Age-hardening by miscibility limit in a multi-purpose dental gold alloy containing platinum

Abstract

This study examined the age-hardening by miscibility limit in a multi-purpose dental gold alloy containing platinum. The hardness increased rapidly in the initial stage of the aging process, reached the maximum value, then decreased continuously with aging time. The significant hardness increase resulted from the heterogeneous precipitation of the Pt-rich phase from the grain boundary of the Au-rich 1 matrix due to the miscibility limit of AuPt system. With increasing aging time, the fine Pt-rich precipitates covered almost the whole matrix, and by further aging, the precipitates grew coarse. The microstructural coarsening reduced the interface between the Au-rich 1 matrix and the Pt-rich precipitates, which released the lattice strains between the two phases, resulting in a softening effect. In the later stage of aging process, the Au-containing Pt 3 In particle-like structure was transformed into the Au-depleted particle-like structure containing relatively large amounts of Cu resulting from the overlapping miscibility limit of both Au-Pt and Ag-Cu systems, which was responsible for the slow decreasing rate in hardness in the later stage of aging.

Age-hardening by grain interior and grain boundary precipitation in an Au-Ag-Pt-Zn-In alloy for multipurpose dental use

“…In the present study with Au-Ag-Pt alloy, the content of Au, together with Ag, was unequal in each layer of the lamellar structure, which was resulted from decreasing miscibility with decreasing aging temperature in Au-Pt and Ag-Pt systems [1,20].…”

“…From the above, it can be concluded that the Pt-rich particle-like structures were composed of the major Pt-Au-rich 2 regions containing equal amounts of Zn and In and the minor Pt-Zn-rich 3 regions in which the contents of Zn were about three times of In, and where the separation of In and Zn progressed with aging time without apparent microstructural changes. In the study with an Au-Ag-Cu-Pt-In alloy, the Au-containing Pt 3 In particle-like structure was transformed into the Au-depleted particle-like structure containing relatively large amounts of Cu that was diffused from the Au-Ag-rich matrix, and which resulted from the overlapped miscibility limit of both Au-Pt and Ag-Cu systems [20]. However, in the present study with an Au-Ag-Pt-Zn-In alloy, such an Au-depletion in the Ptrich particle-like structure was not observed after transformation, as can be seen in Table 2(1,2).…”