Use of gold powder alloys for manufacturing jewellery items by selective laser melting

Abstract

A method of manufacturing yellow, red or white gold jewelry items layer by layer by selective laser melting (SLM) of a 18K, 14K, 10K or 9K gold powder alloy. The alloy comprises: (A) 37.5% to 38.5% by weight or 41.7% to 42.5% by weight or 58.5% to 59.5% by weight or 75% to 76% by weight of gold; and (D) 0.01% to 5% by weight, preferably 0.01% to 3% by weight of at least one metalloid, which may be germanium, silicon, boron, tellurium, phosphorous and selenium.

Claims

1. A method of manufacturing jewelry items layer by layer by selective laser melting (SLM) comprising: providing a 18K, 14K, 10K or 9K yellow, red or white gold powder alloy; and producing a jewelry item by melting the gold powder alloy into a plurality of adjoining layers with at least one laser beam, wherein the at least one laser beam causes the gold powder in each layer to melt completely and produce homogeneous layers, wherein the gold powder alloy consisting of a plurality of particles, each particle having a composition of: (A) 37.5% to 38.5% by weight, 41.7% to 42.5% by weight, 58.5% to 59.5% by weight, or 75% to 76% by weight of gold (Au); (B) X % to Y % by weight of a first element; (C) X % to Y % by weight of a second element; (D) 0.01% to 3% by weight of at least one metalloid; and possible impurities; wherein weight percentages are percentages by weight with respect to a total weight of the gold powder alloy; wherein the at least one metalloid is selected from the group consisting of: germanium (Ge), silicon (Si), boron (B), tellurium (Te), phosphorus (P), selenium (Se) or a mixture of two or more thereof; wherein the gold powder alloy is free of gallium (Ga), platinum (Pt), and tin (Sn); and wherein the gold powder allow further has a composition in which: if the alloy is a yellow or red gold alloy: (B) X is 10, Y is 55, and the first element is copper (Cu), (C) X is 2, Y is 15, and the second element is silver (Ag), and the yellow or red gold alloy is free of palladium (Pd); if the alloy is a white gold alloy: (B) X is 10, Y is 50, and the first element is palladium (Pd), (C) X is 10, Y is 50, and the second element is silver (Ag), wherein the palladium (Pd) and the silver (Ag) are in a weight ratio of 0.75:1 to 1:0.75, or (B) X is 5, Y is 35, and the first element is nickel (Ni), (C) X is 15, Y is 50, and the second element is copper (Cu), wherein the nickel (Ni) and the copper (Cu) are in a weight ratio of 1:2 to 1:3.

2. The method of claim 1, wherein the gold powder alloy has a particle size of 1 m to 60 m.

3. The method of claim 1, wherein laser power is selected to melt completely and homogenously the gold powder hit by the at least one laser beam throughout a total height of a layer.

4. The method of claim 3, wherein the laser power is at least 70 Watt.

5. The method of claim 1, wherein the jewelry items have a total roughness Rt that is less than 65 m.

6. The method of claim 1, wherein the jewelry items have an inner porosity in volume lower than 2%.

7. The method of claim 1, wherein the at least one metalloid is selected from the group consisting of: germanium, silicon or boron, or a mixture of two or more thereof.

8. The method of claim 1, wherein providing the gold powder alloy comprises providing a gold powder alloy produced by atomization.

9. The method of claim 1, wherein the gold powder alloy is a 18K yellow or red gold alloy, and wherein: (A) the gold is 75% to 76% by weight, (B) the copper is 10% to 23% by weight, (C) the silver is 2% to 15% by weight, and (D) the at least one metalloid is 0.01% to 1% by weight.

10. The method of claim 1, wherein the gold is yellow gold, and wherein: (B) the copper is 10% to 14% by weight, and (C) the silver is 10% to 14% by weight.

11. The method of claim 1, wherein the gold is red gold, and wherein: (B) the copper is 18% to 23% by weight, and (C) the silver is 2% to 5% by weight.

12. The method of claim 1, wherein the gold powder alloy is a 14K red gold alloy, and wherein: (A) the gold is 58.5% to 59.5% by weight, (B) the copper is 30% to 40% by weight, (C) the silver is 5% to 10% by weight, and (D) the at least one metalloid is 0.01% to 1.5% by weight.

13. The method of claim 1, wherein the gold powder alloy is a 10K red gold alloy, and wherein: (A) the gold is 41.7% to 42.5% by weight, (B) the copper is 45% to 50% by weight, (C) the silver is 8% to 13% by weight, and (D) the at least one metalloid is 0.01% to 2% by weight.

14. The method of claim 1, wherein the gold powder alloy is a 9K red gold alloy, and wherein: (A) the gold is 37.5% to 38.5% by weight, (B) the copper is 47% to 55% by weight, (C) the silver is 8% to 15% by weight, and (D) the at least one metalloid is 0.01% to 3% by weight.

15. The method of claim 1, wherein the gold powder alloy is a 18K white gold alloy, and wherein: (A) the gold is 75% to 76% by weight, (B) the palladium is 10% to 15% by weight, (C) the silver is 10% to 15% by weight, and (D) the at least one metalloid is 0.01% to 1% by weight.

16. The method of claim 1, wherein the gold powder alloy is a 18K white gold alloy, and wherein: (A) the gold is 75% to 76% by weight, (B) the nickel is 5% to 10% by weight, (C) the copper is 15% to 20% by weight, and (D) the at least one metalloid is 0.01% to 1% by weight.

17. The method of claim 1, wherein the gold powder alloy is a 14K white gold alloy, and wherein: (A) the gold is 58.5% to 59.5% by weight, (B) the palladium is 15% to 25% by weight, (C) the silver is 15% to 25% by weight, and (D) the at least one metalloid is 0.01% to 1.5% by weight.

18. The method of claim 1, wherein the gold powder alloy is a 14K white gold alloy, and wherein: (A) the gold is 58.5% to 59.5% by weight, (B) the nickel is 8% to 20% by weight, (C) the copper is 23% to 35% by weight, and (D) the at least one metalloid is 0.01% to 1.5% by weight.

19. The method of claim 1, wherein the gold powder alloy is a 10K white gold alloy, and wherein: (A) the gold is 41.7% to 42.5% by weight, (B) the palladium is 25% to 45% by weight, (C) the silver is 25% to 45% by weight, and (D) the at least one metalloid is 0.01% to 2% by weight.

20. The method of claim 1, wherein the gold powder alloy is a 10K white gold alloy, and wherein: (A) the gold is 41.7% to 42.5% by weight, (B) the nickel is 12.5% to 35% by weight, (C) the copper is 35% to 50% by weight, and (D) the at least one metalloid is 0.01% to 2% by weight.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a microscopic electronic scan (SEM, EDS) of the powder of example 1.

(2) FIGS. 2 and 3 show views of a sample manufactured with the gold alloy with germanium of example 1.

(3) FIG. 4 shows a sample obtained with laser having a power of 62.5 W.

(4) FIG. 5 shows a sample obtained with laser having a power of 72.5 W.

(5) FIG. 6 shows a sample obtained with laser having a power of 82.5 W.

(6) FIG. 7 shows a sample obtained with laser having a power of 92.5 W.

EXAMPLES

Example 1

Preparation of Yellow and Red Gold Powder

(7) Various examples of powder alloys have been prepared, being different for colour and fineness of gold, in accordance with table 1 below.

(8) TABLE-US-00001 Ex 1-18 Ex 2-18 Ex 3-18 Ex 4-14 Ex 5-10 Ex 6-9 Kt R Kt R Kt Y Kt R Kt R Kt R (A) Au 75.2 75.2 75.2 58.7 41.9 37.7 (B) Cu 20.8 21.0 12.4 33.45 47.06 50.46 (C) Ag 3.6 3.6 12.0 7.45 10.64 11.44 (D) Ge 0.4 0.2 0.4 0.4 0.4 0.4 INDEX .fwdarw. Ex: Example; 18-14-10-9 Kt: 18, 14, 10, 9 K gold alloy; R: red gold alloy; Y: yellow gold alloy.

(9) The alloys of the examples 1-6 of table 1 have been prepared by a gas spray nozzle working in an environment completely protected with argon and atmospheric pressure.

(10) In FIG. 1 the microscopic electronic scan (SEM, EDS) of the powder of example 1, 18K red gold alloy (d.sub.50 15.44 m, d.sub.90 35.90 m) is shown. It is clear that the atomization ensures the formation of powders constituted of particles of mainly spherical shape.

Example 2

Manufacturing of Red Gold Jewellery Items by SLM

(11) A lamellar block (parallelepiped having a length of 10.0 mm, width of 5.0 mm, thickness of 5.0 mm and a uniform nominal spacing between the individual leaves of 500 m) has been manufactured in red gold by means of the powder of example 1.

(12) A SLM 50 (Realizer) device has been used provided with a fiber laser (Wmax=100 Watt) having a spot starting from 10 m and a circular construction table (70 mm), inserted in a chamber with atmosphere protected with inert gas (Ar). The scan speed of the laser has been of 0.33 m/s.

(13) To evaluate the effect of the inclusion of the metalloids in the alloy, in addition to the above sample another sample without metalloids has been manufactured (same size and same device) with a 18K red gold alloy consisting of gold 75.2% by weight, copper 20.8% by weight and silver 4% by weight.

(14) For both samples, the laser power has been set at 72.5 Watts.

(15) As it is visually understood from the comparison of FIGS. 2 and 3, the sample manufactured with the gold alloy with germanium of example 1 led to the formation of surfaces parallel to the table of construction, with a total roughness of about Rt=55 m, that is to say about 30% less than the same alloy free of germanium, whose roughness was Rt=72 m.

(16) The roughness has been measured using a Taylor Hobson profilometer (Talysurf Intra2) provided with a carbon fiber probe with diamond tip having a radius of 2.0 m.

(17) Without being bound by theory, it is possible to state that alloys that after the SLM process provide jewellery items having a total roughness Rt greater than or equal to 66 m are not part of the present invention.

(18) To check the influence of the laser power the same above mentioned solids have been prepared with increasing laser power from 62.5 W to 92.5 W, the rest of the process parameters being equal for all samples. FIG. 4 relates to the sample obtained with laser having a power of 62.5 W, FIG. 5 relates to the sample obtained with laser having a power of 72.5 W, FIG. 6 relates to the sample obtained with laser having a power of 82.5 W, and FIG. 7 relates to the sample obtained with laser having a power of 92.5 W.

(19) The reduction of the laser power causes a thinning of the carriers, since both the volume of the melting material and the time of solidification beginning from the melting state are reduced.

(20) Therefore, to obtain jewellery items having suitable mechanical features it is preferable to set the laser power at least at 70 W. However, with the increase of the scan speed the above mentioned phenomenon is emphasized, so it is preferable to increase the laser power gradually.

(21) To check the porosity of the jewellery items manufactured with alloys according to the invention through the alloy of example 1 it has been manufactured a massive solid of parallelepiped shape (10 mm4.5 mm3 mm) with the same above mentioned process parameters. The inner porosity has been evaluated upon the metallographic sections by means of the ImageJ 1.48B software.

(22) The measurement of porosity has been carried out after the removal of 0.20 mm from the initial thickness of 3 mm. At the thickness of 2.80 mm measurements of the inner porosity have been made in several points. The porosity has always been lower than 1%, and often lower than 0.5%.

(23) These values are indicative of high quality of the jewellery item.

(24) Without being bound by theory, it is possible to state that alloys that after the SLM process provide jewellery items having inner porosity greater than 2% are not part of the present invention.

(25) To evaluate the influence of the presence of the metalloid in the gold alloy regarding the ductility various alloy samples have been prepared of example 1 as mentioned above having an increasing percentage of germanium 0.2% to 2% (Au 75.2%, Ag 3.6%, Cu balance). The values of germanium have been 0.2%, 0.4%, 1%, 1.5%, 2% by weight.

(26) The evaluation of the ductility has been done manually, as often occurs in jewellery. In fact, a jewellery maker often manipulates the jewellery item to work it or set stones.

(27) Samples with germanium 1.5% and 2% by weight break if manipulated, and therefore are unacceptably fragile.

(28) The best results have been shown by the samples with germanium 0.2% and 0.4% by weight.

Example 3

Preparation of White Gold Alloys

(29) Two examples of white gold powder alloys have been prepared, both of 18K fineness.

Sample 1

(30) Gold 72.5% by weight;

(31) Palladium 12.4% by weight;

(32) Silver 12.2% by weight;

(33) Germanium 0.2% by weight.

Sample 2

(34) Gold 72.5% by weight;

(35) Nickel 7.5% by weight;

(36) Copper 17.1% by weight;

(37) Germanium 0.2% by weight.

(38) The alloys of samples 1 and 2 have been prepared by a gas spray nozzle operating in a environment completely protected with argon and atmospheric pressure. The atomization ensures the formation of powders consisting of particles of mainly spherical shape.

Example 4

Manufacturing of Jewellery Items by SLM

(39) Lamellar blocks (parallelepiped having a length of 10.0 mm, width of 5.0 mm, thickness of 5.0 mm and a uniform nominal spacing between the individual leaves of 500 m) have been manufactured in white gold by means of the powders of samples 1 and 2.

(40) A SLM 50 (Realizer) device has been used provided with a fiber laser (Wmax=100 Watt) having a spot starting from 10 m and a circular construction table (70 mm), inserted in a chamber with atmosphere protected with inert gas (Ar). The scan speed of the laser has been of 0.33 m/s.

(41) Both blocks have good mechanical properties and reduced surface roughness, as already verified for the red gold alloys (example 2).