RU2416673C2 - Laser-plasma procedure of synthesis of very hard micro- and nano-structured coatings and device - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: according to procedure there is formed flow of working gas containing gas-carrier and chemically active reagents. The flow is directed onto treated surface at pressure as high as 0.5 at. Also, the flow is subjected to laser pulse-periodic radiation to generate laser plasma in a focus of laser beam. The device for realisation of this procedure consists of a reaction chamber with a gadget for positioning a treated object and with inputs for gas flow and laser radiation, of facility for forming flow of working gas in the reaction chamber, of a pulse-periodic laser and also of a facility for transmitting laser radiation into the reaction chamber and beam focusing.

EFFECT: increased wear, impact, chemical and corrosion resistance of coating.

10 cl, 3 dwg

Description

The invention relates to technologies for producing micro- and / or nanostructured protective and functional coatings on the surfaces of machine parts and mechanisms, pipelines and pumps, housing elements, functional and load-bearing metal structures responsible for the main characteristics, overhaul and full life of the final product or technical system for multiple increase wear resistance, impact resistance, chemical and corrosion resistance.

Metal surfaces, resistant to wear and tear, chemical and oxidative effects, are necessary for various uses, for example, in mechanical engineering, automation, agriculture, railway industry, aircraft manufacturing, chemical, oil and other industries. The cost of restoring worn surfaces of machine parts and mechanisms, pipelines, their elements is very significant. To reduce wear of surfaces during friction and to prevent corrosion, lubricating oil is traditionally used. Also, to harden the surface, nitriding is commonly used, during which baths with cyanide salts are used. However, all these technologies are not only expensive in themselves, but also dangerous for the environment.

To prevent damage from corrosion and impact of the main surfaces, an alternative solution is to cover them with a protective layer, while the surfaces themselves remain intact. However, such coatings can significantly increase the weight of nodes and mechanisms. Although the cost of protecting the surface from mechanical wear is high, the cost of protecting against corrosion and chemical attack is even higher. The German company AUDI has proposed a laser system that uses an ultraviolet excimer laser to modify the surface structure and / or chemical composition to create a protective coating on the surface of the engine. Such a system rotates the engine block, and the laser remains stationary. It is inefficient from the point of view of processing curved surfaces, and has a high cost. For these reasons, the use of such a method and system is limited.

A known method of producing metal carbide and a diamond-like protective carbon composite film, comprising supplying an inert gas to a vacuum chamber having a vacuum pump to create selective vacuum in the vacuum chamber and an inlet for gas, arranging a substrate and carbon graphite target in the chamber, providing means for generating a flow of metal atoms inside the chamber and generating a stream of metal atoms directly on the named substrate, the direction of the laser beam on the named carbon graphite spruce to generate a stream of carbon atoms on the named substrate, where a stream of carbon atoms near the surface forms a composite film of metal carbide in a diamond-like carbon matrix [US Patent No. H1 924, IPC C23C 14/06]. As a result, a thin, strong film is formed on the treated surface.

This method is the closest analogue of the proposed and adopted as a prototype of the invention. The disadvantages of the prototype include its limited creation of only one type of coating on a metal surface.

The invention solves the problem of creating such a method of surface modification, which allows to obtain a variety of high-strength surface coatings.

The problem is solved by the fact that a method for the synthesis of high hard coatings is proposed, according to which a working gas stream containing a carrier gas and chemically active reagents is formed, which is sent to the treated surface at a pressure of at least 0.5 atm, while the said working gas stream is exposed to a laser pulsed-periodic radiation in such a way that a laser plasma is formed in the focus of the laser beam, in which plasma-chemical reactions proceed, are synthesized and precipitated and / or synthesis ed on the treated surface targeted chemicals forming the coating of said treatment surface.

Laser pulsed periodic radiation can be directed across the flow of the working gas and can be directed along it.

As a carrier gas, inert gases can be used: argon, helium, neon, etc., or mixtures of them that do not participate in chemical reactions in the plasma, as well as chemically active gases: oxygen, nitrogen, etc., which can participate in plasma chemical reactions.

The pressure in the gas stream is preferably maintained at atmospheric pressure, but in some cases it may be lower or higher.

Reactive chemicals may be contained in the working gas in the form of gases, vapors, micro- and / or nanoaerosols, including as a stoichiometric mixture of various aerosols, including refractory ones.

The treated surface during the deposition of chemically active reagents on it can move, if necessary.

The method is based on the ignition of a laser plasma in a high-speed flow of a carrier gas containing chemically active reagents, its maintenance and control, as well as the implementation of plasma-chemical reactions both directly in the named plasma and on the surface of the treated object for the purpose of synthesis and deposition of micro- and / or nanostructured functional coatings.

For example, the method is applicable for the deposition of high-hardness coatings from silicon carbonitride compounds (SiCN) or boron (BCN) by forming a laser plasma in a high-speed working gas stream using reactive components in the form of gases, vapors, micro- and / or nanoaerosols and positioning the surface of the treated object relative to the flow of the working gas.

This method can be carried out using the proposed device. A device for producing metal carbide and a diamond-like protective carbon composite film, including a vacuum chamber having a gas inlet, a vacuum pump for creating selective discharge in a vacuum chamber, positioning means in a substrate chamber and a carbon graphite target, means for generating the flux of metal atoms inside the chamber and generating a flux of metallic atoms on the named substrate, a laser radiation source [US Patent No. H1 924, M By S23S 14/06].

A device for producing highly hard coatings by the aforementioned method includes a reaction chamber with means for positioning the treated object, an input for a working gas flow and an input for laser radiation, a working gas source, means for generating a working gas flow in the reaction chamber, a pulse-periodic laser, and a laser delivery means radiation into the reaction chamber and focusing the beam.

The device may also contain a control tool - a control processor.

Figure 1 shows the first embodiment of a device for the synthesis of coatings.

Figure 2 shows a second embodiment of a device for the synthesis of coatings.

Figure 3 shows the sequence of stages of the method of synthesis of coatings.

In figure 1 and figure 2, the following positions mean:

10 - a device for implementing the method with a transverse arrangement of laser radiation relative to the flow of the working gas;

12 - coating;

14 - the processed object;

15 - thermostat;

16 - laser plasma;

17 - means of moving the processed object;

18 - flow of working gas;

19 - products of plasma-chemical reactions, activated compounds and nuclei of nanoparticles;

20 - pulse-periodic laser;

22 - an optical system for transporting and focusing a laser beam;

23 is an optical window for entering the laser radiation reaction chamber;

24 - reaction chamber;

25 - optical window;

26 - laser radiation;

27 - a protective cavity;

28 - means for forming a working gas stream;

29 - a stream of protective gas;

30 - management tool;

32, 33 - systems for measuring and monitoring the characteristics of laser radiation;

34 - a system for measuring and monitoring the characteristics of laser plasma radiation;

35 - adjustable valve

36 - adjustable valve;

37 - adjustable valve;

38 - adjustable valve;

40 - a means of preparing chemicals for the working gas;

42 - carrier gas supply means;

44 - source of carrier gas;

100 - a device for implementing the method with a longitudinal arrangement of laser radiation relative to the flow of the working gas;

102 - element of the reaction chamber, providing a small gap with the surface of the processed object 14;

104 - flow of exhaust gas.

Figure 1 shows a device 10 designed for the synthesis of high hard coatings 12 on the surface of the treated object 14 by activating the starting reagents in the laser plasma 16 with a transverse mutual arrangement of the flow of the working gas and laser radiation.

The radiation 26 of the repetitively pulsed laser 20 by the optical system 22 for transporting and focusing the laser beam is directed into the working chamber 24 and is focused in the high-speed stream 18 of the working gas, consisting of a carrier gas and chemically active reagents. In the region of maximum focusing of the laser beam, an intensity above the threshold for ignition of the laser plasma 16 should be ensured (54, 60 of Fig. 3). For example, for a CO ₂ laser, the level of radiation intensity depending on the type of carrier gas (argon, helium, neon, nitrogen, oxygen, etc.) and the type of reagents (vapors, aerosols) is usually in the range of 1-1000 MW / cm ² . but this range may be wider. Without going into details of physical and physicochemical mechanisms, the synthesis process (60 of FIG. 3) of coating 12 can be divided into four main stages.

Stage 1 (62 figure 3): during the irradiation of the working gas stream 18 with a laser pulse, a laser plasma 16 is formed with its rapid heating to a temperature of 15-25 thousand degrees Celsius, ionization and dissociation (if the carrier gas is molecular or the initial chemical reagents are present working gas in the form of molecular gases, vapors, etc.), evaporation (including ablation) of micro- and / or nanoparticles of chemical reagents, if they are in the working gas in the form of aerosols, followed by dissociation and ionization.

Stage 2 (64 figure 3) - this stage partially coincides in time with the first stage: there is a supersonic (shock-wave) expansion of the laser plasma, which is accompanied by heating of additional areas of the working gas bordering the plasma, including their dissociation, ionization and activation, by equalizing the plasma pressure with the pressure of the surrounding gas and general cooling of the plasma to a temperature 2-3 times lower than the temperature of the plasma at the stage of formation. The cooling rate in this stage can reach 10 G ° K / s or more.

Stage 3 (66 figure 3): there is a further cooling of the laser plasma due to turbulent mixing with the surrounding gas, radiation heat transfer and convective removal to the surface of the object. At this stage, plasma-chemical reactions proceed intensively, which lead to the formation of highly activated compounds and nuclei of nanoparticles, including nanoclusters, nanocrystallites, etc., as shown in Fig. 1, item 19.

Stage 4 (68 figure 3): a heterogeneous synthesis of the coating 12 occurs on the surface of the treated object 14, in which the activated nanoparticles formed in the plasma and brought by the working gas stream are the nuclei of nanocrystalline "grains" in the volume of an amorphous matrix synthesized from activated atoms and compounds, including nanoclusters.

The selection of the repetition rate ƒ and the energy of the laser pulses E, as well as the velocity V and the mass flow rate m of the working gas stream 18 can provide close to complete, and in some cases complete conversion of the working gas into at least partially ionized plasma with activated starting reagents . In this case, the geometry of the cross section of the working gas stream 18 by the element 28 of the reaction chamber 24 is close to the size of the laser plasma after the completion of stage 2, and the preferred flow rate V is set no more than the product of the laser pulse repetition rate ƒ and the size of the laser plasma in the direction of the stream after the completion of stage 2 .

For example, for a CO ₂ laser providing ƒ in the range of 5-100 kHz and energy E in the range of 0.5-0.05 J, the preferred working gas flow rate with increasing frequency ƒ can be in the range from 30 to 300 m / s for cases when the laser radiation is directed transversely to the flow of the working gas (figure 1) and in the range of 100-1000 m / s for the case when the laser radiation is directed along the flow of the working gas (figure 2).

However, these ranges are optional and may be extended. For example, when using the starting reagents in the form of microaerosols, the preferred working gas flow rate V can be significantly and even many times reduced to increase the duration of the action of laser radiation and plasma.

For a cost-effective, high-performance implementation of the laser-plasma coating synthesis method, a laser or a laser system 20 with a high laser pulse repetition rate of more than 1000 Hz (in some cases this frequency may be lower) having laser pulse power such that laser plasma is formed is preferable 16 in the focus of the beam 26. For example, in one of the successful embodiments, a CO ₂ laser was used with a pulse repetition rate from hundreds of Hz to 100 kHz and a pulsed power of tens and hundreds of kV t Other types of lasers can be used - both gas and solid-state with other power ranges.

The optical system 22 is designed to transport and focus the laser radiation, as well as to direct part of the radiation (usually insignificant) to the systems for measuring and monitoring the characteristics of laser radiation 32, 33 and laser plasma radiation 34. For example, system 22 may consist of several mirrors, including movable ones, which ensure the movement of the laser beam, including a reaction chamber moving at the surface of the object being processed, focusing the beam in the flow of working gas 18 in the reaction chamber 24, and that same for alternately directing the laser beam in different reaction chambers, if the device has a plurality of reaction chambers. In another embodiment of the invention, a system for transporting and focusing laser radiation 22 may include an optical fiber for transporting laser radiation in one or more sections of the optical path.

In preferred embodiments, system 22 comprises one or more translucent partially reflective elements, such as optical wedges with flat surfaces through which the laser beam passes, to reflect part of the radiation into systems 32, 34, and at least one lens for focusing the beam or matching sections of the optical path.

The optical system 22 directs the laser radiation to the input window 23 of the reaction chamber 24, which can be made in the form of a lens. The focusing laser beam 26b passes inside the protective cavity 27, into which, to significantly reduce, until completely eliminating, the absorption of laser energy by the flow of the working gas 18 in the beam section in front of the plasma, as well as to protect the entrance window 23 from the undesirable effects of the mixture 18 and the plasma, particular ablation products, shielding gas 29 is supplied, typically a carrier gas under pressure, slightly by 0.01-10 kPa, exceeding the pressure in the reaction chamber 24.

The transmitted laser gas stream 26c is directed through the window 25 to the measurement and control system 33.

In some embodiments of device 10 (FIG. 1), a cooled absorber, such as a calorimeter, may be located in place of window 25 or system 33, and in some other embodiments of device 100 (FIG. 2), window 25 and system 33 are missing.

The reaction chamber 24 may be either sealed, as shown for some embodiments 10 (FIG. 1), or may have an open gas outlet, as shown for some embodiments 100 (FIG. 2).

The design of the reaction chamber 24, in addition to the window 23 for inputting the laser beam, may include windows for diagnosing the laser beam, laser plasma 16 and the resulting coating 12, for example, for video monitoring or optical pyrometry.

To form a cross-section of the working gas stream 18 close to the dimensions of the laser plasma 16, after the completion of stage 2 of the method (64 in FIG. 3), the outlet or nozzle of the means for forming the working gas stream 28 of the reaction chamber 24 may be slotted oblong with the side having a larger size oriented along the laser beam, for embodiments with a transverse arrangement of the laser beam relative to the flow of the working gas (Fig. 1) or may be close to round, for embodiments with a longitudinal arrangement of the laser th beam (2).

The body of the reaction chamber 24 and the heat-stressed structural elements 27, 28, 17 and others can be forced to cool with water or other refrigerant.

The chemical preparation system 40 may consist of one or more subsystems (not shown) with different versions and different types of reagents (gases, vapors, aerosols).

For example, in one embodiment of a device for supplying reagents in the form of hexamethyldisilazane vapors, evaporation is carried out in a carrier gas medium, which is supplied through an adjustable valve 38 from a common gas line 42, and the flow rate and impurity concentration are controlled by the temperature of the evaporator and the flow rate of the carrier gas through the adjustable valve 38. in one successful embodiment, other chemical reagents for supplying a micro- and / or carbon nanospray and Si ₃ N ₄ used adjustable dosing micro- or nanopowders with images Niemi suspension with a carrier gas.

The surface temperature of the treated object, along with other process parameters, has a significant effect on the growth rate, structure and morphology, as well as the properties of the synthesized coatings. Therefore, it is advisable to place the processed object 14 on special tools - supporting tables, etc., which are connected by good thermal contact with the node 15, providing thermostat functions - heating or cooling, i.e. maintaining the temperature of the object within the specified limits, controlled by the control processor 30.

The control processor 30, receiving and processing the signals of the measuring systems 32, 33, 34, etc., as well as nodes 15, 17 through actuators and mechanisms (not shown) controls the operation of the laser 20, nodes 15, 17 and adjustable valves 35, 36, 37, 38 (possibly some others) and ensures that the process is carried out in accordance with the steps shown in FIG. 3.

The node 17 provides positioning and / or relative movement of the processed object and, accordingly, the area of influence of the laser plasma flow on the surface of the object, which can be translational, rotational, combined.

In more detail, the claimed method for the synthesis of coatings, the main stages of which are shown in figure 3, is as follows.

As the processed objects used for coating by this method, there can be parts of various geometric shapes, consisting of metals or alloys, as well as non-metals (e.g. ceramics, crystals, etc.), including parts consisting of a combination of metal and non-metal parts .

Surface preparation of the treated object for coating can in some cases be mechanical (turning, milling, sandblasting, grinding, etc.), in other cases, chemical using detergents and / or chemicals, including using ultrasonic devices etc., as well as combined. It is important to note that in many cases surface pretreatment is not required, as laser plasma in combination with laser radiation, as shown in figure 2, have a strong cleaning effect on the surface of the treated object. Installation and fixing of the processed object 14 in some cases should provide good (with a small temperature difference) thermal contact with the thermostat 15. In some other cases, when the heat transferred to the processed object during laser-plasma synthesis heats the surface of the object to a temperature in some specified optimal limits, thermal contact may be poor or thermostat 15 may not be required.

The preparation of the reaction chamber (52 of Fig. 3), in addition to the obvious preventive cleanings or cleanings when replacing the composition of reactive impurities, consists in some cases (Fig. 1) in its sealing (controlled valves 36, 37, 38 are closed, as well as some others, not shown) and pumping air from its internal volume through a controlled valve 35, followed by inlet of a carrier gas into the chamber. In some other cases, the volume of the reaction chamber is purged with carrier gas, preferably with multiple (3-10 times) replacement of the original air with carrier gas.

The beginning of the laser-plasma process 54 consists in igniting and maintaining for some time the laser plasma 16 in the carrier gas stream (usually without chemicals) to clean, activate and establish some preferred surface temperature of the treated object.

The supply of the mixture of the starting chemical reagents 56 and the formation of the working gas stream occur almost simultaneously after the completion of the laser-plasma process of preparing the surface of the object 54 and continue until the completion of the entire process of coating synthesis.

As the constituent mixtures of the starting reagents, various chemical elements and compounds in various states of aggregation can be used.

For example, in some successful embodiments of this method, pairs of hexamethyldisilazane SiNH (CH ₃ ) ₆ or a mixture of carbon micropowders and Si ₃ N ₄ are used to synthesize SiCN coatings.

In addition, the following types of volatile organosilicon, organoboron and complex volatile complex compounds can be used as starting reactants for the production of silicon and boron carbonitrides, simple and complex refractory metal oxides. These are: silyl derivatives of asymmetric dimethylhydrazine (Me ₂ SiHNHNMe ₂ , Me ₂ Si (NHNMe ₂ ) ₂ , where Me is a methyl group (CH ₃ )), bromosilazane (Si ₂ NBr (Me) ₆ ), B ₃ N ₃ H ₆ , (Me) ₃ N BH ₃ , betadiketonate metal complexes, etc.

Laser-plasma synthesis of coating 60 (including stages 62, 64, 66, 68 described above) is carried out almost simultaneously (with a shift by the time required for applying the initial coating area) with a relative displacement of 70 of the surface of the treated object and the area of influence of the laser plasma stream.

In some other cases, when it is required to obtain an object coverage area with smaller dimensions relative to the size of the laser plasma exposure area (coating synthesis area), aperture masks (not shown) with holes / slots of the required shape that overlap the object surface and limit the object coverage area can be used .

At the end of some predetermined coating synthesis process, the supply of chemical reagents stops, and the laser beam can be blocked or directed to another reaction chamber 74 if the laser-plasma synthesis device contains several reaction chambers.

In some cases, the change of the processed object 76 is carried out after a sufficient time of the presence of the treated object in an inert atmosphere (usually in a carrier gas medium) to lower the temperature of the coating and the surface of the object below a certain temperature, exceeding which may cause undesirable exposure to the air atmosphere.

Compared with a variant of the device 10 (FIG. 1) in the device 100 (FIG. 2), the focusing laser beam 26b propagates mainly along the flow of the working gas. The area of influence of the laser plasma on the surface of the processed object 14 may partially overlap in the area of influence of the part of the laser beam 26c, in which additional heating and activation of the surface of the synthesized coating 12 takes place.

The processed object 14 can be located both in the sealed volume of the reaction chamber 24, as shown in figure 1, and outside it, as shown in figure 2. In this case, the design of the element 102 of the reaction chamber should provide a small gap with the surface of the treated object 14, so that the flow of exhaust gas 104 prevents the flow of atmospheric air into the zone of plasma-chemical reactions and synthesis of the coating 12.

The nodes 15 and 17 or their elements can be located both in the sealed volume of the reaction chamber 24, and outside it. The positioning and relative movement of the area of influence of the laser plasma flow and the surface of the object 14 can be carried out both by moving the processed object, and by moving the reaction chamber or a combination of these movements.

Thus, the proposed method and device allows to obtain highly hard coatings from various compounds, including silicon nitride silicon carbide compounds SiCN or BCN boron by forming a laser plasma in a high-speed working gas stream using reactive components in the form of gases, vapors, micro- and / or nanoaerosols and positioning the surface of the treated object relative to the flow of the working gas.

Claims (10)

1. A method for the synthesis of high hard coatings, comprising treating the surface of an object with a working gas stream when exposed to laser radiation, characterized in that a working gas stream containing carrier gas and chemically active reagents is formed, which is directed to the surface to be treated at a pressure of at least 0.5 atm, in this case, said working gas stream is subjected to pulsed periodic laser radiation to form a laser plasma at the focus of the laser beam. 2. The method according to claim 1, characterized in that the laser pulse-periodic radiation is directed across the flow of the working gas. 3. The method according to claim 1, characterized in that the laser pulse-periodic radiation is directed along the flow of the working gas. 4. The method according to claim 1, characterized in that inert gases are used as a carrier gas: argon, helium, neon, or a mixture thereof. 5. The method according to claim 1, characterized in that as the carrier gas using chemically active gases: oxygen or nitrogen. 6. The method according to claim 1, characterized in that the pressure in the gas stream is mainly maintained at atmospheric pressure. 7. The method according to claim 1, characterized in that the chemically active reagents are contained in the working gas in the form of gases, or vapors, or micro- and / or nanoaerosols. 8. The method according to claim 1, characterized in that the treated surface during the deposition of chemically active reagents on it is moved. 9. A device for producing highly hard coatings, comprising a reaction chamber with positioning means of the workpiece and an inlet for a gas stream, characterized in that it contains a working gas source, means for generating a working gas stream in the reaction chamber, a pulse-periodic laser, and a delivery means laser radiation into the reaction chamber and focusing the beam, while the reaction chamber contains an input for the flow of the working gas and an input for laser radiation. 10. The device according to claim 9, characterized in that it comprises control means in the form of a control processor.

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