RU2349659C1 - Jewelry alloy of white color on basis of palladium - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: jewelry alloy of white color on the basis of palladium contains components in a following ratio, wt %: palladium - 90.0-95.5, cobalt - 3.0-7.0, iridium - 0.03-0.5, copper - the rest. Invention is directed to creation of alloy for manufacturing of products of 950 and 900 hallmarks by method of micro- investment casting.

EFFECT: reduction of alloy hardness.

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Description

The invention relates to the field of metallurgy of precious metals, in particular to palladium-based alloys used for the manufacture of jewelry, mainly for micro-casting of 950 and 900 samples.

Palladium-based alloys are widely used in jewelry production due to their high consumer qualities that bring them closer to platinum products: beautiful appearance, corrosion resistance to external factors, good polishability, the ability to produce alloys with different color shades, good machinability, including methods microlithing, relatively low cost.

Highly demanding palladium jewelry products, in particular 950, 900 and 850 samples, have been in greatest demand in the world market lately. At the same time, in Russia until recently, only jewelry palladium alloys no higher than 850 samples were standardized and produced.

In particular, a white-colored jewelry alloy based on palladium 850 samples is known, which contains, by weight,%:

palladium 85.0 silver 13.0 nickel 2.0

(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).

The disadvantages of this alloy include: the inability to use it in the manufacture of high-grade (900 and 950 samples) jewelry, relatively low casting properties, and a tendency to tarnish under certain environmental conditions. All this complicates its use in the manufacture of jewelry oriented to the world market.

The closest in composition to the claimed is a jewelry alloy based on white palladium, containing by weight,%:

palladium 85.0-90.0 nickel 5.5-12.0 copper 1.5-2.0 zinc 2.0-2.5 indium 1.0-1.5

[RF patent No. 2244762, declared. November 10, 2003, reg. Application No. 2003132834/02, publ. January 20, 2005 Authors: Ermakov A.V., Gorskikh T.S., Syutkina V.I.]

This alloy is adopted as a prototype.

The prototype alloy has a beautiful white color with gloss, resembles platinum, is well polished and has relatively high consumer qualities. The main disadvantages of this alloy include:

- the impossibility of its use in the manufacture of products 950 samples;

- high hardness (N _V = 160 kgf / mm ² in a soft state), which creates a number of difficulties in the initial manual processing of cast jewelry and their turboganting.

In addition, the high nickel content in the alloy (up to 12 wt.%) Is a negative factor that impedes the sale and certification of such jewelry in the markets of the European Union, where in recent years a number of restrictions have been adopted regarding the nickel content in jewelry.

The task to which the proposed technical solution is directed is to develop the composition of a white-colored jewelry alloy based on palladium, which can be used in the manufacture of 950 and 900 samples by the microfusion method, which has lower (compared to the prototype) hardness and does not contain nickel .

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

palladium 90.0-95.5; cobalt 3.0-7.0; iridium 0.03-0.5; copper rest.

Common to the known and claimed jewelry alloys based on palladium is the presence of copper in the alloy.

The palladium content in the alloy is due to compliance with the required fineness of jewelry (950 samples or 900 samples).

The introduction of cobalt into the alloy within the stated concentration limits, in combination with palladium, copper and iridium, provides the alloy with a beautiful white color, similar in tone to platinum alloy products, and gives high casting properties.

Exceeding the cobalt content of more than 7% in the inventive alloy is undesirable, as it leads to an increase in the hardness of the alloy and, consequently, to an increase in labor costs in the manufacture of products by microfusion on the stages of primary manual processing, tumbling and polishing of jewelry.

A decrease in the cobalt content in the alloy below 3% is undesirable, since it leads to a decrease in the fluidity of the alloy and the deterioration of its casting properties.

The addition of iridium to the alloy, within the stated limits, plays the role of an alloy modifier, providing jewelry during microfusion with a fine-grained structure and a smooth and clean surface.

An increase in the iridium content in the alloy above 0.5% is impractical, since it leads to an increase in the refractoriness and hardness of the alloy, and increases the cost of production.

The copper content in the alloy in the declared amount is optimal, since it reduces the melting point of the alloy, reduces the crystallization interval and, in combination with the stated amounts of palladium, cobalt and iridium, provides the required decrease in alloy hardness and the preservation of high casting properties.

An increase in the copper content in the alloy is impractical, since it leads to a deterioration in the white color tone of jewelry.

Alloy Preparation Example

The preparation of a white palladium-based jewelry alloy was carried out by fusing the components in two stages.

At the first stage, copper-iridium ligature was obtained by direct fusion.

For this purpose, the calculated amount of copper and iridium was loaded into the melting crucible of the UIPV-63-10-0.01 induction vacuum unit manufactured by RELTEC. To obtain the ligature, 1500.0 g of M-00 grade copper and 115.0 g of Ir-0 grade iridium were used.

The installation was closed with a lid, the furnace chamber was evacuated using a mechanical vacuum pump to a residual pressure of 60 Pa and then filled with an inert gas, argon. The mixture was melted in argon medium. After complete melting of the components, the obtained melt was held for 30 minutes and drained into a graphite mold.

After cooling, an ingot of the obtained ligature in the form of a squared bar (weighing 1614.5 g or 99.97% of the load) was removed from the mold. The casting at the top had a small shrink shell.

After mechanical cleaning of the surface, the obtained master alloy was tested (a chip sample was taken using a milling machine).

Chemical analysis of the sample indicated that the resulting ligature contains 7.10 wt.% Iridium, the rest is copper.

The resulting ligature ingot was cut into pieces and then used for the second stage of obtaining a palladium-based jewelry alloy.

For this purpose, the calculated amount of the obtained copper-iridium ligature (42.2 g), 93.0 g of K-0 and 2666 cobalt were loaded into a melting crucible made of zirconium dioxide of the induction vacuum unit UIPV-63-10-0.01 of the RELTEC company , 0 g of palladium (99.95% pure).

The installation was evacuated to a residual pressure of 60 Pa and then filled with an inert gas, argon. The mixture was melted in argon medium. After the components were completely melted, the resulting melt was held for 5 minutes and drained into a massive copper mold.

After cooling, an ingot of an alloy in the form of a squared bar weighing 2799.8 g (or 99.95% 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 palladium-based jewelry alloy contains 95.18% palladium, 3.3% cobalt, 0.10% iridium, the rest is copper.

The density of the alloy was measured (11.73 g / cm ³ at 20 ° C) and the hardness of the alloy in the annealed state (N _V = 103.0 kgf / mm ² ) and in the cured state (N _V = 183.2 kgf / mm ² )

The obtained jewelry alloy based on palladium corresponds to 950 samples, has a light tone with a cast tint reminiscent of platinum, less than 1.5 times hardness (in comparison with the prototype) and does not contain nickel. The alloy was used in the manufacture of jewelry by the method of investment casting by investment casting and provided products with a smooth and clean surface. The microhardness of the cast products was N _V = 114.2 kgf / mm ² , which is the optimal value for finishing surface treatment.

Claims (1)

A white palladium-based jewelry alloy containing copper, characterized in that it additionally contains cobalt and iridium in the following ratio of components, wt.%:
palladium 90.0-95.5 cobalt 3.0-7.0 iridium 0.03-0.5 copper rest