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KMID : 0362220110380010065
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Journal of The Korean Research Society for Dental Materials
2011 Volume.38 No. 1 p.65 ~ p.74
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The Hardness and Microstructural Changes by the Cooling Rate in a PFM Gold Alloy during the Porcelain Firing Cycles
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Seol Hyo-Joung
Sim Jae-Seong
Cho Mi-Hyang
Park Mi-Gyoung
Kwon Yong-Hoon
Kim Hyung-Il
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Abstract
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The hardness and microstructural changes by cooling rate in a Pd-free Au-Pt-Zn alloy containing minor ingredients during firing cycles were elucidated by characterizing the age-hardening behavior and age-hardenability, phase transformation and microstructural changes during aging process, changes in hardness after simulated firing with various cooling rates, changes in hardness and microstructure after simulated complete firing with controlled cooling rate. The age-hard ening and softening mechanisms of a Pd-free Au-Pt-Zn alloy were homogeneous grain-interior precipitation of the Pt-rich phase and the subsequent lamellar-forming grain boundary reaction, respectively. The lamellar structure was composed of the Pt-depleted Au-rich α1’ matrix l ayer and the Pt-rich α3 precipitate l ayer, and the growth of l amellar structure was directly connected with the decrease in hardness. The maximum hardness value was obtained at stage 1 after simulated firing with various cooling rates (ice quenching, quick cooling, stage 0, stage 1, stage 2, stage 3). After simulated complete firing with controlled cooling rate (stage 1), the hardness value of t he s olution-treated specimen increased apparently f rom 89.3 (Hv) t o 170 (Hv) without a pparent lamellar-forming grain boundary reaction. It is advisable to control the cooling rate in the final firing stage of the complete firing cycles.
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KEYWORD
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Age-hardening and softening mechanism, Cooling rate, Gold-platinum PFM alloy, Grain-boundary reaction, Grain-interior precipitation
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