18K palladium and platinum containing age hardenable white gold alloy

Abstract

The present invention is directed to an alloy usable for jewelry applications in which the color can be classified as white, the alloy contains both platinum and palladium and is at a metal cost or lower than that of traditional palladium-containing jewelry alloys, and is commercially age hardenable through heat treatment.

Claims

1. An age hardenable alloy composition suitable for jewelry consisting of: 74.5% to 75.5% gold, 8% to 12% silver, 6.5% to 7.5% palladium, 0.5% to 3% platinum, 1.0% to 5% zinc, up to 9.5% copper; and at least one selected from the group consisting of: up to 0.03% lithium, up to 0.5% cobalt, up to 0.1% silicon, and up to 0.03% boron; wherein all values are in w % and said composition exhibits a color which is white and shows age hardening characteristics including an annealed hardness of about 140 Vickers, and an aged hardness of up to 210 Vickers.

2. The composition of claim 1, wherein said composition consists of no more than one from the group consisting of lithium, cobalt, silicon, and boron.

3. The composition of claim 1, wherein said composition has a YI value of about 27.

4. The composition of claim 1, wherein platinum is limited to the range of 1 w % to 2 w %.

5. The composition of claim 4, wherein said composition consists of no more than one from the group consisting of lithium, cobalt, silicon, and boron.

6. The composition of claim 4, wherein said composition has a YI value of about 27.

7. The composition of claim 1, wherein platinum is limited to the range of 1 w % to 1.5 w %.

8. The composition of claim 7, wherein said composition consists of no more than one from the group consisting of lithium, cobalt, silicon, and boron.

9. The composition of claim 7, wherein said composition has a YI value of about 27.

Description

DESCRIPTION OF THE FIGURES

(1) FIG. 1 shows a chart, Chart 1, detailing the 18K Pd-white gold alloy relationship between Yellowness Index (YI) and weight % palladium.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

(2) There is a need in the industry to provide 18K nickel-free palladium containing gold alloy of white color and having commercially adequate age hardening characteristics.

(3) Based on the data shown in Table 2 the values of YI vs. palladium content are plotted in FIG. 1, Chart 1. According to the chart, an alloy containing 10% palladium is expected to show a YI value around 25. In fact, our four experimental alloys with 10% palladium show the variation of yellowness index YI within 25 -26 range—see Table 3. Alloys 1-4 are fairly soft in the annealed condition exhibiting Vickers hardness within the 120-150 range; none of them can be age hardened by a heat treatment.

(4) We find that palladium content in 18K alloy formulations should be below 7% in order to show noticeable age hardening. One example is alloy 5 in Table 3. The Vickers hardness of this alloy in the annealed condition is about 160, and can be increased up to 200 by a heat treatment at 700° F. for about 1 hour. The value of YI for this alloy is about 28.5.

(5) TABLE-US-00003 TABLE 3 Experimental Alloy Au Ag Pd Pt Cu Zn YI 1 75 5 10 5 16 2 75 10 10 5 25 3 75 5 10 10 26 4 75 5 10 5 5 26 5 75 5 7 10.5 2.5 29 6 75 10 7 1.5 5 1.5 27

(6) Such alloys as experimental alloy 5 in Table 3 show inconsistent age hardening as the small temperature variations affect the degree of hardening. Experimental alloy 6 in Table 3 can be age hardened more consistently by the addition of 1.5% platinum. This alloy has an improved white color with YI value of 27 (closer to those of 10% palladium alloys); and can be age hardened from 140 Vickers in the annealing condition up to 210 Vickers by heat treatment at 750° F. for about 1 hour. The total palladium and platinum intrinsic value is less than that of 10% palladium white alloys, and therefore, this alloy is less expensive than 10% palladium containing alloys.

(7) It is not unusual for a production furnace, when set up at 700° F., to have a variation in temperature of ±20° F. over time. An alloy such as experimental alloy 5 shows a narrow age hardening temperature range so that ±20° F. variation in the furnace significantly affects the degree of hardening as material is not exposed to 700° F. all the time. Increasing the aging time may lead to material deterioration due to over-aging. Adding 1.5% Pt broadens the aging temperature range to about ±50° F., and therefore improves the consistency of the hardening procedure, and in addition, increases the aged hardness by about 10 Vickers—from 200 in alloy 5 to 210 Vickers in alloy 6. Typical properties of alloys 1-4 are listed below: Density: 168.3 dwt/in.sup.3 (16.0 g/cm.sup.3) Annealed hardness: 120 Vickers Aged hardness: alloy cannot be age hardened. Annealing temperature: 1250° F. (675° C.) Melting range: 1895° F.-2055° F. (1035° C.-1125° C.) Typical properties of alloy 5 are listed below: Density: 162.5 dwt/in.sup.3 (15.4 g/cm.sup.3) Annealed hardness: 160 Vickers Aged hardness: 190 Vickers Annealing temperature: 1250° F. (675° C.) Aging temperature: 750° F. (400° C.) Melting range: 1645° F.-1725° F. (895° C.-940° C.) Alloy 6 in Table 3 has a preferred composition. The properties of this alloy are: Density: 168.8 dwt/in.sup.3 (16.0 g/cm.sup.3) Annealed hardness: 155 Vickers Aged hardness: 210 Vickers Annealing temperature: 1250° F. (675° C.) Aging temperature: 750° F. (400° C.) Melting range: 1840° F.-1985° F. (1005° C.-1085° C.). Suggested alloy compositional range: Gold: 74.5%-75.5% Silver: 8%-12% Palladium: 6.5%-7.5% Platinum: 0.5%-3% Zinc: 0.5%-5% Copper: balance Possible small additions: Lithium (de-oxidizer): 0%-0.03% Cobalt (grain refiner): 0%-0.5% Silicon (de-oxidizer): 0%-0.1% Boron (improves metal fluidity while casting): 0%-0.03%