Effect of indium addition on microstructure and strength of Au-Pt-Cu-Sn dental biomaterial

Through our previous screening experiments for a new dental alloy design, an Au-11.9Pt-0.6Cu-0.5-Sn alloy was selected as a candidate in terms of good strength and surface properties. In this report, the effects of In (indium) on the microstructures and hardness of a dental Au-11.9Pt-0.6Cu-0.5Sn-xIn alloy (where x = 0, 0.25, 0.5, 0.75, and 1.0 wt.%) was investigated. The hardness of the Au11.9-Pt-0.6Cu-0.5Sn-xIn alloys increased with increasing In content up to 0.75 wt.% and then started to decrease with further increase in In content. Particularly, the alloy containing 0.75% In exhibited noticeably high hardness of 172 Hv. With the addition of In to the Au-Pt-Cu-Sn alloy, grain size decreased and a large number of fine precipitates were formed. The precipitates were identified as Pt₃(Sn, In) by convergent beam electron diffraction (CBED) and nanospot energy dispersive spectroscopy (EDS). The increased hardness with the addition of In was attributed to the precipitation hardening of Pt₃(Sn, In) and the grain refinement.