US3512961A - Fine grained white gold alloy - Google Patents

Description

United States Patent Office 3,512,961 Patented May 19, 1970 3,512,961 FINE GRAINED WHITE GOLD ALLOY George H. Sistare and Ernest S. Chamer, Fairfield, Conn.,

assignors to Handy & Harman, Fairfield, Conn., a corporation of New York No Drawing. Filed Apr. 19, 1968, Ser. No. 722,548

Int. Cl. C22c 5/00 U.S. Cl. 75-165 5 Claims ABSTRACT OF THE DISCLOSURE A 9 /2 to 18 karat white gold alloy is made to have an exceptionally fine grain structure in as-cast condition by the addition of 0.005% to 0.05% by weight rhenium. The rhenium may be added in the form of a master alloy of rhenium and nickel (e.g. a 10% rhenium-nickel alloy). The alloy exhibits a fine grain structure in the cast condition and as annealed after working.

This invention relates to white gold alloys and is particularly directed to the :provision of an improved karat white gold alloy having an exceptionally fine grain structure in the as-cast condition. The new alloy is composed of a standard white gold alloy (generally 9 /2 karat to 18 karat) containing 0.005% to 0.05 by weight of rhenium uniformly dispersed therein. The new alloy is useful for making cast gold alloy jewelry such as school rings. It may be used with particular advantage for making other gold alloy castings which must subsequently be worked, such as cast tubes which are drawn to smaller diameter and wall thickness.

White gold alloys having a fine grain structure are desirable for the manufacture of jewelry articles because the surface quality and appearance of such articles after polishing is affected by the fineness of the grain structure. Alloys having a fine grain structure may be polished to an even lustrous appearance, whereas coarse-grained alloys even in the as-cast condition may after polishing have an uneven orange peel appearance. Fine grained alloys are also stronger than similar alloys in a coarse grained condition, and can be cold worked from this ascast condition without damagea property not possessed in all cases by white gold alloys having the usual coarse as-cast structure.

Various additions have been made heretofore to gold alloys to refine their grain structure in the as-cast condition. Iridium has been. the most effective and most extensively used addition for this purpose, but it has not proved effective in white gold alloys. Cobalt and nickel have been usedfor this purpose in yellow gold jewelry alloys, but the large amounts of the latter element that are required to whiten gold alloys does not have a grain refining effect in such alloys. Cobalt also is ineffective in white golds for grain refining.

The present invention is based upon our discovery that if rhenium is added to karat white gold alloys of 9 /2 to 18 karats, in the concentration range from 0.005% to 0.05% by weight, very effective grain refining of the alloy in the as-cast condition is attained. As little as 0.005% by weight of rhenium in the gold alloy effectively refines the grain structure, but preferably the concentration is from 0.01% to 0.03% by weight.

Accordingly, the invention provides a white gold alloy having a fine grain structure in the as-cast condition, said alloy being composed of a karat-gold alloy containing about 39% to about 80% by weight gold, 0% to about 45% by Weight copper, 0% to about by weight Zinc, 0% to about 2.5% cobalt, about 8% to about 20% by weight nickel, and about 0.005% to about 0.05% by weight rhenium uniformly dispersed throughout the alloy. Preferably the amount of rhenium added is in the range from about 0.01% to about 0.03% by weight of the alloy, most commonly about 0.02% by weight. When the rhenium is added in the form of a rhenium-nickel master alloy, such master alloy usually will contain about 10% rhenium; but rhenium-nickel master alloys of higher rhenium content may be used, containing say up to 15% or even as high as about 20%. by weight rhenium.

Copper may or may not be present in the alloy; but it is used in many karat white gold alloys and its presence is unobjectionable in the amounts conveniently used. Preferred alloys contain it in concentrations from 2% to 41% by weight. Zinc also may or may not be present; it is used in many karat white gold alloys and its presence is unobjectionable. Preferably it is present and is used in an amount from 5% to 13% by weight. Cobalt may be present as a component of commercial grade nickel, or may be added purposely. In the latter case its concentration is preferably from to 2%. Nickel is necessarily present in rather high concentration, generally from 8% to 20% by weight and preferably from 9% to 18% by weight. Usually the nickel concentration increases with the gold content. The gold content will, for standard karat alloys, range from 39.6% by weight (for 9 /2 karat alloys) to 75% by weight (for 18 karat alloys). The alloy may in addition contain such impurities as are found from time to time in karat white gold alloys.

The new alloy is made by the procedures and with the melting and casting apparatus customarily employed in making karat white gold alloys for the jewelry trade. For example, the alloy may be made by melting together the requisite proportions of commercially pure gold, nickel,

and other major ingredients, and then adding to the melt the requisite amount of rhenium in the form of a master alloy with nickel. Alternatively, the karat white gold alloy may be made by melting scrap gold alloy and adding to it such amounts of gold, nickel, copper, zinc, and rhenium as are necessary to adjust the composition to the desired formula. One or more of these metals may, of course, be added wholly or in part in the form of an alloy with one or more of the others. The rhenium may be derived either in whole or in part from scrap gold alloy, provided it has not been lost from such scrap, as it tends to be, by carbonization or by oxidation during remelting or alloying.

When the alloy has been melted and its composition adjusted as desired, it may be cast directly into shaped molds for jewelry, or in grain form, or in the form of conventional ingots, bars or tubes. The grain is remelted for jewelry castings by jewelry manufacturers. The ingots or bars are converted to wrought form such as sheet or wire for use in making wrought jewelry or other wrought gold articles. Tubes may be drawn and sliced to make rmgs.

It is characteristic of the new rhenium-bearing white gold alloy that it has an uncommonly fine grain structure as cast. Typically, the grain size of a conventional 14 karat or 18 karat white gold alloy containing 0.02% by weight rhenium will have in the as-cast condition an average grain size of about 0.010 to 0.020 mm. diameter. The same gold alloy without the rhenium may have in the as-cast condition an average grain size of about 0.200 mm. in diameter or even considerably greater. Similar marked reduction in the cast grain size is found in 14 karat and 18 karat alloys containing greater and lesser amounts of rhenium in the range from 0.005% to 0.05% by weight. In low karat (e.g. 10 karat) alloys containing rhenium the grain size of the metal as cast may be near 0.025 mm.; but it is much smaller than in the same alloy containing no rhenium.

The fine grain structure of the new alloy is found also in cold rolled and annealed metal. For example, a 14 karat white gold containing-0.02% by weight rhenium;

cold rolled from a 0.5 inch cast bar to a thickness of 0.062 inch with one intermediate anneal at 1400 F., and then finally annealed 4 hours at 1400 F., has a grain size close to 0.020 mm. in diameter. The same alloy, but free from rhenium, similarly treated, has a grain size generally substantially exceeding 0.200 mm. after annealing. Accordingly, the new alloy may be used with advantage for making jewelry articles by deep drawing from sheet or by other cold working of sheet, bars, wire or tubes, followed by annealing, without developing objectionable orange peel surface appearance.

The following table sets forth examples of various gold alloys according to this invention (all compositions are given as percent by weight).

1. A white gold alloy having a fine grain structure in the'a's-ca'st conditior'iconsis'ting of 39%1530'75 by'weight gold, 0% to 45% by weight copper, 0% to 15% by weight zinc, 0% to 2.5% by weight cobalt, 8% to by weight nickel, and 0.005% to 0.05% by weight rhenium uniformly'dispersed throughout the alloy.

2. A white gold alloy according to claim 1, in which the rhenium content is in the range from 0.01% to 0.03% by weight. i

3. A white gold alloy according to claim 1, containing 2% to 41% by weight copper and 5% to 13% by weight zinc.

4. A white gold alloy according to claim 3, containing 9% to 18% by weight nickel.

5. A white gold alloy according to claim 4, containing 0.01% to 0.03% by weight rhenium.

Components A B C D E F G 30. 6 39. s 30. 6 5s. 33 5s. 33 75. 00 75. 03 41.0 32.0 34.0 22.07 23. 47 3. 75 ,0.0 12. 15. 66 17. 07 10. so 12. 1s 10. 23 24. 00 7.0 12.7 8.7 8.78 5. 09 5. 04 0.0 0.01 0.04 0.03 0.02 0. 03 0.02 0.07 Grain size as-cast 0. 025 0. 025 0. 025 0. 015-0. 020 0. 0150. 020 0. 010-0. 015 0. 010-0. 015

References Cited UNITED STATES PATENTS I 1,523,026 1/1925 Liebkecht -165 1,647,822 11/1927 Williams 75165 L. DEWAYNE RUTLEDGE, Primary Examiner E. L. WEISE, Assistant Examiner