Hardening behavior after high-temperature solution treatment of Ag-20Pd-12Au-xCu alloys with different Cu contents for dental prosthetic restorations.

Ag-Pd-Au-Cu alloys have been used widely for dental prosthetic applications. Significant enhancement of the mechanical properties of the Ag-20Pd-12Au-14.5Cu alloy as a result of the precipitation of the beta' phase through high-temperature solution treatment (ST), which is different from conventional aging treatment in these alloys, has been reported. The relationship between the unique hardening behavior and precipitation of the beta' phase in Ag-20Pd-12Au-xCu alloys (x=6.5, 13, 14.5, 17, and 20mass%) subjected to the high-temperature ST at 1123K for 3.6ks was investigated in this study. Unique hardening behavior after the high-temperature ST also occurs in Ag-20Pd-12Au-xCu alloys (x=13, 17, and 20) with precipitation of the beta' phase. However, hardening is not observed and the beta' phase does not precipitate in the Ag-20Pd-12Au-6.5Cu alloy after the same ST. The tensile strength and 0.2% proof stress also increase in Ag-20Pd-12Au-xCu alloys (x=13, 14.5, 17, and 20) after the high-temperature ST. In addition, these values after the high-temperature ST increase with increasing Cu content in Ag-20Pd-12Au-xCu alloys (x=14.5, 17, and 20). The formation process of the beta' phase can be explained in terms of diffusion of Ag and Cu atoms and precipitation of the beta' phase. Clarification of the relationship between hardening and precipitation of the beta' phase via high-temperature ST is expected to help the development of more effective heat treatments for hardening in Ag-20Pd-12Au-xCu alloys.