Grain-refined Pd-Cu-Ga dental alloys solidify with a lamellar microstructural constituent that affects a variety of clinically relevant properties. While formation of this constituent has been attributed to eutectic solidification, an alternative mechanism of discontinuous precipitation has been proposed. Using a representative grain-refined Pd-Cu-Ga dental alloy, casting procedures involving two different rates of solidification were used: (a) A standard thin-walled coping configuration for a metal-ceramic restoration was cast into a room temperature mold, followed by rapid quenching into an ice-water mixture. (b) A thin plate specimen was cast into a standard elevated-temperature mold, with the same subsequent rapid quenching procedure. Neither casting was subjected to the standard air-abrasion procedure following devesting that is used in dental laboratories. An outer surface layer, approximately one grain thick, containing only the palladium solid solution, was observed in the microstructures of the two different castings, and the eutectic constituent was present at greater depths. This observation is consistent with physical metallurgy principles for the freezing of an alloy containing a eutectic constituent, and the alternate hypothesis that the lamellar constituents might represent discontinuous precipitates has been discarded.
Brantley, William A.; Cai, Zhuo; Mitchell, John C.; and Vermilyea, Stanley G.
"Mechanism for Formation of Lamellar Constituents in Grain-Refined Pd-Cu-Ga Dental Alloys,"
Cells and Materials: Vol. 7
, Article 6.
Available at: http://digitalcommons.usu.edu/cellsandmaterials/vol7/iss1/6