| Budget Amount *help |
¥6,100,000 (Direct Cost: ¥6,100,000)
Fiscal Year 2000: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 1999: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 1998: ¥4,900,000 (Direct Cost: ¥4,900,000)
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| Research Abstract |
Low precious dental Ag-Pd-Cu-Au-Zn type alloys were conducted with various heat treatments, and then their static and dynamic fracture toughness, and tensile properties were investigated. Solutinizing at relatively lower temperature followed by air cooling, that is, solutionized at 1073 k for 3.6 ks followed by air cooling, we found to exhibit excellent fracture toughness and mechanical properties comparing with generally recommended heat treatment, that is, solutionizing followed by aging. Solutionizing at relatively lower temperature followed by air cooling is not only effective to improve static and dynamic fracture toughness, and tensile strength and elongation, but also simple and low cost heat treatment process because aging process can be omitted during heat treatment process. It was possible to point out that the conventional heat treatment was not always suitable for Ag-Pd-Cu-Au-Zn type alloy because in this study fracture toughness was adopted for evaluating the mechanical pe
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rformance of Ag-Pd-Cu-Au-Zn type alloy in addition to the evaluation of tensile properties, which was the only method for evaluating the mechanical performance of the materials in the dental field to date.
The effect of β phase on the tensile properties and fracture toughness of Ag-Pd-Cu-Au-Zn type alloy. In that case, tensile properties and fracture toughness were evaluated with systematically changing the volume fraction of β phase. Up to the peak age condition, strength increased and elongation decreased with increasing the volume fraction of β phase. Slip bands were observed on the part far from the fracture surface for the as-solutionized alloy, but only very near the fracture surface for the aged alloy. The latter phenomenon could be due to the restriction of slip by β phase, which caused the local deformation. In the under age condition, fracture toughness decreased with increasing the volume fraction of β phase when the size of β phase was constant, while fracture toughness decreased with decreasing the diameter of β phase when the volume fraction of β phase was constant.
Then, the experimental alloys with varying Cu content and without Zn were fabricated. These alloys were variously heat-treated. Then, the effects of Cu and Zn on the fracture toughness of Ag-Pd.-Cu-Au-Zn type alloy were investigated. Since the volume fraction of α_1 phase increased with increasing cu content, 0.2% proof stress decreased, but tensile strength increased due to increasing work hardering coefficient. The strength and elongation of Zn added alloy were greater and smaller, respectively comparing with Zn free alloy. The static fracture toughness of Cu added alloy was relatively greater through solutionizing at relatively higher temperature. the static fracture toughness of Zn free alloy was smaller than that of Zn added alloy. The mechanical properties of both experimental alloys were found to be equal to or greater than those of commercial alloy.
The fatigue characteristics of Ag-Pd-Cu-Au-Zn type alloy conducted with various heat treatments were then investigated in the case of water quenched alloy, fatigue strength was greater with increasing solutionizing temperature because solid solution strengthening of α_2 phase increased in the low cycle fatigue life region. On the other hand, in the high cycle fatigue region, the fatigue strength was greater with decreasing solutionizing temperature because the volume fraction of α_1 phase increased and strain relief was achieved by α_1 phase. However, the volume fraction of β phase was necessary to be taken into ccount in order to increase the absolute value of fatigue strength. For the practical use of the alloy, the fatigue strength should be evaluated in the oral *nyironment. Therefore, the fatigue characteristics of the alloys conducted with various heat treatments were evaluated in the artificial saliva, and compared with those evaluated in air. The fatigue strength of as-solutinized and aged alloys was nearly the same in air and artificial saliva in the low cycle fatigue life region. In the high cycle fatigue life region, the fatigue strength of as-solutionized alloy was nearly the same in air and artificial saliva, but the fatigue strength of aged alloy was smaller in artificial saliva than in air. In the high cycle fatigue region, since the exposure time to corrosion environment was relatively longer, and the interface between β phase and matrix was preferentially corroded. Therefore, the corrosion might be severe in the aged alloy where the voltume fraction of β phase was relatively greater. The stress concentration to the corroded parts might be relatively greater. Chloride was considered to form by the reaction of Cl with Ag in this case of corrosion.
It was important to investigate the fracture toughness of cast alloys because casting products were in general practically used. Fracture behavior of cast Ag-Pd-Cu-Au-Zn type alloys conducted with various heat treatments were investigated. Tensile strength of the cast alloy tended to be smaller than that of the wrought alloy. However, a decrcase in tensile strength of the cast alloy comparing with the wrought alloy was little when solution treatment was done at 1073 K followed by air-cooling. The neat treatment of solutionizing at 1073 K followed by air-cooling was judged to be proper for the cast alloy.
Friction wear characteristics of Ag-Pd-Cu-Au-Zn type alloy was investigated in artificial saliva. Friction wear weight loss was the smallest in aged alloy where the volume fraction of precipitated β phase was relatively greater. The alloy solutionized at 1123 K followed by water quenching with single α_2 phase exhibit the same friction wear weight loss as that of the alloy solutionized at 1073 K followed by water quenching with α_1. phase. Friction wear weight loss of mating pin made of this alloy against the alloy conducted with solutionizing and aging was the smallest Friction wear loss of the alloys solutionized at 1073 K and 1123 K followed by water quenching was greater than that of the alloy conducted with solutionizing and aging, and was the greatest for the alloy conducted with solutionizing at 1123 K followed by water quenching. Friction coefficient between specimen and mating pin was found to relate with the friction wear weight loss of the specimen and mating pin. Less
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