Hardening of Dental Gold-Copper Alloys

X-ray diffraction studies of several pro-prietary dental gold alloys demonstrated that hardening probably is a dual mech-anism of precipitation and order-hardening. Lattice parameter measurements showed that the ordered structure was AuCu. In addition, it was shown that maximum hard-ness occurs at about 75 % full order. The hardening mechanism of gold-copper (AuCu) has been investigated extensively. By means of X-ray diffraction, it has been established that hardening is accompanied by an order-disorder transformation. ' Be-cause the composition of many heat-harden-able dental alloys is primarily gold and copper, it has been assumed that their hardening is the result of this transforma-tion.2- Apparently, however, there has been no experimental confirmation of this sup-position. Therefore, the purpose of this investigation was to determine whether this is the mechanism of hardening in commer-cially available dental gold alloys. Materials and Methods MATERIALS EVALUATED.-Nine proprie-tary alloys of American Dental Association Types III and IV, and a series of six special gold-copper-silver alloyst were investigated. The commercial alloys included in the stud