Microstructure and mechanical properties of Al-assisted sintered Fe/Al2O3 cermets

Fe/Al2O3 composites with metal contents between 23 and 35 vol% have been fabricated via Al-assisted pressureless reaction sintering. The effect of variation of oxygen partial pressure during sintering on phase development, microstructure and mechanical properties has been investigated. The formation of the spinel phase FeO . Al2O3 is found to occur at elevated temperatures if the oxygen partial pressure during sintering exceeds a critical value. Microstructural observations and image analysis reveal that the composites exhibit a microstructure with the ceramic and the metal phase forming interpenetrating networks. The fracture toughness increases with increasing metal content and strongly depends on the phase content of the sintered specimens. In composites containing a small amount of FeO . Al2O3, the maximum toughness is 7.1 MPa root m. A significant toughness enhancement up to 10.2 MPa root m was achieved by avoiding the spinel formation to obtain composites consisting only of Fe and Al2O3. (C) 1999 Elsevier Science Ltd. All rights reserved.