Relationships between microstructure, mechanical and dielectric properties of different alumina materials

Different alumina materials were elaborated in order to vary microstructural parameters (grain size, densification, porosity, inter-granular phase). These ceramic materials were then characterized from the mechanical point of view (hardness, toughness, friction and wear) and dielectric breakdown. The comparison of these various results shows that, for all these properties, the grain size and also, the nature of the secondary phases and the microstructural parameters were the most significant.Moreover, from the tribological point of view, the dielectric characteristic of materials (breakdown strength) has a fundamental role in the creation of agglomerated wear debris (“third body”) and its properties: a finely agglomerated third body will be obtained for high breakdown strength. Such third body will be able to protect the substrate and thus to reduce later wear. In the same logic a correspondence between breakdown strength and toughness was established, thus confirming the existence of mechanical–electrical correlation for non-conductive materials.