum fracture toughness of 6.97 MPa·m1/2 for Si3N4 composites with 20 vol.% Ti3SiC2 are achieved via hot-press sintering at 1700 °C. Pull out of elongated Si3N4 grains, crack bridging, crack branching and crack deflection were demonstrated to dominate enhance fracture toughness of Si3N4 composites.