Papers by Author: Katarzyna Pietrzak

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: Porous ceramic materials are used in medicine as well as in industry. They can be prepared in the form of filter components, thermal insulators, or composite components. Preforms of this type can only be applied if they meet the respective structural requirements. In the present study, such a porous ceramic material was produced by the polymeric sponge method using a polyurethane sponge and a-Al2O3 Almatis. The aqueous suspension was prepared with binders of the two types: polyvinyl alcohol and a dispersion based on methacrylic acid esters and styrene. The aim of this study was to find the relationship between the composition of the weight slips, sintering conditions, and the structure of the porous ceramic obtained. The paper presents the results of studies on the rheological properties of the ceramic slurries and the results of strength tests of the ceramic material.