EP1613786A1 - Production process of a silver alloyworkpiece and alloy used for this process - Google Patents

Production process of a silver alloyworkpiece and alloy used for this process

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Publication number
EP1613786A1
EP1613786A1 EP04725262A EP04725262A EP1613786A1 EP 1613786 A1 EP1613786 A1 EP 1613786A1 EP 04725262 A EP04725262 A EP 04725262A EP 04725262 A EP04725262 A EP 04725262A EP 1613786 A1 EP1613786 A1 EP 1613786A1
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EP
European Patent Office
Prior art keywords
alloy
silver
oxidation
oxygenation
high temperature
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Application number
EP04725262A
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German (de)
French (fr)
Inventor
Pierre Ramoni
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Metalor Technologies International SA
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Metalor Technologies International SA
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Publication date
Application filed by Metalor Technologies International SA filed Critical Metalor Technologies International SA
Priority to EP04725262A priority Critical patent/EP1613786A1/en
Publication of EP1613786A1 publication Critical patent/EP1613786A1/en
Withdrawn legal-status Critical Current

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C32/00—Non-ferrous alloys containing at least 5% by weight but less than 50% by weight of oxides, carbides, borides, nitrides, silicides or other metal compounds, e.g. oxynitrides, sulfides, whether added as such or formed in situ
    • C22C32/001—Non-ferrous alloys containing at least 5% by weight but less than 50% by weight of oxides, carbides, borides, nitrides, silicides or other metal compounds, e.g. oxynitrides, sulfides, whether added as such or formed in situ with only oxides
    • C22C32/0015—Non-ferrous alloys containing at least 5% by weight but less than 50% by weight of oxides, carbides, borides, nitrides, silicides or other metal compounds, e.g. oxynitrides, sulfides, whether added as such or formed in situ with only oxides with only single oxides as main non-metallic constituents
    • C22C32/0021—Matrix based on noble metals, Cu or alloys thereof

Definitions

  • the present invention relates to the field of metal alloys. It concerns, more particularly, on the one hand, a method for obtaining a piece of a silver alloy (Ag) and, on the other hand, the base alloy used to achieve this.
  • the silver-based alloys are common. For example, silver is mixed with a few tenths of percent of magnesium (Mg) and nickel (Ni), the latter acting as a grain refiner. By internal oxidation of magnesium to magnesium oxide (MgO), this alloy becomes very hard and has interesting mechanical qualities. In addition and unlike purely metallic alloys, its hardness and the size of its grains are retained after high temperature treatments, such as brazing. It is also an excellent conductor. Such properties make it suitable for particular use, particularly in electrical contact springs, in certain pieces of jewelry, such as fasteners, and in cable ducts for high temperature superconductor.
  • Mg magnesium
  • Ni nickel
  • nickel is a serious drawback. Indeed, this metal is highly allergenic, which greatly limits its use in jewelry. Furthermore, it has been found that nickel is a poison for the superconducting material and an alloy Ag-Mg-Ni may be used directly in the ducts for superconducting cables at high temperature. As described in EP-02405215.1 in the name of the applicant, it is necessary to insert a layer of pure silver between the alloy layer and the superconducting cable.
  • the various constituents are, for example, melted by induction in a graphite crucible and then, the liquid is poured into a steel ingot mold or graphite.
  • the ingot is then deformed cold or hot in the desired form and exposed to a current of air or oxygen, at a temperature varying from 650 to 730 ° C., which causes the oxidation of magnesium to MgO.
  • This operation makes it possible to harden the alloy while retaining, thanks to the presence of nickel which plays the role of refiner, grains of size less than 20 ⁇ m.
  • GB 866 082 discloses a document direct oxidation process of magnesium of an Ag-Mg alloy. However, if one works well, resulting alloy has large grains, making it brittle and unsuitable for the intended applications.
  • Figure 1 shows a metallographic section of a plate of Ag-Mg alloy (0.9 atomic% of Mg) was exposed for 1 hour to a stream of oxygen at a temperature of 650 ° C. Observations and measurements carried out show that the outer layers 10 of the plate undergo oxidation and exhibit a high hardness of about 155HV, compared with the starting alloy having a hardness of 50HV. It should be noted, however, that the size of the constituent grains of the alloy is of the order of 50 .mu.m.
  • the present invention aims to provide an alloy retaining the Ag-Mg-Ni properties, particularly due to its fine grains, and without the drawbacks mentioned above.
  • the invention relates to a method for producing an alloy part based on silver, characterized in that it consists in building an initial alloy containing silver and at least one metal soluble in silver at contents between 0.04 and 4 atomic%, and capable of forming a stable oxide at high temperature, then successively carrying out the following operations:
  • the oxygenation is carried out by exposing the pre-alloy to an oxygen stream at a temperature of about 300 ° C.
  • the initial alloy is a part having the desired final shape.
  • complete oxidation occurs in the continuity of the partial oxidation.
  • the initial alloy is a part having an intermediate form, such as a wire, a tube or tape.
  • partial oxidation is carried out by placing the oxygenated room for about an hour in an inert atmosphere or under vacuum, at a temperature between 400 and 850 ° C. The part is then put into its final form before total oxidation.
  • the initial alloy is in the form of powder.
  • the powder is compacted before oxygenation, so keep an open porosity throughout its thickness.
  • the piece thus obtained is hot extruded, causing its partial oxidation. It is then put into its final form before total oxidation.
  • the initial alloy is in powder form, but the latter is compacted after oxygenation.
  • the total oxidation is carried out by exposing the workpiece to an oxidizing atmosphere at a temperature between 400 and 850 ° C.
  • the invention also relates to a silver-based alloy, characterized in that it contains at least one metal, soluble in silver and capable of forming an oxide stable at high temperature and which, by internal oxidation, hardens it, while making it possible to obtain a final grain size of less than 20 ⁇ m.
  • the metal alloyed with silver is selected from magnesium, aluminum, titanium, gallium, manganese and zinc or a combination of these metals.
  • the content is between 0.04 and 4 atomic%.
  • Figures 2 and 3 are metallographic sections of Ag-Mg alloy plates, respectively, after step d 'oxygenation and after total oxidation according to the invention.
  • a first implementation mode of the invention one starts from a workpiece in a single Ag-Mg alloy having the desired final shape.
  • the alloy used is generally in the cold worked condition, with a cross-section reduction rate of about 50 to 95%. Any preliminary heat treatments were carried out under an inert or reducing atmosphere at a temperature low enough to maintain a fine grain. Typically, the various operations lasted one hour at a temperature of about 500 ° C.
  • the alloy has a Mg content equal to that referred to the final application. Generally, this content is between 0.04 and 4 atomic%.
  • the first phase of the process consists in subjecting the workpiece oxygenation. To this end, a current of oxygen flows in contact with it, at a temperature of approximately 300 ° C., for a time necessary to obtain the desired penetration. Typically, this period is 24 hours for a penetration of 50 microns but may be reduced by increasing the oxygen partial pressure. Under these conditions, oxygen diffuses inside the room and dissolved in silver without oxidizing the magnesium significantly. The hardness of the alloy is not increased and grain remains end.
  • Figure 2 shows the effect of the oxygenation on an alloy plate
  • the outer layers 12 have small grains, less than 20 ⁇ m.
  • the hardness measurement gives 57HV for the external layers and 51 HV for the central layer 14.
  • the part is placed under a stream of air or oxygen, at a temperature of between 400 and 850 ° C., preferably around 600 ° C.
  • the magnesium is then oxidized to MgO.
  • the duration of this phase depends on the temperature, the partial pressure of oxygen and the thickness of the desired oxide layer.
  • the oxygen dissolved in silver oxide during the step of oxygenating immediately part magnesium.
  • the amount of oxygen dissolved in silver being insufficient to oxidize all the magnesium present in the alloy, the partial oxidation is then and is formed of MgO precipitate particles that fit into the matrix of the alloy and prevent the coarsening of Ag-Mg grains by blocking their joints.
  • the oxygen present in the atmosphere continues the oxidation of magnesium for a while, so as to oxidize at least one outer layer.
  • the alloy hardens so but, thanks to the presence of precipitated particles that act as dispersoid, the size of the grains is less than 20 .mu.m.
  • the prior oxygenation has not been carried out over the entire thickness of the part, it is therefore important that the oxidation takes place at a depth equal to or less than that of the oxygenated layer, in order to '' avoid any risk of breakage.
  • the alloy thus obtained has qualities similar to a conventional Ag-Mg-Ni alloy but, since it does not contain nickel, it is not allergenic and does not pollute superconductive materials at high temperature. However, the alloy formed is very hard and can therefore be difficult to shape.
  • an intermediate piece for example in the form of a wire, a tube or a strip, made of an Ag-Mg alloy. This part first undergoes, as in the first embodiment, an oxygenation phase.
  • the workpiece is placed for approximately one hour in vacuum or in an inert atmosphere (e.g. nitrogen or argon) at a temperature between 400 and 850 ° C.
  • an inert atmosphere e.g. nitrogen or argon
  • MgO magnesium oxide
  • the workpiece is still malleable and its final form is then given to him, for example, by rolling, drawing, cutting, bending, stamping or drawing ..., these techniques being well known to those skilled in the art .
  • the starting material is an alloy of silver and magnesium in powder form, which is then compacted, while maintaining an open porosity throughout its thickness, an intermediate form for example, a cylindrical billet of diameter 100mm and length 500mm. Then, as in the first embodiment, the workpiece undergoes oxygenation phase.
  • the following operation is a hot extrusion of the compacted part. To do this, it is first preheated, to a temperature between 400 ° C and 850 ° C and in an inert atmosphere, which automatically causes the initiation of the partial oxidation phase. We then proceed to the extrusion and final shaping of the part before performing, finally, the complete oxidation of magnesium.
  • the phase of oxygenation may well take place before compacting the alloy.
  • the magnesium content is between 0.04 and 4 atomic%. It goes without saying, however, that the magnesium may be replaced partially or completely by any soluble metal silver to the above contents and capable of curing in forming the high temperature stable oxide. Furthermore, to provide a material with acceptable mechanical properties, these elements must, in the oxidized state, provide alloy grains of size less than 20 ⁇ m. For example, aluminum, titanium, gallium, manganese or zinc can be used, for example.
  • a method which allows to obtain a silver-based alloy, made very hard by the presence of a metal oxide and retaining a grain • particularly fine.
  • the resulting alloy can be particularly used for certain pieces of jewelry, without presenting any particular risk of allergy, or even in sheaths for superconductive cable at high temperature, without polluting the superconductive material.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Powder Metallurgy (AREA)
  • Materials For Medical Uses (AREA)

Abstract

The invention relates to a method of producing a silver-based alloy part. The inventive method consists in using an initial alloy containing silver and at least one silver-soluble metal, at concentrations of between 0.04 and 4 atomic percent, which can form a stable oxide at high temperature. Subsequently, the invention consists in performing the following successive operations comprising: oxygenation of the initial alloy such as to dissolve the oxygen in the silver containing same; partial oxidation of the soluble metal in order to form precipitate particles which prevent the alloy grains from swelling; and total oxidation, on at least one outer layer, of the soluble metal into a stable oxide at high temperature. The invention also relates to a silver-based alloy containing at least one silver-soluble metal which can form a stable oxide at high temperature and which, by means of internal oxidation, hardens same, producing a final grain size of less than 20µm.

Description

PROCEDE DE REALISATION D'UNE PIECE PROCESS FOR PRODUCING A PART
EN ALLIAGE D'ARGENT ET ALLIAGE UTILISE POUR CE PROCEDEALLOY SILVER ALLOY USED FOR THE METHOD
La présente invention se rapporte au domaine des alliages métalliques. Elle concerne, plus particulièrement, d'une part, un procédé permettant d'obtenir une pièce en un alliage à base d'argent (Ag) et, d'autre part, l'alliage de base utilisé pour y parvenir.The present invention relates to the field of metal alloys. It concerns, more particularly, on the one hand, a method for obtaining a piece of a silver alloy (Ag) and, on the other hand, the base alloy used to achieve this.
Les alliages à base d'argent sont courants. Par exemple, l'argent est mélangé avec quelques dixièmes de pour-cent de magnésium (Mg) et de nickel (Ni), ce dernier jouant le rôle d'affineur de grain. Par oxydation interne du magnésium en oxyde de magnésium (MgO), cet alliage devient très dur et présente d'intéressantes qualités mécaniques. De plus et contrairement aux alliages purement métalliques, sa dureté et la taille de ses grains sont conservées après des traitements à haute température, comme le brasage. Il est également un excellent conducteur. De telles propriétés le destinent particulièrement à être utilisé, notamment, dans des ressorts de contact électrique, dans certaines pièces de bijouterie, telles que des fermoirs, et dans des gaines pour câble supraconducteur à haute température.The silver-based alloys are common. For example, silver is mixed with a few tenths of percent of magnesium (Mg) and nickel (Ni), the latter acting as a grain refiner. By internal oxidation of magnesium to magnesium oxide (MgO), this alloy becomes very hard and has interesting mechanical qualities. In addition and unlike purely metallic alloys, its hardness and the size of its grains are retained after high temperature treatments, such as brazing. It is also an excellent conductor. Such properties make it suitable for particular use, particularly in electrical contact springs, in certain pieces of jewelry, such as fasteners, and in cable ducts for high temperature superconductor.
Cependant, la présence de nickel est un grave inconvénient. En effet, ce métal est très allergène, ce qui limite fortement son utilisation en bijouterie. Par ailleurs, il a été constaté que le nickel est un poison pour les matériaux supraconducteurs et un alliage Ag-Mg-Ni ne peut être utilisé directement dans les gaines pour des câbles supraconducteurs à haute température. Comme décrit dans le document EP-02405215.1 au nom de la demanderesse, il est donc nécessaire d'intercaler une couche d'argent pur entre la couche d'alliage et le câble supraconducteur.However, the presence of nickel is a serious drawback. Indeed, this metal is highly allergenic, which greatly limits its use in jewelry. Furthermore, it has been found that nickel is a poison for the superconducting material and an alloy Ag-Mg-Ni may be used directly in the ducts for superconducting cables at high temperature. As described in EP-02405215.1 in the name of the applicant, it is necessary to insert a layer of pure silver between the alloy layer and the superconducting cable.
Dans l'état actuel de la technique, pour fabriquer des pièces en alliage Ag-Mg- Ni traditionnel, les différents constituants sont, par exemple, fondus par induction dans un creuset en graphite puis, le liquide est coulé dans une lingotière en acier ou en graphite. Le lingot est ensuite déformé à froid ou à chaud dans la forme souhaitée et exposé à un courant d'air ou d'oxygène, à une température variant de 650 à 730°C, ce qui provoque l'oxydation du magnésium en MgO. Cette opération permet de durcir l'alliage tout en conservant, grâce à la présence de nickel qui joue le rôle d'affineur, des grains de taille inférieure à 20μm.In the current state of the art, to manufacture parts of traditional Ag-Mg-Ni alloy, the various constituents are, for example, melted by induction in a graphite crucible and then, the liquid is poured into a steel ingot mold or graphite. The ingot is then deformed cold or hot in the desired form and exposed to a current of air or oxygen, at a temperature varying from 650 to 730 ° C., which causes the oxidation of magnesium to MgO. This operation makes it possible to harden the alloy while retaining, thanks to the presence of nickel which plays the role of refiner, grains of size less than 20 μm.
Afin d'éviter les problèmes présentés ci-dessus et causés par la présence de nickel, on pourrait simplement penser à appliquer le même procédé à un mélange d'argent et de magnésium.In order to avoid the problems presented above and caused by the presence of nickel, one could simply think of applying the same process to a mixture of silver and magnesium.
Le document GB 866.082 divulgue un procédé d'oxydation directe du magnésium d'un alliage Ag-Mg. Cependant, si l'on opère ainsi, l'alliage résultant présente de gros grains, le rendant cassant et inadapté aux applications visées. Pour illustrer ce qui précède, la figure 1 présente une coupe métallographique d'une plaque d'alliage Ag-Mg (0.9% atomique de Mg) ayant été exposée pendant 1h à un courant d'oxygène, à une température de 650°C. Les observations et mesures effectuées montrent que les couches externes 10 de la plaque subissent une oxydation et présentent une dureté importante, de l'ordre de 155HV, à comparer avec l'alliage de départ dont la dureté est de 50HV. On notera, en revanche, que la taille des grains constitutifs de l'alliage est de l'ordre de 50μm. La présente invention a pour but de fournir un alliage conservant les propriétés de Ag-Mg-Ni, particulièrement dues à sa finesse de grains, et dépourvu des inconvénients évoqués ci-dessus.GB 866 082 discloses a document direct oxidation process of magnesium of an Ag-Mg alloy. However, if one works well, resulting alloy has large grains, making it brittle and unsuitable for the intended applications. To illustrate the foregoing, Figure 1 shows a metallographic section of a plate of Ag-Mg alloy (0.9 atomic% of Mg) was exposed for 1 hour to a stream of oxygen at a temperature of 650 ° C. Observations and measurements carried out show that the outer layers 10 of the plate undergo oxidation and exhibit a high hardness of about 155HV, compared with the starting alloy having a hardness of 50HV. It should be noted, however, that the size of the constituent grains of the alloy is of the order of 50 .mu.m. The present invention aims to provide an alloy retaining the Ag-Mg-Ni properties, particularly due to its fine grains, and without the drawbacks mentioned above.
De façon plus précise, l'invention concerne un procédé de réalisation d'une pièce en alliage à base d'argent, caractérisé en ce qu'il consiste à se doter d'un alliage initial contenant de l'argent et au moins un métal soluble dans l'argent à des teneurs comprises entre 0.04 et 4% atomique, et susceptible de former un oxyde stable à haute température, puis à effectuer successivement les opérations suivantes :More specifically, the invention relates to a method for producing an alloy part based on silver, characterized in that it consists in building an initial alloy containing silver and at least one metal soluble in silver at contents between 0.04 and 4 atomic%, and capable of forming a stable oxide at high temperature, then successively carrying out the following operations:
- oxygénation de l'alliage initial de manière à dissoudre de l'oxygène dans l'argent qu'il contient, - oxydation partielle du métal soluble de manière à former des particules de précipité empêchant les grains d'alliage de grossir, et- oxygenation of the initial alloy so as to dissolve oxygen in the silver it contains, partial oxidation of the soluble metal so as to form particles of precipitate preventing the grains of alloy from growing, and
- oxydation totale, sur au moins une couche extérieure, du métal soluble en un oxyde stable à haute température.- complete oxidation on at least one outer layer, soluble metal at high temperature stable oxide.
De façon avantageuse, l'oxygénation est effectuée en exposant l'alliage initial à un courant d'oxygène, à une température d'environ 300°C.Advantageously, the oxygenation is carried out by exposing the pre-alloy to an oxygen stream at a temperature of about 300 ° C.
Selon un premier mode de réalisation, l'alliage initial est une pièce ayant la forme finale souhaitée. Dans ce cas, l'oxydation totale a lieu dans la continuité de l'oxydation partielle.According to a first embodiment, the initial alloy is a part having the desired final shape. In this case, complete oxidation occurs in the continuity of the partial oxidation.
Selon un deuxième mode de réalisation, l'alliage initial est une pièce ayant une forme intermédiaire, telle qu'un fil, un tube ou une bande. Dans ce cas, l'oxydation partielle est effectuée en plaçant la pièce oxygénée pendant une heure environ dans une atmosphère inerte ou sous vide, à une température comprise entre 400 et 850°C. La pièce est alors mise dans sa forme finale avant l'oxydation totale.According to a second embodiment, the initial alloy is a part having an intermediate form, such as a wire, a tube or tape. In this case, partial oxidation is carried out by placing the oxygenated room for about an hour in an inert atmosphere or under vacuum, at a temperature between 400 and 850 ° C. The part is then put into its final form before total oxidation.
Selon un troisième mode de réalisation, l'alliage initial est sous forme de poudre. Dans ce cas, la poudre est compactée avant l'oxygénation, de manière à conserver une porosité ouverte sur toute son épaisseur. La pièce ainsi obtenue est extrudee à chaud, ce qui provoque son oxydation partielle. Elle est alors mise dans sa forme finale avant l'oxydation totale.According to a third embodiment, the initial alloy is in the form of powder. In this case, the powder is compacted before oxygenation, so keep an open porosity throughout its thickness. The piece thus obtained is hot extruded, causing its partial oxidation. It is then put into its final form before total oxidation.
Selon un quatrième mode de réalisation, constituant une simple variante du troisième mode, l'alliage initial est également sous forme de poudre, mais cette dernière est compactée après l'oxygénation. Dans tous les cas, l'oxydation totale est réalisée en exposant la pièce à une atmosphère oxydante, à une température comprise entre 400 et 850°C.According to a fourth embodiment, which is simply a variant of the third mode, the initial alloy is in powder form, but the latter is compacted after oxygenation. In all cases, the total oxidation is carried out by exposing the workpiece to an oxidizing atmosphere at a temperature between 400 and 850 ° C.
L'invention concerne également un alliage à base d'argent, caractérisé en ce qu'il contient au moins un métal, soluble dans l'argent et susceptible de former un oxyde stable à haute température et qui, par oxydation interne, le durcit, tout en permettant d'obtenir une taille de grains finale inférieure à 20μm.The invention also relates to a silver-based alloy, characterized in that it contains at least one metal, soluble in silver and capable of forming an oxide stable at high temperature and which, by internal oxidation, hardens it, while making it possible to obtain a final grain size of less than 20 μm.
De façon avantageuse, le métal allié à l'argent est choisi parmi le magnésium, l'aluminium, le titane, le gallium, le manganèse et le zinc ou une combinaison de ces métaux. La teneur est comprise entre 0.04 et 4% atomique.Advantageously, the metal alloyed with silver is selected from magnesium, aluminum, titanium, gallium, manganese and zinc or a combination of these metals. The content is between 0.04 and 4 atomic%.
D'autres caractéristiques de l'invention ressortiront de la description qui va suivre.faite en référence au dessin annexé, dans lequel les figures 2 et 3 sont des coupes métallographiques de plaques d'alliage Ag-Mg, respectivement, après l'étape d'oxygénation et après l'oxydation totale selon l'invention. Selon un premier mode de mise en œuvre de l'invention, on part d'une pièce en un simple alliage Ag-Mg ayant la forme finale souhaitée. L'alliage utilisé est généralement à l'état écroui, avec un taux de réduction de section de l'ordre de 50 à 95%. Les éventuels traitements thermiques préalables ont été effectués sous une atmosphère neutre ou réductrice, à une température suffisamment basse pour conserver un grain fin. Typiquement, les différentes opérations ont duré une heure, à une température d'environ 500°C. L'alliage présente une teneur en magnésium égale à celle visée pour l'application finale. Généralement, cette teneur est comprise entre 0.04 et 4% atomique.Other features of the invention will emerge from the description which suivre.faite with reference to the accompanying drawing, wherein Figures 2 and 3 are metallographic sections of Ag-Mg alloy plates, respectively, after step d 'oxygenation and after total oxidation according to the invention. According to a first implementation mode of the invention, one starts from a workpiece in a single Ag-Mg alloy having the desired final shape. The alloy used is generally in the cold worked condition, with a cross-section reduction rate of about 50 to 95%. Any preliminary heat treatments were carried out under an inert or reducing atmosphere at a temperature low enough to maintain a fine grain. Typically, the various operations lasted one hour at a temperature of about 500 ° C. The alloy has a Mg content equal to that referred to the final application. Generally, this content is between 0.04 and 4 atomic%.
La première phase du procédé consiste à faire subir à la pièce une oxygénation. A cet effet, un courant d'oxygène circule à son contact, à une température d'environ 300°C, pendant une durée nécessaire à l'obtention de la pénétration recherchée. Typiquement, cette durée est de 24 heures pour une pénétration de 50 microns mais elle peut être réduite si l'on augmente la pression partielle d'oxygène. Dans ces conditions, l'oxygène diffuse à l'intérieur de la pièce et se dissout dans l'argent sans oxyder le magnésium de manière sensible. La dureté de l'alliage n'augmente pas et son grain reste fin.The first phase of the process consists in subjecting the workpiece oxygenation. To this end, a current of oxygen flows in contact with it, at a temperature of approximately 300 ° C., for a time necessary to obtain the desired penetration. Typically, this period is 24 hours for a penetration of 50 microns but may be reduced by increasing the oxygen partial pressure. Under these conditions, oxygen diffuses inside the room and dissolved in silver without oxidizing the magnesium significantly. The hardness of the alloy is not increased and grain remains end.
La figure 2 montre bien l'effet de cette oxygénation sur une plaque d'alliageFigure 2 shows the effect of the oxygenation on an alloy plate
Ag-Mg (0.9% atomique de Mg). On distingue que les couches externes 12 présentent des grains de petite taille, inférieure à 20 μm. Par ailleurs, la mesure de la dureté donne 57HV pour les couches externes et 51 HV pour la couche centrale 14. Puis, dans une deuxième phase, la pièce est placée sous un courant d'air ou d'oxygène, à une température comprise entre 400 et 850°C, de préférence environ 600°C. Le magnésium est alors oxydé en MgO. La durée de cette phase dépend de la température, de la pression partielle d'oxygène et de l'épaisseur de la couche d'oxyde recherchée.Ag-Mg (0.9 atomic% of Mg). It can be seen that the outer layers 12 have small grains, less than 20 μm. In addition, the hardness measurement gives 57HV for the external layers and 51 HV for the central layer 14. Then, in a second phase, the part is placed under a stream of air or oxygen, at a temperature of between 400 and 850 ° C., preferably around 600 ° C. The magnesium is then oxidized to MgO. The duration of this phase depends on the temperature, the partial pressure of oxygen and the thickness of the desired oxide layer.
Cependant, si l'on examine, de plus près, le phénomène d'oxydation ainsi effectué, on observe qu'il comporte deux phases. Tout d'abord, l'oxygène mis en solution dans l'argent au cours de l'étape d'oxygénation oxyde immédiatement une partie du magnésium. La quantité d'oxygène dissout dans l'argent étant insuffisante pour oxyder la totalité du magnésium présent dans l'alliage, l'oxydation est alors partielle et il se forme des particules de précipité de MgO qui s'insèrent dans la matrice de l'alliage et empêchent le grossissement des grains d'Ag-Mg en bloquant leurs joints. Puis, dans la continuité, l'oxygène présent dans l'atmosphère poursuit l'oxydation du magnésium pendant un certain temps, de manière à l'oxyder sur au moins une couche extérieure. L'alliage durcit donc mais, grâce à la présence des particules de précipité qui jouent le rôle de dispersoïde, la taille de ses grains est inférieure à 20μm.However, if we examine more closely the phenomenon of oxidation and done, he observed two phases. First, the oxygen dissolved in silver oxide during the step of oxygenating immediately part magnesium. The amount of oxygen dissolved in silver being insufficient to oxidize all the magnesium present in the alloy, the partial oxidation is then and is formed of MgO precipitate particles that fit into the matrix of the alloy and prevent the coarsening of Ag-Mg grains by blocking their joints. Then, in continuity, the oxygen present in the atmosphere continues the oxidation of magnesium for a while, so as to oxidize at least one outer layer. The alloy hardens so but, thanks to the presence of precipitated particles that act as dispersoid, the size of the grains is less than 20 .mu.m.
Ce résultat est illustré sur la figure 3. Les couches externes 16 ayant été oxygénées au cours de la première phase du procédé présentent, après oxydation, des grains fins dont la taille est inférieure à 20μm. La couche centrale 18 n'a pas été oxygénée et, pour souligner l'apport de la phase d'oxygénation, elle a été oxydée au cours de la deuxième phase. Ainsi, la zone centrale peut être directement comparée avec ce que montre la figure 1. Sa dureté est celle d'un alliage Ag-MgO, mais les grains sont gros et rendent le matériau cassant. La mesure de la dureté donne 136HV pour les couches externes et 147HV pour le centre.This result is illustrated in Figure 3. The outer layers 16 having been oxygenated during the first phase of the present process, after oxidation, fine grains whose size is less than 20 .mu.m. The central layer 18 was not oxygenated and, to emphasize the contribution of the oxygenation phase, it was oxidized during the second phase. Thus, the central area can be directly compared with that shown in Figure 1. Its hardness is that of a Ag-MgO alloy, but the grains are large and make the material brittle. The hardness measurement gives 136HV to 147HV and the outer layers to the center.
Pour une utilisation pratique, si l'oxygénation préalable n'a pas été effectuée sur toute l'épaisseur de la pièce, il est donc important que l'oxydation se fasse sur une profondeur égale ou inférieure à celle de la couche oxygénée, afin d'éviter tout risque de rupture. L'alliage ainsi obtenu présente des qualités similaires à un alliage Ag-Mg-Ni classique mais, comme il ne contient pas de nickel, il n'est pas allergène et ne pollue pas les matériaux supraconducteurs à haute température. Cependant, l'alliage constitué est très dur et peut donc être difficilement mis en forme. Selon un deuxième mode de mise en œuvre de l'invention, on part d'une pièce intermédiaire, par exemple sous la forme d'un fil, d'un tube ou d'une bande, réalisée en un alliage Ag-Mg. Cette pièce subit d'abord, comme dans le premier mode de réalisation, une phase d'oxygénation.For practical use, if the prior oxygenation has not been carried out over the entire thickness of the part, it is therefore important that the oxidation takes place at a depth equal to or less than that of the oxygenated layer, in order to '' avoid any risk of breakage. The alloy thus obtained has qualities similar to a conventional Ag-Mg-Ni alloy but, since it does not contain nickel, it is not allergenic and does not pollute superconductive materials at high temperature. However, the alloy formed is very hard and can therefore be difficult to shape. According to a second embodiment of the invention, one starts from an intermediate piece, for example in the form of a wire, a tube or a strip, made of an Ag-Mg alloy. This part first undergoes, as in the first embodiment, an oxygenation phase.
Ensuite, on décompose les deux phases de l'oxydation en ne réalisant, d'abord, que l'oxydation partielle. A cet effet, la pièce est placée pendant une heure environ, sous vide ou dans une atmosphère inerte (par exemple azote ou d'argon), à une température comprise entre 400 et 850°C. Comme précédemment, il se forme un précipité de MgO qui empêche les grains d'alliage de grossir. A ce niveau du procédé, la pièce est encore malléable et sa forme finale lui est alors donnée, par exemple, par laminage, étirage, découpage, pliage, étampage ou emboutissage..., ces techniques étant bien connues de l'homme de métier.Then, decomposes the two phases of oxidation not realizing, first, the partial oxidation. For this purpose the workpiece is placed for approximately one hour in vacuum or in an inert atmosphere (e.g. nitrogen or argon) at a temperature between 400 and 850 ° C. As before, there is formed a precipitate of MgO which prevents alloy grains to grow. At this stage of the process, the workpiece is still malleable and its final form is then given to him, for example, by rolling, drawing, cutting, bending, stamping or drawing ..., these techniques being well known to those skilled in the art .
Ensuite seulement, l'oxydation du magnésium en MgO est achevée, dans des conditions semblables à celles évoquées ci-dessus. L'alliage durcit alors, sans que les grains grossissent.Only then the oxidation of magnesium as MgO is complete under similar conditions to those mentioned above. The alloy then hardens, without the grains growing.
Selon un troisième mode de mise en œuvre de l'invention, on part d'un alliage d'argent et de magnésium sous forme de poudre, qui est ensuite compactée, tout en conservant une porosité ouverte sur toute son épaisseur, sous une forme intermédiaire, par exemple, une billette cylindrique de 100mm de diamètre et de 500mm de longueur. Puis, comme dans le premier mode de réalisation, la pièce subit une phase d'oxygénation.According to a third implementation mode of the invention, the starting material is an alloy of silver and magnesium in powder form, which is then compacted, while maintaining an open porosity throughout its thickness, an intermediate form for example, a cylindrical billet of diameter 100mm and length 500mm. Then, as in the first embodiment, the workpiece undergoes oxygenation phase.
L'opération suivante est une extrusion à chaud de la pièce compactée. Pour ce faire, elle est d'abord préchauffée, à une température comprise entre 400°C et 850°C et en atmosphère inerte, ce qui entraîne automatiquement le déclenchement de la phase d'oxydation partielle. On procède ensuite à l'extrusion et à la mise en forme finale de la pièce avant d'effectuer, enfin, l'oxydation complète du magnésium.The following operation is a hot extrusion of the compacted part. To do this, it is first preheated, to a temperature between 400 ° C and 850 ° C and in an inert atmosphere, which automatically causes the initiation of the partial oxidation phase. We then proceed to the extrusion and final shaping of the part before performing, finally, the complete oxidation of magnesium.
On notera que, selon un quatrième mode de mise en œuvre de l'invention, constituant une variante du troisième mode de mise en œuvre, la phase d'oxygénation peut parfaitement intervenir avant le compactage de l'alliage.Note that, according to a fourth implementation mode of the invention, constituting a variant of the third implementation mode, the phase of oxygenation may well take place before compacting the alloy.
La présente description a été faite en se référant à l'utilisation, au départ du procédé, d'un alliage Ag-Mg, dont la teneur en magnésium est comprise entre 0.04 et 4% atomique. Il va de soi, cependant, que le magnésium peut être remplacé, partiellement ou totalement, par tout métal soluble dans l'argent aux teneurs susmentionnées et susceptible de le durcir en formant un oxyde stable à haute température. Par ailleurs, pour fournir un matériau aux propriétés mécaniques acceptables, ces éléments doivent, à l'état oxydé, fournir des grains d'alliage de taille inférieure à 20 μm. C'est ainsi, par exemple, que l'on peut utiliser, entre autre, de l'aluminium, du titane, du gallium, du manganèse ou du zinc.The present description has been made with reference to the use, starting from the method, an Ag-Mg alloy, the magnesium content is between 0.04 and 4 atomic%. It goes without saying, however, that the magnesium may be replaced partially or completely by any soluble metal silver to the above contents and capable of curing in forming the high temperature stable oxide. Furthermore, to provide a material with acceptable mechanical properties, these elements must, in the oxidized state, provide alloy grains of size less than 20 μm. For example, aluminum, titanium, gallium, manganese or zinc can be used, for example.
Ainsi est proposé un procédé qui permet d'obtenir un alliage à base d'argent, rendu très dur grâce à la présence d'un oxyde métallique et conservant un grain • particulièrement fin. L'alliage résultant peut être particulièrement employé pour certaines pièces de bijouterie, sans présenter de risque particulier d'allergie, ou encore, dans des gaines pour câble supraconducteur à haute température, sans polluer le matériau supraconducteur. Thus is provided a method which allows to obtain a silver-based alloy, made very hard by the presence of a metal oxide and retaining a grain • particularly fine. The resulting alloy can be particularly used for certain pieces of jewelry, without presenting any particular risk of allergy, or even in sheaths for superconductive cable at high temperature, without polluting the superconductive material.

Claims

REVENDICATIONS
1. Procédé de réalisation d'une pièce en alliage à base d'argent, caractérisé en ce qu'il consiste à se doter d'un alliage initial contenant de l'argent et au moins un métal soluble dans l'argent à des teneurs comprises entre 0.04 et 4% atomique, et susceptible de former un oxyde stable à haute température, puis à effectuer successivement les opérations suivantes :1. A method of making a part made of silver-based alloy, characterized in that it consists in building an initial alloy containing silver and at least one soluble metal money in amounts between 0.04 and 4 atomic%, and capable of forming a high temperature stable oxide, and then successively carrying out the following operations:
- oxygénation de l'alliage initial de manière à dissoudre de l'oxygène dans l'argent qu'il contient,- oxygenation of the initial alloy so as to dissolve oxygen in the money in it,
- oxydation partielle du métal soluble de manière à former des particules de précipité empêchant les grains d'alliage de grossir, et- the partial oxidation of soluble metal to form precipitate particles preventing the alloy grains of fat, and
- oxydation totale, sur au moins une couche extérieure, du métal soluble en un oxyde stable à haute température.- complete oxidation on at least one outer layer, soluble metal at high temperature stable oxide.
2. Procédé selon la revendication 1 , caractérisé en ce que l'oxygénation est effectuée en exposant l'alliage initial à un courant d'oxygène.2. Method according to claim 1, characterized in that oxygenation is effected by exposing the pre-alloy to an oxygen stream.
3. Procédé selon la revendication 2, caractérisé en ce que l'oxygénation a lieu à une température d'environ 300°C.3. A method according to claim 2, characterized in that the oxygenation takes place at a temperature of about 300 ° C.
4. Procédé selon l'une des revendications 1 à 3, caractérisé en ce que l'alliage initial est une pièce ayant la forme finale souhaitée et en ce que l'oxydation totale a lieu dans la continuité de l'oxydation partielle.4. A method according to one of claims 1 to 3, characterized in that the initial alloy is a part having the desired final shape, and in that the total oxidation is carried out in the continuity of the partial oxidation.
5. Procédé selon l'une des revendications 1 à 3, caractérisé en ce que l'alliage initial est une pièce ayant une forme intermédiaire, telle qu'un fil, un tube ou une bande, en ce que l'oxydation partielle est effectuée en plaçant la pièce oxygénée pendant environ une heure, sous vide ou dans une atmosphère inerte, à une température comprise entre 400 et 850°C, et en ce que, avant son l'oxydation totale, la pièce est mise dans sa forme finale.5. A method according to one of claims 1 to 3, characterized in that the initial alloy is a part having an intermediate form, such as a wire, a tube or a band, in that the partial oxidation is carried out placing the piece hydrogen for about one hour, under vacuum or in an inert atmosphere at a temperature between 400 and 850 ° C, and in that, before its complete oxidation, the workpiece is brought into its final shape.
6. Procédé selon l'une des revendications 1 à 3, caractérisé en ce que l'alliage initial est sous forme de poudre, en ce que ladite poudre est compactée avant l'oxygénation tout en conservant une porosité ouverte sur toute son épaisseur, en ce que la pièce ainsi obtenue est extrudee à chaud, ce qui provoque son oxydation partielle et en ce que, avant son oxydation totale, la pièce est mise dans sa forme finale.6. Method according to one of claims 1 to 3, characterized in that the initial alloy is in powder form, in that said powder is compacted before oxygenation while retaining an open porosity over its entire thickness, in that the part thus obtained is hot extruded, which causes its partial oxidation and in that, before its total oxidation, the part is put into its final form.
7. Procédé selon l'une des revendications 1 à 3, caractérisé en ce que l'alliage initial est sous forme de poudre, en ce que ladite poudre est compactée après l'oxygénation, en ce que la pièce ainsi obtenue est extrudee à chaud, ce qui provoque son oxydation partielle et en ce que, avant son oxydation totale, la pièce est mise dans sa forme finale.7. A method according to one of claims 1 to 3, characterized in that the starting alloy is in powder form, in that said powder is compacted after oxygenation, in that the part thus obtained is melt-extruded , causing its partial oxidation and in that, before its complete oxidation, the workpiece is brought into its final shape.
8. Procédé selon l'une des revendications 1 à 7, caractérisé en ce que l'oxydation totale est réalisée en exposant la pièce à une atmosphère oxydante, à une température comprise entre 400 et 850°C.8. A method according to one of claims 1 to 7, characterized in that the total oxidation is carried out by exposing the workpiece to an oxidizing atmosphere at a temperature between 400 and 850 ° C.
9. Alliage à base d'argent, caractérisé en ce qu'il contient au moins un métal, soluble dans l'argent et susceptible de former un oxyde stable à haute température et qui, par oxydation interne, le durcit, tout en permettant d'obtenir une taille de grains finale inférieure à 20μm.9. Alloy based on silver, characterized in that it contains at least one metal, soluble in silver and capable of forming a high temperature stable oxide and that, by internal oxidation, hardens, while allowing '' obtain a final grain size of less than 20 μm.
10. Alliage selon la revendication 9, caractérisé en ce que ledit métal est choisi parmi le magnésium, l'aluminium, le titane, le gallium, le manganèse et le zinc ou une combinaison de ces métaux.10. An alloy according to claim 9, characterized in that said metal is selected from magnesium, aluminum, titanium, gallium, manganese and zinc or a combination of these metals.
11. Alliage selon l'une des revendications 9 et 10, caractérisé en ce que la teneur dudit métal, seul ou en combinaison, est comprise entre 0.04 et 4% atomique. 11. Alloy according to one of claims 9 and 10, characterized in that the content of said metal, alone or in combination, is between 0.04 and 4 atomic%.
EP04725262A 2003-04-04 2004-04-02 Production process of a silver alloyworkpiece and alloy used for this process Withdrawn EP1613786A1 (en)

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