Flexible cord for supplying a thermal spray torch, and thermal spray device

Abstract

A cord, the cord having an equivalent outer diameter (d) of 1 mm to 3.5 mm and comprising a core (18) in the form of a wire and a sheath (20) covering the core along its entire length, The core is Median diameter (D 50 a collection of inorganic particles (22) having a diameter of less than 10 micrometers, wherein the inorganic particles occupy more than 40% and less than 80% of the volume of the core; and A matrix that binds the inorganic particles (24) It consists of: The matrix comprises a polymeric binder and, optionally, a matrix lubricant, which together occupy greater than 90% of the volume of the matrix; the sheath has a thickness of 50 micrometers to 500 micrometers and comprises a sheath polymer and preferably a sheath lubricant, which together occupy greater than 90% of the volume of the sheath; Including, The volume percentages are determined without taking into account the possible presence of solvent. The code.

Description

[Technical field]

[0001] The present invention relates to a flexible cord intended to serve as a feedstock for a thermal spray torch to produce a coating. The present invention also relates to a method for producing said cord and to a thermal spray device using said cord. [Background technology]

[0002] The technique of thermal spraying involves melting a collection of inorganic particles, initially in the form of wires or powder, using a thermal energy source and a kinetic energy source, and spraying the at least partially molten particles onto a substrate. Upon impact, the at least partially molten particles spread over the substrate and cool. Thus, as they cool, they can effectively adhere to each other and to the substrate and form a coating.

[0003] There are various techniques classified according to "combustion enthalpy", "electric discharge" and "momentum density".

[0004] The "enthalpy of combustion" class includes the "detonation gun" technology, the "powder flame" technology (which generates particle velocities <80 m / s and can only use powder as feedstock), the "wire flame" technology (which generates particle velocities >150 m / s and can use a medium selected from wire, cord or rod as feedstock) and finally the "high-velocity flame" technology (which generates particle velocities >500 m / s). Among the "high-velocity flame" technologies, the "D-gun detonation" technology, the "High Velocity Oxy-Fuel" technology (HVOF) technology, the "High Velocity Suspension Flame Spray" (HVSFS) technology and the "High Velocity Air Fuel" technology (HVAF) technology can use powder, suspension (in the case of HVSFS) or even wire as feedstock.

[0005] The "electric discharge" class includes "electric arc" and "plasma" technologies, the latter category including processes performed in controlled atmospheres and temperatures, referred to as "atmospheric" or APS (Atmospheric Plasma Spray), such as "VPS / LPPS" (Vacuum or Low Pressure Plasma Spray) technologies, "VLPPS / PS-PVD" (Very low pressure plasma spray and Plasma Spray enhanced Physical Vapor Deposition) technologies, "SPS" (Suspension Plasma Spray) technologies, "SPPS" (Solution Precursor Plasma Spray) technologies, "Induction Plasma" (Induction Plasma) technologies, and "WSP" (Water Stabilized Plasma) technologies. These systems allow particles to be sprayed at velocities ranging from 150 m / s to 500 m / s, depending on the type and parameters of the process used. These "plasma" systems have a median diameter D 50 D 50 Dry powders, or liquids (including chemical precursors, e.g. salts, or 50 In the case of suspensions containing inorganic particles having a particle size of less than 10 micrometers,

[0006] The "Momentum Density" class includes "low-pressure" technologies, "high-pressure" technologies, and "Cold Spray" technologies including "recirculated helium" technologies.

[0007] All these techniques are well known and are described, inter alia, in the ASM Handbook vol 5a-Thermal Spray Technology.

[0008] Each technology is associated with its own constraints and therefore the problems encountered and the solutions used to overcome them typically vary depending on the technology considered.

[0009] The present invention is particularly directed to the following subset groupings: In the "Enthalpy of Combustion" class, "flame-wire" and "high-velocity flame" technologies; and Technologies from the "electric discharge" class, especially "plasma" technologies Regarding.

[0010] For the sake of clarity, in this specification, the torches or guns used in these techniques will generally be referred to as "torches". The term "torch" includes in particular flame guns of the flame-wire (WFS, i.e. Wire Flame Spray) type, or plasma torch systems, or finally "High-Velocity Flame Spray" devices as defined above. Recent developments in these techniques include the use of suspensions or solutions of liquid precursors as feedstocks in these devices (the suspensions being made up of a solvent and a crystalline solid having a median diameter D 50The conventional method consists of a method for preparing a suspension of a liquid precursor, which consists of fine inorganic particles with a diameter typically less than 5 micrometers. Such evolution towards very fine particles (or in situ formation of materials in the case of liquid precursors) has made it possible to generate new types of microstructures, for example very finely structured, very dense, or columnar or "feathery" microstructures (having the appearance of juxtaposed feathers when observed in a micrograph in cross section). Although these evolutions open the way to new perspectives, they face constraints and limitations in the robustness, stability and reproducibility of the method, linked to the fact that particle suspensions are not always completely stable. However, the evaporation of the solvent has a negative impact on the energy efficiency during the spray phase. Moreover, suspensions contain particles of different composition, especially with different densities. The preparation of such stable suspensions, without any settling or agglomeration of the particles, is difficult, if not impossible, to master on an industrial scale.

[0011] Japanese Patent Publication No. JP2016156058A describes a raw material medium consisting of a composite wire. The coating is a dense electrolytic membrane for making a fuel cell. Such wires can be difficult to manufacture and do not allow for the creation of ceramic (e.g. oxide) coatings with good control over the size of the sprayed particles. In particular, the medium contains fine particles embedded in a matrix. Tests have demonstrated that a large amount of matrix leads to detrimental fluctuations in enthalpy during spraying.

[0012] US 4,593,856 also describes a feedstock medium in the form of a wire, however, the melting of the wire may be incomplete, which has a detrimental effect on the quality of the coating.

[0013] As materials for welding torches for applying thick layers (overlays or hardfacings) metallurgically bonded to metal substrates, cords are known that include a core covered with a sheath. They are not suitable for producing coatings by thermal spraying, which may be applied without resorting to a welding process, may consist of ceramics and may be applied to any type of substrate. These cords intended for welding consist of inorganic particles with a size of more than 10 micrometers.

[0014] A cord for arc welding is also known from US Pat. No. 3,701,444. Such cord is not routinely used as a feedstock for thermal spray torches to form coatings, since these two applications (welding / spraying) are very different from each other. In particular, the aggregates of inorganic particles generally have a median diameter of 100 micrometers or more.

[0015] Finally, French Patent No. FR 1,443,142 describes a cord comprising a core coated with a sheath. The aggregate of inorganic particles has a median diameter D which is not compatible for obtaining a very uniform or finely structured coating. 50 has.

[0016] Therefore, there continues to be a need for a feed medium suitable for spraying using a plasma torch or flame torch: This allows the torch to be fed substantially continuously and reliably; In particular, being in a solid, easy to handle and preferably capable of being wound on a reel, makes it possible to overcome the constraints or limitations of liquid suspension or liquid solution type media; resulting in highly uniform or finely structured coatings; without excessive wear on the torch; and At the expense of limited energy consumption. Summary of the Invention [Problem to be solved by the invention]

[0017] The present invention seeks to at least partially address this need. [Means for solving the problem]

[0018] According to the invention, the object is to provide a cord having an equivalent outside diameter between 1 mm and 3.5 mm and having a core in the form of a wire, i.e. a center, and a sheath surrounding said core along its entire length, The core is Median diameter (D 50 ) less than 10 micrometers, wherein the inorganic particles occupy more than 40% to less than 80% of the volume of the core; and A matrix that binds the inorganic particles It consists of: The matrix comprises a polymeric binder and, optionally, a matrix lubricant, e.g., glycerin, which together occupy greater than 90% of the volume of the matrix, with the complement to 100% being made up of impurities; the sheath has a thickness of 50 micrometers to 500 micrometers and comprises a sheath polymer and optionally a sheath lubricant, which may be the same as or different from the optional matrix lubricant described above, which together occupy more than 90% of the volume of the sheath, with the complement to 100% preferably being made up of impurities and optionally color pigments; The volume percentages are determined without taking into account the possible presence of solvent residue. This is achieved by the above code.

[0019] Surprisingly, the inventors have found that the cord according to the invention allows the torch to be fed continuously and reliably while producing a high quality coating which offers a number of advantages over the use of particulate suspensions: The stability of the process is improved and the problems associated with the stability of particle suspensions (risk of sedimentation and clumping) are eliminated; Low energy consumption due to the absence of evaporation of the aqueous solvent used in the suspension; There is no aggregation of particles at the time of injection or during flight, unlike that observed during thermal spraying of suspensions; The flow rate of inorganic material can be better controlled and is advantageously proportional to the rate at which the cord is fed into the spray device, whereas injection of the suspension can vary this flow rate significantly.

[0020] Moreover, the feedstock medium in the form of a cord advantageously contains much less solvent than the suspension: the low solvent, in particular water, content of the cord is typically less than 5% by weight, considerably limiting the energy losses during thermal spraying of the medium intended to completely or partially melt the inorganic particles.

[0021] Without being bound by this theory, the inventors finally found that the properties of the cord only result in slight fluctuations in enthalpy when sprayed. Therefore, the fluctuations in enthalpy have a much less destructive effect on the thermal spray process compared to the spraying of dry powder and the use of prior art cords. In particular, the inventors found that the combination of a core and sheath with a fairly low matrix content allows for more reliable enthalpy fluctuations than composite cords without a sheath and with a higher matrix content, such as those in JP 2016-156058A. In general, the presence of a minimum amount of polymer is necessary to give the particularly required flexibility, and the inventors found that in order to maintain this flexibility, it is preferable to increase the concentration of inorganic particles in the core of the cord and add a sheath rather than to reduce the concentration of inorganic particles in the composite cord.

[0022] In a particularly advantageous embodiment, the ratio R of the equivalent outer diameter in micrometers of the cord to the median diameter in micrometers of the aggregate of inorganic particles is between 200 and 2000, preferably between 200 and 1600. Notably, this configuration is associated with a volume fraction of the inorganic particles relative to the volume of the core of the cord of more than 40%, preferably more than 50%, or even more preferably more than 60%, to less than 80%, preferably less than 78%, preferably less than 75%, which allows a better dispersion of the particles when they are ejected into the jet of plasma or into the flame after the sheath is broken. This improvement in the dispersion is particularly advantageous for high-speed plasma or flame torches, in particular high-speed plasma or flame torches with axial injection.

[0023] This results in a better compromise between the following properties and characteristics: When this code is used in a thermal spraying process, it makes it possible for the inorganic particles to be optimally dispersed in the spray jet without agglomerating together, thereby obtaining coatings with a fine structure; the flexibility of said cord makes it easy to handle without risk of breakage; The low enthalpy required to decompose organic compounds and convert them into non-toxic gases.

[0024] The code according to the invention may also include one or more of the following optional and preferred features: the ash content of the combined entity of the matrix and sheath of said cord is less than 5%, preferably less than 3%, as a mass percentage based on the dry mass of said cord; The median diameter D of the aggregate of inorganic particles 50 is less than 5 micrometers, preferably less than 4 micrometers, more preferably less than 3 micrometers, more preferably less than 1 micrometer, especially to form a columnar structure; the viscosity of the polymer binder of the core and / or the sheath polymer and / or the material constituting the core and / or the material constituting the sheath is 30-300 mPa.s or 30-300 centipoise at 20° C., wherein the viscosity is measured using a Hoppler viscosimeter on a mixture containing 2% by weight of dry powder of the polymer binder of the core and / or the sheath polymer and / or the material constituting the core and / or the material constituting the sheath in demineralized water; the sheath and / or the matrix is ​​a cellulose derivative, i.e. a component comprising cellulose molecules, preferably methylhydroxyethylcellulose, a cellulose derivative having a viscosity particularly suitable for thermal spraying and a low ash content associated therewith; said inorganic particles occupy, as a volume percentage, more than 45%, preferably more than 50% and / or preferably more than 70%, preferably more than 75%, based on the volume of the core of the cord excluding any potential solvent; The inorganic particles are Particles of one or more metal oxides, preferably particles of alumina, zirconia, titanium oxide, chromium oxide, yttrium oxide or some combination of these oxides, such as particles of mullite or particles of spinel, and / or Particles of one or more metal oxides, preferably particles of alumina, zirconia, titanium oxide, chromium oxide, yttrium oxide or some combination of these oxides, such as particles of mullite or particles of spinel, and / or Particles of a carbide-based cermet, where the carbides can be, for example, chromium carbides and / or tungsten carbides and / or titanium carbides and / or tantalum carbides and / or zirconium carbides and / or niobium carbides, which carbides are associated with a metallic phase, and / or Inorganic particles containing SiC and YAG (Yttrium-Aluminium-Garnet) phases allow for thermal spraying of SiC-based compounds; particles of ceramic, preferably chosen from among nitrides, borides or carbonitrides, optionally associated with a metallic phase in the form of a cermet; Particles made from a refractory metal or refractory metal alloy, preferably having a melting point higher than 2500K; Particles made of special metals, preferably selected from amorphous metals, quasi-crystals or approximants, more broadly metal alloys that cannot be wire drawn; Particles preferably made of a brittle material, preferably a brittle metal or an alloy of a brittle metal. and The inorganic particles are selected from among ceramic particles, metal alloy particles, amorphous metal particles, quasicrystalline particles, or near-crystalline phase particles; the thickness of the sheath is greater than 100 micrometers, preferably greater than 150 micrometers, and more preferably less than 400 micrometers; For a cord with an outer diameter of 2.5 to 3.5 mm, the thickness of the sheath is 200 to 400 micrometers; For a cord with an outer diameter of 1 to 2.5 mm, the thickness of the sheath is 100 to 250 micrometers; the ash content of the cord is, expressed as a mass percentage based on the dry mass of the cord, less than 2.5%, preferably less than 2%, more preferably less than 1%, preferably less than 0.7%, more preferably less than 0.5%; said polymeric binder and optionally a matrix lubricant, which may be the same or different from the matrix lubricant of said sheath, together comprising, as a volume percentage based on the volume of the matrix, more than 95%, preferably more than 97%, more preferably more than 99%, preferably substantially 100%, not taking into account any solvent residues; said polymeric binder, which is preferably a cellulose derivative, more preferably methylhydroxyethylcellulose, expressed as a volume percentage based on the volume of the core of the cord, more than 5%, preferably more than 10% and / or less than 25%, preferably less than 20% or even less than 15%, without taking into account any solvent residues; The matrix is ​​preferably expressed as a volume percentage based on the volume of the core of the cord, more than 25%, preferably more than 30%, preferably more than 40%, or even more preferably more than 45%, and / or preferably less than 70%, preferably less than 60%, preferably less than 55%, preferably less than 50%, without taking into account any solvent residues; In one embodiment, the matrix comprises a matrix lubricant, the content of the matrix lubricant being, as a volume percentage based on the volume of the core of the cord, more than 5%, more than 10% and / or less than 25%, or less than 20%, without taking into account any solvent residues; the matrix lubricant is selected from polyols, glycerides, in particular glycerol and its derivatives, stearates, aminoalcohols, preferably glycerin and triethanolamine, more preferably glycerin; The solvent for the matrix is ​​water or denatured alcohol, preferably water; the content of residual solvent, preferably water, in the core is less than 5% by mass percentage based on the dry mass of the core of the cord; said matrix being composed of greater than 99%, preferably substantially 100%m, organic matter, said percentages being volume percent; the sheath polymer and the optional sheath lubricant together are greater than 95%, preferably greater than 97%, preferably greater than 99%, preferably substantially 100%, as a volume percentage based on the volume of the sheath, not considering any solvent residue; the sheath comprises a sheath lubricant, which may be the same or different from the optional matrix lubricant described above, in a volume percentage based on the volume of the sheath of more than 10%, preferably more than 20%, preferably more than 30%, and / or less than 50%, preferably less than 40%, not taking into account possible presence of solvent residue; the sheath polymer content, as a volume percentage based on the volume of the sheath, is more than 45%, preferably more than 55%, preferably more than 60%, and / or preferably less than 80%, preferably less than 75%, more preferably less than 70%, without taking into account any solvent residues; the polymeric binder and the sheath polymer comprise the same polymer, preferably by one or more polymers, only the same polymer, preferably in the same proportions; the impurities in said matrix and / or in said sheath consist, for more than 90%, preferably more than 95%, more preferably substantially 100%, thereof, of organic impurities and / or impurities containing the element hydrogen H and / or metallic impurities; impurities in the matrix and / or sheath are less than 5%, preferably less than 3%, more preferably less than 1%, by volume percentage based on the volume of the matrix and / or the sheath, respectively, not taking into account any solvent residues; the sheath comprises a color pigment, which may be any commonly used colorant, which is less than 1% of the volume of the sheath, preferably less than 0.5%, preferably less than 0.4%, preferably less than 0.1%, or even less than 0.05%; The solvent of the sheath is preferably water or denatured alcohol, preferably water; the content of residual solvent, preferably water, in the sheath is less than 10%, preferably less than 5%, expressed as a mass percentage based on the mass of the sheath of the cord; said sheath being greater than 99%, preferably substantially 100%, of organic material, the percentages being by volume; The cord is wound on itself in the form of a roll or reel, preferably on a spool having a diameter greater than 50 mm, preferably greater than 100 mm, preferably greater than 150 mm, or even more preferably greater than 200 mm, and / or less than 1000 mm, preferably less than 500 mm, preferably less than 400 mm, preferably less than 300 mm.

[0025] The cord according to the invention is not intended for welding. Preferably, it does not contain any fluxes, which are agents commonly used for cleaning and deoxidizing the weld zone, or for forming a protective slag.

[0026] Preferably, the cord according to the invention does not contain fluxes selected from spath fluor or calcium fluoride, cryolite, a fluoride of alumina and sodium, and borates.

[0027] The present invention also provides a thermal spray device, the thermal spray device comprising: a torch comprising a plasma or flame generator and an injection device; and A cord according to the invention arranged so that it can be injected by the injection device into the plasma or into the flame generated by the generator. Equipped with the torch is capable of at least partially melting the inorganic particles of the cord and of ejecting the at least partially melted inorganic particles at a velocity preferably greater than 150 m / s; Regarding the above thermal spray device.

[0028] The torch is preferably capable of spraying at least partially molten inorganic particles at a velocity of more than 150 m / s and / or less than 1000 m / s, where the spray velocity is conventionally measured at the exit of the torch.In one embodiment, the particles are sprayed at a velocity of more than 300 m / s, preferably more than 500 m / s, preferably more than 600 m / s, preferably more than 700 m / s.In one embodiment, the particles are sprayed at a velocity of more than 150 m / s and less than 300 m / s.

[0029] The injection device is preferably arranged to inject the cord along an injection axis extending in a radial plane passing through the axis X of the plasma stream or flame and making an angle θ with a plane P transverse to the axis X that is greater than 60°, 70°, 80°, preferably greater than 85° in absolute value, where the injection axis I is preferably substantially parallel to the axis X, and the injection or "feed" of the feedstock is considered as an "axial" injection or feed. The torch is preferably an axial-feed torch.

[0030] An angle θ close to 90° advantageously promotes uniform combustion of the sheath and of the matrix, and therefore uniform distribution of the inorganic particles discharged at high speed into the plasma stream or flame, which makes it possible to ensure centering and optimal path of the particles in the jet nozzle of the torch, reducing the risk of fouling of the jet nozzle and therefore of malfunctions of the process and defects in the coating.

[0031] Preferably, the injection is performed upstream of the jet nozzle through which the stream or "jet" of plasma or, in the case of a flame torch, the flame flows. Preferably, in the case of a flame torch, the cord is driven to a combustion chamber. Preferably, in the case of a plasma torch, which is preferably a multi-cathode torch with axial injection of the material to be sprayed, the cord is driven to the confluence zone of the elementary streams of plasma emanating from the cathodes, i.e., upstream of the jet nozzle through which the plasma jet resulting from the confluence of these two elementary streams of plasma flows.

[0032] In particular, the cord according to the invention is sufficiently flexible to be wound and unwound while being sufficiently stiff to permit axial injection, preferably using a conventional drive device located behind (upstream of) the torch.

[0033] The injection device preferably opens into the interior of the torch.

[0034] As shown in FIG. 1, the injector is preferably positioned to introduce the cord into a plasma or combustion chamber 17, preferably into a portion 2 of the plasma or flame stream that extends less than 10 cm, preferably less than 5 cm, and / or more than 2 cm, preferably more than 3 cm, from one or more orifices 7 through which the plasma or flame stream exits the generator.

[0035] The torch may in particular be an axial-injection multi-cathode plasma torch, or a high velocity flame torch of the HVOF or HVAF type, or a conventional flame-wire torch, or a torch of the HVOF-Wire or HVAF-Wire type.

[0036] The invention also relates to a method for coating the surface of a substrate with a coating agent, in which a cord according to the invention is injected into a stream of plasma or into a flame from a torch and inorganic particles of the cord, which are at least partially melted in the plasma stream or flame, are sprayed onto said surface.

[0037] Finally, the invention relates to a method of thermal spraying by means of a thermal spraying device according to the invention, in which a torch is supplied with a cord according to the invention so as to form a coating on the surface of a substrate.

[0038] The substrate is preferably a metallic, ceramic, cermet, polymer, organic or composite substrate, preferably having a ceramic matrix.

[0039] The substrate may exhibit various shapes, for example with planar or revolutionary geometries, especially cylindrical or complex shapes, the only limitation being the accessibility by the jet of at least partially molten inorganic particles, which is advantageously improved by an axial feed upstream of the spray nozzle or upstream of the jet nozzle.

[0040] In one embodiment, the coating provides a surface functionality to the substrate, preferably improving wear resistance, modifying the coefficient of friction, or forming a thermal or electrical insulating barrier.

[0041] The coatings are intended to provide thermal, chemical or mechanical protection to components, particularly components within reactors, for example forming columnar thermal barriers on aero or stationary turbine components, forming environmental barriers on ceramic-ceramic composite components or forming functional layers in solid oxide fuel cell devices, by way of example only.

[0042] The cord and thermal spray device according to the invention are most particularly advantageous for producing columnar-structure coatings and nanostructured coatings by injection of submicron particles contained in said cord, thereby avoiding the disadvantages of the SPS or SPPS method. The "columnar structures" are described inter alia in the doctoral dissertation by Benjamin Bernard on thermal barriers by suspension plasma spraying, which can be found at the following website: http: / / docnum.univ-lorraine.fr / public / DDOC_T_2016_0212_BERNARD.pdf.

[0043] Another advantage of the present invention is the possibility of using thermal spraying to form hybrid coatings, i.e. coatings comprising different materials, from cords containing particles with different physicochemical properties.

[0044] The production of the hybrid coating can be accomplished using known thermal spray techniques.

[0045] A hybrid coating may be obtained from a cord containing particles of a ceramic oxide material and metal particles.

[0046] The present invention makes it possible to combine different materials that are otherwise difficult to combine, especially due to their different sizes or densities, which is a major problem in thermal spraying, especially where suspensions or dry powders need to be co-injected in the thermal spray.

[0047] Further features and advantages of the present invention will become more apparent upon reading the following detailed description and examining the accompanying drawings. [Brief description of the drawings]

[0048] [Figure 1] FIG. 1 shows a schematic diagram of a thermal spray device according to the present invention. [Diagram 2] FIG. 2 shows diagrammatically a cross section of a cord according to the invention. [Diagram 3] FIG. 3 shows a schematic diagram of the apparatus used in the examples to evaluate flexibility.

[0049] The same references are used in the various figures to denote identical or similar elements.

[0050] definition

[0051] The "equivalent outer diameter" of a cord is the diameter of a disk having the same surface area as the cross-section of the cord at its midpoint length.

[0052] On the cumulative particle size distribution curve, the particle sizes corresponding to the percentages of 10%, 50%, and 90% by number of particle sizes of a particle population (classified in the order of increasing particle sizes) are respectively called the 10th percentile (D 10 ), 50th percentile (D 50 ) and the 90th percentile (D 90 According to this definition, if 10% of the particles in a particle collection are D 10 The particle size is smaller than D 10 The particle size distribution curve can be generated using a laser granulometer. A SYSMEX FPIA 3000 instrument can be advantageously used to obtain such a curve.

[0053] 50th percentile D of particle ensemble 50 is referred to as the "median size." The median size therefore separates the particles of a collection of particles into a first and second population equal in number, where the first and second populations contain only particles having a size equal to or greater than the median size, respectively.

[0054] The percentiles for the size of the inorganic particles of the cord are measured on the powder of inorganic particles used to manufacture the cord. They can be estimated by removing the binder from the cord by calcination, removing the organic components and recovering the inorganic particles. The removal of the binder is preferably carried out in a neutral atmosphere, for example in argon, as the inorganic particles may be oxidized and are easily damaged by the binder removal temperature. The particle size distribution of the inorganic particles extracted by the binder removal can then be measured by volume, for example by laser granulometry. The particle distribution by volume can be easily calculated for the volume of the cord, the volume of the core or the volume of the sheath, the dimensions of which can be measured, for example, with a micrometer or a vernier caliper before and after removing the sheath of the cord.

[0055] Measurement of the percentage based on the "dry weight" of the cord can be carried out on a 100 g sample of the cord after drying the cord at 110° C. for 1 hour.

[0056] When a volume percentage is calculated based on the cord, the core, or the sheath, the volume of the cord, the core, or the sheath is the volume of the cord, the core, or the sheath that is enclosed by the outer surface of the cord, the core, or the sheath.

[0057] The lubricant content by volume can be estimated from the amount of lubricant introduced into the starting charge during production. The lubricant can be liquid or solid (graphite, BN, etc.).

[0058] The concept of "color pigment" is well known to those skilled in the art. Pigments are powders that provide color during the manufacture of the cord. Color pigments are conventionally in the form of powders with a median particle size of less than 1 micrometer. Color pigments may in particular be "oxide pigments", i.e. pigments consisting of oxides.

[0059] "Inorganic" particles are particles made of non-organic materials, i.e. materials that do not contain hydrocarbon chains as one of their main components. This family of materials includes metals, glasses and ceramics, as well as composite materials made from metals, glasses or ceramics. Preferably, the inorganic particles do not contain hydrocarbon chains.

[0060] Materials that are neither metallic nor organic, such as materials selected from oxides, nitrides, carbides and chlorides, are called "ceramics". Ceramic materials include in particular glasses, cermets and vitreous ceramics. Within the context of the present invention, diamond, graphite, graphene and carbides of metals or semimetals are considered to be ceramic materials.

[0061] By "cermet" is meant a material that contains at least two phases, at least one of which is ceramic and at least one of which is metallic.

[0062] The term "brittle" refers to a material in which the range of plastic deformation under load before fracture is less than 5%, preferably less than 1%, of the range of elastic deformation, and preferably substantially zero. In other words, the range of stress loads that will cause plastic deformation without fracture represents less than 5%, preferably less than 1%, of the range of stress loads that will cause elastic deformation.

[0063] Those components of the cord whose presence is undesired, i.e., components other than inorganic particles, polymeric binder, sheath polymer and optionally one or more lubricants, are referred to as "impurities". Solvent residues are not considered impurities. The impurities may include not only impurities contained in the raw materials, but also residues of additives used during the manufacture of the cord, such as residues of plasticizers.

[0064] The "ash content" of the cord corresponds to the residues left by the combustion of the cord sheath and the core matrix. The ash content can be determined according to the NF T30-012 standard by measuring the difference between the mass resulting from firing at a temperature of 450°C and that resulting from firing at a temperature of 950°C. The temperature of 450°C allows all organic components to be decomposed, and the temperature of 950°C allows the evaporation of any residues liable to hinder the melting of the inorganic particles. The firing must be sufficient to extract substantially all the organic components from the cord. It is preferably carried out for a time sufficient for said extraction to be substantially complete. The firing time is therefore adjusted to the dimensions of the cord sample to be analysed.

[0065] The "volume content of mineral material" is measured by dividing the volume of mineral material by the volume of the cord core. According to techniques well known to those skilled in the art, the volume of the cord core can be measured geometrically. The volume of mineral material is determined using the Archimedes method by weighing the mineral material extracted from the cord core after binder removal.

[0066] A percentage is determined as "solvent-free" when the basis on which the percentage is calculated does not take into account any solvent that may be present. In particular, the solvent is preferably water, and then the volume percentage of, in particular, inorganic particles, polymeric binders, matrix lubricants, sheath polymers or sheath lubricants is measured by dividing the volume of the component concerned by the volume of the dry basis, i.e., without taking into account water that may be present. The dry basis is in particular In the case of inorganic particles, the core, In the case of the polymer binder and the matrix lubricant, the matrix, In the case of the sheath polymer and the sheath binder, It is possible.

[0067] These percentages may be measured after thorough drying, so as not to take moisture into account.

[0068] As used herein, the modifiers "upstream" and "downstream" are used with reference to the direction of flow along the "flow axis" or "axis of flow" of the plasma-generating gas flow or flame gas flow.

[0069] The expression "based on" conventionally means that the corresponding amount is more than 50% by weight.

[0070] A "transverse plane" is a plane perpendicular to the axis X.

[0071] The "radial plane" is the plane that contains the axis X.

[0072] For clarity, a distinction is made between the "polymeric binder" of the core of the cord and the "sheath polymer" of the sheath. The polymeric binder and the sheath polymer may be the same or different. The polymeric binder and the sheath polymer may be the same or different.

[0073] Also, for clarity, a distinction is made between a "matrix" binder and a "sheath" binder, which may be the same or different.

[0074] The words "comprise," "include," "contain," and "have" are to be interpreted broadly and without limitation. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0075] Detailed Description

[0076] Spray Equipment

[0077] FIG. 1 shows diagrammatically a thermal spraying device 10 according to the invention, comprising a torch 12 and a cord 15 according to the invention for supplying inorganic particles to the torch.

[0078] The torch is in particular a multi-cathode torch capable of axial injection; a flame torch; preferably a torch of the high-velocity oxy-fuel (or HVOF) or high-velocity air-fuel (or HVAF) type, or a conventional flame-wire torch, or a torch of the HVOF-wire or HVAF-wire type.

[0079] In a conventional manner, the torch 12 is equipped with one or more plasma or, in the case of a flame torch, combustion gas generators 13 and an injection device 14 for injecting a cord 15 along an injection axis I through an injection orifice 4 into a stream 16 of plasma or flame generated in a chamber 17 upstream of the spray nozzle or upstream of the jet nozzle 21 of the torch.

[0080] The axis of the plasma stream or frame is referred to as "axis X."

[0081] The projection of the injection axis I on a radial plane containing the axis X and passing through the centre of the injection orifice forms an angle θ with the axis X. The angle θ is preferably greater than 60°, greater than 70°, greater than 80°, preferably greater than 85°. Preferably, the axis X is contained within said radial plane, preferably completely coinciding with the axis X.

[0082] code

[0083] 2 shows diagrammatically a cross section of a cord 15 according to the invention, in which in particular one can distinguish the core 18 and the sheath 20 which surrounds said core.

[0084] The cord preferably has a cross-section which is constant over its entire length. The cord preferably has a circular cross-section and preferably has an equivalent outer diameter greater than 1.5 mm, preferably greater than 2 mm, and / or less than 3.3 mm, preferably less than 3.2 mm, with an equivalent outer diameter of 3 mm being preferred.

[0085] The cord is preferably wound on a spool and is preferably packaged in the form of a reel which is easy to handle and which can be unwound for feeding into the spray device.

[0086] Preferably, said cord does not contain metal salts or hydroxides, for example any aluminum hydroxide (boehmite) that forms a gel during the preparation of the paste, and also does not contain ammonium acetate, since the inventors have discovered that these ingredients mentioned in the prior art can have a detrimental effect. In particular, the formation of an inorganic gel, for example as a result of the use of aluminum hydroxide, leads to the inorganic particles agglomerating during spraying, which means that the individual particles are not all released, which is therefore detrimental to obtaining a finely structured layer. These ingredients also result in low flexibility in cords in which the inorganic particles have a median size smaller than 10 micrometers.

[0087] core

[0088] The core 18 is in the form of a wire, preferably of constant cross section over the entire length of the cord, preferably of circular cross section, and its equivalent outer diameter is preferably greater than 2 mm and / or preferably less than 3.2 mm.

[0089] The core comprises inorganic particles 22, which are melted into droplets in the stream or flame of plasma and then sprayed onto a substrate to form a coating on the substrate.

[0090] These inorganic particles preferably occupy more than 40%, preferably more than 50%, preferably more than 55% and / or less than 80%, preferably less than 75%, preferably less than 70%, preferably less than 65% of the volume of the core of the cord. A volume content of inorganic particles less than 40% increases the energy consumption required to decompose the organic components of the binder matrix and sheath during spraying. A volume content of inorganic particles greater than 80% adversely affects the flexibility of the cord.

[0091] The median diameter D of the aggregate of inorganic particles 50 is less than 10 micrometers. This very low median diameter is intended to make it possible to obtain coatings with a very fine structure.

[0092] The median diameter D of the aggregate of inorganic particles 50 is preferably less than 5 micrometers and more preferably greater than 0.1 micrometers.

[0093] The median size of said aggregates of inorganic particles is preferably between 1 and 5 micrometers in order to obtain a dense coating intended to provide mechanical and / or chemical protection.

[0094] The median diameter of the aggregates of inorganic particles is preferably 0.2 to 0.5 micrometers in order to obtain a coating formed of columnar or "feathery" layers with a more insulating microstructure, in particular to obtain a thermal barrier.

[0095] A median diameter of greater than 0.1 micrometers can advantageously reduce safety issues during manufacture of the cord.

[0096] In a preferred embodiment, the median diameter D of the inorganic particles 50The ratio R of the equivalent outer diameter d (micrometers) of the cord to the equivalent outer diameter d (micrometers) is between 200 and 20,000, preferably less than 500, preferably greater than or equal to 1,000 and / or less than 10,000, preferably less than 5,000, preferably less than 2,000. A ratio R between 200 and 1,600 is particularly advantageous, especially for cords intended for high-speed flame or plasma torches with axial injection of the feedstock.

[0097] Preferably, (D 90 -D 10 ) / D 50 is greater than 1 and / or less than 1.8.

[0098] In one embodiment, the 10th percentile (D 10 ) is preferably greater than 50 nm, preferably greater than 100 nm, preferably greater than 150 nm, and the 90th percentile (D 90 ) is preferably less than 1,000 nm, preferably less than 900 nm, preferably less than 850 nm.

[0099] In one embodiment, the 10th percentile (D 10 ) is preferably greater than 0.1 micrometers, more preferably greater than 0.5 micrometers, and the 90th percentile (D 90 ) is preferably less than 10 micrometers, preferably less than 8 micrometers.

[0100] The nature of the inorganic particles is determined according to the properties of the coating desired.

[0101] Preferably, the inorganic particles are made of a material consisting of one or more of the following oxides, alone or in solid solution, for more than 80%, preferably more than 90%, preferably more than 95% or even substantially 100% of their mass: Al 2 O3 , SiO 2 , ZrO 2 , Cr 2 O 3 and TiO 2 .

[0102] The inorganic particles are non-oxide materials, in particular Metal oxides, preferably made of alumina, zirconia, titanium oxide, chromium oxide, yttrium oxide, or a combination of some of these oxides, such as mullite or spinel, and / or Carbide-based cermets, where the carbides can be, for example, carbides of chromium, tungsten, titanium, tantalum, zirconium, the carbides being associated with a metallic phase, and / or SiC-YAG composites (YAG stands for Yttrium-Aluminum Garnet) allow for the thermal spraying of SiC-based compounds and / or in association with a metallic phase in the form of ceramics, for example nitrides, borides and carbonitrides, possibly cermets, and / or a refractory metal or a refractory metal alloy, preferably a refractory metal having a melting point higher than 2500 K, and / or Special metal alloys, e.g. amorphous metals, quasi-crystalline or near-crystalline metals, and more generally metal alloys that cannot be wire drawn The insulating layer may be made of a non-oxide material selected from the group consisting of:

[0103] The alloys of the special metals are conventionally metals, in particular alloys that undergo brittle mechanical fracture, such as amorphous metals or metallic glasses, quasicrystals or quasicrystals (i.e. quasicrystals with crystalline phase approximations), e.g. those described in https: / / www.universalis.fr / encyclopedie / quasi-cristaux / 4-phases-approximantes-et-defauts.

[0104] Preferably, the inorganic particles are selected from among particles made of ceramic, particles made of metal alloys, particles made of amorphous metals, particles made of quasicrystals, or particles made of approximant crystalline phases.

[0105] Inorganic particles made from carbides are particularly suitable for HVOF technology.

[0106] The inorganic particles are embedded, and preferably substantially uniformly dispersed, in a matrix 24 which binds the inorganic particles together.

[0107] The matrix is ​​substantially composed of organic material and is therefore capable of being reduced to an ash form upon spraying.

[0108] The volume content of the plasticizer can be, as a volume percentage, more than 1%, preferably more than 4%, and / or less than 10%, preferably less than 8%, based on the volume of the core or matrix excluding the solvent. The plasticizer can be any known plasticizer, such as a phthalate, in particular BDP (butyl benzyl phthalate) or polyvinyl alcohol (known by the abbreviation PVA).

[0109] In one preferred embodiment, 100% of the polymer binder in the matrix, excluding impurities and solvent residues, comprises, and preferably consists of, a lubricant, preferably glycerin, which may in particular occupy 10% to 20% of the volume of the core.

[0110] sheath

[0111] The sheath 20 contributes to the flexibility of the cord by increasing its ability to bend without damage, in particular allowing the cord to be wound without visible damage, in particular without cracking or disintegrating its components, thus contributing to the tenacity of the cord, which is necessary due to the small equivalent outer diameter of the cord, and imparting a surface finish that promotes slippage, facilitating the passage of the cord through the injection orifice of the torch, thereby reducing wear on the parts of the torch that the cord contacts, in particular the injection orifice.

[0112] The sheath surrounds the core over the entire length of the cord and preferably has a thickness that is constant in any plane perpendicular to the length of the cord, preferably in any plane perpendicular to the length of the cord.

[0113] Preferably, the ratio of the thickness of the sheath (micrometers) to the equivalent outer diameter of the cord (micrometers) is greater than 0.03 and less than 0.6, preferably greater than 0.05 or even greater than 0.1 and / or less than 0.5 or even less than 0.3 or even less than 0.2. A ratio of 0.05 to 0.5 is particularly suitable when the aggregate of inorganic particles has a median diameter of less than 5 micrometers.

[0114] Preferably, the main component of the sheath is a polymer of the same family, or even of the same chemical composition, or even of the same empirical formula, as the polymer binder of the matrix of the core of the cord. The cross-linking monomers forming the sheath polymer are preferably the same as those of the polymer binder.

[0115] The sheath polymer preferably occupies between 55% and 75%, preferably approximately 65%, of the volume of the sheath excluding solvent.

[0116] Preferably, the sheath contains a lubricant, preferably glycerin, referred to as "sheath lubricant", preferably in a content of more than 25% by volume of the sheath excluding solvent, which facilitates coextrusion during its manufacture, reduces wear on the parts of the torch on which the cord slides, and facilitates slippage, thereby limiting the risk of the cord buckling when injected into the plasma stream or flame, thereby contributing to the quality of the coating produced.

[0117] A 100% complement of the sheath polymer and the sheath lubricant preferably consists of organic impurities, in particular resulting from organic additives, such as plasticizers, used to shape the sheath of the cord when it is manufactured.

[0118] Generally, the composition of the matrix and the sheath is determined so as to obtain a low ash content of the cord. The ash content resulting from the presence of the polymer binder, matrix lubricant, sheath polymer, sheath lubricant and plasticizer used is preferably less than 2.5%, more preferably less than 2%, or even less than 1%, in mass percentage based on the mass of the cord. Those skilled in the art know how to adapt the composition to reduce its ash content by carrying out some simple tests.

[0119] Ash contents above 3% result in high organic content which causes severe contamination of the torch, thereby resulting in significant drawbacks to the process and causing defects in the coatings obtained by thermal spraying.

[0120] In particular, preferably the sheath polymer and / or the polymeric binder of the matrix, preferably the organic charge consisting of the sheath polymer and the polymeric binder of the matrix, consists or consists of more than 80% by weight, more than 90% by weight, more than 95% by weight, preferably substantially 100% by weight, of a cellulose derivative, where the percentages are vol.% based on the sheath or the polymeric binder, respectively, excluding solvent. Cellulosic derivatives advantageously allow a very low ash content, typically less than 1% by weight based on the weight of the cord.

[0121] Preferably, the cellulose derivative is selected from cellulose ethers, preferably from methyl cellulose (MC), ethyl cellulose (EC), methyl ethyl cellulose (MEC), hydroxymethyl cellulose (HMC), hydroxyethyl cellulose (HEC), methyl hydroxyethyl cellulose (MHEC), hydroxymethyl ethyl cellulose (HMEC), hydroxypropyl cellulose (HPC), hydroxypropyl methyl cellulose (HPMC), hydroxypropyl ethyl cellulose (HEPC), carboxymethyl cellulose (CMC) and combinations thereof. Preferably, the cellulose derivative is selected from hydroxyethyl cellulose, in particular methyl hydroxyethyl cellulose, since this subfamily of cellulose has rheological properties suitable for the manufacture of small diameter cords, in which all inorganic particles have a median diameter of less than 10 micrometers.

[0122] The alkali content, in particular the Na content, in the cellulose derivative is preferably less than 1% as a mass percentage based on the mass of the cellulose derivative. This feature advantageously makes it possible to limit the ash content and the long-term corrosion of the torch. Preferably, the cellulose derivative contains no or almost no cellulose fibers.

[0123] The cord according to the invention can be manufactured using any conventional method, in particular by co-extrusion of a first paste intended to form the core of the cord and a second paste intended to form the sheath, a method of this kind being in particular described in patent FR 1,443,142.

[0124] Methods such as those described in UK Patent Application Publication No. GB ​​1,151,091A are particularly suitable.

[0125] The flexibility of the cord can be easily adjusted by adjusting the amount and viscosity of the polymer binder contained in the core and / or the viscosity of the sheath polymer.

[0126] Purpose

[0127] The cord according to the invention is particularly suitable for plasma torches, in particular plasma torches with axial injection, in particular multi-cathode plasma torches, also called "multi-chamber" torches.

[0128] The flexibility of the cord according to the invention allows it to be wound on a spool so that it can be unwound while the coating is being made. Thus, the spray can be substantially continuous. The sheath also ensures a smooth contact with the injection orifice, thereby reducing wear on the injection orifice.

[0129] However, the cord is sufficiently stiff to allow for substantially axial injection, preferably using an offset drive upstream of the torch, which promotes uniform heating of the inorganic particles and uniform distribution of the jet of inorganic particles within the jet nozzle, thereby limiting inorganic particle smearing and improving coating repeatability and quality.

[0130] The limited amount of liquid phase, particularly solvent, limits the amount of energy consumed and maximizes the energy available to pyrolyze the sheath and the matrix and to melt the inorganic particles.

[0131] The size of the inorganic particles is selected according to the spray equipment and the microstructure desired for the coating.

[0132] From the moment the cord enters the torch chamber 17, the following sequence of events occurs: happen: the sheath and the polymer binder are pyrolyzed; Individual inorganic particles are released without clumping-together effects; The inorganic particles are rapidly entrained in the (flame or plasma) jet and completely or partially melt during flight; The at least partially molten inorganic particles impact the substrate and then solidify to form the coating.

[0133] In particular, the code can be used to produce: Coatings which provide mechanical or chemical protection, in particular against corrosion by chemical species, vapors, etching plasmas; environmental or thermal barrier; Coatings with tribological function, anti-wear coatings, electrically insulating coatings, or conductive coatings.

[0134] Preferably, the coating has a thickness of 10 to 500 micrometers.

[0135] Working Example

[0136] The following non-limiting examples are presented for the purpose of illustrating the present invention.

[0137] Experimental Example 1 was carried out by extruding a first paste according to the teachings of Japanese Patent Publication No. JP2016156058.

[0138] In another example, the following first paste was prepared in accordance with the teachings of British Patent Application Publication No. GB ​​1,151,091A: A powder of alumina particles having a median diameter of 7.5 μm and a purity of more than 99.5%, obtained by melt solidification; and Methylhydroxyethylcellulose (polymer binder) with a viscosity of 50 mPa.s.

[0139] The viscosity of methylhydroxyethylcellulose was measured at 20° C. using a Hoppler viscometer on a 2% mass content of methylhydroxyethylcellulose powder mixed with demineralized water.

[0140] The weight ratios of the components of this first paste are shown in Table 1 below.

[0141] A second paste intended to form the sheath was then prepared, for which the same methylhydroxyethylcellulose used to prepare the first paste was mixed with a given amount of water, a given amount of glycerin and a given amount of color pigment, according to the weight ratios shown in Table 1 below.

[0142] The first and second pastes were co-extruded in an extrusion press to produce a 3 mm flexible cord precursor having a substantially circular cross-section with an outer diameter of 3 mm and a sheath substantially 350 micrometers thick.

[0143] Drying of the cord precursor resulted in a cord having a residual water content of less than 5%. Measurements of the residual moisture showed values ​​of the order of 3%. The cord was wound onto a spool with a diameter of 70 mm.

[0144] Diameter and thickness

[0145] The outer diameter of the cord and the thickness of the sheath are determined by the digital Tesa Micromaste 登録商標 Measured using 0-30mm.

[0146] Flexibility Test

[0147] For each experimental example, A sample of at least 0.5 metres of the cord to be tested is wound in succession on a cylindrical rod of 25 mm diameter, as shown in Figure 3. This operation must not break the cord; A sample of at least 0.5 meters of the cord to be tested was wound around a cylindrical rod of 70 mm diameter to form a continuous winding, as illustrated in Figure 3. The sheath of the cord must be free of cracks visible to the naked eye from the outside, or internal cracks visible from the outside through a color change resulting from the translucency of the sheath; A sample of at least 0.5 meters of the cord is subjected to a cord drive test in which a 2 kg roller with a diameter of 26 mm is moved along the sample at a speed of 1 m / s. The cord is slightly deformed, a change in diameter of less than 15% is permitted, but it must not have any cracks visible to the naked eye from the outside.

[0148] If the code passes these three tests, the flexibility is acceptable. If the code fails at least one of these three tests, the flexibility is unacceptable.

[0149] Ash content

[0150] The ash content is (m 0 -m 1 ) / m 0 is determined by, where m 0 and m 1are the masses of 3 cm long cords after firing for 1 hour in air at 450°C and 950°C, respectively.

[0151] ratio R

[0152] The ratio R is the median diameter (D 50 ) (micrometers) to the equivalent outer diameter of the cord (micrometers).

[0153] Change in enthalpy

[0154] The change in enthalpy associated with the decomposition of the organic components of the cord at 2300K was determined based on the formulation. being injected upstream of the flame or plasma stream, i.e. between the orifice where the plasma stream or flame exits said generator and the spray nozzle (or jet nozzle); In the case of high-velocity plasma torches, a neutral atmosphere, i.e., no oxygen and hydrogen and C x H y There is no atmosphere with decomposition products due to the decomposition of the code of the type; In the case of high-velocity oxygen flame (HVOF type) torches, CO 2 and H 2 Decomposition directly into O and Residual moisture in the cord after drying is 3% Considering the above, we consider the facts for each experimental example. 登録商標 was calculated using the software.

[0155] The addition of organic compounds resulting from the potential presence of the sheath was taken into consideration to determine the amount and nature of the organic products of the cord.

[0156] In Table 1 below, the change in enthalpy is given in kJ / mole of alumina.

[0157] It is considered to be particularly advantageous if the change in enthalpy in a neutral atmosphere is as low as possible, especially below 1000 kJ / mole of alumina in absolute value.

[0158] The change in enthalpy in an oxidizing atmosphere is believed to be particularly advantageous when it is less than +1000 kJ / mole of alumina.

[0159] The amount of inorganic particles is given as a volume percentage based on the volume of the cord core, without taking into account the solvent.

[0160] Example 1 (comparative example) was carried out according to the teachings of Japanese Patent Publication No. JP2016156058 and does not have a sheath. Example 3 (comparative example) was carried out according to the teachings of British Patent Application Publication No. GB1,151,091A, but with finer inorganic particles. Examples 4* and 5* are according to the present invention.

[0161] [Table 1]

[0162] As is now evident, the invention provides a cord which, due to its flexibility, can advantageously be introduced into the centre of the flame or plasma, continuously, substantially along the axis of the torch. The inorganic particles are adequately distributed as they are sprayed. The pyrolysis characteristics of the cord, in particular its very low variation in enthalpy at 2300K, make it possible to obtain, with limited energy consumption, a coating which advantageously exhibits a controlled roughness and is free of defects.

[0163] Of course, the invention is not limited to the described examples and embodiments, which are provided as illustrative and non-limiting examples.

Claims

1. A cord intended to serve as a feedstock for a thermal spray torch to produce a coating, said cord having an equivalent outside diameter (d) between 1 mm and 3.5 mm and comprising a core (18) in the form of a wire and a sheath (20) covering said core along its entire length, The core is Median diameter (D 50 a collection of inorganic particles (22) having a diameter of less than 10 micrometers, wherein the inorganic particles occupy more than 40% and less than 80% of the volume of the core, the inorganic particles being particles of one or more metal oxides and / or particles of carbide-based cermets and / or inorganic particles of SiC-YAG and / or particles comprising or made of ceramic materials and / or particles made of one or more metals or metal alloys having a melting point higher than 2500 K and / or particles made of special metal alloys; and A matrix that binds the inorganic particles (24) It consists of: The matrix is A polymer binder, the mass of which is more than 80% of which is a cellulose derivative, and Optionally, a matrix lubricant Including, the polymer binder and the matrix lubricant together occupy greater than 90% by volume of the matrix; The sheath (20) has a thickness of 50 micrometers to 500 micrometers, and A polymer, referred to as a "sheath polymer", whose mass is more than 80% composed of cellulose derivatives, and Preferably, the lubricant is referred to as a "sheath lubricant." Including, the sheath polymer and the sheath lubricant together occupy greater than 90% of the volume of the sheath; said volume percent being determined without regard to the possible presence of solvent residues; The median size of a collection of particles is the 50th percentile of the collection of particles corresponding to the 50% percentage by number on a cumulative particle size distribution curve of the particle sizes of the collection of particles, determined using a laser granulometer, said particle sizes being ranked in increasing order. The code.

2. The cord has an ash content of less than 5%, and the ash content is (m 0 -m 1 ) / m 0 2. The cord of claim 1, wherein m0 and m1 are the masses of a 3 cm sample length of the cord after firing in a furnace at 450° C. and 950° C., respectively, in air for a duration of 1 hour.

3. 3. The cord of claim 2, wherein the ash content of the matrix and the ash content of the sheath of the cord are less than 1%.

4. The median diameter in micrometers of the aggregate of inorganic particles (D 50 The cord according to any one of claims 1 to 3, wherein the ratio (R) of the equivalent outer diameter (d) in micrometers of the cord to the equivalent outer diameter (d) in micrometers of the cord is 200 to 20,000.

5. The code according to claim 4, wherein the ratio (R) is from 200 to 2000.

6. The median diameter D of the aggregate of inorganic particles 50 The cord according to any one of claims 1 to 5, wherein the thickness is less than 5 micrometers.

7. The cord according to any one of the preceding claims, wherein the viscosity of the polymer binder of the core and / or of the sheath polymer is between 30 and 300 mPa.s at 20°C.

8. The cord according to any one of claims 1 to 7, wherein the sheath comprises a sheath lubricant, the content of the sheath lubricant being greater than 10% and less than 50% by volume, based on the volume of the sheath without taking into account the possible presence of solvent.

9. The inorganic particles are Particles of alumina, zirconia, titanium oxide, chromium oxide, yttrium oxide, or some combination of these oxides; and / or and / or particles of cermets containing more than 50% by weight of carbides selected from carbides of chromium and / or carbides of tungsten and / or carbides of titanium and / or carbides of tantalum and / or carbides of zirconium and / or carbides of niobium; and / or Particles of a ceramic material in the form of a nitride, a boride or a carbonitride, said ceramic material optionally being associated with a metallic phase in the form of a cermet; and / or Particles of brittle material; and / or Particles of amorphous metal alloys, quasi-crystalline or near-crystalline particles, or particles of metal alloys that cannot be drawn into wire The code according to any one of claims 1 to 8, which is selected from:

10. The cord according to any one of claims 1 to 9, wherein the thickness of the sheath is greater than 200 micrometers and less than 400 micrometers.

11. The cord of any one of claims 1 to 10, wherein the polymeric binder and the sheath polymer comprise the same polymer.

12. 12. An assembly comprising a spool having a diameter of less than 500 mm and a cord according to any one of claims 1 to 11 wound on said spool.

13. 1. A thermal spray device, comprising: a torch (12) having a plasma stream or flame generating device (13) and an injection device (14); and The cord (15) according to any one of claims 1 to 11, arranged so as to be injected by the injection device into the plasma stream or the flame generated by the generator. It is equipped with the torch is capable of at least partially melting the inorganic particles and ejecting the at least partially melted inorganic particles at a velocity of greater than 150 m / sec; The thermal spray device.

14. 14. A thermal spray device according to claim 13, wherein the injection device is arranged to inject the cord along an injection axis (I) extending in a plane passing through the axis (X) of the plasma stream or the axis (X) of the flame and making an angle θ with a plane perpendicular to said axis (X) that is greater than 60°, preferably greater than 80°, in absolute value.

15. 15. A thermal spray device according to claim 13 or 14, wherein the injection device is arranged to inject the cord upstream of a spray nozzle of the torch or upstream of a jet nozzle of the torch.

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