Relationship between Unique Hardening Behavior and Microstructure of Dental Silver Alloy Subjected to Solution Treatment

The purpose in this study is to investigate the effect of microstructure on the unique hardening behavior of dental silver alloy, Ag-20Pd-14.5Cu-12Au (mass%), fabricated by hot rolling process (AS material), which is in as-received condition, and liquid rapid solidification (LRS) process (LRS material). The following results were obtained. The microstructure of AS material is consisted of α1, α, and β phases. The microstructure of AS material changes to α, β, and β′ phases through a solution treatment (ST). The microstructure of LRS material is consisted of α, α1, and α2 phases without β phase. The microstructure of LRS material becomes single α phase through ST. Relatively large β phases with the diameter of tens of μm on AS material coarsen according to increasing the ST time, while the small those with the diameter of a few μm are solid-soluted into the matrix. On the other hand, the coherent participation of β′ phases with long and short axes of around 100 nm and 10 nm, respectively, also occurs during ST although the amount of β′ phase decreases with increasing the ST time. The hardness and tensile strength of LRS material and LRS material subjected to ST are relatively smaller than those of AS material and AS material subjected to the same treatment. From this results, the effect of solid solution hardening of α, α1, and α2 phases is lower than that of precipitation hardening of β′ phases. In a case of the unique hardening seems to occur because the precipitation of β′ phases are enhanced during ST.