Al/Al2O3 composites by arc discharge melting

Abstract

Alumina is a widely used advanced ceramic in technical applications where a material of high strength and resistance to thermal stresses is required. Unfortunately, as with most ceramics, alumina is brittle due to the dependence of its strength on severe defects such as cracks or pores. Several toughening methods have been developed. One such method modifies the microstructure, in particular the grain size. Modification may also be achieved by the inclusion of elongated grains or dispersion of a suitable secondary phase. In non-transforming ceramics such as alumina, the dominant toughening mechanism is known as "grain bridging," where interlocking grains along the crack wake partially shield the crack tip from the applied stress. In another study, Al, was dispersed in an Al₂O₃ matrix via a reactive metal penetration method. Aluminum enhanced the toughness by crack bridging, by which the ductile phase is intercepted by the propagating crack, deforms plastically, and dissipates energy.
This work utilizes an alternative method in arc discharge melting. This involves the use of an electric arc produced by passing a high current from a tungsten cathode to a crucible anode, which acts as the container for the composite material to be synthesized. It is a rapid preparation method able to reach temperatures approximately 3000 K, hence it is sufficient to melt Al₂O₃ (melting point 2050°C) and boil-off aluminum (melting point 660°C, boiling point: 2467°C). Its suitability is investigated in the preparation of Al/Al₂O₃ ceramic composites.