COPPER PARTICLES BEARING A PROTECTIVE LAYER, POWDERS COMPRISING THEM, AND THEIR USE FOR THE PREPARATION OF COPPER PARTS

Abstract

The present invention relates to copper particles carrying a protective layer, and to the powders comprising them. The invention also relates to the use of said powders for the preparation of copper parts by a powder shaping process, in particular by binder projection, as well as to the corresponding preparation processes. (no figure)

Description

Title of the invention: COPPER PARTICLES BEARING A PROTECTIVE LAYER, POWDERS COMPRISING THEM, AND THEIR USE FOR THE PREPARATION OF COPPER PARTS

[0001] The present invention relates to copper particles carrying a protective layer, and to the powders comprising them. The invention also relates to the use of said powders for the preparation of copper parts by a powder shaping process, in particular by binder projection, as well as the corresponding preparation processes.

[0002] Additive manufacturing, also known as 3D printing, is a process in which material is built up layer by layer to form an object. Binder jetting is an additive manufacturing technique based on the use of a binder to bind particles of a powder together to form a three-dimensional object. In particular, the binder is jetting onto successive layers of the powder in a build volume, where the formed layers of powder and binder adhere to each other to form a three-dimensional object. Further processing, including in particular binder removal, annealing, depowdering of unbound powder and sintering of bound powder, is generally required to transform the printed three-dimensional part into a finished part.

[0003] Additive manufacturing by laser powder bed fusion is becoming increasingly popular, for example, for the production of high-performance electrical and thermal management components. This popularity is explained by the intrinsic advantages of additive manufacturing processes, which allow the manufacture of geometrically complex components, with great design freedom compared to conventional manufacturing processes. These characteristics of additive manufacturing processes, combined with the high electrical and thermal conductivity of pure copper and copper alloys, are increasingly being studied in the field of electricity and heat transfer applications.

[0004] Although it is possible to produce copper parts by spraying binder, the problem of reusing the copper powder used constitutes a barrier, both technical and economic, to its development.

[0005] Indeed, the copper powders used in a binder projection process generally have a particle size of 10 to 30 μm. During the air hardening stage ("curing"), the high reactivity of the copper powder can in particular cause two problems:

[0006] - if this step is carried out at too high a temperature, in particular higher than 100°C, the formation of aggregates or even the solidification of the entire copper block is generally observed. Depowdering will then be difficult or even impossible without causing damage, given the low mechanical strength of the parts produced. The powder, which does not constitute the part and is too compact, cannot then be reused;

[0007] - if this step is carried out at too low a temperature (generally <100°C), the The mechanical properties of the parts produced are poor, with a risk of breakage. In addition, even at low temperatures, the powder is affected by the curing treatment, which will modify the surface properties of the powder. Its reuse for a new printing cycle may then be questionable.

[0008] Given these constraints, it is certainly possible to produce copper parts by binder projection, but the costs linked to the non-recovery of unused copper powder and the fragility of the parts produced make this process unattractive.

[0009] In the context of additive manufacturing of copper, mainly in the field of laser powder bed fusion where the reflectivity problems of the copper powder can be very damaging, the surface properties of the powder used have been identified as the key to obtaining quality parts with the desired properties and yield. In particular, the formation of a protective carbide layer on the surface of a copper powder has been described. But in this case, it is essential to have a chromium fraction within the powder to be able to form said protective layer. This cannot therefore be applied in the case of pure copper, and is of little interest for the binder jetting process. It should also be noted that the addition of carbon generally impacts the final properties of the material in an unfavorable way.It has also been proposed to create a protective layer, consisting of a fatty acid, on the surface of a copper powder, by treating the copper powder in an aqueous solution containing an acid, a reducing agent and an alkali metal salt of fatty acid. But this method requires the use of several chemicals. In addition, it is dedicated only to small copper powders, between 1 and 10 pm.

[0010] The invention aims to avoid the aforementioned drawbacks.

[0011] The invention therefore aims to provide a copper powder which makes it possible to avoid the formation of aggregates, at room temperature or during temperature rise, or the setting of said powder into a block, and therefore to facilitate the depowdering and reuse of the unbound powder thus recovered.

[0012] Another object of the invention is to provide copper powders with the above-mentioned advantageous characteristics, in particular those formed from copper particles having a size adapted to the binder projection process (generally 10 to 30 pm), without inducing major modifications to the different stages of the process, and in particular: - on the ability of the powder to be spread during the formation of the powder bed, therefore to retain its flowability properties; - on the curing conditions, which must generally be at least 110°C and preferably 130°C; and / or up to 180°C; and / or - on the physical properties of the final parts, particularly thermal and electrical.

[0013] Thus, the protection method of the invention improves the flowability of the powder, even when used (when it is recycled) and therefore facilitates its spreading during coating. It also makes it possible to avoid, during the "curing" step, the powder clumping around the parts and therefore to allow depowdering. In addition, it provides this powder with stable surface properties against humidity, and against the agglomeration of powders at room temperature, in particular during reuse and / or storage of the powder.

[0014] Yet another object of the invention is to provide a copper powder having properties of resistance to agglomeration at temperature and at room temperature while making it possible to significantly reduce the number of chemicals necessary for the formation of a protective layer on the surface of the particles of the copper powder, but also a copper powder whose protective layer is easily removed during sintering.

[0015] Thus, according to a first aspect, the invention relates to a particle consisting of or comprising copper, which carries on all or part of its surface a layer consisting of or comprising copper (I) oxide, and the largest dimension of which is from 1 to 30 pm, for example from 10 to 30 pm.

[0016] This largest dimension is in particular that of the total particle, that is to say of the particle and of the layer consisting of or comprising copper (I) oxide.

[0017] According to a particular embodiment, said layer covers from 50 to 100% of the surface of the particle as defined previously. According to a particular embodiment, said layer has a thickness of from 10 to 800 nm, in particular from approximately 500 to approximately 600 nm.

[0018] For example, if we consider a layer with a thickness of 500 nm, this layer represents approximately 6% by volume of the total particle, layer consisting of or comprising copper (I) oxide included.

[0019] According to a particular embodiment, the particle as defined previously is of spherical or spheroidal shape.

[0020] By “spheroid” is meant in particular that all the dimensions of the particle are between 0.9 and 1 times the largest dimension of said particle.

[0021] According to a particular embodiment, the particle as defined above is free of chromium, or is made of copper or substantially made of copper.

[0022] By "substantially consisting of copper" is meant in particular a particle comprising more than 90% by weight, relative to the total weight of the particle, in particular more than 95, 98, or 99% of copper, preferably more than 99% of copper.

[0023] According to another aspect, the present invention also relates to a powder formed from particles as defined above.

[0024] By “powder formed from particles” is meant in particular a powder consisting of or comprising said particles.

[0025] All embodiments described above in relation to a particle also apply here, alone or in combination.

[0026] According to a particular embodiment, the invention relates to a powder as defined above, which has: - a D50 value of between 8 and 13 pm, in particular of approximately 10 pm; and / or - a D10 value of between 3 and 7pm, in particular around 5pm; and / or - a D90 value between 19 and 25pm, in particular around 22pm; and / Or - a gap (D90-D10) / D50 of 0.75 to 1.7, in particular of approximately 1.7.

[0027] According to another aspect, the present invention also relates to a process for preparing a particle as defined above, or a powder as defined above, said process consisting of or comprising a step (i) of bringing a copper powder into contact with a carboxylic acid of formula R-COOH with R being H, Me or COOH.

[0028] According to a particular embodiment, the carboxylic acid is formic acid.

[0029] According to another particular embodiment, the carboxylic acid is acetic acid.

[0030] According to yet another particular embodiment, the carboxylic acid is oxalic acid.

[0031] According to a particular embodiment, the invention relates to a process as defined above in which the carboxylic acid is in the form of an aqueous solution of carboxylic acid, in particular at a level of 1 to 20% by weight, in particular at a level of 1 to 10 or 15% by weight, for example at a level of approximately 10% by weight.

[0032] According to a particular embodiment, the invention relates to a process as defined previously in which step (i) is carried out at a temperature of between 15 to about 40°C, in particular 20 to 25°C, and / or for a period of 10 minutes to 8 hours, in particular 10 minutes to 2 hours, or 2 to 4 or 6 hours.

[0033] According to a particular embodiment, the invention relates to a process as defined previously in which step (i) is preceded by a step (o) of deoxidation of the copper powder, in particular under hydrogen, for example at approximately 150°C and / or for approximately 2 hours.

[0034] The powder obtained at the end of step (i) can be dried, in particular by any technique well known to those skilled in the art, for example using a rotary evaporator (or rota vapor or rotavap), or a vacuum pump.

[0035] The powder obtained at the end of step (i), or of a drying step, can be granulated, in particular by any technique well known to those skilled in the art, for example by means of a mixer, in particular of the Turbula type, or a ball mill.

[0036] The powder obtained at the end of step (i), a drying step, or a granulation step, can be sieved, in particular by any technique well known to those skilled in the art, for example using a 90 μm sieve.

[0037] According to another aspect, the present invention also relates to a process for preparing a particle as defined above, or a powder as defined above, said process consisting of or comprising the following steps:

[0038] (i') a step of oxidation in air of a copper powder at a temperature Ta between 90 and 130°C, in particular around 100°C, for a period of between 4 and 10 hours, in particular for around 6 hours; the powder thus obtained then being granulated;

[0039] (ii') optionally, an oxidation step in air at a temperature Tb, higher at Ta, between 110 and 145°C, in particular approximately 130°C, for a duration of between 4 and 10 hours, in particular for approximately 6 hours; the powder thus obtained then being granulated;

[0040] (iii') an oxidation step in air at a temperature Tc, higher than Ta, and, when step (ii') exists, higher than a temperature Tb, between 130 and 180°C, in particular approximately 160°C, for a duration between 4 and 10 hours, in particular for approximately 6 hours; the powder thus obtained then being granulated.

[0041] According to a particular embodiment, the granulated powder obtained at the end of step (i'), optionally (ii'), and / or (iii'), is sieved, in particular using a 90 μm sieve.

[0042] According to a particular embodiment, the invention relates to a method as defined previously, consisting of or comprising the following steps:

[0043] (i') A step of oxidation in air of a copper powder at a temperature Ta between 90 and 115°C, in particular around 100°C, for a period of between 4 and 10 hours, in particular for around 6 hours; the powder thus obtained then being granulated;

[0044] (ii') an oxidation step in air at a temperature Tb, higher than Ta, included from 115 to 145°C, in particular approximately 130°C, for a duration of 4 to 10 hours, in particular for approximately 6 hours; the powder thus obtained then being granulated;

[0045] (iii') an oxidation step in air at a temperature Tc, higher than Ta, and, when step (ii') exists, higher than a temperature Tb, between 130 and 180°C, in particular approximately 160°C, for a duration between 4h and 10h, in particular for approximately 6 hours; the powder thus obtained then being granulated.

[0046] According to another particular embodiment, the invention relates to a method as defined previously, consisting of or comprising the following steps:

[0047] (i') A step of oxidation in air of a copper powder at a temperature Ta between 100 and 130°C, in particular approximately 115°C, for a period of between 4 and 10 hours, in particular for approximately 6 hours; the powder thus obtained then being granulated;

[0048] (iii') an oxidation step in air at a temperature Tc, higher than Ta, of between 130 and 180°C, in particular approximately 160°C, for a duration of between 4 and 10 hours, in particular for approximately 6 hours; the powder thus obtained then being granulated.

[0049] According to a particular embodiment, step (i') is preceded by a step (o) of deoxidation of the copper powder, in particular under hydrogen, for example at approximately 150°C and / or for approximately 2 hours.

[0050] According to another aspect, the present invention also relates to a process for preparing a protected copper particle, or a powder formed from said particles, said process consisting of or comprising a step (i) of contacting a copper powder with a carboxylic acid of formula R-COOH with R being H, Me or COOH.

[0051] All embodiments described above relating to a particle, powder or method also apply here, alone or in combination.

[0052] According to another aspect, the present invention also relates to the protected copper particle or the powder formed from protected copper particles capable of being obtained by the method as defined above.

[0053] According to another aspect, the present invention also relates to a method of preparing a protected copper particle, or a powder formed from said particles, said method consisting of or comprising the following steps:

[0054] (i') a step of oxidation in air of a copper powder at a temperature Ta between 90 and 130°C, in particular around 100°C, for a period of between 4h and 10h, in particular for around 6 hours; the powder thus obtained then being granulated;

[0055] (ii') optionally, an oxidation step in air at a temperature Tb, higher at Ta, between 110 and 145°C, in particular around 130°C, for a period between 4h and 10h, in particular for around 6 hours; the powder thus obtained then being granulated;

[0056] (iii') an oxidation step in air at a temperature Tc, higher than Ta, and, when step (ii') exists, higher than a temperature Tb, between 130 and 180°C, in particular approximately 160°C, for a duration between 4h and 10h, in particular for approximately 6 hours; the powder thus obtained then being granulated.

[0057] All embodiments described above relating to a particle, powder or method also apply here, alone or in combination.

[0058] According to another aspect, the present invention also relates to the protected copper particle or the powder formed from protected copper particles capable of being obtained by the method as defined above.

[0059] According to another aspect, the present invention also relates to the use of a powder as defined above, for the manufacture of a copper device, in particular by a method of shaping powder by projection of binder.

[0060] According to another aspect, the present invention also relates to a method of preparing a copper device, which comprises the following steps:

[0061] a) Optionally, a step of sieving a powder as defined previously;

[0062] b) A step of forming a powder bed, from the powder as defined previously or that obtained at the end of step a) on a construction space;

[0063] c) A step of selectively depositing binder on the powder bed obtained at the end of step b), to obtain a slice of the device to be prepared;

[0064] Steps b) and c) being repeated until said device is obtained;

[0065] d) An annealing step;

[0066] e) A depowdering step;

[0067] f) A sintering step.

[0068] Step a) can, if necessary, make it possible to avoid powder agglomerates.

[0069] The thickness of the powder bed obtained at the end of step b) is in particular between 30 and 100 μm.

[0070] Step c) is in particular carried out under conditions well known to those skilled in the art, in particular at a temperature of 50 to 70°C, for example at 55°C.

[0071] Step c) makes it possible in particular to bind the powder particles together and to form a slice of the part to be produced.

[0072] Step d) is in particular carried out under conditions well known to those skilled in the art, for example at a temperature of from 110 to 200°C, in particular from 110 to 180°C, for example approximately 130°C, and / or in air.

[0073] Step d) makes it possible in particular to evaporate part of the binder and to allow consolidation of the parts.

[0074] Step e) is in particular carried out under conditions well known to those skilled in the art, for example by means of a vacuum cleaner and / or a blower.

[0075] Step d) makes it possible in particular to remove excess powder, i.e. the unbound powder located around the part to be produced.

[0076] In the context of step f), the depowdered part is for example positioned in a furnace in order to be densified by a suitable sintering treatment, as well known to those skilled in the art.

[0077] According to a particular embodiment, the powder defined with respect to step a) comes from a depowdering step e) carried out during a prior process. This powder is optionally deoxidized, in particular as defined previously, then optionally treated chemically or physically as defined previously, after said depowdering and prior to a new process according to steps a) to f).

[0078] The copper devices capable of being obtained according to the method defined above find use in markets of interest, for example relating to the manufacture of cooling systems (heat exchangers), the manufacture of EDM electrodes, electric motors, luxury goods, and space. Definitions

[0079] For the purposes of this description, percentages refer to percentages by mass relative to the total mass of the formulation, unless otherwise indicated.

[0080] As used herein, the value ranges in the form of "xy" or "from x to y" or "(included) between x and y" include in particular the limits x and y.

[0081] By “D50” is meant in particular the particle size such that half by volume of the constituent particles of the powder are of a size greater than D50.

[0082] By “D90” is meant in particular the particle size such that 10% by volume of the constituent particles of the powder are of a size greater than D90.

[0083] By “D10” is meant in particular the particle size such that 10% by volume of the constituent particles of the powder are of a size less than D10.

[0084] The characteristics of the powder, and in particular the values ​​of D50, D90 and D10, are in particular measured using a laser granulometer. The device measures the diffraction profile generated by the passage of particles suspended in a gas or a liquid through a laser, and obtains, by a mathematical transformation based on the theory of Mie diffraction, the particle size distribution and the volume concentration of the particle in question in the gas or liquid.

[0085] The apparent density is measured in particular by placing a known mass of powder in a graduated cylinder. Dividing the mass of powder by its volume allows the apparent density of a powder to be obtained. The tapped density of a powder is measured in particular by placing a known mass of powder in a graduated cylinder. This cylinder is then tapped 1000 times by a standardized device (for example Autotap Autotap from the Anton Paar brand) and the final volume is measured. Dividing the mass of powder by the volume occupied by it after tapping allows the tapped density to be obtained.

[0086] The avalanche angle is measured, in particular, by means of a rotating drum. The avalanche angle is measured, for example, by means of a REVOLUTION Powder Analyzer rotating drum. When the drum rotates, an avalanche of powder is triggered and the avalanche angle is thus measured. The given value of the avalanche angle is, for example, averaged over 150 avalanches. FIGURES

[0087] [Fig.l] shows a photograph obtained using a conventional XL30 type electron microscope of a powder obtained according to example 1, then cold coated in a resin, and finally polished.

[0088] [Fig.2] illustrates the state of powder A (A, invention), of the initial powder (B, called Virgin) as well as a powder having undergone a deoxidation treatment under hydrogen (C, called Dox) after treatment under air at 130°C for 6 hours according to example 3.

[0089] [Fig. 3] shows examples of copper parts produced by a method according to the invention from a copper powder according to the invention. These are electrodes for electroerosion (or EDM for "Electrical discharge machining"), which have been used successfully for machining complex shapes. EXAMPLES

[0090] Example 1: Preparation of a copper powder according to the invention by chemical treatment

[0091] A copper powder (50 g, marketed by Sandvik) was immersed in a bath of 10% formic acid (this acid can be replaced by acetic or oxalic acid) for a time ranging from 10 min to 8 h, for example 2 hours, then dried, granulated and sieved.

[0092] The copper powder thus obtained has the following particle size: Di0=5pm; D50 = 10pm; D9o= 22pm, and will be referred to below as powder A.

[0093] The powder can then be used directly or stored.

[0094] The chemical treatment has the effect of generating a surface oxide layer ( <lpm ), [Fig.l]. Cette couche a été caractérisée en XPS comme étant du Cu2O, alors que la surface de la poudre de départ en est dépourvue. La poudre ainsi obtenue peut être utilisée dans la cadre d’un procédé de « binder jetting » afin de produire des pièces de cuivre.

[0095] Example 2: Preparation of a copper powder according to the invention by heat treatment

[0096] A copper powder (Sandvik, see previous example) was treated as follows:

[0097] - Deoxidation treatment under hydrogen at 150°C for 2 hours. This treatment allows the thermal history of the powder to be erased. The powder is then granulated using a turbulator and then sieved with a 90 pm sieve to remove any agglomerates;

[0098] - Oxidation treatment in air at 100°C for 6 hours. The powder is then granulated using a turbulator then sieved with a 90pm sieve to remove any agglomerates;

[0099] - Oxidation treatment in air at 130°C for 6 hours. The powder is then granulated using a turbulator then sieved with a 90pm sieve to remove any agglomerates;

[0100] - Oxidation treatment in air at 160°C for 6 hours. The powder is then granulated using a turbulator then sieved with a 90pm sieve to remove any agglomerates.

[0101] After treatment at 160°C the powder is ready.

[0102] The heat treatment has the effect of generating a surface oxide layer ( <lpm ). La poudre ainsi obtenue peut être utilisée dans la cadre d’un procédé de « binder jetting » afin de produire des pièces de cuivre.

[0103] The copper powder thus will be referred to below as powder B.

[0104] Example 3: Demonstration of the improvement in flowability within the framework of the invention

[0105] Powder A was poured into a ceramic ring and then treated in air at 130°C for 6 hours. Two controls, namely the initial powder (called Virgin) and a powder having undergone a deoxidation treatment under hydrogen (called Dox), underwent the same treatment, 130°C 6 hours in air.

[0106] After treatment, the ceramic ring is removed. In the case of powder A, the powder spreads immediately, Figure 2A. In the case of the initial powder (Figure 2B) and the deoxidized powder (Figure 2C), the powder forms a block that does not flow.

[0107] Similarly, powder B according to the invention was tested by subjecting it to heat treatments in air at 100°C and 130°C, for 6 hours. At the end of these treatments, the powder showed no signs of agglomeration.

[0108] In addition, the flowability and apparent density of powder B were measured and compared to the initial powder (Virgin) and to a Dox powder, controls as defined above. These measurements are reported in Table 2.

[0109] Compared to the initial powder, powder B has equivalent flowability and apparent density, therefore perfectly compatible with the process.

[0110] It will be noted that the Dox powder has low flowability, highlighting the impact of surface oxidation on this property. Sample Avalanche angle Apparent density [deg] SD [%] SD Virgin 39.8 2 53.0 Dox 68.5 22 41.5 0.2 powder B 44.4 2 47.9 0.3

[0111] Example 4: Preparation of a copper part from a powder of the invention according to example 1

[0112] In order to measure their thermal and electrical properties, parts of simple shapes were produced, with Virgin powder (control outside the invention) and A (invention) as described above, by reproducing the steps of the binder jetting process. The properties of the parts produced are reported in the following table 1. Raw density % Sintered density % Electrical conductivity % IACS Thermal conductivity Wm-lk-1 Parts produced with powder A Average of at least 3 measurements 50.62 92.3 81 340 (81%) Standard deviation 1.25 0.8 1 18 Parts produced with powder Virgin Average of at least 3 measurements 57.6 92.7 77 318 (79%) Standard deviation 0.9 0.4 1 4

[0113] Table 1 shows that the final properties of the parts obtained using the powder of the invention are equivalent or even superior to those obtained using the original powder.

Claims

1.

2. Claims Process for the preparation of a particle consisting of or comprising copper, which carries on all or part of its surface a layer consisting of or comprising copper (I) oxide, and the largest dimension of which is between 10 and 30 pm, said process: - consisting of a step (i) of bringing a copper powder into contact with an aqueous solution of a carboxylic acid of formula R-COOH with R being H, Me or COOH; Or - consisting of or comprising the following steps: (i') A step of oxidation in air of a copper powder at a temperature Ta of 90 to 130°C, in particular approximately 100°C, for a duration of 4 hours to 10 hours, in particular for approximately 6 hours; the powder thus obtained then being granulated; (ii') optionally, an oxidation step in air at a temperature Tb, higher than Ta, between 110 and 145°C, in particular approximately 130°C, for a duration between 4h and 10h, in particular for approximately 6 hours; the powder thus obtained then being granulated; (iii') an oxidation step in air at a temperature Tc, higher than Ta, and, when step (ii') exists, higher than a temperature Tb, between 130 and 180°C, in particular approximately 160°C, for a duration between 4h and 10h, in particular for approximately 6 hours; the powder thus obtained then being granulated. The method of claim 1, wherein: - The carboxylic acid is in the form of an aqueous carboxylic acid solution, in an amount of 1 to 20% by weight, in particular in an amount of 1 to 10 or 15% by weight, for example in an amount of about 10% by weight; and / or - Step (i) is carried out at a temperature of 15 to 40°C, and / or for a period of 10 minutes to 8 hours, in particular 10 minutes to 2 hours, or 2 to 4 or 6 hours.

3. Method according to claim 1 or 2, in which step (i) is preceded by a step (o) of deoxidation of the copper powder, in particular under hydrogen, for example at approximately 150°C and / or for approximately 2 hours.

4. Method according to claim 1, in which the granulated powder obtained at the end of step (i'), optionally (ii'), and / or (iii'), is sieved, in particular using a 90 μm sieve.

5. Method according to claim 1 or 4, in which step (i') is preceded by a step (o) of deoxidation of the copper powder, in particular under hydrogen, for example at approximately 150°C and / or for approximately 2 hours.

6. Method according to any one of the preceding claims, in which said layer: - covers from 50 to 100% of its surface; and / or - has a thickness of from 10 to 800 nm, in particular from approximately 500 to approximately 600 nm.

Images