The influence of chromium addition on the toughness of gamma-Ni/alpha-Al2O3 interfaces

Experimental studies designed to characterize the fracture resistance of interfaces between Al2O3 and either pure Ni or a gamma-Ni alloy containing Cr have revealed a profound influence of Cr on the debond toughness. The interface between the pure Ni and Al2O3 is susceptible to stress corrosion caused by moisture, resulting in a fracture energy of the order of 10 J/m(2). The interface between the alloy and the Al2O3 cannot be fractured, even at strain energy release rates in excess of 100 J/m(2). An analysis of these interfaces has identified two influences of the alloy addition that might govern its role in eliminating stress corrosion: (i) the Cr ''getters'' the C near the interface by forming a Cr-carbide reaction product, and (ii) the alloy dissolves some of the alumina during bonding, exposing virgin material to the alloy at the interface. The factors that lead to carbide formation and alumina dissolution are discussed. (C) 1997 Acta Metallurgica Inc.