RU2439180C1 - Jewellery alloy based on platinum - Google Patents

Abstract

FIELD: metallurgy. ^ SUBSTANCE: invention refers to alloys based on platinum, which can be used for manufacture of jewelleries of rate 990. Platinum-based jewellery alloy containing the following, wt %, is proposed: platinum - 99.0-99.5, iridium - 0.1-0.7, cobalt - 0.1-0.5, and gallium is the rest. ^ EFFECT: obtaining platinum-based jewellery alloy allowing to use it at manufacture of jewellery of rate 990 by means of micro casting on molten models, and by using plastic deformation at manufacture of chains, including by machine method. ^ 1 ex

Description

The invention relates to the field of metallurgy of noble metals, in particular to platinum-based alloys used for the manufacture of jewelry, mainly for the manufacture of rings, chains and microcasting of investment casting products.

Platinum-based alloys are widely used in jewelry production due to their high consumer qualities. They have a beautiful appearance, corrosion resistance to external factors, combine perfectly with precious stones, are well processed.

Recently, high-quality platinum jewelry items, in particular, 990 and 950 samples, have been in greatest demand on the world market. At the same time, until recently, only jewelry platinum alloys no higher than 950 samples were standardized and produced in Russia.

In particular, a jewelry alloy based on sample platinum 950 is known, containing by weight,%:

- platinum - 95.0-95.5

- iridium - the rest

(Interstate standard GOST 30649-99. "Alloys based on precious metals jewelry. Stamps. Interstate Council for Standardization, Metrology and Certification. Minsk, p. 4, publ. 28.05.99).

This alloy is the closest in composition to the claimed and adopted as a prototype.

The prototype alloy can be used in the manufacture of jewelry 950 samples, has a beautiful appearance with gloss, is well polished and has a relatively high consumer quality, especially when used for stamping and micro casting for investment casting. The main disadvantages of this alloy include:

- the impossibility of its use in the manufacture of products 990 samples;

- insufficient stability of the physico-mechanical properties of semi-finished products (rods and wires) obtained from this alloy, which reduces the yield when used for the manufacture of chains by machine method.

All this complicates its use in the manufacture of jewelry oriented to the world market.

The task to which the proposed technical solution is directed is to develop the composition of a platinum-based jewelry alloy that can be used in the manufacture of high-quality 990 samples, using both investment casting methods and plastic deformation in the manufacture of chains, including machine ones method.

The technical result is achieved by the fact that a platinum-based jewelry alloy containing iridium additionally contains cobalt and gallium in the following ratio of components, wt.%:

Platinum - 99.0-99.5

Iridium - 0.1-0.7

Cobalt - 0.1-0.5

Gallium - the rest.

Common to the known and claimed platinum-based jewelry alloys is the presence of iridium in the alloy.

The platinum content in the alloy is due to the need to provide the required sample for high-grade jewelry (990 samples).

The presence of iridium in the alloy in the specified concentration range is optimal and contributes to the formation of sufficiently fine grains during crystallization of the melt.

The inclusion of additional alloying components in the composition of the alloy (cobalt and gallium) lowers the melting point of the alloy, increases its casting properties, leads to an improvement in the structure formed during crystallization of the melt, subsequent heat treatment and plastic deformation, and increases its strength and technological properties.

The introduction of cobalt and gallium into the alloy within the stated concentration limits, in combination with platinum and iridium, provides the alloy with a beautiful color characteristic of platinum, sufficient strength for jewelry, structural stability and physico-mechanical characteristics both along the length of the wire being made and along its cross section, which allows the use of this alloy for the manufacture of both rings and chains.

Exceeding the content of alloying components (both cobalt and gallium) above the stated limits is impractical, since it leads to an increase in the unwanted yellowness of the alloy in the yellow-blue color region of the spectrum, and also increases the likelihood of gas porosity in the castings.

Example.

The jewelry alloy based on platinum 990 was obtained by direct fusion of pure components, namely, platinum refined in ingots (PLA-0, 99.98% purity); powder-refined iridium (99.95% pure); cobalt in the plates, grade K-0; gallium (99.95% purity, supplier of Laverna-Holding CJSC).

Linn loaded the charge composed of the calculated amount of components, namely platinum - 347.0 g into the melting crucible made of zirconia of the Platicast 5000 VAC induction melting plant of Linn company; iridium - 1.1 g; cobalt - 1.1 g; gallium - 1.1 g.

The installation was evacuated to a residual pressure of 30 Pa and then filled with an inert gas, argon. The mixture was melted in argon medium. After the components were completely melted, the obtained melt was held for 30–40 s and the melt was centrifugally drained into a massive graphite mold.

After cooling, an ingot of the obtained alloy weighing 350.0 g (or 99.9% of the load) was removed from the mold.

After mechanical cleaning of the surface, the obtained ingot was tested, the sample was subjected to chemical analysis.

Chemical analysis of the sample showed that the obtained platinum-based jewelry alloy contains 99.10% platinum; 0.31% iridium; 0.30% cobalt; the rest is gallium.

The obtained jewelry alloy based on platinum corresponds to 990 samples, has a beautiful, characteristic color for platinum, sufficient microhardness for jewelry making (1100 MPa in the cast state).

The metallographic analysis of thin sections showed that the microstructure of the obtained cast alloy is represented by grains formed as a result of the process of collective recrystallization. The grain boundaries are even, with an angle at the junction of about 120 ° C. The grain size varies between 100-250 microns, which indicates the completion of diffusion processes associated with the formation of a homogeneous grain structure in this alloy. The color measurements of the alloy showed that it is slightly inferior in terms of brightness to pure platinum (L = 88.9 versus 89.6 for pure platinum), similar in color to it in the red-green and yellow-blue spectral regions.

The resulting alloy was forged into a bar, which was used for the manufacture of experimental batches of various jewelry, both by stamping methods, and by rolling and drawing wires for machine chaining.

Claims (1)

A platinum-based jewelry alloy containing iridium, characterized in that it additionally contains cobalt and gallium in the following ratio of components, wt.%:
Platinum 99.0-99.5 Iridium 0.1-0.7 Cobalt 0.1-0.5 Gallium rest