The microsegregation of alloying elements during the solidification of metallic alloys is a concept that is difficult to evaluate in complex alloys. Predicting the degree of microsegregation, which will occur in an alloy system, requires accurate values for the partition coefficients that describe the concentrations of alloying elements in solid and liquid phases during the freezing process. Values for partition coefficients can be determined from phase diagrams for binary alloys. Karat gold jewelry alloys typically contain three or four major alloying elements, and phase diagrams, if available, cannot be used to determine values for partition coefficients. Platinum jewelry alloys are unusual in that several binary platinum alloys are in common use for jewelry applications. Solute redistribution during the solidification of Pt-Co, Pt-Ru and systems was calculated and compared with results obtained in commercial investment casting procedures. An effort was made to compare and contrast microsegregation in Pt casting alloys with solute redistribution patterns in typical 14K yellow and white gold jewelry alloys.

Author(s): John C. McCloskey, Dr. Shankar Aithal