EP0667810A1

EP0667810A1 - Method for the production of composite materials or coatings and system for implementing it

Info

Publication number: EP0667810A1
Application number: EP94900853A
Authority: EP
Inventors: Piotr Vasilievich Nikitin; Youri Pavlovich Frolov; Youri Yeniaminovich Dikun
Original assignee: Societe Europeenne de Propulsion SEP SA
Current assignee: Societe Europeenne de Propulsion SEP SA
Priority date: 1993-09-15
Filing date: 1993-09-15
Publication date: 1995-08-23
Also published as: WO1995007768A1

Abstract

Method of forming a coating by cold gasodynamic deposition of particules on a substrate consisting in placing in suspension the particles by means of a gas flow, injecting the particle-gas mixture so formed into a main gas flow (carrier gas) having a temperature considerably lower than the melting point of the material(s) constituting the particles, accelerating the resulting two-phase gas stream to supersonic speed, and projecting the supersonic jet on the substrate. The gas temperature is between 300 and 600 K and the ejection speed of the two-phase stream is between Mach 1 and Mach 2. The invention also concerns a system for implementing said method.

Description

Process for the production of composite materials or coatings and installation for its implementation.

The invention relates to the methods used for the formation of surface layers (coatings), or even of solid material or of composite material, which make it possible both to change the physico-chemical and technological properties of the base material (substrate) and of obtain a new material having new physico-chemical properties and new surface properties (multifunction coatings), for example in order to protect the surface from various factors such as heat flux, corrosion, chemical attack, etc. It also relates to an installation for the implementation of this process.

Methods of coating formation by thermal deposition are well known based on heating and acceleration of particles (powders) by a gas flow at high temperature. Among the drawbacks of these types of processes, mention may be made of a relatively weak adhesion of the coating to the substrate, requiring post-deposition thermal treatments, and the presence of chemical reactions between the projected particles and the gas flow (absorption of oxygen , formation of oxides, nitride, etc.). Another known method for producing coatings consists in accelerating the particles of the coating material in a gas flow and impact on the substrate material (A.S. N92461 cl. C.23. C4 / 18, 1982). The disadvantages of this method are on the one hand, a weak cohesion between the particles of the coating and a weak adhesion of the coating to the substrate material, and on the other hand, insufficient mechanical characteristics of the coating which make it impossible for example to machine subsequent mechanics (weak cohesion, etc.).

The object of the invention is to increase the characteristics and properties of the coating by changing the physico-chemical properties of the surface of the deposited material.

This objective is achieved by a coating formation process by cold gasodynamic deposition of particles on a substrate, characterized in that it comprises the following stages:

.suspension of the particles by a gas flow, .injection of the particle-gas mixture thus created into a main gas flow (carrier gas) brought to a temperature much lower than the melting temperature of the material or materials constituting these particles,

.acceleration to a supersonic speed of the resulting biphasic gas flow, and

.projection of the supersonic jet on the substrate.

This process for forming coatings and composite materials makes it possible to eliminate all the drawbacks of the thermal flow processes, to exclude the chemical interaction between the particles and the carrier gas, which makes it possible to use compressed air as the carrier gas. thus reducing the cost of the operation. However, inert gases, to ensure higher cleanliness of the coating, as well as a mixture of gases can also be used.

Likewise, this moderate temperature process (or cold spraying, that is to say for which the carrier gas is brought to a temperature much lower than the melting temperature of the materials constituting the particles to be sprayed) makes it possible to produce coatings with from mixtures of powders of different materials, in all kinds of proportions, whether metallic, metalloceramic, organometallic, etc. It is thus possible to obtain composite materials and coatings with a very wide range of physicochemical and / or technological properties such as for example: mechanical resistance, resistance to friction or to erosion, thermal or corrosion protection, electrical conductivity, etc.).

Preferably, the temperature of the carrier gas is between 300 and 600 K and the speed of ejection of the two-phase flow is between Mach 1 and Mach 2.

The substrate is animated with a relative movement with respect to the supersonic jet, which makes it possible to treat large surfaces but also, by adjusting the distance between the jet and the substrate, to modify one of the projection parameters, the thickness of the layer and the deposition rate in particular depend on the projection parameters, the thickness for example possibly varying from a few microns to several tens of millimeters.

The invention also relates to an installation for implementing the above method comprising a mixing chamber in which a particle-gas mixture coming from a particle supply device is injected into a main gas flow coming from an apparatus heating system in which this flow generated by a gas supply circuit from a gas storage tank is brought to a temperature much lower than the melting temperature of the material or materials constituting it, the particle supply device ensuring prior mixing of the particles by the gas flow delivered by the gas supply circuit , and the mixing chamber delivering via a supersonic nozzle a two-phase gas flow to be projected onto the substrate.

Advantageously, it further comprises a valve disposed at the outlet of the supersonic nozzle to prevent any deposition of particles during a determined transitional period of start-up of the installation. Other characteristics and advantages of the present invention will emerge more clearly from the following description, given by way of non-limiting illustration, with reference to the appended drawings in which:

- Figure 1 represents a functional diagram of the installation allowing the implementation of the method according to the invention, - Figure 2 is an example of embodiment of the mixing chamber, and

- Figure 3 is an embodiment of the particle supply device.

This installation, illustrated in FIG. 1, comprises a mixing chamber 1 provided with an interchangeable nozzle 10 and which performs a mixing of particles coming from a device 2 for supplying particles 2a under a gas flow delivered at the outlet d a gas heating appliance 3. A gas supply circuit 4 delivers the carrier gas necessary for the reaction both to the supply device 2 and to the heating appliance 3, from a reservoir of storage 5. The material to be coated 6 (and the servomechanism for moving the part 7) is placed at the outlet of the nozzle 10 of the mixing chamber 1.

The installation can be a fixed station comprising either a robot for moving the parts to be coated in front of the nozzle, or a robot for handling the nozzle in front of a fixed part, or both. The installation can also be mobile, the displacement of the nozzle in front of the part being done manually. FIG. 2 shows more precisely an exemplary embodiment of the mixing chamber 1. This chamber comprises a chamber body 12 to which an inlet pipe for the carrier gas 14 coming from the heating appliance 3 ends, and from which emerges a starting pipe 10 for the two-phase flow formed in the chamber. This outlet conduit is in the form of a nozzle with a converging part 10a, a neck 10b and a diverging part 10c. The inlet pipe is pierced with an auxiliary pipe 16 which provides injection into the body of chamber of the pseudoliquefied particle mixture coming from the particle supply device 2. Advantageously, the connection between this duct 14 and the chamber body 12 is produced by a divergent wall 17. Temperature measuring devices 18, such as a thermocouple for example, and of pressure 20 such as a pressure gauge are also present at the level of the mixing chamber 1. FIG. 3 represents an exemplary embodiment of the device for supplying particles. This device 2 is very simply constituted by a chamber 22 comprising an inlet orifice 24 through which the gas supplied by the supply circuit 4 enters and an outlet orifice 26 which delivers the mixture of pseudoliquefied particles generated inside the chamber by mixing the gas with the particles initially suspended in the chamber. In an alternative embodiment, the particles can be introduced continuously into the chamber 22 in parallel with the gas.

The operation of the installation according to the invention is as follows. The gas supply circuit 4 is divided into two parts. In the first part 40, the carrier gas coming from the tank or storage system 5 arrives at a regulator 42 which makes it possible, via a control station 45, to establish the desired pressure. This gas is then brought to the necessary temperature by the heating system 3 (heating resistor, for example). The hot gas is then led into the mixing chamber 1 where it receives the particles to be sprayed from the particle supply device 2. The two-phase mixture is finally accelerated through the nozzle 10 and sprayed onto the part to be coated 6 (substrate ).

In the second part 50, the gas also passes through a pressure regulator 52 allowing the control station 45 to regulate the pressure and the operating flow. Then, the gas is brought into the particle supply device 2, the volume of which is previously filled or continuously supplied (in 2a) with particles (powder or mixture of powders). This pseudo-liquid mixture (particles-gas) is then brought to the mixing chamber 1 where it mixes with the main flow of the carrier gas. The necessary concentration of particles in the two-phase flow is obtained by the aforementioned regulation of the gas flow rate in the second part of the gas supply circuit.

At the start of the installation, during the transitional period, a valve 8 placed in front of the nozzle prevents the projection of particles at an unsuitable speed on the substrate. As soon as the necessary parameters are obtained (stationary mode), the valve is withdrawn and the deposition on the substrate begins. The dimensions of the two-phase flow being limited (in diameter and in length), it is necessary to move either the substrate in front of the supersonic jet, or the nozzle in front of the part, or both together, so that the surface to be coated 6 is located at a given distance and perpendicular to the axis of the jet. The coating process can take place in the open air, or in a ventilated enclosure. In this second case, the collected gas containing non-deposited particles is filtered in order to remove these particles and returned to the atmosphere or stored for recycling.

Depending on the particle-substrate pair, the coating method is adapted by varying the parameters of the installation: pressure in the second supply circuit, temperature of the carrier gas in the main circuit, pressure in the mixing chamber, distance between the outlet of the nozzle and the surface of the substrate.

It will now be explained the physico-chemical principles at the origin of the process implemented in the aforementioned installation.

The process (called cold gasodynamics) consists of the formation of coatings, materials, or composite materials by projection, using a very high kinetic energy of the particles in a supersonic gas flow whose temperature is very much lower than their melting temperature. (temperature not exceeding 600 K). This means that the physico-chemical transformations as well as the phase transformations of the material of the particles inside the gas flow are excluded. The collision of these particles with the substrate, which takes place at high speed, causes reciprocal plastic deformations, activation and physical contact due to very high local pressure in the contact spot.

Following the impact charges acting on the materials of the particles and the substrate, and following the transformation of the kinetic energy of the particles into heat which creates a maximum temperature located in the collision spot, the particles undergo physico-chemical transformations and phase transformations, both in the interface zone between the coating and the substrate and within the coating. Materials also undergo transformations of crystal lattices and new materials can be formed. Such transformations are notably recorded for the Cu-Zn, Ni-Al, Cu-Al, etc. systems, both for the case of deposition with pure elements (Zn, Ni, Cu, etc.) on a Cu or in Al, than for the case of deposition with mixtures of powders Zn and Cu, Ni and Al, Cu and Al, on an Al substrate. In the first case, the intermetallic compounds of the Cu-Zn (brass), Ni-Al, Cu-Al system are formed in a transient zone at the interface between the substrate and the coating. In the second case, the compounds are formed within the coating.

In addition, the use of powder mixture makes it possible to reduce the spraying speed corresponding to the formation of coatings having good adhesion and cohesion properties, at other equal parameters. This is possible thanks to the additional energy provided during the deposition by gas flow, by the release of heat during the formation of solid solutions of the intermetallic and chemical compounds following the exothermic reactions which take place between the components of the mixture of powders at the time of collisions between the particles and the substrate.

The temperature required to start these exothermic reactions is reached locally in the contact spot between the sprayed powder and the surface of the part (MX Chormorov, JA Kharlemov "Physico-chemical principles of depositing coatings by explosion gases "M. NAOUKA, 1978, p.78).

By way of example, the interaction of nickel and aluminum particles results in the formation of intermetallic compounds and gives off an energy of 62.7 kJ / g. Atom in the form of heat, for particles of boron carbide and of titanium carbide, an energy of 3260.4 kJ / kg, for particles of silicon carbide and titanium carbide, an energy of 1701.26 kJ / kg of initial material (NV Audeev "Metallization" M. MACHINOSTRENIE, 1978, p. 64-65).

The sprayed powders can be either powders or a mixture of powders of pure elements, or pre-alloyed powders, or powders of pure elements coated with a second element.

The use of these powder mixtures makes it possible to deposit materials such as carbides, borides, oxides, silicides and other compounds which are difficult to fuse, which cannot be obtained with, for example, the deposition process in a gas flow cited in the introduction, which uses only pre-alloyed powders. The following reactions can in particular be caused during the formation of the deposit on the substrate:

B4C + 3Ti> 2TiB2 + TiC

3SiC + 8 Ti> Ti ₅ Si3 + 3TiC

Whereas with the cited process of the prior art, it is necessary to reach much higher speeds and temperatures since there is no activation thermal process of formation of new compounds by exothermic chemical reactions. And, moreover, an intermetallic coating thus obtained (from pre-alloyed powders) is less efficient than that produced with the process of the invention for the following reasons: - the cohesion and the adhesion of the coatings obtained are higher with the proposed method, because these coatings are formed as a result of one or more chemical reactions which are part of the deposition process. The synthesis of an intermetallic compound by the proposed process ends with an ultra-rapid cooling of the molten material (the fusion is due to the chemical reaction), which results in a very high hardness within the coating material. (R. Prummer "Treatment of powdered materials by explosion" M. MIR, 1990, p. 81)

- the proposed process is more economical since it does not require:. a preliminary synthesis of intermetallic compounds which is done by vacuum fusion

. the development of the powder from the intermetallic compound which requires much greater energy than for pure elements.

All of the features mentioned above make it possible to produce all kinds of composite or non-composite materials allowing an economical technological process to be associated with the desired performance of coated parts. Furthermore, it has been established that the residual porosity of the coatings obtained by this process is less than 1%. Mechanical resistance, corrosion resistance, wear resistance are considerably higher than those obtained on reference samples having the same chemical composition. As a comparative example, the deposition of nickel powder on an aluminum substrate makes it possible to generate a transition zone with the inter-metallic Ni-Al compound 60 μm thick for a deposition time (collision) of a few tens seconds, while a chemical-thermal method tradition¬ nel makes it possible to form a transition zone 30 .mu.m thick 9 h at a temperature of 690 ^° C. the proposed method has also given excellent results for the formation of brass throughout the coating volume in the case of depositing a mixture of copper and zinc powders on a substrate.

These results make it possible to affirm that the proposed process has an original character and does not resemble in any way the other processes for producing materials and composite coatings. The applications of the method according to the present invention are multiple. Let us quote for example the development of a brass coating:

A mixture of powders comprising 40% copper and 60% zinc (by mass), the size of which is between 10 and 50 μm, is placed in the particle supply device, where these are stirred by a current compressed air. The mixture then arrives at the entrance to the mixing chamber where it is injected into the main gas flow brought to the temperature of 293 K. The two-phase gas flow is then accelerated, in the nozzle, to the speed of Mach 2 for coating on an aluminum substrate. During the formation of the coating, the chemical reactions which take place lead to the formation of a new material corresponding to brass by the composition of phases observed in X-ray analysis (microhardness 450 Nickers). To intensify the processes which take place at the time of collisions, this process allows the displacement of the substrate in front of the nozzle or the vibration of this substrate.

Another example of use of the process according to the invention makes it possible to obtain a refractory ceramic coating on a composite material with carbon fibers and matrix of silicon carbide.

A mixture of powder B4C, titanium and silicon, with a particle size of less than 50 μm, is placed in the feed device, the proportions by mass being as follows: 45% of B4C, 40% of Ti, and 15% of Yes.

The mixture is conveyed by a first compressed air flow and injected into the mixing chamber where the second air flow (main flow) gives the particles a supersonic speed. The particles are then projected onto the surface of a C / SiC composite material on which they form a coating.

The C / SiC sample is moved regularly in front of the jet to obtain a uniform deposit over the entire surface to be coated.

An adherent and compact coating is obtained, the analysis shows that this coating contains new phases (TiB2 and SiC). With the techniques of the prior art, obtaining these new phases would have required high-temperature heat treatment (> 1100 ^° C).

The use of the process according to the invention made it possible to obtain this cold coating.

This coating also gives new properties to the surface of the composite such as wear resistance and resistance to oxidizing atmospheres. The same procedure is used with a powder composition enriched with Silicon (40% B4C, 30% Ti, 30% Si) and is sprayed according to the invention on the surface of a Carbon-Carbon composite, a layer is thus obtained. hard and adherent which protects the material from oxidation.

Claims

1. A method of forming a coating by cold gasodynamic deposition of particles on a substrate, characterized in that it comprises the following steps: suspension of the particles by a gas flow,

.injection of the particle-gas mixture thus created into a main gas flow (carrier gas) brought to a temperature much lower than the melting temperature of the material or materials constituting these particles,

.acceleration to a supersonic speed of the resulting biphasic gas flow, and

.projection of the supersonic jet on the substrate.

2. Method according to claim 1, characterized in that the temperature of the carrier gas is between 300 and 600 K and the speed of ejection of the biphasic flow is between Mach 1 and Mach 2.

3. Method according to claim 1 or claim 2, characterized in that the particles consist of a mixture of powders of different materials.

4. Method according to any one of claims 1 to 3, characterized in that the carrier gas is compressed air.

5. Method according to any one of claims 1 to 4, characterized in that the substrate is animated with a relative movement relative to the supersonic jet.

6. Installation for implementing the method according to any one of the preceding claims, characterized in that it comprises a mixing chamber (1) in which a particle-gas mixture coming from a device for supplying particles (2) is injected into a main gas flow coming from a heating device (3) in which this flow generated by a gas supply circuit (4) from a gas storage tank (5) is brought to a temperature much lower than the melting temperature of the material or materials constituting it, the particle supply device ensuring prior mixing of the particles by a part of the gas flow delivered by the gas supply circuit (4) , and the mixing chamber (1) delivering via a supersonic nozzle (10) a two-phase gas flow to be projected onto the substrate.

7. Installation according to claim 6, characterized in that the particle supply device (2) is initially filled with particles.

8. Installation according to claim 6, characterized in that the particle supply device (2) is continuously supplied with particles in parallel with the introduction of the gas flow delivered by the gas supply circuit (4).

9. Installation according to claim 6, characterized in that it further comprises a valve (8) disposed at the outlet of the supersonic nozzle (lθ) to prevent any deposition of particles during a determined transitional period of start-up of the installation.