Journal of Dental Research, Vol 65, 75-79, Copyright © 1986 by International & American Associations for Dental Research Online Journals
The relationship between hardness and structure of Pd-Cu-Ga alloys
A. Oden and H. Hero
Most Pd-Cu-Ga alloys on the market have a yield strength of the order of
1000 MPa, which is too high for an adequate adjustment of the margins of a
crown and may promote wear of an opposing natural tooth. In the present
work, the structure of a commercial Pd-10 wt% Cu-9 wt% Ga alloy has been
shown by means of TEM to consist of thin (5-25 nm) laths with two ordered
fct phases with the composition Pd3GaxCu1-x. The c/a ratios in these fct
phases are, alternatingly, greater than 1 and less than 1. The
transformation of an fcc structure by short atomic movements into the fct
structures occurs rapidly below 500 degrees C, as judged by thermal
expansion measurements. Such fct structures are likely to provide
substantial resistance to dislocation movement and thus a high yield stress
and hardness. By adding 6 wt% Ag to the Pd-Cu-Ga alloy and reducing the Ga
and Cu content correspondingly, a predominantly fcc structure occurred with
nearly no fct laths. At the same time, the hardness was reduced to
approximately half the value for the initial Pd-Cu-Ga alloy.
