F. Cipri, C. Bartuli, University of Rome, Rome, Italy; T. Valente, Rome University "la Sapienza", Rome, Italy; F. Casadei, Centro Sviluppo Materiali S.p.A., Roma, Italy
The physico-chemicals and thermo-mechanical properties of alumino-silicate ceramics (high melting point, low thermal expansion coefficient, excellent thermal shock resistance, low density and good corrosion resistance) make this class of materials a good option for high temperature structural applications.
Especially mullite, 3Al2O3·2SiO2, shows an excellent refractory behaviour allowing a wide use as a wear resistant thermal barrier coatings, in metallurgical and glass plants and in high temperature heat exchangers. Moreover the low values of thermal expansion coefficient and of complex permittivity allows to extend the use of this ceramic for microelectronic devices, radome for antennas and electromagnetic windows for microwaves and infrared.
The present paper presents the results of an extensive experimental activity carried out to produce thick mullite coatings by plasma spray technique. APS deposition parameters were optimized on the basis of a surface response approach, as specified by design of experiments (DOE) methodologies. All samples of the factorial design were tested for phase composition, total porosity, microstructure, microhardness and deposition efficiency. Further mechanical properties, such as fracture toughness and modulus of rupture were investigated for optimized products. Mullite coatings exhibited very interesting performance in terms of fracture toughness and ability of efficiently covering metallic substrates even after strong deformation.
Finally, coatings were characterized for their particularly interesting electromagnetic properties: complex permittivity was measured at microwave frequency using a network analyzer via free space.
Summary: Mullite, 3Al2O3•2SiO2, shows an excellent refractory behaviour allowing a wide use as a wear resistant thermal barrier coatings, in metallurgical and glass plants and in high temperature heat exchangers. Moreover the low values of thermal expansion coefficient and of complex permittivity allows to extend the use of this ceramic for microelectronic devices, radome for antennas and electromagnetic windows for microwaves and infrared.
The present paper presents the results of an extensive experimental activity carried out to produce thick mullite coatings by plasma spray technique. APS deposition parameters were optimized on the basis of a surface response approach, as specified by design of experiments (DOE) methodologies.
