Fundamental study high strength Au-Pd-Cu alloys

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The purpose of this study was to obtain fundamental data for the development of high strength dental gold alloys. Twenty Au-Pd-Cu alloys containing 10,20,30,40 and 50 mass% Pd, 10,20,30 and 40 mass% Cu and 10-80 mass% Au were made using induction melting in argon gas atmosphere, Melting point, Vickers hardness, tarnish resistance, and specific gravity were measured, and the phases of the alloys were determined using X-ray diffraction. The following summary is drawn.1) The liquidus point of experimental alloys ranged from 1035ﾟC to 1388ﾟC,and increased with the decrease of Cu content and the increase of Pd content. For the practical use, this result indicates that the liquidus point should be lowered by adding the other metal elements.2) The experimental alloys containing 20-30 mass% Cu showed the highest brightness (L^*) after the tarnish test. The defference in the brightness (DELTAL^*) before and after the test increased with the increase of the Cu content. On the other hand, the as cast, quenched and heat-hardened alloys had L^*=70, showing good tarnish resistance.3) Vickers hardness number ranged from 63.2-319 for the as cast alloys, 74.4-197 for the quenched alloys and 74.5-291 for the heat-hardened alloys. Assuming that the tensile strength is 1/3 of Hv number, experimental alloys with high Hv may have more than 95kgf/mm^2 tensile strength. From this result, the composition of high strength alloys is estimated to be 50-70Au-20-30Cu-10-30Pd.4) The result of specific gravity measurement suggests that more blow holes can be produced in the alloys containing either 50 mass% Pd or 10mass% Cu.5) The alloy phase analysis using X-ray diffraction indicates that the hardening of the alloys is based on the formation of AuCu and PdCu superlattice.