RU2439181C1 - Jewellery alloy based on platinum of rate 950 - Google Patents

Abstract

FIELD: metallurgy. ^ SUBSTANCE: platinum-based jewellery alloy containing the following, wt %, is proposed: platinum 95.0-95.5, cobalt 1.5-3.5, gallium 0.5 - less than 1.0, copper is the rest. Jewellery alloy can be used at manufacture of various pieces of rate 950, mainly by micro casting on molten models. ^ EFFECT: alloy has good casting properties and is more resistant to pore formation. ^ 1 ex

Description

The invention relates to the field of metallurgy of precious metals, in particular to platinum-based alloys used for the manufacture of jewelry, mainly by investment casting.

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. In Russia, only jewelry platinum alloys no higher than 950 samples are standardized and produced.

In particular, a jewelry alloy based on sample platinum 950 containing wt. %:

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. 28.05.99).

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

The analog alloy has a beautiful appearance, it is mainly used for making rings by stamping methods. Relatively low casting properties and a high temperature range of melting complicate its use for microwashing jewelry using investment casting.

The prior art jewelry alloy based on platinum, containing, wt.%: Platinum 84.0-96.0, gallium 1.0-10.0, copper 0.5-10.0, manganese and / or cobalt 0, 01-5.0 [JP 61133340 A (TANAKA KIKINZOKU), C22C 5/04, 06/20/1986].

This alloy can be used for microcasting in jewelery, is the closest in composition to the claimed one and adopted as a prototype.

The prototype alloy is characterized by relatively high consumer qualities. The disadvantages of this alloy include the fact that in some cases its use in microwelding leads to the formation of scattered gas porosity, which is formed at the stage of casting semi-finished products and is preserved from the initial workpieces to finished products.

The task to which the proposed technical solution is directed is to develop the composition of a jewelry alloy based on platinum 950, which has good casting properties and is less prone to pore formation.

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

platinum 95.0-95.5 cobalt 1,5-3,5 gallium 0.5-less than 1.0 copper rest.

The presence in the alloy of gallium and cobalt in combination with copper in the stated concentration limits avoids pore formation during casting and crystallization of the melt, provides its good casting properties.

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

The presence of gallium and cobalt in the alloy in the indicated concentration ranges along with copper is optimal.

A decrease in the concentration in the alloy of both cobalt to less than 1.5% and gallium - less than 0.5% is highly undesirable, since it leads to the need to increase the casting temperature and worsens the casting properties of the alloy.

When the content in the inventive alloy of cobalt is more than 3.5%, or gallium 1.0% or more, the alloy acquires an undesirable shade - yellowness appears and the gloss deteriorates.

Example

Obtaining a jewelry alloy based on platinum 950 was carried out by direct fusion of pure components, namely, platinum refined in ingots (PLA-0 with a purity of 99.98%); cobalt in K-0 grade plates; gallium (99.95% purity, supplier of Cavern-Holding CJSC) and copper in granules of the MO brand.

Linn loaded a charge composed of the calculated number of components, namely platinum - 333.0 g into a melting crucible made of zirconia of the Platicast 5000 VAC induction melting plant of Linn company; cobalt - 6.9 g; gallium - 3.5 g, copper - 6.9 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 349.5 g (or 99.8% 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 95.11% platinum; 1.95% cobalt; 0.97% gallium, the rest is copper.

The resulting platinum-based jewelry alloy corresponds to 950 samples, has a beautiful platinum color tone sufficient for microhardness for finished cast jewelry (1900 MPa in molten state).

Metallographic analysis of thin sections showed that the microstructure of the cast alloy is represented by equiaxed grains, the size of which varies in the range of 60-70 microns. In the alloy, there is practically no chemical heterogeneity and porosity. In terms of gloss, the alloy, although slightly inferior to slightly pure platinum, is superior to the prototype alloy (the claimed alloy has a gloss value of L = 87.9 versus 87.5 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 used for the manufacture of various jewelry using the investment casting method. Good casting properties of the alloy and the absence of porosity in the products are noted.

Claims (1)

A platinum-based jewelry alloy containing cobalt, gallium and copper, characterized in that it contains components in the following ratio, wt.%:
platinum 95.0-95.5 cobalt 1,5-3,5 gallium 0.5 less than 1.0 copper rest