Mechanical properties of silicon nitride-based ceramics and its use in structural applications at high temperatures

Silicon nitride (Si3N4) based ceramics are gaining more and more attention due to their promising high-temperature thermal and mechanical properties. They have been expected to be the main candidates for applications such as turbocharger rotors and gas turbine engine components which can withstand severe conditions of temperature and heavy loads. Although a big number of studies on silicon nitride are published, a continuous progress in monolithic Si3N4 as well as Si3N4/Si3N4 composites (seeded materials) leads to new scientific and technological data providing new insight that should be reviewed taking into account their excellent properties at high temperatures. Silicon nitride possesses a bunch variety of interesting properties that can be specifically designed to produce a given behavior profile. That is why the room temperature and high-temperature properties are discussed and described in more detail. (C) 2009 Elsevier B.V. All rights reserved

Dense and near-net-shape fabrication of Si3N4 ceramics

With silicon nitride significant progress has been made in order to search for fully dense, strong, reliable structural ceramics to find wide use in applications at high temperatures which are allowing new and innovative solutions to component design problems. Taking into account that more and more ceramic components based on Si3N4 are being used in the aerospace and automobile industries, it is a great challenge to fabricate such complex-shaped components with high reliability and with defect-free microstructures such as pores, inclusions or any other inhomogeneity at acceptable costs. On the other side, the high hardness Of Si3N4 ceramics is almost always cost prohibitive to shape components by hard machining. It is therefore great effort exhibited in the development of near-net-shape fabrication processes that can produce complex-shaped components with a minimum of machining as well as to minimize the number and size of microstructural defects within design limits. In this review, the fabrication of near-net-shape Si3N4 ceramics is given in detail. All kinds of these techniques (injection molding, gel-casting, robocasting, mold shape deposition, rapid prototyping) and their advantages and disadvantages are explained. (C) 2008 Elsevier B.V. All rights reserved

Novel process for the production of 3Y-TZP ceramics: comparison between ageing in artificial saliva and accelerated ageing

The degradation of tetragonal zirconia polycrystalline (3Y-TZP) ceramics prepared by a novel film growth technique, and by sintering at 1400 °C, was evaluated for one year using two processes: (i) degradation under oral conditions in artificial saliva (37 °C and pH 6.8) and (ii) accelerated degradation by autoclaving at 134 °C at 0.2 MPa of pressure. X-ray diffraction analysis of 3Y-TZP ceramics sintered at 1400 °C showed a phase transformation (tetragonal to monoclinic) in 3Y-TZP ceramics after the fifth month in artificial saliva. After 12 months in artificial saliva, there was ∼11% of monoclinic phase present in 3Y-TZP ceramics, but only ∼2% of monoclinic phase in samples that were subjected to accelerated degradation for 5 h. No correlation was found between the level of ageing during accelerated degradation and degradation in artificial saliva. There was no degradation of 3Y-TZP ceramics prepared by a novel film growth technique, independently of the degradation method used, which suggests that this material could be used for dental prosthetics

Experimental and theoretical determination of the stopping power of ZrO2 films for protons and α-particles

We report the results of an experimental-theoretical study on the stopping power of ZrO2 films for swift H and He ion beams. The experiments, using the Rutherford Backscattering technique, were done for protons with incident energies in the range 200–1500 keV and for α-particle beams with energies in the range 160–3000 keV. The theoretical calculations were done in the framework of the dielectric formalism using the MELF-GOS model to account for the ZrO2 target electronic response. It is shown that for both ion beams, the agreement between theory and experiment is quite remarkable.This work has been financially supported by the Brazilian CNPq Agency (Contract 150757/2007). EDC acknowledges support from the Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Argentina