1993 Fiscal Year Final Research Report Summary
Elucidation of Characteristic Strengthening Mechanisms in Dental Gold Alloys by High Resolution Electron Microscopy
| Project/Area Number |
03452277
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
補綴理工系歯学
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| Research Institution | Nagasaki University |
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Principal Investigator |
YASUDA Katsuhiro Nagasaki Univ., Dent.Mater.Sci., Professor, 歯学部, 教授 (50013884)
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| Co-Investigator(Kenkyū-buntansha) |
BABA Kohmei Technology Center of Nagaski, Senior Scientist, 研究員
TANAKA Yasuhiro Nagasaki Univ., Dent.Mater.Sci., Research Associate, 歯学部, 助手 (10217086)
UDOH Koh-ichi Nagasaki Univ., Dent.Mater.Sci., Research Associate, 歯学部, 助手 (60145266)
HISATSUNE Kunihiro Nagasaki Univ., Dent.Mater.Sci., Associate Professor, 歯学部, 助教授 (20037526)
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| Project Period (FY) |
1991 – 1993
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| Keywords | Gold Alloy / Phase Transformation / Age-hardening / Electron Microscopy / Electron and X-ray Diffraction / Order-Disorder Transformation / Spinodal Decomposition / Ordering Spinodal |
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| Research Abstract |
Age-hardening characteristics and associated phase transformations were studied by means of electrical resistivity measurements, hardness tests, X-ray and electron diffraction, transmission electron microscopy and scanning electron microscopic observations in an AuCu-14at.%Ag pseudobinary alloy. The critical temperature for ordering was determined to be 650 K and the spinodal temperature was estimated to be 640 K.Age-hardening at 623 K was attributed to nucleation and growth processes of the AuCu II' metastble ordered phase even though the ageing temperature was just below the spinodal temperature. While 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 ageing temperature.
The age-hardening mechanism of a commercial dental gold alloy containing platinum and palladium (Au-32at.%Cu-7.6at.%Ag-6.2at.%Zn-3.8at.%Pd-3.5at.%Pt) was also studied. The sequence of phase transformations during isothermal ageing below the critical temperature of ordering, Tc=825 K, 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 phase (fct) + equilibrium alpha_2 desordered phase (fcc). High resolution electron microscopic observation revealed that the hardening was due to the introduction of coherency strain at the interface between the AuCu I' ordered platelet and the surrounding matrix.
The spinodal ordering which was predicted by the CVM was confirmed by means of TEM, SAED and XRD examinations in the equiatomic AuCu alloy using direct ageing. The coherent phase boundary, Tc', and the spinodal ordering temperature, Ts, were identified from differences of microstructural features and changes in XRD patterns during ageing at verious temperatures. The Tc' and Ts were determined to be 648 K and 630 K.
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