Age-hardenability and related microstructural changes during and after phase transformation in an Au-Ag-Cu-based dental alloy

• Main Authors: Hyung-Il Kim, Tae-Wan Kim, Young-Oh Kim, Su-Yeon Cho, Gwang-Young Lee, Yong Hoon Kwon, Hyo-Joung Seol
• Format: Article
• Language: English
• Published: Associação Brasileira de Metalurgia e Materiais (ABM); Associação Brasileira de Cerâmica (ABC); Associação Brasileira de Polímeros (ABPol) 2012-01-01
• Series: Materials Research
• Subjects: spinodal decomposition; metastable phase; age-hardening; lamellar-forming grain boundary reaction
• Online Access: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392012005000169

The aim of this study was to clarify how the microstructural changes during and after phase transformation determine the age-hardenability of an Au-Ag-Cu-based dental alloy. The rapid increase in hardness in the initial stage was the result of rapid atomic diffusion by spinodal decomposition into metastable Ag-rich' and Cu-rich' phases. The constant hardening after apparent initial hardening was the result of a subsequent transformation of the metastable Ag-rich' and Cu-rich' phases to the stable Ag-rich α1phase and AuCu I phase through the metastable AuCu I' phase. During the increase in hardness, fine block-like structure with high coherency formed in the grain interior, which changed to a fine cross-hatched structure. A relatively coarse lamellar structure composed of Ag-rich α1and AuCu I phases grew from the grain boundaries, initiating softening before the grain interior reached its maximum hardness. As a result, the spinodal decomposition attributed to rapid hardening by forming the fine block-like structure, and the subsequent ordering into AuCu I, which is a famous hardening mechanism, weakened its hardening effect by accelerating the lamellar-forming grain boundary reaction.