Alloy and manufacturing method thereof

Abstract

The invention provides an alloy and a manufacturing method thereof. The alloy is provided with an interference film. In one embodiment, the alloy consists essentially of 55.0 to 78.0 wt% of Au, 8.0 to 24.0 wt% of Ag, 8.0 to 24.0 wt% of Cu, and 0.0 to 3.0 wt% of a deoxidizer; the interference film is grown directly from the inside of the alloy to one surface of the alloy and has a thickness of less than 200 nanometers; the interference film is characterized in that the interference film presents a surface color.

Description

Technical Field

[0001] This invention relates to surface coloring on gold alloys. Background Technology

[0002] In jewelry making, precious metals of different colors can be combined to create beautiful and desirable products. Traditionally, gold alloys come in a variety of colors, with yellow, white, and rose gold being the most common. Different colors can be achieved by changing the ratio of silver to copper in the composition of gold-silver-copper alloys. New colors can also be brought to gold alloys through surface treatments such as electroplating and anodizing.

[0003] Oxidation coloring is a method of forming a thin colored layer on the surface of a metal, typically bronze and copper, through oxidation. The green patina of copper and bronze, whether natural or man-made, is usually bluish-green. Oxidation coloring is generally used as a method to provide a protective coating for metals, but in the jewelry industry, it is more often used as a technique for coloring jewelry alloys. The color of an oxidized metal alloy surface depends on the composition of the alloy and the heat treatment method. For example, chromium-containing jewelry alloys may appear red after heat treatment due to the formation of Cr(VI) oxides, while iron-containing alloys may appear green due to the formation of iron(II) oxides.

[0004] European Patent No. EP0438980 discloses a patent application that is 400... o C to 1100 o A black cobalt oxide layer is formed on a cobalt-containing gold alloy (Au-Ag-Cu-Co) by heat treatment for 15 minutes to one hour. However, the application of cobalt is limited by its very susceptibility to oxidation. Using a high percentage (3-5%) of cobalt is detrimental to investment casting due to over-oxidation and its high melting point. Investment casting is crucial in the jewelry manufacturing industry because it produces high-precision surface finishes and offers great flexibility in product design. The inability to perform investment casting will cause numerous difficulties in the manufacturing process. Furthermore, only a black oxide layer can be obtained from this alloy.

[0005] Similarly, Japanese Patent No. JP2185934 discloses a patent with a patent number of 850. o C to 900 o Heat treatment at C for 2 minutes yields gold alloys (Au-Mn-Fe, Au-Mn-Co, and Au-Ag-Mn-Fe) with a brown surface. However, using high percentages (5-40%, respectively) of manganese, iron, and cobalt in jewelry investment casting can cause problems because manganese, iron, and cobalt are all highly susceptible to oxidation.

[0006] U.S. Patent No. 5,059,255 discloses in 450 o C to 600 oThe gold alloy (Au-Fe-Ni) of C appears blue after heat treatment for 10-12 minutes. It is well known that nickel is a common cause of skin allergies. Therefore, nickel is avoided in the new jewelry alloy invention.

[0007] The present invention uses a gold alloy with only the addition of copper and silver, free of toxic substances and allergens. This alloy can be easily produced by investment casting without the drawbacks due to oxidation. Unlike the above invention, the present invention can create a range of predetermined color effects for the same gold alloy. This will provide opportunities and benefits for the jewelry manufacturing and design industry.

[0008] The distinction of the present invention from the existing gold alloy oxidation coloring technique must be emphasized. In the present invention, a wide range of various colors can be produced by controlling the heating time, while other gold alloy oxidation coloring processes can only generate one or two colors. The most significant difference is the source of the oxidation color. The oxidation color in the prior art comes from a few microns thick metal oxide layer, and the oxidation color depends on the color of the metal oxide. However, in the present invention, the surface color comes from the thin film interference of the nanoscale oxide layer. SUMMARY

[0009] The present invention provides an alloy with an interference film. In one embodiment, the alloy consists essentially of 55.0-78.0 wt% Au, 8.0-24.0 wt% Ag, 8.0-24.0 wt% Cu, and 0.0-3.0 wt% deoxidizer; the interference film grows on one surface of the alloy and has a thickness of less than 200 nanometers; the interference film exhibits a surface color.

[0010] The present invention provides an alloy with an interference film. In one embodiment, the alloy consists essentially of 55.0-78.0 wt% Au, 8.0-24.0 wt% Ag, 8.0-24.0 wt% Cu, and 0.0-3.0 wt% deoxidizer; the interference film grows on one surface of the alloy and has a thickness of less than 200 nanometers; the interference film exhibits a surface color.

[0011] The present invention also provides a decorative item comprising the alloy of the present invention.

[0012] The present invention further provides a method of preparing an alloy having an interference film. In one embodiment, the method comprises the steps of: (a) providing the alloy consisting essentially of 55.0-78.0 wt% Au, 8.0-24.0 wt% Ag, and 8.0-24.0 wt% Cu, and 0.0-3.0 wt% deoxidizer; the alloy including a surface for forming the interference film; and (b) heating the alloy in an inert environment to a temperature of 400 to 500 o C for a period of time to cause the interference film to form on the surface; the interference film having a thickness of less than 200 nanometers and exhibiting a surface color.

[0013] The present invention further provides a method of preparing an alloy having an interference film, the method comprising the steps of: (a) providing the alloy consisting essentially of 55.0-78.0 wt% Au, 8.0-24.0 wt% Ag, and 8.0-24.0 wt% Cu, and 0.0-3.0 wt% deoxidizer; the alloy including a surface for forming the interference film; and (b) heating the alloy in an inert environment to a temperature of 400 to 500 o C for a period of time to cause the interference film to grow in situ from the alloy to a surface of the alloy; the interference film having a thickness of less than 200 nanometers and exhibiting a predetermined surface color. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1A is a general representation of the present invention.

[0015] Figure 1B is a general representation of the pre-treatment in one embodiment of the present invention.

[0016] Figure 2 is a FESEM image at 80,000X magnification showing that the thickness of the purple surface color layer is no more than 200 nanometers. The cross-section was ion beam milled and polished.

[0017] Figure 3 is a FESEM image at 100,000X magnification showing that the thickness of the blue surface color layer is no more than 200 nanometers. The cross-section was ion beam milled and polished. DETAILED DESCRIPTION

[0018] The following terms will be used in describing the present invention. To the extent a term is not specifically defined herein, it shall be construed in accordance with the common meaning of that term as understood by one of ordinary skill in the art.

[0019] In this document, the expression "BSE" refers to backscattered electrons.

[0020] In the present context, the expression "FESEM" refers to Field Emission Scanning Electron Microscope.

[0021] It is an object of the present application to provide a method of coloring gold alloys.

[0022] It is another object of the present application to provide a method of coloring gold alloys using conventional alloys and conventional processes including but not limited to investment casting.

[0023] It is another object of the present application to provide a method of coloring gold alloys wherein the resultant color includes but is not limited to orange, red, purple, blue, green, yellow, etc. The surface layer color can be measured by a three-dimensional color measurement system CIELAB coordinates. The L* axis is defined as black at 0 and white at 100 to measure lightness, the a* axis is defined as red at positive values and green at negative values to measure red-green component, and the b* axis is defined as yellow at positive values and blue at negative values to measure yellow-blue component.

[0024] The present application provides a method of inducing color on gold alloys. In one embodiment, the gold alloy can essentially include 55.0 to 78.0 wt% Au; 8.0 to 24.0 wt% Ag; and 8.0 to 24.0 wt% Cu.

[0025] In one embodiment, the gold alloy can essentially include not more than 3.0 wt% deoxidizer in place of Ag and Cu.

[0026] In one embodiment, the deoxidizer is selected from Zn or Si or a mixture thereof.

[0027] In one embodiment, the gold alloy essentially includes 55.0 to 62 wt% Au; 17.0 to 24.0 wt% Ag and 17.0 to 24.0 wt% Cu.

[0028] In one embodiment, the gold alloy essentially includes 72.0 to 78.0 wt% Au; 8.0 to 17.0 wt% Ag; and 8.0 to 17.0 wt% Cu.

[0029] In one embodiment, the gold alloy essentially includes 56.8 to 59.8 wt% Au; 19.3 to 22.4 wt% Ag; and 19.3 to 22.4 wt% Cu.

[0030] In one embodiment, the gold alloy essentially includes 73.5 to 76.5 wt% Au; 11.0 to 14.0 wt% Ag; and 11.0 to 14.0 wt% Cu.

[0031] In one embodiment, the gold alloy consists essentially of 58.3 wt% Au; 20.85 wt% Ag; and 20.85 wt% Cu.

[0032] In one embodiment, the gold alloy consists essentially of 75.0 wt% Au; 12.5 wt% Ag; and 12.5 wt% Cu.

[0033] In one embodiment, the present invention provides a method for producing a gold alloy having predetermined color characteristics. A general representation of the method is shown in Figure 1A In one embodiment, the method further comprises a pre-treatment as shown in Figure 1B The method of the present invention can comprise the following steps: melting gold, silver, copper and optionally added deoxidizers and pouring the alloy into a predetermined shape mold; etching the alloy; polishing the alloy; first heating the alloy in air to 400 o C to 800 o C until a visible gray-black color appears; cooling the alloy to room temperature; second etching the alloy; polishing the alloy; second heating the alloy in an inert environment to 400 o C to 500 o C; and cooling the alloy to room temperature in air.

[0034] In one embodiment, the alloy is produced by a conventional investment casting process.

[0035] In one embodiment, the alloy is etched by a dilute acid.

[0036] In one embodiment, the dilute acid is dilute sulfuric acid or dilute hydrochloric acid.

[0037] In one embodiment, the surface of the alloy is polished to a mirror finish in the areas where coloring is desired.

[0038] In one embodiment, the first heat treatment of the alloy is performed at a furnace temperature between 400 and 800°C in normal atmospheric air for a duration of at least 10 minutes. For example, normal air can be used. The alloy will exhibit a gray-black surface which is then cooled to room temperature.

[0039] In one embodiment, the second heat treatment of the alloy is performed in an inert environment at a furnace temperature between 400°C and 500°C. When the alloy is cooled to room temperature, a color change in the polished surface will be observed.

[0040] In one embodiment, the inert environment is argon.

[0041] In one embodiment, the surface color of the alloy is dependent on the duration of the second heat treatment.

[0042] In one embodiment, the color difference (Delta E) of the surface layer color formed before and after the second heat treatment step is at least 10.0.

[0043] In one embodiment, the surface layer color of the alloy includes, but is not limited to, orange, red, purple, blue, green to yellow.

[0044] In one embodiment, the surface layer color of the polished surface of the alloy is uniform.

[0045] In one embodiment, the thickness of the surface layer color layer is no more than 200 nanometers. Figure 2 and Figure 3 A BSE FESEM view of a typical cross-section of an oxidatively colored gold alloy exhibiting one embodiment of the present invention, with a surface layer color layer thickness of less than 200 nanometers.

[0046] In one embodiment, if a change in the existing oxidation color of the alloy is desired, the alloy can be etched, polished and heat treated again in an inert environment at 400°C to 500°C. The duration of the heat treatment can be adjusted according to the corresponding color specified by the second heat treatment described above.

[0047] The present invention provides an alloy having an interference film. In one embodiment, the alloy consists essentially of 55.0-78.0 wt% Au, 8.0-24.0 wt% Ag, 8.0-24.0 wt% Cu, and 0.0-3.0 wt% deoxidizer; the interference film is grown on a surface of the alloy and has a thickness of less than 200 nanometers; and the interference film exhibits a surface layer color.

[0048] The present invention provides an alloy having an interference film. In one embodiment, the alloy consists essentially of 55.0-78.0 wt% Au, 8.0-24.0 wt% Ag, 8.0-24.0 wt% Cu, and 0.0-3.0 wt% deoxidizer; the interference film is grown on a surface of the alloy and has a thickness of less than 200 nanometers; and the interference film exhibits a surface layer color.

[0049] In one embodiment, the surface layer color includes orange, red, purple, blue, green or yellow.

[0050] In one embodiment, the predetermined surface layer color includes orange, red, purple, blue, green or yellow.

[0051] In one embodiment, the surface layer color has a color difference (ΔΕ) of at least 10.0 compared to the surface when unoxidized.

[0052] In one embodiment, the predetermined surface layer color has a color difference (ΔΕ) of at least 10.0 compared to the surface when unoxidized.

[0053] In one embodiment, the alloy consists essentially of: i) 55.0 to 62 wt% Au; 17.0 to 24.0 wt% Ag and 17.0 to 24.0 wt% Cu; ii) 72.0 to 78.0 wt% Au; 8.0 to 17.0 wt% Ag and 8.0 to 17.0 wt% Cu; iii) 56.8 to 59.8 wt% Au; 19.3 to 22.4 wt% Ag and 19.3 to 22.4 wt% Cu; iv) 73.5 to 76.5 wt% Au; 11.0 to 14.0 wt% Ag and 11.0 to 14.0 wt% Cu; v) 58.3 wt% Au; 20.85 wt% Ag and 20.85 wt% Cu; or vi) 75.0 wt% Au; 12.5 wt% Ag and 12.5 wt% Cu.

[0054] In one embodiment, the oxygen scavenger includes one or more of zinc or silicon.

[0055] In one embodiment, the alloy is formed by investment casting.

[0056] The present invention also provides an ornament comprising the alloy of the present invention.

[0057] In one embodiment, the ornament is a piece of jewelry.

[0058] The present invention further provides a method of making an alloy having an interference film. In one embodiment, the method includes the steps of: (a) providing the alloy consisting essentially of 55.0-78.0 wt% Au, 8.0-24.0 wt% Ag and 8.0-24.0 wt% Cu and 0.0-3.0 wt% oxygen scavenger; the alloy including a surface for forming the interference film; and (b) heating the alloy in an inert environment to a temperature of 400 to 500 °C for a time period to allow the interference film to form on the surface; the interference film having a thickness of less than 200 nanometers and exhibiting a surface layer color.

[0059] The present invention further provides a method of making an alloy having an interference film. In one embodiment, the method comprises the steps of: (a) providing the alloy consisting essentially of 55.0-78.0 wt% Au, 8.0-24.0 wt% Ag, and 8.0-24.0 wt% Cu, and 0.0-3.0 wt% deoxidizer; the alloy including a surface for forming the interference film; and (b) heating the alloy in an inert environment to a temperature of 400 to 500 o C for a period of time to cause the interference film to grow directly from the alloy onto the surface of the alloy; the interference film having a thickness of less than 200 nanometers and exhibiting a predetermined surface color.

[0060] In one embodiment, the method further comprises pre-treating the surface of the alloy in step (a) prior to step (b).

[0061] In one embodiment, the pre-treating comprises the steps of: (i) heating the alloy in air to a temperature of 400 to 800 o C; and (ii) etching and polishing the surface.

[0062] In one embodiment, step (i) comprises heating the alloy for at least 10 minutes or until a grayish-black or black discoloration is observed.

[0063] In one embodiment, the surface color is orange, red, purple, blue, green, or yellow.

[0064] In one embodiment, the color resulting from the interference film is orange, red, purple, blue, green, or yellow.

[0065] In one embodiment, the interference film causes a color difference (Delta E) of at least 10.0 in the surface compared to before.

[0066] In one embodiment, the inert environment is argon.

[0067] In one embodiment, the method further comprises forming the alloy in step (a) by investment casting prior to step (b).

[0068] In one embodiment, the method further comprises repeating step (b) to change the surface color until a predetermined color is obtained.

[0069] In one embodiment, the method further comprises etching and polishing the surface of the alloy prior to repeating step (b).

[0070] In one embodiment, the period of time is controlled in accordance with one or more parameters, including the size of the surface, the size of the alloy, or the temperature of step (b).

[0071] In one embodiment, the period of time will be shortened when the temperature of step (b) is higher.

[0072] The application will be better understood by the following examples, but the person of ordinary skill in the art will readily perceive that the specific examples of the detailed description are merely illustrative and are not meant to limit the application described herein, which is defined by the claims that follow.

[0073] In this application, various references or publications are cited. The disclosures of these references or publications in their entireties are hereby incorporated by reference into this application in order to more fully describe the state of the art to which this application pertains. It will be appreciated that the transitional term "comprising" is not meant to exclude additional, unrecited elements or method steps.

[0074] Example 1

[0075] A 6 gram gold alloy ring was prepared according to the method of the present application having the composition 75.0 wt% Au, 12.5 wt% Ag, 12.5 wt% Cu. The alloy was cast, etched with dilute sulfuric acid and polished. After a first heat in air at 500°C for 15 minutes, the oxidized alloy exhibited a dark grey coloration. The CIELAB coordinates of the alloy at this stage were as follows: L* 42.61, a* -0.35, b* -1.58. The alloy was then etched with dilute sulfuric acid and polished again. The CIELAB coordinates of the polished surface of the alloy were measured (Test 1) and are shown in Table 1. The alloy was heated in argon at 450°C for 2 minutes and allowed to cool to room temperature in air. The polished surface of the alloy exhibited a red surface color as shown by the CIELAB measurements in the table below (Test 2). The alloy was etched, polished and heated in argon at 450°C for four different durations. It can be seen that different heating durations on the same alloy resulted in different surface colors (Tests 3 to 6).

[0076] Experiments 7 through 9 compare different alloys consisting of 75.0 wt% Au, 12.5 wt% Ag, and 12.5 wt% Cu. The heat treatment conditions and CIELAB measurements of the resulting alloy surfaces are shown in Table 1 below. Comparing the CIELAB results of Experiments 7, 8, and 5 shows that the heat treatment step of first heating in air at 500°C for 15 minutes is necessary to achieve the predetermined surface color. Comparing the CIELAB results of Experiments 9 and 5 shows that the inert environment must be maintained during the second heat treatment step of heating at 450°C for 5 minutes to achieve a bright and attractive color on the alloy.

[0077] Table 1. Experimental Results

[0078]

[0079] Example 2

[0080] Two 6 gram gold alloys were prepared according to the method of the present application and compared. The compositions of these alloys are listed in Table 2. These alloys were cast, etched in dilute sulfuric acid, and polished. After the first heat treatment step of heating in air at 500°C for 15 minutes, the CIELAB coordinates of Experiments 10 and 11 were L* 49.91, a* -0.44, b* 0.76 and L* 57.10, a* -2.08, b* 5.60, respectively. These alloys were etched in dilute sulfuric acid and polished before the second heat treatment step. The CIELAB coordinates before and after the second heat treatment step of heating in argon at 450°C for 5 minutes are listed in Table 2. The surface color of Experiment 10 was a brown color that did not achieve the predetermined result. ΔE is a measure that quantifies the difference between two colors, where any value below 2 is almost undetectable by the human eye. The ΔE of the CIELAB results of Experiment 11 before and after the second heat treatment was only 1.54, which indicates that the predetermined surface color was not achieved. Comparing the CIELAB results of Experiments 5 (Table 1), 10, and 11 (Table 2) shows that deviating from the specific embodiments of the present application in the alloy composition will not result in the predetermined surface color.

[0081] Table 2. Experimental Results

Claims

1. An alloy having an interference thin film, characterized in that: i. The alloy is basically composed of 55.0-78.0wt% Au, 8.0-24.0wt% Ag, 8.0-24.0wt% Cu and 0.0-3.0wt% deoxidizer; ii. The interference film is grown directly from within the alloy to a surface of the alloy and the interference film has a thickness of less than 200 nanometers; Its characteristic is that the interference film exhibits a predetermined surface color.

2. The alloy according to claim 1, characterized in that: The predetermined surface color includes orange, red, purple, blue, green, or yellow.

3. The alloy according to claim 1, characterized in that: The predetermined surface color has a color difference (ΔE) of at least 10.0 compared to the unoxidized surface.

4. The alloy according to claim 1, characterized in that: The alloy basically includes: i. 55.0 to 62 wt% Au; 17.0 to 24.0 wt% Ag and 17.0 to 24.0 wt% Cu; ii. 72.0 to 78.0 wt% Au; 8.0 to 17.0 wt% Ag and 8.0 to 17.0 wt% Cu; iii. 56.8 to 59.8 wt% Au; 19.3 to 22.4 wt% Ag and 19.3 to 22.4 wt% Cu; iv. 73.5 to 76.5 wt% Au; 11.0 to 14.0 wt% Ag and 11.0 to 14.0 wt% Cu; v.58.3 wt% Au; 20.85 wt% Ag and 20.85 Cu; vi.75.0 wt% Au; 12.5 wt% Ag and 12.5 wt% Cu.

5. The alloy according to claim 1, characterized in that: The deoxidizer includes one or more of zinc or silicon.

6. The alloy according to claim 1, characterized in that: The alloy is formed by investment casting.

7. An ornament, characterized by: The decorative item comprises the alloy of claim 1.

8. The decorative item according to claim 7, characterized in that: The ornament is a piece of jewelry.

9. A method for preparing an alloy, the alloy having an interference thin film, characterized in that: The method includes the following steps: a. Providing the alloy substantially composed of 55.0-78.0 wt% Au, 8.0-24.0 wt% Ag, and 8.0-24.0 wt% Cu, and 0.0-3.0 wt% deoxidizer; the alloy comprising a surface for forming the interference film; and b. Heat the alloy in an inert environment to 400 to 500 degrees Celsius. o At a temperature of C for a period of time, the interference film is grown directly from within the alloy onto a surface of the alloy; the thickness of the interference film is less than 200 nanometers and exhibits a predetermined surface color.

10. The method of claim 9, further comprising pre-treating the surface of the alloy in step (a) prior to step (b).

11. The method according to claim 10, characterized in that: The preprocessing includes the following steps: i. Heat the alloy in air to 400 to 800 degrees Celsius. o C; and ii. Etch and polish the surface.

12. The method according to claim 11, characterized in that: Step (i) includes heating the alloy for at least 10 minutes or until a grayish-black or black coloration is observed.

13. The method according to claim 9, characterized in that: The interference film is orange, red, purple, blue, green, or yellow.

14. The method according to claim 9, characterized in that: The color difference (ΔE) between the interference film and the unoxidized surface is at least 10.

0.

15. The method according to claim 9, characterized in that: The inert environment is argon.

16. The method of claim 9, further comprising forming the alloy in step (a) by investment casting prior to step (b).

17. The method of claim 9, further comprising repeating step (b) to change the surface color until a predetermined color is obtained.

18. The method of claim 17, further comprising etching and polishing the surface of the alloy prior to repeating step (b).

19. The method according to claim 9, characterized in that: The time period is controlled according to one or more parameters, including the size of the surface, the size of the alloy, or the temperature of step (b).

20. The method according to claim 19, characterized in that: When the temperature in step (b) is high, the time period will be shortened.

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