Ordering behaviors and age-hardening in experimental AuCu–Zn pseudobinary alloys for dental applications

Precipitation hardening of a Cu-free Au–Ag–Pd–In dental alloy

“…From the above, it was revealed that the early stage of the phase transformation of ␣ 1 into α 1 that corresponded to the hardness increase was caused in the early stage of precipitation, and that the hardness decrease corresponded to the coarsening of the fine lamellar precipitates. It was reported in several studies of various dental alloys that coherency strains are formed during the initial stage of the phase transformation, which was attributed to the hardness increase of the alloy [2,10], and that the release of them caused the decrease in hardness [11][12][13]. From those reports and the above experimental results, it is assumed that the coherency strains were formed by the diffusion and aggregation of some elements from the matrix during the early stage of precipitation, which caused the hardness increase in the present research.…”

“…Such an age-hardenability is closely related to the element composition of the alloy. Cu has broadly been used in various dental casting alloys to impart age-hardenability by the formation of the AuCu I or AuCu II ordered phase [1,2], by the precipitation of the CuPd phase [3] and by the precipitation of the Cu-rich phase [4]. However, the use of Cu was avoided lately because of its low corrosion and tarnish resistance, and thus a proper element that substitute Cu is requested.…”

Age-hardening and overaging mechanisms related to the metastable phase formation by the decomposition of Ag and Cu in a dental Au–Ag–Cu–Pd–Zn alloy

“…In a dental commercial low-gold alloy aged at 400°C after solution treatment at 900°C and in a dental commercial Ag-Pd-based alloy aged at 350°C after solution treatment at 750°C, the minor ingredient, Zn-having relatively low melting temperature-tended to form extra phases preferably with Pd which is having relatively high melting temperature [2,22]. However, in the equiatomic AuCu alloy, the single AuCu phase was made with Zn addition up to 20 at% at 300°C and 350°C after solution treatment at 500°C [23]. Moreover, the addition of Zn to the AuCu system promoted the AuCu-type ordering, and stabilized the AuCu-type structure, which made it possible for the AuCu-Zn alloy to have an excellent agehardenability [23][24][25][26].…”

“…However, in the equiatomic AuCu alloy, the single AuCu phase was made with Zn addition up to 20 at% at 300°C and 350°C after solution treatment at 500°C [23]. Moreover, the addition of Zn to the AuCu system promoted the AuCu-type ordering, and stabilized the AuCu-type structure, which made it possible for the AuCu-Zn alloy to have an excellent agehardenability [23][24][25][26]. In the present study, Zn was concentrated in the AuCu I layer containing Pd without formation of an extra phase.…”

Age-hardening by grain interior and grain boundary precipitation in an Au-Ag-Pt-Zn-In alloy for multipurpose dental use

“…From the above, in the later stage of aging process, the phase transformation of 2 into 2 ' and 3 into 3 ' progressed, and which slowed the decreasing rate of hardness for a while. The phase transformation must have produced lattice strains resulting in hardening, as it was in various dental alloys [12][13][14][15]. However, it did not stop the softening process.…”