Abstract
Dental alloys, such at Type IV gold and 12wt% Au-Pd-Ag alloy, are softened by heating to a temperature of 750℃ for 30min followed by quenching, and are hardened by reheating at 350℃〜450℃ for 30min. Not only the hardness of both alloys is altered by the heat hardening treatment, but also their strength and ductility are modified. The effects of heat temperature on the mechanical properties, such as tensile strength, elongation, hardness and fatigue strength of these dental alloys were examined. The Type IV gold alloys were hardened when slowly cooled or heated for 30min at 350℃〜450℃, whole its ductility decreased and its tensile strength and hardness increased. On the other hand, the 12wt% Au-Pd-Ag alloy was softened when quenched from 700℃〜750℃; the ductility increased and tensile strength and hardness were reduced. However, these alloys were hardened, when quenched from 800℃ to 850℃, but ductility was not reduced and other mechanical properties were improved. These alloys were hardened when heated for 30min at 400℃ and then its ductility decreased with the same tensile strength and hardness as those at 800℃. Hence, 12wt% Au-Pd-Ag alloys had 1.8 times greater fatigue strength at 800℃ than at 400℃. Furthermore, its fatigue properties became similar to those of gold alloys. This is probably due to the fact that the ductility of the alloy increased and its tensile strength improved.
