Χύτευση ακριβείας και διεπιφανειακά φαινόμενα σε συστήματα κεραμικών σε επαφή με τήγματα μετάλλων

Abstract

Engineering ceramics are being considered for technological applications due to their strong and sometimes unique properties. The pronounced evolution in the quality of advanced engineering ceramics has stimulated interest in the combination of ceramics with metallic phases for ceramic joining purposes or for the manufacturing of composite materials with enhanced properties. In all this cases the surface and interfacial energies of the materials or the materials systems used, as well as the wetting and bonding phenomena at the interface, play a key role in obtaining materials with the desired properties and microstructure. The aim of the present work is the study of adhesion and interfacial properties in ceramic oxide / liquid metal systems and particularly in systems of polycrystalline ceria (CeO2) in contact with liquid metals. At the first part of this work, in framework of the PENED 2001 programs, the investment casting process was studied at the stages where fracture of the ceramic shell can occur (dewaxing, sintering, casting of liquid metal) in order to optimize the conditions of the production procedure. Moreover, the interactions at the ceramic shell / liquid metal interface which can affect the shape and dimensions of the final cast product were investigated. At the second part of the present work the multiphase equilibration technique has been used for the determination of the equilibrium angles that develop at the interphase boundaries of a solid-liquid-vapor system and the surface and interfacial energies in polycrystalline CeO2 and CeO2/Cu systems were determined in argon atmosphere at the temperature range 1473-1773 K. Linear temperature functions were obtained by extrapolation, for the surface energy and the grain-boundary energy of the ceramic, as well as for the interfacial energy and the work of adhesion of the CeO2/Cu system. Grain-boundary grooving studied on polished surfaces of CeO2 annealed in argon atmosphere at the same temperature range has shown that surface diffusion was the dominant mechanism for the mass transport and the surface diffusion coefficient has been estimated. Engineering ceramics are being considered for technological applications due to their strong and sometimes unique properties. The pronounced evolution in the quality of advanced engineering ceramics has stimulated interest in the combination of ceramics with metallic phases for ceramic joining purposes or for the manufacturing of composite materials with enhanced properties. In all this cases the surface and interfacial energies of the materials or the materials systems used, as well as the wetting and bonding phenomena at the interface, play a key role in obtaining materials with the desired properties and microstructure. The aim of the present work is the study of adhesion and interfacial properties in ceramic oxide / liquid metal systems and particularly in systems of polycrystalline ceria (CeO2) in contact with liquid metals. At the first part of this work, in framework of the PENED 2001 programs, the investment casting process was studied at the stages where fracture of the ceramic shell can occur (dewaxing, sintering, casting of liquid metal) in order to optimize the conditions of the production procedure. Moreover, the interactions at the ceramic shell / liquid metal interface which can affect the shape and dimensions of the final cast product were investigated. At the second part of the present work the multiphase equilibration technique has been used for the determination of the equilibrium angles that develop at the interphase boundaries of a solid-liquid-vapor system and the surface and interfacial energies in polycrystalline CeO2 and CeO2/Cu systems were determined in argon atmosphere at the temperature range 1473-1773 K. Linear temperature functions were obtained by extrapolation, for the surface energy and the grain-boundary energy of the ceramic, as well as for the interfacial energy and the work of adhesion of the CeO2/Cu system. Grain-boundary grooving studied on polished surfaces of CeO2 annealed in argon atmosphere at the same temperature range has shown that surface diffusion was the dominant mechanism for the mass transport and the surface diffusion coefficient has been estimated.