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Microstructural changes in grain interior and grain boundary by formation of metastable and stable phases related to age-hardening in an Au-Cu-Ag-Pd alloy

Published online by Cambridge University Press:  12 April 2013

Su-Yoen Cho ,
Gwang-Young Lee ,
Ji-In Jeong ,
Yong Hoon Kwon ,
Hyung-Il Kim  and
Hyo-Joung Seol
Su-Yoen Cho
Affiliation:
Department of Dental Materials, School of Dentistry and Medical Research Institute, Pusan National University, Beomeo-Ri, Mulgeum-Eup, Yangsan-Si, Gyeongsangnam-Do, 626-814, South Korea
Gwang-Young Lee
Affiliation:
Department of Dental Materials, School of Dentistry and Medical Research Institute, Pusan National University, Beomeo-Ri, Mulgeum-Eup, Yangsan-Si, Gyeongsangnam-Do, 626-814, South Korea
Ji-In Jeong
Affiliation:
Department of Dental Materials, School of Dentistry and Medical Research Institute, Pusan National University, Beomeo-Ri, Mulgeum-Eup, Yangsan-Si, Gyeongsangnam-Do, 626-814, South Korea
Yong Hoon Kwon
Affiliation:
Department of Dental Materials, School of Dentistry and Medical Research Institute, Pusan National University, Beomeo-Ri, Mulgeum-Eup, Yangsan-Si, Gyeongsangnam-Do, 626-814, South Korea
Hyung-Il Kim
Affiliation:
Department of Dental Materials, School of Dentistry and Medical Research Institute, Pusan National University, Beomeo-Ri, Mulgeum-Eup, Yangsan-Si, Gyeongsangnam-Do, 626-814, South Korea
Hyo-Joung Seol*
Affiliation:
Department of Dental Materials, School of Dentistry and Medical Research Institute, Pusan National University, Beomeo-Ri, Mulgeum-Eup, Yangsan-Si, Gyeongsangnam-Do, 626-814, South Korea
*
a)Address all correspondence to this author. e-mail: seol222@pusan.ac.kr
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Abstract

The hardness changes caused by formation of the metastable and stable phases were examined and correlated with the microstructural changes in grain interior and grain boundary during aging at 350 °C to clarify the age-hardening and softening mechanism of a low-gold Au-Cu-Ag-Pd dental alloy. Aging in this context refers to the time-delay that occurs wherein such alloys are kept at elevated temperatures for periods upto many hours to allow precipitation or ordering to take place. During the period of increasing hardness, the matrix was separated into the Ag-rich α1 and AuCu I phases through the metastable phases, forming block-like structure. The apparent hardening was attributed primarily to lattice strain due to the tetragonality of AuCu I′ [the primer (′) here indicates a metastable phase; likewise (I) and (I′) indicate stable AuCu I and metastable AuCu I′ phases, respectively] and AuCu I phases along the c-axis, secondarily to the coherency or semicoherency strain between the metastable α1′ and AuCu I′ phases and between the α0 and AuCu I phases along the a-axis. The apparent softening was caused primarily by growth and coarsening of the lamellar structure in the grain boundaries, secondarily by coarsening of the block-like structure in the grain interior.

Keywords

phase transformationmicrostructurealloy
Type
Articles
Information
Journal of Materials Research , Volume 28 , Issue 9 , 14 May 2013 , pp. 1211 - 1217
Copyright
Copyright © Materials Research Society 2013 

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