Method for producing welding or facing rods of which the filler material is a metal superalloy

Abstract

One aspect of the invention relates to a method for producing a facing or welding rod, characterized in that it comprises the following successive steps: • a step (E1) of providing a mixture comprising 50% to 90% by volume of a powdered nickel- and / or cobalt-based metal superalloy, and a powdered thermoplastic-polymer- and / or wax-based binder; • a step (E2) of forming a mixed wire from the mixture resulting from step (E1), this wire being designated a "green" wire; • a step (E3) of debinding the "green" wire resulting from step (E2) and obtaining a debound wire designated a "brown" wire; • a step (E4) of sintering the "brown" wire resulting from step (E3) and obtaining a sintered wire that can be used as a facing or welding rod.

Description

Process for manufacturing welding or resurfacing rods whose filler material is a metallic superalloy TECHNICAL FIELD OF THE INVENTION

[0001] The technical field of the invention is that of welding and resurfacing in which the material supply is provided by a rod comprising a filler material, this filler material being a metallic superalloy.

[0002] The present invention relates to a new manufacturing method for such a welding or resurfacing rod. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0003] Many welding or hardfacing processes use a filler material supplied in the form of a rod and a heat source.

[0004] As a reminder, welding is a technique for assembling parts with the addition of a filler material at the junction between said parts. Hardfacing is a variant of welding which consists, not of assembling metal parts together, but of covering their surface with one or more layers of a filler material. Thus, the filler material of a welding or hardfacing rod either fills the gap between two parts to be assembled, or adds material to the surface of a part.

[0005] The rods used for welding or resurfacing processes, hereinafter simply referred to as “rods”, can have different diameters, usually between approximately 0.3 and 5 mm.

[0006] Currently, there are very few rods designed to provide superalloy-based metal filler material. Furthermore, the available rods have a diameter greater than 2 mm. Rods with a thin diameter, i.e., between 0.1 and 2 mm, are therefore not available on the market.

[0007] This lack of availability for these rods results from the difficulty in producing them and the fact that the market share is quite low for this type of grade of metal filler material.

[0008] Indeed, nickel and / or cobalt-based metal filler materials are materials that are complex to implement by wire drawing due to their material properties generated by complex chemistries.

[0009] As a reminder, superalloy or high-performance alloy means a complex alloy of metallic materials, essentially based on nickel or cobalt, having excellent mechanical strength and good creep resistance at high temperatures, good surface stability as well as good resistance to corrosion and oxidation. In the context of this invention, we are particularly interested in superalloys based on nickel and / or cobalt.

[0010] There is therefore a need for a new manufacturing process that allows the production of rods, particularly small diameter rods whose filler material is a nickel and / or cobalt-based superalloy. SUMMARY OF THE INVENTION

[0011] The invention provides a solution to the problems discussed above by providing a new method for manufacturing rods based on metal injection molding (MIM) technology, which belongs to the broader technology family of powder injection molding (PIM), as well as ceramic powder injection molding (CIM).

[0012] The MIM process consists of producing components by injecting a mixture of metal powder and a thermoplastic polymer binder, commonly referred to as feedstock. This mixture or feedstock is usually reduced to granules and then injected into a mold using equipment similar to that used for plastic injection. It then undergoes a step called debinding, aimed at removing the thermoplastic polymer binders thermally and / or chemically depending on the nature of said binders, then a step called sintering, aimed at generating strong bonds by diffusion of material, densifying and eliminating porosities in the material.

[0013] As an example, [Fig. 1] and [Fig. 2] illustrate the use of a conventional MIM process for producing a part 10 by injecting a material 20 based on of metal powder and binder into a mold 30 through an injection nozzle 40.

[0014] Whereas in a conventional MIM process, an injection nozzle 40 injects a feedstock 20 into a mold 30 in order to produce a given part geometry 10, the invention proposes to modify the MIM process by not installing a mold, which makes it possible to shape the material in the form of a rod, not necessarily rectilinear. The method of the invention can however use the equipment usually used in a conventional MIM process, except for the mold 30, where the injection nozzle 40 then fulfills the role of an extrusion die.

[0015] Instead of injection, we can then speak of extrusion, the injection nozzle acting as a die and having an internal diameter greater than the section of the rod to be obtained. Indeed, after extrusion of the feedstock 20, we do not directly obtain a rod with the desired dimensions. Instead, we obtain a preform called a "green" part which then undergoes a debinding step, at the end of which we obtain a "brown" part or debinded part, then which undergoes a sintering step at the end of which we obtain a sintered part, these last two steps causing a material shrinkage linked to the removal of the binder and the densification of the material. This material shrinkage is linked in particular to the powder charge rate in the feedstock, which can be significant.

[0016] One aspect of the invention relates to a method for manufacturing a recharging or welding rod, which comprises the following successive steps: a step E1 of providing a mixture comprising: from 50 to 90% by volume of a powder of a metal superalloy based on nickel and / or cobalt, and a powder of a binder based on wax and / or thermoplastic polymer; a step E2 of forming a mixture wire 60 from the mixture resulting from step E1, this wire being designated as a “green” wire; a step E3 of debinding the “green” wire resulting from step E2 and obtaining a debinded wire designated as a “brown” wire; a step E4 of sintering the “brown” wire 100 resulting from step E3 and obtaining a sintered wire usable as a recharging or welding rod.

[0017] The advantage of this process is that it allows all shades of material to be formed (nickel base, cobalt, titanium, aluminum, etc.).

[0018] Thanks to the invention, by adjusting the extrusion parameters (dimensions of the extrusion die, extrusion speed, extrusion pressure, temperature, etc.) and taking into account the shrinkage factor, it is advantageously possible to manufacture rods of different diameters, for example greater than 2 mm if necessary, and of different lengths, for example from 1 to 30 cm, the filler material of which is a nickel and / or cobalt-based superalloy.

[0019] Indeed, although it may seem counter-intuitive to form rods that are not necessarily straight, the rods manufactured by the method according to the invention are sufficiently elongated to be able to be advantageously used with the usual welding or resurfacing processes. In addition, the possible variations in the diameter of the rods thus formed, of the order of + / - 0.1 mm, remain largely acceptable for most welding or resurfacing applications. The rods produced according to the method of the invention can therefore be used like conventional rods during welding or resurfacing processes.

[0020] According to one aspect of the invention, the superalloy powder used has a particle size whose D50 is between 5 and 15 μm.

[0021] According to another aspect of the invention, during step E1, the grains of the superalloy powder used are subspherical or spherical in shape.

[0022] According to a further aspect of the invention, during step E1, the superalloy powder and the binder powder used are hot mixed. The resulting mixture can be ground into granules after cooling and hardening. It can also be hot extruded through a die.

[0023] According to one aspect of the invention, during step E1, the binder mainly comprises polyethylene, polypropylene, polystyrene, polyoxymethylene or a mixture thereof.

[0024] According to another aspect of the invention, during step E2, the formation of a “green” thread is carried out by extrusion of the mixture resulting from step E1 through a die.

[0025] According to an additional aspect of the invention, during step E2, the main extrusion parameters are as follows: Extrusion temperature: 50 to 250°C; Extrusion speed: 10 to 100 cm 3 / s ; Extrusion pressure: 50 to 1500 bars.

[0026] According to one aspect of the invention, during step E2, the die has a section whose diameter is between 0.1 and 10 mm.

[0027] According to another aspect of the invention, during step E3, the “green” wire resulting from step E2 is immersed for a period of between 10 and 200 hours in a solvent whose temperature is between 20 and 100°C.

[0028] According to an additional aspect of the invention, during step E3, the “green” wire resulting from step E2 is placed for a period of between 1 and 30 hours in an enclosure heated to a temperature of between 50 and 250°C.

[0029] According to one aspect of the invention, during step E4, the sintering is carried out for a period of between 2 and 20 hours under a protective atmosphere or under vacuum, at a temperature of between 1000 and 1500°C.

[0030] One aspect of the invention also relates to a recharging or welding method, using a recharging or welding rod comprising a powder of a nickel and / or cobalt-based superalloy, said recharging or welding rod being a product resulting from the method described above.

[0031] The invention and its various applications will be better understood by reading the following description and examining the accompanying figures. BRIEF DESCRIPTION OF THE FIGURES

[0032] The figures are presented for information purposes only and in no way limit the invention.

[0033] [Fig. 1] and [Fig. 2] schematically illustrate the use of a classic MIM process for the production of a part in a mold.

[0034] [Fig. 3] schematically illustrates the different stages of the method according to the invention.

[0035] [Fig. 4], [Fig. 5] and [Fig. 6] schematically illustrate an example of use of the method according to the invention for producing a recharging or welding rod. DETAILED DESCRIPTION

[0036] Unless otherwise specified, the same element appearing in different figures has a single reference.

[0037] Superalloys are complex alloys of metallic materials, mainly based on nickel and / or cobalt, with good mechanical strength at high temperatures (above 500 to 550 °C) and a certain resistance to oxidation or corrosion when hot. Indeed, their usual properties are as follows: good creep resistance, good corrosion resistance, good oxidation resistance, good resistance to thermal fatigue and thermal shock, absence of excessive brittleness, medium density.

[0038] Superalloys are widely used in the production of industrial and marine gas turbines, aeronautical turbomachines and, to a more limited extent, in the furnace and chemical industries.

[0039] Several classes of superalloys exist today, however the most widely used and most important class of superalloys is a priori the nickel-based one. Indeed, nickel as a basic element has excellent plasticity and heat resistance properties. In addition, its high-temperature resistance is greatly enhanced by alloying it with chromium, titanium, cobalt and especially aluminum with which it forms γ precipitates that contribute to its structural hardening.

[0040] Superalloys usually consist of: mainly an austenitic matrix y in which Ni can be substituted by Co, Cr, Mo, W, as well as by Nb, Al, Ti, Ta; ordered intermetallic precipitates y': Ni3(Ti,AI) or y": NisNb which occupy from 30 to 70% of the volume and whose dimensions vary between 10 nm and a few micrometers; or primary (MC type) and secondary (M23C6 type) carbides, preferentially precipitated at the grain boundaries.

[0041] Nickel and / or cobalt-based superalloys are widely known to those skilled in the art and will not be described here.

[0042] As examples, some examples of compositions of nickel or cobalt-based superalloys are nevertheless given in the table below where the values ​​indicated are % by mass:

[0043] [Table 1] 0044] In the context of this description, by nickel-based superalloy, respectively cobalt-based, is meant a high-performance alloy whose majority component by mass is nickel, respectively cobalt; while by nickel- and cobalt-based superalloy is meant a high-performance alloy whose majority component by mass is a mixture of nickel and cobalt.

[0045] There are several types of nickel-based superalloys, which often have references or trade names such as: INCONEL®, RENE®, HASTELLOY®, NIMONIC®, MONEL®, MAR-M 246, MAR-M 247, MAR-M 200+Hf, MAR-M 002, UDIMET®, Triballoy®, SIEMET®, WASPALLOY®, PERMENDUR, KOVAR®, INVAR®, ALNICO®, etc.

[0046] There are also cobalt-based superalloys, which often have references or trade names such as: HS25 (L605), HS30, HS31 (X40), HS188, FSX-414,

[0047] The invention relates to a method for manufacturing a reloading or welding rod 50 (see [Fig. 3]).

[0048] This method comprises a first step of preparing a mixture to be shaped into wire, for example by extrusion. This first step notably comprises a step E1 of providing a mixture 60 comprising a metal powder and a powder binder.

[0049] The volume proportion of metal powder in the mixture 60, also referred to as the filler rate, is between 50 and 90%. Preferably, the filler rate is between 60 and 80% in order to guarantee both good extrusion capacity and good cohesion during debinding as well as a high and homogeneous final density.

[0050] According to an exemplary embodiment of the invention, the mixture 60 may further comprise up to three additives, for example at least 80% of a main binder, a secondary binder which represents 90% of the remainder and a dispersant-type adjuvant which represents the last 10%.

[0051] The metal powder is preferably a nickel and / or cobalt-based metal superalloy, while the binder is preferably a wax and / or thermoplastic polymer-based binder.

[0052] The metal powder preferably has a particle size distribution with a D50 of between 5 and 15 pm, which means that 50% of the grains (by number) have a diameter less than a value d such that 5 < d < 15 pm. The grains of the superalloy powder are preferably subspherical or spherical in shape. As is known in the field of particle size distribution, a subspherical grain is understood to mean a grain whose shape is close to that of a ball.

[0053] According to an exemplary embodiment of the invention, the particle size of the binder and the other additives is substantially equivalent. For these materials, it is possible in particular to use pellets having a length and diameter of between 1 and 4 mm.

[0054] In the case where it is based on a thermoplastic polymer, the binder comprises, for example, mainly polyethylene, polypropylene, polystyrene, polyoxymethylene or a mixture thereof. As an additive, the thermoplastic polymer-based binder may comprise a fluidizing agent, such as paraffin or polyethylene glycol, or a wetting agent such as stearic acid.

[0055] In the case where it is wax-based, the binder comprises, for example, mainly paraffin wax, carnauba wax or a mixture thereof. As an additive, the wax-based binder may comprise stearic acid.

[0056] The binder can also be a mixture of thermoplastic polymer and wax, which lowers the viscosity of the binder and opens up a porosity facilitating its removal.

[0057] As an additive, the binder may also include surfactants to improve the miscibility of the components.

[0058] During the first preparation step, the metal superalloy powder is preferably added gradually to the binder, which is preferably in the molten state. This addition is preferably carried out using mixers or extruders which allow for high shear rates, thus ensuring the homogeneity of the system. The mixture 60 obtained, once homogeneous, is for example cooled and hardened, then put into the form of granules (also referred to as feedstock) so that it can then be shaped into wire, for example by extrusion. The mixture 60 obtained, once homogeneous, can also be kept hot, so that it can be extruded through a die 70 during step E2 of forming a wire of mixture 60, and this before the mixture 60 cools and hardens.

[0059] After step E1 of providing a mixture 60, the method according to the invention comprises a step E2 of forming a mixture yarn 60 designated as “green” yarn, preferably by extruding the mixture 60 resulting from step E1 through a die 70 (see [Fig. 4]).

[0060] If the 60 mixture is in the form of granules, it must be melted by heating before extrusion.

[0061] During step E2, the main preferred extrusion parameters are for example: Extrusion temperature: 50 to 250°C; Extrusion speed: 10 to 100 cm 3 / s ; Extrusion pressure: 50 to 1500 bars.

[0062] The extrusion temperature corresponds to the temperature at which the mixture 60 is extruded. It is generally heated to this temperature upstream of the die 70, whether for example during the formation of the mixture 60 or by melting said mixture 60 when it is in the form of granules. The extrusion die 70 can also be maintained at this extrusion temperature or at a temperature close to it.

[0063] The extrusion speed corresponds to the flow rate of mixture 60 through the die 70 when it is extruded.

[0064] The extrusion pressure corresponds to the pressure to which the mixture 60 is subjected to be extruded through the die 70.

[0065] The internal diameter of the outlet orifice of the die 70, i.e. the cross-section of the die 70, is preferably between 0.1 and 10 mm. The cross-section of the die 70 is preferably circular in shape. It may also be oval, polygonal, star-shaped or otherwise. Apart from the shrinkage factor, it is the shape and diameter of the cross-section of the die 70 which substantially determines the shape and diameter of the mixture wire 60 obtained by the method of the invention. Depending on the diameter of the wire obtained, instead of the term "wire", the term "cord" could also be used. The term wire is used here generically for an elongated body extruded through an extrusion die.

[0066] The “green” yarn of mixture 60 obtained during step E2 can be cut to the desired length, this length being for example between 1 and 30 cm (see [Fig. 5])-

[0067] After step E2 of forming a “green” wire, the method according to the invention comprises a step E3 of debinding said “green” wire (see [Fig. 6]).

[0068] Debinding is a step well known to those skilled in the art which aims to remove the binder thermally and / or chemically depending on the nature of said binder in order to obtain a “brown” part. Indeed, the main debinding techniques are thermal degradation, dissolution in a solvent or a combination of the two.

[0069] The debinding parameters (temperature, atmosphere, etc.) depend not only on the nature of the binder, but also on the nature of the metal powder. The choice of these parameters is well known to those skilled in the art.

[0070] The debinding step must be perfectly controlled because it can be a source of damage to the part. In fact, poorly controlled debinding risks causing defects such as cracking, but also chemical pollution due to carbon residues.

[0071] The term thermal debinding covers several techniques that can be distinguished and are well known to those skilled in the art, such as: degradation; evaporation under a controlled atmosphere or under vacuum; or drainage in the liquid state on a porous substrate.

[0072] For binders that require thermal debinding, the “green” wire 60 is placed for a period of 1 to 30 hours in a heated enclosure 80 whose temperature is between 50 and 250°C depending on the case. This step can, for example, be carried out with an acid atmosphere.

[0073] Among the binders that require thermal debinding, we can notably cite polyoxymethylene and polypropylene.

[0074] For binders that require chemical debinding, the “green” wire 60 is immersed for a period of 10 to 200 hours in a solvent 90 (organic solvent, aqueous solvent, neutral, basic or acidic, etc.) at a temperature between 20 and 100°C depending on the case.

[0075] Among the binders that require chemical debinding, we can notably cite polyoxymethylene.

[0076] After step E3 of debinding the “green” wire 60, the method according to the invention comprises a step E4 of sintering the debinded wire 100 or “brown” wire resulting from step E3 (see [Fig. 6]).

[0077] Sintering is a step well known to those skilled in the art which aims to create strong bonds between the particles, eliminate porosities and densify the “brown” wire 100 so as to give it strength and a solid structure. Sintering is a process for manufacturing parts that involves heating a powder without melting it. Under the effect of heat, the grains weld together, which forms the cohesion of the part.

[0078] The sintering parameters (temperature, duration, etc.) depend not only on the diameter of the “brown” wire 100, but also on the nature of the metal powder used in the mixture 60. The choice of these parameters is well known to those skilled in the art.

[0079] This sintering step E4 is preferably carried out in a sintering furnace 110 for a period of between 2 and 20 hours, under a protective atmosphere or under vacuum, for example at a temperature of between 1000 and 1500°C.

[0080] Following this sintering step E4, the sintered wire obtained forms the recharging or welding rod 50 according to the invention.

[0081] The invention also relates to a recharging or welding method, which uses a recharging or welding rod 50 based on superalloy obtained by the method according to the invention.

[0082] Although described through a number of examples, variations and embodiments, the methods according to the invention include various variations, modifications and improvements which will be obvious to those skilled in the art, it being understood that these variations, modifications and improvements are part of the scope of the invention.

Claims

CLAIMS

1. Method for manufacturing a reloading or welding rod (50), characterized in that it comprises the following successive steps: - a step (E1) of providing a mixture (60) comprising: o 50 to 90% by volume of a powder of a metallic superalloy based on nickel and / or cobalt, and o a powder of a binder based on wax and / or thermoplastic polymer; - a step (E2) of forming a mixture yarn (60) from the mixture resulting from step (E1) of providing a mixture (60), this yarn being designated as “green” yarn; - a step (E3) of debinding the “green” yarn (60) and obtaining a debinded yarn (100) designated as “brown” yarn; - a step (E4) of sintering the “brown” wire (100) resulting from the debinding step (E3) and obtaining a sintered wire usable as a recharging or welding rod (50).

2. Method according to claim 1, characterized in that during step (E1) of providing a mixture (60), the superalloy powder used has a particle size whose D50 is between 5 and 15 pm.

3. Method according to claim 1 or 2, characterized in that during the step (E1) of providing a mixture (60), the grains of the superalloy powder used are of subspherical or spherical shape.

4. Method according to any one of the preceding claims, characterized in that during step (E2) of forming a mixture yarn (60), the formation of a "green" yarn (60) is carried out by extruding the mixture resulting from step (E1) of providing a mixture (60) through a die (70).

5. Method according to the preceding claim, characterized in that during step (E2) of forming a mixture thread (60), the main extrusion parameters are as follows: - Extrusion temperature: 50 to 250°C; Extrusion speed: 10 to 100 cm 3 / s ; Extrusion pressure: 50 to 1500 bars.

6. Method according to claim 4 or 5, characterized in that during step (E2 of forming a mixture thread (60)), the die (70) has a section whose diameter is between 0.1 and 10 mm.

7. Method according to any one of the preceding claims, characterized in that during the debinding step (E3), the “green” yarn resulting from the step (E2) of forming a mixture yarn (60) is immersed for a period of between 10 and 200 hours in an organic or aqueous solvent (90) whose temperature is between 20 and 100°C.

8. Method according to any one of claims 1 to 6, characterized in that during the debinding step (E3), the “green” yarn resulting from the step (E2) of forming a mixture yarn (60) is placed for a period of between 1 and 30 hours in an enclosure (80) heated to a temperature of between 50 and 250°C.

9. Method according to any one of the preceding claims, characterized in that during the sintering step (E4), the sintering is carried out for a period of between 2 and 20 hours under a protective atmosphere or under vacuum, at a temperature of between 1000 and 1500°C.

10. A method of recharging or welding, characterized in that it uses a recharging or welding rod (50) comprising a powder of a superalloy based on nickel and / or cobalt, said recharging or welding rod (50) being a product resulting from the method according to any one of the preceding claims.

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