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

Phase Equilibria of the In-Pd-Sn System at 500 °C and 800 °C: Experimental Study and CALPHAD Modeling

Phase equilibria in the In-Pd-Sn system were investigated by a combination of key experiments and thermodynamic modeling. Partial isothermal sections at 500 °C and 800 °C of the In-Pd-Sn system for Pd contents above 66 at.% have been plotted experimentally using scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM/EDX) and X-ray diffraction (XRD). The solubility of the third component in binary compounds InPd₃ and Pd₃Sn was determined. The new ternary compound τ₁ was found in Pd contents ranging from 20 to 25 at.% and at Sn contents varying from 5 to approximately 17 at.% Sn. This compound crystallizes in an Al₃Ti-type tetragonal structure. Isostructural InPd₂ and Pd₂Sn phases from the In-Pd and Pd-Sn binary compositions form a continuous phase field in the ternary system at both temperatures. The temperatures of the solidus, liquidus, and phase transitions of the alloys along the Pd-In50Sn50 line were measured using DTA/DSC. Thermodynamic calculation of the In-Pd-Sn ternary system is performed using the CALPHAD method using the Thermo-Calc^® software. The thermodynamic properties of the disordered fcc and liquid phases were described by the Redlich-Kister-Muggianu model. To describe intermetallic phases, namely, InPd₃, Pd₃Sn, τ₁ and Pd₂(In_xSn_1-x), a two-sublattice models was used. Thermodynamic description of the In-Pd-Sn system obtained in this study is in good agreement both with our results and the published experimental data.

Investigation on the effect of recasting palladium-silver alloy by argon arc vacuum pressure casting process

Background/purpose

Palladium-silver (Pd-Ag) alloys are important as an alternative to gold-based alloys. The purpose of this study was to investigate the effect of an argon-arc vacuum pressure casting process on the recasting of the Pd-Ag alloy.

Materials and methods

The recasting Pd-Ag alloys were compared with conventional horizontal centrifugal (HC) casting to an argon (Ar)-arc vacuum pressure (Ar-arc/VP) casting. The first-generation castings were made from a Pd-Ag alloy purchased from a supplier. Next-generation castings were made from 50 wt% Pd-Ag alloy before casting and 50 wt% from previous castings. This sequence was repeated over three generations to form the 2nd, 3rd and 4th recasting ingots. The ingots were then measured for marginal accuracy, interfacial oxidation, hardness and phase identification.

Results

The recasting success rate of recastibility reached 100%. Compared with the HC group, the Ar-arc/VP group had better edge precision, smaller oxide layer thickness and lower hardness. The comparison of X-ray diffraction intensity showed that the relative intensities of Pd and Ag in the first, second and third generations recasting of the Ar-arc/VP group were significantly higher than those of the HC group. Phase analysis showed that the trace elements of indium and tin contents in the Pd-Ag recasting ingots of the Ar-arc/VP group were higher than those of the HC group.

Conclusion

The results showed that the casting process used for recasting affected the quality of the Pd-Ag alloy. Therefore, Ar-arc/VP casting process could improve the effect of Pd-Ag recasting and maintain the alloy properties in comparison with HC casting.