Abstract: Alumina-SiC nanocomposites have attracted the interest of material scientists due to their excellent mechanical and thermomechanical properties. Compared to alumina they offer higher strength, toughness and reliability. The high creep resistence of alumina-SiC makes it attractive for high temperature structural applications.
Commercial applications however require performing and reliable manufacturing technologies. Ceramic injection molding (CIM) was chosen for the production of small and complex shaped components with narrow dimensional tolerances used in engineering applications. For axially symmetric, elongated component geometries such as tubes or rods, thermoplastic extrusion is a more appropriate forming technology. In this study the complete process cycle of thermoplastic extrusion and injection molding was evaluated with the aim to evaluate their suitability for industrial production of alumina-SiC nanocomposites. Compounding of the feedstocks, forming by CIM and extrusion and the subsequent thermal treatment – debinding and pressureless sintering were investigated. Intermediate and final products were characterized with respect microstructure and mechanical.
Abstract: The paper demonstrates the possibility to control the degree of tetragonal zirconia
stabilization, microstructure and physical and mechanical behavior of Al2O3 -ZrO2(Y2O3) ceramic
Control is exerted via the process variables during deposition synthesis of nanosized composite
powders from hydroxide salts, and their subsequent heat treatment and consolidation.
Morphology features of nanosized powder systems and microstructures of the consolidated
nanostructured materials were characterized by BET surface are measurements, scanning electron
microscopy (both standard and HR), and large-angle X-ray diffraction.
Correlations are established between microstructure parameters, physical and mechanical behavior
of composite ceramics and a degree of stabilization of tetragonal ZrO2.
Abstract: One of the most recent alternatives in the development of materials with high mechanical
properties and wear resistance is the addition of nanometric and/or micrometric particles of a
secondary phase into ceramic matrices. Nanostructured materials can be defined as systems that
have at least one microstructural characteristic of nanometric dimensions (less than 100nm). In this
work, alumina-diamond nanocomposites were produced using nanometric diamond powder
obtained by high energy milling in a SPEX mixer mill for 6h. The crystallite size was 30nm. After
deagglomeration, the diamond powder was added to the alumina matrix in a ratio of 5wt%. The
samples were isostatically pressed and high-vacuum sintered. The resulting nanocomposites and
composites were characterized by X-ray diffraction (XRD) and scanning electron microscopy
(SEM), and by microhardness, diametral compression and wear resistance tests. The results
confirmed the promising wear characteristics of the alumina-diamond nanocomposite.
Abstract: One of the most important problems in both the fabrication and exploitation of ceramicmetal
composites are residual thermal stresses. The paper presents the results of a numerical
analysis (by the Finite Elements Method) of the stress state induced in the NiAl matrix composites
reinforced with spherical particles of a ceramic phase (Al2O3, ZrO2, TiC), including examinations of
the dependence of this stress state on the volumetric fraction of the ceramics (20 to 40vol.%). The
stress state prevailing in this composite appeared to be complex. In all the samples, the stresses
active in the ceramic regions were compressive whereas those active in the metal matrix were
tensile in the circumferential direction and compressive in the radial direction. An increase of the
ceramic volumetric fraction resulted in an increase of the tensile stresses in the NiAl matrix and a
decrease of the compressive stresses in the ceramic particles.
These theoretical results were verified experimentally by examining the properties of the
NiAl-Al2O3, NiAl-ZrO2 and NiAl-TiC (20 and 30 vol.% fraction of the ceramics) composites
produced by hot-pressing. The microstructure, density, and bending strength of these composites
were examined, and the results are discussed in the paper.
Abstract: This work is focused on the modeling of thermal stresses induced during the fabrication
of the metal/ceramic composites. On example of Cr-Al2O3 composite processed by powder
metallurgy, thermal stresses after fabrication are determined by FEM model for different contents of
metal and ceramic phases. Numerical model of microcracking induced by thermal stresses is then
proposed and applied to compute the overall elastic properties of the damaged composite.
Comparison of the model predictions with the measured data for Young's modulus is presented.
Abstract: Yttria is an interesting material for the production of high performance ceramic cores
for Directionally Solidified investment casting. DS casting of superalloys of the last generation
challenge conventional silica ceramic cores, because of the high temperatures and the long times
involved. Compared to silica, yttria is characterized by improved mechanical properties and higher
chemical resistance at high temperatures. Submicronic and nanometric SiC reinforcements were
tested in order to increase compression creep resistance of yttria. Oxidation resistance of both
reinforcements was tested in conditions simulating the industrial process. The experimental results
demonstrated the increase of compression creep resistance and showed that the industrial
application of yttria ceramic cores reinforced with submicronic SiC is possible with minimal
changes to current practices, thanks to a high enough oxidation resistance.
Abstract: There is a growing interest in the application of ceramic as high wear resistance materials due to the unique properties. Although brittleness and low toughness, recent improvements in alumina processing have lessen this restrictions and suggest improvements in wear resistance which in turn have driven some research on this. Since a direct comparison between the many published works regarding this wear improvement is complicated due to the fact that wear resistance is a response of the microstructure, material and testing condition, the work herein presented aims to first do a literature review on the main parameters to be controlled in a pin-on-disc apparatus on the wear of alumina and then discuss preliminary test results and analyze the influence of critical parameters as load and sliding speed in a pin-on-disc wear test in a dense and sub micrometer grain size alumina.
Abstract: Machining processes require tool materials with properties such as high hardness at elevated temperature, high fracture toughness and chemical stability with the workpiece. Advances in science and industry, as well as the development of harder materials have permitted cutting tool technology to evolve. In cutting processes, the contribution of different wear mechanisms to total wear is related to the mechanical and chemical properties of the two materials in contact. The high temperatures at tool-workpiece contact zones often result in diffusion of material from the workpiece to the cutting tool. Diffusion experiments were carried out to understand wear mechanisms involved at cutting edges of ceramic tools and the influence of microstructure on diffusion without the interference of mechanical wear processes. The chemical stability was analyzed from static interaction couple experiments at 1100°C with ceramic composite materials and gray cast iron. To investigate the influence of grain size on diffusion, sub-micrometric and nanometric alumina based composites with NbC as the second phase were used. These experiments showed that the influence of grain size on diffusion and the relative inertness of the composites in the presence of gray cast iron.