Korean J Dent Mater.  2020 Dec;47(4):181-192. 10.14815/kjdm.2020.47.4.181.

The effect of cooling rate on hardness and microstructure of a metal-ceramic Au-Pt-Pd alloy during simulated firing

Affiliations
  • 1Department of Dental Materials, School of Dentistry, Pusan National University, Yangsan-si, Korea

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.

Keyword

Au-Pt-Pd metal-ceramic alloy; simulated firing; cooling rate
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