WO2009125284A1

WO2009125284A1 - Laser-plasma method and system for surface modification

Info

Publication number: WO2009125284A1
Application number: PCT/IB2009/005213
Authority: WO
Inventors: Pavel Yurievich Smirnov; Sergey Nikolaevich Bagayev; Tamara Pavlovna Smirnova; Aleksandr Leonidovich Smirnov; Gennadii Nikolaevich Grachev; Viktor Nikolaevich Demin
Original assignee: Pavel Yurievich Smirnov; Sergey Nikolaevich Bagayev; Tamara Pavlovna Smirnova; Aleksandr Leonidovich Smirnov; Gennadii Nikolaevich Grachev; Viktor Nikolaevich Demin
Priority date: 2008-04-09
Filing date: 2009-04-08
Publication date: 2009-10-15

Abstract

A method and system for treating a surface of an object is provided. The method and system generally includes producing a flow of working gas. The flow of working gas is directed to a zone of action at or proximate the surface being treated. Laser radiation is directed onto the working gas into the zone of action to produce a laser plasma. The surface is then exposed to the laser plasma thereby treating the surface. The plasma may thus be used to thermally transform the phase structure of the surface, chemically and/or physically react with the surface, additionally or alternatively synthesize and deposit a coating on the surface.

Description

LASER-PLASMA METHOD AND SYSTEM FOR SURFACE

MODIFICATION

FIELD OF THE INVENTION

The invention relates generally to a method and system for the modification of a surface. More particularly, it relates to a method and system for treating a surface of an object using a plasma and to technologies for changing the structure and/or chemical composition of the near-surface layer of an object and for synthesizing protective and functional surface coatings.

BACKGROUND OF THE INVENTION

Metal, including alloy, surfaces with wear and shock resistance as well as chemical and corrosion stability are needed in many applications, for example machining, automotive industry, agricultural industry, locomotive industry, aeronautical industry, chemical industry, petroleum industry, defence industry.

The cost of regular and overhaul maintenance and repair of the surfaces of machine parts and mechanisms, pipelines, elements of casing, functional and bearing metal structures is significant.

Lubricating oils may be used on surfaces to reduce wear from friction and prevent corrosion. Surface hardening via nitriding using cyanide salt baths is also commonly used. However, use of lubricating oils and cyanide salt baths can be not only costly but hazardous and environmentally unfriendly requiring special handling and regulated disposal thereof. Alternatively, surfaces may be covered with a protective layer to prevent damage from corrosion and shock to the underlying surface that can affect overall structural integrity. However, such coatings can adversely increase the overall weight of the part or mechanism. Although the cost of protecting the surfaces from frictional wear and tear is great, the cost of protecting the metal/alloy surfaces from corrosion and shock is even greater.

The German company AUDI has introduced a laser system that utilises an ultraviolet (UV) excimer laser to modify surface structure and/or chemistry and to produce a protective coating on the surfaces of an engine block. This system rotates the engine block while the UV excimer laser remains fixed. Moreover, it is not very efficient at treating curved surfaces. As such, this type of system has limited practical use while being fairly expensive.

US patent 7,465,362 describes a plasma-assisted method of nitriding a surface region of an object. The method can include subjecting a gas to electromagnetic radiation, e.g. microwave radiation, in the presence of a plasma catalyst to initiate a plasma containing nitrogen. The system requires a cavity to form the plasma therein.. This requirement causes the system to be also of limited practical use. Still the distribution of plasma within the processing cavity can strongly depend on the distribution of the applied radiation, this can lead to problems of uniformity with the plasma and hence with the treatment of the surface. This system does not allow to easily target specific areas along the surface of the object for treatment and is geared towards nitriding/carbiding treatments of the surface.

There is therefore still a need for a more practical method for obtaining surfaces with improved wear and shock resistance as well as chemical and corrosion stability which allows for targeted surface treatment and is flexible enough to accommodate several types of surface treatments. SUMMARY OF THE INVENTION

An object of the present invention is to provide a method for treating a surface that satisfies the above-mentioned need.

According to one aspect of the present invention, that object is achieved with a method for treating a surface of an object that includes the steps of:

(a) providing a working gas;

(b) flowing the working gas in a zone of action at or proximate to the surface of the object;

(c) directing laser radiation onto the working gas into the zone of action to produce a laser plasma; and

(d) exposing the surface to the laser plasma and thereby treating the surface.

Preferably, the working gas is kept at or near atmospheric pressure.

The working gas in step (a) may contain a carrier gas and at least one of a chemically active reagent and an alloying element. Thus, in step (c), the directing laser radiation onto the working gas produces a laser plasma containing activated products, and in step (d) the surface is exposed to the laser plasma containing activated products.

The laser radiation may be a pulsed periodic laser radiation. The pulsed periodic laser radiation may have a frequency of about 5 to 100 kHz.

The treating of the surface may include a physical or chemical reaction of the activated products with the surface. It may include depositing a coating on the surface. It may also include thermally transforming the surface.

According to another aspect of the present invention, there is provided a system for treating a surface of an object that includes: (a) a reaction chamber with a zone of action, the zone of action being devised to be positioned at or proximate the surface to be treated, the reaction chamber including:

(i) a gas inlet for receiving a flow of working gas containing a carrier gas and at least one of a chemically active reagent and an alloying element; (ii) a radiation inlet for receiving laser radiation; and (iii) an emission outlet for outputting gas emissions;

(b) a working gas flow arrangement in fluid communication with the gas inlet, comprising means for flowing the working gas in the zone of action; and

(c) a laser arrangement for supplying the laser radiation to the radiation inlet and directing the laser radiation onto the zone of action to produce with the working gas a laser plasma thereby treating the surface with the laser plasma.

The working gas may contain a carrier gas and at least one of a chemically active reagent and an alloying element, and thus the laser plasma contains activated products for treating the surface.

The laser radiation may be a pulsed periodic laser radiation. The gas inlet may have a cross-sectional area substantially identical to the cross-sectional area of the laser beam so as to optimize the zone of action. The laser arrangement may include a CO₂ laser.

Thanks to the fact that the method and system of the present invention use a laser plasma that can be easily produced in discrete locations close to the surface to be treated, any type of irregular surfaces, such as curved surfaces can be effectively treated.. Furthermore, the method and system also allow the laser radiation source to be moved relative to the object or the other way around, the object to be moved relative to the laser radiation source.

Also advantageously, the present invention provides a cost and energy efficient method and system for obtaining surfaces with improved wear and shock resistance as well as chemical and corrosion stability.

The objects, advantages and other features of the present invention will become more apparent and be better understood upon reading of the following non-restrictive description of the invention, given with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1A is a schematic flow-chart diagram illustrating a first preferred embodiment of a method for treating a surface of an object, according to the invention.

Fig. 1B is a schematic representation of a first preferred embodiment of a system for treating a surface of an object, according to the invention.

Fig. 2A is a schematic representation of a second preferred embodiment of a system for treating a surface of an object, according to the invention.

Fig. 2B is a detail view of portion A of Figure 2A showing laser plasma action on an object surface.

Fig. 3 is a schematic representation of a third preferred embodiment of a system for treating a surface of an object, according to the invention.

Fig.4 is a schematic flow-chart diagram illustrating a second preferred embodiment of a method for treating a surface of an object, according to the invention.

Fig. 5 is a schematic representation of a fourth preferred embodiment of a system for treating a surface of an object according to another embodiment of the invention.

Fig. 6 is a schematic representation of a fifth preferred embodiment of a system for treating a surface of an object according to yet another embodiment of the invention, used to synthesize coatings on the surface layer.

Fig. 7 is a schematic flow-chart diagram illustrating a third preferred embodiment of a method for treating a surface of an object according to another embodiment of the invention.

Fig. 8A is a graphic illustration of the hardness of six SiCN film samples: 2421/1 , 2421/2, and 1 to 4;

Figure 8B is a graphic illustration of the reduced modulus of the six SiCN film samples.

Fig. 9 is a graph of force versus displacement curves from indents performed on the six SiCN film samples.

Fig. 10 shows topographical in-situ images of selected indents on each of the six SiCN film samples.

Fig. 11A is a graphic illustration of the hardness of five BCN film samples: 5 to 9;

Figure 11 B is a graphic illustration of the reduced modulus of the five BCN film samples.

Fig. 12 is a graph of force versus displacement curves from indents performed on the five BCN film samples.

Fig. 13 shows topographical in-situ images of selected indents on each of the five BCN film samples.

Fig. 14 shows topographical surface images obtained for each of the six SiCN film samples and for each of the five BCN film samples. 13

7 following reference numerals are used in Figs. 1 to 7:

- method of treating a surface of an object;

- providing a working gas;

- surface of object undergoing treatment;

- flowing the working gas;

- object;

- directing laser radiation onto the working gas to produce a laser plasma;

- laser plasma;

- exposing the surface to the laser plasma, treating the surface;

- working gas;

- a system for treating a surface of an object;

- zone of action;

- reaction chamber;

- a gas inlet for receiving a flow of working gas and inputting the flow into the reaction chamber;

- laser radiation; 27 - a radiation inlet;

29 - working gas flow arrangement;

33 - laser arrangement;

41 - emission outlet;

110 - an embodiment of the surface modification system used to carry out the method of modifying external surfaces or internal open cavities with a curvature radius of the surface of no less than 0.1 m;

112 - modified surface layer;

112a - surface zone consisting mainly of target compounds or a layer of alloying elements/compounds synthesized in the plasma or on the surface;

112b - zone whose properties and characteristics are determined mainly by the diffusion of alloying elements;

112c - zone whose properties and structure are mainly determined by thermal phase transformations;

114 - object being treated,

115 - thermostat, means to heat or cool the object being treated;

116 - laser plasma;

117 - means for positioning/moving the object being treated and/or reaction chamber; 118 - working gas flow;

120 - pulsed-periodic laser;

122 - optical system to transfer and form irradiation zone on the object surface;

123 - optical window (lens) for the input of laser radiation to the reaction chamber;

124 ~ reaction chamber;

126a - laser radiation; 126b - focused or redirected laser radiation;

127 - element to channel the beam and protective gas;

128 - means to form the working gas flow;

129 -protective gas flow;

130 - control means;

132 - system to measure and control laser radiation characteristics;

134 - system to measure and control the characteristics of laser plasma radiation and the treated surface temperature;

136 - control valve;

137 - control valve/valves;

138 - control valve/valves;

140 - means for preparing/mixing the working gas with alloying additions and chemical reagents;

142 - means for carrier gas supply;

144 - source(s) of carrier gas (gases) and/or active gas (gases);

146 - reaction chamber element providing a small gap with the surface of object 14 being treated;

148 - flow of exhaust working gas;

150 - embodiment of the surface modification system used to carry out the method for modifying internal cylindrical surfaces with a rotating reaction chamber;

152 - movable platform;

154 - means for rotating the reaction chamber;

156 - casing also serving as a collector for supplying gases to reaction chamber and cooling them;

158 - internal circular grooves;

159 - through holes;

160 - gaskets;

162 - means for supplying gas;

164 - mirror;

165 - end of means 28 on the side of the surface of object 14; 210 - an embodiment of the system used to carry out the method where laser radiation is transverse to the working gas flow;

212 - surface coating;

214 - object being treated;

215 - thermostat;

216 - laser plasma;

217 - means for moving the object being treated;

218 - working gas flow;

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

220 - pulsed-periodic laser;

222 - optical system for laser beam transfer and focusing;

223 - optical window for the input of laser radiation to the reaction chamber;

224 - reaction chamber;

225 - optical window;

226a - laser radiation; 226b - focused or redirected laser radiation;

227 - protective cavity; 228 - means for forming the working gas flow;

229 - protective gas flow;

230 - control means;

232, 233 - systems for measuring and controlling laser radiation characteristics;

234 - system for measuring and controlling laser plasma radiation characteristics;

235 - control valve;

236 - control valve;

237 - control valve;

238 - control valve;

240 - means for preparing chemical reagents for the working gas;

242 - means for supplying carrier gas;

244 - carrier gas source;

2100 - an embodiment of the system used to carry out the method where laser radiation is longitudinal with respect to the working gas flow;

2102 - reaction chamber element providing a small gap with the surface of object 214 being treated;

2104 - exhaust working gas flow. DESCRIPTION OF THE INVENTION

GENERAL DESCRIPTION

While the invention will be described in conjunction with example embodiments, it will be understood that it is not intended to limit the scope of the invention to such embodiments. On the contrary, it is intended to cover all alternatives, modifications and equivalents. The following description is to be read with reference to Figs. 1A to 14.

The expressions "treating a surface" and "modifying a surface" are used interchangeably herein and include modification of the structure and/or chemical composition of a surface, for example quenching (e.g. quenching of austenite to form martensite), nitridation and cementation, as well as synthesis/deposition of a hard coating on the surface. The term "surface" used herein is not limited to a side of an object, but may include a layer of material proximate the side, i.e. a near-surface layer. The tilde symbol "~" used herein means approximately or about.

The present invention relates to a method and system for treating a surface of an object. The object whose surface is undergoing treatment may be any object which can benefit from improvements to its durability, i.e. improvements to wear due to friction, fatigue, shock, chemical and/or corrosion resistance. For example, as explained earlier, the method and system may be used to treat the surface of an engineering or workshop tool, an engine, a pipe, a casing, etc. Although the surface, or near-surface layer, may preferably made of a metal, an alloy, or metal composite, it may be made of any other suitable chemical composition. The surface need not be of the same composition as the underlying substrate layers of the object. Moreover, this method and system allows to target the surface to be treated, that is to say certain areas or regions of the surface may be singled out for treatment. Method

Referring to Fig. 1A, the method (10) for treating the surface generally includes providing a working gas (11), flowing the working gas in a zone of action at or proximate to the surface of the object (13), directing laser radiation onto the working gas into the zone of action to produce a laser plasma (15), and exposing the surface to the laser plasma and thereby treating the surface (17).

This laser plasma may thus be used to thermally transform the phase structure of the surface, chemically and/or physically modify the surface, and/or synthesize and deposit a coating on the surface.

The working gas

The working gas that is provided includes, at the minimum, a gas capable of yielding, forming, a plasma.

The working gas may contain a carrier gas and at least one of a chemically active reagent and an alloying element. In the latter case, when laser radiation is directed onto the working gas, the laser plasma produced contains activated products used to treat the surface.

The working gas may be provided pre-mixed, that is to say with all the constituents present in the appropriate stoichiometric concentrations, or it may be mixed on-the-go by regulating the concentration of the individual constituents.

Inert gases (such as argon, helium, neon, etc. or their mixtures) not participating in the chemical reactions in the plasma as well as chemically active gases (such as oxygen, nitrogen, carbon monoxide, ammonia, propane, etc. or their mixtures) that can participate in the chemical reactions in the plasma may be sources of activated products for the working gas.

Alloying elements and/or chemically active reagents may be contained in the working gas in the form of a powder, nanoparticle, liquid, gas, vapor, micro-aerosol, nano- aerosols, in the form of a stoichiometric mixture of different aerosols (including high- melting ones), or any combination thereof.

The working gas is made to flow into a zone of action at or near the surface of the object being treated. The pressure of the working gas flow is preferably kept at or near atmospheric pressure. In some cases, however, it may be below atmospheric pressure, for instance, when the working gas contains toxic gases producing harmful emissions which should be disposed of appropriately.

The velocity of the working gas flow provides the supply of the initial reacting/alloying components and may be selected taking into consideration the laser radiation used, e.g. the repetition rate and energy of a pulsed periodic laser radiation.

The working gas may be made to flow at a rate in the range from 10 m/s to 1000 m/s.

The laser radiation

The laser radiation is directed onto the working gas into the zone of action to produce a laser plasma. The zone of action is basically the zone where the laser radiation and working gas interact to produce a plasma. The laser radiation has an intensity capable of initiating a plasma. The intensity may be from about 0.1 MW/cm² to about 1000 MW/cm². The laser radiation may be preferably provided by a CO₂ laser, but it may be provided by any appropriate laser, e.g. a solid-state laser, a photonic crystal laser, etc. The laser radiation need not be operated in continuous wave mode, and may be preferably operated in a pulsed periodic mode with a frequency of about 5 to OO kHZ. The method may therefore include repeated (preferably not less than 3 to 5 tnes, preferably tens to hundreds of times) action of periodic-pulsed laser radiation, "his may be accomplished by a series of laser pulses aimed at a stationary object or by ϊonstantly repeating laser pulses at a relative motion of the irradiation zone and the >bject surface (e.g. moving the laser pulses with respect to the object surface).

The laser radiation may be directed transverse to or along the flow of working gas. With :he laser directed transverse to the flow of working gas, the working gas may be made to :low at rate of about 30 m/s to about 300 m/s. With the laser radiation directed along the Flow of working gas, the rate of flow of the working gas may be higher, from about 100 m/s to about 1000 m/s.

As mentioned previously hereinabove, the laser plasma may thus be used to thermally transform the phase structure of the surface, chemically and/or physically react with the surface, additionally or alternatively synthesize and deposit a coating on the surface.

By exposing the surface of the object to the laser plasma, it is possible to heat the surface. This heating action of the plasma may be used to thermally transform the microstructure of the surface, including to thermally harden the surface with or without the diffusion of alloying elements.

In the case where the working gas contains a carrier gas and at least one of a chemically active reagent and an alloying element, the laser plasma will contain activated products. The activated products may include chemically active compounds, nanoparticles, or alloying elements or any combination thereof. The surface is then exposed to these activated products via exposure to the laser plasma thereby treating the surface. For example, the activated products may contain carbon used for carbiding the surface to produce a hard carbide surface layer, or chemical compounds used to synthesize and deposit a coating on the surface, say a resistant nanostructured protective coating. If necessary, the surface being treated may be made to move during the process of laser-plasma modification.

According to an embodiment, the pressure of the working gas flow is preferably kept at or near atmospheric pressure and the surface is subjected to repeated action of pulsed laser radiation so that a near-surface laser plasma is formed in the zone of action, which effectively heats the surface to high temperatures (in particular, above the melting point), permitting the creation of a resistant near-surface layer through saturation of the near- surface layer with alloying elements (for instance, for nitriding, cementation, etc.) as well as through thermal phase-structural transformations (for instance, austenite-martensite transformation). In addition, by tailoring the working gas and using the plasma-chemical reactions that take place in the laser plasma, target chemical substances may be synthesized and deposited onto the surface of the object being treated to form a resistant external coating of the surface. The intensity of action of the laser radiation and near-surface plasma (usually more than 1 MW/cm² ) in the initial part of a series of laser pulses (e.g. approximately the first 20% of the total number of pulses) mainly provides heating of the object surface above the melting point whereas the pulse repetition rate in the main part of the series (after the initial part) provides maintenance of the surface temperature between pulses in the range from a temperature somewhat lower (by 30 - 100 degrees C or K) than the melting temperature to a temperature approximately half the melting temperature (which, for instance, is typically higher than the austenization temperature for irons and steels). The shape of the zone of laser radiation action on the surface is similar to that of the zone of working gas flow action. The radiation intensity nay be mostly constant in the surface irradiation zone.

System

n accordance with another aspect of the invention, there is provided a corresponding system for treating a surface of an object. Referring to Fig. 1B₁ the system 20 generally includes a reaction chamber 24 with a zone of action 23, the zone of action being devised to be positioned at or proximate the surface 12 to be treated. The reaction chamber 24 has a gas inlet 25 for receiving a flow of working gas 18, a radiation inlet 27 for receiving laser radiation 26, and includes an emission outlet 41 for outputting gas emissions. In accordance with another embodiment, the reaction chamber may further enclose a support onto which the object to be treated may be placed. The position of the support may be adjusted using a positioner. The positioner, for example a simple step motor attached to the support, may be used to position the support dynamically relative to the zone of action so as to expose the different regions of the surface. In accordance with yet another embodiment, the reaction chamber may simply provide an area for the laser plasma formation, and may include a laser plasma outlet which is located at or proximate the zone of action. In such an embodiment, a positioner for positioning the laser plasma outlet dynamically relative to the surface so as to expose different regions of the surface to the laser plasma may be provided.

The system also includes a working gas flow arrangement 29 in fluid communication with the gas inlet 25, including means for flowing the working gas in the zone of action 23. The working gas flow arrangement 29 may include a source of working gas 18 containing a carrier gas and at least one of a chemically active reagent and an alloying element. The source of working gas may include a single source supplying the pre- mixed working gas or multiple sources used to mix together the various constituents of the working gas on-the-go. Thus, there may also be included preparatory means, for sxample a manifold connected to the various constituents of the working gas, for Dreparing the working gas. The working gas flow arrangement may include control Tieans for controlling a flow of the working gas into the gas inlet of the reaction chamber, for example a control valve associated with the source of working gas. The control means may be at the source or anywhere along the supply line.

\lso included, is a laser arrangement 33 for supplying the laser radiation 26 to the radiation inlet 27 and directing the laser radiation 26 on the zone of action 23 to produce with the working gas 18 a laser plasma 16 thereby treating the surface 12 with the laser plasma 16. The laser arrangement may include a laser, such as a CO2 laser or any appropriate laser capable of igniting a plasma. Preferably, the laser radiation has a beam of a predetermined cross-sectional area and the gas inlet, from which the working gas outflows, has a cross-sectional area substantially identical to the cross-sectional area of the laser beam so as to optimize the zone of action. An intensity controller to control the intensity of the laser radiation may also be provided. The laser radiation may be a pulsed periodic laser radiation and the laser arrangement may include a frequency controller, for example for controlling the frequency of the pulsed periodic laser radiation. To better target the surface to treated, the laser arrangement may include elements for redirecting the laser radiation or for focusing the laser radiation or both onto the zone of action. These elements may be optical elements, such as lenses or gratings. (It should be noted that the qualifier "optical" is used to qualify all electromagnetic radiation and is not limited to radiation in the visible portion of the electromagnetic spectrum.)

A control processor operatively connected to the working gas flow arrangement and to the laser arrangement may be used to control the operations of the system.

The present invention may be used to treat one or more surfaces of an object (such as a machine part and/or mechanism, a casing element, a functional and/or bearing metal/alloy structure) to extend the maintenance overhaul period and service life of the object. Useful application of the invention may be found in machining (e.g. tools), construction, the automotive industry (e.g. engines), the agricultural industry (e.g. tractors), the locomotive industry and railway construction (e.g. diesel engine, wheel pair of carriages), ship building and repair, aircraft manufacture and aerospace, the chemical industry, the petroleum industry (e.g. pumps, compressors, pipelines), the defence industry, etc. just to name a few.

The method and/or system may be used for nitriding and/or cementation of the surfaces of irons and steels, for alloying by pure metals or alloys with the formation of oversatu rated solid solutions and the formation of intermetallides, or for alloying by the carbides of refractory metals (TiC, VC, TaC, WC, etc.). In addition, this method and/or system may be used for highly efficient laser-plasma modification of the surfaces of cylinder liners of internal combustion engines with the formation of a very hard nanostructured surface layer having a thickness of tens to hundreds of nanometers and containing ferric carbides and nitrides and the formation of a sublayer having a thickness of up to tens of microns and a mainly martensite structure. The method and/or system may also be used to deposit very hard coatings made from carbonitride compounds of silicon (SiCN) or boron (BCN) by forming a laser plasma in a high-speed working gas flow with the use of reacting components in the form of gases, vapors, micro and/or nanoaerosols and positioning of the surface of an object being treated with respect to the working gas flow.

DETAILED DESCRIPTION OF PREFERRED MODES OF REALIZATIONS

A more detailed description of various features of various preferred embodiments of the present invention follows.

Surface modification via change in physical or chemical structure of surface

The present invention may be used to modify the surface of an object via a change in the physical or chemical structure of the surface.

One application of the invention is in laser hardening of metals through nanostructural modification of metal surfaces, for example cast iron (steel and alloy) surfaces. The technology of the invention supports two regimes of processing. A high surface processing rate (for example, 50 cm²/s to 100 cm²/s) results in the formation of uniform (approximately 20 GPa) nitrogenized superplastic nanostructured iron nitride and iron carbide surface layers of approximately 100 to 200 nm thickness. A low surface processing rate (for example, 10 cm²/s) allows to increase the surface thickness to approximately 500 nm and to form an austenite-martensite sublayer which may be thermal hardened up to 10 GPa.

Advantageously, the method and system of the present invention is cost-efficient, economical and ecological. It reduces the use of lubricating oils and materials and reduces maintenance, e.g. 2.5 to 5.0 times less lubricating oil may be used, and a 90% reduction in wear and tear may be observed.

As compared with traditional laser-thermal hardening with CO₂ lasers, where the effectiveness of radiant energy absorption of the cast irons and steels changes when they are heated from 4-5% to 10-12% (liquid), the laser plasma technology of the present invention permits, in spite of effective nitridation of the surface layer from plasma, and due to the diffusion up to 15% nitrogen, to increase the effectiveness of radiant energy absorption by up to 30%, and, accordingly, to increase the productivity.

In 2004, the German company AUDI introduced a laser technology which uses an UV excimer laser to laser harden the surfaces of engine blocks. However, with the AUDI system, the engine block is rotated around the laser grip portion. With the present invention, it is the laser grip portion, preferably lighter in weight and more compact, that is rotated and not the engine block. This simplifies the design of the equipment and the production line. Preferably, the present invention uses a 5 kW CO₂ laser which may allow for an increase in productivity, for example an increase of three to five times the current productivity may be possible which translates to processing 600 000 to 800 000 engines a year. Advantageously, the system of the present invention is also less expensive than the AUDI system.

Fig. 2A shows an embodiment according to the present invention of system 110 used to carry out the surface treatment method used for modifying external surfaces or internal surfaces of open cavities that have a radius of curvature of preferably no less than 0.1 m.

Radiation 126 of pulsed periodic laser 120 by means of optical system 122 for laser beam transfer and formation is directed to reaction chamber 124 and combined with high-speed working gas flow 118 comprising the carrier gas, alloying elements, and chemically active reagents. In the laser-beam-action zone on the surface, an intensity higher than the threshold intensity must be provided to ignite a near-surface laser plasma 116 (Fig. 4). For instance, for the CO₂ laser, the radiation intensity level - depending on the type of carrier gas (argon, helium, neon, nitrogen, oxygen, etc.), reagents and alloying additions (vapors, aerosols), and on the duration and repetition rate of laser pulses - is typically in the range from 0.1 to 100 MW/cm²; this range can be wider. If we do not consider the details of the physical and physical-chemical mechanisms, the process of formation (180, Fig.4) of modified surface layer 112 can be divided into four main stages. This process will be considered for the main part of the series of pulses (which is after the initial part), where the process is stable and repetitive.

Stage 1 (182, Fig. 4): laser plasma formation. In the first phase of stage 1 , there occurs fast heating of the surface layer at the laser pulse leading edge (112a, Fig. 2B), accompanied by thermal/photoemission of electrons. These electrons, together with those left from the previous laser plasma, initiate avalanching development of an optical discharge. To decrease ablation of layer 112a, this phase should preferably be realized in a short time (less than 50 ns, preferably 10-20 ns). In the second phase, during the action of the laser pulse main part, there occurs formation and development of near- surface laser plasma 116 with its fast heating to a temperature of 10000 °C-20000 ⁰C, ionization and dissociation (if the carrier gas is molecular or the initial chemical reagents are present in the working gas in the form of molecular gases, vapors, etc.), heating, and at least partial melting and evaporation (including ablation) of microparticles of alloying additions if they are in the working gas in the form of aerosols. In the second phase, dense laser plasma practically completely absorbs laser radiation, and the surface is heated mainly by the plasma radiation and heat transfer.

Stage 2 (184, Fig.4): the time of this stage partially coincides with that of the first stage: supersonic (shock-wave) laser plasma expansion takes place, which is accompanied by the heating of additional working gas zones adjacent to the plasma, in particular, their dissociation, ionization, and activation, equalization of the plasma pressure with the ambient gas pressure and overall plasma cooling to a temperature by a factor of 2-3 lower than that of the plasma at the stage of formation.

In stages 1 and 2, there is more intensive heating of the surface to high temperatures (generally, higher than the melting point), as well as saturation of the surface layer (112a) with alloying elements. Conditions for the formation of thermal and diffusion flows (of alloying elements) to the object material are created.

Stage 3 (186, Fig. 4): laser plasma energy is transferred to the object surface (and to microparticles of alloying additions if they are present). This is accompanied by laser plasma cooling and some stabilization of the surface temperature (generally, higher than the melting point). At this stage, intensive plasma-chemical reactions take place. They lead to the formation of highly activated compounds and nuclei of nanoparticles if the initial reagents are in the form of gases or vapors. If there are alloying additions in the form of microparticles, then, at least partial, melting occurs. The products of plasma- chemical reactions and/or (at least partially) melted microparticles of alloying additions are carried by the flow to the object surface synthesizing/forming layer 112a (Fig. 2B). Diffusion and thermal waves propagate in the object material forming zones 112b and 112c (Fig. 2B), respectively.

Stage 4 (188, Fig. 4): cooled, practically completely recombined plasma is blown off by the working gas flow, which brings a "fresh" portion of chemically active and alloying additions. Since the heat is removed deep into the metal, the temperature of the surface being treated decreases, preferably below the melting point, to eliminate the hydrodynamic effects of surface shape distortion, in particular, spitting of the melt by laser plasma pressure from the following radiation pulse.

Final formation of zones 112b and 112c (Fig. 2B) takes place after the completion of a series of laser pulses and phase-structural transformations in the metal of the object. It should be noted that the delineation of zones 112b and 112c is relatively nominal, since they have no clear boundaries. The concentration of diffusing alloying additions (and/or compounds with their participation) as well as their influence on the structure and properties of the material in zone 112b gradually decreases with increasing distance from the surface. The same is true for the zone of thermal phase transformations 112c, which can be absent in some cases.

For effective use of alloying additions and/or chemical reagents, it is preferable to have the cross-section of working gas flow -formed by element 128 of reaction chamber 124 - practically coinciding with the shape of the zone of laser action of laser beam 126b on the object surface. The flow velocity is preferably set to be no more than the product of the repetition rate of laser pulses and the laser plasma size in the flow direction after the completion of stage 2.

For instance, for a CO₂ laser providing a repetition rate of laser pulses in the range from 5 to 100 kHz, the preferable velocity of working gas flow with increasing frequency can be in the range from 10 to 100 m/s.

The above ranges, however, are not obligatory and can be widened. For instance, when using alloying additions in the form of rather large (more than 10-20 μm) microaerosols, preferably, the velocity of working gas flow can be decreased considerably and even severalfold to increase the time of action of laser radiation and plasma.

For an economically effective and highly efficient realization of the laser-plasma method to modify metal surfaces, it is preferable to have laser or laser system 120 with a high repetition rate of laser pulses of more than 5000 Hz (in some cases, this frequency can be lower) having such a power of laser pulses that laser plasma 16 can be formed. For instance, one of successful embodiments used a CO₂ laser with a pulse repetition rate from hundreds of Hz to 100 kHz and a pulsed power of tens and hundreds of kW. Lasers of other types, both gas and solid-state ones, having other power ranges can also be used.

Optical system 122 is designed for the transfer and formation of laser radiation and for directing a part (which is, generally, a negligibly small portion) of radiation to systems of measurement and control of the characteristics of laser radiation 132 and radiation of laser plasma and the temperature of surface 134 being treated. For instance, system 122 can consist of several mirrors, in particular, moving mirrors providing laser beam motion, including those with a reaction chamber moving at the surface of an object being treated. Besides, system 122 serves to provide beam formation in working gas flow 118 on the object surface, as well as for alternating laser beam direction to different reaction chambers if the apparatus has several reaction chambers. In another embodiment of the invention, system to transfer and focus laser radiation 122 can include optical fibers to transfer laser radiation in one or several sections of the optical tract.

In preferable variants of the embodiments consistent with this invention, system 122 contains at least one diffraction mirror to form the zone of laser beam action in the shape preferable for a specific technology (for instance, close to the rectangular or round shape) with an illumination intensity close to a uniform one.

In preferable variants of the embodiments consistent with this invention, system 122 contains one or several semitransparent partially reflecting elements, for instance, optical wedges with plane surfaces through which the laser beam passes, to reflect a part of radiation to systems 132, 134, as well as at least one lens for beam focusing or matching of the optical tract sections. Optical system 122 directs laser radiation to input window 123 of reaction chamber 124, which can be lens-shaped. Convergent laser beam 126b passes inside protective cavity 127 (Fig. 2A). Protective gas 129 (typically, carrier gas) under static pressure exceeding the pressure in flow formation means 128 by only 0.1 kPa -1 kPa is supplied to the cavity. This is done to decrease considerably, and preferably completely eliminate, laser energy absorption by working gas flow 118 in the beam section in front of the plasma and to prevent input window 23 from undesirable action of mixture 118 and plasma, in particular, ablation products.

The construction of reaction chamber 124, besides window 123 for laser beam input, can have windows to diagnose laser plasma 16 and obtained coating 112, for instance, for video control or optical pyrometry.

The laser radiation may have a beam of a predetermined cross-sectional area and the gas inlet may have a cross-sectional area substantially identical to the cross-sectional area of the laser beam so as to optimize the zone of action. To form a cross-section of working gas flow 118 close to the size of laser plasma 116, the shape of the outlet hole or nozzle of the means to form working gas flow 128 of reaction chamber 124 should be made similar to that of the zone of action of the laser beam.

The casing of reaction chamber 124 and heat-intensive elements of construction 127, 128, some parts of means 117 and systems 122 and others can be force-cooled by water or another cooling agent.

System to prepare chemical reagents 140 can consist of one or several subsystems (which are not shown) with different variants of realization and different kinds of reagents (gases, vapors, aerosols).

For instance, in one embodiment of the present invention, to supply reagents in the form of hexamethyl disilazan vapors, evaporation takes place in the medium of the carrier gas which is supplied through control valve 138 from the main line of gas 142, and the flow rate and concentration of the addition are regulated by the temperature of the evaporator and the flow rate of the carrier gas through control valve 138. In one of other successful embodiments, to supply chemical reagents in the form of microaerosols of carbon and SJsN₄, regulated dosing units of micropowders with the formation of a suspension with the carrier gas are used.

The temperature of the object being treated, as well as other parameters of the process, affect considerably the diffusion rate of alloying elements, the structure, phase composition, and properties of near-surface zones 112b and 112c being formed. For instance, to increase the martensite structural component at the treatment of high- carbon steels and irons, additional cooling of the object is desirable. Therefore, it is reasonable to locate object 114 being treated on special means, such as support tables, etc., which have a good thermal contact with means 115 providing the functions of a thermostat - heating or cooling - that is, maintaining the temperature of the object within the given limits controlled by processor 130.

Control processor 130, which receives and processes signals from measurement systems 132, 134, and others, as well as means 115, 117 through execution units and mechanisms (which are not shown) controls the operation of laser 120, means 115, 117, means 140, 154, and others, control valves 136, 137, 138 (and, possibly, some others) and provides the process realization in accordance with the stages shown in Fig. 4.

Unit/units of means 117 provide the positioning and/or relative motion of an object being treated and, hence, the zone of action of laser plasma on the surface of the object, which can be translational, rotational, or combined.

A more detailed description of a method according to the present invention that is used to treat a surface, and whose main stages are shown in Fig. 4, follows. IB2000/005213

28

>bjects whose surface is to be treated by means of this method can include parts of arious geometrical shapes consisting of metals or alloys.

i some cases, the surface of object being treated is prepared (170, Fig.4) mechanically turning, milling, sand-blasting, honing, grinding, etc.) for treatment. In other cases, the surface is prepared chemically, with the use of cleaners and/or chemical means, in (articular, with ultrasonic and other devices; the preparation can be combined. It should >e noted that in many cases, preliminary treatment of the surface is not needed >ecause laser plasma together with laser radiation have a strong cleaning action on the surface of the object being treated. In some cases, the installation and fixing of object 114 being treated must provide a good (with a small temperature difference) thermal contact with thermostat 115. In some other cases, when the heat transferred to the object being treated in the process of laser-plasma treatment heats the object surface to a temperature in some given optimal ranges, the thermal contact can be poor or the aperation of thermostat 115 is not required.

In some cases, the preparation of the reaction chamber (172, Fig. 4), besides evident prophylactic cleanings or cleanings when the composition of alloying additions and initial reagents is changed (Fig. 2A₁ 2B), consists in the blowing of a carrier gas through the reaction chamber volume, and repeated (3-10 times) replacement of the initial air by the carrier gas is preferable.

The onset of laser-plasma process 174 (Fig. 4) is the ignition and sustaining for some (short) time of laser plasma 116 in the carrier gas flow (typically, without alloying additions and chemical reagents) for cleaning, activation, and setting of some preferable temperature of the surface of the object being treated.

The supply of mixture of alloying additions and/or initial chemical reagents and the formation of working gas flow (176, Fig.4) take place practically simultaneously after the completion of the laser-plasma process of surface preparation of object 174 and continue until the entire process of the object surface modification is completed.

Various chemical elements and compounds in different aggregate states can be used as components of the mixtures of alloying additions and initial reagents.

For instance, in some successful embodiments of the invention, it is sufficient to use gaseous nitrogen (N₂) without other additions to modify (nitride) an iron surface.

The laser-plasma modification of surface 180 (including stages 182, 184, 186, and 188 described above) may be performed practically simultaneously (with a time shift needed to modify the initial zone) with relative move 190 of the surface of the object being treated and the zone of action of laser plasma flow. The laser plasma process is repeated (192, Fig. 4) to treat the desired areas of the surface.

In some other cases when one needs to obtain a modification zone of the surface of an object whose size is smaller than that of the laser plasma action zone, aperture masks (which are not shown) with holes/slots of needed shapes are used. They are placed on the surface of the object and limit the object treatment zone.

On completion of some specified process of surface modification, the supply of chemical reagents is terminated, and the laser beam can be shuttered or directed to other reaction chamber 194 if the laser-plasma modification apparatus has several reaction chambers.

In some cases, it is the object 196 being treated that is changed, removed from the chamber after spending a sufficient amount of time in an inert atmosphere (for example, in the carrier gas medium) to make certain the temperature of the treated surface of the object has dropped below a certain prescribed temperature; if the surface of the object is not cooled sufficiently prior to removing the object from the inert atmosphere, there can be an undesirable reaction of the treated surface with the air when exposed to the air, for example unwanted oxidation.

In comparison to embodiment 110 of the apparatus (Fig. 2A), embodiment 150 (Fig. 3) is designed for realizing the method of modifying internal cylindrical surfaces with the possibility of rotation of the reaction chamber to treat cumbersome objects (for instance, cylinder blocks of internal combustion engines) or when the diameter of the cylinder treated is not more than ~0.2 m.

The casing of reaction chamber 124 is placed into casing 156 fixed on platform 152 which can move by means 117. Rotating means 154, which can also be placed on platform 152, makes it possible, with the use of control means 130 (not shown in Fig. 3) to rotate the reaction chamber about the axis of the cylindrical casing. Casing 156 also serves as a collector to supply gases (carrier gas and/or working gas) to the reaction chamber by means of internal circular grooves 158 and holes (at least one hole) 159. If necessary, at least one groove, 158, can be used to cool the reaction chamber casing by water or another cooling agent. Sliding seals 160 (for instance, made from graphitized fluoroplastic) can be used to pressurize, divide the volumes of grooves 158, and provide the sliding of the cylindrical casing of reaction chamber 124 in casing 156. Mirror 164 is used to direct laser beam 126b through flow formation means 128 of working gas 118 to the surface of object 114 being treated to form laser plasma 116. If it is necessary to separate the flows of carrier gas and working gas, working gas can be supplied by means 162 from circular groove 158 in casing 156 to similar groove 158 and through holes 159 in flow formation means 128. Means 128 for forming the working gas flow can be cooled similarly. To keep a small (~ 0.1-0.3 mm) almost constant gap between the treated surface of object 114 and end 165 of means 128 directed to the surface being treated, means 128 can slide in the axial direction in the casing of reaction chamber 124. Spring 166 is used to stabilize the gap; it compensates the vector sum of the centrifugal force and the force resulting from the pressure difference in chamber 124 and in the gap with allowance for the Bernoulli effect. The construction of element 146 of the reaction chamber must provide a small gap with the surface of object 114 being treated for the flow of exhaust gas 148 to prevent the entering of atmospheric air to surface modification zone 112.

The positioning and relative motion of the zone of action of the laser plasma flow and the surface of object 114 can be realized by moving both the object being treated and the reaction chamber or by a combination of these motions.

Surface modification via synthesis and deposition of a coating

The present invention may also be used to modify the surface of an object via synthesis and deposition of a coating onto the surface of an object undergoing treatment.

Fields of application of the technology of the present invention requiring superhard coatings on surfaces include: tools used in high-speed metals processing, strengthening of measuring, cutting and deforming tools, tube rolling (processing of the tubes used for the transportation of petroleum and gas), strengthening of rollers and axis of rotation in strained components (without the use of oil lead-ins in vacuum and chemical equipment), biomedical materials, percussion resistance e.g. armour, shipbuilding (ship steel), machine building, strengthening of carcasses e.g. building carcasses, and friction (tribological) resistance e.g. in precision machining.

Loading conditions, the form of the contact components, the coating thickness, the physical-mechanical characteristics of the substrate material and coating are all key to ensuring a dependable and reliable frictional resistant component, and more particularly a dependable and reliable frictional resistant coating.

With the present method and system, coating (film) deposition rates of 2 to 3 μm/min and coating (film) deposition onto plane and subcurved surfaces of 300000 m²/year are possible. This technology is of beneficial interest to the armour steel production industry and to the railway industry, the latter being interested in the production of a minimum of 50 000 strengthened wheel pairs. The present method and system allows for real-time spatial-temporal diagnostics during processing and hence quality control of the final product.

Directed synthesis of superhard (≥ 80 GPa) composites with nanostructural topology having the assigned/desired frictional properties is possible using the plasma laser technology of the present invention. Advantageously, coatings may include amorphous and monocrystalline "diamond-like" carbon nanostructured coatings based on diamond- like nanotube and fullerene structures. The material of these coatings are characterized not only by their unique dimension factor but also by enhanced physical-chemical, strength and frictional properties, many exhibiting a combination of such unique properties as superhardness at high resistance, low electron work function, radiation and corrosive resistance, low constant of friction, and good compatibility with habitable tissue. The hardness (H) is not the additive sum of the constituents, but increases with decreasing nanocrystal size according to low of Kholl-Petch: H(d)= H₀ + Kd^"1/2, where d is the specific size of the crystal.

The present laser-plasma technology may also be used to obtain thick (0.5-2.0 mm and greater) two-layer coatings consisting of a sublayer of superhard alloyed steels and a top surface layer (50-200 μm) on the base of the superhard SiCN, BCN or carbonic (down to diamond-like polycrystalline) nanocomposite, for use for example in the production of instruments and reconstruction of out of order components.

Existing methods for producing superhard nanocomposite coatings on various substrates include: magnetron sputtering, high-frequency plasma, plasma of glow discharge, and vacuum electric arc sputtering. To obtain the nanocomposite material, it is necessary to precisely control the grain structure and dimensions. The above- mentioned existing methods are performed in reaction chambers under low pressure (10^"1-10^"5 Torr) and are characterized by their low deposition rate (1-2 μm/hour), and consequently are not quite suitable for obtaining thick (several microns) coatings. The main complexities regarding obtaining nanocomposite coatings with existing technologies include: low deposition rates, use of high vacuum reaction chambers, and difficulties coating surfaces of complex configuration.

The technology of the present invention does not experience these problems and may be adapted for industrial-scale use. The coating synthesis and deposition may be carried out at low pressure (P > 1 atm) and does not require expensive vacuum systems, and the film deposition on voluminous structures with complex surface geometries may be carried using program-controlled manipulators. Because the present method and system does not require vacuum conditions, high deposition rates, of up to 100 - 1000 times the rates of existing methods, are possible. Advantageously, the present method and system uses easily accessible precursors: gases, liquid, aerosols. By controlling the flow rate and the laser radiation, the coating characteristics may be controlled. Directional synthesis of the nanomaterials may be done using low cost precursors, precursors comprising the stoichiometric mixtures of the aerosols and refractories needed. However, one of the main advantages of this laser-plasma method and system is the high rate of plasma cooling (10 GK/s), which allows homogenous nucleation, decreased particle size, suppression of particle coalescence, obtaining not only nanoparticles but also nanoclusters. This laser-plasma method and system also provides the high level of activation of the deposited nanoclusters and of the substrate surface via the intrinsic plasma radiation. This results in the intensification of the heterogeneous processes through the active migration of the nanoclusters on the surface, in the transition from the 3-dimensional to the 2-dimensional mechanism of the coating formation; it is the required coating condition for uniform coating formation with good adhesion to surface.

Fig. 5 shows an embodiment of surface modification system 210 used to synthesize very hard coatings 212 on the surface of object 214 being treated by activating initial reagents in laser plasma 216 when the working gas flow is transverse with respect to laser radiation. Radiation 226 of pulsed-periodic laser 220 by optical system 222 for laser beam transfer and focusing is directed to work chamber 224 and focused in high-speed working gas flow 218 consisting of the carrier gas and chemically active reagents. In the zone of maximum laser beam focusing, intensity higher than the threshold intensity to ignite laser plasma 216 (274, 280, Fig. 7) must be provided. For instance, for the CO₂ laser the threshold radiation intensity level depending on the kind of gas carrier (argon, helium, neon, nitrogen, oxygen, etc.) and reagents (vapors, aerosols) is typically in the range from 1 to 1000 MW/cm²; this range can be wider. If we do not consider the details of the physical and physical-chemical mechanisms, the synthesis process (280, Fig. 7) of coating 212 can be divided into four main stages.

Stage 1 (282, Fig. 7): during the irradiation of working gas flow 218 by laser pulse, there occurs formation of laser plasma 16 with its fast heating to a temperature of 15000-25000 ⁰C, ionization and dissociation (if the carrier gas is molecular or the initial chemical reagents are present in the work 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, with subsequent dissociation and ionization.

Stage 2 (284, Fig. 7): the time of this stage partially coincides with that of the first stage: supersonic (shock-wave) laser plasma expansion takes place. It is accompanied by the heating of additional working gas zones adjacent to the plasma, in particular, their dissociation, ionization, and activation, equalization of the plasma pressure with the ambient gas pressure and overall plasma cooling to a temperature by a factor of 2-3 lower than that of the plasma at the stage of formation. The cooling rate at this stage can be as much as 10 G°K/s and more.

Stage 3 (286, Fig. 7): the laser plasma cools further due to turbulent mixing with the ambient gas, radiation heat transfer, and convective carryover to the object surface. At this stage there are intensive plasma-chemical reactions, which lead to the formation of highly activated compounds and nuclei of nanoparticles, including nanoclusters, nanocrystrallites, etc., as shown in (219, Fig. 5).

Stage 4 (288, Fig. 7): heterogeneous synthesis of coating 212 on the surface of object 214 being treated takes place. The activated nanoparticles formed in the plasma and brought by the work gas flow are the nuclei of nanocrystralline "granules" in the volume of the amorphous matrix synthesized from activated atoms and compounds, in particular, nanoclusters.

By choosing the repetition rate f and the energy of laser pulses E, as well as the velocity V and mass flow rate m of work gas flow 218, one can provide almost complete or, in some cases, complete conversion of the working gas into at least partially ionized plasma with activated initial reagents. In this case, the cross-section geometry of working gas flow 218 by means of element 228 of reaction chamber 224 is made close to the size of laser plasma after the completion of stage 2, and preferable flow velocity V is set to be no more than the product of the repetition rate f of laser pulses and the laser plasma size in the flow direction after the completion of stage 2.

For instance, for the CO₂ laser providing fin the range from 5 to 100 kHz and energy E in the range from 0.5 to 0.05 J, the preferable velocity of working gas flow with increasing frequency f can be in the range from 30 to 300 m/s for the case when laser radiation is directed transverse to the working gas flow (Fig. 5) and in the range from 100 to 1000 m/s for the case when laser radiation is directed along the working gas flow (Fig. 6).

The above ranges, however, are not obligatory and can be widened. For instance, at the use of initial reagents in the form of microaerosols, preferably velocity V of working gas flow can be decreased considerably and even severalfold to increase the time of action of laser radiation and plasma. For an economically effective and high-efficiency realization of the laser-plasma method to synthesize coatings, it is preferable to use laser or laser system 220 with a high repetition rate of laser pulses of more than 1000 Hz (in some cases, this frequency can be lower) having such a power of laser pulses that laser plasma 216 can be formed in the focus of beam 226. For instance, one of successful embodiments used a CO₂ laser with a pulse repetition rate from hundreds of Hz to 100 kHz and pulsed power of tens and hundreds of kW. Lasers of other types, both gas and solid-state ones, having other power ranges can also be used.

Optical system 222 is designed for the transfer and focusing of laser radiation and for directing a part (which is typically negligible) of radiation to systems to measure and control the characteristics of laser radiation (232, 233) and laser plasma radiation (234). For instance, system 222 can consist of several mirrors, in particular, moving mirrors providing laser beam motion, and the reaction chamber can move near the surface of an object being treated. The mirrors of system 222 can also provide beam focusing in working gas flow 218 in reaction chamber 224. The system is also designed for alternating laser beam direction to different reaction chambers if the apparatus has several reaction chambers. In another embodiment of the invention, system to transfer and focus laser radiation 222 can include optical fibers to transfer laser radiation in one or several sections of the optical tract.

In preferable variants of embodiment, system 222 contains one or several semitransparent partially reflecting elements, for instance, optical wedges with plane surfaces through which the laser beam passes, to reflect a part of radiation to systems 232, 234, as well as at least one lens for beam focusing or matching of the optical tract sections.

Optical system 222 directs laser radiation to input window 223 of reaction chamber 224, which can be lens-shaped. Focused laser beam 226b passes inside protective cavity 227. Protective gas 229 (as a rule, carrier gas) under a pressure somewhat exceeding, by of 0.01-10 kPa, the pressure in reaction chamber 224 is supplied to the cavity. This is done to decrease considerably, up to complete elimination, laser energy absorption by working gas flow 218 in the beam section in front of the plasma, and to prevent input window 223 from undesirable action of mixture 218 and plasma, in particular, ablation products.

Laser radiation 226c passing through the working gas flow is directed through window 225 to measurement and control system 233.

In some variants of the embodiment of system 210 (Fig. 5), a cooled absorber, for instance, a calorimeter, can be placed instead of window 225 or system 233. In some other variants of the embodiment of system 2100 (Fig. 6), window 225 and system 233 are absent.

Reaction chamber 224 can be pressurized, as shown for some embodiments of system 210 (Fig. 5), and have an open gas outlet, as shown for some embodiments of system 2100 (Fig. 6).

The construction of reaction chamber 224, besides window 223 for laser beam input, can have windows to diagnose the laser beam, laser plasma 216 and obtained coating 212, for instance, for video control or optical pyrometry.

To form a cross-section of working gas flow 218 close to the size of laser plasma 216, after the completion of stage 2 of the method (284 in Fig. 7), the outlet hole or nozzle of the means to form working gas flow 228 of reaction chamber 224 can be slit-like and extended, with a large wall oriented along the laser beam, for embodiments consistent with this invention in which the laser beam is transverse to the working gas flow (Fig. 5). The hole can also be fairly round for variants with longitudinal location of the laser beam (Fig. 6). The casing of reaction chamber 224 and heat-intensive elements of construction 227, 228, 217 and others can be force-cooled by water or another cooling agent.

The system 240 to prepare chemical reagents can consist of one or several subsystems (which are not shown) with different variants of realization and different kinds of reagents (gases, vapors, aerosols).

For instance, in one embodiment of the apparatus consistent with this invention, to supply reagents in the form of hexamethyl disilazan vapors, evaporation takes place in the medium of the carrier gas, which is supplied through control valve 238 from the main line of gas 242, and the flow rate and concentration of the addition are regulated by the temperature of the evaporator and the flow rate of the carrier gas through control valve 238. In another successful embodiment consistent with this invention, to supply chemical reagents in the form of micro and/or nanoaerosols of carbon and SJsN₄, regulated dosing units of micro- or nanopowders with the formation of a suspension with the carrier gas are used.

The temperature of the surface of an object being treated, as well as other parameters of the process, affects considerably the growth rate, structure, morphology, as well as the properties of synthesized coatings. Therefore, it is reasonable to locate object 214 being treated on special means, such as support tables, etc., which have a good thermal contact with means 215 providing the functions of a thermostat - heating or cooling - that is, maintaining the temperature of the object within the given limits controlled by processor 230.

Control processor 230 - which receives and processes signals from measurement systems 232, 233, 234, and others, as well as means 215, 217 through execution units and mechanisms (which are not shown) - controls the operation of laser 220, means 215, 217, and controlled valves 235, 236, 237, 238 (and, possibly, some others) and provides the process realization in accordance with the stages shown in Fig. 7. Means 217 provides the positioning and/or relative motion of an object being treated and, hence, the zone of action of the laser plasma flow on the surface of the object, which can be translational, rotational, or combined.

A more detailed description of a method according to the invention that is used to synthesize and deposit coatings, and whose main stages are shown in Fig. 7, follows.

Objects that can be coated by this method can include parts of various geometrical shapes consisting of metals or alloys, as well as non-metals (for instance, ceramics, crystals, etc.), in particular, parts made of a combination of metal and non-metal parts.

In some cases, the surface of an object is prepared (270, Fig. 7) mechanically (turning, milling, sand-blasting, grinding, etc.) for the application of a coating. In other cases, it is prepared chemically, with the use of cleaners and/or chemical means, in particular, with ultrasonic and other devices; the preparation can be combined. It is important that in many cases preliminary treatment of the surface is not needed, because laser plasma together with laser radiation, as shown in Fig. 6, have a strong cleaning action of the surface of the object being treated. In some cases, the installation and fixing of object 214 must provide a good (with a small temperature difference) thermal contact with thermostat 215. In some other cases, when the heat transferred to the object being treated in the process of laser-plasma synthesis heats the surface of the object to a temperature in some given optimal ranges, the thermal contact may be poor or the operation of thermostat 215 is not required.

In some cases, the preparation of reaction chamber (272, Fig.7), besides evident prophylactic cleanings or cleanings when the composition of reacting admixtures is changed (Fig. 5), consists in its pressurizing (controlled valves 236, 237, 238, as well as some others, which are not shown, are closed) and air evacuation from its inner volume through controlled valve 235, with subsequent injection of the carrier gas to the chamber. In some other cases, the carrier gas is blown through the reaction chamber volume, and multiple (3-10 times) replacement of the initial air by the carrier gas is preferable.

The onset of laser-plasma process 274 is the ignition and sustaining for some time of laser plasma 216 in the carrier gas flow (as a rule, without chemical reagents) for cleaning, activation, and setting of some preferable temperature of the surface of an object being treated.

The supply of mixture of initial chemical reagents and the formation of working gas flow 276 take place practically simultaneously after the completion of the laser-plasma process of surface preparation of object 274 and continue until the entire process of coating synthesis is completed.

Various chemical elements and compounds in different aggregate states can be used as components of the mixtures of initial reagents.

For instance, in some successful embodiments of this method to synthesize SiCN coatings, vapors of hexamethyl disilazan SiNH(CHa)₆ or a mixture of carbon and SJaN₄ micropowders are used.

Besides, this method can employ the following types of volatile organic silicon, organic boron, and complex volatile compounds as the initial reacting substances for obtaining silicon and boron carbonitrides, high-melting simple and complex metal oxides. These are the silyl derivatives of nonsymmetric dimethylhydrazine (Me2SiHNHNMe2, Me₂Si(NHNMe₂)_{2 ,} where Me is the methyl group (CH₃)), silasan bromide (Si₂NBr(IvIe)₆), B₃N₃H₆₁ (Me)₃N-BH₃, beta-diketonate metal complexes, etc.

Referring to Fig. 7, the laser-plasma synthesis of coating 280 (including stages 282, 284, 286, and 288 described above) is performed practically simultaneously (with a time shift needed to apply the initial zone of the coating) with relative move 290 of the surface of the object being treated and the zone of action of the laser plasma flow. The laser plasma process is repeated (292, Fig. 7) to treat the desired areas of the surface.

In some other cases when one needs to obtain a coating zone whose size is smaller than that of the laser plasma action zone (coating synthesis zone), aperture masks (which are not shown) with holes/slots of needed shapes are used. They are placed on the surface of the object and limit the object coating zone.

On completion of some specified process of coating synthesis, the supply of chemical reagents is terminated, and the laser beam can be shuttered or directed to other reaction chamber 294 if the laser-plasma synthesis apparatus has several reaction chambers.

In some cases, object being treated is changed 296 after spending a sufficient amount of time in an inert atmosphere (for example, in the carrier gas medium) to make certain the temperature of the treated surface of the object has dropped below a certain prescribed temperature; if the surface of the object is not cooled sufficiently prior to removing the object from the inert atmosphere, there can be an undesirable reaction of the treated surface with the air when exposed to the air.

In comparison to embodiment 210 of the system shown in Fig. 5, in embodiment 2100 shown in Fig. 6, focusing laser beam 226b propagates mainly along the working gas flow. The zone of laser plasma action on the surface of object 214 being treated can partially overlap with the zone of action of laser beam part 226c, in which additional heating and activation of the surface of synthesized coating 212 takes place.

Object 214 being treated can be in both the pressurized volume of reaction chamber 224, as shown in Fig. 5, and outside it, as shown in Fig. 6. In this case, the construction of element 2102 of the reaction chamber must provide a small gap with the surface of object 214 being treated for exhaust gas flow 2104 to prevent the entering of atmospheric air to the zone of plasma-chemical reactions and synthesis of coating 212.

Means 215 and 217 or their elements can be located in both the pressurized volume of reaction chamber 224 and outside it. The positioning and relative motion of the zone of action of laser plasma flow and the surface of object 214 can be realized both by the motion of the object being treated and by the motion of the reaction chamber or a combination of these motions.

Test Samples

An analysis of thin film test samples prepared according to the invention was conducted and the results are presented hereinbelow with reference to Figs. 8 to 14.

Sample Analysis Report

A Hysitron Tribolndenter® nanomechanical test instrument was successful in performing measurements of the mechanical properties of eleven ceramic coatings on silicon substrates.

Twelve indents were performed on each of 11 samples labelled 2421/1 , 2421/2 and 1 to 9.

Samples 2421/1 , 2421/2, and 1 to 4 consisted of SiCN films of varying thickness on silicon substrates. Samples 5 to 9 consisted of BCN films of varying thickness on silicon substrates.

Sample 5 showed the highest hardness and highest reduced modulus. Sample 3 showed the lowest hardness and lowest reduced modulus. Roughness measurements were taken using Hysitron's in-sitυ imaging capabilities. Sample 2421/1 showed the highest surface roughness. Sample 140 showed the lowest surface roughness. Experiments

Tests for the sample were performed on a Hysitron Tribolndenter®, which is a high- resolution nanomechanical test instrument that performs nanoscale indents by applying a force to an indenter tip while measuring tip displacement into the sample. During indentation, the applied load force and tip displacement are continually measured, creating a load-displacement curve for each indent.

Twelve indents were performed on each of 11 samples labelled 2421/1 , 2421/2, and 1 to 9. Samples 2421/1 , 2421/2, and 1 to 4 consisted of SiCN films of varying thickness on silicon substrates. Samples 5 to 9 consisted of BCN films of varying thickness on silicon substrates. Indents were performed on each of the samples using a diamond Berkovich indenter probe. The load function for all indents consisted of a five second linear loading segment to a peak load, followed by a two second hold segment at the peak load, and finally a five second linear unloading segment. Peak loads were selected for each sample to yield a contact depth of approximately 10% of the film thickness.

In Scanning Probe Microscopy mode, the Tribolndenter® can provide in-situ images of the sample before and after indentation. Such imaging is accomplished quickly and easily by utilizing the same tip for imaging as indentation. Images of the tested surface can be generated immediately before and after the indentation or scratch when the instrument is operated in scanning probe microscopy mode. These images provide useful information about sample tests and surface morphologies of the sample. Color changes, as indicated by the scale bar, can show the roughness of the sample surfaces. Finally, because the images are created in-situ, scanned with the same tip as the indenter tip, the combination of the imaging and indenting/scratching capability is very powerful in positioning the tip and investigating the interested features. Roughness measurements were taken of selected bond pads to measure surface roughness, (mages were taken at 10 μm to show the total roughness of the samples.

Results

Table 1 lists the film thickness and indentation load used for each sample.

Table 1

Sample Film Thickness (nm) Indentation Load (μN)

2421/1 900 4000

2421/2 900 4000

1 806 3000

2 718 2500

3 1900 14000

4 1780 14000

5 1374 13000

6 1487 9000

7 1415 10000

8 1124 7500

9 1200 11000

Table 2 lists the results of the indentation tests performed on each sample. Including hardness, reduced modulus, and contact depth with standard deviations. Sample 5 showed the highest hardness and highest reduced modulus. Sample 3 showed the lowest hardness and lowest reduced modulus. Table 2

Sample Hardness (GPa) Reduced Modulus (GPa) Contact Depth (nm)

2421/1 16.91 +/- 0.33 44.6 +/- 2.6 86.0 +/- 0.9

2421/2 16.85+/- 0.56 142.4 +/-2.6 86.2+/- 1.5

1 15.68+/- 0.68 138.2 +/-2.6 76.4+/- 1.8

2 17.43+/- 0.41 154.1 +/- 1.8 64.9 +/- 0.9

3 13.40+/- 0.18 114.0+/- 1.0 192.8+/- 1.4

4 16.58+/- 0.29 139.6+/- 1.2 172.1 +/- 1.6

5 25.86+/- 0.62 215.6 +/-2.4 130.2+/- 1.7

6 14.50+/- 0.33 130.6+/- 1.9 145.9+/- 1.8

7 18.18+/- 0.53 156.6+/- 3.0 136.7+/- 2.1

8 19.53+/-0.38 173.1 +/- 2.1 112.4 +/-1.2

9 25.36+/- 1.13 214.5 +/-4.7 120.2 +/-2.9

Table 3 shows the RMS roughness and average roughness from each of the samples. Sample 2421/1 showed the highest surface roughness. Sample 1 showed the lowest surface roughness.

Table 3. RMS and average roughness of each sample

Sample RMS Roughness (nm) Average Roughness (nm)

2421/1 18.89 8.61

2421/2 12.58 6.91

1 0.84 0.64

2 2.06 0.88

3 1.30 0.97

4 1.20 0.93

5 1.08 0.86

6 1.64 1.27 7 1.74 1.37

8 1.42 1.11

9 0.93 0.74

Fig. 8 shows the hardness and reduced modulus of each SiCN sample.

Fig. 9 shows the load versus displacement curves from each indent on the SiCN samples.

Fig. 10 shows topographical in-situ images of selected indents on each of the SiCN samples.

Fig. 11 shows the hardness and reduced modulus of each of the BCN samples.

Fig. 12 shows the load versus displacement curves from each of the indents performed on the BCN samples.

Fig. 13 shows topographical in-situ images of selected indents on each of the BCN samples.

Fig. 14 shows topographical surface images from each sample.

Although illustrative embodiments of the preset invention have been described herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to those embodiments and that various other changes and modifications may be affected therein by one skilled in the art without departing from the scope of the invention.

Claims

1. A method for treating a surface of an object, the method comprising the steps of:

(a) providing a working gas;

(d) exposing the surface to the laser plasma and thereby treating the surface.

2. The method according to claim 1 , wherein in step (a) the working gas contains a carrier gas and at least one of a chemically active reagent and an alloying element and in step (c) the directing laser radiation onto the working gas produces a laser plasma containing activated products, and wherein therefore in step (d) the surface is exposed to the laser plasma containing activated products.

3. The method according to claim 2, wherein the activated products comprise chemically active compounds, nanoparticles, or alloying additions, or any combination thereof.

4. The method according to claim 2, wherein the chemically active reagent or the alloying element is in the form of a powder, liquid, gas, vapor, micro-aerosol or nano- aerosol, nanoparticle, or any combination thereof.

5. The method according to any one of claims 1 to 4, wherein the working gas is kept at or near atmospheric pressure.

6. The method according to any one of claims 1 to 5, wherein the working gas flows at a rate of about 10 to 1000 m/s.

7. The method according to any one of claims 1 to 6, wherein, in step c), the laser radiation is directed transverse the flow of working gas and the working gas flows at a rate of about 30 to 300 m/s.

8. The method according to any one of claims 1 to 7, wherein, in step c), the laser radiation is directed along the flow of working gas and the working gas flows at a rate of about 100 to 1000 m/s.

9. The method according to any one of claims 1 to 8, wherein the laser radiation has an intensity of about 0.1 to 1000 MW/cm².

10. The method according to any one of claims 1 to 9, wherein the laser radiation is a pulsed periodic laser radiation with a frequency of about 5 to 100 kHz.

11. The method according to any one of claims 1 to 10, wherein the laser radiation is provided by a CO₂ laser.

12. The method according to any one of claims 1 to 11 , wherein said exposing the surface to the laser plasma further comprises heating the surface.

13. The method according to any one of claims 1 to 12, wherein said treating the surface of the object comprises a chemical or physical reaction of the activated products with the surface.

14. The method according to any one of claim 1 to 13, wherein said treating the surface of the object comprises depositing a coating on the surface.

15. The method according to claim 14, wherein the coating is a nanostructured protective coating.

16. The method according to any one of claims 1 to 15, wherein said surface has a given microstructure and wherein said treating the surface of the object comprises thermally transforming the microstructure of the surface.

17. The method according to claim 16, wherein the thermally transforming the surface comprises hardening of the surface by diffusion of alloying of elements.

18. A system for treating a surface of an object, the system comprising:

(a) a reaction chamber with a zone of action, the zone of action being devised to be positioned at or proximate the surface to be treated, the reaction chamber comprising

(i) a gas inlet for receiving a flow of working gas; (ii) a radiation inlet for receiving laser radiation; and (iii) an emission outlet for outputting gas emissions;

(c) a laser arrangement for supplying the laser radiation to the radiation inlet and directing the laser radiation on the zone of action to produce with the working gas a laser plasma thereby treating the surface with the laser plasma.

19. The system according to claim 18, wherein the working gas contains a carrier gas and at least one of a chemically active reagent and an alloying element, and thus the laser plasma contains activated products for treating the surface.

20. The system according to claim 18, wherein the working gas flow arrangement comprising control means for controlling a flow of the working gas.

21. The system according to claim 18, wherein the laser arrangement comprises an intensity controller to control the intensity of the laser radiation.

22. The system according to claim 18, wherein the laser arrangement comprises a frequency controller to control the frequency of the laser radiation.

23. The system according to claim 18, wherein the laser radiation is a pulsed periodic laser radiation.

24. The system according to claim 18, wherein the laser arrangement comprises a CO₂ laser.

25. The system according to claim 18, wherein the reaction chamber encloses a support for the object to be treated.

26. The system according to claim 25, comprising a positioner to position the support dynamically relative to the zone of action so as to expose different regions of the surface.

27. The system according to claim 18, wherein the reaction chamber has a laser plasma outlet located at or proximate the zone of action.

28. The system according to claim 27, comprising a positioner to position the laser plasma outlet dynamically relative to the surface so as to exposed different regions of the surface.

29. The system according to claim 18, wherein the laser radiation has a beam of a predetermined cross-sectional area and the gas inlet has a cross-sectional area substantially identical to the cross-sectional area of the laser beam so as to optimize the zone of action.

30. The system according to claim 18, wherein the working gas flow arrangement comprises preparatory means for preparing the working gas. 5213

51

Y\. The system according to claim 18, comprising a control processor operatively .onnected to the working gas flow arrangement and to the laser arrangement to control Dperations of the system.