Optimization of a Ductile‐Particle‐Toughened Ceramic

Abstract

The nature of the interfacial bond has a major effect on the degree of toughening that can be achieved in a ductile‐particle‐reinforced ceramic‐matrix composite. The effect of variation of oxygen partial pressure during fabrication on the bonding in an alumina‐nickel composite has been investigated. Calculations suggest that wetting of alumina by nickel should always be accompanied by spinel (NiAl2O4 formation. A range of microstructures within a single specimen have been produced, however, indicating that wetting occurs more rapidly than spinel formation and that reduction of oxygen partial pressure during the hot‐pressing process can prevent spinel formation after wetting has occurred. Within this specimen, interfaces that have been formed under nonwetting conditions or conditions under which spinel formation has occurred are weak, whereas wetting without spinel formation produces chemically strengthened and mechanically interlocked interfaces that lead to crack interaction with the metallic particles and a higher toughening increment than for other microstructures. Subsequent specimens fabricated from preconsolidation‐heat‐treated powder exhibit favorable microstructures throughout, are tougher, and show more‐desirable resistance‐curve behavior in double‐cantilever‐beam tests than specimens produced from unreacted powder.