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1.
Korean Journal of Dental Materials ; (4): 135-144, 2023.
Article in English | WPRIM | ID: wpr-1002151

ABSTRACT

The objective of this study was to investigate the effect of different cooling rates and subsequent post-firing heat treatment on the final hardness of a metal-ceramic alloy. For this, Specimens of Pd-Ag-In-Sn alloy underwent simulated firing at two different cooling rates, followed by post-firing heat treatment. Hardness measurement, microstructure observation, and crystal structure analysis were conducted on the firing simulated and post-firing heat-treated specimens to analyze the causes of hardness variations. The experimental results showed that the difference in cooling rates during simulated firing had an impact on the final hardness of the alloy, and the specimens cooled at the slowest rate (Stage 3) exhibited higher hardness at all firing Stages compared to the specimens cooled at the highest rate (Stage 0). Regardless of the difference in cooling rates during the firing process, the hardness of the alloy significantly increased by the post-firing heat treatment. The increase in hardness by the post-firing heat treatment was attributed to the formation of fine precipitates in the matrix, and the precipitation reaction occurred as a result of the decrease in solubility of (Pd, Ag, Au) 3 (In, Sn, Zn) phase in the Pd-Ag-rich matrix. The clinical significance of this study is that performing the post-firing heat treatment demonstrates effectiveness in increasing the reduced hardness after porcelain firing in metal-ceramic alloys.

2.
Korean Journal of Dental Materials ; (4): 181-192, 2020.
Article in English | WPRIM | ID: wpr-901894

ABSTRACT

In this study, Au-Pt-Pd metal-ceramic alloy was examined by varying cooling rate during simulated porcelain firing cycles to investigate the effect of cooling rate on hardness and related microstructure during simulated firing. The final hardness was different according to the cooling rate after the simulated porcelain firing cycles. The reduction in hardness value was smaller after cooling at the faster cooling rate (Stage 0) than the value after slower rate (Stage 3). In the ice-quenched specimens after oxidation treatment (OXI-IQ), homogenization was slightly occurred, and the hardness decreased apparently compared to that of the as-cast specimens (AS-CAST). In the specimens cooled at Stage 0 and Stage 3 after oxidation, the hardness increased apparently compared to the ice-quenched specimens, even though the hardness decreased later by further firing simulation.The final hardness was lower in the specimen cooled at the slower rate (Stage 3) than the faster rate (Stage 0), and it seems to be due to the coarsening of the microstructure. The matrix and precipitates were consisted of FCC (face-centered-cubic) structure rich in Au. The Au content was higher in the matrix and the Pt content was higher in the precipitates, which corresponded to the Au-Pt binary phase diagram.

3.
Korean Journal of Dental Materials ; (4): 181-192, 2020.
Article in English | WPRIM | ID: wpr-894190

ABSTRACT

In this study, Au-Pt-Pd metal-ceramic alloy was examined by varying cooling rate during simulated porcelain firing cycles to investigate the effect of cooling rate on hardness and related microstructure during simulated firing. The final hardness was different according to the cooling rate after the simulated porcelain firing cycles. The reduction in hardness value was smaller after cooling at the faster cooling rate (Stage 0) than the value after slower rate (Stage 3). In the ice-quenched specimens after oxidation treatment (OXI-IQ), homogenization was slightly occurred, and the hardness decreased apparently compared to that of the as-cast specimens (AS-CAST). In the specimens cooled at Stage 0 and Stage 3 after oxidation, the hardness increased apparently compared to the ice-quenched specimens, even though the hardness decreased later by further firing simulation.The final hardness was lower in the specimen cooled at the slower rate (Stage 3) than the faster rate (Stage 0), and it seems to be due to the coarsening of the microstructure. The matrix and precipitates were consisted of FCC (face-centered-cubic) structure rich in Au. The Au content was higher in the matrix and the Pt content was higher in the precipitates, which corresponded to the Au-Pt binary phase diagram.

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