Dental bridge alloy

Abstract

A highly ductile cobalt-chromium-nickel dental alloy suited for crown and bridge applications which require deformation by hand burnishing in the mouth of a patient, has a controlled high stacking fault energy and a ductility of about 20 percent elongation or more, a yield strength of about 35,000 psi or less and low work hardening characteristics and is free of hardening precipitates resulting from the inclusion of significant amounts of carbon, boron, molybdenum, titanium, aluminum, and tungsten in the alloy. Preferably, the nickel-cobalt ratio in the alloy base ranges from a low of about 1:3, by weight, to prevent the normal transformation of cobalt from a ductile face centered cubic lattice to a hexagonal close pack structure upon cooling to room temperature to a high of 2:1 since higher concentrations of nickel produce CoNi.sub.3. The alloy base preferably includes 20 percent chromium to provide the necessary corrosion resistance and an additional amount of 2 percent nickel is required in the alloy base to offset the adverse effects of chromium on the ductility of the alloy. A small quantity of niobium or tantalum, both of which have substantial solubility in the alloy base, are added to form nuclei of crystallization for the alloy to promote fineness of crystal size and uniformity of physical properties from melt-to-melt. Niobium and tantalum also counteract the adverse effect of chromium on the stacking fault energy of the alloy with 1 percent of niobium, or approximately 2 percent of tantalum, counteracting the adverse effect of 1.25 percent chromium so that the nickel used in the alloy base can be reduced according to the amount of niobium or tantalum added to the alloy.