Hardening of Dental Gold-Copper Alloys
X-ray diffraction studies of several proprietary dental gold alloys demonstrated that hardening probably is a dual mechanism of precipitation and order-hardening. Lattice parameter measurements showed that the ordered structure was AuCu. In addition, it was shown that maximum hardness occurs at about 75% full order.
Dimensional changes related to ordering in an AuCu-3wt%Ga alloy at intraoral temperature.
OBJECTIVES
The purpose of this study was to evaluate the distortion behavior of a gold alloy with age-hardening ability at intraoral temperature induced by phase transformations.


METHODS
Bridge-type specimens were prepared using AuCu-3wt%Ga alloy with age-hardening ability at 37 degrees C. Dimensional changes, hardness and surface roughness were measured. Transmission electron microscopy observation was carried out using AuCu-3wt%Ga discs aged at 37 degrees C for 30 d.


RESULTS
Hardening was brought about rapidly in the initial stage of aging at 37 degrees C owing to ordering. The ordering was attributed to the formation of AuCu I and AuCu II superlattices. A linear contraction of 0.04% was induced by aging at 37 degrees C for 3 d. Distortion of the bridge-type specimen was brought about by a combination of linear contractions. The surface roughness increased in the initial stage of aging due to the surface relief effect of internal coherency strain caused by tetragonality.


SIGNIFICANCE
The mode of distortion may be more advantageous for use in crown-type rather than inlay-type restorations, and the amount of contraction may not produce any problems in clinical use.
Änderung des Elastizitätsmoduls von AuCu-Legierungen bei Überstrukturbildung
ZusammenfassungEs wurde der Dehnungsmodul an Gold-Kupferkristallen der Zusammensetzung AuCu gemessen. Er ergab sich im Falle der Überstrukturbildung erheblich kleiner als im statistisch ungeordneten Zustand der Atome.