New high-palladium casting alloys: studies of the interface with porcelain

This investigation studied the metal ceramic interface for two representative high-palladium alloys each of the Pd-Cu-Ga and Pd-Ga systems, using scanning electron microscopy and x-ray energy dispersive spectroscopy. The Pd-Cu-Ga alloys produced complex subsurface oxidation regions with thickness ranging from 15 to 20 microns for one alloy and 5 to 10 microns for the other alloy. Ga, In, and Sn accumulated at the interfaces, and Ga-rich deposits were found in the subsurface scale. One Pd-Ga alloy presented a surface oxidation region which dissolved in the ceramic, producing "islands" rich in Pd and Ga with a width that ranged from 1 to 2 microns. These islands were separated from the alloy by a band rich in Ga and Si which was 1 to 2.5 microns thick. While the other Pd-Ga alloy presented similar interfacial microstructures, the "islands" formed for this alloy were relatively sparse. The Pd-Cu-Ga alloys had a more favorable interface for metal ceramic bonding, which agrees with previous characterization of bond failures between these alloys and dental porcelain.