INCREASEING THE TENSILE AND FATIGU STRENGTH MECHANISM OF DENTAL ALLOY

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Commercially available 12% Au-20% Pd-Ag-Cu alloys have been standardized at 12wt% Au and 20wt%Pd with the content of Ag and Cu varying from 45-55wt% and 15-20wt% respectively. By increasing the amount of Cu in this alloy to the limit of the eutectic composition shown in the ternary alloy phase diagram it is possible to lower the liquidus line. Moreone, the crystallization ratio of phase a1 and a2 of the eutectic phase becomes larger and, compared with the composition near the a1 solid-solution phase, a general enhancement of toughness can be anticipated.An experimental alloy was made for this study in which the amount of Cu in the commercial 12wt% Au-Pd-Ag alloy was increased to 25wt% and a study was made of the relationship between the heat treatment and the tensile characteristics of this experimental alloy. As a further study, 2wt% of Zn was added to this experimental alloy to see what effect shis might have on the mechanical properties.The re results of this study indicates :1) I am possible to give toughness to the aged area and solid-solution hardening area by seeking the amount if Cu in a 12wt%Au-20wt%Pd-Ag-Cu alloy on the eutectic line of a ternary phase diagram. The experimental alloy (standard alloy) had a improved elongation by from 15% to 22% compared with that of S-12 wrought material.2) At 905.6ﾟC,the liquidus phase temperature of standard alloy was lower than that of 945.5ﾟC for S-12 and 915.9ﾟC for Castwell MC.Also, the liquidus phase temperature for Zn added alloy was 907.3ﾟC.3) An addition of 2wt%Zn to the experimental alloy used in this experiment caused embrittlement. However, when this alloy is given air-cooled treatment outside the furnace, some of it's tensile strength is sacrificed but it's toughness increases and an elongation.