High temperature strength of YSZ joints brazed with palladium silver copper oxide filler metals

The Ag–CuOx system is being investigated as potential filler metals for use in air brazing high temperature electrochemical devices such as solid oxide fuel cells and gas concentrators. The current study examines the effects of palladium addition on the high temperature joint strength of specimens prepared from yttria stabilized zirconia (YSZ) bars brazed with the binary Ag–CuOx, and 15Pd–Ag–CuO. It was found that while the binary Ag–CuOx system exhibits stronger room temperature strength than the 15Pd system the strength is reduced to values equivalent of the 15Pd system at 800 °C. The 15Pd system exhibits a lower ambient temperature strength that is retained at 800 °C. In both systems the failure mechanism at high temperature appears to be peeling of the noble metal component from the oxide phases and tearing through the noble metal phase whereas sufficient adhesion is retained at lower temperatures to cause fracture of the YSZ substrate.