The Structure of a Commercial Dental Ag-Pd-Cu-Au Casting Alloy

Abstract

The structure of a commercial dental Ag-Pd-Cu-Au casting alloy has been studied by microprobe and X-ray diffraction analyses after various heat treatments. The composition of phases in equilibrium was established. After being annealed at 400°C, 500°C, and 600°C for seven wk, the alloy consisted of three phases: a Cu- and Pd-rich fcc phase (α₁) with a = 0.372nm, a Ag-rich matrix (α ₂) with a = 0.399nm, and an ordered CsCl-type bcc PdCu phase with a = 0.296nm. The PdCu phase was not observed above 600°C, and the proportion of the α₁ phase decreased sharply above 700°C. After being annealed at 900°C, the alloy matrix was partly decomposed at the Cu-enriched grain boundaries. The decomposed areas grew into the grain interior during subsequent precipitation hardening. No segregation of Au was detected after casting, and the element was evenly distributed throughout the alloy structure after all heat treatments.