Metal-ceramic interfaces: Sources and sinks for mass transfer

The closure of interface voids during metal-ceramic diffusion bonding has been studied for a number of metal foils joined to TZP zirconia. In the case of bonds to large grained Cu and Ni foils the final voids to close on the interface are found to rest on grain boundaries in the metal foil where they intersect the metal-ceramic interface. Bonds made to foils of smaller grain sized Fe and Ni do not show this behaviour. When the final interface voids occur at the intersections of metal grain boundaries with the metal--ceramic interface, voids are also seen to nucleate on grain boundaries within the metal foil away from the interface. These observations suggest that the metal-ceramic interface does not act as an efficient vacancy sink during interface formation. Possible mass transfer routes are proposed to allow vacancies to sink on metal grain boundaries within the foil during interface void closure. The nucleation of voids within the metal foil during diffusion bonding is possibly caused by interactions of creep and diffusional mass transfer during bonding.