RU2528293C1 - Platinum-based jewellery alloy - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: proposed alloy comprises copper, tungsten, iridium at the following ratio of components, wt %: platinum - 95.0-95.5, tungsten - 0.01-3.0, iridium - 0.01-1.0, copper making the rest.

EFFECT: more stable physical and mechanical properties of jewellery articles on the basis of 950-rate platinum.

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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 of 990 and 950 samples are in greatest demand on the world market.

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

platinum 95.0-95.5 copper rest

(Interstate standard GOST 30649-99 "Alloys based on precious metals jewelry. Stamps. Interstate Council for Standardization, Metrology and Certification. Minsk, p. 4, publ. 05/28/99).

This alloy is widely used in jewelry and can be adopted as an analogue to the claimed alloy.

An analog alloy is used mainly for the manufacture of rings by stamping methods and, to a lesser extent, for chain linking. Insufficient surface hardness and low wear resistance of products made from this alloy complicate its widespread use for the manufacture of jewelry chains.

The prior art jewelry alloy based on platinum, containing, wt.%: Platinum 84.0-96.0, copper 1.0-15.0, molybdenum and / or tungsten 0.1-7.0 [JP 61- 186438 A (TANAKA KIKINZOKU KOGYO KK) C22C 5/04, 08/20/1986].

This alloy can be used both for microcasting in jewelery, and in the manufacture of chains, is the closest in composition to the inventive alloy and adopted as a prototype.

The prototype alloy has a beautiful appearance, is characterized by relatively high consumer qualities, including increased surface hardness and wear resistance of products made from it. The main disadvantage of this alloy is the lack of stability of its physicomechanical properties, caused by the frequent manifestation of heterogeneity of the structure, which is formed at the stage of casting semi-finished products and is preserved from the initial workpieces and up to finished products.

The task to which the proposed technical solution is directed is to develop the composition of a jewelry alloy based on sample 950 platinum, which has increased stability of physical and mechanical properties and is not inferior to the prototype alloy in appearance (in terms of gloss).

The technical result is achieved in that the platinum-based jewelry alloy containing copper and tungsten additionally contains iridium in the following ratio of components, wt.%:

platinum 95.0-95.5 tungsten 0.01-3.0 iridium 0.01-1.0 copper rest

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

The platinum content in the alloy is due to the need to provide the required 950 samples for the final jewelry.

The inclusion of an additional component, iridium, in the alloy leads to an improvement in the structure formed during crystallization of the melt. Iridium is an effective alloy modifier and, together with tungsten, positively affects the formation of a fine-grained homogeneous structure, increasing the stability of the physicomechanical properties of the alloy, which favorably affects the results of its subsequent heat treatment and the nature of plastic deformation, and increases its strength and technological properties.

The presence of iridium, tungsten and copper in the alloy in the specified ratio of the components is optimal. Exceeding the iridium content of more than 1% in the inventive alloy is impractical, since it leads to an undesirable increase in the refractoriness and hardness of the alloy.

A decrease in the iridium content in the alloy below 0.01% is also undesirable, since it leads to a decrease in this case of the modifying effect of iridium on the structure of the crystallizing melt

Example

Obtaining a jewelry alloy based on platinum 950 samples was carried out by direct fusion of the following components: refined ingot platinum (PLA-0, 99.98% purity); tungsten powder (99.95 %% purity, supplier of Laverna Holding CJSC); copper-iridium ligatures in granules (iridium content - 2.22%, the rest is copper).

Linn loaded a charge composed of the calculated amount of components into the melting crucible made of zirconia of the Platicast 5000 VAC induction melting plant of Linn company, namely: platinum - 333.0 g; tungsten - 0.5 g; copper-iridium ligature - 16.7 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 complete melting of the components, the obtained melt was held for 30–40 s and centrifugal melt was drained into a massive graphite mold.

After cooling, an ingot of the obtained alloy weighing 349.4 g (or 99.77% 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 95.30% platinum; 0.10% iridium; 0.08% tungsten; the rest is copper.

The obtained platinum-based jewelry alloy corresponds to 950 samples, has a beautiful color characteristic of platinum, sufficient for the manufacture of jewelry microhardness (1735 MPa in the cast state).

The metallographic analysis of thin sections showed that the obtained cast alloy throughout the volume has an equiaxed fine-grained structure with a grain size in the range of 35–40 μm, which is due to the combined modifying effect of iridium and tungsten. In the alloy, there is practically no chemical heterogeneity and porosity. In terms of brilliance, the alloy is slightly inferior to pure platinum, but slightly superior to the prototype alloy (the claimed alloy has a value of L = 87.9 against 87.8 for the prototype alloy). In the red-green and in the yellow-blue region of the spectrum, the claimed alloy in color is close to pure platinum.

The resulting alloy was forged into a bar, which was then used to make jewelry chains "Gourmet" and "Rollo", with high yields. The alloy showed the stability of physico-mechanical properties both along the length of the rod and along its cross section.

Claims (1)

A platinum-based jewelry alloy containing copper and tungsten, characterized in that it additionally contains iridium in the following ratio of components, wt.%:
platinum 95.0-95.5; tungsten 0.01-3.0; iridium 0.01-1.0; copper rest.