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KMID : 1035320170440030207
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Korean Society for Dental Materials
2017 Volume.44 No. 3 p.207 ~ p.216
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Effect of cooling rate on precipitation hardening of a Pd-Cu-Ga-Zn metal-ceramic alloy during porcelain firing simulation
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Kim Min-Jung
Shin Hye-Jung
Kwon Yong-Hoon
Kim Hyung-Il
Seol Hyo-Joung
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Abstract
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The effect of cooling rate on precipitation hardening of a Pd-Cu-Ga-Zn metal-ceramic alloy during porcelain firing simulation was investigated and the following results were obtained. When the cooling rate was fast (Stage 0), the hardness of the alloy increased at each firing step and the high hardness value was maintained. When the cooling rate was slow (Stage 3), the hardness was the highest at the first stage of the firing, but the final hardness of the alloy after complete firing was lower. The increase in hardness of the specimens cooled at the cooling rate of Stage 0 after each firing step was caused by precipitation hardening. The decrease in hardness of the specimens cooled at the cooling rate of Stage 3 after each firing step was attributed to the coarsening of the spot-like precipitates formed in the matrix and plate-like precipitates. The matrix and the plate-like precipitates were composed of the Pd2(Cu,Ga,Zn) phase of CsCl-type, and the particle-like structure was composed of the Pd-rich α-phase of face-centered cubic structure. Through the porcelain firing process, Cu, Ga, and Zn, which were dissolved in Pd-rich αparticles, precipitated with Pd, resulting in the phase separation of the Pd-rich αparticles into the Pd-rich α" particles and β" precipitates composed of Pd2(Cu,Ga,Zn). These results suggested that the durability of the final prosthesis made of the Pd-Cu-Ga-Zn alloy can be improved when the cooling rate is fast during porcelain firing simulation.
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KEYWORD
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Porcelain firing simulation, Pd-Cu-Ga-Zn alloy, Precipitation hardening, Cooling rate
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