GOLD-ALUMINUM GLASSES BEARING RARE-EARTH METALS

Abstract

The disclosure provides Au—Al-Rare-Earth metallic glass-forming alloys and metallic glasses comprising various other additions including but not limited to Cu, Pd, Sn and Mg. In certain embodiments, the metallic glasses according to the disclosure satisfy the 18-Karat Gold Alloy Hallmark, and demonstrate colors that include yellow and pink/rose.

Description

FIELD

The disclosure is directed to Au—Al-RE alloys, where RE is a rare earth metal, capable of forming a metallic glass.

BACKGROUND

U.S. Pat. No. 5,593,514 entitled “Amorphous Metal Alloys Rich in Noble Metals Prepared by Rapid Solidification Processing”, the disclosure of which is incorporated herein by reference in its entirety, discloses ternary Au-RE glass-forming alloys bearing various other elements. However, the patent does not disclose glass-forming Au-RE compositions bearing Al.

BRIEF SUMMARY

The disclosure provides Au—Al-RE metallic glass-forming alloys and metallic glasses comprising various other additions including, but not limited to, Cu, Pd, Sn and Mg. The symbol “RE” designates a rare-earth metal selected from Y, Sc and the Lanthanides, which include La, Ce Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, or a combination thereof.

In one embodiment, the disclosure provides a metallic glass-forming alloy or metallic glass that comprises at least Au, Al, and RE, where the atomic fraction of Au is in the range of 40 to 90 percent, the atomic fraction of Al is in the range of 0.5 to 40 percent, and the atomic fraction of RE is in the range of 1 to 20 percent.

In another embodiment, RE is one of Y, Er, or Dy, or combinations thereof.

In another embodiment, RE is Y.

In another embodiment, the atomic fraction of Al is in the range of 2 to 20 percent.

In another embodiment, the atomic fraction of Al is in the range of 4 to 18 percent.

In another embodiment, the atomic fraction of Y is in the range of 3 to 15 percent.

In another embodiment, the atomic fraction of Y is in the range of 5 to 12 percent.

In another embodiment, the alloy or metallic glass also comprises Cu in an atomic fraction in the range of up to 20 percent.

In another embodiment, the alloy or metallic glass also comprises Cu in an atomic fraction in the range of 0.5 to 10 percent.

In another embodiment, the alloy or metallic glass also comprises Cu in an atomic fraction in the range of 1 to 5 percent.

In another embodiment, the alloy or metallic glass also comprises Pd in an atomic fraction in the range of up to 25 percent.

In another embodiment, the alloy or metallic glass also comprises Pd in an atomic fraction in the range of 0.5 to 20 percent.

In another embodiment, the alloy or metallic glass also comprises Pd in an atomic fraction in the range of 1 to 15 percent.

In other embodiments, the disclosure provides an alloy or a metallic glass having a composition represented by the following formula (subscripts denote atomic percentages):

Au_{(100-a-b-c-d)}Al_aRE_bCu_cPd_d  EQ. (1)

where:

a ranges from 0.5 to 40;

b ranges from 1 to 20;

c is up to 20; and

d up to 25.

In another embodiment of the alloy or metallic glass, a ranges from 2 to 20.

In another embodiment of the alloy or metallic glass, a ranges from 4 to 18.

In another embodiment of the alloy or metallic glass, b ranges from 3 to 15.

In another embodiment of the alloy or metallic glass, b ranges from 5 to 12.

In another embodiment of the alloy or metallic glass, c ranges from 0.5 to 10.

In another embodiment of the alloy or metallic glass, c ranges from 1 to 5.

In another embodiment of the alloy or metallic glass, d ranges from 0.5 to 20.

In another embodiment of the alloy or metallic glass, d ranges from 1 to 15.

In another embodiment, the weight fraction of Au is at least 75 percent.

In another embodiment, the alloy or metallic glass also comprises Sn in an atomic fraction in the range of up to 10 percent.

In another embodiment, the alloy or metallic glass also comprises Sn in an atomic fraction in the range of 0.5 to 5 percent.

In another embodiment, the alloy or metallic glass also comprises Mg in an atomic fraction in the range of up to 20 percent.

In another embodiment, the alloy or metallic glass also comprises Mg in an atomic fraction in the range of 0.5 to 10 percent.

In another embodiment, the alloy or metallic glass also comprises Mg in an atomic fraction in the range of 0.5 to 5 percent.

In another embodiment, the alloy or metallic glass also comprises any of Ag, Pt, Rh, Ir, Fe, Ni, Co, Ru, Cr, Mo, Mn, Ti, Zr, Hf, W, Re, Be, Ca, Si, P, S, Ge, Ga, In, Sb, and Bi, or combinations thereof, in an atomic fraction of up to 10 percent.

In another embodiment, the alloy or metallic glass also comprises any of Ag, Pt, Rh, Ir, Fe, Ni, Co, Ru, Cr, Mo, Mn, Ti, Zr, Hf, W, Re, Be, Ca, Si, P, S, Ge, Ga, In, Sb, and Bi, or combinations thereof, in an atomic fraction of up to 5 percent.

In another embodiment, the alloy demonstrates a critical casting thickness of at least 1 micrometer.

In another embodiment, the alloy demonstrates a critical casting thickness of at least 10 micrometers.

In another embodiment, the alloy demonstrates a critical casting thickness of at least 50 micrometers.

In another embodiment, the alloy demonstrates a critical casting thickness of at least 100 micrometers.

In another embodiment, the alloy demonstrates a critical casting thickness of at least 500 micrometers.

In another embodiment, the alloy demonstrates a critical casting thickness of at least 1 millimeter.

In another embodiment, the alloy demonstrates a critical casting thickness of at least 5 millimeters.

In another embodiment, the metallic glass is a coating or film having a thickness of at least 100 nanometers.

In another embodiment, the metallic glass is a coating or film having a thickness of at least 100 nm.

In another embodiment, the metallic glass is a coating or film having a thickness of at least 1 micrometer.

In yet another embodiment, the temperature of the melt prior to quenching is at least 100° C. above the liquidus temperature of the alloy.

In yet another embodiment, the temperature of the melt prior to quenching is at least 1000° C.

In yet another embodiment, the metallic glass demonstrates a glass transition temperature of at least 150° C.

In yet another embodiment, the metallic glass demonstrates a glass transition temperature of at least 200° C.

In yet another embodiment, the metallic glass demonstrates a glass transition temperature of at least 250° C.

In yet another embodiment, the metallic glass demonstrates a Vickers hardness value of at least 400 kgf/mm².

In yet another embodiment, the metallic glass demonstrates a Vickers hardness value of at least 440 kgf/mm².

In yet another embodiment, the metallic glass demonstrates a yellow color.

In yet another embodiment, the metallic glass demonstrates a pink or rose color.

In yet another embodiment, the metallic glass demonstrates a color having CIELAB coordinates with L* in the range of 65 to 120, a* in the range of −5 to 15, and b* in the range of 5 to 40.

In yet another embodiment, the metallic glass demonstrates a color having CIELAB coordinates with L* in the range of 65 to 85, a* in the range of 0 to 3, and b* in the range of 5 to 20.

The disclosure is also directed to an alloy or a metallic glass having compositions selected from a group consisting of: Au₇₄Cu₂Y₈Al₁₅Sn₁, Au₇₂Cu₃Y₈Al₁₆Pd₁, Au_72.5Cu₂Y₉Al_15.5Pd₁, Au_71.5Cu₂Y₉Al_15.5Pd₂ Au_69.5Cu₂Y₉Al_15.5Pd₄, Au₇₂Y₈Al₁₀Pd₁₀, Au_71.5Y₉Al_15.5Pd₄, and Au₇₀Cu₂Y₈Al₁₀Pd₁₀.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure will be readily understood by the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements, and in which:

FIG. 1 provides an x-ray diffractogram verifying the amorphous structure of a 68 μm thick metallic glass foil with composition Au_69.5Cu₂Y₉Al_15.5Pd₄ (Example 5).

FIG. 2 provides calorimetry scans for sample metallic glasses in accordance with embodiments of the disclosure. The glass transition temperature T_g (where detectable), crystallization temperature T_x, solidus temperature T_s, and liquidus temperature T_l are indicated by arrows.

DETAILED DESCRIPTION

Reference will now be made in detail to representative embodiments illustrated in the accompanying drawings. It should be understood that the following descriptions are not intended to limit the embodiments to one preferred embodiment. To the contrary, it is intended to cover alternatives, modifications, and equivalents as can be included within the spirit and scope of the described embodiments as defined by the appended claims.

The following disclosure relates to Au—Al-RE based metallic glass-forming alloys and metallic glasses.

Au-based jewelry alloys typically contain Au at weight fractions of less than 100%. Hallmarks are used by the jewelry industry to indicate the Au metal content. Au weight fractions of about 75.0% (18 Karat), 58.3% (14 Karat), 50.0% (12 Karat), and 41.7% (10 Karat) are commonly used hallmarks in gold jewelry. In certain embodiments, this disclosure is directed to glass-forming Au-based alloys or metallic glasses that satisfy the 18 Karat hallmark. Hence, in such embodiments the Au weight fraction ranges from 74 to 90 percent.

In the disclosure, the glass-forming ability of each alloy is quantified by the “critical casting thickness,” defined as the largest lateral dimension in which the amorphous phase can be formed when processed by a method of quenching an alloy from the high temperature melt state. The glass-forming ability of each alloy can also be quantified by the “critical rod diameter,” defined as the largest rod diameter in which the amorphous phase can be formed when processed by a method of water quenching a quartz tube having 0.5 mm thick walls containing a molten alloy.

A “critical cooling rate,” which is defined as the cooling rate required to avoid crystallization and form the amorphous phase of the alloy (i.e. the metallic glass), determines the critical casting thickness. The lower the critical cooling rate of an alloy, the larger its critical casting thickness. The critical cooling rate R_c in K/s and critical casting thickness t_c in mm are related via the following approximate empirical formula:

R _c=1000/t_c²  Eq. (2)

According to Eq. (2), the critical cooling rate for an alloy having a critical casting thickness of about 1 mm is about 10³ K/s.

Generally, three categories are known in the art for identifying the ability of a metal alloy to form glass (i.e. to bypass the stable crystal phase and form an amorphous phase). Metal alloys having critical cooling rates in excess of 10¹² K/s are typically referred to as non-glass formers, as it is physically impossible to achieve such cooling rates over a meaningful thickness. Metal alloys having critical cooling rates in the range of 10⁵ to 10¹² K/s are typically referred to as marginal glass formers, as they are able to form glass over thicknesses ranging from 1 to 100 micrometers according to Eq. (2). Metal alloys having critical cooling rates on the order of 10³ or less, and as low as 1 or 0.1 K/s, are typically referred to as bulk glass formers, as they are able to form glass over thicknesses ranging from 1 millimeter to several centimeters. The glass-forming ability of a metallic alloy is, to a very large extent, dependent on the composition of the alloy. The compositional ranges for alloys capable of forming marginal glass formers are considerably broader than those for forming bulk glass formers.

Description of Alloys and Metallic Glass Compositions

Specific embodiments of alloys, and/or metallic glasses formed of alloys, with compositions with Au weight fraction of at least 75.0 percent satisfying the 18-Karat hallmark are presented in Table 1. In certain variations, the metallic glasses may be in the form of foils. Several example metallic glasses in the form of foils are presented. The foil thicknesses of the example metallic glasses along with the Au weight percentages are listed in Table 1.

TABLE 1
Sample metallic glasses formed of alloys with compositions with Au
weight fraction of at least 75.0 percent satisfying the 18-Karat hallmark
			Splat
		Au	thickness
Example	Composition	wt. %	[μm]
1	Au74Cu2Y8Al15Sn1	91.5	41
2	Au72Cu3Y8Al16Pd1	90.8	51
3	Au72.5Cu2Y9Al15.5Pd1	90.8	67
4	Au71.5Cu2Y9Al15.5Pd2	90.0	43
5	Au69.5Cu2Y9Al15.5Pd4	88.5	68
6	Au72Y8Al10Pd10	87.4	46
7	Au71.5Y9Al15.5Pd4	89.5	69
8	Au70Cu2Y8Al10Pd10	86.4	63

FIG. 1 provides an x-ray diffractogram verifying the amorphous structure of a 68 μm thick metallic glass foil with composition Au_69.5Cu₂Y₉Al_15.5Pd₄ (Example 5).

FIG. 2 provides calorimetry scans for the sample metallic glasses listed in Table 1. The glass transition temperature T_g (where detectable), crystallization temperature T_x, solidus temperature T_s, and liquidus temperature T_l are indicated by arrows in FIG. 2, and are listed in Table 2. The enthalpy of crystallization ΔH_x, for each of the sample metallic glasses is also listed in Table 2. As seen in FIG. 2 and Table 2, T_g is generally detectable for the Pd-bearing alloys. The glass transition temperature of the rest of the alloys in Table 2 is expected to be at least 250° C. In general, the alloys according to the disclosure are expected to exhibit a T_g of at least 150° C., and in some embodiments, at least 200° C. In some aspects, the addition of Pd and Sn can decrease the liquidus temperature of the alloy as compared to the Pd-free and Sn-free alloys respectively. The decrease in liquidus temperature can reduce the driving force of crystallization and can increase the critical casting thickness of the alloy.

TABLE 2
The glass transition temperature Tg (where detectable), crystallization
temperature Tx, solidus temperature Ts, and liquidus temperature Tl,
and enthalpy of crystallization ΔHx of sample metallic
glasses according to the disclosure.
		Tg	Tx	Ts	Tl	ΔHx
Example	Composition	(° C.)	(° C.)	(° C.)	(° C.)	(J/g)
1	Au74Cu2Y8Al15Sn1	—	292	466	793	−8.1
2	Au72Cu3Y8Al16Pd1	—	319	477	800	−7.2
3	Au72.5Cu2Y9Al15.5Pd1	292	314	476	803	−6.1
4	Au71.5Cu2Y9Al15.5Pd2	294	326	496	794	−6.5
5	Au69.5Cu2Y9Al15.5Pd4	294	325	540	783	−7.2
6	Au72Y8Al10Pd10	251	282	607	789	−14.1
7	Au71.5Y9Al15.5Pd4	286	309	514	782	−7.0
8	Au70Cu2Y8Al10Pd10	251	279	635	773	−18.7

The metallic glasses of the disclosure demonstrate various colors, particularly yellow and pink/rose colors. The sample metallic glasses listed in Tables 1 and 2 have a yellow color. The CIELAB color coordinates of the sample metallic glasses listed in Tables 1 and 2 are listed in Table 3.

TABLE 3
CIELAB color coordinates of the sample metallic glasses according to
the disclosure
Example	Composition	L*	a*	b*
1	Au74Cu2Y8Al15Sn1	74.82	0.84	14.70
2	Au72Cu3Y8Al16Pd1	79.46	1.00	12.72
3	Au72.5Cu2Y9Al15.5Pd1	77.96	0.69	10.52
4	Au71.5Cu2Y9Al15.5Pd2	71.31	0.66	9.84
5	Au69.5Cu2Y9Al15.5Pd4	74.08	1.11	12.84
6	Au72Y8Al10Pd10	70.19	1.93	15.25

TABLE 3
CIELAB color coordinates of the sample metallic glasses according to
the disclosure
Example	Composition	L*	a*	b*
7	Au71.5Y9Al15.5Pd4	72.34	1.22	11.93
8	Au70Cu2Y8Al10Pd10	72.84	1.81	15.06

The Vickers hardness values of sample metallic glasses according to the current disclosure are listed in Table 4. The Vickers hardness values of the sample metallic glasses are shown to be greater than 440 Kgf/mm², ranging from about 447 to about 500 Kgf/mm².

TABLE 4
Vickers hardness of the sample metallic glasses according to the disclosure
		Vickers Hardness
Example	Composition	(Kgf/mm2)
1	Au74Cu2Y8Al15Sn1	489.3 ± 19.2
2	Au72Cu3Y8Al16Pd1	492.5 ± 10.4
3	Au72.5Cu2Y9Al15.5Pd1	484.8 ± 28.6
4	Au71.5Cu2Y9Al15.5Pd2	500.6 ± 38.5
5	Au69.5Cu2Y9Al15.5Pd4	498.7 ± 14.9
6	Au72Y8Al10Pd10	447.1 ± 6.4
7	Au71.5Y9Al15.5Pd4	488.0 ± 37.8
8	Au70Cu2Y8Al10Pd10	472.6 ± 39.5

Description of Methods of Processing the Ingots of the Sample Alloys

In various aspects, one method for producing the alloy ingots involves arc melting of the appropriate amounts of elemental constituents over a water-cooled copper hearth under inert atmosphere. The alloy ingots for the sample alloys of Tables 1 and 2 were produced using this method. The purity levels of the constituent elements were as follows: Au 99.99%, Al 99.999%, Y 99.9%, Cu 99.995%, Pd 99.95%, and Sn 99.999%. Alternatively, the ingots may be produced by inductively melting the elemental constituents, where the melting crucible may be a ceramic such as alumina or zirconia, graphite, sintered crystalline silica, or a water-cooled hearth made of copper or silver.

Description of Methods of Processing the Sample Metallic Glasses

In various aspects, one method for producing metallic glass foils from the alloy ingots involves a splat quench processing. The sample metallic glasses of Tables 1 and 2 were produced using this method. A spherical alloy ingot of about 100 mg is levitated and melted inductively under a pressure of 0.05 mbar reaching a temperature of at least 1000° C., and the spherical liquid droplet was subsequently dropped and splatted between two copper platens to form a cylindrical splat foil having a diameter between 10 and 20 mm and thickness between 10 and 100 μm.

In other embodiments, the metallic glass can be a coating or film. In some embodiments, the metallic glass is a coating or film having a thickness of at least 100 nanometers. In still other embodiments, the metallic glass is a coating or film having a thickness of at least 1 micrometer.

In other embodiments, the metallic glass can be applied using coating processes, including spray coating, chemical or electrochemical plating, thermal spraying, physical vapor deposition (PVD) processes, chemical vapor deposition (CVD) processes, sputtering or other suitable coating process. By way of example, without intending to be limiting, the Au—Al-RE alloy can be applied to a substrate using a spray coating process in some embodiments. The Au—Al-RE alloy can be atomized by passing through a stream of gas (e.g. argon) and through a nozzle to impact a surface of the substrate. When the atomized the Au—Al-RE alloy deposits on the surface of the substrate, it solidifies and bonds to the substrate creating a metallic glass coating or film.

Test Methodology for Differential Scanning Calorimetry

Differential scanning calorimetry was performed on sample metallic glasses at a scan rate of 20 K/min to determine the glass-transition, crystallization, solidus, and liquidus temperatures of sample metallic glasses.

Test Methodology for Measuring Color Coordinates

Standard methods can be used to evaluate cosmetic appeal including color, gloss, and haze. The color of objects may be determined by the wavelength of light that is reflected or transmitted without being absorbed, assuming incident light is white light. The visual appearance of objects may vary with light reflection or transmission. Additional appearance attributes may be based on the directional brightness distribution of reflected light or transmitted light, commonly referred to glossy, shiny, dull, clear, and haze, among others.

Color measurements were taken using a Konica Minolta CM700d hand-held spectrophotometer with a 3-mm SAV aperture, SCI specularity, 10-degree angle, and F2 light source. Color evaluation by brightness (L*), a* (between red and green) and b* (between blue and yellow) can be performed. Measurements are according to CIE/ISO standards for illuminants, observers, and the L* a* b* color scale. For example, the standards include: (a) ISO 11664-1:2007(E)/CIE S 014-1/E:2006: Joint ISO/CIE Standard: Colorimetry—Part 1: CIE Standard Colorimetric Observers; (b) ISO 11664-2:2007(E)/CIE S 014-2/E:2006: Joint ISO/CIE Standard: Colorimetry—Part 2: CIE Standard Illuminants for Colorimetry, (c) ISO 11664-3:2012(E)/CIE S 014-3/E:2011: Joint ISO/CIE Standard: Colorimetry—Part 3: CIE Tristimulus Values; and (d) ISO 11664-4:2008(E)/CIE S 014-4/E:2007: Joint ISO/CIE Standard: Colorimetry—Part 4: CIE 1976 L* a* b* Colour Space.

Test Methodology for Measuring Hardness

The Vickers hardness (HV0.1) of sample metallic glasses was measured using a Vickers microhardness tester. Eight tests were performed where micro-indentions were inserted on ˜50 μm-thick metallic glass splats using a load of 100 g and a duel time of 10 s. A load of 100 g resulted in indentation depth of 2 to 3 μm, which ensures the validity of the hardness measurements, as the indentation depth is less than 10% of the sample thickness. Measurements were performed on a metallic substrate with hardness of 607 HV0.5, which is considerably higher than the measured hardness of the Sample metallic glass.

Products and Devices

The alloys, metallic glasses, and various non-limiting embodiments as described herein can be included in various products. Such products can be any product known in the art. The products can be a device, such as an electronic device. For example, the device can be a telephone, such as a mobile phone, and a land-line phone, or any communication device, such as a smart phone, including, for example an iPhone®, and/or an electronic email sending/receiving device. The alloys, metallic glasses, and various non-limiting embodiments can be used in conjunction with a display, such as a digital display, a TV monitor, an electronic-book reader, a portable web-browser (e.g., iPad®), a watch (e.g., Apple Watch™), and/or a computer monitor. The device can also be an entertainment device, including a portable DVD player, conventional DVD player, Blue-Ray disk player, video game console, music player, such as a portable music player (e.g., iPod®), etc. Devices include control devices, such as those that control the streaming of images, videos, sounds (e.g., Apple TV®), or a remote control for a separate electronic device. The device can be a part of a computer or its accessories, laptop keyboard, laptop track pad, desktop keyboard, mouse, and speaker.

Having described several embodiments, it will be recognized by those skilled in the art that various modifications, alternative constructions, and equivalents may be used without departing from the spirit of the invention. Additionally, a number of well-known processes and elements have not been described in order to avoid unnecessarily obscuring the present invention. Accordingly, the above description should not be taken as limiting the scope of the invention.

Those skilled in the art will appreciate that the presently disclosed embodiments teach by way of example and not by limitation. Therefore, the matter contained in the above description or shown in the accompanying drawings should be interpreted as illustrative and not in a limiting sense. The following claims are intended to cover all generic and specific features described herein, as well as all statements of the scope of the present method and system, which, as a matter of language, might be said to fall therebetween.

Claims

1. An alloy capable of forming a metallic glass, the alloy comprising: an atomic fraction of Au in the range of 40 to 90 percent,an atomic fraction of Al in the range of 0.5 to 40 percent, andan atomic fraction of RE is in the range of 1 to 20 percent; andwherein RE is a rare earth metal.

2. The alloy of claim 1 wherein RE is selected from Y, Er, Dy and a combination thereof.

3. The alloy of claim 1, wherein the atomic fraction of Al is in the range of 2 to 20 percent.

4. The alloy of claim 2, wherein RE comprises Y in an atomic fraction of 3 to 15 percent.

5. The alloy of claim 1, further comprising an atomic fraction of Cu of up to 20 percent.

6. The alloy of claim 1, further comprising an atomic fraction of Pd of up to 25 percent.

7. The alloy of claim 1, further comprising Sn in an atomic fraction of up to 10 percent.

8. The alloy of claim 1, further comprising Mg in an atomic fraction of up to 20 percent.

9. The alloy of claim 1, further comprising at least one additional element selected from Ag, Pt, Rh, Ir, Fe, Ni, Co, Ru, Cr, Mo, Mn, Ti, Zr, Hf, W, Re, Be, Ca, Si, P, S, Ge, Ga, In, Sb, and Bi, or combinations thereof, in an atomic fraction of up to 10 percent.

10. The alloy of claim 1, wherein the alloy has a critical casting thickness of at least 1 micrometer.

11. A metallic glass comprising an alloy of claim 1.

12. The metallic glass of claim 11, wherein the metallic glass has a glass transition temperature of at least 150° C.

13. The metallic glass of claim 11, wherein the metallic glass has a Vicker's hardness of at least 400 kgf/mm2.

14. The metallic glass of claim 11, wherein the metallic glass has a color having CIELAB coordinates with L* in the range of 65 to 120, a* in the range of −5 to 15, and b* in the range of 5 to 40.

15. A metallic glass-forming alloy having a composition represented by the following formula (subscripts denote atomic percentages): Au(100-a-b-c-d)AlaREbCucPdd where:a ranges from 0.5 to 40;b ranges from 1 to 20;c is up to 20;d up to 25; andwherein RE is a rare earth metal.

16. The metallic glass-forming alloy of claim 15, where a ranges from 2 to 20.

17. The metallic glass-forming alloy of claim 15, where b ranges from 3 to 15.

18. The metallic glass-forming alloy of claim 15, where c ranges from 0.5 to 10.

19. The metallic glass-forming alloy of claim 15, where d ranges from 0.5 to 20.

20. The metallic glass-forming alloy of claim 15, where the weight fraction of Au is at least 75 percent.

21. The metallic glass-forming alloy of claim 15, wherein the alloy has a critical casting thickness of at least 1 micrometer.

22. A metallic glass comprising an alloy of claim 15.

23. The metallic glass of claim 22, wherein the metallic glass has a glass transition temperature of at least 150° C.

24. The metallic glass of claim 22, wherein the metallic glass has a Vicker's hardness of at least 400 kgf/mm2.

25. The metallic glass of claim 22, wherein the metallic glass has a color having CIELAB coordinates with L* in the range of 65 to 120, a* in the range of −5 to 15, and b* in the range of 5 to 40.

26. A method of producing a metallic glass comprising: melting an alloy comprising: an atomic fraction of Au in the range of 40 to 90 percent,an atomic fraction of Al in the range of 0.5 to 40 percent, andan atomic fraction of RE is in the range of 1 to 20 percent; andwherein RE is a rare earth metal into a molten state; andquenching the melt at a cooling rate sufficiently high to prevent crystallization of the alloy.