Papers by Author: K. Konopka

Abstract: The fabrication of 3D interpenetrating phases in ceramic-metal composites by high pressure sintering of ceramic powder coated with Ni-P nanoparticles produced by electro-less chemical plating is reported. Electro-less nickel plating resulted in a nano-metric layer of spherical Ni-P nanoparticles of approximately 20-50 nm diameter over the entire surface of the ceramic powder. The coated powders were consolidated by hot pressing (HP) process followed by pressureless sintering after cold isostatic pressing (CIP). SEM, TEM and XRD methods were used to investigate the influence of the consolidation temperature and pressure on the microstructure of composites and particularly the morphology of metallic Ni-P phase. The homogeneity of the interpenetrating network structure was measured by computer image analysis and compared with the results of electric resistance measurements. The results indicate that the use of electroless nickel plating and high pressure consolidation process enables the fabrication of uniform 3D interpenetrating continuous metal-ceramic composites and controlled-density composites possessing a metallic phase of nano- or micro-metre size.

Abstract: An Al2O3/Ni-P composite was formed by hot pressing of alumina powder, coated with chemically plated nano Ni-P. The powders were consolidated at room temperature, 600 and 1000oC. The consolidated specimens were studied by SEM, TEM/HRTM, MFM (magnetic force microscopy) and tested or hardness. It was found that the fabrication method results in a structure of interpenetrating phases of high electric conductivity and that samples consolidated at room temperature and sintered at 600oC retain the nanometric grain size of the metallic phase. Hardness measurements are discussed in terms of the fabrication temperature and structure of the composites.

Abstract: Nanoparticles of carbides, nitrides and carbonitrides can be used to reinforce polymer matrix nanocomposites to obtain the required strength, hardness, corrosion and wear resistance. In order to efficiently achieve the desirable properties the polymer matrix and nanoparticles must be optimised. This paper reports on studies undertaken on TiC reinforced polymer matrix nanocomposites. The TiC nanoparticles were produced by sol-gel method and nanocomposites were obtained in situ, via the reaction and synthesizing of polyether-ester copolymer (PEE). TiC nanoparticles were characterised with a scanning electron microscopy (SEM) and the microstructure of the composites was examined by SEM and atomic force microscopy (AFM). Tensile properties were determined. For comparison, samples of polymer were also studied and composites with submicron size of TiC particles. The results, which are discussed in terms of size of the TiC particles, showed that the particles incorporated in the polymer matrix, influence the strength of the composites.

Abstract: This paper describes the technology and microstructure of Al2O3-Fe functionally graded composites, FGM, obtained by slip-casting under magnetic field. Alumina a-Al2O3, provided by Alcoa (symbol A16SG), with average grain size of 0.5 µm, and iron powder, (symbol Distaloy AB) from Hoganas, with average grain size of 35 µm, were used to produce a series of specimens which differed in contents of Fe particles in Al2O3. As a source of magnetic force a permanent magnet was used. Preforms were sintered in a vacuum at temp. 1470oC. The microstructures of the specimens were quantitatively described via stereological methods. Sections, parallel to the magnetic field lines were analyzed using special image analysis software. Stereological methods presented in this work have been used to determine gradient in the volume fraction of the Fe particles and variation in their size and dispersion. These parameters are essential for controlling the technological process of interest and to design microstructure for needed properties (fracture toughness).

Abstract: The influence of sintering temperature and high pressure on Ni-P nanoparticles in Al2O3/Ni-P nanocomposites was investigated in this paper. The fine-grained alumina powder was covered with Ni-P nanoparticles of 20 – 50 nm size by electroless nickel plating. The material was sintered in temperatures from 900 to 1400oC using pressures above 5 GPa. It was found that sintering in such conditions give a possibility to maintain nanometrical size of Ni-P particles. In the case of 1400oC the metallic phase melts and non-uniform grain growth of ceramic was observed. Hot pressing at 900oC allowed for the metal to remain in solid state and ensured uniform microstructures of the nanocomposites, with uniform distribution of nanometrical Ni-P grains in the ceramic matrix. In this temperature the grain growth of the ceramic was not observed. The results are discussed in terms of technology for production of ceramic-metal composites for various applications.

Abstract: This paper describes technology, which can be used to obtain ceramic-metal composites with a gradient of metal particles concentration. Graded composites, have been obtained by slip casting. The gradient of iron concentration was induced by magnetic field. Microstructures of the specimens have been investigated using a light and scanning electron microscopy. Quantitative analysis of microstructures has been carried out with the help of image analyzer. The obtained results prove the possibility to produce Al2O3-Fe functionally graded materials under the magnetic field.

Abstract: The present paper is focused on ceramic–metal composites obtained via different technologies which leads to different microstructures in terms of size and distribution of metal phase. Composites analysed in paper were produced by the following methods:(a) infiltration of porous ceramics by metal, (b) consolidation under high pressure and (c) sintering of ceramic powder coated by metal. Their microstructures were investigated by scanning and transmission electron microscopy methods. The three methods of composite fabrication employed in the present study result in specific spatial distribution and dispersion of metal phase. Presureless infiltration of porous ceramics by liquid metal is driven by capillary force and make it possible to produce microstructure with percolation of metal phase in ceramic matrix. The volume fraction of metal phase in this case depends on the size of pores. The size of pores influence also the kinetics and extent of infiltration. Ceramic preforms with small size of pore are not fully infiltrated. This method is useful for composite with size of metal phase in the range of micrometers. Hot pressing under high pressure produces microstructures of composites with metal phase grain size in the range from nano to micrometers. Moreover, it allows to achieve the nanometric size of ceramic grains. In the case of ceramic powders covered by metal, compression and hot pressing preserves nanometric size of metal. The grain growth of ceramic grains is suppressed.