Metal powder for metal injection moulding method

Abstract

The invention relates to a metal powder for a metal injection moulding method, the metal powder being formed of a cobalt-based alloy comprising: - between 23.00 wt% and 24.25 wt% chromium; - between 9.00 wt% and 11.00 wt% nickel; - between 6.50 wt% and 7.50 wt% tungsten; - between 3.00 wt% and 4.00 wt% tantalum; - between 0.45 wt% and 0.60 wt% carbon; - between 0.30 wt% and 0.50 wt% zirconium; - between 0.15 wt% and 0.25 wt% titanium; - at most 2.00 wt% iron; - at most 0.30 wt% silicon; - at most 0.10 wt% manganese; - at most 0.10 wt% copper; - at most 0.015 wt% sulphur; - at most 0.015 wt% phosphorus; - at most 0.010 wt% boron; - at most 200 ppm oxygen; - at most 200 ppm nitrogen; - at most 100 ppm hydrogen.

Description

[0001] Metal powder for metal injection molding process

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to the field of metal injection molding and more particularly to metal powder for implementing a metal injection molding process.

[0004] STATE OF THE ART

[0005] The metal injection molding process involves producing more or less complex metal parts by injecting a mixture of metal powder and a polymer binder. This process can be used to manufacture parts for turbomachinery.

[0006] There are various materials obtained by metal injection molding process available commercially such as the Inconel 718 alloy. However, this material is limited in temperature to 650°C maximum, which is too low a temperature to be used for example in a turbine or combustion chamber of a turbomachine. There is also the Hastelloy X alloy which resists temperatures up to 950°C, but which is mechanically limited and can therefore only be used for the production of parts subjected to low mechanical loads. There is also the IN738 alloy which has good mechanical strength and good average oxidation / corrosion up to 1000°C.

[0007] Unfortunately, all these alloys have maximum operating temperatures below 1050°C, or even 1000°C. They cannot therefore be used for the manufacture of certain aeronautical parts, particularly turbomachine parts, subject to high mechanical stresses and temperatures above 1000°C, such as fuel injection systems, combustion chambers, turbine distributor sleeves or sealed sectors of turbine blades.

[0008] There is therefore a need for solutions that make it possible to obtain parts, from a metal injection molding process, which have average resistance to traction, fatigue, creep and very good resistance to oxidation / corrosion at least up to 1000°C, or even up to 1050°C.

[0009] STATEMENT OF THE INVENTION

[0010] An aim of the invention is therefore to provide a metal powder for a metal injection molding process, which makes it possible to obtain a part having average resistance to traction, fatigue, creep and very good resistance to oxidation / corrosion at least up to 1000°C, or even up to 1050°C. Another aim of the invention is to provide a metal injection molding process for obtaining a part having the aforementioned characteristics.

[0011] According to a first aspect, there is provided a metal powder for a metal injection molding process, the metal powder being formed from a cobalt-based alloy comprising:

[0012] - between 23.00% and 24.25% by weight of chromium,

[0013] - between 9.00% and 11.00% by weight of nickel,

[0014] - between 6.50% and 7.50% by weight of tungsten,

[0015] - between 3.00% and 4.00% by weight of tantalum,

[0016] - between 0.45% and 0.60% by weight of carbon, preferably between 0.45% and 0.55%, 0.55% being excluded, by weight of carbon,

[0017] - between 0.30% and 0.50% by weight of zirconium,

[0018] - between 0.15% and 0.25% by weight of titanium,

[0019] - maximum 2.00% by weight of iron,

[0020] - maximum 0.30% by weight of silicon,

[0021] - maximum 0.10% by weight of manganese,

[0022] - maximum 0.10% by weight of copper,

[0023] - maximum 0.015% by weight of sulfur,

[0024] - maximum 0.015% by weight of phosphorus,

[0025] - maximum 0.010% by weight of boron,

[0026] - maximum 200 ppm of oxygen,

[0027] - maximum 200 ppm of nitrogen,

[0028] - maximum 100 ppm of hydrogen.

[0029] According to advantageous and non-limiting characteristics, taken alone or in any combination: the powder has a distribution of grain diameters such that the value D10 is between 3 pm and 10 pm; the powder has a distribution of grain diameters such that the value D50 is between 10 pm and 20 pm; the powder has a distribution of grain diameters such that the value D90 is between 20 pm and 40 pm.

[0030] According to a second aspect, a method of manufacturing a powder presented previously is proposed, by atomization.

[0031] According to a third aspect, a method for injection molding of metal from a powder presented previously is proposed, comprising steps of: a) feeding an injection press with a primary mixture for molding a part called a green part, said primary mixture comprising the powder and at least one polymer binder, b) debinding the green part to obtain a part called a brown part, c) sintering the brown part to obtain a part called a sintered part, d) obtaining a part called a final part, the final part corresponding to the sintered part or corresponding to the sintered part after the latter has undergone one or more heat treatments.

[0032] According to advantageous and non-limiting characteristics, taken alone or in any combination: the debinding step is a water-solvent or catalytic type debinding step; the injection molding method further comprises a thermal debinding step; the injection molding method further comprises a hot isostatic compaction treatment step of the sintered part; the injection molding method further comprises a step of quenching the sintered part; the powder is obtained from the manufacturing method according to the second aspect.

[0033] According to a fourth aspect, a part obtained by the injection molding process presented above is provided.

[0034] According to advantageous and non-limiting characteristics: the part is formed from a cobalt-based alloy comprising:

[0035] - between 23.00% and 24.25% by weight of chromium,

[0036] - between 9.00% and 11.00% by weight of nickel,

[0037] - between 6.50% and 7.50% by weight of tungsten,

[0038] - between 3.00% and 4.00% by weight of tantalum,

[0039] - between 0.55% and 0.65% by weight of carbon,

[0040] - between 0.30% and 0.50% by weight of zirconium,

[0041] - between 0.15% and 0.25% by weight of titanium,

[0042] - maximum 2.00% by weight of iron,

[0043] - maximum 0.30% by weight of silicon,

[0044] - maximum 0.10% by weight of manganese,

[0045] - maximum 0.10% by weight of copper,

[0046] - maximum 0.015% by weight of sulfur,

[0047] - maximum 0.015% by weight of phosphorus,

[0048] - maximum 0.010% by weight of boron, - maximum 450 ppm of oxygen,

[0049] - maximum 300 ppm of nitrogen,

[0050] - maximum 125 ppm of hydrogen.

[0051] According to a fifth aspect, a turbomachine is proposed comprising at least one part presented previously.

[0052] DESCRIPTION OF FIGURES

[0053] Other characteristics and advantages of the present invention will appear on reading the following description of a preferred embodiment. This description will be given with reference to the appended figures including:

[0054] Figure 1 shows steps in the metal injection molding process.

[0055] DETAILED DESCRIPTION OF THE INVENTION

[0056] Powder

[0057] A metal powder is proposed for a metal injection molding process. The metal powder is formed from a cobalt-based alloy. In other words, the metal powder consists predominantly, by weight, of cobalt.

[0058] The metal powder alloy further includes:

[0059] - between 23.00% and 24.25% by weight of chromium,

[0060] - between 9.00% and 11.00% by weight of nickel,

[0061] - between 6.50% and 7.50% by weight of tungsten,

[0062] - between 3.00% and 4.00% by weight of tantalum,

[0063] - between 0.45% and 0.60% by weight of carbon, preferably between 0.45% and 0.55%, 0.55% being excluded, by weight of carbon,

[0064] - between 0.30% and 0.50% by weight of zirconium,

[0065] - between 0.15% and 0.25% by weight of titanium,

[0066] - maximum 2.00% by weight of iron,

[0067] - maximum 0.30% by weight of silicon,

[0068] - maximum 0.10% by weight of manganese,

[0069] - maximum 0.10% by weight of copper,

[0070] - maximum 0.015% by weight of sulfur,

[0071] - maximum 0.015% by weight of phosphorus,

[0072] - maximum 0.010% by weight of boron,

[0073] - maximum 200 ppm of oxygen,

[0074] - maximum 200 ppm of nitrogen,

[0075] - a maximum of 100 ppm of hydrogen. The metal powder may also comprise other elements, called polluting elements, in minimal quantities. Preferably, the metal powder comprises a maximum of 50 ppm of the same polluting element. Also preferably, the sum of the proportions of the polluting elements in the metal powder is a maximum of 500 ppm.

[0076] The remainder of the composition detailed above is cobalt.

[0077] It is understood that the “rates” or “contents” of each element of the metal powder expressed as percentages are expressed in mass terms (i.e. mass of said element over the total mass of the metal powder).

[0078] By "between" it is understood that the lower and upper limits are included. For example, "between 23.00% and 24.25% by weight of chromium" means that 23.00% and 24.25% are included as possible proportions by weight of chromium in the metal powder.

[0079] When only "at most" is specified, it is understood that the proportion of the corresponding element may be zero, i.e. the element may be absent from the metal powder. For example, "at most 2.00% by weight of iron" means that the metal powder may comprise 0.00% by weight of iron, i.e. it does not comprise or substantially does not comprise iron. As a second example, "at most 200 ppm of oxygen" means that the metal powder may comprise 0 ppm of oxygen, i.e. it does not comprise or substantially does not comprise oxygen.

[0080] By "ppm" we mean "parts per million", 1 ppm corresponding to 1 mg / kg. Therefore, for example, "200 ppm oxygen" means that 1 kg of metal powder contains 200 mg (i.e. 0.2 g) of oxygen. In other words, "200 ppm oxygen" means that the metal powder contains 200 millionths by weight of oxygen, i.e. 0.02% by weight of oxygen.

[0081] As explained, metal powder is a cobalt-based alloy. Therefore, the cobalt content in metal powder is 100% less the sum of the contents of the other constituent elements of the metal powder presented above. Thus, the metal powder comprises by weight a minimum of 49.31% cobalt and a maximum of 57.60% cobalt.

[0082] This specific metal powder makes it possible, when used in a metal injection molding process, to obtain parts with average tensile, fatigue, and creep resistance and very good oxidation / corrosion resistance at least up to 1000°C, or even up to 1050°C. This metal powder therefore has the advantage of allowing the manufacture of specific aeronautical parts subjected to significant mechanical stresses and high temperatures (greater than or equal to 1000°C, or even 1050°C). Preferably, the manufacturing process of the metal powder is atomization. Also preferably, the metal powder is obtained by atomization of an alloy whose composition is close to that of the Mar-M 509 alloy which is cobalt-based. The main components of the Mar-M 509 alloy are iron (0% - 2% by weight), nickel (9% - 11% by weight) and cobalt. Additionally, Mar-M 509 alloy may include titanium (0% - 0.4% by weight), chromium (22% - 25% by weight), zirconium (0.3% - 0.7% by weight), tantalum (3% - 4% by weight), tungsten (6% - 8% by weight), trace carbon (0.55%-0.65% by weight) and other elements in an amount of less than 50 ppm. However, the Mar-M 509 alloy is a typical foundry alloy and is therefore not used in powder form. The composition of the alloy forming the metal powder according to the invention has been optimized for the injection molding process.

[0083] Thus, the maximum oxygen and nitrogen contents of the alloy forming the powder according to the invention are higher than those of the Mar-M 509 alloy, which are less than 50 ppm, but remain acceptable in terms of the final properties of the material. On the other hand, the carbon content is lower than that of the Mar-M 509 alloy, which is between 0.55 and 0.65% on casting, to compensate for the fact that at the end of the injection molding process, the carbon content will have increased due to residues of the binder.

[0084] Therefore, the powder according to the invention advantageously comprises between 0.45% and 0.55%, 0.55% being excluded, by weight of carbon. In other words, the carbon content of the powder is advantageously greater than or equal to 0.45% and strictly less than 0.55% by weight.

[0085] According to a particular arrangement, 10% of the grains of the metal powder have a diameter less than a value (D10 value) between 3 pm and 10 pm, 50% of the grains have a diameter less than a value (D50 value) between 10 pm and 20 pm and 90% of the grains have a diameter less than a value (D90 value) between 20 pm and 40 pm. The particle size parameters D10, D50 and D90 are measured by laser particle size measurement according to the ISO 13320 or ASTM B822 standard.

[0086] This specific particle size allows for the combination of optimal powder density when used in a MIM manufacturing process with good injection, while having optimal feedstock rheology at injection and promoting sintering. This reduces the risk of cracking during injection and sintering, good dimensional stability and sintering giving a consistent density.

[0087] In particular, the D10 value specifies the dimensions of the finest powder grains intended to fill the voids between the larger grains. These dimensions are optimized to be small enough to fill the voids well and promote sintering. The D50 value represents the average value of the grains.

[0088] The D90 value indicates the maximum grain size, the upper limit of D90 therefore ensures grains large enough not to add too much friction to the injection and break the parts during injection. The combination of the three dimension parameters D10, D50 and D90 corresponds to a Gaussian distribution of grain sizes presenting the best compromise for injection and sintering.

[0089] Process

[0090] A metal injection molding process is proposed from the metal powder presented previously.

[0091] The metal injection molding technique, also known as "MIM" ("Metal Injection Molding" in English), allows the production of large series of metal parts, particularly metal parts with complex shapes, from a metal powder. Indeed, the injection of the parts can be carried out at a high rate and the debinding can be carried out in batches comprising a plurality of parts.

[0092] Furthermore, the parts obtained have an excellent surface finish and have fine dimensional tolerances.

[0093] The metal injection molding process allows the production of parts, particularly aeronautical parts such as fuel injection systems, combustion chambers, turbine distributor sleeves or sealed sectors of turbine blades.

[0094] Figure 1 shows steps in the metal injection molding process.

[0095] According to a certain embodiment, the molding method firstly comprises a preliminary step of mixing the metal powder with at least one polymer binder to obtain a mixture called the primary mixture. During the mixing step, the grains of metal powder are advantageously coated by the binder(s). In the specific terminology of metal injection molding, the primary mixture is called "feedstock".

[0096] The primary mixture is in the form of granules and preferably comprises between 55% and 75% metal powder and therefore, respectively, between 45% and 25% binder. The binder is a polymer, preferably thermoplastic, and may, for example, be polyethylene or polyethylene glycol. Preferably, the metal powder is mixed with polyethylene and polyethylene glycol.

[0097] The granules of the primary mixture preferably have a diameter greater than 1 mm and less than 5 mm. Preferably, the hot fluidity of the primary mixture is greater than 60 cm 3 / 10 min and less than 85 cm 3 / 10 min.

[0098] The method may also include a granulation step to obtain the primary mixture. In other words, the metal powder is mixed with the binder(s) and undergoes granulation to obtain the primary mixture.

[0099] The method comprises a step a) of feeding an injection molding machine with primary mixture for molding a part called a green part. The injection molding machine is a typical press for implementing a metal injection molding process. The primary mixture is heated in the injection molding machine to a temperature sufficient for the binder(s) to melt without the metal elements melting. The heating temperature depends on the geometry of the green part to be formed. Preferably, the heating temperature is between 170°C and 200°C. This temperature will allow a green part to be obtained without porosity. The heated primary mixture is injected into a mold corresponding to the shape of the green part to be obtained. After cooling and solidification of the binder, the green part can be extracted from the mold.

[0100] The process then includes a step b) of debinding the green part to obtain a part called a brown part. Debinding removes a major part of the binder present in the green part.

[0101] Debinding can be water-solvent or catalytic debinding.

[0102] Water-based solvent debinding involves bathing the green part in water so that the binder dissolves. For example, the green part can be bathed in demineralized water at a temperature between 20°C and 150°C for a period of between 100 and 300 hours, with the water being agitated.

[0103] Catalytic debinding involves placing the green part in a furnace so that the binder is vaporized and then burned by injecting acid vapor into the furnace. For example, the green part can be placed in a furnace at a temperature between 100°C and 150°C, for a period of between 2 hours and 10 hours in a nitrogen atmosphere introduced at a flow rate of between 60 and 100 L / min with the introduction of nitric acid vapor at a flow rate of between 2 and 5 mL / min.

[0104] At the end of debinding step b), a major part of the binder(s) from the green part is removed, preferably at least 95% of the binder, and the brown part obtained is therefore porous.

[0105] Advantageously, the method comprises a thermal debinding step for removing the remaining binder in the brown part. For example, the thermal debinding may comprise two consecutive stages, namely a first stage in which the brown part is subjected to a temperature of between 450°C and 550°C for a period of between 150 and 300 minutes under 200 to 500 mbar of argon and a second stage in which the brown part is subjected to a temperature of between 550°C and 650°C for a period of between 150 and 300 minutes under an atmosphere of 200 to 500 mbar of argon.

[0106] The method then comprises a step c) of sintering the brown part (or, where appropriate, the brown part having undergone thermal debinding) to obtain a part called a sintered part. During sintering, the brown part is heated to a temperature close to the melting temperature of the constituent metals of the brown part (i.e. the constituent metals of the metal powder used) but lower than this melting temperature.

[0107] Sintering causes a homothetic reduction, or shrinkage, of the part because the grains of metal powder bind together by diffusion, thus causing a densification of the brown part.

[0108] Preferably, during sintering, the brown part is subjected to a temperature between 1200°C and 1300°C for a period of between 4 and 8 hours under an atmosphere of 20 to 50 mbar of argon.

[0109] These sintering parameters are easily applicable industrially and make it possible to obtain a sintered part with good dimensional stability and a good quality microstructure, in which defects, for example microcracks or porosity, are minimized.

[0110] Advantageously, the sintered part is made of a cobalt-based alloy which includes:

[0111] - between 23.00% and 24.25% by weight of chromium,

[0112] - between 9.00% and 11.00% by weight of nickel,

[0113] - between 6.50% and 7.50% by weight of tungsten,

[0114] - between 3.00% and 4.00% by weight of tantalum,

[0115] - between 0.55% and 0.65% by weight of carbon,

[0116] - between 0.30% and 0.50% by weight of zirconium,

[0117] - between 0.15% and 0.25% by weight of titanium,

[0118] - maximum 2.00% by weight of iron,

[0119] - maximum 0.30% by weight of silicon,

[0120] - maximum 0.10% by weight of manganese,

[0121] - maximum 0.10% by weight of copper,

[0122] - maximum 0.015% by weight of sulfur,

[0123] - maximum 0.015% by weight of phosphorus,

[0124] - maximum 0.010% by weight of boron,

[0125] - maximum 450 ppm of oxygen, - maximum 300 ppm of nitrogen,

[0126] - maximum 125 ppm of hydrogen.

[0127] The sintered part obtained thus has good mechanical properties and resistance to temperatures greater than or equal to 1000°C, or even 1050°C.

[0128] Compared to powder, the sintered part has a higher content of carbon, oxygen and nitrogen because these elements are binder residues that impregnate the alloy.

[0129] The sintered part has a microstructure (i.e. the size of the metallurgical grains) between 3 and 9 ÀTSM (ÀTSM standard no. E112). 3 ÀTSM correspond to 127 pm and 9 ÀTSM correspond to 15.9 pm. The microstructure of the part obtained is therefore fine, which allows for improved fatigue resistance, as well as fracture and elastic resistance.

[0130] The sintered part can be used directly or can undergo various treatments depending on the desired final application.

[0131] The method thus comprises a step d) of obtaining a part called the final part. The final part corresponds to the sintered part or corresponds to the sintered part after it has undergone one or more heat treatments. Heat treatments are presented below.

[0132] Advantageously, the method includes a hot isostatic compaction treatment step for the sintered part. This compaction step makes it possible to densify the sintered part. Indeed, this step makes it possible to reduce residual sintering porosities as much as possible, the porosity rate thus going from a rate of less than 6% to a rate of less than 0.4%. Indeed, it makes it possible to fill the porosities, thus obtaining a healthy part with less dimensional dispersion and improved mechanical properties.

[0133] Hot isostatic compaction treatment consists, for example, of subjecting the sintered part to a temperature of 1260°C + / -20% for a period of 3 hours + / - 1 hour under an atmosphere of 1020 bars + / - 10% argon with air-type cooling.

[0134] The method may additionally or alternatively comprise a step of quenching the sintered part. This quenching step makes it possible in particular to homogenize the microstructure and precipitations of the sintered part.

[0135] Quenching can, for example, consist of subjecting the sintered part to 1260°C + / -20% for a period of 3 hours + / - 1 hour under an argon atmosphere with air-type cooling.

[0136] The heat treatments presented (hot isostatic compaction or quenching) allow in particular good precipitations and recrystallization without modification of the grain size. The final part obtained thus presents good mechanical properties and resistance to temperatures greater than or equal to 1000°C, or even 1050°C. The final part is sound, that is to say that it presents an adequate microstructure for an optimal mechanical resistance in traction, creep and fatigue and presents an optimal resistance to oxidation and corrosion. More precisely, the final part obtained presents a mechanical resistance in traction of 300 MPa at 950°C and 1300 MPa at 20°C + / -50 MPa. The final part also presents a conventional yield strength of 290 MPa at 950°C and 750 MPa at 20°C + / -50 MPa. In addition, the final part has a creep rupture resistance at 900°C of 140 MPa for more than 20 hours.The final part can be used in a turbomachine and can, for example, be part of a turbine.

[0137] The invention is not limited to the embodiment described and shown in the attached figure. Modifications remain possible, in particular from the point of view of the constitution of the various technical characteristics or by substitution of technical equivalents, without departing from the general teaching.

Claims

CLAIMS 1. Metal powder for a metal injection molding process, the metal powder being formed from a cobalt-based alloy comprising: - between 23.00% and 24.25% by weight of chromium, - between 9.00% and 11.00% by weight of nickel, - between 6.50% and 7.50% by weight of tungsten, - between 3.00% and 4.00% by weight of tantalum, - between 0.45% and 0.60% by weight of carbon, - between 0.30% and 0.50% by weight of zirconium, - between 0.15% and 0.25% by weight of titanium, - maximum 2.00% by weight of iron, - maximum 0.30% by weight of silicon, - maximum 0.10% by weight of manganese, - maximum 0.10% by weight of copper, - maximum 0.015% by weight of sulfur, - maximum 0.015% by weight of phosphorus, - maximum 0.010% by weight of boron, - maximum 200 ppm of oxygen, - maximum 200 ppm of nitrogen, - maximum 100 ppm of hydrogen.

2. Metal powder according to claim 1 having a grain diameter distribution such that the value D10 is between 3 pm and 10 pm.

3. Metal powder according to any one of claims 1 and 2 having a grain diameter distribution such that the D50 value is between 10 pm and 20 pm.

4. Metal powder according to any one of claims 1 to 3 having a grain diameter distribution such that the D90 value is between 20 pm and 40 pm.

5. Method of manufacturing a powder according to any one of claims 1 to 4, by atomization.

6. Method for injection molding metal from a powder according to any one of claims 1 to 4, comprising steps of: a) feeding an injection press with a primary mixture for molding a part called a green part, said primary mixture comprising the powder and at least one binder in polymer, b) debinding of the green part to obtain a part called a brown part, c) sintering of the brown part to obtain a part called a sintered part, d) obtaining a part called a final part, the final part corresponding to the sintered part or corresponding to the sintered part after it has undergone one or more heat treatments.

7. The method of claim 6, wherein the debinding step is a water-solvent or catalytic type debinding step.

8. Method according to any one of claims 6 and 7, further comprising a thermal debinding step.

9. Method according to any one of claims 6 to 8, further comprising a step of hot isostatic compaction treatment of the sintered part.

10. Method according to any one of claims 6 to 9, further comprising a step of quenching the sintered part.

11. Method according to any one of claims 6 to 10, in which the powder is obtained by atomization.

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