WO2025040987A1 - Use of a silver alloy for the realization of precious objects by means of a processes based on sinterization, as well as the precious object obtained therewith - Google Patents

Use of a silver alloy for the realization of precious objects by means of a processes based on sinterization, as well as the precious object obtained therewith Download PDF

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Publication number
WO2025040987A1
WO2025040987A1 PCT/IB2024/057598 IB2024057598W WO2025040987A1 WO 2025040987 A1 WO2025040987 A1 WO 2025040987A1 IB 2024057598 W IB2024057598 W IB 2024057598W WO 2025040987 A1 WO2025040987 A1 WO 2025040987A1
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Prior art keywords
weight
silver alloy
comprised
further element
silver
Prior art date
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PCT/IB2024/057598
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French (fr)
Inventor
Andrea FRISO
Riccardo BERTONCELLO
Mattia LAGO
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Legor Group S.P.A.
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Publication of WO2025040987A1 publication Critical patent/WO2025040987A1/en

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C1/00—Making non-ferrous alloys
    • C22C1/04—Making non-ferrous alloys by powder metallurgy
    • C22C1/0466—Alloys based on noble metals
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
    • B22F1/05—Metallic powder characterised by the size or surface area of the particles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F10/00—Additive manufacturing of workpieces or articles from metallic powder
    • B22F10/10—Formation of a green body
    • B22F10/14—Formation of a green body by jetting of binder onto a bed of metal powder
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F10/00—Additive manufacturing of workpieces or articles from metallic powder
    • B22F10/10—Formation of a green body
    • B22F10/18—Formation of a green body by mixing binder with metal in filament form, e.g. fused filament fabrication [FFF]
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
    • B22F3/10—Sintering only
    • B22F3/1017—Multiple heating or additional steps
    • B22F3/1021—Removal of binder or filler
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
    • B22F3/22—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces for producing castings from a slip
    • B22F3/225—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces for producing castings from a slip by injection molding
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B33—ADDITIVE MANUFACTURING TECHNOLOGY
    • B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
    • B33Y10/00—Processes of additive manufacturing
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B33—ADDITIVE MANUFACTURING TECHNOLOGY
    • B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
    • B33Y70/00—Materials specially adapted for additive manufacturing
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B33—ADDITIVE MANUFACTURING TECHNOLOGY
    • B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
    • B33Y80/00—Products made by additive manufacturing
    • 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
    • C22C5/06—Alloys based on silver
    • 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
    • C22C5/06—Alloys based on silver
    • C22C5/08—Alloys based on silver with copper as the next major constituent

Definitions

  • the present invention generally relates to the technical field of jewellery, and it relates to the use of a silver alloy for manufacturing precious objects by means of a process based on sintering, as well as a precious object thus obtained.
  • Binder Jetting also abbreviated with “BJ” is used to indicate an additive manufacturing process in which the powder is selectively soaked, after it has been spread a surface, with a binder in multiple layers to obtain a semi-finished product, called raw workpiece. Subsequently, the obtained raw workpiece should be densified through a thermal process referred to as sintering.
  • Metal Injection Moulding also abbreviated with “MIM” is used to indicate a manufacturing process starting from powders where the metal powder is mixed with an appropriate binder and then injected into a pressing machine to obtain a semi-finished product, referred to as raw workpiece. The raw workpiece thus obtained is then densified by sintering.
  • Lithography-based Metal Manufacturing also abbreviated with “LMM” is used to indicate a manufacturing process starting from powders based on the selective lithographic polymerisation of a binder to obtain a semifinished product, referred to as raw workpiece.
  • the workpiece thus obtained is then densified by sintering.
  • FDM Fusion Modelling
  • the expression "Semi-finished product” also referred to as “raw workpiece” is used to indicate an object resulting from the mould or injection process, consisting of a mixture of metal powder and binder, which already has the shape of the end object, but with lower mechanical strength than the end workpiece, which will result from the sintering process.
  • the expression "Debinding" is used to indicate an initial step of the sintering process, in which the polymeric binder required to hold the mass of metal powder together after the moulding, is removed.
  • the expression "Sintering” is used to indicate a process that is thermally activated due to which semi-finished product consisting of a mixture of metal powders and a binder is densified until there is obtained a compact solid object, by removing the binder and thermally or thermal-mechanically joining the powder particles.
  • the expression "consists" or its derivatives associated with a composition or product of interest made up of two or more components is used to indicate, unless indicated otherwise, that the product or composition in question is entirely made up of the listed components, that is the total of the listed components amount to 100% of the composition or of the product, except for the usual impurities generally present in that product or composition.
  • precious object or its derivatives is used to indicate, unless indicated otherwise, a finished product, of any shape and size, resulting from the processing an alloy in a predefined manner.
  • the expression "percentage by weight” or “% by weight” or its derivatives is used to indicate, unless indicated otherwise, the percentage by weight of a component of interest with respect to the total weight of the composition in which the component of interest is included.
  • binder jetting or metal binder jetting which enables, starting from a CAD drawing uploaded on a special printer, to obtain a large amount of semi-finished products called "raw workpieces" within a short time and with ultra-high repeatability due to the speed of the printer, then followed by a sintering process, which can also be carried out on a large number of workpieces.
  • a sintering process which can also be carried out on a large number of workpieces.
  • optimised process the workpieces that are obtained are characterised by good surface quality and controlled dimensional tolerances.
  • the Japanese patent application JP2019-007057 discloses a silver alloy which is incompatible with sintering processes aimed at obtaining high densification precious objects, in particular with the Binder Jetting technique.
  • An object of the present invention is to at least partly overcome the drawbacks illustrated above, by using a silver alloy in form of powder for manufacturing precious objects through a process which comprises the following steps: a) adding a binder, preferably polymeric, to the silver alloy for providing a semifinished product; b) sintering said semi-finished product.
  • the silver alloy may consist of:
  • first further element that is one or more first elements, selected from the group consisting of: Tin (Sn), Gallium (Ga), Copper (Cu), Palladium (Pd), Platinum (Pt), Zinc (Zn), Silicon (Si); and the usual impurities.
  • the percentages by weight mentioned above are percentages by weight with respect to the total weight of the alloy.
  • the at least one first further element (C) is tin (Sn )
  • the at least one first further element (C) is Gallium (Ga)
  • it may be present in the silver alloy in a range comprised between 0.01% by weight and 4.00% by weight, and preferably comprised between 0. 01% by weight and 2.00% by weight;
  • the at least one first further element (C) is Copper (Cu), it may be present in the silver alloy in a range comprised between 0.01% by weight and 6.00% by weight;
  • the at least one first further element (C) is Palladium (Pd), it may be present in the silver alloy in a range comprised between 0.01% by weight and 5.00% by weight;
  • the at least one first further element (C) is Platinum (Pt), it may be present in the silver alloy in a range comprised between 0.01% by weight and 4.00% by weight;
  • the at least one first further element (C) is Zinc (Zn), it may be present in the silver alloy in a range comprised between 0.01% by weight and 1.00 % by weight;
  • the at least one first further element (C) is Silicon (Si), it may be present in the silver alloy in a range comprised between 0.01% by weight and 0.20 % by weight.
  • the at least one first further element (C) mentioned above may be Tin (Sn).
  • Tin Tin
  • such element has properties similar to Indium in lowering the eutectic amount, and it costs less than Indium.
  • the silver alloy according to the present invention may further comprise at least one further element (D) selected from Copper (Cu), Palladium (Pd) and Platinum (Pt), in particular in low Silver content alloys.
  • D further element selected from Copper (Cu), Palladium (Pd) and Platinum (Pt), in particular in low Silver content alloys.
  • the silver alloy mentioned above is compatible with the atomisation manufacturing process. In addition, it significantly improves efficiency during the sintering step due to a greaterthermal resistance, given by the minimisation or removal of the presence of eutectic steps. As a matter of fact, with the silver alloy mentioned above, during the implementation of the sintering step it is possible to optimise the densification process, so as to obtain precious objects with minimum porosity and high mechanical properties.
  • the full removal or reduction of the copper content has the advantage of increasing both the liquidus and solidus temperature of the alloys, with increase in the amount of thermal energy that can be transferred to the workpieces during the sintering without the latter being damaged morphologically (dissolution or softening of the workpieces).
  • the full removal or reduction of the copper content also has a positive effect in reducing the risk of oxidation of the powder after the production thereof, resulting in facilitating he sintering process.
  • silver alloys normally have a titre of 800 or 925 and above.
  • a silver alloy according to the present invention may consist of:
  • the silver alloy mentioned above contains two or more elements selected from the group consisting of: Tin (Sn), Copper (Cu), Palladium (Pd) and Platinum (Pt).
  • the alloy mentioned above may have an 800 titre.
  • the silver alloy mentioned above contains Tin (Sn), it may be present in the silver alloy in a range comprised between 1.00 % by weight and 3.00 % by weight, and it may further be present in at least one second further element (D) selected from the group consisting of: Copper (Cu), Palladium (Pd) and Platinum (Pt).
  • the silver alloy mentioned above contains Copper (Cu), it may be present in the silver alloy in a range comprised between 2.00 % by weight and 6.00 % by weight.
  • Cu Copper
  • the silver alloy mentioned above contains Palladium (Pd), it may be present in the silver alloy in a range comprised between 1.00 % by weight and 5.00 % by weight.
  • a silver alloy 800 according to the present invention may have the composition below:
  • a further example of silver alloy 800 according to the present invention may have the composition below:
  • a further silver alloy according to the present invention may consist of:
  • (B) 1.00 % by weight - 6.00 % by weight, preferably 1.50 % by weight - 5.00 % by weight, of Indium (In);
  • the alloy mentioned above may have a 925 or higher titre.
  • the silver alloy mentioned above may have a 925 or higher titre.
  • the at least one first further element (C) is Tin (Sn), it may be present in the silver alloy in a range comprised between 1.00 % by weight and 5.00 % by weight;
  • the at least one first further element (C) is Copper (Cu), it may be present in the silver alloy in a range comprised between 1.00 % by weight and 4.00 % by weight;
  • the at least one first further element (C) is Palladium (Pd)
  • it may be present in the silver alloy in a range comprised between 1.00 % by weight and 4.50 % by weight.
  • a silver alloy 925 according to the present invention may have the composition below:
  • a further example of silver alloy 925 according to the present invention may have the composition below:
  • the alloys according to the present invention may be produced by atomisation and they may have a particle size comprised between 0.1 and 100 micron, which can be sifted depending on the needs with particle size comprised between 0.1 and 30 micron, and an as cast hardness comprised between 40 HV and 120 HV measured in accordance with the ISO 6507-1:2018 standard.
  • the hardness may be comprised between 40 and 60 HV for alloys with Silver at 92.5% or above, and they may be comprised between 100 HV and 120 HV in alloys with Silver at 80%.
  • such alloys may have a high sphericity, an aspect that improves the densification during the sintering.
  • the process mentioned above may be selected from binder jetting (BJ), metal injection moulding (MIM), lithography-based metal manufacturing (LMM), fused deposition modelling (FDM).
  • BJ binder jetting
  • MIM metal injection moulding
  • LMM lithography-based metal manufacturing
  • FDM fused deposition modelling
  • sintering process essentially in two steps: a first debinding step at temperatures greater than 400 °C and preferably comprised between 400 °C and 500 °C and a subsequent sintering step at temperatures greater than 800 °C and preferably comprised between 800 °C and 1000 °C.
  • the powder and binder mixture be sufficiently thermally resistant to evacuate the binder present, without the formation - at low temperature (that is at a temperature lower than the evaporation temperature of the binder) - of closed porosity, which would be characterised by the residual presence of the binder trapped in the object no longer without the possibility of removing it.
  • the measurement of the residual amount of carbon after sintering is a parameter useful for indirectly identifying the behaviour of the alloy during the debinding step: the read value of carbon is proportional to the one present in the residual porosity.
  • the subsequent sintering step there is carried out the densification of the workpieces, increase in mechanical strength and dimensional decrease which leads to the finished workpiece.
  • the end quality of the workpiece depends on this step above all.
  • the quality depends on the sintering temperature: in absolute terms, the higher the sintering temperature and the closer it is to the solidus temperature of the alloy, the greater the efficiency.
  • the precious objects produced with the silver alloys according to the invention are characterised by good processability, acceptable hardness, low surface roughness and low internal porosity, facilitating the process for finishing the objects and improving the end appearance thereof.
  • samples E 1 - E 35 were produced, comparing them with a sample of Sterling 925 (Ctr 1) and 800 (Ctr 2) silver.
  • the samples have the following composition. Preparation of the samples
  • FIGS. 1 and 2 show a photo under scanning electron microscope (SEM-EDX) and the particle size analysis of the silver alloy of example 4 mentioned above, characterised by dimensions of dlO 5 pm - d90 22 pm and high sphericity, an aspect that improves the densification during sintering.
  • the high magnification visual inspection serves to verify the morphology of the powder, in particular sphericity and absence of satellites (that is small powder particles attached to larger particles).
  • a MASTERSIZER 2000 laser particle size analyser with an automatic sampling unit for moist powders was used for particle size analysis.
  • the samples of the silver alloys mentioned above were subjected to hardness measurements according to the ISO 6507-1:2018 standard and after thermosetting with a two-step process, consisting of a solubilisation of the alloy at the temperature of 730°C for 30' followed by an immediate tempering with water, and subsequently by a hardening process at 300°C for 60' followed by tempering with air.
  • the hardness obtained on workpieces produced by means of metallurgy of the powders confirmed the values initially obtained starting from alloys mixed conventionally, starting from pure metals and mixing them by means of induction melting in a graphite crucible.
  • curing is a thermal treatment which is carried out in a range between 130 and 180°C, under vacuum, for a duration between 3 and 4 h.
  • each sample raw workpiece was subjected to a sintering process.
  • the sintering process was tested on two different furnaces (Elnik and Carbolite HTK8), with a specific ascent ramp in hydrogen atmosphere with an ascent step of the temperature 230°C for 3 h, 450°C for 2 h, 600°C for 2 h, 830°C for 4 h.
  • the porosity and deviations from the nominal dimension measurements were carried out on objects produced using the cubic-shaped Binder Jet test technique, nominal side 10 mm.
  • the measurement of the deviation from the workpiece as a CAD project was made on sintered workpieces, by means of manual measurements on the different growth and sintering planes.
  • the workpieces were prepared metallographically on three faces (xy plane, xz plane, yz plane), indicating the various directions of printing and sintering of the object.
  • 0.3 mm were removed from the surface of the object using sandpapers, followed by metallographic polishing.
  • the residual porosity and average pore size measurements were carried out using Keyence VHX-7000 image processing software according to internal operating procedure.
  • the carbon value is markedly higher and may be related to the carbon residually contained in the porosity of the objects produced. Likewise, the residual porosity, the pore size and the absolute deviation from the raw workpiece, which is associated with a lower degree of densification, are markedly higher.
  • Samples 4, 5, 12 and 19 are particularly preferred because they represent the best balance between sintering efficiency, hardness and alloy cost.
  • FIG. 3 - Control sample For these samples 4, 5, 12 and 19, SEM/EDX surveys were carried out on sections of the obtained workpieces (FIG. 3 - Control sample; FIGS. 4 - 7 respectively Samples 4, 5, 12 and 19). Such surveys also show that the workpieces obtained with the silver alloy samples according to the invention were qualitatively and mechanically superior than the one obtained with the control samples.
  • indium (In) has excellent properties of lowering the eutectic amount, and its presence in the silver alloys of the present invention is therefore necessary.
  • Tin (Sn) has properties similar to indium in lowering the eutectic amount and it costs less than indium, and it is therefore particularly preferred in the silver alloys of the present invention.
  • Tin can be chromatically balanced with other elements, such as for example Copper (Cu), Palladium (PD) and Platinum (PT), in particular in low silver content alloys.
  • Tin may be present in higher percentages, until 5% by weight with respect to the total weight of the silver alloy, so that the amount of Indium is the lowest possible to reduce the cost of the alloy.
  • the Tin may be present at relatively lower percentages, up to the maximum of 3% by weight with respect to the total weight of the silver alloy. Beyond such percentage, silver alloys become incompatible with sintering processes aimed at obtaining high densification end products, and in particular with the Binder Jetting technique, and more generally with the production of precious objects.
  • the low processability of the Ctr 3 - Ctr 6 samples was verified according to an internal operating procedure which provides for the melting of a 100 g sample in an induction melting machine to obtain a 30 mm wide and 6 mm thick sheet and subsequent cold rolling in a flat roller mill, starting from the initial thickness of 6 mm and gradually thinning the sample with thickness decrements of 0.2 mm for each deformation step. Processing is carried out on a single sample, thinning without annealing thermal treatments until the thickness at which cracks occur due to excessive stress on the alloy under examination is identified. Therefore, the thinner the sheet can be made without cracking, the greater its degree of processability is.

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  • Materials Engineering (AREA)
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Abstract

The use of a silver alloy for manufacturing precious objects by means of a process which includes the following steps: a) adding a polymeric binder to the silver alloy for providing a semi-finished product; and b) sintering the semi-finished product. Besides the common impurities, silver alloy consists of: 80.00 % by weight - 97.50 % by weight of Silver (Ag); 0.01 % by weight - 15.00 % by weight of Indium (In); 0.01 % by weight - 15.00 % by weight of at least one first further element consisting of: Tin (Sn), Gallium (Ga), Copper (Cu), Palladium (Rd), Platinum (Pt), Zinc (Zn), Silicon (Si). A precious object made starting from such silver alloy.

Description

USE OF A SILVER ALLOY FOR THE REALIZATION OF PRECIOUS OBJECTS BY MEANS OF A PROCESSED BASED ON SINTERIZATION, AS WELL AS THE PRECIOUS OBJECT OBTAINED THEREWITH
DESCRIPTION
Technical field of the invention
The present invention generally relates to the technical field of jewellery, and it relates to the use of a silver alloy for manufacturing precious objects by means of a process based on sintering, as well as a precious object thus obtained.
Definitions
In the present document, the expression “Binder Jetting” also abbreviated with "BJ" is used to indicate an additive manufacturing process in which the powder is selectively soaked, after it has been spread a surface, with a binder in multiple layers to obtain a semi-finished product, called raw workpiece. Subsequently, the obtained raw workpiece should be densified through a thermal process referred to as sintering.
In the present document, the expression “Metal Injection Moulding” also abbreviated with “MIM” is used to indicate a manufacturing process starting from powders where the metal powder is mixed with an appropriate binder and then injected into a pressing machine to obtain a semi-finished product, referred to as raw workpiece. The raw workpiece thus obtained is then densified by sintering.
In the present document, the expression “Lithography-based Metal Manufacturing” also abbreviated with "LMM" is used to indicate a manufacturing process starting from powders based on the selective lithographic polymerisation of a binder to obtain a semifinished product, referred to as raw workpiece. The workpiece thus obtained is then densified by sintering.
In the present document, the expression “Fused Deposition Modelling” also abbreviated with "FDM" is used to indicate a manufacturing process starting from powders based on the construction of three-dimensional shapes starting from thermoplastic polymer filaments containing metal powder. The raw workpiece thus obtained is then densified by sintering.
In the present document, the expression "Semi-finished product" also referred to as "raw workpiece" is used to indicate an object resulting from the mould or injection process, consisting of a mixture of metal powder and binder, which already has the shape of the end object, but with lower mechanical strength than the end workpiece, which will result from the sintering process.
In the present document, the expression "Debinding" is used to indicate an initial step of the sintering process, in which the polymeric binder required to hold the mass of metal powder together after the moulding, is removed.
In the present document, the expression "Sintering" is used to indicate a process that is thermally activated due to which semi-finished product consisting of a mixture of metal powders and a binder is densified until there is obtained a compact solid object, by removing the binder and thermally or thermal-mechanically joining the powder particles.
In the present document, the expression "consists" or its derivatives associated with a composition or product of interest made up of two or more components is used to indicate, unless indicated otherwise, that the product or composition in question is entirely made up of the listed components, that is the total of the listed components amount to 100% of the composition or of the product, except for the usual impurities generally present in that product or composition.
In the present document, the expression "precious object" or its derivatives is used to indicate, unless indicated otherwise, a finished product, of any shape and size, resulting from the processing an alloy in a predefined manner.
In the present document, the expression "percentage by weight" or "% by weight" or its derivatives is used to indicate, unless indicated otherwise, the percentage by weight of a component of interest with respect to the total weight of the composition in which the component of interest is included.
State of the Art
It is known that the conventional jewellery manufacturing technologies reveal problems relating to the type of drawings that can be obtained, the efficiency of the manufacturing processes in terms of proportion between the amount of alloy used and weight of the end object and surface quality.
Various techniques have been designed to overcome these drawbacks. Among these, there is known the technology called binder jetting or metal binder jetting which enables, starting from a CAD drawing uploaded on a special printer, to obtain a large amount of semi-finished products called "raw workpieces" within a short time and with ultra-high repeatability due to the speed of the printer, then followed by a sintering process, which can also be carried out on a large number of workpieces. With an optimised process, the workpieces that are obtained are characterised by good surface quality and controlled dimensional tolerances.
Sterling, the silver alloy conventionally used in the jewellery industry when used in the binder jetting technique entails problems when removing the binder as well as morphology and dimensional tolerance problems on the end workpiece, with the risk of the workpieces collapsing.
The Japanese patent application JP2019-007057 discloses a silver alloy which is incompatible with sintering processes aimed at obtaining high densification precious objects, in particular with the Binder Jetting technique.
Summary of the invention
An object of the present invention is to at least partly overcome the drawbacks illustrated above, by using a silver alloy in form of powder for manufacturing precious objects through a process which comprises the following steps: a) adding a binder, preferably polymeric, to the silver alloy for providing a semifinished product; b) sintering said semi-finished product.
The silver alloy may consist of:
(A) 80.00% by weight - 97.50% by weight of Silver (Ag);
(B) 0.01 % by weight - 15.00 % by weight, and preferably 1.00 % by weight - 5.00 % by weight, of Indium (In);
(C) 0.01% by weight - 15.00% by weight of at least one first further element, that is one or more first elements, selected from the group consisting of: Tin (Sn), Gallium (Ga), Copper (Cu), Palladium (Pd), Platinum (Pt), Zinc (Zn), Silicon (Si); and the usual impurities. The percentages by weight mentioned above are percentages by weight with respect to the total weight of the alloy.
In particular:
- if the at least one first further element (C) is tin (Sn ), may be present in the silver alloy in a range comprised between 0.01% by weight and 5.00 % by weight, and preferably comprised between 1.00 % by weight and 3.00 % by weight;
- if the at least one first further element (C) is Gallium (Ga), it may be present in the silver alloy in a range comprised between 0.01% by weight and 4.00% by weight, and preferably comprised between 0. 01% by weight and 2.00% by weight;
- if the at least one first further element (C) is Copper (Cu), it may be present in the silver alloy in a range comprised between 0.01% by weight and 6.00% by weight;
- if the at least one first further element (C) is Palladium (Pd), it may be present in the silver alloy in a range comprised between 0.01% by weight and 5.00% by weight;
- if the at least one first further element (C) is Platinum (Pt), it may be present in the silver alloy in a range comprised between 0.01% by weight and 4.00% by weight;
- if the at least one first further element (C) is Zinc (Zn), it may be present in the silver alloy in a range comprised between 0.01% by weight and 1.00 % by weight;
- if the at least one first further element (C) is Silicon (Si), it may be present in the silver alloy in a range comprised between 0.01% by weight and 0.20 % by weight.
Preferably, the at least one first further element (C) mentioned above may be Tin (Sn). As a matter of fact, such element has properties similar to Indium in lowering the eutectic amount, and it costs less than Indium.
Suitably, it may be balanced because it has less chromatic appeal with respect to Indium. Therefore, advantageously, the silver alloy according to the present invention may further comprise at least one further element (D) selected from Copper (Cu), Palladium (Pd) and Platinum (Pt), in particular in low Silver content alloys.
Thanks to such composition, the silver alloy mentioned above is compatible with the atomisation manufacturing process. In addition, it significantly improves efficiency during the sintering step due to a greaterthermal resistance, given by the minimisation or removal of the presence of eutectic steps. As a matter of fact, with the silver alloy mentioned above, during the implementation of the sintering step it is possible to optimise the densification process, so as to obtain precious objects with minimum porosity and high mechanical properties.
As a matter of fact, if the difference between the debinding and the solidus temperature is too low, the powder is not perfectly sintered, with poor-quality result. Furthermore, the higher the sintering temperature, the higher the expected densification of the workpiece, with higher quality results. The Sterling silver alloy conventionally used in conventional technologies for silver 800 and 925 products revealed to be inappropriate for use with the processes mentioned above due to the presence of the eutectic step which limits the maximum sintering temperature, making the densification process less efficient.
Compared to the conventional Sterling silver alloy, the full removal or reduction of the copper content has the advantage of increasing both the liquidus and solidus temperature of the alloys, with increase in the amount of thermal energy that can be transferred to the workpieces during the sintering without the latter being damaged morphologically (dissolution or softening of the workpieces).
Besides positively affecting the solidus temperature, the full removal or reduction of the copper content also has a positive effect in reducing the risk of oxidation of the powder after the production thereof, resulting in facilitating he sintering process.
As known, silver alloys normally have a titre of 800 or 925 and above.
In particular, a silver alloy according to the present invention may consist of:
(A) 80.00% by weight - 85.00% by weight of Silver (Ag);
(B) 5.00 % by weight - 15.00 % by weight, preferably 8.00 % by weight - 15.00 % by weight, of Indium (In);
(C) 5.00 % by weight - 15.00 % by weight, preferably 8.00 % by weight - 15.00 %by weight, of one or more elements selected from the group mentioned above, and in particular selected from the group consisting of: Tin (Sn), Copper (Cu), Palladium (Pd) and Platinum (Pt).
Preferably, besides Silver and Indium, the silver alloy mentioned above contains two or more elements selected from the group consisting of: Tin (Sn), Copper (Cu), Palladium (Pd) and Platinum (Pt). For example, the alloy mentioned above may have an 800 titre.
Suitably, if the silver alloy mentioned above contains Tin (Sn), it may be present in the silver alloy in a range comprised between 1.00 % by weight and 3.00 % by weight, and it may further be present in at least one second further element (D) selected from the group consisting of: Copper (Cu), Palladium (Pd) and Platinum (Pt).
Suitably, if the silver alloy mentioned above contains Copper (Cu), it may be present in the silver alloy in a range comprised between 2.00 % by weight and 6.00 % by weight.
Furthermore, if the silver alloy mentioned above contains Palladium (Pd), it may be present in the silver alloy in a range comprised between 1.00 % by weight and 5.00 % by weight.
For example, a silver alloy 800 according to the present invention may have the composition below:
(A) 80.00 % by weight of Silver (Ag);
(B) 12.00 % by weight of Indium (In);
(C) 2.00 % by weight of Tin (Sn);
(D) 6.00 % by weight of Copper (Cu).
A further example of silver alloy 800 according to the present invention may have the composition below:
(A) 80.00 % by weight of Silver (Ag);
(B) 11.00 % by weight of Indium (In);
(C) 5.00 % by weight of Palladium (Pd);
(D) 4.00 % by weight of Copper (Cu).
A further silver alloy according to the present invention may consist of:
(A) 90.00% by weight - 97.50% by weight of Silver (Ag);
(B) 1.00 % by weight - 6.00 % by weight, preferably 1.50 % by weight - 5.00 % by weight, of Indium (In);
(C) 1.00 % by weight - 6.00 % by weight, preferably 1.50 % by weight - 5.00 % by weight, of the at least one first further element selected from the group mentioned above.
For example, the alloy mentioned above may have a 925 or higher titre. Suitably, in the silver alloy mentioned above:
- if the at least one first further element (C) is Tin (Sn), it may be present in the silver alloy in a range comprised between 1.00 % by weight and 5.00 % by weight;
- if the at least one first further element (C) is Copper (Cu), it may be present in the silver alloy in a range comprised between 1.00 % by weight and 4.00 % by weight;
- if the at least one first further element (C) is Palladium (Pd), it may be present in the silver alloy in a range comprised between 1.00 % by weight and 4.50 % by weight.
For example, a silver alloy 925 according to the present invention may have the composition below:
(A) 93.00 % by weight of Silver (Ag);
(B) 4.00 % by weight of Indium (In);
(C) 3.00 % by weight of Tin (Sn).
A further example of silver alloy 925 according to the present invention may have the composition below:
(A) 93.00 % by weight of Silver (Ag);
(B) 2.00 % by weight of Indium (In);
(C) 2.00 % by weight of Tin (Sn);
(D) 2.00 % by weight of Copper (Cu);
(E) 1.00 % by weight of Palladium (Pd).
Advantageously, the alloys according to the present invention may be produced by atomisation and they may have a particle size comprised between 0.1 and 100 micron, which can be sifted depending on the needs with particle size comprised between 0.1 and 30 micron, and an as cast hardness comprised between 40 HV and 120 HV measured in accordance with the ISO 6507-1:2018 standard. In particular, the hardness may be comprised between 40 and 60 HV for alloys with Silver at 92.5% or above, and they may be comprised between 100 HV and 120 HV in alloys with Silver at 80%.
Suitably, such alloys may have a high sphericity, an aspect that improves the densification during the sintering.
Advantageously, the process mentioned above may be selected from binder jetting (BJ), metal injection moulding (MIM), lithography-based metal manufacturing (LMM), fused deposition modelling (FDM).
Upon obtaining the raw workpieces, they may be subjected to the sintering process essentially in two steps: a first debinding step at temperatures greater than 400 °C and preferably comprised between 400 °C and 500 °C and a subsequent sintering step at temperatures greater than 800 °C and preferably comprised between 800 °C and 1000 °C.
During the debinding step, it is of particular importance that the powder and binder mixture be sufficiently thermally resistant to evacuate the binder present, without the formation - at low temperature (that is at a temperature lower than the evaporation temperature of the binder) - of closed porosity, which would be characterised by the residual presence of the binder trapped in the object no longer without the possibility of removing it. The measurement of the residual amount of carbon after sintering is a parameter useful for indirectly identifying the behaviour of the alloy during the debinding step: the read value of carbon is proportional to the one present in the residual porosity.
During the subsequent sintering step there is carried out the densification of the workpieces, increase in mechanical strength and dimensional decrease which leads to the finished workpiece. The end quality of the workpiece depends on this step above all. The quality depends on the sintering temperature: in absolute terms, the higher the sintering temperature and the closer it is to the solidus temperature of the alloy, the greater the efficiency.
The precious objects produced with the silver alloys according to the invention are characterised by good processability, acceptable hardness, low surface roughness and low internal porosity, facilitating the process for finishing the objects and improving the end appearance thereof.
The invention will be clearer in the light of the following examples, which are provided by way of non-limiting examples of the invention.
Examples
Various samples (samples E 1 - E 35) were produced, comparing them with a sample of Sterling 925 (Ctr 1) and 800 (Ctr 2) silver. The samples have the following composition.
Figure imgf000011_0001
Figure imgf000011_0002
Figure imgf000011_0003
Preparation of the samples
Atomisation
All formulations were first tested by characterising alloy samples produced conventionally, by melting alloy ingots obtained from pure elements in the proportions according to the recipe in a melting system in an inert chamber. The pure metals below were used for manufacturing the samples:
Silver purity 99.99%;
Copper Oxygen-free purity 99.99%;
Indium purity 99.99%; Tin purity 99.9%;
Gallium purity 99.99%;
Platinum purity 99.95%;
Palladium purity 99.95%;
Silicon purity 99.9%;
Zinc purity 99.99%.
Subsequently, all samples were prepared by atomisation in an Indutherm atomiser model AUG1000 in inert gas. FIGS. 1 and 2 show a photo under scanning electron microscope (SEM-EDX) and the particle size analysis of the silver alloy of example 4 mentioned above, characterised by dimensions of dlO 5 pm - d90 22 pm and high sphericity, an aspect that improves the densification during sintering. The high magnification visual inspection serves to verify the morphology of the powder, in particular sphericity and absence of satellites (that is small powder particles attached to larger particles). A MASTERSIZER 2000 laser particle size analyser with an automatic sampling unit for moist powders was used for particle size analysis.
The samples of the silver alloys mentioned above were subjected to hardness measurements according to the ISO 6507-1:2018 standard and after thermosetting with a two-step process, consisting of a solubilisation of the alloy at the temperature of 730°C for 30' followed by an immediate tempering with water, and subsequently by a hardening process at 300°C for 60' followed by tempering with air.
The results of such measurements are shown in the table below:
Figure imgf000012_0002
Figure imgf000012_0003
Figure imgf000012_0001
Figure imgf000013_0001
The hardness obtained on workpieces produced by means of metallurgy of the powders confirmed the values initially obtained starting from alloys mixed conventionally, starting from pure metals and mixing them by means of induction melting in a graphite crucible.
Binder jetting and sintering
Subsequently, the various alloy samples were moulded using the binder jetting technique using a Desktop Metal printer model Pl (printer platform size H50 x L200 x P100) and using a HP MetalJet Alpha printer (printer chamber size H200 x L430 x P310).
After the printing, the curing process was carried out for each sample at 150 °C by means of a HP device connected to the printer; curing is a thermal treatment which is carried out in a range between 130 and 180°C, under vacuum, for a duration between 3 and 4 h.
Subsequently, each sample raw workpiece was subjected to a sintering process. The sintering process was tested on two different furnaces (Elnik and Carbolite HTK8), with a specific ascent ramp in hydrogen atmosphere with an ascent step of the temperature 230°C for 3 h, 450°C for 2 h, 600°C for 2 h, 830°C for 4 h.
Workpieces with various geometries were selected to verify aspects relating to morphological tolerance on objects of various sizes, and to verify the quality of the sintering process as a function of the size of the workpieces. All objects with sizes contained by way of example in a cube with side measuring 5 cm are to be considered compatible for comparison.
The debinding, solidus, liguidus, curing, and sintering temperatures for each sample were:
Figure imgf000013_0002
Figure imgf000014_0001
Figure imgf000014_0002
This table shows that the samples of the present invention have a significantly higher debinding temperature and sintering temperature with respect to the control samples made from Sterling Ag.
Sample characterisation
The carbon values according to the ASTM E1019:2018 standard, the residual porosity, the average pore size and the scale factor between the raw workpiece and sintered workpiece were measured for each sample.
The porosity and deviations from the nominal dimension measurements were carried out on objects produced using the cubic-shaped Binder Jet test technique, nominal side 10 mm. The measurement of the deviation from the workpiece as a CAD project was made on sintered workpieces, by means of manual measurements on the different growth and sintering planes. The workpieces were prepared metallographically on three faces (xy plane, xz plane, yz plane), indicating the various directions of printing and sintering of the object. 0.3 mm were removed from the surface of the object using sandpapers, followed by metallographic polishing. The residual porosity and average pore size measurements were carried out using Keyence VHX-7000 image processing software according to internal operating procedure.
The results of such measurements are shown in the table below.
Figure imgf000015_0001
Figure imgf000015_0002
Figure imgf000015_0003
Figure imgf000015_0004
In the case of Sterling Ag alloy, the carbon value is markedly higher and may be related to the carbon residually contained in the porosity of the objects produced. Likewise, the residual porosity, the pore size and the absolute deviation from the raw workpiece, which is associated with a lower degree of densification, are markedly higher.
Among examples 1 - 35 mentioned above, the minimum porosity values are obtained with high-melting point alloys based on Palladium and Platinum. However, such alloys are relatively expensive.
Samples 4, 5, 12 and 19 are particularly preferred because they represent the best balance between sintering efficiency, hardness and alloy cost.
For these samples 4, 5, 12 and 19, SEM/EDX surveys were carried out on sections of the obtained workpieces (FIG. 3 - Control sample; FIGS. 4 - 7 respectively Samples 4, 5, 12 and 19). Such surveys also show that the workpieces obtained with the silver alloy samples according to the invention were qualitatively and mechanically superior than the one obtained with the control samples.
Influence of the presence of Tin (Sn) and Indium (In) in the silver alloy of the present invention
As mentioned above, indium (In) has excellent properties of lowering the eutectic amount, and its presence in the silver alloys of the present invention is therefore necessary.
On the other hand, Tin (Sn) has properties similar to indium in lowering the eutectic amount and it costs less than indium, and it is therefore particularly preferred in the silver alloys of the present invention.
However, it has less chromatic appeal than indium, and its percentage shall not exceed 5% by weight with respect to the total weight of the silver alloy. Furthermore, preferably, the presence of Tin can be chromatically balanced with other elements, such as for example Copper (Cu), Palladium (PD) and Platinum (PT), in particular in low silver content alloys.
In the silver alloys in which silver is present in higher percentages (90% by weight - 97.5% by weight with respect to the total weight of the alloy) Tin may be present in higher percentages, until 5% by weight with respect to the total weight of the silver alloy, so that the amount of Indium is the lowest possible to reduce the cost of the alloy.
On the other hand, in the silver alloys in which silver is present at lower percentages (80% by weight - 85.0% by weight with respect to the total weight of the alloy) the Tin may be present at relatively lower percentages, up to the maximum of 3% by weight with respect to the total weight of the silver alloy. Beyond such percentage, silver alloys become incompatible with sintering processes aimed at obtaining high densification end products, and in particular with the Binder Jetting technique, and more generally with the production of precious objects.
In order to demonstrate this, experimental tests were carried out among the samples E31 and E32 mentioned above and some control samples (Ctr 3 - 6), obtained according to the description outlined above, whose formulations are given in the table below.
Figure imgf000017_0001
For each of the samples Ctr 3 - Ctr 6 mentioned above, the hardness (HV, as cast and after thermosetting), the debinding, solidus, liquidus, curing, and sintering temperatures during the moulding of the samples with the Binder Jetting technique and subsequent sintering and the residual porosity were measured as described above. The results obtained are reported in the table below.
Figure imgf000017_0002
As clear, Ctr 3 - Ctr 6 samples with respect to E31 - E32 samples have lower hardness, solidus temperatures, significantly lower melting range and sintering temperatures, and much higher residual porosity, which inevitably leads to poorly densified, highly brittle and poorly processed end products, as well as of course poor surface quality.
These aspects make the Ctr 3 - Ctr 6 samples incompatible with the manufacturing of jewels, which by their nature must be processed, for example to bring them to a certain size or to set precious stones.
The low processability of the Ctr 3 - Ctr 6 samples was verified according to an internal operating procedure which provides for the melting of a 100 g sample in an induction melting machine to obtain a 30 mm wide and 6 mm thick sheet and subsequent cold rolling in a flat roller mill, starting from the initial thickness of 6 mm and gradually thinning the sample with thickness decrements of 0.2 mm for each deformation step. Processing is carried out on a single sample, thinning without annealing thermal treatments until the thickness at which cracks occur due to excessive stress on the alloy under examination is identified. Therefore, the thinner the sheet can be made without cracking, the greater its degree of processability is.
Without focusing too much on theory, it can be assumed that should the sample be able to be deformed by at least 40% reduction (therefore moving from 6 mm thickness to 3.6 mm thickness or lower thickness), the deformability thereof is considered acceptable for the purposes of the present invention.
While the E 31 - E 32 samples have shown a thinning rate of at least 40% compared to the initial thickness, and are therefore acceptable, the Ctr 3 - Ctr 6 ones showed a thinning rate well below 30% compared to the initial thickness, and are therefore unacceptable for the purposes of the present invention. The results obtained are reported in the table below.
Figure imgf000018_0001

Claims

1. The use of a silver alloy in powdered form for manufacturing precious objects through a process which includes the following steps: a) adding a binder to the silver alloy for providing a semi-finished product; b) sintering said semi-finished product; the silver alloy consisting of:
(A) 80.00% by weight - 97.50% by weight of Silver (Ag);
(B) 0.01% by weight - 15.00% by weight of Indium (In);
(C) 0.01% by weight - 15.00% by weight of at least one first further element selected from the group consisting of: Tin (Sn), Gallium (Ga), Copper (Cu), Palladium (Pd), Platinum (Pt), Zinc (Zn), Silicon (Si); and the usual impurities; wherein if said at least one first further element (C) is Tin (Sn):
• if the silver alloy contains
(A) 80.00 % by weight - 85,00 % by weight of Silver (Ag), then
(B) Indium (In) is comprised between 5.00 % by weight and 15.00 % by weight;
(C) Tin (Sn) is comprised between 1.00 % by weight and 3.00 % by weight;
(D) the silver alloy further comprises at least one second further element selected from the group consisting of: Copper (Cu), Palladium (Pd), Platinum (Pt); wherein said at least one first and one second further element (C + D) are present in the alloy in a percentage comprised between 5.00 % by weight and 15.00 % by weight; or
• if the silver alloy contains
(A) 90.00 % by weight - 97,50 % by weight of Silver (Ag), then
(B) Indium (In) is comprised between 1.00 % by weight and 6.00 % by weight and
(C) Tin (Sn) is comprised between 1.00 % by weight and 5.00 % by weight; wherein the percentages by weight are percentages by weight with respect to the total weight of the alloy.
2. Use according to the preceding claim, wherein:
- if said at least a first further element (C) is Gallium (Ga), it is present in said silver alloy in a range comprised between 0.01% by weight and 4.00% by weight, and preferably comprised between 0. 01% by weight and 2.00% by weight;
- if said at least one first further element (C) is Copper (Cu), it is present in said silver alloy in a range comprised between 0.01% by weight and 6.00% by weight;
- if said at least one first further element (C) is Palladium (Pd), it is present in said silver alloy in a range comprised between 0.01% by weight and 5.00% by weight;
- if said at least one first further element (C) is Platinum (Pt), it is present in said silver alloy in a range comprised between 0.01% by weight and 4.00% by weight;
- if said at least one first further element (C) is Zinc (Zn), it is present in said silver alloy in a range comprised between 0.01% by weight and 1.00% by weight;
- if said at least one first further element (C) is Silicon (Si), it is present in said silver alloy in a range comprised between 0.01% by weight and 0.20% by weight.
3. Use according to claim 1 or 2, wherein said at least one first further element (C) is tin (Sn), the silver alloy containing 80.00 % by weight - 85.00 % by weight of Silver (Ag), wherein:
- if said at least one second further element (D) is Copper (Cu), it is present in said silver alloy in a range comprised between 2.00% by weight and 6.00% by weight;
- if said at least one second further element (D) is Palladium (Pd), it is present in said silver alloy in a range comprised between 1.00% by weight and 5.00% by weight.
4. Use according to claim 1 or 2, wherein the silver alloy consists of:
(A) 80.00% by weight - 85.00% by weight of Silver (Ag);
(B) 5.00 % by weight - 15.00 % by weight, preferably 8.00 % by weight - 15.00 % by weight, of Indium (In);
(C) 5.00 % by weight - 15.00 % by weight, preferably 8.00 % by weight - 15,00 % by weight, of said at least one first further element; wherein: - if said at least one first further element (C) is Copper (Cu), it is present in said silver alloy in a range comprised between 2.00% by weight and 6.00% by weight;
- if said at least one first further element (C) is Palladium (Pd), it is present in said silver alloy in a range comprised between 1.00% by weight and 5.00% by weight.
5. Use according to claim 1 or 2, wherein the silver alloy consists of:
(A) 90.00% by weight - 97.50% by weight of Silver (Ag);
(B) 1.00 % by weight - 6.00 % by weight, preferably 1.50 % by weight - 5.00 % by weight, of Indium (In);
(C) 1.00 % by weight - 6.00 % by weight, preferably 1.50 % by weight - 5,00 % by weight, of said at least one first further element; wherein:
- if said at least one first further element (C) is Copper (Cu), it is present in said silver alloy in a range comprised between 1.00% by weight and 4.00% by weight;
- if said at least one first further element (C) is Palladium (Pd), it is present in said silver alloy in a range comprised between 1.00% by weight and 4.50% by weight.
6. Use according to any one of the preceding claims, wherein said at least one first further element (C) is Tin (Sn).
7. Use according to any one of the preceding claims, wherein said alloy further comprises at least one second further element (D), the latter and said at least one first further element (C) being selected from the group consisting of Tin (Sn), Copper (Cu), Palladium (Pd) and Platinum (Pt).
8. Use according to any one of the preceding claims, wherein said silver alloy has a particle size measured in accordance with the ISO 13320:2020 standard comprised between 0.1 pm and 65 pm, and preferably comprised between 0.1 pm and 30 pm.
9. Use according to any one of the preceding claims, wherein in said silver alloy:
- when the Silver (Ag) is comprised between 80.00 % by weight and 85.00 % by weight, Vickers as cast hardness measured in accordance with the ISO 6507-1:2018 standard is comprised between 100 HV and 130 HV;
- when the Silver (Ag) is comprised between 90.00 % by weight and 97.50 % by weight, the Vickers as cast hardness measured in accordance with the ISO 6507-1:2018 standard is comprised between 40 HV and 60 HV.
10. Use according to any one of the preceding claims, wherein said process is selected from the group consisting of: binder jetting (BJ), metal injection moulding (MIM), lithographybased metal manufacturing (LMM), fused deposition modelling (FDM).
11. Use according to the preceding claim, wherein said sintering step is preceded by a de-binding step, the latter being carried out at a working temperature above 400 °C and preferably comprised between 400 °C and 500 °C, the sintering step being carried out at a working temperature above 800 °C and preferably comprised between 800 °C and 1000 °C.
12. A precious object obtained by means of a method comprising the steps of: a) providing the silver alloy defined in one or more of the preceding claims; b) adding a polymeric binder to said the silver alloy for providing a semi-finished product; c) sintering said semi-finished product.
13. Object according to the preceding claim, wherein the average residual porosity is less than 3%.
PCT/IB2024/057598 2023-08-21 2024-08-06 Use of a silver alloy for the realization of precious objects by means of a processes based on sinterization, as well as the precious object obtained therewith WO2025040987A1 (en)

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
ITUB20152713A1 (en) * 2015-07-31 2017-01-31 Legor Group S P A Aging-resistant sterling silver alloy with? Tarnishing resistance? improved and mother alloy composition for its production
JP2019007057A (en) * 2017-06-27 2019-01-17 三菱マテリアル株式会社 Ag ALLOY IMPALPABLE POWDER
US20210162502A1 (en) * 2019-12-03 2021-06-03 Desktop Metal, Inc. Additive manufacturing techniques using noble metals and/or copper metal and related methods and compositions
US20210371955A1 (en) * 2018-12-07 2021-12-02 The Swatch Group Research And Development Ltd Method for manufacturing precious metal alloys and precious metal alloys thus obtained

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
ITUB20152713A1 (en) * 2015-07-31 2017-01-31 Legor Group S P A Aging-resistant sterling silver alloy with? Tarnishing resistance? improved and mother alloy composition for its production
JP2019007057A (en) * 2017-06-27 2019-01-17 三菱マテリアル株式会社 Ag ALLOY IMPALPABLE POWDER
US20210371955A1 (en) * 2018-12-07 2021-12-02 The Swatch Group Research And Development Ltd Method for manufacturing precious metal alloys and precious metal alloys thus obtained
US20210162502A1 (en) * 2019-12-03 2021-06-03 Desktop Metal, Inc. Additive manufacturing techniques using noble metals and/or copper metal and related methods and compositions

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