Three commercial palladium alloys (PdCuGa, PdCoGa, and PdAgSn) were melted and cast in graphite and ceramic crucibles in order to introduce small, but different levels of carbon impurities in the alloys. The solubility of carbon is known to become smaller with decreasing temperature, and in the present alloys small amounts of carbon were found to cause a substantial reduction in ductility as measured by the elongation in a tensile test. For the PdCuGa-alloy only 2% elongation was observed when it was melted in graphite crucibles. Scanning electron microscopy revealed that carbon caused increased destabilization of this alloy. Furthermore, carbon impurities were observed to cause gas porosities along the alloy/ceramic interface. At the same time the bond strength was found to be substantially reduced. The PdAgSn alloy in contrast to the other 2 alloys was little affected by being melted in a graphite crucible.
Carbon impurities and properties of some palladium alloys for ceramic veenering.
Herø H, Syverud M