Effect of ice-quenching on the change in hardness of a Pd-Au-Zn alloy during porcelain firing simulation

Abstract

This study examined the effect of ice-quenching after degassing on the change in hardness of a Pd-Au-Zn alloy during porcelain firing simulations. By ice-quenching after degassing, the specimens were softened due to homogenization without the need for an additional softening heat treatment. The lowered hardness by ice-quenching after degassing was recovered greatly from the first stage of porcelain firing process by controlling the cooling rate. The increase in hardness during cooling after porcelain firing was attributed to the precipitation of the f.c.t. PdZn phase containing Au, which caused severe lattice strain in the interphase boundary between the precipitates and matrix of the f.c.c. structure. The final hardness was slightly higher in the ice-quenched specimen than in the specimen cooled at stage 0 (the most effective cooling rate for alloy hardening) after degassing. This was attributed to the more active grain interior precipitation during cooling in the ice-quenched specimen after degassing.

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

“…From the above, it can be determined that oxidation followed by ice-quenching reduced the hardness temporarily without sacrificing the final hardness at both, the relatively high and low cooling rates (p < 0.05). In previous studies that used a single cooling rate, such a recovery of hardness was observed in Pd−Au and Pd−Cu alloys, as well as in Pd-Ag alloy [8,9,13]. In particular, in Pd−Cu alloys, the final hardness far exceeded that of the non-quenched alloy [13].…”

“…Thus, if the alloy is rapidly quenched in ice brine (ice-quenching, IQ) Metals 2021, 11, 680 2 of 13 in place of the normal cooling step after oxidation, the hardness can be lowered without performing an additional heat treatment. In previous studies, the hardness of Pd-based alloys was lowered by oxidation treatment followed by ice-quenching, and recovered thereafter as firing proceeded [8,9]. Therefore, ice-quenching after oxidation was thought to be effective in softening the alloy to enable easy trimming without sacrificing the final hardness.…”