Studies on improvement of superelasticity in dental gold alloys

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Experiments were performed to improve the characteristics of super-elastic gold alloy for denture clasps, in which stability of the characteristics was investigated increasing the fineness of crystal grains.At first, using 65wt% Au-12Cu-23Zn as base alloy, Ru and Hf and additional 0-1% lanthanoid metals, La, Ce, Nd, Sm, Gd, were added to perform fatigue test, and investigate the fineness of crystal grains. Good characteristics were obtained by the further addition of Sm, Gd, and Ld when only Ru was added to the base alloy, and by additionally adding Sm, Gd, and La when Hf and Ru were added to the base alloy.Next, using 7 types of base alloys [No.30 (64wt% Au-12Cu-24Zn), No.31 (65wt% Au-11Cu-24Zn), No.36 (64wt%Au-13Cu-23Zn), No.37 (65wt%Au-12Cu-23Zn), No.38 (66wt% Au-11Cu-23Zn), No.40 (65wt% Au-13Cu-22Zn), No.41 (6Gwt% Au-12Cu-22Zn)], 0.5wt% Ru and additional 0.5% La, Sm, and Gd, or 0.5wt% Ru + 0.25 Hf and additional 0.25% La, Sm, and Gd were added to the base alloys to perform hardness test, tensile strength test, abrasion test, and fatigue test, and to investigate the fineness of the crystal grains. The following results were obtained:1.Increases in the fineness of the crystal grains were greatest when 0.5wt% Ru + 0.5 Sm were added to No.40 base alloy, and second greatest when 0.5wt% Ru + 0.25 Hf + 0.25 Sm, or 0.5wt% Ru + 0.5 Gd, or 0.5wt% Ru + 0.25 Hf + 0.25 Gd were added to No.30 base alloy.2.By fatigue test, approximately 12,000 times were obtained when 0.5wt% Ru + 0.25 Hf + 0.25 La were added to No.37 base alloy, and when 0.5wt% Ru + 0.5 Sm were added to No.40 base alloy. More than 20,000 times were obtained when 0.5wt% Ru + 0.25 Hf + 0.25 Sm were added to No.41.Therefore, it was found that good characteristics were obtained under these conditions of the types and amounts of additions.