Cunisn alloy with spinodal decomposition and method of producing the same

Abstract

[Spinodal decomposition CuNiSn alloy and method for preparing same] The invention relates to a spinodal decomposition CuNiSn alloy based on copper (Cu), nickel (Ni) and tin (Sn), said alloy being composed of, in mass %: - Ni in a proportion of between 4.0 and 20.0%, - Sn in a proportion of between 2.0 and 10%, - Mn in a proportion of between 0.1 and 0.3%, - Nb in a proportion of between 0.04 and 0.09%, - Ti in a proportion of between 0.002 and 0.07%, - O in a proportion of between 0.0010 and 0.0100%, the remainder being copper, and a proportion of less than 0.5% of unavoidable impurities, said alloy also having, in its metallic matrix, oxides of Ti and Nb with dimensions of between 50 and 1000 nm.

Description

[0001] The present invention relates to the field of alloys and, more particularly, to ternary alloys comprising copper (Cu), nickel (Ni) and tin (Sn), these alloys being denoted CuNiSn.

[0002] Such alloys can be produced in foundries by continuous casting and semi-continuous casting, and these alloys are characterized by their structural hardening mode, with spinodal decomposition and ordered precipitation.

[0003] This method of structural hardening makes it possible to give CuNiSn alloys high mechanical characteristics, comparable to those of copper beryllium alloys (CuBe), without presenting the environmental and health disadvantages linked to the presence of beryllium in the alloy.

[0004] In addition to these mechanical characteristics, it also has good resistance to corrosion in aggressive environments, such as marine, hydrogenated or sulphurous environments, as well as good tribological properties, namely a low coefficient of friction and resistance to abrasion.

[0005] Such CuNiSn alloys are produced in the form of foundry products, including bars, ingots, plates, sheets, strips, wires and tubes, which are then intended to be hot or cold processed after a prior homogenization step to absorb the foundry segregations resulting from the high tin contents of the alloy.

[0006] Transformations can be carried out by rolling, forging, extrusion, drawing, wire drawing, with the possibility of carrying out intermediate annealing, with quenching.

[0007] Structural hardening is achieved by a tempering treatment, after solution treatment of the alloy. A cold deformation step between solution treatment and tempering is possible.

[0008] In the state of the art, there is known in particular, from patent documents US 11643713 and EP 2 989 223, a CuNiSn spinodal alloy comprising between 5 and 20% by weight of nickel, between 5 and 10% by weight of tin, the remainder of the composition of the alloy being copper.

[0009] Minor additions to this alloy composition may be made, including boron (B), zirconium (Zr), iron (Fe), niobium (Nb), magnesium (Mg) and manganese (Mn), each of which may be present in an amount of less than 0.3% by weight.

[0010] However, in this type of alloy, poor control of the final niobium content does not allow the achievement of the necessary and homogeneous mechanical and microstructural characteristics throughout the final product, whether it is a bar, an ingot, a plate, a tube or a wire.

[0011] However, the element niobium is likely to undergo oxidation during the production in a foundry of an alloy containing niobium, in particular when carrying out traditional foundry processes, i.e. processes which do not use melting and casting under vacuum or under atmosphere.

[0012] Consequently, the final Nb content in a product made from such an alloy will be substantially lower than the content initially introduced but also very heterogeneous within the same foundry product. The mechanical and microstructural characteristics of said product will therefore be degraded.

[0013] Furthermore, manganese does not act as an effective protector against the oxidation of niobium, since the affinity of manganese for oxygen is lower than the affinity of niobium for this element.

[0014] Therefore, niobium will be oxidized before manganese.

[0015] It should also be noted that the use of magnesium should be avoided in the context of a CuNiSn alloy containing niobium and manganese, because magnesium forms compounds with niobium (oxides, silicates, aluminates), which are found in the final product in the form of inclusion chains, visible on the Figure 3 attached drawings. However, these are detrimental to the mechanical properties of the alloy.

[0016] Therefore, it is necessary to find a solution to control the final niobium content of a CuNiSn alloy containing Nb, in order to avoid its loss during the alloy production, in order to guarantee the achievement of homogeneous mechanical and microstructural characteristics throughout the finished product.

[0017] It is important to specify that the loss by oxidation of niobium during the casting time cannot be compensated simply by an initial overdose of niobium because with too high a percentage of Nb in the alloy, the kinetics of structural hardening would be much too slow during tempering.

[0018] In an inventive approach, the inventors were able to demonstrate that the addition of titanium (Ti) to the liquid metal bath, using a particular methodology, during the melting of the alloy, makes it possible to control the Nb content in the solidified product.

[0019] To this end, the present invention provides a CuNiSn alloy with spinodal decomposition based on copper (Cu), nickel (Ni) and tin (Sn), said alloy being characterized in that it consists of, in % by mass: nickel (Ni) in a proportion of between 4.0 and 20.0%, tin (Sn) in a proportion of between 2.0 and 10%, manganese (Mn) in a proportion of between 0.1 and 0.3%, niobium (Nb) in a proportion of between 0.04 and 0.09%, titanium (Ti) in a proportion of between 0.002 and 0.07%, oxygen (O) in a proportion of between 0.0010 and 0.0100%, the remainder being copper and unavoidable impurities, the proportion of unavoidable impurities being less than 0.5% by mass, said alloy also being characterized in that it has, in its metallic matrix, oxides of Ti and Nb having dimensions between 50 and 1000 nm.

[0020] Please note that the composition detailed above concerns the alloy in its raw casting state, or raw foundry state, after casting and solidification.

[0021] The dimensions indicated above, namely that the oxides of Ti and Nb have a size between 50 and 1000 nm, are understood to be the largest dimension of said oxides.

[0022] Generally, these Ti and Nb oxides have a generally spherical or elliptical shape, so that their diameter or their largest axis has a dimension between 50 and 1000 nm, more particularly between 100 and 500 nm.

[0023] According to particular embodiments of the present alloy: the mass ratio between the proportion of Ni and Sn (Ni / Sn) in the alloy is between 1.4 and 2; the Ni / Sn mass ratio is equal to 1.88 for a nickel proportion of between 14 and 16% and a tin proportion of between 7 and 9%; the Ni / Sn mass ratio is equal to 1.5 for a nickel proportion of between 8 and 10% and a tin proportion of between 5 and 7%; the proportion of Nb in the solidified alloy is between 0.065 and 0.085% by mass; the proportion of Ti in the solidified alloy is between 0.002 and 0.06% by mass, preferably between 0.002 and 0.04% by mass.

[0024] The invention also relates to a method for obtaining the CuNiSn alloy with spinodal decomposition as described above, from a composition consisting of Ni in a proportion of between 4.0 and 20.0% by mass, Sn in a proportion of between 2.0 and 10% by mass, Mn in a proportion of between 0.1 and 0.3% by mass, Nb in a proportion of between 0.05 and 0.09%, Ti in a proportion of between 0.01 and 0.07% by mass, the remainder being copper and unavoidable impurities, the proportion of unavoidable impurities being less than 0.5% by mass, said method comprising the following steps, taken in order: melting the various constituents of the composition with the exception of Ti and Nb and obtaining a liquid bath with a mass proportion of dissolved oxygen in the alloy of the order of 0.0010 to 0.0100% relative to the total mass of the alloy, this proportion having been determined by infrared absorption reductive fusion on a sample of alloy taken from the liquid bath and then solidified; introduction of Ti at the end of melting, into the liquid bath, when the temperature of said liquid bath is greater than or equal to 1230°C; introduction of Nb into said liquid bath containing the Ti, in the form of an Nb-Ni master alloy or in the form of an Nb-Ni-Sn master alloy, when the temperature of said liquid bath is greater than or equal to 1250°C.

[0025] The following Table 1 illustrates the oxygen content measured on an alloy sample solidified by the infrared absorption reductive fusion method for two ingots of the CuNi9Sn6 alloy and for six ingots of the CuNi15Sn8 alloy: Oxygen content (%) Alloy Ingot 1 0,0050 CuNi 9 Sn 6 Ingot 2 0,0060 Ingot 3 0,0022 CuNi 15 Sn 8 Ingot 4 0,0011 Ingot 5 0,0037 Ingot 6 0,0024 Ingot 7 0,0026 Ingot 8 0,0052

[0026] According to a particular characteristic of the process of the invention, the Nb is added to the liquid bath in the form of an Nb-Ni mother alloy with an Nb / Ni mass ratio of the order of, or equal to, 1.7.

[0027] The melting process of the invention is preferably carried out without using a vacuum or inerting device.

[0028] The implementation of this process allows, as described above, to achieve a level of residual oxygen in the liquid bath which is not possible with a vacuum melting process or with inerting. In this way, a small amount of oxygen remains present which allows the formation of Ti and Nb oxides in the metal matrix of the alloy, after melting of the different elements and solidification of the alloy, said oxides having a beneficial effect on the microstructure.

[0029] Other aims and advantages of the present invention will appear during the description which follows relating to embodiments which are given only as indicative and non-limiting examples.

[0030] Understanding of this description will be facilitated by referring to the attached drawings in which: [ Fig. 1] represents two bar diagrams illustrating the incidence of the element titanium on the loss of niobium, in % by mass relative to the initial mass of Nb, during the production of a CuNi15Sn8 alloy ( FIG.1A ) and during the development of a CuNi9Sn6 alloy ( FIG.1 B) , each of the bars in the diagram representing an ingot on which the percentage of loss of niobium was calculated, in the presence of different proportions of titanium (tests carried out on eleven ingots for the CuNi15Sn8 alloy of the Figure 1A and on five ingots for the CuNi9Sn6 alloy of the Figure 1B ) and in the absence of titanium (tests carried out on four ingots for the CuNi15Sn8 alloy of the Figure 1A and on an ingot for the CuNi9Sn6 alloy of the Figure 1B ). [ Fig.2] corresponds to an image obtained by scanning electron microscopy (magnification X10,000) on a section showing a polyhedral inclusion of NbNi in the metallic matrix of a CuNi 15 Sn 8 alloy remaining in an alloy once solidified, in other words in the raw foundry state, if the temperatures recommended by the melting process of the invention, for the addition of Ti and Nb in the liquid bath, are not respected, the polyhedral inclusion, harmful to the properties of the final alloy, being circled for highlighting. FIG.3 ] corresponds to an image obtained by scanning electron microscopy (magnification X1000) on a polished section illustrating inclusion chains, harmful to the properties of the alloy, present in the matrix of a CuNiSn alloy and composed of niobium and magnesium oxide. [ Fig. 4 ] illustrates two images, the first image, on the Figure 4 A, was obtained by scanning electron microscopy (magnification X250) on a polished section illustrating oxides containing titanium and niobium, identified by arrows, in a metallic matrix made of the CuNi15Sn8 alloy in the as-cast state, while the second image, on the Figure 4 B , was obtained by scanning electron microscopy (magnification X10,000) illustrating a Ti and Nb oxide identified by an arrow, in a metallic matrix made of the CuNi15Sn8 alloy in the as-cast state. Fig. 5] illustrates a scatter plot representing the Vickers hardness, expressed as Hv on the ordinate, as a function of the tempering time, expressed in hours on the abscissa, for three bars of the CuNi15Sn8 alloy after casting, homogenization treatment, cold deformation, solution treatment and final hardening heat treatment (tempering), with different proportions of niobium, namely 0.0527% Nb (results expressed by triangles), 0.0710% Nb (results expressed by circles) and 0.0940% Nb (results expressed by diamonds).

[0031] The present invention relates to a CuNiSn alloy with spinodal decomposition based on copper (Cu), nickel (Ni) and tin (Sn), said alloy being obtained from an initial composition consisting of, in % by mass, relative to the total mass of the composition: Ni in a proportion of between 4.0 and 20.0%, Sn in a proportion of between 2.0 and 10%, Mn in a proportion of between 0.1 and 0.3%, Nb in a proportion of between 0.05 and 0.09%, preferably between 0.065% and 0.085% Ti in a proportion of between 0.01 and 0.07%, preferably between 0.01% and 0.04%.

[0032] The rest of the basic composition of the alloy consists of copper and unavoidable impurities, these being present in the composition in a maximum proportion of 0.5%.

[0033] The composition of the spinodal decomposition CuNiSn alloy of the invention does not contain any other constituent except for unavoidable impurities, due to manufacturing, in a maximum proportion of 0.5%.

[0034] In the initial composition, the mass ratio between the proportion of Ni and Sn (Ni / Sn) is between 1.4 and 2.

[0035] In an exemplary embodiment of the alloy composition, the Ni / Sn mass ratio is equal to 1.88 for a nickel proportion of between 14 and 16% and a tin proportion of between 7 and 9%.

[0036] In a second embodiment, the Ni / Sn mass ratio is equal to 1.5 for a nickel proportion of between 8 and 10% and a tin proportion of between 5 and 7%.

[0037] The inventors have determined that the addition of Ti to the composition of the present alloy, in the proportions indicated above, has an essential effect on the control of the chemical composition of the alloy during its production process. More particularly, it has been demonstrated that, thanks to Ti, the Nb composition of the alloy is kept constant, or almost constant, throughout this production process, and that the residual Ti compounds do not create brittleness.

[0038] Specifically, and as will be illustrated in the remainder of the description through the presentation of test results, the presence of Ti within the basic composition of the alloy makes it possible to control the final Nb content of the product, once the alloy has solidified.

[0039] Nb has a very strong affinity with oxygen, which leads to its oxidation during the manufacture of an alloy containing this element, in particular when implementing traditional processes, without the use of inerting or vacuum devices, if the liquid bath is not properly covered, or during transfers of liquid metal, for example to an ingot mold.

[0040] Thus, the presence of Ti is fundamental in the liquid metal bath during the melting of the different constituents of the alloy, then during the solidification of the latter, to avoid a substantial loss of Nb between the beginning and the end of the process of producing said alloy.

[0041] The CuNiSn alloy of the invention further comprising Mn, Ti and Nb can therefore be, most preferably, produced by traditional foundry techniques, i.e. without the use of inert atmosphere, vacuum or other devices.

[0042] Thus, the CuNiSn alloy with spinodal decomposition, once solidified, and obtained from the composition described above, is made up of, in % by mass: nickel (Ni) in a proportion of between 4.0 and 20.0%, tin (Sn) in a proportion of between 2.0 and 10%, manganese (Mn) in a proportion of between 0.1 and 0.3%, niobium (Nb) in a proportion of between 0.04 and 0.09%, titanium (Ti) in a proportion of between 0.002 and 0.07%, oxygen (O) in a proportion of between 0.0010 and 0.0100%, the remainder being copper and unavoidable impurities, the proportion of unavoidable impurities being less than 0.5% by mass, said alloy also being particular in that it presents, in its metallic matrix, in the raw foundry state after solidification, oxides of Ti and Nb having dimensions between 50 and 1000 nm.

[0043] Generally, these Ti and Nb oxides have a generally spherical or elliptical shape, so that their diameter or their largest axis has a dimension between 50 and 1000 nm, more particularly between 50 and 500 nm.

[0044] Controlling the final Nb content in the product once it has solidified, between 0.04 and 0.09%, preferably between 0.065% and 0.085%, by mass relative to the total mass of the alloy, makes it possible to guarantee the mechanical and microstructural characteristics of said product.

[0045] Due to its characteristics, the present alloy according to the invention may advantageously be used for the manufacture of bars, ingots, plates, sheets, strips, wires, tubes subsequently intended to be used in numerous fields of application, such as aerospace and aeronautics, gas and oil exploitation, mining, watchmaking or even electronics.

[0046] Indeed, the CuNiSn alloy with spinodal decomposition of the invention has excellent mechanical characteristics, as well as good resistance to corrosion in aggressive environments, such as marine, hydrogenated or sulphurous environments, and good tribological properties, in particular a low coefficient of friction, and good resistance to abrasion.

[0047] Most preferably, in the spinodal decomposition CuNiSn alloy of the invention, the mass ratio between the proportion of Ni and the proportion of Sn (Ni / Sn, in % by mass) in the solidified alloy is between 1.4 and 2.

[0048] More preferably still, such a mass ratio is equal to 1.88 for a proportion of nickel between 14 and 16% and a proportion of tin between 7 and 9%.

[0049] In another embodiment, the Ni / Sn mass ratio is equal to 1.5 for a nickel proportion of between 8 and 10% and a tin proportion of between 5 and 7%.

[0050] Most preferably, in the alloy of the present invention, the proportion of Nb is between 0.065 and 0.085% by mass in the solidified alloy.

[0051] It is indeed important that the proportion of Nb in the alloy of the invention remains less than or equal to 0.09%, and preferably between 0.065% and 0.085%, because a proportion of Nb greater than this value of 0.09% would result in structural hardening kinetics that are much too slow during a subsequent tempering heat treatment to which a part manufactured from said alloy is subjected. This aspect will be illustrated below, with reference to the Figure 5 attached drawings.

[0052] As regards the proportion of Ti in the alloy in the raw cast state, once it has solidified, this is more preferably between 0.002 and 0.06% by mass, preferably between 0.002 and 0.04%.

[0053] The invention also relates to a method for obtaining the CuNiSn alloy with spinodal decomposition as described above, from a basic composition consisting of Ni in a proportion of between 4.0 and 20.0% by mass, Sn in a proportion of between 2.0 and 10% by mass, Mn in a proportion of between 0.1 and 0.3% by mass, Nb in a proportion of between 0.05 and 0.09%, Ti in a proportion of between 0.01 and 0.07% by mass, the remainder being copper and unavoidable impurities in a maximum proportion of 0.5%.

[0054] Said method, which is the subject of the present invention, comprises at least the following steps, taken in order: melting the various constituents of the alloy with the exception of Ti and Nb and obtaining a liquid bath; introducing Ti at the end of melting, into the liquid bath, when the temperature of said liquid bath is greater than or equal to 1230°C; introducing Nb into said liquid bath containing Ti, in the form of an Nb-Ni mother alloy or in the form of an Nb-Ni-Sn mother alloy, when the temperature of said liquid bath is greater than or equal to 1250°C.

[0055] Most preferably, according to a particular characteristic of the CuNiSn alloy fusion process with spinodal decomposition, the Nb is added in the form of an Nb-Ni master alloy with an Nb / Ni mass ratio equal to 1.7.

[0056] The spinodal decomposition CuNiSn alloy melting process is carried out without the use of a vacuum or inerting device.

[0057] This results in the subsistence of a certain quantity of dissolved oxygen in the liquid bath in a proportion of between 0.0010 and 0.0100% (between 10 and 100 ppm), preferably between 0.0010 and 0.0060% (between 10 and 60 ppm), and which persists in the alloy once it has solidified.

[0058] Such a proportion of oxygen in the alloy was determined by reductive fusion infrared absorption on a sample of the alloy taken from the liquid bath, then solidified.

[0059] This proportion of oxygen leads to the formation of oxides containing titanium and niobium. These Ti and Nb oxides have a beneficial effect on the microstructure by allowing its refining during hot alloy transformation and recrystallization heat treatment operations.

[0060] This aspect will be illustrated below, with reference to the Figure 4 attached drawings.

[0061] The addition of niobium to the alloy must be in the form of a master alloy NbNi or NbNiSn.

[0062] In fact, the use of a master alloy makes it possible to lower the melting point compared to that of the pure metal (2477°C) but also to limit oxidation when it is introduced into the liquid bath.

[0063] The liquid bath temperatures from which Nb and Ti can be introduced must be carefully chosen to ensure the diffusion of these metals in the bath.

[0064] Thus, titanium must be introduced when the bath has reached at least 1230 °C and niobium when the bath has reached at least 1250 °C. If this condition is not met, then unmelted particles may remain once the alloy has solidified which are detrimental to the mechanical properties, particularly in the form of polyhedral inclusions of NbNi in the metallic matrix of the CuNiSn alloy, one of these inclusions being illustrated in the Figure 2 attached drawings.

[0065] The following examples, given for information purposes only and not being limiting of the invention, make it possible in particular to illustrate the beneficial effect of the addition of Ti on the final Nb content of the solidified product. Example 1 : Impact of titanium on niobium loss during the production of two alloys CuNi15Sn8 and CuNi9Sn6

[0066] Casting tests of several ingots made from two alloys CuNi15Sn8 and CuNi9Sn6 were carried out under industrial conditions.

[0067] More specifically, during these tests, fifteen rectangular section ingots (length / width ratio = 2) and a mass of 3 t were produced from the CuNi15Sn8 alloy.

[0068] Of these fifteen ingots, four were produced from a CuNi15Sn8 alloy composition not comprising Ti but containing Nb. One ingot was produced from a CuNi15Sn8 alloy composition comprising Ti in a proportion lower than the proportion of Ti in the composition of the alloy of the invention, and Nb. Ten ingots were produced according to the composition of the alloy of the invention, with initial Ti and Nb proportions in accordance with the present composition.

[0069] Also, six similar ingots were produced from the CuNi9Sn6 alloy, one of which was produced from an initial composition not containing Ti but containing Nb, and the other five ingots were produced according to the composition defined previously, with different proportions of Ti and Nb within the ranges of values ​​of said initial composition.

[0070] All the alloy compositions after solidification (solidified sample taken at the start and end of casting) which were tested are detailed in Table 2 below.

[0071] To produce all of these ingots, the various constituents of the alloys tested are melted in an electric furnace.

[0072] The solid charge consisting of cathodes or manufacturing scraps ready for remelting is melted by induction. It can therefore include new metals and / or first-grade scraps.

[0073] The addition of Ti and Nb was done according to the sequence of introduction into the liquid bath presented above, when describing the alloy melting process. Table 2: Elemental composition in Nb and Ti of industrial ingots Ingot Ti (%) - Start of casting Ti (%) - End of casting Nb (%) - Start of pouring Nb (%) - End of casting Proportion of loss in Nb Alloy 1 - - 0,0408 0,0010 98% CuNi155n8 2 - - 0,0380 0,0088 77% 3 - - 0,0366 0,0040 89% 4 - - 0,0492 0,0028 94% 5 0,0094 0,0010 0,0737 0,0390 47% 6 0,0339 0,0139 0,0805 0,0694 14% 7 0,0342 0,0188 0,0787 0,0708 10% 8 0,0285 0,0194 0,0801 0,0766 4% 9 0,0399 0,0211 0,0802 0,0683 15% 10 0,0351 0,0203 0,0844 0,0786 7% 11 0,0356 0,0181 0,0844 0,0800 5% 12 0,0330 0,0184 0,0773 0,0641 17% 13 0,0117 0,0036 0,0459 0,0420 8% 14 0,0356 0,0100 0,0792 0,0558 30% 15 0,0318 0,0036 0,0660 0,0497 25% 16 - - 0,0302 0,0010 97% CuNi9Sn6 17 0,0312 0,0226 0,0712 0,0642 10% 18 0,0255 0,0116 0,0834 0,0750 10% 19 0,0281 0,0145 0,0835 0,0807 3% 20 0,0215 0,0114 0,0826 0,0753 9% 21 0,027 0,0135 0,0781 0,0684 12%

[0074] The contents of the Ti and Nb constituents, at the beginning (in the solidified alloy) and at the end of casting (in the solidified alloy), were determined by spark source spectrometry.

[0075] The results obtained are also illustrated on the two bar charts of the Figure 1 , showing the positive impact of the titanium initially present in the composition, on the loss of niobium during the production of a CuNi15Sn8 alloy ( FIG.1A ) and a CuNi9Sn6 alloy ( FIG.1B ) also containing Mn and Nb, each bar of the diagram representing the loss of Nb (in %) on an ingot, the number of which is given on the abscissa.

[0076] The results clearly show that, in the absence of Ti in the starting composition, a significant proportion, greater than 77%, of Nb is lost between the start and the end of the casting.

[0077] The results obtained for ingot No. 5, whose alloy, once solidified, contains a proportion of titanium, at the start of casting, equal to 0.0094% by mass, in other words a proportion lower than that of the alloy composition as defined previously (between 0.01 and 0.07% by mass of Ti), and an initial proportion of Nb of 0.0737% by mass, demonstrate that an insufficient initial proportion of Ti results, here again, in a substantial loss of Nb between the start and the end of casting, of the order of 47%. This results in a final proportion of Nb in the ingot of 0.039%.

[0078] Thus, the minimum content of 0.04% Nb in the alloy once solidified, at the end of casting, is no longer respected.

[0079] However, this has an impact on the mechanical characteristics of the alloy, and in particular on its elongation, as will be illustrated below.

[0080] On the contrary, when the composition of the alloy includes Ti in a proportion within the range of values ​​defined previously, namely between 0.01 and 0.07%, and most preferably between 0.01 and 0.04%, the loss of Nb is substantially reduced, and is less than or equal to 30% between the start and the end of casting.

[0081] These results demonstrate that Ti provides protection for the Nb contained in the metal bath, by eliminating an essential part of the residual oxygen contained in the bath, or the oxygen present at the interface between the bath and the atmosphere.

[0082] Let us note here that a part of the initial proportion of Ti is also eliminated, with this residual oxygen; thus, if the initial proportion of Ti in the basic composition of the alloy is between 0.01 and 0.07% by mass relative to the total mass of the composition, the final proportion of Ti, in the solidified alloy, in the as-cast state, is between 0.002% and 0.07%, preferably between 0.002% and 0.06% by mass relative to the total mass of the alloy, preferably between 0.003 and 0.04%, as illustrated by the results given in Table 2 above.

[0083] In other words, in the absence of titanium, or in the presence of titanium in too low proportions, a significant proportion of niobium is lost during the casting of the ingots, whereas in the presence of titanium in an adequate range in the initial alloy composition, the niobium is preserved. It is therefore possible to produce such an alloy using traditional foundry processes. Example 2 : Impact of Ti and Nb on elongation at break and on microstructure

[0084] In addition to the advantages set out above, the presence of titanium and niobium in the alloy once it has solidified makes it possible to improve its mechanical properties, particularly the elongation at break and the size of the microstructure by allowing a refinement of the grain size.

[0085] Thus, in the CuNi15SN8 alloy in the as-cast state, the presence of inclusions of spherical shape and size between 50 and 1000 nm, more particularly between 50 and 500 nm, identified by arrows on the Figure 4 A and on the Figure 4 B .

[0086] These inclusions are composed of oxides containing Ti and Nb formed from the residual oxygen that has not been eliminated. These compounds are very fine and homogeneously distributed in the matrix, which has an effect on the size of the microstructure, in particular a refining of the grain size by Zener pinning effect. It is therefore the combination of Ti, Nb and O in the alloy once it has solidified that is favorable to the refining of the microstructure.

[0087] As mentioned above, in the absence of titanium, the niobium content cannot be ensured in the alloy, which leads to obtaining insufficient mechanical properties.

[0088] Table 3 below demonstrates the difference in elongation for a CuNi15Sn8 alloy as a function of different Nb contents, of which the values ​​at the start and end of casting (measured on samples of the solidified alloy) are detailed, as are the values ​​at the start and end of casting with regard to the Ti proportions.

[0089] Thus, it was found, in example 1, that the absence of titanium in the basic composition, or the presence of the latter in proportions lower than those defined, does not make it possible to ensure a niobium content corresponding to that claimed; this has consequences on the mechanical properties of the alloy since, at the same level of mechanical resistance (Rm), the elongation at break is degraded compared to products containing titanium and niobium.

[0090] The results shown in Table 3 below were obtained for CuNi15Sn8 products from the foundry process described above. The cast products then underwent a transformation sequence with, in this order: a homogenization treatment, hot deformation, solution treatment, then a final hardening treatment. Table 3: Measurement of mechanical characteristics Rm (tensile strength in MPa) and elongation A (in %) of products obtained with a CuNi15Sn8 alloy with different Nb and Ti contents in the solidified alloy. Rm (MPa) A (%) Nb (%) - Start of casting Nb (%) - End of casting Ti (%) - Start of casting Ti (%) - End of casting 1018 9 0,0474 0,0038 0,0021 - 1036 7,3 0,0474 0,0038 0,0021 - 945 5,5 0,0474 0,0038 0,0021 - 964 4 0,0474 0,0038 0,0021 - 970 21,8 0,0787 0,0708 0,0342 0,0188 942 24,5 0,0787 0,0708 0,0342 0,0188 1014 17,8 0,0787 0,0708 0,0342 0,0188 962 15,3 0,0787 0,0708 0,0342 0,0188 1019 16,5 0,0787 0,0708 0,0342 0,0188 960 16,5 0,0787 0,0708 0,0342 0,0188 1047 13,8 0,0787 0,0708 0,0342 0,0188 969 16,3 0,0787 0,0708 0,0342 0,0188 1006 14 0,0787 0,0708 0,0342 0,0188 1033 14,3 0,0787 0,0708 0,0342 0,0188 957 17,8 0,0787 0,0708 0,0342 0,0188 957 17 0,0787 0,0708 0,0342 0,0188

[0091] It is found that the mechanical tensile strength Rm is similar, between 942 and 1047 Mpa on the one hand, and between 945 and 1036 Mpa on the other hand, obtained respectively for a CuNi15Sn8 alloy in accordance with the invention, containing Nb at 0.0787% and Ti at 0.0342% measured on the alloy once solidified, and for a similar CuNi15Sn8 alloy but containing proportions of Nb and Ti lower than the claimed proportions (respectively 0.0474% and 0.0021% on a solidified sample at the start of casting).

[0092] However, the elongation at break A (%) is significantly higher, between 13.8% and 24.5%, for a CuNi15Sn8 alloy of the invention with Nb at 0.0787% and Ti at 0.0342% in the solidified alloy, for which a large part of the Nb was retained in the alloy once solidified (0.0708%), in comparison with the elongation at break values ​​obtained with a CuNi15Sn8 alloy having lower proportions of Nb and Ti (elongation between 4 and 9%) in the solidified alloy, for which a large part of the Nb was removed during the casting process. Example 3 : Influence of the initial Nb content in the alloy on the hardening time and on the final hardness level

[0093] It has already been mentioned, previously in the description, that the maximum niobium content in the alloy once solidified must not exceed 0.09% by mass.

[0094] Indeed, beyond this value, the final mechanical properties of the alloy are not achieved during the final hardening treatment by spinodal decomposition and precipitation.

[0095] This is particularly true of hardness.

[0096] There Figure 5 attached drawings illustrate this phenomenon.

[0097] The results were obtained for bars of the CuNi15Sn8 alloy after casting, homogenization treatment, cold deformation, solution treatment and final hardening heat treatment (tempering).

[0098] These results show that, at a content of 0.0940% Nb in the alloy, and beyond, we observe, initially, a time lag in hardening, measured by a Vickers hardness test, during the tempering heat treatment.

[0099] Also observed for an alloy with an Nb content of 0.0940% are lower hardness levels than those obtained for alloys containing 0.0710% or 0.0527% Nb. The latter two are included in the alloy composition range which is the subject of the present invention.

[0100] The time lag in hardening is problematic. It requires significantly longer heat treatment times, which has a significant impact on the economic performance of the industrial process.

Claims

1. Spinodal decomposition CuNiSn alloy based on copper (Cu), nickel (Ni) and tin (Sn), said alloy being characterized in that it is made up of, in % by mass: - nickel (Ni) in a proportion of between 4.0 and 20.0%, - tin (Sn) in a proportion of between 2.0 and 10%, - manganese (Mn) in a proportion of between 0.1 and 0.3%, - niobium (Nb) in a proportion of between 0.04 and 0.09%, - titanium (Ti) in a proportion of between 0.002 and 0.07%, - oxygen (O) in a proportion of between 0.0010 and 0.0100%, the remainder being copper and unavoidable impurities, the proportion of unavoidable impurities being less than 0.5% by mass, said alloy also being characterized in that It presents, in its metallic matrix, oxides of Ti and Nb with dimensions between 50 and 1000 nm.

2. Spinodal decomposition CuNiSn alloy, based on copper (Cu), nickel (Ni) and tin (Sn), according to claim 1, characterized in that the mass ratio between the proportion of Ni and Sn (Ni / Sn) is between 1.4 and 2.

3. Spinodal decomposition CuNiSn alloy, based on copper (Cu), nickel (Ni) and tin (Sn), according to claim 2, characterized in that the Ni / Sn mass ratio is equal to 1.88 for a nickel proportion of between 14 and 16% and a tin proportion of between 7 and 9%.

4. Spinodal decomposition CuNiSn alloy, based on copper (Cu), nickel (Ni) and tin (Sn), according to claim 2, characterized in that the Ni / Sn mass ratio is equal to 1.5 for a nickel proportion of between 8 and 10% and a tin proportion of between 5 and 7%.

5. Spinodal decomposition CuNiSn alloy, based on copper (Cu), nickel (Ni) and tin (Sn), according to any one of the preceding claims, characterized in that the proportion of Nb is between 0.065 and 0.085% by mass.

6. Spinodal decomposition CuNiSn alloy, based on copper (Cu), nickel (Ni) and tin (Sn), according to any one of the preceding claims, characterized in that the proportion of Ti is between 0.002 and 0.06% by mass, preferably between 0.003 and 0.04% by mass.

7. A method for obtaining the spinodal decomposition CuNiSn alloy according to any one of the preceding claims, from a composition consisting of Ni in a proportion of between 4.0 and 20.0% by mass, Sn in a proportion of between 2.0 and 10% by mass, Mn in a proportion of between 0.1 and 0.3% by mass, Nb in a proportion of between 0.05 and 0.09%, Ti in a proportion of between 0.01 and 0.07% by mass, the remainder being copper and unavoidable impurities, the proportion of unavoidable impurities being less than 0.5% by mass, said method comprising the following steps, taken in order: - melting the various constituents of the composition with the exception of Ti and Nb and obtaining a liquid bath and obtaining a liquid bath with a proportion by mass of oxygen dissolved in the alloy of the order of 0.0010 to 0.0100% relative to the total mass of the alloy,this proportion having been determined by reductive fusion infrared absorption on a sample of alloy taken from the liquid bath then solidified; - introduction of Ti at the end of fusion, into the liquid bath, when the temperature of said liquid bath is greater than or equal to 1230 °C; - introduction of Nb into said liquid bath containing Ti, in the form of an Nb-Ni master alloy or in the form of an Nb-Ni-Sn master alloy, when the temperature of said liquid bath is greater than or equal to 1250 °C., 8. A method of melting the spinodal decomposition CuNiSn alloy according to the preceding claim, wherein the Nb is added in the form of an Nb-Ni master alloy with an Nb / Ni mass ratio equal to 1.

7.

9. A method of melting the spinodal decomposition CuNiSn alloy according to claim 7 or claim 8 characterized in that it is carried out without the use of a vacuum or inerting device.

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