Interface Reactions Between Metals and Ceramics: I, Sapphire‐Nickel Alloys

The mechanism of bond formation between alloys of Ni and single‐crystal alumina (sapphire) was investigated. Ni‐Ti and Ni‐Cr powder mixtures were melted individually on the sapphire surface at 1500°C under a pressure of 10 −4 mm of Hg. Interfacial energy was measured by the sessile‐drop method. Two basic mechanisms were involved in the bond formation, viz., solute metal segregation at the interface and an interfacial reaction. The selective adsorption and segregation of the solute atoms at the interface was confirmed by X‐ray fluorescence analysis and by interfacial tension measurements. X‐ray diffraction studies on the interface produced definite evidence of the formation of α‐Ti 2 O 3 in the Ni‐Ti and sapphire system. Although green coloration of the sapphire crystal adjacent to the interface with Ni‐Cr suggested the diffusion of Cr in Al 2 ,O 3 , no compound or oxide of Cr could be identified.