Papers by Author: J. Michalski

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: 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.