Papers by Keyword: Ceramic

Abstract: This aim of this study is to investigate the effect of UV (Ultra Violet ray) irradiation on the interfacial adhesion strength between thin ceramic films and polymer substrate. Electric conductive films based on polymer substrates have attracted attention for use in flexible optoelectronic devices. It is well known that the mechanical properties of polymeric materials are degraded by UV irradiation. Therefore, it is considered that the UV irradiation also affects the interfacial adhesion strength between ceramic coating and polymer substrate. The interfacial adhesion strength was measured by Multi-stages peel test. The results show that the interfacial strength decreases with UV irradiation. However, if a filter layer is installed between ceramic and polymer substrate, the degradation ratio becomes small.

Abstract: As an advanced in-core material in high temperature gas-cooled reactors (HTGRs), superplastic ceramics is attractive due to the possibility of the plastic working. For the application to the nuclear fields, the basic concept of design criteria was studied for typical superplastic ceramics, tetragonal zirconia polycrystals containing 3mol% yttria (3Y-TZP). The experimental results on 3Y-TZP showed that it is possible to apply the Weibull weakest-link theory to decide the stress limits in the criteria. The Weibull parameter m was evaluated as 9.5 for the bending and as 26.5 for the compressive. The applicability of the Weibull theory was also verified by the bending test results with different span. Based on the graphite structural design guidelines for the High Temperature Engineering Test Reactor (HTTR), the design stress limits for 3Y-TZP was proposed. It was shown that the proposed stress limits have appropriate safety margin and thought to be effective to evaluate the integrity of in-core structure made of 3Y-TZP.

Abstract: The anisotropy that is inherent to piezoelectricity is directly tied to the symmetry of domains within the crystals of polycrystalline piezoelectrics. Alloy design for these oxide materials is often focused on influencing pinning of domain walls in polycrystals that have been subjected to high fields and elevated temperatures to introduce the ‘poled’ condition from which most piezoelectric devices operate. We have investigated a wide range of these oxides consisting of single phases or mixtures of phases that may be all or partially piezoelectric in character. Crystal symmetries investigated include tetragonal, orthorhombic, rhombohedral and monoclinic with some phase transitions evolving during high-temperature processing or during poling. Materials investigated include a range of bismuth titanates, lead titanates, lead zirconate titanates and sodium niobates. A variety of texture evaluation techniques, including area detector x-ray diffraction, synchrotron x-ray sources, and neutron sources have been utilized along with Rietveld diffraction modeling tools to enable a deeper understanding of domain textures, domain texture evolution and synergistic relations between crystallographic textures and domain textures. This paper documents an understanding of texture and anisotropy in these materials, and provides insight on approaches to optimize textures for high performance in these materials and demonstrates how these tools can be used to evaluate processing variations from production of these materials.

Abstract: A BN interphase has been deposited by infiltration of a Hi-Nicalon fibre tow in a Low Pressure Chemical Vapour Deposition reactor using a boron nitride molecular precursor: the tris(dimethylamino)borane (TDMAB), an halogen-free precursor. This precursor prevents fibre and CVD apparatus from chemical damage. Then SiC/BN/SiC 1D mini-composites were produced by classical CVD of SiC from hydrogen and methyltrichlorosilane mixture. The interphase composition was characterised using FT-IR and XPS analyses and the presence of carbon in the BN has be related to surface pollution and not from carbon bounded to the coating. The tensile properties of the mini-composites were tested with unload-reload cycles and have shown very good mechanical properties corresponding to a high interfacial shear stress. The observations of the interphase using TEM reveal that it is made of an anisotropic turbostratic BN. The fibre/matrix debounding, which occurs during mechanical loading, was shown to be located within the BN interphase.

Abstract: The high-strength reaction-sintered silicon carbide (RS-SiC) developed by TOSHIBA is one of the most excellent materials for large-scale space-borne optics. The bending strength of the high-strength RS-SiC is two times higher than other SiC ceramics. The purpose of this study is to investigate the ELID grinding properties of the high strength RS-SiC. Two types of metal bond diamond wheels (cup type and straight type) were used to grinding tests. The ground surface properties, such as roughness, subsurface damage and micro-step were made clear by measurement or observation. It was confirmed that, both the surface roughness and the depth of micro-step produced by cup-wheel were lower than those produced by straight-wheel. When a #20000 grit sized cup-wheel was used, a considerably high quality mirror surface (Ra<0.8nm) can be achived.

Abstract: This paper describes the technology and microstructure of Al2O3-Fe functionally graded composites, FGM, obtained by slip-casting under magnetic field. Alumina a-Al2O3, provided by Alcoa (symbol A16SG), with average grain size of 0.5 µm, and iron powder, (symbol Distaloy AB) from Hoganas, with average grain size of 35 µm, were used to produce a series of specimens which differed in contents of Fe particles in Al2O3. As a source of magnetic force a permanent magnet was used. Preforms were sintered in a vacuum at temp. 1470oC. The microstructures of the specimens were quantitatively described via stereological methods. Sections, parallel to the magnetic field lines were analyzed using special image analysis software. Stereological methods presented in this work have been used to determine gradient in the volume fraction of the Fe particles and variation in their size and dispersion. These parameters are essential for controlling the technological process of interest and to design microstructure for needed properties (fracture toughness).

Abstract: New functionally graded Al2O3/Y-ZrO2 ceramics are developed as a new material for production of hip prosthesis, especially all-ceramic hip bearings. The used concept of graded ceramics is expected to provide better long-term performance based on improved mechanical properties and lower clinical risks. Mechanical properties are strongly dependent on the distribution of residual stresses resulting mainly from phase specific stresses after cooling from the sintering temperature. However, these stresses could be optimized by an appropriate selection of a concentration profile of constituent phases. The non-destructive neutron diffraction mapping of residual stresses has been used to investigate this problem experimentally. In addition, the smallangle neutron scattering technique was applied to study the porosity in the ceramics as function of the production parameters.

Abstract: Ultrafine hydroxyapatite (HA) and fluorhydroxyapatite (FHA) powders were synthesized and dense bioceramic samples were fabricated thereof. The samples were treepoint bend tested in different environments, i.e. in ambient air, distilled water and simulated human saliva, in the wide deformation rate range. Weibull’ statistics test was performed under standard testing conditions but in different media. The stress velocity exponent was evaluated from the dynamic fatigue testing data. The mean strength is shown to decrease when both ceramics are exposed to water or to simulated saliva. HA ceramics is more susceptible to the environment compared to FHA ceramics, due to the later is less subjected to the stress corrosion. Fracture surface observations revealed the crack propagation is of mixed trans- and intergranular mode. Strength distribution changes from uni-modal in air environment to bimodal in harsh conditions of water and saliva, indicating slow increment of flaw size in ceramics. Crack velocity exponent values correspond to transient region from dissociative chemisorption to ion solvation mechanisms of stress corrosion in both HA and FHA ceramics. Generally, FHA ceramics is considered to be much more reliable for application in bone defects replacement or dental reconstruction.

Abstract: Laser scanning confocal microscopy (LSCM) is a microscopic technique which allows for height discrimination. The ability to gather 3D data, along with adequate resolution (around 400 nm), makes the technique suitable for fractography; however, its applications in this area are not sufficiently explored. In this work, LSCM and SEM are applied to the study of fracture surfaces in sapphire and ruby fibers submitted to tensile stress in high-temperature conditions. The obtained qualitative and quantitative information demonstrates the validity of LSCM as a fractographical technique, allowing for clear identification of fractographical features and providing novel insight in the phenomenon of subcritical crack growth (SCG).

Abstract: The process of edge flaking of brittle materials is a significant limitation in design, handling and use of components. Simple quasistatic tests to identify resistance to edge flaking can be based on near-edge indentation and scratching towards an edge, and these produce rankings of materials that broadly correlate with GIc or KIc. However, most edge damage occurs in practice by impact. Using a drop-weight impact tester, edge chipping tests have been performed dynamically on a range of brittle materials, using repeated impact with step-wise height increments until fracture. It has been found that when impact energy rather indentation force is used as the correlative parameter against distance of the impact site from the edge of the test-piece, a similar relationship to that of quasistatic indentation is found. The shapes of edge flakes produced may also similar. This suggests that even when a relatively blunt impactor is used, compared with conventional indenters, the mechanics of the failure are similar. However, the occurrence of ring cracks can lead to unusual flake shapes. It follows that simpler-to-perform quasistatic tests can model the less well-defined dynamic impact situation in terms of testing for the effects of geometry or for comparing performance of different material types.