Contribution of β′ and β precipitates to hardening in as-solutionized Ag–20Pd–12Au–14.5Cu alloys for dental prosthesis applications

Dental Ag–20Pd–12Au–14.5Cu alloys exhibit a unique hardening behavior, which the mechanical strengths enhance significantly which enhances the mechanical strength significantly after high-temperature (1123 K) solution treatment without aging treatment. The mechanism of the unique hardening is not clear. The contribution of two precipitates (β′ and β phases) to the unique hardening behavior in the as-solutionized Ag–20Pd–12Au–14.5Cu alloys was investigated. In addition, the chemical composition of the β′ phase was investigated. The fine β′ phase densely precipitates in a matrix. The β′ phase (semi-coherent precipitate), which causes lattice strain, contributes greatly to the unique hardening behavior. On the other hand, the coarse β phase sparsely precipitates in the matrix. The contribution of the β phase (incoherent precipitate), which does not cause lattice strain, is small. The chemical composition of the β′ phase was determined. This study reveals that the fine β′ phase precipitated by high-temperature solution treatment leads to the unique hardening behavior in dental Ag–20Pd–12Au–14.5Cu alloys in the viewpoints of the lattice strain contrast and interface coherency. It is expected to make the heat treatment process more practical for hardening. The determined chemical composition of β′ phase would be helpful to study an unknown formation process of β′ phase.