1990 Fiscal Year Final Research Report Summary
High-Resolution Electron Microscopy Study on Characterization of Interfaces induced by Phase Transformation in Dental Gold Alloys
| Project/Area Number |
01460241
|
|---|
| Research Category |
Grant-in-Aid for General Scientific Research (B)
|
| Allocation Type | Single-year Grants |
|---|
| Research Field |
補綴理工系歯学
|
|---|
| Research Institution | Nagasaki University School of Dentistry |
|---|
Principal Investigator |
YASUDA Katsuhiro Nagasaki University School of Dentistry, Department of Dental Materials Science, Professor, 歯学部, 教授 (50013884)
|
|---|
| Co-Investigator(Kenkyū-buntansha) |
UDOH Koh-ichi Nagasaki University School of Dentistry, Department of Dental Materials Science,, 歯学部, 助手 (60145266)
HISATSUNE Kunihiro Nagasaki University School of Dentistry, Department of Materials Science, Associ, 歯学部, 助教授 (20037526)
|
|---|
| Project Period (FY) |
1989 – 1990
|
| Keywords | Transmission electron microscopy, / X-ray diffraction, / Dental Gold Alloys, / Gold-Copper-Silver Ternary Alloys, / Phase Transformation, / Age-hardening, / Transitional Ordering, |
|---|
| Research Abstract |
(1) Age-hardening characteristics and the associated phase transformations were studied by means of electrical resistivity, hardness tests, X-ray and electron diffractions, TEM and SEM observations in a AuCu-14at. %Ag pseudobinary alloy. Critical temperature of the ordering was determined to be at 650K, besides spinodal locus was estimated at 640K. Age-hardening at 623K was attributed to the nucleation and growth process of AuCu II' metastable ordered phase though the aging temperature was just below spinodal temperature, while the hardening in the lower temperature range took place at two stages, the former was due to spinodal decomposition and the latter was brought about by ordering of AuCu I' and/or AuCu II' metastable phases depending on aging temperature. The overaging was induced by grain boundary precipitation of AuCu I and/or AuCu II ordered and silver-rich alpha_2 equilibrium phases.
(2) Age-hardening mechanism in a AgCu-40at. %Au alloy was also studied same experimental procedure the above. Two stages of hardening were found by isothermal aging below 648K which was higher than the critical temperature of ordering, T_c = 620K. The first stage of hardening took place by formation of a modulated structure resulting from spinodal decomposition. Further hardening was brought about by ordering yielding metastable AuCu I' and/or AuCu II' ordered platelets grown from copper-rich portion of the modulated structure. Transitional ordering which gave rise to a marked hardening of second stage was found even though the temperature below 648K which was higher than T_c for ordering in the present alloy. Drastic softening was also found by disappearance of the transitional ordered phases. Although the modulated structure was observed by aging ta 773K, there was no hardening.
|
