Amorphous alloy

Abstract

This invention provides an amorphous alloy. In one embodiment, the amorphous alloy consists essentially of: i) 52.55-80.12 at. % of Au; ii) 11.74-15.55 at. % of Ge; iii) 8.13-10.77 at. % of Si; iv) 5-21.13 at. % being at least one element selected from the group consisting of Ag, Bi, Pd and Pt.

Claims

1. An amorphous alloy consisting of: i. 52.55-75.13 at. % of Au; ii. 11.74-15.55 at. % of Ge; iii. 8.13-10.77 at. % of Si; iv. 5-21.13 at. % being at least one element selected from the group consisting of Ag, Bi, Pd and Pt.

2. The amorphous alloy of claim 1, wherein said at least one element is selected from the group consisting of: i. 5-10 at. % of Ag; ii. 0.01-8.69 at. % of Bi; iii. 0.01-2.44 at. % of Pd; iv. 0.01-2.44 at. % of Pt; and v. 0.01-2.44 at. % of Pd and Pt in total.

3. The amorphous alloy of claim 1, wherein said amorphous alloy consists of: 69.4 at. % of Au; 13.65 at. % of Ge; 9.45 at. % of Si; and 7.5 at. % of Ag.

4. The amorphous alloy of claim 1, wherein said amorphous alloy consists of: 68.2 at. % of Au; 13.65 at. % of Ge; 9.45 at. % of Si; 7.5 at. % of Ag; and 1.2 at. % of Pd.

5. The amorphous alloy of claim 1, wherein said amorphous alloy consists of: 65.83 at. % of Au; 13.65 at. % of Ge; 9.45 at. % of Si; 7.5 at. % of Ag; 1.2 at. % of Pd; and 2.37 at. % of Bi.

6. The amorphous alloy of claim 1, wherein said amorphous alloy consists of: 63.46 at. % of Au; 13.65 at. % of Ge; 9.45 at. % of Si; 7.5 at. % of Ag; 1.2 at. % of Pd; and 4.74 at. % of Bi.

7. The amorphous alloy of claim 1, wherein said amorphous alloy consists of 63.68-73.59 at. % of Au, 12.65-15.55 at. % of Ge, 8.76-10.77 at. % of Si and 5-10 at. % of Ag.

8. The amorphous alloy of claim 1, wherein said amorphous alloy consists of 61.28-72.99 at. % of Au, 12.65-15.55 at. % of Ge, 8.76-10.77 at. % of Si, 5-10 at. % of Ag and 0.6-2.4 at. % of Pd.

9. The amorphous alloy of claim 1, wherein said amorphous alloy consists of 52.59-71.49 at. % of Au, 12.65-15.55 at. % of Ge, 8.76-10.77 at. % of Si, 5-10 at. % of Ag, 0.6-2.4 at. % of Pd; and 1.5-8.69 at. % of Bi.

10. The amorphous alloy of claim 1, wherein said amorphous alloy consists of 66.85-71.85 at. % of Au, 12.65-14.65 at. % of Ge, 9-10 at. % of Si; and 6.5-8.5 at. % of Ag.

11. The amorphous alloy of claim 1, wherein said amorphous alloy consists of 64.45-70.95 at. % of Au, 12.65-14.65 at. % of Ge, 9-10 at. % of Si, 6.5-8.5 at. % of Ag and 0.9-2.4 at. % of Pd.

12. The amorphous alloy of claim 1, wherein said amorphous alloy consists of 58.95-69.15 at. % of Au, 12.65-14.65 at. % of Ge, 9-10 at. % of Si, 6.5-8.5 at. % of Ag, 0.9-2.4 at. % of Pd and 1.8-5.5 at. % of Bi.

13. The amorphous alloy of claim 1, wherein said amorphous alloy comprises one or more of the following properties: i. a minimum critical casting thickness of 0.5 mm; ii. a minimum glass transition temperature at 315K; iii. a supercooled liquid region of minimum 10K.

14. A method for manufacturing the amorphous alloy of claim 1, comprising the step of adding elements to a crucible in one of the following order, from bottom to top: PdAgAuBiGeSi.

15. A method for manufacturing the amorphous alloy of claim 1, comprising the step of adding elements to a crucible in one of the following order, from bottom to top: PtAgAuBiGeSi.

16. A method for manufacturing the amorphous alloy of claim 1, comprising the step of adding elements to a crucible in one of the following order, from bottom to top: Pd together with Pt followed by AgAuBiGeSi.

17. A decorative item comprising at least one component made of the amorphous alloy of claim 1.

18. The decorative item of claim 17, wherein said decorative item is a jewelry or an ornament.

19. The decorative item of claim 17, wherein said at least one component is formed by thermoplastic forming or molding.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 is the x-ray diffractogram patterns of as cast Alloy 5 to 8 at their critical casting thickness.

(2) FIG. 2 is the DSC thermograms of as cast Alloy 5 to 8.

(3) FIG. 3A is an as cast ?3 mm rod of Alloy 7.

(4) FIG. 3B is the rod in FIG. 3A deformed into u-shape after bending in 328K (under 10? magnification).

DETAILED DESCRIPTION OF THE INVENTION

(5) The following terms shall be used to describe the present invention. In the absence of a specific definition set forth herein, the terms used to describe the present invention shall be given their common meaning as understood by those of ordinary skill in the art.

(6) As used herein, the expression BMG refers to bulk metallic glass.

(7) As used herein, the expression a.t. % refers to atomic percentage.

(8) As used herein, the expression d.sub.c refers to critical casting thickness.

(9) As used herein, the expression T.sub.g refers to glass transition temperature.

(10) As used herein, the expression T.sub.x refers to crystallization temperature.

(11) As used herein, the expression ?T.sub.x refers to supercooled liquid region, the difference between T.sub.g and T.sub.x.

(12) As used herein, the expression T.sub.1 refers to liquidus temperature.

(13) As used herein, the expression YI refers to yellowness index.

(14) As used herein, the expression XRD refers to x-ray diffraction.

(15) As used herein, the expression DSC refers to differential scanning calorimetry.

(16) As used herein, the expression ?E* refers to the separation between two colours. ?E* is calculated by the following equation:
?E*=?{square root over (?L*.sup.2+?a*.sup.2+?b*.sup.2)} while L*, a* and b* are axes in CIELAB coordinates.

(17) This invention provides an amorphous alloy. In one embodiment, said amorphous alloy consists essentially of: i) 52.55-80.12 at. % of Au; ii) 11.74-15.55 at. % of Ge; iii) 8.13-10.77 at. % of Si; iv) 5-21.13 at. % being at least one element selected from the group consisting of Ag, Bi, Pd and Pt.

(18) In one embodiment, said at least one element is selected from the group consisting of: i) 5-10 at. % of Ag; ii) 0.01-8.69 at. % of Bi; iii) 0.01-2.44 at. % of Pd; iv) 0.01-2.44 at. % of Pt; and v) 0.01-2.44 at. % of Pd and Pt in total.

(19) In one embodiment, said amorphous alloy consists essentially of: 69.4 at. % of Au; 13.65 at. % of Ge; 9.45 at. % of Si; and 7.5 at. % of Ag.

(20) In one embodiment, said amorphous alloy consists essentially of: 68.2 at. % of Au; 13.65 at. % of Ge; 9.45 at. % of Si; 7.5 at. % of Ag; and 1.2 at. % of Pd.

(21) In one embodiment, said amorphous alloy consists essentially of: 65.83 at. % of Au; 13.65 at. % of Ge; e 7.5 at. % of Ag; 1.2 at. % of Pd; and 2.37 at. % of Bi.

(22) In one embodiment, said amorphous alloy consists essentially of: 63.46 at. % of Au; 13.65 at. % of Ge; 9.45 at. % of Si; 7.5 at. % of Ag; 1.2 at. % of Pd; and 4.74 at. % of Bi.

(23) In one embodiment, said amorphous alloy consists essentially of one or more combination of elements selected from the group consisting of: i) 63.68-73.59 at. % of Au, 12.65-15.55 at. % of Ge, 8.76-10.77 at. % of Si and 5-10 at. % of Ag; ii) 61.28-72.99 at. % of Au, 12.65-15.55 at. % of Ge, 8.76-10.77 at. % of Si, 5-10 at. % of Ag and 0.6-2.4 at. % of Pd; iii) 52.59-71.49 at. % of Au, 12.65-15.55 at. % of Ge, 8.76-10.77 at. % of Si, 5-10 at. % of Ag, 0.6-2.4 at. % of Pd; and 1.5-8.69 at. % of Bi; iv) 66.85-71.85 at. % of Au, 12.65-14.65 at. % of Ge, 9-10 at. % of Si; and 6.5-8.5 at. % of Ag; v) 64.45-70.95 at. % of Au, 12.65-14.65 at. % of Ge, 9-10 at. % of Si, 6.5-8.5 at. % of Ag and 0.9-2.4 at. % of Pd; and vi) 58.95-69.15 at. % of Au, 12.65-14.65 at. % of Ge, 9-10 at. % of Si, 6.5-8.5 at. % of Ag, 0.9-2.4 at. % of Pd and 1.8-5.5 at. % of Bi.

(24) In one embodiment, said amorphous alloy comprises one or more of the following properties: i) a minimum critical casting thickness of 0.5 mm; ii) a minimum glass transition temperature at 315K; iii) a supercooled liquid region of minimum 10K; iv) an improved thermal stability over the ternary AuGeSi alloys; v) an improved glass forming ability over the ternary AuGeSi alloys; vi) an improved tarnish resistance over the AuCuSi based BMGs.

(25) In one embodiment, said amorphous alloy further comprises one or more of the following properties: i) a minimum Vickers hardness of 200HV; ii) a minimum compressive strength of 480 MPa.

(26) This invention also provides a method for manufacturing the amorphous alloy of this invention. In one embodiment, said method comprises the step of adding elements to a crucible in one of the following order, from bottom to top: i) PdAgAuBiGeSi; ii) PtAgAuBiGeSi; iii) Pd/PtAgAuBiGeSi.

(27) This invention further provides a decorative item comprising at least one component made of the amorphous alloy of this invention.

(28) In one embodiment, said decorative item is a jewelry or an ornament.

(29) In one embodiment, said at least one component is formed by thermoplastic forming or molding.

(30) In one embodiment, said jewelry alloy has improved glass forming ability compared Au.sub.76.9Ge.sub.13.65Si.sub.9.45. In TABLE 1, Alloys 1 and 4 are listed for comparative purpose from previous literature, while our invention Alloys 5 to 8 were produced according to the conditions below. The alloys were prepared from individual elements of fineness >99.99%. Individual elements were melted in induction furnace with graphite crucible. The following order of the elements in the crucible can be maintained (from bottom to top): Pd/PtAgAuBiGeSi because it can reduce the formation of palladium and/or platinum silicides or other intermetallic compounds that may lead to crystallization. To achieve rapid cooling, the melts were cast into copper molds. The weight percentage of Au of all example alloys are over 75% so they can be hallmarked as 18 karat gold.

(31) TABLE-US-00001 TABLE 1 shows the composition of the alloy example of the current invention and for comparative purpose. Alloy Au at % Ag at % Cu at % Ge at % Si at % Pd at % Bi at % Sn at % Ga at % 1 (Comp.) 76.9 13.65 9.45 2 (Comp.) 49.0 5.5 26.9 16.3 2.3 3 (Comp.) 51.6 5.8 20.2 13.3 2.4 6.7 4 (Comp.) 51.6 5.8 20.2 13.3 2.4 6.7 5 (Inv.) 69.4 7.5 13.65 9.45 6 (Inv.) 68.2 7.5 13.65 9.45 1.2 7 (Inv.) 65.83 7.5 13.65 9.45 1.2 2.37 8 (Inv.) 63.46 7.5 13.65 9.45 1.2 4.74

(32) The amorphous structures of Alloys 5 to 8 were verified by X-ray diffractometer (Rigaku SmartLab 9KW), using Cu K.sub.? radiation. The diffractograms are shown in FIG. 1; d.sub.c and thermal behavior of Alloys 1 to 8 are listed in TABLE 2. The critical casting thicknesses of Alloys 5 to 8 range from 2 to 7 mm. Compared to the splatted thickness of 20 ?m produced of Alloy 1, the examples of present invention showed phenomenal improvement in critical casting thickness. In addition, Bi is highly preferred to add into the system. When Bi is added, d.sub.c can even be increased up to 7 mm. This shows the addition of Bi resulted in a remarkable improvement in glass forming ability in the AuGeSi system.

(33) TABLE-US-00002 TABLE 2 Critical thicknesses (d.sub.c) and thermal behavior of selected alloys. Data of Alloys 1 to 4 are quoted from previous literature. d.sub.c T.sub.g T.sub.x ?T.sub.x T.sub.l Alloy (mm) (K) (K) (K) (K) 1 (Comp.) 20 ?m 293 304 11 / 2 (Comp.) 5 401 459 58 644 3 (Comp.) 4 370 / / 655 4 (Comp.) 3 376 428 52 681 5 (Inv.) 2 317 334 17 672 6 (Inv.) 3 318 344 26 671 7 (Inv.) 5 323 346 23 670 8 (Inv.) 7 324 346 22 665

(34) In one embodiment, said jewelry alloy has improved thermal stability. All thermal properties were measured by differential scanning calorimeter (Mettler Toledo DSC3) at a heating rate of 20K/min. The temperatures are also listed in TABLE 2. T.sub.g of Alloy 1 was reported to be 290-295K, and ?T.sub.x was 11K. T.sub.g of examples of present invention (Alloys 5-8) range from 317 to 324K, while ?T.sub.x is as high as 26K. Higher T.sub.g and larger ?T.sub.x indicate higher stability of the supercooled liquid and also higher feasibility in jewelry production by plastic deformation. Introducing Bi into the system does not significantly lower ?T.sub.x nor T.sub.g but increase the glass forming ability of the BMG.

(35) In one embodiment, the hardness of said jewelry alloy is suitable for jewelry application. In one embodiment, the Vickers hardness (0.2 kg) of said jewelry alloy is at least 200HV. The Vickers hardness of as-cast Alloy 5 to 8 are shown in TABLE 3.

(36) TABLE-US-00003 TABLE 3 Vickers Hardness (0.2 kg) of as-cast alloys of present invention Alloy Hardness (HV0.2) 5 (Inv.) 200 6 (Inv.) 211 7 (Inv.) 215 8 (Inv.) 208

(37) In one embodiment, the strength of said jewelry alloy is suitable for jewelry application. In one embodiment, the compressive strength of said jewelry alloy is at least 480 MPa. A rod-shaped sample of Alloy 7 with ?4 mm diameter and 8 mm height (aspect ratio 1:2) was prepared for compressive strength test. The compressive strength of Alloy 7 was 487 MPa.

(38) In one embodiment, said jewelry alloy has improved tarnish resistance. Tarnish resistance test were performed with reference to ISO 10271. About 8?8?1 mm plates of Alloys 2-7 were prepared. The surfaces of the samples were sanded prior to the test to remove oxide residues formed during casting process. The samples were then immersed into artificial sweat solution and incubated at 37?2? C. for 14 days. The extent of tarnish can be presented by ?E* and ?YI compared with their as-polished states. ?E* describes the total colour deviated. YI is a number calculated from spectrophotometric data that describes the change in colour from colorless through to yellow. All colour measurements were presented in CIELAB coordinates and YI is calculated according to ASTM D1925. The sample alloys of present invention have attractive as polished white colour. Having YI below 13, all sample alloys can be graded as premium white. All colour measurements are listed in TABLE 4. From the value of ?a* and ?b*, it can be seen that the AuCuSi system metallic glass (Alloy 2 to 4) tarnished to red hue, while the present invention (Alloy 5 to 8) tarnished to yellow hue. Alloys 3 and 4, of which Cu is partially substituted by Sn and Ga respectively, are the alloys said to improve tarnish resistance over Alloy 2. In our experiment, ?E* and ?YI of Alloys 3 and 4 were lowered by 2.0-4.1%, showing a slight improvement in tarnish resistance. However, selected alloys in the present invention showed at least 22% reduction in ?E* and ?YI. The tarnish resistance of alloys disclosed in this invention definitely has a notable improvement over the previous inventions. High tarnish resistance makes the present invention more suitable in jewelry application.

(39) TABLE-US-00004 TABLE 4 Tarnish resistance performance of selected alloys. Alloy ?L* ?a* ?b* ?E* ?YI 2 (Comp.) ?15.35 +15.05 +16.80 27.28 +56.68 3 (Comp.) ?12.25 +12.35 +19.54 26.16 +55.54 4 (Comp.) ?14.09 +9.61 +20.06 26.57 +55.25 5 (Inv.) ?1.65 +2.45 +20.20 20.41 +41.00 6 (Inv.) ?2.20 +3.69 +17.32 17.85 +37.62 7 (Inv.) ?5.64 +6.09 +18.73 20.49 +44.30

(40) In one embodiment, said jewelry alloy is suitable for jewelry manufacturing. Suggested in previous work (Schroers, J. The superplastic forming of bulk metallic glasses, The Journal of the Minerals, Metals & Materials Society. 57(5), 35-39 (2005)), one possible method to manufacture metallic glasses is thermoplastic forming. Amorphous feedstock materials like granules or other simple geometries with thickness up to 3 mm can be prepared. Under applied pressure, at temperature within supercooled liquid region of the material, the feedstock material can be pressed into a mold of desire shape. Plastic deformation can be observed in Alloys 5 to 8 within their respective ?T.sub.x. FIG. 3 shows an example of plastic deformation of an as cast ?3 mm rod of Alloy 7. The rod was bent at 328K, 5K above its T.sub.g. The rod deformed into a U-shape without any fatigue.