Stability of single crystal sapphire in nickel and nickel-alloy matrices

The object of this investigation was to study the chemical interaction between single-crystal sapphire filaments and nickel and nickel alloy matrices, and to determine the effect of these reactions on filament strength. It was found that the reaction between pure nickel and sapphire in an inert atmosphere resulted in pitting of the sapphire during heat treatment, and in the formation of nickel spinel in an oxidizing atmosphere. The presence of 18 pct Cr in the nickel markedly decreased the severity of attack in both atmospheres, and in an oxidizing atmosphere a reaction product of NiO and NiAl₂O₄ was formed at the sapphire Jmetal interface. For the case of a Udimet-700 matrix, all pressing conditions resulted in severe rod fragmentation.