Journal of Materials Science, Vol.43, No.1, 23-32, 2008
Brazing of yttria-stabilized zirconia (YSZ) to stainless steel using Cu, Ag, and Ti-based brazes
Copper and silver-base active metal brazes containing Ti (Cu-ABA, Ticusil, and Ticuni) were tested for oxidation resistance to 750-850 degrees C, and for their effectiveness in joining yttria-stabilized-zirconia (YSZ) to a corrosion-resistant ferritic stainless steel. The braze oxidation behavior was characterized using thermogravimetric analysis (TGA), optical and scanning electron microscopy (SEM), and energy dispersive spectrometry (EDS). Ticusil and Ticuni at 750 degrees C exhibited sluggish oxidation kinetics whereas Copper-ABA at 850 degrees C displayed the fastest kinetics and relatively large weight gain. The SEM and EDS examination of the steel/braze and YSZ/braze interfaces showed the dissolution of Y and Zr from YSZ in braze, diffusion of Ag in the YSZ, and formation of a thin Ti-rich interphase between YSZ and Ti-base brazes. These compositional changes and interface reconstruction yielded metallurgically sound joints. The Knoop microhardness profiles showed a rather abrupt discontinuity across the YSZ/braze interfaces and a more uniform distribution across the steel/braze interface.