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

Abstract

The invention relates to a cord having an equivalent diameter (d) of between 1 mm and 3.5 mm and made of a core (18) in the form of a wire and a sheath (20) covering the core along its entire length, the core being formed of: - an array of inorganic particles (22, the median size (D50) of which is smaller than 10 micrometres, the inorganic particles representing more than 40% and less than 80% of the volume of the core; and - a matrix (24) binding the inorganic particles, the matrix comprising a polymer binder and, optionally, a matrix lubricant, together representing more than 90% of the volume of the matrix; the sheath having a thickness of between 50 micrometres and 500 micrometres and comprising a sheath polymer and, preferably, a sheath lubricant together representing more than 90% of the volume of the sheath, the volume percentages being determined without taking into account the possible presence of a solvent.

Description

[0001] Description

[0002] FLEXIBLE CORD FOR POWERING A THERMAL SPRAY TORCH AND THERMAL SPRAY DEVICE

[0003] Technical field

[0004] The invention relates to a flexible cord for supplying a thermal spray torch for coating. It also relates to a method for manufacturing said cord and a thermal spray device using said cord.

[0005] Prior art

[0006] Thermal spraying involves using a source of thermal and kinetic energy to melt a set of inorganic particles, initially in the form of wire or powder, and projecting the at least partially melted particles onto a substrate. Upon impact, the at least partially melted particles spread out and cool on the substrate. They can thus effectively adhere to each other and to the substrate as they cool, and form a coating.

[0007] There are different technologies, which can be classified into the classes "enthalpy of combustion", "electric discharge" and "momentum density".

[0008] The "enthalpy of combustion" class includes "detonation gun" "flame-powder" technologies (generating particle speeds < 80 m / s and can only be fueled by powders), "flame-wire" (generating particle speeds > 150 m / s and can be fueled by means of a medium chosen from a wire, a cord or a rod) and finally "high speed flame" (generating particle speeds > 500 m / s). Among the "high speed flame" technologies, we distinguish the "detonation D-Gun", "HVOF" (High velocity Oxy-Fuel)", "HVSFS" (High Velocity Suspension Flame Spray) and "HVAF" (High Velocity Air Fuel) technologies which can be fueled by powders, suspensions (case of HVSFS), or even wires.

[0009] The "electric discharge" class includes "electric arc" and "plasma" technologies, the latter category including so-called "atmospheric" processes, or APS (Atmospheric Plasma Spray), processes in controlled atmospheres and temperatures, for example "VPS / LPPS" (Vacuum or Low Pressure Plasma Spray), "VLPPS / PS-PVD" (Very low pressure plasma spray and Plasma Spray enhanced Physical Vapor Deposition), "SPS" (Suspension Plasma Spray), "SPPS" (Solution Precursor Plasma Spray), "Induction Plasma", and "WSP" (Water Stabilized Plasma). These systems can propel particles at speeds ranging from 150 m / s to 500 m / s depending on the variants and process parameters used.These “plasma” systems can be used with dry powders whose particle size is such that the median size D50 is typically greater than 10 micrometers, or liquids (chemical precursors such as salts, or suspensions comprising inorganic particles whose median size D50 is less than 10 micrometers).

[0010] The "momentum density" class includes "Cold Spray" technologies, which include "low pressure", "high pressure" and "recycled helium" technologies.

[0011] All these technologies are well known, and notably described in the ASM Handbook vol 5a - Thermal Spray Technology.

[0012] Each technology is associated with constraints specific to it, so that the problems encountered, and the solutions provided to address them, are generally different depending on the technology considered.

[0013] The invention is particularly interested in the set comprising:

[0014] - in the “enthalpy of combustion” class, “wire-flame” and “high-speed flame” technologies; and

[0015] - technologies of the “electric discharge” class, and in particular “plasma” technologies.

[0016] For the sake of clarity, in this description and generically, the term "torch" refers to a torch or gun used in these technologies. By "torch" is included in particular a flame gun of the wire flame type (WFS or Wire Flame Spray), or a plasma torch system, or finally, a "High Speed ​​Flame" projection device as defined above. A recent development in these technologies consists of feeding these devices with liquid precursor suspensions or solutions (the suspensions being made up of a solvent and fine inorganic particles, having a median size D50 of less than 5 micrometers typically).This evolution towards very fine particles (or even the formation of the material in situ in the case of liquid precursors) has made it possible to generate new types of microstructures, for example very finely structured, very dense, or even columnar, or "feathery" (having the characteristics of juxtaposition of feathers when observed in micrographic section). These developments open up new perspectives, but come up against constraints and limitations of process robustness, stability and reproducibility linked to the fact that particle suspensions are not always perfectly stable. However, the vaporization of the solvent is detrimental to energy efficiency during the projection phase. Furthermore, when the suspensions contain particles of different compositions, in particular those with different densities.The formulation of such stable suspensions, without sedimentation or agglomeration of particles, is difficult, if not impossible, to control industrially.

[0017] JP2016156058A describes a feed medium consisting of a composite wire. The coating is a dense electrolytic film for the production of fuel cells. Such a wire can be difficult to manufacture and does not allow the production of ceramic coatings (e.g. oxides) with good control of the size of the projected particles. In particular, this media comprises fine particles embedded in a matrix. Tests have shown that the large quantity of matrix leads, during projection, to detrimental enthalpy variations.

[0018] US 4,593,856 also describes a feed medium in the form of a wire. However, the melting of the wire may be incomplete, which affects the quality of the coating.

[0019] Cords with a core coated with a sheath are known for feeding brazing torches for depositing thick layers ("overlay" or "hardfacing" in English) bonded metallurgically onto a metal support. They are not suitable for the manufacture of coatings by thermal spraying, which coatings can be deposited without resorting to a brazing step, and can be made of ceramics and deposited on any type of support. These cords intended for brazing are made of inorganic particles larger than 10 micrometers.

[0020] Furthermore, an arc welding bead is known from US 3,701,444. Such a bead is not conventionally used to supply a thermal spray torch in order to produce a coating, these two applications (welding / spraying) being distant from each other. In particular, all of the inorganic particles generally have a median diameter greater than or equal to 100 micrometers.

[0021] FR 1 443 142 finally describes a cord which comprises a core coated with a sheath. The set of inorganic particles has a median size D50 incompatible with obtaining a very homogeneous or finely structured coating.

[0022] There is therefore a continuing need for a feed media suitable for projection by a plasma or flame torch:

[0023] - allowing a substantially continuous supply of the torch, reliably,

[0024] - allowing to overcome the constraints and limitations of Suspension or Liquid Solution type media, in particular by being presented in a solid and stable form, easily handled, preferably windable onto a reel;

[0025] - leading to a very homogeneous or finely structured coating;

[0026] - without excessive abrasion of the torch; and

[0027] - at the cost of limited energy consumption.

[0028] The present invention aims to at least partially satisfy this need.

[0029] Summary of the invention

[0030] According to the invention, this aim is achieved by means of a cord having an equivalent external diameter of between 1 mm and 3.5 mm and consisting of a core, or "soul", in the form of a wire, and a sheath covering the core over its entire length, the core being made up

[0031] - a set of inorganic particles whose median size D50 is less than 10 micrometers, the inorganic particles representing more than 40% and less than 80% of the volume of the core; and

[0032] - a matrix binding said inorganic particles, the matrix comprising a polymer binder and optionally a matrix lubricant, for example glycerin, together representing more than 90% of the volume of the matrix, the remainder to 100% possibly consisting of impurities; the sheath having a thickness of between 50 micrometers and 500 micrometers and comprising a sheath polymer and preferably a sheath lubricant, identical to or different from the optional matrix lubricant, together representing more than 90% of the volume of the sheath, the remainder to 100% preferably consisting of impurities and a possible coloring pigment, the volume percentages being determined without taking into account the possible presence of residues of a solvent.

[0033] Surprisingly, the inventors discovered that a cord according to the invention allows a continuous and reliable supply of the torch, while leading to a high-quality coating, with several advantages compared to the use of suspensions of fine particles:

[0034] - better process stability and elimination of problems associated with the stability of particle suspensions (risks of sedimentation, agglomeration);

[0035] - lower energy consumption, due to the absence of evaporation of the aqueous solvents used in the suspensions;

[0036] - absence of agglomeration of particles at the injection point or in flight, unlike what is observed during thermal projection of a suspension;

[0037] - better control of the flow rate of inorganic material, advantageously proportional to the speed of advance of the bead in the projection device, whereas the injection of suspension leads to significant variations in this flow rate.

[0038] Furthermore, a feed medium in the form of a bead advantageously contains much less solvent than a suspension. The low solvent content, particularly water, of a bead, typically less than 5% by mass, considerably limits energy losses during thermal projection of the medium, aimed at totally or partially melting the inorganic particles.

[0039] Without being bound by this theory, the inventors finally found that the characteristics of the cord lead, during projection, to a small variation in enthalpy. The variation in enthalpy therefore disturbs the thermal projection process much less than during projection of dry powders and the use of cords of the prior art. In particular, the inventors found that the combination of a core comprising a low matrix content and a sheath allows a smaller variation in enthalpy than a composite cord without a sheath and having a higher matrix content, as in JP2016156058A.Generally, the presence of a minimum amount of polymer is necessary, particularly to provide the required flexibility, and the inventors have found that increasing the concentration of inorganic particles in the core of the cord and adding a sheath to maintain this flexibility is preferable to a lower concentration of inorganic particles within a composite cord.

[0040] In a particularly advantageous embodiment, the ratio R of the equivalent external diameter of the cord, in micrometers, to the median size of all the inorganic particles, in micrometers, is between 200 and 20,000, preferably between 200 and 1600. Remarkably, this configuration, associated with a volume content of inorganic particles, relative to the volume of the core of said cord, of greater than 40%, preferably greater than 50%, or even greater than 60% and less than 80%, preferably less than 78%, preferably less than 75% allows better dispersion of the particles during their expulsion into the plasma jet or the flame, after decomposition of the sheath. This improvement in dispersion is particularly advantageous for high-velocity plasma or flame torches, and in particular axial injection torches. This results in a better compromise between the following properties and characteristics:

[0041] - optimal dispersion of inorganic particles in the projection jet when using this cord in a thermal projection process, without agglomeration of the inorganic particles between them, which allows the production of coatings with fine microstructures; - flexibility of the cord allowing its easy handling without risk of breakage;

[0042] - low enthalpy required for the decomposition of organic compounds and their conversion into non-toxic gases.

[0043] A cord according to the invention may also include one or more of the following optional and preferred features:

[0044] - the ash content of the matrix and sheath assembly of said cord is less than 5%, preferably less than 3%, as a mass percentage based on the dry mass of said cord;

[0045] - the median size D50 of the set of inorganic particles is less than 5 micrometers, preferably less than 4 micrometers, preferably less than 3 micrometers, preferably less than 1 micrometer, in particular to constitute a columnar structure;

[0046] - the viscosity of the polymer binder of the core and / or of the sheath polymer and / or of the material constituting the core and / or of the material constituting the sheath is / are between 30 and 300 mPa.s, or between 30 and 300 centipoise at 20°C, said viscosity being measured, with a Hôppler viscometer, on a mixture comprising 2% by mass of a dry powder of the polymer binder of the core and / or of the sheath polymer and / or of the material constituting the core and / or of the material constituting the sheath, respectively, in demineralized water;

[0047] - the sheath and / or the matrix is / are made of a cellulose derivative, that is to say a constituent comprising cellulose molecules, preferably methylhydroxyethylcellulose, a cellulose derivative having a viscosity and a low associated ash content particularly well suited to thermal spraying;

[0048] - the inorganic particles represent more than 45%, preferably more than 50%, and / or preferably less than 70%, preferably less than 75%, as a percentage by volume based on the volume of the core of the cord, excluding any solvent;

[0049] - inorganic particles are:

[0050] - particles of one or more metal oxides, preferably alumina, zirconia, titanium oxide, chromium oxide, yttrium oxide, or a combination of several of these oxides, for example mullite or spinel, and / or - carbide-based Cermet particles, the carbides being able to be, for example, carbides of chromium and / or tungsten and / or titanium and / or tantalum and / or zirconium and / or niobium, said carbides being associated with a metallic phase, and / or

[0051] -inorganic particles comprising SiC and the YAG (Yttrium-Aluminium Gamet) phase allowing the thermal projection of a SiC-based compound;

[0052] - particles made of a ceramic, preferably chosen from nitrides, borides and carbo-nitrides, optionally associated with a metallic phase in the form of Cermets;

[0053] - particles made of a refractory metal or a refractory metal alloy, preferably having a melting point greater than 2500 K;

[0054] - particles of a special metal, preferably chosen from metallic amorphous materials, quasi-crystals or approximants, and more broadly non-drawn metallic alloys;

[0055] - preferably particles made of a brittle material, preferably a brittle metal or a brittle metal alloy;

[0056] - the inorganic particles are chosen from particles made of a ceramic, particles made of an intermetallic alloy, particles made of a metallic amorphous material, and particles made of a quasi-crystal or an approximate phase;

[0057] - the thickness of the sheath is greater than 100 micrometers, preferably greater than 150 micrometers, preferably less than 400 micrometers;

[0058] - for a cord with an external diameter of 2.5 to 3.5 mm, the thickness of the sheath is between 200 and 400 micrometers;

[0059] - for a cord with an external diameter of 1 to 2.5 mm, the thickness of the sheath is between 100 and 250 micrometers;

[0060] - the ash content of said cord is less than 2.5%, preferably less than 2%, preferably less than 1%, preferably less than 0.7%, preferably less than 0.5% as a mass percentage based on the dry mass of said cord;

[0061] - the polymer binder and the optional matrix lubricant, identical or different from that of the sheath, together represent more than 95%, preferably more than 97%, preferably more than 99%, preferably substantially 100%, in volume percentage based on the volume of the matrix, without taking into account any solvent residues;

[0062] - the polymer binder, preferably a cellulose derivative, more preferably a methylhydroxyethylcellulose, represents more than 5%, preferably more than 10% and / or less than 25%, preferably less than 20%, or even less than 15% as a percentage by volume, based on the volume of the core of the cord, without taking into account any solvent residues; - the matrix preferably represents more than 25%, preferably more than 30%, preferably more than 40%, or even more than 45%, and / or preferably less than 70%, preferably less than 60%, preferably less than 55%, preferably less than 50%, as a percentage by volume based on the volume of the core of the cord, without taking into account any solvent residues;

[0063] - in one embodiment, the matrix comprises a matrix lubricant, the content of said matrix lubricant being greater than 5%, greater than 10% and / or less than 25%, or less than 20%, as a percentage by volume based on the volume of the core of the bead, without taking into account any solvent residues;

[0064] - the matrix lubricant is chosen from polyols, glycerides, in particular glycerol and its derivatives, stearates, amino alcohols, preferably from glycerin and triethanolamine, more preferably is glycerin;

[0065] - the matrix solvent is water or denatured alcohol, preferably water;

[0066] - the residual solvent content, preferably water, in the core, is less than 5%, as a percentage by mass based on the dry mass of the core of the cord;

[0067] - the matrix is ​​made up, for more than 99%, preferably substantially 100% of an organic material, in volume percentage;

[0068] - the sheath polymer and the optional sheath lubricant together represent more than 95%, preferably more than 97%, preferably more than 99%, preferably substantially 100%, in volume percentage based on the volume of the sheath, without taking into account any solvent residues;

[0069] - the sheath contains a sheath lubricant, identical to or different from the optional matrix lubricant, the content of which is greater than 10%, preferably greater than 20%, preferably greater than 30%, and / or preferably less than 50%, preferably less than 40%, as a percentage by volume based on the volume of the sheath, without taking into account any solvent residues;

[0070] - the content of the sheath polymer is greater than 45%, preferably greater than 55%, preferably greater than 60%, and / or preferably less than 80%, preferably less than 75%, preferably less than 70%, as a percentage by volume based on the volume of the sheath, without taking into account any solvent residues;

[0071] - the polymer binder and the sheath polymer contain an identical polymer, preferably contain, as polymer(s), only identical polymers, preferably in the same proportions;

[0072] - the impurities of the matrix and / or the sheath consist, for more than 90%, preferably more than 95%, preferably substantially 100% of organic impurities and / or impurities comprising the hydrogen element H, and / or metallic impurities;

[0073] - the impurities of the matrix and / or the sheath represent less than 5%, preferably less than 3%, preferably less than 1%, in volume percentage based on the volume of the matrix and / or the sheath, respectively, without taking into account any solvent residues;

[0074] - the sheath contains a coloring pigment, which may be any conventionally used colorant, which represents less than 1%, preferably less than 0.5%, preferably less than 0.4%, preferably less than 0.1%, or even less than 0.05% of the volume of the sheath;

[0075] - the solvent of the sheath is preferably water or denatured alcohol, preferably water;

[0076] - the residual solvent content, preferably water, in the sheath is less than 10%, preferably less than 5%, as a mass percentage based on the mass of the cord sheath;

[0077] - the sheath is made up, for more than 99%, preferably substantially 100% of an organic material, in volume percentage;

[0078] - the cord is wound on itself, in the form of a roll or a coil, preferably wound on a mandrel with a diameter greater than 50 mm, preferably greater than 100 mm, preferably greater than 150 mm, or even greater than 200 mm, and / or less than

[0079] 1000 mm, preferably less than 500 mm, preferably less than 400 mm, preferably less than 300 mm.

[0080] A bead according to the invention is not intended for welding. Preferably, it does not contain a fluxing agent (flux), such a fluxing agent being conventionally used to clean and deoxidize the welding zone or to form a protective slag.

[0081] Preferably, a cord according to the invention does not comprise a fluxing agent chosen from fluorspar or calcium fluoride, cryolite which is an alumina and sodium fluoride, and borates.

[0082] The invention also relates to a thermal projection device comprising:

[0083] - a torch comprising a plasma or flame generator and an injection device; and

[0084] - a cord according to the invention arranged so as to be injectable, by the injection device, into the plasma or the flame generated by said generator, the torch being capable of at least partially melting the inorganic particles of the cord and of projecting the at least partially melted inorganic particles, preferably at more than 150 m / s. Preferably, the torch is capable of projecting the at least partially melted inorganic particles at more than 150 m / s and / or less than 1000 m / s, the projection speed being conventionally measured at the outlet of the torch. In one embodiment, the particles are projected at 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 projected at more than 150 m / s and less than 300 m / s.

[0085] The injection device is preferably arranged so as to inject the bead along an injection axis extending in a radial plane, i.e. passing through the X axis of the plasma flow or the flame, and forming with a plane P transverse to the X axis an angle 0, in absolute value, greater than 60°, greater than 70°, greater than 80°, preferably greater than 85°, the injection axis I being preferably substantially parallel to the X axis, the injection or "feeding" being referred to as "axial" injection or feeding. The torch is preferably axially fed.

[0086] An angle 9 close to 90° advantageously promotes homogeneous combustion of the cladding and matrix, and therefore a uniform dispersion of inorganic particles released into the plasma flow or high-speed flame. This ensures a centered and optimal trajectory of the particles in the torch nozzle, and reduces the risk of nozzle fouling, and therefore the risk of process malfunctions and defects in the cladding.

[0087] Preferably, the injection is carried out upstream of the flow nozzle of the plasma stream, or "jet", or of the flame in the case of a flame torch. Preferably, for a flame torch, the bead is driven to the combustion chamber. Preferably, for a plasma torch, preferably multi-cathode with axial injection of the material to be projected, the bead is driven to the confluence zone of the elementary plasma streams coming from the cathodes, upstream of the flow nozzle of the plasma jet resulting from the fusion of these elementary plasma streams.

[0088] Remarkably, a cord according to the invention has sufficient flexibility to be wound and unwound while being sufficiently rigid to allow axial injection, preferably using a conventional drive device located at the rear (upstream) of the torch.

[0089] The injection device preferably opens inside the torch.

[0090] As illustrated in Figure 1, preferably, the injection device is arranged to introduce the cord into the plasma or combustion chamber 17, preferably into a portion 2 of the plasma flow or flame which extends less than 10 cm, preferably less than 5 cm, and / or more than 2 cm, preferably more than 3 cm, from the orifice(s) 7 through which the plasma flow(s) or flame exit(s) the generator.

[0091] The torch may in particular be a multi-cathode axial injection plasma torch or a high-speed flame torch of the HVOF or HVAF type or a conventional flame-wire type torch, or of the HVOF-Wire or HVAF-Wire type.

[0092] The invention also relates to a method for coating a surface of a substrate with a coating, in which method a bead according to the invention is injected into a plasma flow or into a flame of a torch so as to project, onto said surface, inorganic particles of the bead at least partly melted in the plasma flow or the flame.

[0093] The invention finally relates to a thermal spraying method using a thermal spraying device according to the invention, a method in which the torch is supplied with a cord according to the invention so as to create a coating on the surface of a substrate.

[0094] The substrate is preferably a substrate made of a metal, a ceramic, a cermet, a polymer, an organic material or a composite material, in particular a ceramic matrix.

[0095] The substrate may have various shapes, for example having flat or revolution geometries, in particular cylindrical, or complex geometries, the only limit being accessibility by the jet of at least partly molten inorganic particles. The axial supply upstream of the spray nozzle or the flow nozzle advantageously improves this accessibility.

[0096] In one embodiment, the coating provides surface functionality to the substrate, preferably improves abrasion resistance, modifies coefficient of friction, or creates a thermal barrier or electrical insulation.

[0097] The coating may be intended in particular for thermal, chemical or mechanical protection of parts, in particular in a reactor, for example for the production of columnar thermal barriers on parts of aeronautical turbines or stationary turbines, environmental barriers on ceramic-ceramic composite parts, or for the production of functional layers in solid electrolyte fuel cell devices, these applications being cited only as examples. The bead and the thermal spraying device according to the present invention are particularly advantageous for the production of columnar structure coatings and nanostructured coatings, thanks to the projection of submicron particles contained in said bead. However, they avoid the disadvantages of the “SPS” or “SPPS” processes.The “columnar structure” is notably described in Benjamin Bernard’s doctoral thesis on Thermal barriers by plasma projection of suspensions, available on the site: httn: / / docnum.univ-lorraine.fr / nublic / DDOC T 2016 0212 BERNARD. ndf.

[0098] Another advantage of the present invention is the possibility of producing, by thermal spraying, hybrid coatings, i.e. coatings comprising different materials, from a bead comprising particles of different physicochemical natures.

[0099] The manufacture of a hybrid coating can be carried out by known thermal spraying techniques.

[0100] A hybrid coating can be obtained from a bead comprising particles of a ceramic oxide material and metallic particles.

[0101] The invention allows in particular combinations of different materials which would be difficult to combine by other methods, because of their different densities or sizes. This is particularly a major problem for the thermal projection of suspensions or dry powders to be co-injected in thermal projection.

[0102] Brief of the fi

[0103] Other characteristics and advantages of the invention will become apparent upon reading the detailed description which follows and upon examining the attached drawing in which:

[0104] - [Fig 1] Figure 1 schematically illustrates a thermal projection device according to the invention;

[0105] - [Fig 2] Figure 2 schematically illustrates the section of a cord according to the invention;

[0106] - [Fig 3] Figure 3 schematically illustrates a device used for the examples to evaluate flexibility.

[0107] In the various figures, identical references are used to designate identical or similar parts.

[0108] Definitions The "equivalent outside diameter" of a cord is the diameter of a disc with the same surface area as its cross-section at mid-length of the cord.

[0109] The 10th (denoted Dio), 50th (denoted D50) and 90th (denoted D90) percentiles of a set of particles are called "percentiles", the particle sizes corresponding to the percentages equal to 10%, 50% and 90% respectively, by number, on the cumulative particle size distribution curve of the particle sizes of the set of particles, said particle sizes being classified in ascending order. According to this definition, 10% by number of the particles of the set of particles thus have a size less than Dio and 90% of the particles, by number, have a size greater than or equal to Dio. The particle size curve can be produced using a laser particle size analyzer. The SYSMEX FPIA 3000 device advantageously makes it possible to obtain such curves.

[0110] The "median size" of a set of particles is called the 50th percentile, D50. The median size therefore divides the particles of the set of particles into first and second populations equal in number, these first and second populations containing only particles having a size greater than or equal to, or less than, respectively, the median size.

[0111] The percentiles relative to the sizes of the inorganic particles in a bead are those measured on the inorganic particle powder used to manufacture this bead. They can be estimated from the bead by debinding the bead by calcination in order to eliminate the organic constituents and recover said inorganic particles. If the inorganic particles are oxidizable and likely to be damaged by the debinding temperature, the debinding is preferably carried out in a neutral atmosphere, for example under Argon. The size distribution of the inorganic particles extracted by debinding can then be measured in volume, for example by laser particle size analysis. The volume distribution of particles can be easily calculated relative to the volume of the bead, the core or the cladding, the dimensions of which can be measured, for example, using a micrometer or a caliper before and after removing the cladding from the bead.

[0112] The measurement of a percentage based on the “dry mass” of the cord can be carried out on a 100 g sample of the cord, after drying at 110°C for one hour.

[0113] When a volume percentage is calculated on the basis of the cord, core or sheath, the volume of the cord, core or sheath is that delimited by the outer surface of the cord, core or sheath. The volume content of lubricant can be evaluated from the quantity of lubricant introduced into the starting charge, during manufacture. The lubricant can be liquid or solid (Graphite, BN, ...).

[0114] The concept of "coloring pigment" is well known to those skilled in the art. A pigment is a powder which, during the manufacture of the cord, results in a coloring. A coloring pigment typically has the form of a powder with a median particle size of less than 1 micrometer. A coloring pigment may in particular be an "oxide pigment", i.e. made up of oxides.

[0115] By "inorganic" particles is meant particles made of a non-organic material, i.e., one that does not include carbon-hydrogen chains as one of its main components. This family of materials includes metals, glasses and ceramics and composites made of metal, glass or ceramic. Preferably, the inorganic particles do not include carbon-hydrogen chains.

[0116] A "ceramic" is a material that is neither metallic nor organic, for example chosen from oxides, nitrides, carbides and borides. Ceramic materials include in particular glasses, cermets and glass-ceramics. In the context of the present invention, diamond, graphite, graphene and carbides of metals or metalloids are considered to be ceramic materials.

[0117] The term "cermet" means a material comprising at least two phases, at least one phase being ceramic and at least one other phase being metallic.

[0118] By "brittle" is meant a material whose plastic deformation range under load before rupture represents less than 5%, preferably less than 1% of the elastic deformation range, preferably is substantially zero. In other words, the width of the stress range leading to plastic deformation without rupture represents less than 5%, preferably less than 1% of the width of the stress range leading to elastic deformation.

[0119] “Impurities” are the constituents of the cord whose presence is not desired, i.e., constituents other than inorganic particles, the polymer binder, the sheath polymer and the optional lubricant(s). Solvent residues are not considered impurities. Impurities may include impurities present in the raw material sources, but also residues of additives used during the manufacture of the cord, for example, plasticizer residues. The “ash content” of the cord corresponds to the residue left by the combustion of the sheath and the core matrix of the cord. It can be determined by calcination according to standard NF T30-012, by measuring the difference in mass between the mass resulting from calcination at a temperature of 450°C, and the mass resulting from calcination at a temperature of 950°C.The temperature of 450°C allows decomposition of all organic constituents and the temperature of 950°C allows vaporization of residues which are likely to disturb the fusion of inorganic particles. Calcination must therefore be sufficient to extract substantially all organic constituents from the cord. It is preferably carried out for a sufficient time for said extraction to be substantially complete. The duration of calcination is therefore adapted to the dimensions of the sample of the cord analyzed.

[0120] The "mineral matter volume ratio" is measured by dividing the volume of mineral matter 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 matter is determined according to the Archimedes method, by weighing the mineral matter extracted from the cord core after debinding.

[0121] A percentage is determined "solvent-free" when the basis for calculating this percentage does not take into account any solvent that may be present. In particular, the solvent is preferably water, and the volume percentages, in particular in inorganic particles, polymer binder, matrix lubricant, sheath polymer or sheath lubricant, are then measured by dividing the volume of the constituent considered by the volume of a dry base, i.e. without taking into account any water. The base may be in particular

[0122] - the core, for inorganic particles,

[0123] - the matrix, for the polymer binder and the matrix lubricant,

[0124] - the sheath, for the sheath polymer and the sheath binder.

[0125] To ignore water, these percentages can be measured after complete drying.

[0126] In this description, the terms "upstream" and "downstream" are used with reference to the direction of flow, along a "flow axis" of the plasma gas flow or flame gases.

[0127] By “based on”, it is classically understood that the corresponding quantity is greater than 50% by mass.

[0128] A "transverse plane" is a plane perpendicular to the X axis. A "radial plane" is a plane containing the X axis.

[0129] The "polymer binder" of the cord core and the "sheath polymer" of the sheath are distinguished for clarity. The polymer binder and sheath polymer may be the same or different.

[0130] For clarity, a distinction is also made between the "matrix" binder and the "sheath" binder. These binders may be the same or different.

[0131] “Behave” or “include” or “present” shall be interpreted in a non-limiting manner.

[0132] Figure 1 schematically illustrates a thermal projection device 10 according to the invention, comprising a torch 12 and a cord 15 according to the invention supplying said torch with inorganic particles.

[0133] The torch may in particular be a multi-cathode type torch allowing axial injection, a flame torch, preferably high velocity or high speed of the air-oxygen (or HVOF) or air-gas (or HVAF) type, or a conventional flame-wire type torch, or of the HVOF-Wire or HVAF-Wire type.

[0134] The torch 12 conventionally comprises one or more generators 13 of plasma or combustion gas in the case of a flame torch, and an injection device 14 for injecting, through an injection orifice 4 and along an injection axis I, the bead 15 into the flow 16 of plasma or the flame produced in the chamber 17, upstream of the spray nozzle or flow nozzle 21 of the torch.

[0135] The axis of the plasma flow or flame is called the "X axis".

[0136] In a radial plane containing the X axis and passing through the center of the injection orifice, the projection of the injection axis I forms, with the X axis, an angle 9. The angle 9 is preferably greater than 60°, greater than 70°, greater than 80°, preferably greater than 85°. Preferably, the X axis is contained in said radial plane, preferably perfectly coincident with the X axis.

[0137] Cord Figure 2 schematically illustrates the section of a cord 15 according to the invention. In particular, the core 18 and the sheath 20, surrounding the core, can be seen.

[0138] The cord preferably has a constant cross-section along the entire length of the cord. It 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, an equivalent outer diameter of 3 mm being preferred.

[0139] The cord is preferably wound on a mandrel, preferably packaged in the form of an easily handled and unwound reel for supplying the projection device.

[0140] Preferably, the cord does not comprise metal salts or hydroxides, for example does not comprise aluminum hydroxide (boehmite), which forms a gel during the preparation of the paste, nor ammonium acetate. The inventors have indeed found that these constituents mentioned in the prior art can have a negative impact. In particular, the formation of an inorganic gel, for example due to the use of aluminum hydroxides, leads to an agglomeration of inorganic particles during projection, which does not allow all the individual fine particles to be released, and therefore impairs the production of finely structured layers. These constituents also lead to less flexibility for cords whose inorganic particles have a median size of less than 10 micrometers.

[0141] Heart

[0142] The core 18, in the form of a wire, preferably of constant section over the entire length of the cord, preferably has a circular section. Its equivalent external diameter is preferably greater than 2 mm, and / or preferably less than 3.2 mm.

[0143] The core contains a set of inorganic particles 22 intended to be melted in the form of droplets in the plasma flow or flame, then projected onto a substrate, in order to form a coating on the substrate.

[0144] The inorganic particles preferably represent 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 of less than 40% increases the energy consumption required, during projection, to decompose the organic components of the binder matrix and the sheath. A volume content of inorganic particles of more than 80% is unfavorable to the flexibility of the cord.

[0145] The median D50 size of all inorganic particles is less than 10 micrometers. This very low median size is intended to allow the production of a very finely structured coating.

[0146] The median size D50 of all inorganic particles is preferably less than 5 micrometers and preferably greater than 0.1 micrometers.

[0147] The median size of all inorganic particles is preferably between 1 and 5 micrometers to obtain a dense coating intended for mechanical and / or chemical protection.

[0148] The median size of all the inorganic particles is preferably between 0.2 and 0.5 micrometers to obtain a coating formed of columnar or “feathery” layers with a more thermally insulating microstructure, in particular to obtain a thermal barrier.

[0149] A median size greater than 0.1 micrometer advantageously reduces safety issues during cord manufacturing.

[0150] Preferably, the ratio R of the equivalent external diameter d of the cord, in micrometers, to the median size D50 of the inorganic particles, in micrometers, is between 200 and 20,000, preferably greater than 500, preferably greater than 1,000 and / or less than 10,000, preferably less than 5,000, preferably less than 2,000. A ratio R of between 200 and 1,600 is particularly advantageous, in particular for cords intended for plasma or high-velocity flame torches with axial material injection.

[0151] Preferably, (Dço-Dioj / Dso is greater than 1 and / or less than 1.8.

[0152] In one embodiment, for a median inorganic particle size of 0.2 to 0.5 micrometers, the 10th percentile (D10) of the set of inorganic particles is preferably greater than 50 nm, preferably greater than 100 nm, preferably greater than 150 nm, and the 90th percentile (D90) of the set of inorganic particles is preferably less than 1000 nm, preferably less than 900 nm, preferably less than 850 nm.

[0153] In one embodiment, for a median inorganic particle size of between 1 and 5 micrometers, the 10th percentile (D10) of the set of inorganic particles is preferably greater than 0.1 micrometers, preferably greater than 0.5 micrometers, and the 90th percentile (Dço) of the set of inorganic particles is preferably less than 10 micrometers, preferably less than 8 micrometers.

[0154] The nature of the inorganic particles is determined according to the nature of the desired coating.

[0155] Preferably, the inorganic particles are made of a material consisting, for more than 80%, preferably more than 90%, preferably more than 95%, or even substantially 100% by mass, of one or more of the following oxides, alone or in solid solution: AI2O3, SiO2, ZrO2, Cr2O3, and TiO2.

[0156] The inorganic particles may be made of a non-oxide material, in particular chosen from:

[0157] - metal oxides, preferably alumina, zirconia, titanium oxide, chromium oxide, yttrium oxide, or a combination of several of these oxides, for example mullite or spinel, and / or

[0158] - carbide-based cermets, the carbides being able to be, for example, chromium, tungsten, titanium, tantalum, zirconium carbides, said carbides being associated with a metallic phase, and / or

[0159] - SiC-YAG composites, “YAG” meaning “Yttrium-Aluminium Gamet”, allowing the thermal projection of a SiC-based compound, and / or

[0160] - ceramics such as nitrides, borides and carbo-nitrides, possibly associated with a metallic phase in the form of cermets, and / or

[0161] - refractory metals or refractory metal alloys preferably having a melting temperature above 2500 K, and / or

[0162] - special metal alloys such as metallic amorphous, quasi-crystals or approximants, and more broadly non-drawn metal alloys.

[0163] Special metal alloys are classically intermetallic alloys, and in particular alloys with brittle mechanical fracture such as metallic amorphous or metallic glasses, quasi-crystals or approximants (i.e. the approximate phases of quasi-crystals), as described for example in https: / / www.universalis.fr / encyclopedie / quasi-cristaux / 4-phases-approximantes-et-defauts / .

[0164] Preferably, the inorganic particles are selected from ceramic particles, intermetallic alloy particles, metallic amorphous particles and quasi-crystal or approximate phase particles. Inorganic carbide particles are particularly well suited to HVOF technology.

[0165] The inorganic particles are embedded, preferably dispersed substantially uniformly, in a matrix 24 binding said inorganic particles.

[0166] The matrix is ​​substantially made of an organic material, so as to be reduced to ash during projection.

[0167] The plasticizer volume content may be greater than 1%, preferably greater than 4% and / or less than 10%, preferably less than 8%, as a percentage by volume based on the volume of the core or matrix, excluding solvent. The plasticizer may be any known plasticizer, for example a phthalate, in particular BBP (ButylBenzylPhthalate), or polyvinyl alcohol (or "PVA" for short).

[0168] In a preferred embodiment, the 100% balance of the polymer binder in the matrix comprises, preferably consists of, excluding impurities and solvent residues, a lubricant, preferably glycerin. The lubricant may in particular constitute 10% to 20% of the volume of the core.

[0169] Sheath

[0170] The sheath 20 contributes to the flexibility of the cord by enhancing its ability to undergo bends without degradation. In particular, it allows the cord to be wound without visible degradation, in particular without cracking or separation of its components. The sheath also contributes to the toughness of the cord, necessary due to the small equivalent outside diameter of the cord, and provides a surface condition that promotes sliding, which facilitates advancement of the cord through the injection orifice of the torch and limits the wear caused on the parts of the torch with which the cord is in contact, and in particular the injection orifice.

[0171] The sheath surrounds the core along the entire length of the cord. It preferably has a constant thickness in a plane perpendicular to the direction of the cord length, preferably in any plane perpendicular to the direction of the cord length.

[0172] Preferably, the ratio of the thickness of the sheath, in micrometers, to the equivalent outside diameter of the bead, in 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 between 0.05 and 0.5 is particularly suitable when the set of inorganic particles has a median size of less than 5 micrometers. Preferably, the main constituent of the sheath is a polymer of the same family, or even of the same chemical composition, or even of the same molecular formula as the polymer binder of the matrix of the core of the bead. The monomer crosslinked to form the sheath polymer is preferably the same as that of the polymer binder.

[0173] The sheath polymer preferably represents between 55% and 75%, preferably approximately 65% ​​of the sheath volume, excluding solvent.

[0174] Preferably, the sheath comprises a lubricant, called a "sheath lubricant", preferably glycerin, in a content preferably greater than 25%, in percentage by volume on the basis of the sheath, excluding solvent. The sheath lubricant facilitates co-filing during its manufacture, limits the wear of the parts of the torch on which the bead slides, and, by facilitating sliding, limits the risk of buckling of the bead during its injection into the plasma flow or the flame, which contributes to the quality of the manufactured coating.

[0175] The 100% balance of sheath polymer and sheath lubricant preferably consists of organic impurities, particularly resulting from organic additives such as a plasticizer used to shape the cord sheath during its manufacture.

[0176] Generally, the compositions of the matrix and the sheath are determined so as to obtain a low ash content for the cord. The ash content, resulting from the presence of the polymer binder, the matrix lubricant, the sheath polymer, the sheath lubricant and the plasticizer used, is preferably less than 2.5%, preferably less than 2%, or even less than 1%, as a mass percentage based on the mass of the cord. A person skilled in the art knows how to adapt a composition in order to reduce the ash content, possibly by carrying out a few simple tests.

[0177] An ash content above 3% implies a high organic component content and significant pollution of the torch. This results in significant process disruptions and a source of defects in the coating obtained by thermal spraying.

[0178] In particular, preferably, the sheath polymer and / or the polymer binder of the matrix, preferably the organic filler consisting of the sheath polymer and the polymer binder of the matrix is / are made up, for more than 80%, more than 90%, more than 95%, preferably substantially 100% by mass, of a cellulose derivative, in percentage by volume based on the sheath or the polymer binder, respectively, excluding solvent. A cellulose derivative advantageously allows a very low ash content, typically less than 1%, in percentage by mass based on the mass of the bead.Preferably, the cellulose derivative is chosen from cellulose ethers, preferably from methylcellulose (MC), ethylcellulose (EC), methylethylcellulose (MEC), hydroxymethylcellulose (HMC), hydroxyethylcellulose (HEC), methylhydroxyethylcellulose (MHEC), hydroxymethylethylcellulose (HMEC), hydroxypropylcellulose (HPC), hydroxypropylmethylcellulose (HPMC), hydroxypropylethylcellulose (HEPC), carboxymethylcellulose (CMC) and mixtures thereof. Preferably, the cellulose derivative is chosen from hydroxyethylcelluloses, in particular methylhydroxyethylcellulose, because this cellulose subfamily has rheological properties well suited to the manufacture of a small diameter cord and of which all the inorganic particles have a median size of less than 10 micrometers.

[0179] The alkali content, particularly Na, in the cellulose derivative is preferably less than 1%, as a mass percentage based on the mass of said cellulose derivative. This characteristic advantageously makes it possible to limit the ash content and long-term corrosion of the torches. Preferably, the cellulose derivative has little or no cellulose fibers.

[0180] A cord according to the invention may be manufactured by any conventional method, in particular by co-spinning a first paste intended to form the core of the cord and a second paste intended to form the sheath. A method of this type is in particular described in FR 1 443 142.

[0181] A method as described in GB 1 151 091A is particularly suitable.

[0182] The flexibility of the cord can be easily adjusted by adjusting the amount of core polymer binder as well as its viscosity and / or the viscosity of the sheath polymer.

[0183] A cord according to the invention is particularly well suited for plasma torches, and in particular for axial injection plasma torches, in particular for multi-cathode plasma torches, also referred to as “multi-chamber”.

[0184] The flexibility of the cord according to the invention allows it to be wound around a mandrel in order to be unwound during the coating process. The projection can thus be substantially continuous. The sheath also ensures smooth contact with the injection orifice, which limits its wear.

[0185] The rigidity of the bead is, however, sufficient to allow a substantially axial injection, preferably using a drive device located upstream of the torch. This axial injection promotes uniform heating of the inorganic particles, homogenizes the distribution of the jet of inorganic particles in the flow nozzle, which limits fouling, and improves the reproducibility and quality of the coating.

[0186] The limited amount of liquid phase, and in particular solvent, limits the amount of energy consumed and maximizes the energy available to pyrolyze the sheath and matrix and melt the inorganic particles.

[0187] The size of the inorganic particles is chosen according to the projection device and the desired microstructure for the coating.

[0188] From the entry of the cord into chamber 17 of the torch, the following sequence of events takes place:

[0189] - pyrolysis of the sheath and the polymer binder;

[0190] - release of individual inorganic particles without agglomeration effect between them;

[0191] - rapid entrainment in the jet (flame or plasma) and fusion, total or partial, in flight, of inorganic particles;

[0192] - impact of at least partially melted inorganic particles on the substrate, then solidification so as to create the coating.

[0193] In particular, the cord can be used to make:

[0194] - a mechanical or chemical protective coating, in particular against corrosion by chemical species, vapors, etching plasma;

[0195] - an environmental barrier or a thermal barrier;

[0196] - a tribologically functional coating, an anti-wear coating, an electrically insulating coating, or an electrically conductive coating.

[0197] Preferably, the coating has a thickness of between 10 and 500 micrometers.

[0198] The following non-limiting examples are given for the purpose of illustrating the invention.

[0199] Example 1 was carried out according to the teaching of JP2016156058, by spinning the first paste.

[0200] For the other examples, a first paste was made, in accordance with the teaching of GB 1 515 091, from

[0201] - a powder of alumina particles obtained by fusion-solidification, with an average size of 7.5 micrometers and a purity greater than 99.5% and

[0202] - methylhydroxyethylcellulose (polymer binder) with a viscosity of 50 mPa.s.

[0203] The viscosity of methylhydroxyethylcellulose was measured by a Hopler viscometer at 20°C on the basis of methylhydroxyethylcellulose powder mixed with demineralized water at a mass loading of 2%.

[0204] The mass proportions of the constituents of this first paste are shown in table 1 below.

[0205] A second paste is then prepared to form the sheath. To this end, the same methylhydroxyethylcellulose used to prepare the first paste is mixed with a quantity of water, glycerin and coloring pigment according to the mass proportions indicated in Table 1 below.

[0206] Co-spinning the first and second pastes in a press makes it possible to obtain a flexible cord precursor of 3 mm, of substantially circular section, of external diameter of 3 mm and comprising a sheath having a thickness of substantially 350 micrometers.

[0207] Drying the cord precursors results in cords with a residual moisture content of less than 5%. Residual moisture measurements indicate a value of around 3%. The cords are wound onto a 70 mm diameter mandrel.

[0208] The outer diameter of the cord and the thickness of the sheath were measured using a Tesa Micromaster® 0-30 mm digital micrometer.

[0209] For each example:

[0210] - a sample of at least 0.5 meters of the cord to be tested is wound around a cylindrical bar with a diameter of 25 mm, so as to form contiguous turns, as shown in figure 3. The cord must not break during this operation;

[0211] - a sample of at least 0.5 meters of the cord to be tested is wound around a cylindrical bar with a diameter of 70 mm, so as to form contiguous turns, as shown in Figure 3. The sheath of the cord must not have any cracks visible externally, to the naked eye, or internal cracks visible externally, to the naked eye, by a change in color resulting from the semi-transparency of the sheath;

[0212] - a sample of at least 0.5 meters of cord is subjected to a training test consisting of rolling, over the sample and at a speed of 1 m / s, a roller of 26 mm diameter and 2 kg. The cord may deform slightly and present a variation in diameter of less than 15%, but it must not present any cracks visible externally, to the naked eye.

[0213] If the cord passes these three tests, it has acceptable flexibility. If it fails at least one of these three tests, it has unacceptable flexibility.

[0214] Ash content

[0215] The ash content is determined by (mo - mi) / mo, mo and nu being respectively the masses after calcination of a sample of the cord 3 cm long, in a furnace at 450°C and 950°C in air, respectively, for a duration of 1 h.

[0216] R Report

[0217] The ratio R is the ratio of the equivalent outer diameter of the cord, in micrometers, to the median size (D50) of the inorganic particles, in micrometers.

[0218] Enthalpy variation

[0219] The enthalpy variation linked to the decomposition of the organic constituents of the cord at 2300 K was calculated with the Factsage® software for each example on the basis of its formulation, considering:

[0220] - an injection of the bead upstream of the flame or plasma flow, between the orifice through which the plasma flow or flame exits the generator and the spray nozzle (or flow nozzle);

[0221] - in the case of a high velocity plasma torch, a neutral atmosphere, i.e. without oxygen or hydrogen, and decomposition products of the type C cord x H y , ;

[0222] - in the case of a high velocity flame torch (HVOF type), an oxidizing atmosphere and direct decomposition in the form of CO2 and H2O;

[0223] - a residual water measurement in the bead of 3% after drying.

[0224] The contribution of organic compounds due to the presence of a possible sheath was taken into account for the determination of the quantity and nature of the organic products of the cord.

[0225] In Table 1 below, the enthalpy change is provided in kJ / mol of alumina.

[0226] The enthalpy variation in a neutral atmosphere is considered particularly advantageous when it is as low as possible, in particular less than or equal, in absolute value, to 1000 kJ / mol of alumina. The enthalpy variation in an oxidizing atmosphere is considered particularly advantageous when it is less than + 1000 kJ / mol of alumina.

[0227] The amount of inorganic particles is provided as a volume percentage based on the core volume of the cord, without taking into account the solvent. Example 1 (comparative) carried out according to the teaching of JP2016156058 does not include a sheath. Example 3 (comparative) is carried out according to the teaching of GB 1 151 091, but with finer inorganic particles. Examples 4* and 5* are according to the invention.

[0228] Table 1] As is now clearly apparent, the invention provides a bead which, thanks to its flexibility, can advantageously be introduced, continuously, substantially along the axis of the torch, into the heart of the flame or plasma. The inorganic particles are well dispersed at the time of their projection. The thermal decomposition properties of the bead, in particular its very low enthalpy variation at 2300 K, make it possible to obtain a coating which advantageously has a controlled and defect-free roughness, with limited energy consumption.

[0229] Of course, the invention is not limited to the examples and embodiments described, provided as illustrative and non-limiting examples.

Claims

Claims: A cord intended for supplying a thermal spray torch for applying a coating, said cord having an equivalent outside diameter ( ) between 1 mm and 3.5 mm and consisting of a core (18) in the form of a wire, and a sheath (20) covering the core along its entire length, the core being made - of an array of inorganic particles (22) whose median size (D50) is less than 10 micrometers, the inorganic particles representing more than 40% and less than 80% of the core volume, said inorganic particles being particles of one or more metal oxides and / or carbide-based cermet particles, and / or SiC-YAG inorganic particles and / or particles comprising or being made of a ceramic material and / or particles of one or more metals or metal alloys having a melting point above 2500 K and / or particles of a special metal alloy; and - of a matrix (24) binding said inorganic particles, the matrix comprising: - a polymer binder consisting, for more than 80% by mass, of a cellulosic derivative, and - optionally a matrix lubricant, the polymer binder and the matrix lubricant together representing more than 90% of the matrix volume, the sheath (20) having a thickness between 50 micrometers and 500 micrometers and comprising: - a polymer, known as a "sheath polymer", consisting of more than 80% by mass of a cellulosic derivative, and - preferably a lubricant, called a "sheath lubricant", the sheath polymer and the sheath lubricant together representing more than 90% of the sheath volume, the volume percentages being determined without taking into account the possible presence of solvent residues, the median size of a set of particles being the 50th percentile of said set of particles corresponding to the percentage of 50% by number, on the cumulative particle size distribution curve of said set of particles, measured using a laser particle size analyzer, said particle sizes being ranked in ascending order. Cord according to the preceding claim, wherein the ash content of said cord is less than 5%, the ash content being determined by (mO - ml) / mO, mO and ml being respectively the masses after calcination of a 3 cm long sample of said cord, in an oven at 450°C and 950°C under air, respectively, for a period of 1 hour. Cord according to the preceding claim, wherein the ash content of said matrix and of the sheath of said cord is less than 1%. Cord according to any one of the preceding claims, wherein the ratio (R) of the equivalent outside diameter ( ) of the cord, in micrometers, to the median size (D50) of the inorganic particle set, in micrometers, is between 200 and 20,000.Cord according to the immediately preceding claim, wherein said ratio (R) is between 200 and 2,000. Cord according to any one of the preceding claims, wherein the median size D50 of the inorganic particle assembly is less than 5 micrometers. Cord according to any one of the preceding claims, wherein the viscosity of the core polymer binder and / or the sheath polymer is between 30 and 300 mPa·s at 20°C. Cord according to any one of the preceding claims, wherein the sheath contains a sheath lubricant, the content of said sheath lubricant being greater than 10% and less than 50%, by volume percentage based on the sheath volume, without regard to the possible presence of a solvent. Cord according to any one of the preceding claims, wherein the inorganic particles are selected from. - particles of alumina, zirconia, titanium oxide, chromium oxide, yttrium oxide, or a combination of several of these oxides, and / or - cermet particles comprising more than 50% by mass of a carbide selected from chromium and / or tungsten and / or titanium and / or tantalum and / or zirconium, and / or niobium, and / or - particles in a ceramic material in the form of a nitride, a boride, or a carbonitride, said ceramic material being optionally associated with a metallic phase in the form of a cermet, and / or - particles in a fragile material, and / or - particles of an amorphous metallic alloy, or of a quasicrystal or near-crystal, or of a non-drawingable metallic alloy. Cord according to any one of the preceding claims, wherein the sheath thickness is greater than 200 micrometers and less than 400 micrometers. Cord according to any one of the preceding claims, wherein the polymer binder and the sheath polymer contain an identical polymer. Assembly comprising a mandrel of a diameter less than 500 mm and a cord according to any one of the preceding claims wound on said mandrel. Thermal spraying device comprising - a torch (12) comprising a plasma flow or flame generator (13) and an injection device (14); and - a cord (15) according to any one of claims 1 to 11 arranged so as to be injectable, by the injection device, into said plasma stream or said flame generated by said generator, the torch being capable of at least partially melting the inorganic particles and of projecting the at least partially melted inorganic particles at more than 150 m / s. Thermal projection device according to the immediately preceding claim, in which the injection device is arranged so as to inject the cord along an injection axis (I) extending in a plane passing through the axis (X) of the plasma stream or the flame and forming with a plane perpendicular to said axis (X) an angle 9, in absolute value, greater than 60°, preferably greater than 80°.Thermal projection device according to any one of the two immediately preceding claims, wherein the injection device is arranged to inject the bead upstream of a torch spray nozzle or a torch flow nozzle.

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