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KMID : 0362120000220010069
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Journal of Technologic Dentistry
2000 Volume.22 No. 1 p.69 ~ p.78
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The Effect of Burn-out Temperature and Cooling Rate on the Microstructure and Corrosion Behavior of Dental Casting Gold Alloy
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Lee Sang-Hyeok
Ham Duck-Sun
Kim Hak-Kwan
Jang Ju-Woong
Kim Myung-Ho
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Abstract
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The microstructure and corrosion behavior of commercially dental casting gold alloys were investigated to clarify the effect of burn-out temperature and cooling rate. In the case of water quenching after casting, only the αphase, which is typical dendritic microstructure of golda alloy, was detected. However, the precipitates along the grain boundary were detected only at the slow cooling rate and they increased inversely proportional to the burn-out temperature. This might be due to the time difference which solute atom could diffuse. EPMA and SEM results also demonstrated that the precipitate should be lamellar structure consisted of Ag rich phase() and Cu rich phase (). In terms of corrosion, the galvanic coupling was formed due to the difference of composition between precipitates and matrix at the slow cooling rate. In the case of water quenching, the critical current density() which indicate the degree of corrosion was lowest at and below the burnout temperature, increased with it because of the effect of grain boundary segregation. But above the temperature, increased with it. This may be due to the strain field effect by residual thermal stress.
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