Journal of Dental Research, Vol 70, 1350-1357, Copyright © 1991 by International & American Associations for Dental Research Online Journals
Age-hardening mechanisms in a commercial dental gold alloy containing platinum and palladium
T. Tani, K. Udoh, K. Yasuda, G. Van Tendeloo and J. Van Landuyt
Department of Dental Materials Science, Nagasaki University School of Dentistry, Japan.
The age-hardening mechanism of a commercial dental gold alloy containing
platinum and palladium (in wt.%, 15 Cu, 6 Ag, 5 Pt, 3 Pd, 3 Zn, with the
balance as gold) was elucidated by means of electrical resistivity,
hardness tests, x-ray and electron diffraction and electron microscopy, as
well as high-resolution electron microscopy. The sequence of phase
transformations during isothermal aging below the critical temperature, 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 disordered phase (FCC). 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.
