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Key engineering materials
Trans Tech Publications Ltd.
Key engineering materials

Trans Tech Publications Ltd.

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1013-9826

Key engineering materials/Journal Key engineering materials
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    Superplasticity in ceramics: applications and new trends

    A.Dominguez-RodriguezD. Gomez-Garcia
    3-13页
    查看更多>>摘要：In this review paper, the macro and microcharacteristics of superplasticity will be analyzed. Based on the macroscopic features of the superplasticity, the joining of ceramics as a new application will be analyzed with special emphasis in the fabrication of functional gradient ceramics materials. Finally, the new trends as high strain rate superplasticity (HSRS) or superplasticity at low homologous temperature will be discussed.
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    Structural effect on the plastic behavior in highly porous glasses

    T. WoignierA. Hafidi AlaouiJ. PrimeraJ. Phalippou...
    15-24页
    查看更多>>摘要：Silica aerogels have been studied with the objective of understanding the mechanical behavior of these extremely porous (pore volume higher than 85%) glassy materials. Elastic and plastic behaviors are investigated using Hg porosimetry. Because of the peculiar structure of these materials, Hg liquid cannot enter their porous network and consequently induces an isostatic pressure. Due to the high compliance of the solid network, under isostatic pressure aerogels display an irreversible shrinkage caused by plastic deformation. The magnitude of the plastic shrinkage and the increase of the associated mechanical properties depend on the different parameters (porosity, elastic properties and structural features). The structural features are followed by X Rays scattering. The irreversible compaction can be explained by siloxane bond formation between clusters constituting the porous materials, retaining the strained structure. The pore collapse mechanism is favored by the large pores structure and loose cluster structure (low fractal dimension). This densification process could offer a new way to synthesize porous glasses at room temperature.
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    Grain Size Strengthening in Microcrystalline Copper: A Three-Dimensional Dislocation Dynamics Simulation

    C. de SansalB. DevincreL. Kubin
    25-32页
    查看更多>>摘要：This article reports on a study of the microstructure and mechanical response of copper polycrystals with grain sizes in the micrometer range. Three-dimensional dislocation dynamics simulations are used for the first time to investigate grain boundary strengthening and the Hall-Petch law. The methodology, which involves constructing a microcrystalline representative volume element with periodic boundary conditions, is briefly presented. Simulation results show that the initial density of dislocation sources and the cross-slip mechanism are two key factors controlling the heterogeneity of plastic deformation within the grains. At yield, the smaller the grains size, the more plastic deformation is heterogeneously distributed between grains and homogeneously distributed inside the grains. A size effect is reproduced and it is shown that the Hall-Petch exponent decreases from the very beginning of plastic flow and may reach a stable value at strains larger than the conventional proof stress.
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    Study of erosion behaviour of conventional and nanostructured WC-12Co coatings sprayed by atmospheric plasma

    V. BonacheM.D. SalvadorJ.C. GarciaV. Garcia...
    35-40页
    查看更多>>摘要：Thermal sprayed WC-Co coatings are used extensively to enhance the wear resistance of a wide range of engineering components. In this paper, erosive resistance of plasma atmospheric sprayed WC-12Co coatings has been evaluated. Solid particle erosion tests were conducted on these coatings at different angles of impact with silica and alumina abrasives of size 250 μm. Coatings have been deposited by using micrometric and nanometric agglomerated powders, employing H_2 and He as plasmogen gas. In order to determine the erosion regime (ductile or brittle), the influence of impact angle on the erosion rate has been studied. Optical microscope and FESEM have been used to analyze the eroded surface. The influence of the plasmogen gas and the powder employed on the erosive behaviour of the coating has been evaluated. An attempt to connect the erosive behaviour with mechanical properties and microstructure has been made. Hardness has been determined by means of several measurements of Vickers microhardness; fracture toughness has been estimated through indentation method. Identification of phases has been made by means of X Ray diffraction.
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    Influence of thermal effects produced by laser treatment on the tribological behavior of porcelain ceramic tiles

    F. Gutierrez MoraA. Dominguez RodriguezV.V. LennikovG.F de la Fuente...
    41-46页
    查看更多>>摘要：Commercial porcelain ceramic tiles have been irradiated with a laser to evaluate the thermal effects on their surface and in their tribological behavior. Different irradiation patterns were followed, varying the density of points where the laser was focused, from 25 to 150 dots per inch. Hardness and toughness were evaluated using Vickers indentations. Tribological behavior was studied using a ball-on-flat apparatus with alumina balls. An increase in the wear rate was observed in the higher irradiated samples, which can be correlated to a decrease in their toughness. A mechanism of severe wear by fracture propagation and material pullout is proposed to explain the experimental data and the observed corresponding microstucture.
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    Wear resistance of metal oxide sol-gel coatings deposited over ceramic glazes

    R. GalindoC. GargoriS. CerroJ. Badenes...
    47-53页
    查看更多>>摘要：This paper analyse the wear resistance of high reflective metal oxide films of TiO_2 (anatase), Fe_2O_3 (hematite), ZrO_2 (Zirconia) and SnO_2 (Casiterite) deposited by screen printing over a conventional ceramic glaze (molar composition 0,2CaO.0,15ZnO.0,05K_2O.0,1Al_2O_3 0,45SiO_2.0,05ZrO_2). All oxide coatings increase the gloss of the substrate producing a lustre effect. Anatase films stand out for their high gloss valour and low roughness R_a. Likewise, all lustres improve the wear resistance of the glaze substrate. Hematite and casiterite coatings stand out for their relatively high wear resistance maintaining relatively high reflectivity.
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    Effect of the crystalline phase on the brittleness index of glass ceramic surfaces

    C. GargoriR. GalindoM.A. TenaA. Garcia...
    55-60页
    查看更多>>摘要：Different crystalline phases (tetragonal zirconia, titanite, celsian, diopside, anortite, zircon, scheelite, casiterite, gahnite and spodumene) have been devitrificated into a transparent ceramic glaze by addition of oxides that acts as crystallisation agents. Microstructure, wear resistance and gloss of glass ceramic surface obtained on fired modified glazes are studied. All crystalline phases diminish the brittleness index of the original transparent glaze. Anortite stands out among reinforcing phases that produces dull surfaces associated with high roughness. On the other hand, zircon stands out among the phases that improve gloss surface together wear resistance.
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    On the high-temperature plasticity of ceria-doped zirconia nanostructured polycrystals

    S. de Bernardi-MartinE. Zapata-SolvasD. Gomez-GarciaA. Dominguez-Rodriguez...
    61-66页
    查看更多>>摘要：Ceria-zirconia ceramic alloys with the following molar composition: 0.12CeO_2-0.88ZrO_2 have been sintered by high-temperature annealing. Monolithic specimens haven been crept in compression at high temperatures. Creep experiments have been rationalized to an empirical constitutive equation which is consistent with a classical Ashby-Verrall creep regime. This result has been assessed through microstructural characterization of as-received and post-mortem specimens. A pure Ashby-Verrall creep is contrary to the conventional mechanism controlling creep in other zirconia alloys. A discussion on the explanation for such mechanism is outlined.
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    Spark plasma sintering and microstructural characterization of additive- free polycrystalline β-SiC

    A. LaraR. PoyatoA. MunozA. L. Ortiz...
    67-72页
    查看更多>>摘要：Additive-free β-SiC powders were sintered by means of Spark Plasma Sintering System. Experiments were performed in the temperature range from 1650℃ to 2200℃, 3 to 10 min holding time and pressure from 50 until 150 MPa. In order to favour sinterization, the starting powder was mechanically activated: defect concentration was increased by centrifugal ball milling. Applied temperature, holding time and/or pressure were varied to analyze their effect on the densification and grain growth kinetics. The full sinterization of the material was obtained for temperatures as high as 1900℃ and over. The relative density of the obtained material was high, up to 97.0 ± 0.6 % the theoretical density for 2200℃ sintering temperature. An intense grain growth took place while sintering. The final microstructure exhibited a grain size distribution range from 1.0 to 2.5 μm, depending on the sintering conditions. Such grain growth strongly depends on the sintering time, not so much on the sintering temperature.
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    A Method for Elasticity Modulus Calculation in Porous Media with known Geometry using the Monte Carlo Technique

    Liz AnezJuan PrimeraAnwar HasmyPedro Franceschini...
    75-82页
    查看更多>>摘要：This study introduces a method for a computational calculus of the Elasticity Modulus (E) of simulated porous media using the Monte Carlo technique. The porous media of known geometry is simulated as an elastic network of central forces, to which a known deformation is applied. The minimum strain energy is calculated applying the Monte Carlo technique. The Elasticity Modulus is obtained from the theoretical relations between the elastic energy of a system and its deformation. The computational method is validated by applying it in systems of known analytic solution and over porous media generated through aggregation algorithm in two dimensions i.e. Random Sequential Aggregation and Diffusion Limited Cluster-Cluster Aggregation (RSA and DLCA respectively). The latter used to simulate the structure of silica aerogels. As for the range of concentrations studied for the DLCA and RSA systems, it was found that the elasticity modulus E decreases as the porosity of the system increases, being the E value higher for the DLCA system with respect to RSA. The method used is able to differentiate the elastic properties for two different aggregation models. Being E values different for equal porosities, the coordination number (Z) was the geometric parameter that best explains the behavior of the Elasticity Modulus.
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