Abstract: 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.
Abstract: 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.
Abstract: 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.
Abstract: 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 H2 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.
Abstract: 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.
Abstract: This paper analyse the wear resistance of high reflective metal oxide films of TiO2 (anatase), Fe2O3 (hematite), ZrO2 (Zirconia) and SnO2 (Casiterite) deposited by screen printing over a conventional ceramic glaze (molar composition 0,2CaO.0,15ZnO.0,05K2O.0,1Al2O3 0,45SiO2.0,05ZrO2). 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 Ra. 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.
Abstract: 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.
Abstract: Ceria-zirconia ceramic alloys with the following molar composition: 0.12CeO2-0.88ZrO2 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.