Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C5/00—Alloys based on noble metals
  • C22C5/04—Alloys based on a platinum group metal
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/14—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of noble metals or alloys based thereon

Definitions

• the present invention relates to a platinum alloy and a method of production thereof.
• the present invention relates to platinum alloys that are suitable for the fabrication of ornamental articles such as rings, necklaces, bracelets, earrings, watch bands, watch bodies and other jewelry.
• the present invention relates to an ornamental article made from the platinum alloy and a method of production thereof.
• Platinum is a precious metal and is relatively expensive. In recent years platinum has come into increasing prominence as a metal used for jewelry fabrication. Platinum for fine jewelry is commonly sold in high concentrations of over 85 percent by weight.
• Platinum alloys are desirable for their neutral color when combined with gems, they are hypo-allergenic, they have high tensile strength, and a pleasurable heft due to their high-density.
• the jewelry industry uses three main classes of platinum alloys. These classes are Pt950, Pt900 and Pt850. These alloys have a platinum content of 95, 90 and 85 wt. %, respectively.
• Commercially available alloys frequently used in the fabrication of jewelry include Pt/Ir 900/100 (90 wt. % platinum and 10 wt. % iridium), PtCu950 (95 wt. % of platinum and 5 wt. % of copper) and PtCo950 (95 wt. % of platinum and 5 wt. % of cobalt).
• high platinum. content refers to platinum alloys having a platinum content equal or greater than 85 wt. %.
• U.S. Pat. No. 4,165,983 describes an alloy for fabricating jewelry containing at least 95 wt. % platinum, 1.5 to 3.5 wt. % gallium, and a balance of at least one of indium, gold, palladium, silver, copper, cobalt, nickel, ruthenium, iridium and rhodium.
• U.S. Pat. No. 5,846,352 describes a heat-treated platinum-gallium alloy for fabricating jewelry containing 1 to 9 wt. % gallium and a small amount of palladium.
• Japanese published patent application JP 61-133340 describes an alloy for fabricating jewelry consisting of 84 to 96 wt. % platinum, 1 to 10 wt.
• Japanese published patent application JP 61-034133 describes an alloy for fabricating jewelry containing 84-to 96 wt. % platinum, 0.5 to 10 wt. % cobalt, 0.5 to 10 wt. % copper and 0.01 to 0.5 Y, B, CaB mischmetal.
• low platinum content refers to platinum alloys having a-platinum content smaller than 85 wt. %.
• U.S. Pat. No. 6,048,492 describes a platinum alloy composition for use in jewelry products containing about 58.5 wt. % of platinum, 26.5 to 36.5 wt. % of palladium and 5 to 15 wt. % of either iridium, copper or ruthenium.
• U.S. Pat. No. 2,279,763 describes a ductile platinum alloy containing 10 to 80 wt. % of platinum, 12 to 90 wt. % of palladium, and 1 to 15 wt. % of ruthenium.
• WO2004/059019 A1 describes PT-base bulk solidifying amorphous alloys utilizing platinum and other ingredients and requiring the presence of phosphorous.
• the amorphous alloys described in this document are prepared by quenching the molten alloy from above the melt temperature to ambient temperatures and thus achieving a substantially (i.e. non-crystalline) structure of the alloy and requiring more than 50% to be in the amorphous state.
• a disadvantage of known low platinum content jewelry materials is that they often have inferior mechanical and physical properties compared to the high platinum content jewelry materials.
• the castability of known low platinum content jewelry materials is not as good as that of high platinum content alloys.
• the color of known low platinum content jewelry materials differs from the typical “platinum color” of Pt950 alloys that is desired by most customers of fine jewelry.
• low platinum content jewelry materials are often rejected by customers for aesthetical reasons.
• an improved low platinum content alloy composition that contains 63.01 to 69.99 wt. % of platinum, 1.5 to 10 wt. % of cobalt and 20.01 to 35.49 wt. % of copper.
• the alloys according to the present invention are particularly well suited for the fabrication of ornamental articles, such as rings, necklaces, earrings, watch bands, watch bodies and other jewelry.
• the alloys of the present invention exhibit excellent mechanical and optical properties that make them extremely suitable for the manufacturing of ornamental products such as jewelry of any kind. Due to the lower density of the alloys of the present invention it is possible to manufacture thinner, lighter constructions and castings at considerable less cost than with high platinum content alloys. (e.g. Pt850, Pt900, Pt950).
• the platinum alloys of the present invention have a lower melting range compared to known low platinum content alloys as described in, for example, U.S. Pat. No. 6,048,492. Due to their relatively low melting temperature they cast easier than previously known platinum alloys and are more energy efficient. This lower temperature alloy also allows a lower mold temperature, decreasing defect rate due to shrinkage porosity, investment cracking, inclusions, and contaminations that occur more readily at highly-elevated temperatures.
• the alloys according to the present invention are particularly well suited for the fabrication of jewelry due to their improved hardness, workability, castability, deformability, wear and abrasion properties, and resistance to corrosion.
• the platinum alloy composition of the invention appears and looks no different than 95 percent platinum, but is substantially lighter, less dense, and thus, less expensive to produce. In fact, the platinum alloy composition of the present invention has essentially the same color and appearance as PtCu950 alloy.
• the invention further relates to a method of preparing the alloys of the present invention by formulating and mixing the components of the alloy in the specified amounts and melting them together.
• the alloy may be formed into a desired shape. Such operations are many and include casting or fabricating. Some examples of fabrication can be by rolling of the alloy into a sheet, drawing a wire, molding, casting, forging, stamping or constructing the object or shape useful as a jewelry component.
• the invention also relates to a method of manufacturing an ornamental article, which comprises formulating one of the platinum alloys described above and then utilizing the alloy as a component of jewelry.
• the invention also relates to the use of such alloys in the production of ornamental articles such as jewelry. Still further, the invention relates to ornamental articles comprising such alloys.
• Still another object of the invention is to provide an improved platinum alloy composition that is suitable for use in jewelry for the mass commercial market.
• a further object of the invention is to provide an improved platinum alloy composition which is substantially lighter and less dense than conventional platinum alloy compositions.
• the platinum alloy compositions of the invention include platinum in an amount of 63.01 to 69.99 wt. %.
• the platinum content of the alloy compositions of the invention is significantly lower than that of conventional Pt850, Pt900 and Pt950 platinum alloys commonly used in the jewelry industry.
• the platinum content of this alloy is from 63.5 to 66.5 wt. % , in particular from 64 to 66 wt. %, based on the total alloy composition. If the platinum content of the alloy is smaller than about 63 wt. % the workability and stampability of the alloy decrease significantly and the alloy loses its platinum-like color. If the platinum content of the alloy is greater than about 70 wt. %, the costs for the production of the alloy increase significantly while, at the same time, the mechanical and chemical properties of the alloy do not improve significantly.
• the cobalt content of the alloys of the present invention is from 1.5 to 10 wt. %, in particular 2.0 to 8.0 wt. % or 2.0 to 6.0 wt. %, based on the total alloy composition. If the cobalt content of the alloy is smaller than about 1.5 wt. %, the mechanical properties and the workability of the alloy decrease significantly and the alloy loses its platinum-like color. If the cobalt content of the alloy is greater than about 8 wt. % the alloy becomes too hard.
• any balance in the alloys of the present invention is made up by copper.
• the platinum alloys of the present invention may further comprise 0.001 to 2 wt. % of at least one first metal selected from the group consisting of iridium and ruthenium. A combination of these elements may also be added, so long as the total amount does not exceed 2 wt. % of the alloy composition.
• Iridium and/or ruthenium can be added as metal hardeners in order to improve the hardness of the alloy, with iridium being the preferred hardener since it offers gradual hardness improvements over a wide range of concentrations, with no deterioration of alloy properties.
• the platinum alloys of the present invention may further comprise 0.001 to 2 wt. % of at least one second metal selected from the group consisting of indium and gallium. A combination of these elements may also be added, so long as the total amount does not exceed 2 wt. % of the alloy composition. Indium and gallium may be added to improve the precipitation hardening of the alloy.
• the platinum alloys of the present invention may further comprise palladium in an amount of 0.001 to 5 wt. %, preferably 0.25 to 2.5 wt. %. An addition of palladium is useful in order to vary the color of the alloy.
• the platinum alloys of the present invention may further comprise silicon in an amount of 0.001 to 0.5 wt. %, preferably in an amount of 0.1 to 0.3 wt. %. It was found that an addition of silicon in the specified amount improves the casting properties of the alloy and results in a smoother surface of the casted article. This effect is particularly desirable when the alloy of the present invention is used for the manufacture of an ornamental article where excellent casting properties are required. It was found that silicon in the amounts specified is soluble in the Pt—Co—Cu alloys of the present invention and results in the aforementioned effect. In contrast thereto, addition of silicon to high content platinum alloys generally results in inhomogeneous low melting phases and is thus undesirable.
• the platinum alloys of the present invention may further comprise zirconium in an amount of 0.001 to 0.5 wt. %, preferably in an amount of 0.1 to 0.3 wt. %. It was found that an addition of zirconium in the specified amount improves the workability of the alloys.
• the total amount of other elements present in the platinum alloy besides Pt, Cu, and Co does not exceed about 10 wt. %, preferably about 7.5 wt. %, even more preferably about 5 wt. %, and most preferably about 4 wt. %, based on the total weight of the platinum alloy.
• the platinum alloy of the present invention may be present in a crystalline state or in an amorphous state.
• the platinum alloy of the present invention is present in a substantially crystalline state.
• substantially crystalline state means that the platinum alloy is greater than fifty percent crystalline by volume.
• the platinum alloy is at least about ninety percent crystalline by volume, more preferably at least ninety five percent crystalline by volume and most preferably about one hundred percent crystalline by volume.
• the addition of phosphorous to the alloy of the present invention is not particularly preferred since it is not desired to produce an amorphous alloy. Therefore, if phosphorous is added to the platinum alloy of the present invention, such an addition should be done in moderate amounts.
• the amount of phosphorous contained in the platinum alloy of the present invention is less than 4.2 wt. %, more preferably less than 3.4 wt. %, even more preferably less than 2.3 wt. % and most preferably less than about 1.5 wt. % of phosphorous, based on the total alloy composition.
• the platinum alloy of the present invention contains less than about 2.0 wt. % and more preferably less than about 1 wt. % of phosphorous, based on the total alloy composition.
• the alloy can include any one of a number of property enhancing agents, including a deoxidizing agent, grain reducing agent, a viscosity decreasing agent or a color variation agent.
• the number and amount of the other additives may vary depending on the desired mechanical properties of the alloy and can readily be determined by a person of ordinary skill in the art by means of routine experiments.
• the platinum alloy consists essentially of, apart from impurities
• the alloys of the present invention exhibit excellent mechanical and physical properties such as tensile strength, Vickers hardness and elongation at break.
• the tensile strength of the platinum alloys of the present invention is in the range of 450 to 800 N/mm 2 .
• the Vickers hardness of the platinum alloys of the present invention, measured at softened state, is in the range of 130 to 210 HV10.
• the elongation at break of the platinum alloys of the present invention is at least about 20%.
• a further advantage of the present invention is that the color tone of the platinum alloy corresponds essentially to the platinum white color tone of a PtCu950 alloy, which is aesthetically very appealing.
• the alloys of the present invention may be prepared by conventional alloying methods that are well known in the art.
• the preparation of the alloy generally includes the step of melting platinum, cobalt and copper and any other component in the specified amounts.
• the method may further include the step of hardening the alloy by cold working or heat treatment.
• the method may include the steps of annealing and then quenching the alloy, before hardening the alloy.
• the alloys are usually cast from melts under a shielding gas and then shaped. After shaping, they may be subjected to heat treatment, possibly under a shielding gas, to improve their mechanical properties.
• a high temperature melting process is carried out. This can achieved using induction melting equipment, as is well known in the art. At all times, extreme care should be exercised in order to limit metal contamination, as platinum is easily contaminated by many elements routinely present in the environment. Such care can be achieved by melting the metals in either a vacuum or an inert gas atmosphere, by preventing contact with other metals, and by preventing mixing with silica-based products.
• the platinum alloy is preferably melted and blended together by induction heating in appropriate crucibles for platinum alloys. After melting, the alloy can be poured through water to create grain-shot and can then be dried, weighed and used for casting.
• the components of the inventive composition are preferably melted in a silica crucible (for small, fast melts) or a zirconium oxide (for large, slow melts) crucible in an induction oven. It is preferred to use a vacuum or inert gas in the melting process and to place all components of the alloy composition in the crucible at the same time.
• the molten metals should preferably be “turned” (utilizing medium to low frequency induction fields) in order to obtain an appropriate mixing of the metals.
• the resulting alloy nugget elements can be subjected to cold rolling and/or annealing in order to improve mechanical qualities of the mix. Thereafter, the mixed metal composition can optionally be re-melted as before, and a shot or plate be produced.
• the preparation of the platinum alloys of the present invention can further comprise an annealing step.
• Annealing can be carried out either in a furnace or with a torch, as is well known in the art.
• the annealing temperature depends on the platinum content and the melting point of the alloy and will readily be determined by a person of ordinary skill by routine experiments.
• the annealing is done in a furnace that is atmosphere controlled with shielding gas.
• the shielding gas can be any of the non-oxidizing inert gasses, such as argon, nitrogen, or mixtures thereof; anti-oxidizing gasses such as hydrogen, carbon monoxide, or “forming” or “cracked ammonia” gas (nitrogen with a few percent of hydrogen).
• the piece can also be protected from oxidation by enveloping them with commercially available heat-treating wraps.
• the alloys can be used for a wide variety of jewelry components, such as rings, clasps, spring parts, even compression-spring settings for gemstones, and the like.
• the alloys can be repeatedly annealed and heat-treated/age-hardened, if desired.
• the term “age-hardening” is essentially synonymous with the term “precipitation hardening” which results from the formation of tiny particles of a new constituent (phase) within a solid solution. The presence of these particles create stress within the alloy and increase its yield strength and hardness. See, B. A. Rogers, “The Nature of Metals”, p. 320 (Iowa State University Press, 1964); H. W. Polock, “Materials Science and Metallurgy”, p. 266 (Reston Pub. Inc. 1981) and “The Metals Handbook”, pp. 1-2 (Am. Soc'y Metals, 1986).
• the alloys can be worked by standard jewelry-making techniques: they can be rolled, drawn, soldered to, shaped, bent, stamped, etc. These alloys can be applied to a variety of designs for springs, gemstone mountings in rings, pendants, bracelets, chains, precious metal art objects, and the like.
• the ornamental product can be made by casting.
• the hardness of the alloys may also be further increased by heat treatment.
• the heat treatment may be carried out in a range of from 300 to 950° C. with a suitable value being in the range of from 600 to 950° C., and typically of the order of 800° C.
• the alloys can be softened by standard annealing procedures, typically at about 1000° C. to 1030° C., or higher.
• the alloys may be used in the form of wire, sheet or other manufactured article and may be given intricate shapes and forms due to their great hardness combined with great ductility.
• the alloys according to the present invention can be used, for example, in the fabrication of wedding bands.
• weddings bands are generally produced by sawing blanks from tubes and then further working the blanks by suitable measures, such as milling, drawing, forging, and polishing.
• Other jewelry articles that can be manufactured from the alloys according to the present invention include, for example, rings, necklaces, bracelets, earrings, bangles, stickpins, watch bands, watch bodies, wristwatches, tooth picks as well as other decorative articles such as ballpoint pens, letter openers, pocket knife handles, and the like.
• An alloy of the composition as specified in the following table was weighted and molten under vacuum in a zirconia crucible in a vacuum induction furnace at a temperature of 1480 to 1500° C. to obtain a homogeneous melt.
• the alloy was cast into a steel mold to form blocks having a dimension of 20 ⁇ 140 mm.
• the melting range was determined by measuring the cooling curve of the alloy with a Degussa resistance furnace HR1/Pt/PtRH10 equipped with a Linseis thermo element and a temperature-time-plotter L250.
• the Vickers hardness was determined according to DIN 50133 using a Wolpert V-Testor 4521 instrument.
• the tensile strength, elongation at break and yield stress were determined according to DIN 50145 using a Zwick Z010 instrument. The color was determined visually.
• a commercially available Pt/Cu 950/50 alloy was weighted and molten under vacuum in a zirconia crucible in a vacuum induction furnace to obtain a homogeneous melt.
• the alloy was cast into a steel mold to form blocks having a dimension of 20 ⁇ 140 mm.
• EXAMPLE 2 EXAMPLE Composition Pt 65 wt. % Pt 65 wt. % Pt 95 wt. % Cu 31.5 wt. % Cu 31.25 wt. % Cu 5 wt. % Co 3.5 wt. % Co 3.5 wt. % Si 0.25 wt.
• the experimental results indicate that the alloy according to the present invention exhibits superior casting, wear and abrasion properties when compared to a conventional Pt/Cu 950/50 alloy.
• the results of Example 1 further indicate that the castability of the alloy of the present invention is enhanced by addition of small amounts of silicon.
• the, experimental results indicate that the forming properties and the color tone of the alloy according to the present invention are comparable to those of a conventional Pt/Cu 950/50 alloy.
• the alloy according to the present invention was found to be an excellent material for the manufacture of jewelry articles such as rings, bracelets or necklaces

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