Effects of trace added calcium or palladium on annealing characteristics of cold-worked pure gold

This study investigates the influence of trace added calcium or palladium on the annealing characteristics of cold-worked pure gold. The electrical resistance of Au-0.018 mol%Pd, Au-0.020 mol%Ca, and pure gold (99.999 mass%) were measured in the temperature range from room temperature to 873 K. The samples were annealed at temperatures where peculiar changes in electrical resistivity were observed and subsequently investigated through tensile tests, metallographic observations, and transmission electron microscopy. The electrical resistivity of Au-0.018 mol%Pd and pure gold decreased rapidly between 340 K and 390 K. Within this temperature range, mechanical properties of the sample also changed rapidly toward recrystallization. The electrical resistivity of Au-0.020 mol%Ca was observed to decrease in 3 gradual steps between 410 K and 750 K. The mechanical properties also changed gradually over this temperature range. Recrystallization structures were observed at 750 K. Whereas the recovery and recrystallization of cold-worked pure gold was unaffected by the addition of trace palladium, these processes were significantly affected by trace added calcium. This appears to be related to the fixing of dislocation with calcium atoms and the strong interaction between vacancies and calcium atoms.