| Project/Area Number |
01044112
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| Research Category |
Grant-in-Aid for international Scientific Research
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| Allocation Type | Single-year Grants |
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| Section | Joint Research |
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| Research Institution | Nagasaki University School of Dentistry |
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Principal Investigator |
YASUDA Katsuhiro (1990) Professor, Department of Dental Materials Science, Nagasaki University School of Dentistry, 歯学部, 教授 (50013884)
安田 克広 長崎大学, 歯学部, 教授
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| Co-Investigator(Kenkyū-buntansha) |
TENDELOO G.V アントワープ大学(RUCA), 教授
LANDUYT J.Va アントワープ大学(RUCA), 教授
UDOH Koh-ichi Research Associate, Department of Dental Materials Science, Nagasaki University, 歯学部, 助手 (60145266)
VAN TENDELOO Gustaaf
VAN LANDUYT Joseph Professor, Center of High Voltage Electron Microscopy for Materials Research, U
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| Project Period (FY) |
1989 – 1990
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| Project Status |
Completed (Fiscal Year 1990)
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| Budget Amount *help |
¥7,100,000 (Direct Cost: ¥7,100,000)
Fiscal Year 1990: ¥3,500,000 (Direct Cost: ¥3,500,000)
Fiscal Year 1989: ¥3,600,000 (Direct Cost: ¥3,600,000)
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| Keywords | High-Resolution Electron Microscopy / X-ray diffraction / Dental Gold Alloy / Gold-Copper-Silver Ternary Alloy / Phase Transformation / Age-Hardening |
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| Research Abstract |
Changes in structural configuration arose from AuCu ordering and two-phase decomposition were studied by means of TEM and HREM observations in a AuCu-14at. %Ag pseudobinary alloy. Two different types of precipitates, spindle-type and chaintype, were found at 643K formed by nucleation and growth process. These precipitates were named as composite precipitate because they had a sandwich structure consisted of a cuboidal block of silver-rich fcc phase and an LPAPB AuCu II ordered thin platelets across their longitudinal axis, and were covered with the AuCu II Platelets on the top and bottom table planes. Their lateral faces were not covered and opened to connect with the matrix. By aging just below spinodal temperature, the cuboidal blocks of fcc phase were also sandwiched by the AuCu II ordered thin platelets. This sandwich structure was surrounded by the AuCu II ordered phase all around. Models of these configurations were proposed. A modulated structure was found by aging at low temperature range for early stage in the present alloy.
The age-hardening mechanism of a commercial dental gold alloy containing platinum and palladium, Au-15wt. %Cu-6wt. %Ag-5wt. %Pt-3wt. %Pd-3wt. %Zn, was also studied. The sequence of phase transformations during isothermal aging below the critical temperature for ordering, T_C=825K, was described as follows : disordered solid solution alpha_0 fcc --- metastable AuCu I' ordered phase (fct) + metastable alpha_2' disordered phase (fcc) --- equilibrium AuCu I ordered + equilibrium alpha_2 disordered phase. The hardening was due to the introduction of coherency strain at the interface between the AuCu I' platelet and the matrix. These ordered platelets had mutually perpendicular c-axes to compensate for the strain introduced by their tetragonality. A loss of coherency at the interface brought about softening of the alloy, i. e., over-aging.
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