WO2015193659A2

WO2015193659A2 - Alloy compositions

Info

Publication number: WO2015193659A2
Application number: PCT/GB2015/051765
Authority: WO
Inventors: Christopher Quayle
Original assignee: ALLIED GOLD Ltd
Current assignee: ALLIED GOLD Ltd
Priority date: 2014-06-16
Filing date: 2015-06-16
Publication date: 2015-12-23
Anticipated expiration: 2016-12-16
Also published as: WO2015193659A3

Abstract

Precious metal-containing alloy compositions having good fusibility as well as good colour and workability properties comprise: (i) at least one precious metal selected from gold (Au), platinum (Pt) and palladium (Pd); and (ii) a fusibility-promoting amount of an alloying component comprising: (iia) copper, and (iib) germanium; with the balance being one or more optional adjunct components and/or impurities.

Description

ALLOY COMPOSITIONS

TECHNICAL FIELD This invention relates to alloy compositions, especially alloy compositions based on one or more precious metals. More particularly, though not exclusively, the invention relates to precious metal-containing alloy compositions which include certain adjunct components which impart particular desirable physical properties thereto. BACKGROUND

Items of jewellery manufactured principally in either silver, gold, platinum or palladium (which are the recognised precious metals in the jewellery trade) typically comprise individual components which are joined together by soldering (more correctly termed "brazing") or occasionally by welding. However, such techniques are frequently disadvantageous, in that either the one or more filler metals used in the soldering/brazing joining process is/are typically of a different colour from the main jewellery components, or the actual welding of the parent metal(s) themselves creates distortions or melting of the pieces being joined.

Soldering and brazing typically employ a filler metal which melts below the melting- point of the parent metal(s) being joined. This filler metal "wets" onto both parent metal surfaces and is drawn into the joint gap therebetween by capillary attraction, where it solidifies to give a strong, ductile bond. Different filler metal alloys melt at different temperatures, making it possible, if desired or necessary, to "step" joints that are close together, e.g. starting with a higher melting-point filler metal or alloy and then progressively using a lower melting-point filler metal or alloy. Also, some filler metals flow better than others: more free-flowing filler metals are better for very tight or narrow joint gaps, whereas less flowable (i.e. more "stodgy") filler metals are better at filling wider joint gaps.

Brazing operations are generally defined as taking place at about 450 °C (-840 °F) or above, and soldering generally takes place below about 450 °C, but otherwise the two processes are in general terms the same. However, silversmiths and goldsmiths frequently refer to the higher temperature brazing process as "soldering" and this can be a cause of some confusion. Therefore, as used herein the higher temperature joining process will be referred to as "soldering (brazing)" to differentiate it from the lower temperature "soldering" process and also to maintain the silversmith/goldsmith convention of nomenclature.

With regard to welding, this is also a process for joining same or similar metals, although in this case the parent metals being joined are heated to above their melting point and a filler metal may also be applied. By definition this is typically a higher temperature process than either soldering or brazing and typically takes place in the temperature range of about 800-1635 °C (1500-3000 °F). Solders and brazing alloys that are used for the joining of jewellery items have a different colour to the parent metals they are used to join, owing to the necessity of the lower melting-point ranges and the requirement for the alloy to flow during the soldering/brazing procedure. As a result, the resulting soldered/brazed seams or joints are then conventionally disguised by one or more subsequent plating operations, e.g. plating with silver and rhodium for silver items, palladium and rhodium for white golds and gold plate for yellow gold items. This is a disadvantage, as it involves yet another manufacturing stage and it also involves use of more, costly raw materials, both of which factors detract from the economy of the overall jewellery manufacturing process. It is also known in the art that components of certain silver-copper-germanium alloys can be joined by means of a fusing technique, such as those disclosed in published UK Patent Application no. GB2283934A. In the technique described there a joint is made between the silver-copper-germanium alloy surfaces to be joined by heating them to below the solidus temperature of the constituent materials of the parts being joined. However, hitherto such joining techniques have not been applied to known gold- or other precious metal-based alloys, because conventional wisdom is that such techniques are incompatible therewith because of the need to carefully balance end colour properties of the alloy(s) being joined (germanium being a noted whitening element and copper being a noted reddening element) and because acceptable levels of other physical properties such as workability cannot be assured or even expected in the context of germanium and/or copper alloying elements.

SUMMARY OF THE INVENTION We have now surprisingly found a new and useful range of alloys based on gold or certain other precious metals which have unexpectedly advantageous fusibility properties, which lend them particularly usefully to being joinable by means of a diffusion process. In addition these new alloys also have an unexpectedly good balance of other physical properties, in particular colour and workability, which render them especially suitable for manufacture into jewellery and other articles. Aspects of the present invention relate to a precious metal-containing alloy composition, a method of making the alloy composition, an article made from the alloy composition, a method of joining together two elements at least one of which comprises the said alloy composition, and a method of increasing or enhancing the fusibility of a precious metal- containing alloy composition.

In a first aspect of the invention there is provided an alloy composition comprising:

(i) at least one precious metal selected from gold (Au), platinum (Pt) and palladium (Pd); and

(ii) a fusibility-promoting amount of an alloying component comprising:

(iia) copper, and

(iib) germanium;

with the balance being one or more optional adjunct components and/or impurities.

In some practical embodiments the alloy compositions of the above first aspect of the invention may further comprise one or more secondary alloying elements or adjunct components conventionally included in gold or other precious metal alloy compositions for imparting thereto or enhancing one or more particularly desirable end properties, such as one or more of the following: whiteness, specific desired colour, hardness, workability, ductility, flowability, precious metal content.

In some practical embodiments of the invention the alloy compositions may further comprise one or more adjunct components selected from:

(a) one or more castability-enhancing components, e.g. in an amount of from about 0.0 or 0.1 or 0.5 up to about 3.0 or 4.0 or 5.0 % by weight of the composition;

(b) one or more grain refining components, e.g. in an amount of from about 0.0 or

0.05 or 0.1 up to about 0.5 or 1 .0 or 2.0 or 3.0 or 4.0 or 5.0 % by weight of the composition;

(c) one or more flow- or ductility-enhancing components;

(d) one or more workability-enhancing components;

(e) one or more adjunct precious metal components;

(f) one or more impurities. Suitable components (a) for enhancing castability of the resulting alloy compositions may be selected from any suitable elements (or compounds) known in the art for that purpose. Examples may include one or more of indium (In), gallium (Ga) and tin (Sn). Suitable components (b) for acting as grain refiners may be selected from any suitable elements (or compounds) known in the art for that purpose. Examples may include one or more of silicon (Si), iridium (Ir), boron (B) and ruthenium (Ru).

Suitable components (c) for acting as flow- or ductility-enhancing components may be selected from any suitable elements (or compounds) known in the art for that purpose, e.g. one or more adjunct metals known for that purpose, e.g. silver, zinc. When present, such one or more flow- or ductility-enhancing components may be included in the alloy composition in any suitable amount that imparts to the alloy a sufficient or desired degree of ductility or flow characteristics, e.g. depending on the alloy's composition of other components, its intended use or its treatment in any subsequent processing stage. Suitable such amounts of this flow- or ductility-enhancing component (c) (or collectively such components (c), if more than one such component (c) is used) included in the composition for this purpose may be for example in the range of from about 0.0 or 0.1 or 0.5 up to about 5.0 or 10 or 15 or 20 or 30 or 40 or 50 or 60 or 65 % by weight of the composition. Such amounts may include any amount of the same flow- or ductility- enhancing component (c) when it is optionally present in the composition for one or more other purposes, e.g. under optional components (d) and/or (e) below.

Suitable components (d) for acting as workability-enhancing components may be selected from any suitable elements (or compounds) known in the art for that purpose, e.g. one or more adjunct metals known for that purpose, e.g. silver, zinc. When present, such one or more workability-enhancing components may be included in the alloy composition in any suitable amount that imparts to the alloy a sufficient or desired degree of workability or balance of workability properties, e.g. depending on the alloy's composition of other components, its intended use or its treatment in any subsequent processing stage. Suitable such amounts of this workability-enhancing component (d) (or collectively such components (d), if more than one such component (d) is used) included in the composition for this purpose may be for example in the range of from about 0.0 or 0.1 or 0.5 up to about 5.0 or 10 or 15 or 20 or 30 or 40 or 50 or 60 or 65 % by weight of the composition. Such amounts may include any amount of the same workability-enhancing component (d) when it is optionally present in the composition for one or more other purposes, e.g. under optional components (c) above and/or (e) below. One or more adjunct precious metal components (e) may optionally be included in the alloy compositions of the invention, one example of which is silver or a silver-containing alloy, which silver may thus be present in its own right as an adjunct precious metal in addition to or alternatively from its optional presence (under optional components (c) and/or (d)) as a ductility-enhancing and/or workability-enhancing component. Suitable such amounts of this adjunct precious metal component (e) (or collectively such components (e), if more than one such component (e) is used), included in the composition for this purpose may be for example in the range of from about 0.0 or 0.1 or 0.5 up to about 5.0 or 10 or 15 or 20 or 30 or 40 or 50 or 60 or 65 % by weight of the composition. Such amounts may include any amount of the same adjunct precious metal component (e) when it is optionally present in the composition for one or more other purposes, e.g. under optional components (c) and/or (d) above. It is also to be understood that the alloy compositions of the invention may further include one or more other elements or compounds of the nature of impurities (f), e.g. derived from any of the starting materials used for forming the alloys or from any of the processing steps used for their production. In embodiments such impurity components(s) may for example be present in no more than about 0.0001 , 0.0005, 0.001 , 0.005, 0.01 , 0.05, 0.1 , 0.5, 1 .0, 1 .5 or even 2.0 % by weight of the total composition.

In some embodiments the alloy composition may be a gold-based alloy composition, in which case the alloy composition preferably comprises:

(i) from about 33.3 up to about 76.0 % by weight of gold;

(ii) from about 1 up to about 65 % by weight of silver;

(iii) from about 0.01 or 0.05 or 0.1 or 0.2 or 0.3 or 0.4 or 0.5 up to about 69 % by weight of copper;

(iv) from about 0.01 or 0.05 or 0.1 or 0.2 or 0.3 or 0.4 or 0.5 up to about 6.0 % by weight of germanium;

(v) optionally from about 0.0 up to about 10.0 % by weight of zinc;

In some embodiments of the above gold alloys a preferred amount of germanium may for example be in the range of from about 2 or 3 % by weight up to about 5 or 6 % by weight. In other embodiments the alloy composition may be a platinum-based alloy composition, in which case the alloy composition preferably comprises:

(i) from about 95 up to about 99% by weight of platinum;

(ii) from about 0.01 or 0.05 or 0.1 or 0.2 or 0.3 or 0.4 or 0.5 up to about 4.5 % by weight of copper;

(iii) from about 0.01 or 0.05 or 0.1 or 0.2 or 0.3 or 0.4 or 0.5 up to about 4.5 % by weight of germanium;

with the balance being one or more optional adjunct components and/or impurities. In other embodiments the alloy composition may be a palladium-based alloy composition, in which case the alloy composition preferably comprises:

(i) from about 95 up to about 99% by weight of palladium;

In embodiments of the first aspect of the invention in which the alloy composition is a gold-based alloy composition, the alloy composition may comprise gold in combination with one or more alloying elements that are typical of and/or are consistent with generally established definitions or physical appearances of gold-based alloys commonly termed any of the following: yellow gold, white gold, rose gold, crown gold, red gold, pink gold, spangold, green gold, grey gold. Such gold-alloying elements may include for example silver and/or copper (e.g. as defined in the embodiments above), and/or any other alloying elements known for use in such coloured gold-based alloys.

Gold-based alloy compositions of the invention that are of the "white gold" type, may be particularly useful, as they may be designed to have high whiteness properties, yet without the deleterious effects and health risks (especially because of allergic reactions) often associated with such alloys based conventionally on nickel (Ni) as a major alloying element in addition to the gold.

In embodiments of the first aspect of the invention in which the alloy composition is a gold-based alloy composition, the alloy composition may comprise gold in a total amount (by weight of the total composition) appropriate for satisfying a particular selected or predefined carat (or karat) rating for the gold alloy in question. Such overall gold contents for particular carat gold alloys are well known in the art and examples will be given hereinbelow in the context of preferred embodiments and working examples illustrating same. In a second aspect of the invention there is provided a method of making an alloy composition of the first aspect of the invention or any embodiment thereof, the method comprising:

(i) heating together the appropriate amounts of the essential precious metal(s) and alloying components, optionally together with any optional alloying or adjunct components, preferably under a controlled atmosphere to prevent oxidation of the said metals or other components; and

(ii) cooling the thus-formed alloy, e.g. to a working temperature appropriate to its further treatment or use in making a desired item. In a third aspect of the invention there is provided an article, especially an item of jewellery or other decorative item, formed at least in part from an alloy composition according to the first aspect of the invention or any embodiment thereof.

In some embodiments of this third aspect the article may comprise a plurality of component parts, at least one of which is joined, preferably by means of a fusion or diffusion process, to at least one other component part thereof, wherein at least one of, preferably each of, said component parts is, or is formed from, an alloy composition according to the first aspect of the invention or any embodiment thereof. In other embodiments of this third aspect the article may comprise a plurality of component parts, at least one of which is joined, preferably by means of a fusion or diffusion process, to at least one other component part thereof, wherein at least one first component part thereof is, or is formed from, an alloy composition according to the first aspect of the invention or any embodiment thereof, and at least one second component part thereof is, or is formed from, a metal or alloy other than an alloy composition according to the first aspect of the invention or any embodiment thereof.

In such preceding embodiments the at least one second component part may be, or may be formed from, another precious metal or precious metal alloy, i.e. a precious metal or alloy other than gold, platinum or palladium or gold-based, platinum-based or palladium- based, e.g. silver or a silver-based alloy, e.g. an Argentium (RTM) silver composition. The Argentium (RTM) silver composition may comprise at least 92.5% by weight silver, the balance being substantially copper and germanium. In many cases the amount of germanium present may be such as to replace a minor proportion of the customary 7.5% by weight of copper normally present in a standard Sterling silver composition. In an embodiment the Argentium (RTM) silver may be substantially 92.5% silver, with the balance provided substantially by copper and germanium. The amount of germanium may for example be present in the range from about 0.05 to about 1 or 2 or 3 or 4 or possibly even up to about 7% by weight, optionally from about 0.4% to about 1 or 2 or 3 or 4% by weight. Boron may optionally be present as a grain refiner in the silver composition, e.g. in an amount of up to about 20ppm in some embodiments.

In a fourth aspect of the invention there is provided a method of making an article according to the third aspect or any embodiment thereof, the method comprising joining the said component parts using a fusion or diffusion process. In embodiments of the above fourth aspect the method may comprise fusing together the said component parts by placing the said component parts together so as to define at least one area or region of each in mutual contact with the other, and heating at least the said area or region so that the said alloy composition of each component undergoes incipient melting and a solid metal bond is formed between the two component parts upon cooling of the said areas or region.

In a fifth aspect of the invention there is provided a method of increasing or enhancing the fusibility of a precious metal-containing alloy composition, wherein the alloy composition comprises at least one precious metal selected from gold (Au), platinum (Pt) and palladium (Pd), together with one or more optional components and/or impurities, wherein the method comprises incorporating in the alloy composition a fusibility- promoting or enhancing amount of an alloying component comprising:

(iia) copper; and

(iib) germanium.

In embodiments of this fifth aspect of the invention the alloy composition may comprise:

- the said copper and germanium in any amounts as defined above in the context of the alloy compositions of the first aspect or any embodiment thereof; and/or

- one or more additional or optional components as defined above in the context of the alloy compositions of the first aspect or any embodiment thereof.

It is to be understood that alloy compositions in accordance with many embodiments of the present invention may exist in the form of discrete articles, bodies, masses, coatings or other volumes of any desired shape which consist of or comprise the said alloy composition. However it is also possible within the scope of the invention that alloy compositions in accordance with certain embodiments of the present invention may exist in the form of one or more portions or regions or phases within or forming a part of a larger article, body, mass, coating or other volume of any desired shape, which portion(s), region(s) or phase(s) consists of or comprises the said alloy composition. In such instances such an alloy composition may be formed for example in situ in such a portion, region or phase, e.g. at or in an interfacial region or portion between two or more discrete articles, bodies, masses, coatings or other volumes which each contain or contribute at least one component of the resulting alloy composition which is formed in situ when the two or more discrete articles, bodies, masses, coatings or other volumes are united, joined, bonded, soldered, brazed, fused or alloyed together, preferably by a fusion or diffusion process.

Thus, an example of such an in s/fu-formed alloy composition within the scope of some embodiments of the invention may be that formed in an interfacial region or portion upon diffusion-bonding an article of gold (or e.g. white or other species of gold) with an article of Argentium silver, whereby in the interfacial diffusion region an alloy composition comprising at least gold (from the gold-based article), and copper and germanium (from the silver-based article) is formed in situ. Thus, in such an example the advantageous properties of the gold-based alloy composition of the invention may be realised at the in situ site, region or portion of formation of the alloy composition itself. Within the scope of this application it is expressly envisaged that the various aspects, embodiments, examples and alternatives, and in particular the individual features thereof, set out in the preceding paragraphs, in the claims and/or in the following description and drawings, may be taken independently or in any combination. For example features described in connection with one embodiment are applicable to all embodiments, unless such features are incompatible.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawing, in which:

FIGURE 1 is a graphical illustration of the CIELab system of colour measurement showing orthogonal axes L^*, a^* and b^*.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION AND EXAMPLES Embodiments and examples of the invention in its various aspects will now be described in detail, by way of non-limiting example only, by way of the following detailed description.

Whiteness of precious metal alloys and particularly white gold alloys has been reviewed elsewhere, for example in:

- Corti, Christpher W., The Santa Fe Symposium on Jewelry Manufacturing Technology, Proceedings of the Santa Fe Symposium in Albuquerque, New Mexico, Ed. E. Bell and J. Haldeman, pp.103-1 19, May 2005, "What is White Gold? Progress on the Issues!";

- Normandeau, Greg, Gold Bull., 1992, 25 (3), pp. 94 103, "White Golds: A

Review of Commercial Material Characteristics & Alloy Design Alternatives";

- MacCormack, I Bruce and Bowers, John E., Gold Bull., 1981 , 14 (1 ), pp. 19- 24, "New White Gold Alloys";

all of which disclosures are incorporated herein by reference.

In the early stages of the making of the present invention, initial interest was in developing a novel white gold alloy which could be bonded to other precious metals (i.e. silver, (yellow) gold, platinum and palladium) by means of a fusing process. Examples of such a fusion process, in which each component to be joined is heated (at least in the abutting or contacting region(s) or area(s)) so as to undergo incipient melting and a solid metal bond is formed between the two component parts upon cooling thereof, are disclosed for example in UK Patent Application no. GB2283934B.

In developing this white gold alloy, initially at the 37.5% Au (9 carat) purity and subsequently at the 75.0% Au (18 carat) purity level it was noticed that the germanium addition had a much improved whitening effect compared to the palladium and/or nickel it replaced as the typical whitening additions in gold alloys (as described in the Corti and Normandeau references cited above). As there are already concerns regarding nickel additions in precious metal alloys regarding nickel sensitivity and palladium additions in gold alloys have been known to induce delayed stress cracking phenomena, it was decided to develop a range of nickel- and palladium- free white gold alloys with the desired fusing properties. It is important to note that although these initial developments were at the 9 carat and 18 carat levels this work can equally be applied to gold alloys with any of 8 carat (33.3% Au), 10 carat (41 .7% Au) or 14 carat (58.3% Au) contents which are popular in, but not limited to, respectively, Europe, USA and Russia and the USA and Canada.

What these references cited above show is that traditional white gold alloys are not white but grey and they conventionally require a hard metallic white rhodium plating to give them an appearance that is sufficiently "white" for the jewellery-buying public to accept.

Whiteness of precious metal alloys can be best measure using the CIELab system of colour measurement, which is well-known in the art and well-understood by the skilled person. This system uses a colour photo-spectrometer and describes the colour as having three coordinates, as represented by the diagram of FIG. 1 . Coordinate L^* measures the degree of brightness or lightness from 0 (which is black) to 100 (which is white) and is a measure of reflectivity; the coordinate a^* measures the red-green component of colour, from green (-a) to red (+a); and the coordinate b^* measures the yellow-blue colour component, from blue (-b) to yellow (+b). A perfect pure white would have L^* = 100, a^* = 0, and b^* = 0.

In addition a measurement called the Yellowness Index (Yl), originally developed to assess aging in plastics, is also widely established for describing the degree of whiteness of white gold alloys, and is discussed in the above-cited Corti reference. The Yellowness Index (Yl) is calculated from the CIE tri-stimulus values, X, Y and Z, thus:

Yl = [100 (1 .28X-1 .06Z) / Y ] The Yl scale is linear: as the number decreases, so the alloy is whiter.

Table 1 below gives the typical Yellowness Index and CIELab values for various known "white" precious metal alloys, the rhodium plating used to make white gold alloys "white" and the initial colour measurements of the 9 carat and 18 carat germanium- containing white gold alloys according to embodiments of the present invention. Table 1 - Surface Colour Measurement of various "white" precious metals/alloys

⁽¹⁾ Example alloys according to the present invention, as exemplified in the Examples below.

⁽²⁾ Averaged values from a range of commercially available white golds,

Table 1 clearly demonstrates how much whiter these white gold alloys were that contain germanium, in accordance with embodiments of the present invention, as compared with the traditional "white gold" alloys. It is also important to note that this improvement in whiteness is based on relatively small additions of germanium compared with the levels of nickel and/or palladium which would conventionally be present as traditional whitening elements. In other words, germanium is 3 or 4 times a more effective whitening addition component compared with the conventional metal(s) it replaces.

EXAMPLES

Various examples of white, yellow and red gold alloys according to embodiments of the present invention were prepared and tested as follows:

(i) 9 carat white gold alloys

For the initial 9 carat white gold trials, samples started with a 1 % germanium addition and ranged up to a 5% germanium addition. From these initial trials, as shown in the test results presented further below, it was noted that a germanium addition in the range 2 - 3% was the preferred minimum requirement to obtain consistent fusion results, and specifically for the white gold alloys an addition of 3 - 5% germanium may be more beneficial.

Various example 9 carat white gold alloys according to the present invention were prepared, as described further below, with the following compositions as shown in Table 2 below (all amounts being given as % by weight of the total composition):

Table 2 - 9 carat white gold alloys according the invention

Based on this work and the subsequent forming and fusing operations carried out on these alloys, as shown in the test results presented further below, it is possible to state that (in addition to the points made above): The copper : germanium ratio required to achieve a workable alloy increases with the amount of the germanium addition. Therefore, for example, for an alloy with a 1 % germanium addition a workable alloy is achievable with a 1 % copper addition (i.e. a 1 :1 ratio). However, to achieve a workable alloy with a 5% germanium addition, the amount of copper needed increases to a 2.5:1 copper : germanium ratio.

In general, it can be expected that for white gold alloys this ratio requires a balance to be struck between the best alloy for its fusing ability and the best alloy in terms of its colour, since any copper addition will tend to make the alloy more red.

At the 5% germanium level in the 9 carat white gold composition the white colour was very good but the alloy was found to exhibit poor working characteristics, as shown in the test results presented further below.

(ii) 9 carat yellow and red gold alloys

For yellow and red gold alloys this critical ratio of copper : germanium may not be so much of a concern, as one will always have sufficient copper present to give the yellow or red colour component. Rather, the main requirement here is to ensure that the germanium addition achieves optimum fusability of the alloy, but does not overly whiten the alloy resulting in "washed out" yellow gold or red gold colours. Initial trials for 9 carat yellow and 9 carat red alloys have been carried out with a 2% germanium addition: various example 9 carat yellow and 9 carat red gold alloys according to the present invention were prepared, as described further below, with the following compositions as shown in Table 3 below (all amounts being given as % by weight of the total composition):

Table 3 - 9 carat yellow and red gold alloys according the invention

Initial assessments of these alloys showed that they had good colour and fusing ability, as shown in the test results presented further below.

(iii) 14 carat white and red gold alloys

Examples of 14 carat white and 14 carat red gold alloys according to the invention had compositions as shown in Table 4 below (all amounts being given as % by weight of the total composition): Table 4 - 14 carat white and red gold alloys according the invention

(iv) 18 carat white gold alloys

For 18 carat white gold alloys trials were conducted on the following alloy compositions: various 18 carat white gold alloys according to the present invention were prepared, as described further below, with the following compositions as shown in Table 5 below (all amounts being given as % by weight of the total composition): Table 5 - 18 carat white gold alloys according the invention

The 4% germanium addition showed good colour but poor workability, as shown in the test results presented further below. It is believed that the workability may be improved by reducing the germanium addition to the 3% level whilst maintaining the exceptional whiteness of this alloy. For the white gold alloys the limit of improved whiteness visually appears to be at around the 4% germanium level.

(v) Palladium and Platinum based alloys Examples of palladium- and platinum-based alloys according to the invention had compositions as shown in Table 6 below (all amounts being given as % by weight of the total composition):

Table 6 - Pd- and Pt-based alloys according the invention

(vi) Preparation and analysis procedures (a) Alloy make-up

For gold alloys, the constituent metals were place in a controlled atmosphere melting machine to prevent oxygen being absorbed by the molten metal. The gold and silver were initially alloyed together, followed by the copper and germanium, and then finally the metal temperature was reduced prior to adding the zinc (to reduce metal fuming) if this metal was required. Pd and Pt-based alloys were made up likewise.

It is important to note that there may be benefits in adding small amounts of other alloying constituents such as, but not limited to, indium, gallium and/or tin for the production of a casting grain. Furthermore, a grain refiner component such as silicon, iridium, boron and/or ruthenium may also be usefully considered.

(b) Fusion Process

The parts to be fused had to be clean, free from oils, greases and surface oxides. They needed to be assembled so that they fitted tightly together and they were then heated to a temperature below the melting point of the parent metals, held at that temperature for a period then removed and cooled.

Exact temperatures and times depended on the size and shape of the components being fused and also the parent metal compositions. Use of protective atmospheres may not be generally required with these germanium-containing alloys. (c) Alloy Testing

To assess the ability of each of various alloys presented in the Tables above to fuse adequately, slugs in each alloy were cast, rolled and then formed by a mandrel into a disc or washer shape. This washer was then used as an insert on a ring which was manufactured in a non-fusing precious metal composition. The two pieces were cleaned and placed into metal to metal contact and then heated to the fusing temperature and allowed to subsequently cool. To assess the fused joint strength the ring was sectioned and it was attempted to remove the insert by peeling it from the backing material. Where delamination did not occur then the fused joint was considered adequate. Where the fused joint did not peel and no edge gaps were observed then the fused joint was considered good. The formability and fusion rating results are shown in Table 7 below, and indicated as follows:

x = poor

* = adequate

*^* = good

Table 7 - Physical characteristics of alloys under trial

Alloy Colour Formability Fusability

18W1 ** X **

18W2 ** ** It is to be understood that the above description of embodiments and aspects of the invention has been by way of non-limiting examples only, and various modifications may be made from what has been specifically described and illustrated whilst remaining within the scope of the invention as defined in the appended claims.

Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of the words, for example "comprising" and "comprises", mean "including but not limited to", and are not intended to (and do not) exclude other moieties, additives, components, integers or steps.

Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith.

Claims

1 . An alloy composition comprising:

(ii) a fusibility-promoting amount of an alloying component comprising:

(iia) copper, and

(iib) germanium;

2. An alloy composition according to Claim 1 , further comprising one or more secondary alloying elements or adjunct components for imparting thereto or enhancing one or more end properties selected from: whiteness, specific desired colour, hardness, workability, ductility, flowability, precious metal content.

3. An alloy composition according to Claim 1 or Claim 2, which comprises one or more adjunct components selected from:

(a) one or more castability-enhancing components, optionally in an amount of from about 0.0 up to about 5.0 % by weight of the composition;

(b) one or more grain refining components, optionally in an amount of from about 0.0 up to about 5.0 % by weight of the composition;

(c) one or more flow- or ductility-enhancing components;

(d) one or more workability-enhancing components;

(e) one or more adjunct precious metal components;

(f) one or more impurities.

4. An alloy composition according to Claim 3, which comprises (a) one or more castability-enhancing elements selected form one or more of: indium (In), gallium (Ga) and tin (Sn).

5. An alloy composition according to Claim 3 or Claim 4, which comprises (b) one or more grain refining components selected form one or more of: silicon (Si), iridium (Ir), boron (B) and ruthenium (Ru).

6. An alloy composition according to any one of Claims 3 to 5, which comprises (c) one or more flow- or ductility-enhancing components selected from one or more of: silver, zinc.

7. An alloy composition according to any one of Claims 3 to 6, which comprises (d) one or more workability-enhancing components selected from one or more of: silver, zinc.

8. An alloy composition according to any one of Claims 3 to 6, which comprises (e) one or more adjunct precious metal components, optionally silver or a silver-containing alloy.

9. An alloy composition according to any preceding Claim, which is a gold-based alloy composition comprising:

(i) from about 33.3 up to about 76.0 % by weight of gold;

(ii) from about 1 up to about 65 % by weight of silver;

(v) optionally from about 0.0 up to about 10.0 % by weight of zinc;

10. An alloy composition according to Claim 9, wherein germanium is present in an amount of from about 2 or 3 % by weight up to about 5 or 6 % by weight.

1 1 . An alloy composition according to any one of Claims 1 to 10, which is a platinum- based alloy composition comprising:

(i) from about 95 up to about 99% by weight of platinum;

12. An alloy composition according to any one of Claims 1 to 10, which is a palladium-based alloy composition comprising:

(i) from about 95 up to about 99% by weight of palladium;

13. An alloy composition according to any one of Claims 1 to 10, which is a gold- based alloy composition comprising gold in a total amount (by weight of the total composition) which at least satisfies a particular selected or predefined carat rating for the gold alloy in question.

14. A method of making an alloy composition according to any one of Claims 1 to 13, the method comprising:

(i) heating together appropriate amounts of the essential precious metal(s) and alloying components, optionally together with any optional alloying or adjunct components, preferably under a controlled atmosphere to prevent oxidation of the said metals or other components; and

(ii) cooling the thus-formed alloy, e.g. to a working temperature appropriate to its further treatment or use in making a desired item.

15. An article formed at least in part from an alloy composition according to any one of Claims 1 to 13.

16. An article according to Claim 15, which is an item of jewellery or other decorative item.

17. An article according to Claim 15 or Claim 16, which comprises a plurality of component parts, at least one of which is joined to at least one other component part thereof, wherein each said component part is formed from an alloy according to any one of Claims 1 to 13.

18. An article according to claim 17, comprising a plurality of component parts, at least one of which is joined, optionally by means of a fusion or diffusion process, to at least one other component part thereof, wherein at least one of, optionally each of, said component parts is, or is formed from, an alloy composition according to any one of claims 1 to 13.

19. An article according to claim 17, comprising a plurality of component parts, at least one of which is joined, optionally by means of a fusion or diffusion process, to at least one other component part thereof, wherein at least one first component part thereof is, or is formed from, an alloy composition according to any one of claims 1 to 13, and at least one second component part thereof is, or is formed from, a metal or alloy other than an alloy composition according to any one of claims 1 to 13.

20. An article according to claim 19, wherein the at least one second component part comprises a precious metal or precious metal alloy other than of gold, optionally of silver.

21 . A method of making an article according to any one of Claims 16 to 20, the method comprising joining the said component parts using a fusion or diffusion process.

22. A method according to Claim 21 , wherein the method comprises fusing together the said component parts by placing the said component parts together so as to define at least one area or region of each in mutual contact with the other, and heating at least the said area or region so that the said alloy competition of each component undergoes incipient melting and a solid metal bond is formed between the two component parts upon cooling of the said areas or region.

23. A method of increasing or enhancing the fusibility of a precious metal-containing alloy, wherein the alloy comprises at least one precious metal selected from gold (Au), platinum (Pt) and palladium (Pd), together with one or more optional components and/or impurities, wherein the method comprises incorporating in the alloy a fusibility-promoting or enhancing amount of an fusibility-promoting or enhancing amount of an alloying component comprising:

(iia) copper; and

(iib) germanium.

24. An alloy composition, or a method of making an alloy composition, or an article formed at least in part from an alloy composition, or a method of making an article, or a method of increasing or enhancing the fusibility of a precious metal-containing alloy, substantially as any described herein and exemplified in any one of the Examples hereof.