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-degrees-C in vacuum. Bonds fabricated below 1000-degrees-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-degrees-C, anneals in vacuum also resulted in a decrease in bond strength but with a much less marked effect. Pd-ZrO2 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 Pd-Zr binary system and evidence for the presence of a liquid phase at the Pd-ZrO2 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.