Effect of cooling rate on hardness and microstructure of Pd–Ag–In–Sn−Ga alloy during porcelain firing simulation

Effect of Cooling Rate on Hardness and Phase Transformation of a Pd-Ag-Based Metal–Ceramic Alloy with or without Ice-Quenching

“…To validate this, the GL-(S0 )IQ specimen was further treated at the glaze temperature (880 • C) for 80 min, but homogenization did not occur (Figure 5). In previous study with 60.55 Pd-27.72 Ag-6.12 In-2.24 Sn-3.21 Ga-0.16 Ru (at%) alloy [10], the homogenization proceeded during glazing at 930 • C, showing apparent hardening while cooling after glazing, unlike the results of this study. Considering that the specimen alloy in this study showed remarkable hardening while cooling at the oxidation temperature (1040 • C), it can be said that the influence of the cooling rate on the hardness became stronger when the specimen was in a homogenized state before cooling.…”

“…This indicated that a coherency strain field was generated at the interface between the matrix and the metastable precipitates owing to the slight gap between their lattice constants [15], resulting in a significant increase in hardness (p < 0.05). Such hardening through the formation of a metastable phase has been reported in several Pd-Ag-based metal-ceramic alloys [10,16], as well as in dental Au-based alloys that form a tetragonal AuCu I phase [17,18]. The relatively lower hardness of OX-S3 than that of OX-S0 must be resulted from the fact that the coherency strain field was released to some extent as the precipitates composed of the stable phase grew at the expense of the fine precipitates composed of the metastable phase [19].…”

“…Our previous study with a Pd-Ag-based alloy showed that the final hardness varies depending on the cooling rate during the firing process [10]. Based on these results, we hypothesize that the hardness recovery pattern of an ice-quenched specimen depends on the cooling rate during the subsequent firing process.…”

“…The α phase corresponds to the face centered cubic (f.c.c.) Pd-Ag-rich phase with a lattice constant of a = 3.994 Å; the β phase corresponds to the InPd 3 -based phase with a tetragonal structure and lattice constants of a = 4.119 Å and c = 3.673 Å [10]. The β phase corresponds to the metastable InPd 3 -based phase that has a c/a ratio larger than that of the stable InPd 3 (β) phase.…”

“…From XRD (Figure 7) and FE-EPMA (Table 7) of the specimens at the glaze step, the matrix was confirmed to be the f.c.c. Pd-Ag-rich phase and a lattice constant of a = 3.994 Å; the precipitates were the InPd 3 -based phase with a tetragonal structure and lattice constants of a = 4.119 Å and c = 3.673 Å [10]. Table 7.…”