1989 Volume 53 Issue 4 Pages 429-438
Atomic structure in the diffusion-bonded alumina/niobium was observed by high resolution electron microscopy. A minor impurity calcium was contained in the surface layer of niobium in the form of inclusion particles, which resulted in the formation of hibonite (CaO·6Al2O3) about 0.15 μm thick when the joining was performed without removing the surface layer. The hibonite layer served not only as warning to control the minor element but also as a useful marker of the original interface and allowed us to assess the amount of alumina back-precipitated from niobium during cooling of the joined specimen. The back-precipitation is consided responsible for the observed ordering in the structure of the bonded interface. It must be a useful mechanism to relax the thermal stresses which develop at the ceramic/metal interface during the cooling of the joined specimen.
