Changes in hardness and microstructure of a Pd-Ag-In-Ga-based metal-ceramic alloy during porcelain firing simulation and subsequent cooling

Shin, Hye Jeong; Kwon, Yong Hoon; Seol, Hyo Joung

Abstract

In this experiment, the alloy having the composition of 49.5Pd-40Ag-9In-1Ga (wt.%) was used to find the most effective cooling rate for the hardening of alloy during porcelain firing simulation. In each stage of firing simulation, ice-quenching or cooling at the most effective cooling rate for hardening of the alloy was done after firing to observe changes in the hardness and associated microstructures during the firing and subsequent cooling. For this purpose, the firing simulated alloy was characterized by analyzing the changes in hardness, microstructure, crystal structure and the elemental distribution. The hardness of alloy decreased by cooling after oxidation treatment, which was induced by the homogenization of the specimen. In this alloy, the most effective cooling rate for alloy hardening after oxidation treatment was Stage 0. During the porcelain firing simulation until the final firing stage, the cooling rate was set to Stage 0, and the complete firing simulation was performed until the final firing stage, Glaze. As a result, the final hardness of the metal substructure obtained after complete firing simulation was lower than that of the as-cast specimen. The decrease in hardness caused by the porcelain firing simulation results from a reduction in the interface between the precipitates of face-centered tetragonal structures and the matrix of face-centered cubic structures as the precipitates coarsen.