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

Abstract

The complex precipitation mechanisms related to the age-hardening of Cu-free Au-Ag-Pt-Zn-In alloy for multipurpose dental use was studied by means of hardness test, X-ray diffraction (XRD) studies, field emission scanning electron microscopic (FE-SEM) observations, energy dispersive spectrometer (EDS) analysis, and electron probe microanalysis (EPMA). The early diffusion and then clustering of the In-concentrated phase in the grain interior, together with the early diffusion and then ordering of the PtZn phase in the grain boundary, introduced the internal strains in the Au-Ag-rich 1 matrix, resulting in the hardening process. As the Au-Ag-rich 1 and PtZn lamellarforming grain boundary reaction progressed, the phase boundaries between the solute-depleted face-centered cubic (FCC) 1 matrix and the face-centered tetragonal (FCT) PtZn precipitate reduced, resulting in softening. In the particlelike structures composed of the major Pt-Au-rich 2 phase and the minor Pt-Zn-rich 3 phase, the separation of In and Zn progressed producing the In-increased Pt-Au-rich 2 phase and the