Palladium-zirconia diffusion bonds: Mechanical properties and interface reactions

High strength and toughness diffusion bonds have been fabricated using palladium foils between TZP zirconia blocks at temperatures above 1000°C in vacuum. Bonds fabricated below 1000°C in vacuum and under all conditions in air showed negligible strength. Strong, vacuum made bonds lost almost all their strength on annealing in air above 1000°C, anneals in vacuum also resulted in a decrease in bond strength but with a much less marked effect. PdZrO2 interfaces have been characterised by cross-sectional TEM and a thin reaction zone identified. Microanalysis identified the presence of Pd, Zr and O in a ratio of approximately 30:52:18 in the reaction interlayer. This composition has a Pd:Zr ratio close to that of a steep eutectic in the PdZr binary system and evidence for the presence of a liquid phase at the PdZrO2 interface during bonding is presented. The strength and toughness of the bonds are shown to be strongly dependent on the perfection of the bonded interface with the presence of a small fraction of voids causing a significant reduction in bond strength and toughness. Simple slip-line field methods are used to illustrate the influence of interface voids on the plastic constraint of bonded thin ductile layers. © 1992.