Changes in hardness and microstructure of a solution-treated Au-Pd-In alloy for porcelain bonding during porcelain firing simulation

Abstract

Changes in hardness and microstructure of a solution-treated Au-Pd-In alloy for porcelain bonding during porcelain firing simulation were elucidated by means of hardness test, field emission scanning electron microscope (FE-SEM) observations, X-ray diffraction (XRD) analysis and energy dispersive spectrometer (EDS) analysis. The most effective hardening of alloy during cooling after porcelain firing was obtained when the firing chamber moved immediately to upper end position and then air cooled. In the solution-treated specimen after casting, the hardness decreased dramatically. However, after degassing treatment which is the first firing stage, the hardness value of solution-treated specimen increased rapidly, and such a high hardness was maintained during the consecutive firing stages. In a Cu-free Au-Pd-In alloy for porcelain bonding, the hardening effect of the solution treatment on simulated porcelain firing was caused by the grain interior precipitates of fine scale, which was composed of the ordered Ga₂Pd<SUB>5</SUB> phase containing Au and In. From the above results, solution treatment is recommended to improve hardness of the Au-Pd-In alloy during porcelain firing.