WO2009155702A1

WO2009155702A1 - Low-temperature oxy-fuel spray system and method for depositing layers using same

Info

Publication number: WO2009155702A1
Application number: PCT/CA2009/000879
Authority: WO
Inventors: Sanjeev Chandra; Valerian Pershin; Javad Mostaghimi-Tehranii; Libing Jia
Original assignee: Sanjeev Chandra; Valerian Pershin; Javad Mostaghimi-Tehranii; Libing Jia
Priority date: 2008-06-25
Filing date: 2009-06-25
Publication date: 2009-12-30

Abstract

The present invention provides a low temperature oxy-fuel thermal spray torch which operates at relatively low gas temperatures, 800K to 2500K. The torch includes a combustion chamber, a mixing region, a Laval nozzle, and a cylindrical barrel. Gaseous fuel and oxygen are continuously fed into the combustion chamber wherein heat is released. Downstream, large amounts of cold nitrogen are radially injected to regulate temperature. After being forced through the nozzle, the jet travels supersonically down the barrel and out of the spray torch. The unique design of this thermal spray system allows the gas temperature to vary within a much wider range than conventional high-velocity oxygen-fuel systems, so particles being sprayed can maintain high velocity while their temperature are manipulated. With this high velocity, low temperature, thermal spray torch, dense and less oxidized coatings can be applied for a variety of materials including metals, alloys, polymers and cermets.

Description

LOW-TEMPERATURE OXY-FUEL SPRAY SYSTEM AND METHOD FOR DEPOSITING LAYERS USING SAME

CROSS REFERENCE TO RELATED APPLICATION

This patent application relates to, and claims the priority benefit from,

United States Provisional Patent Application Serial No. 61/075,592 filed on 25 June 2008 entitled LOW-TEMPERATURE OXY-FUEL SPRAY SYSTEM AND METHOD FOR DEPOSITING LAYERS USING SAME and which is incorporated herein in its entirety.

FIELD OF THE INVENTION

The present invention relates to a low-temperature oxy-fuel spray system for spray deposition of coatings.

BACKGROUND OF THE INVENTION

The present invention is directed to a thermal spray apparatus for deposition of coatings. Thermal spraying involves the spraying of molten powder or wire feedstock onto a target surface to form a protective coating. This technique is widely used to protect articles from wear, corrosion, or high temperature.

In terms of coating density and bonding strength, the high-velocity oxygen-fuel (HVOF) spray (as described in US Patents Nos. 4,416,421 ; 6,634,611 ; 4,836,447; 5,019,686) is best among all thermal spray systems that have been developed. In the HVOF apparatus, hot gases from oxygen fuel combustion are forced through an exhaust nozzle attached to the combustion chamber creating a high temperature and high velocity jet. Spray materials usually in form of powder are heated and accelerated by the high velocity jet toward the target surface for deposition.

Because the particle travels at a velocity of 400 to 800 m/s upon impact, a dense coating can be produced. However, the maximum flame temperature (above 2800K) is well above the melting points of most metals involved in powder feedstock. So, particles being sprayed are molten or semi-molten before hitting the substrate (target surface). High particle temperature can result in quick oxidation of materials and/or undesirable phase transformations. Both are detrimental to coating quality. The high temperature jet sometimes also poses a threat to substrate where coating will be formed. Protection is often needed to prevent overheating of the target surface. Additionally, these processes are rather expansive due to large consumption of compressed oxygen. Finally, clogging of the long nozzle by molten spraying particles creates a lot of problems in operation of the HVOF devices.

As a cheaper alternative of the HVOF process, high-velocity air fuel system (HVAF) was developed (US Patent Nos. 5,120,582; 5,271 ,965; 6,245,390) using air instead of pure oxygen as the oxidizer. The fuel-air combustion takes place at a temperature much lower than fuel-oxygen combustion. However, it is difficult to maintain stable combustion under high gas flow rate when air is the oxidizer. Because stable combustion only takes place in a narrow fuel-to-air ratio, a pilot flame or catalyst member made of noble metals has to be used for combustion stabilization. In addition, a rather large combustion chamber is required to complete the combustion. With the advent of gas dynamic spray (or kinetic spray) process, dense and almost oxide free coatings can be applied without using combustion as heating source. The gas dynamic spray apparatus (US Patent Nos. 5,302,414; 6,402,050 B1 ; 6,623,796 B1) creates a supersonic jet by driving compressed gases (helium, nitrogen, air, or their mixture) through a small Laval nozzle (convergent-divergent nozzle). Fine powder particles (1-50 μm) are accelerated to high velocity by the supersonic jet. When the particle velocity exceeds a critical value which is material dependent, particles will stick to the target surface upon impact. The working gas is often electrically heated to a temperature up to about 800 ⁰C to increase particle velocity. Because the gas temperature is considerably lower than the melting temperature of the powder material, particles remain in solid state upon impact. The particles are substantially not molten, which significantly suppresses the oxidation of particles. However, the low temperature limits the materials that can be deposited using gas dynamic spray. Only ductile materials like copper, steel etc. can be easily deposited. Hard metals and alloys are either difficult to deposit or poorly bonded to the target surface.

Figure 1 shows typical ranges of particle temperatures and velocities that can be obtained with commercially available thermal spray equipment. FS denotes flame spray; WA, wire arc; HVOF, high-velocity oxygen-fuel; CS, cold spray; and X, the combination of particle temperature and velocity that cannot be attained with conventional thermal spray technologies. The chart highlights the wide range of particle temperatures which cannot be achieved, X, lying below that provided by HVOF, but higher than that which can be attained by cold spray. A thermal spray process that can provide particle temperatures and velocities in this entire range will allow temperature sensitive materials that degrade at the high temperatures of APS (Atmospheric Plasma Spraying) and HVOF flames, to be sprayed even if their hardness is too high for them to be sprayed with cold spray. More recently, the Warm Spray (PCT No. JP2007/067998) has been proposed that builds on the HVOF design. In the design shown therein, cooled nitrogen is injected into the combustion gasses and the particles are injected after a Laval nozzle. However, this technology has a number of limitations. Firstly, the resultant gaseous stream contains unreacted fuel and oxygen and a large quantity of water vapour. The stream of gas obtained is therefore not as clean as that obtainable from cold spraying. Secondly, the flow rate of nitrogen injected must be sufficiently low to ensure that combustion is not destabilized. As nitrogen is introduced in higher quantities to further cool combustion gases, the rate of reaction decreases. Further injection of nitrogen creates combustion instabilities and disrupts the continuous flow of gas driving the particles. Therefore, the achievable temperature range is limited. Thirdly, the powder used to inject into the stream must be introduced downstream in the device, after gas has been accelerated to supersonic speed. Therefore, the speeds achievable are limited, as particles introduced further downstream exit at a lower velocity.

Should one attempt to inject powder further upstream, particle temperature will become too high and they will stick to the nozzle and produce unwanted clogging effects. An example of a material that degrades when sprayed by APS or HVOF is tungsten carbide, which is widely used to make wear resistant coatings. During the spray process, tungsten carbide particles heated in the presence of oxygen undergo decarburization in which the WC phase disassociates to form W₂C, CO₂, free tungsten, and carbon. Although W₂ C is harder than WC, in most applications W₂C is not desirable due to its brittleness. Being able to spray WC without decarburization would be of great commercial benefit. Other materials that would benefit from being sprayed at lower temperatures include metals such as steel, which oxidizes in an HVOF spray, and polymers that cannot withstand high temperatures.

Therefore, it would be highly advantageous to provide a thermal spray system that addresses concerns associated with convention spray apparatus mentioned above in order to spray particles with desired thermal and kinetic energy needed to form a high-quality coating.

SUMMARY OF THE INVENTION

In order to provide particles with a thermal and kinetic energy needed to form a high-quality coating, a new thermal spray system is disclosed herein to address some of the concerns associated with apparatus mentioned in the previous section. The present invention provides a low temperature oxy-fuel

(LTOF) thermal spray torch which operates at relatively low gas temperatures, between about 800K and about 2500K. As described in detail hereinafter, the LTOF includes: a combustion chamber, a mixing region, a Laval nozzle, and a cylindrical barrel. Gaseous fuel and oxygen are continuously fed into the combustion chamber where heat is released. Downstream from the combustion chamber, large amounts of cold nitrogen are radially injected into the hot combusted gases for temperature regulation.

To maintain stable combustion at high gas flow rate, the combustion region is separated from the mixing region. The combustion completes before mixing with cold nitrogen, so gas temperature can be significantly reduced without destabilizing combustion. The resultant warm gas mixture is driven through a Laval nozzle under high pressure, thus forming a supersonic jet. Powder can be injected into the gas stream either in subsonic region or in supersonic region depending on the materials being sprayed. By use of a higher chamber pressure than HVOF and HVAF device, the reduction in particle velocity due to gas temperature drop can be compensated.

Increased gas density provides higher drag on particles even when gas velocity drops with the reduction of gas temperature. The unique design of this thermal spray system allows the gas temperature to vary within a much wider range than conventional HVOF systems, so particles being sprayed can maintain high velocity while their temperature are manipulated. With this high velocity, low temperature, thermal spray torch, dense and less oxidized coatings can be applied for a variety of materials including metals, alloys, polymers and cermets. Other non-limiting examples include ceramics, carbides, mixtures of materials and materials that degrade upon heating.

In an aspect of the present invention there is provided a thermal spray apparatus for depositing coatings onto a target location, the apparatus comprising: a combustion region having at least one inlet for injection of a fuel and oxygen; an elongate conduit defining a downstream direction and an upstream direction, the elongate conduit having a throat, a first end, and a second end, wherein the first end is in fluid communication with the combustion region and the second end has an outlet; at least one cooling fluid inlet in the elongate conduit for injection of a cooling fluid, where the fluid inlet is upstream of the throat; and at least one particle inlet for injection of particles, where at least one of the at least one particle inlet is upstream of the throat. The cooling fluid may be an inert gas; some non-limiting examples are air, nitrogen, argon, helium, and carbon dioxide, and combinations thereof. In another aspect of the present invention, the combustion region may be substantially annular, comprising a mixing region in the center of the annular combustion region. This mixing region is in fluid communication with the combustion region and with the elongate conduit, wherein at least one of the at least one particle inlet is a mixing region particle inlet and is in the mixing region. In this embodiment, an additional powder port may be positioned to inject particles into the mixing region. In a further aspect of the invention, the annular combustion chamber may be porous and ceramic. The burner may be split into a number of subregions, wherein each subregion includes at least one inlet for injection of a fuel and oxygen, and wherein each subregion is in fluid communication with the central mixing region. The particles may be accelerated prior to

The apparatus may be cooled by a cooling system that provides providing a cooling system that that has at least one fluid inlet, at least one fluid outlet, and a circulation religion in fluid communication with both the at least one fluid inlet and the at least one fluid outlet; wherein the circulation region is capable of containing and allowing circulation of a fluid; and wherein the cooling system is not in fluid communication with the elongate conduit or the combustion chamber. The present invention further provides a method of depositing coatings onto a target location, comprising the steps of: a) combusting a fuel and oxygen, wherein combustion of the fuel and oxygen is substantially completed, thereby forming a first gas; b) reducing the temperature of the first gas by injecting a cooling fluid into the first gas, thereby forming a second gas; c) directing the second gas into a narrow region such that the flow velocity of the second gas increases to a supersonic velocity, thereby forming a third gas; d) mixing at least one preselected gas with: at least one carrier fluid and a plurality of particles of at least one material, wherein each preselected gas chosen from the group consisting of: the first gas, the second gas, and the third gas; e) directing the third gas against the target location, wherein at least a portion of the plurality of particles stick to the target location

The preselected gas may be chosen such that a substantial fraction of the plurality particles are substantially not molten when said plurality of particles contact the target location.

A further understanding of the functional and advantageous aspects of the present invention can be realized by reference to the following detailed description and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention will now be described, by way of example only, with reference to the drawings, in which:

Figure 1 shows typical particle temperatures and velocities in commercial thermal spray processes; X denotes that which cannot be attained with conventional thermal spray technologies;

Figure 2 shows a schematic drawing of a low temperature oxy-fuel (LTOF) thermal spray torch constructed in accordance with the present invention; Figure 3 shows a schematic diagram of components of the torch of

Figure 2;

Figure 4 shows copper coatings produced at a stand-off distance of 50 mm with nitrogen flow rate of (a) 100 standard litres per minute (SLPM) and (b) 500 SLPM respectively; Figure 5 shows an electron microscope image of a tungsten carbide- cobalt coating deposited on a stainless steel substrate with the LTOF gun of the present invention;

Figure 6 shows a schematic drawing of a LTOF thermal spray torch wherein the combustion chamber is annular in shape; Figure 7 is a schematic view of the torch as in Figure 6 with angled injection inlets;

Figure 8 is a schematic view of the torch as in Figure 6 with a porous ceramic burner in the annular combustion chamber;

Figure 9 is a schematic view of the torch as in Figure 8 wherein multiple ceramic burners are used; and

Figure 10 is a graph of particle axial velocity (in meters per second) versus axial distance from the torch exit (in meters) showing experimental and numerically predicted results particle velocities for tungsten carbide-cobalt coatings. DETAILED DESCRIPTION OF THE INVENTION

Without limitation, the majority of the systems described herein are directed to a low-temperature oxy-fuel spray system. As required, embodiments of the present invention are disclosed herein. However, the disclosed embodiments are merely exemplary, and it should be understood that the invention may be embodied in many various and alternative forms.

The figures are not to scale and some features may be exaggerated or minimized to show details of particular elements while related elements may have been eliminated to prevent obscuring novel aspects. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention. For purposes of teaching and not limitation, the illustrated embodiments are directed to a low-temperature oxy-fuel spray system. As used herein, the term "fluid" refers to: any liquid, any gas, or any substance that continually deforms under an applied shear stress.

As used herein, the term "about", when used in conjunction with ranges of dimensions, velocities, temperatures or other physical properties or characteristics is meant to cover slight variations that may exist in the upper and lower limits of the ranges of dimensions as to not exclude embodiments where on average most of the dimensions are satisfied but where statistically dimensions may exist outside this region. For example, in embodiments of the present invention dimensions of components of a low-temperature oxy- fuel spray system are given but it will be understood that these are non- limiting.

Figure 1 shows typical particle temperatures and velocities in commercial thermal spray processes. In the figure, FS denotes flame spray; WA, wire arc; HVOF, high-velocity oxygen-fuel; CS, cold spray; and X, the combination of particle temperature and velocity that cannot be attained with conventional thermal spray technologies. A new thermal spray system, known as low temperature oxy-fuel (LTOF) spray, has been developed that bridges the gap between HVOF and cold spray systems. It operates at high particle velocities, approaching those of cold spray systems, but over a much wider range of gas temperatures, 800 to 2500K.

Figures 2 and 3 show cross-sectional diagrams of a low temperature oxy-fuel (LTOF) thermal spray torch constructed in accordance with the present invention, shown generally at 10 in Figure 2. As can be seen in

Figure 2, the LTOF torch is an elongate conduit comprised of a number of distinct regions: a combustion chamber 12, a mixing region 14, a Laval nozzle 16, and a cylindrical barrel 18. Gaseous fuel and oxygen are continuously fed into inlets 30 and 32 respectively, further into the combustion chamber 12 where heat is released. The gaseous fuel is typically methane, though other non-limiting fuels can be used such as hydrocarbon fuels, combustible gasses, combustible liquids, and combinations thereof. Specific examples include, but are not limited to: methane, hydrogen, propane, kerosene, propylene, acetylene, and combinations thereof. Downstream from the combustion chamber, cooled, high-pressure nitrogen is injected via cooling fluid inlet 22 into the hot combustion products in the mixing region 14 to regulate their temperature. The fuel is completely burned before mixing with cold nitrogen from inlet 22, so gas temperature can be significantly reduced without destabilizing combustion. While nitrogen is utilized in the preferred embodiment of this invention, it would be understood by those skilled in the art that other non-reactive fluids may be used. Some non-limiting examples include: argon, helium, carbon dioxide, and any other suitable fluid that lowers the temperature of the hot combustion products in the mixing region 14. The resulting gas mixture is driven through Laval nozzle 16 which consists of a converging region and a diverging region collectively forming a throat 20 of reduced diameter. Upon exiting nozzle 16 under high pressure, the mixture forms a supersonic jet in barrel 18. Powder is injected into the gas stream either in the subsonic region via inlet 24 or supersonic region via inlet 28, depending on the materials being sprayed. Some non-limiting examples of powder include: metals, alloys, polymers, cermets, materials that degrade upon heating, tungsten carbide in a metal matrix, and any other suitable powder consisting of small particles.

To maintain operable temperatures, a cooling fluid may be supplied to inlet 26 and circulated through circulation region 30, exiting via outlet 34. The inlet 26, outlet 34, and circulation region 30 collectively form an external cooling system. Any cooling fluid may be used; water and air are common examples.

The unique design of this thermal spray system allows the gas temperature to vary over a much wider range than conventional HVOF systems, so particles being sprayed can maintain high velocities while their temperature is regulated. By use of a higher chamber pressure than HVOF and HVAF device, the reduction in particle velocity due to a lower gas temperature is compensated for by the higher gas density that provides a higher drag on particles. With this high-velocity, low-temperature thermal spray torch, dense and low oxide content coatings can be applied with a variety of powdered materials including metals, alloys, polymers and cermets. Other non-limiting examples include: ceramics, carbides in a metal matrix, mixtures of materials, and materials that degrade upon heating. Figure 3 shows a diagram of the parts forming an embodiment of the present invention. This embodiment of the LTOF torch external casing consists of, left to right, back cap 34, injector seat 36, combustor shell 38, barrel connector 42, and barrel shell 46. The conduit through which fluid travels is comprised of, in order of downstream travel: combustor tube 52, mixing tube 54, Laval nozzle 40, barrel gun 44, and finally spray outlet 56. In the combustor tube 52, gaseous fuel enters via inlet 30 and through injector 48; oxygen via inlet 32 and through conduit 50. In the mixing tube 54, nitrogen enters via radial inlet 58 and powder may optionally enter via inlet 24. In the barrel connector 42, powder may alternatively enter via inlet 28. Inlet 26 and outlet 34 are elements of the cooling system wherein a cooling fluid such as water is circulated to maintain operable temperatures. The source of ignition may be an internal or external spark ignition and is not shown explicitly in Figure 3. It would be understood by those skilled in the art that other combinations of parts may be used to produce the necessary the channels and inlets for combustion and mixing; the particular arrangement of pieces in Figure 3 is a non-limiting example of the present invention.

Figure 6 shows a further embodiment of the Low Temperature Oxy- Fuel Spray torch where the combustion chamber 86 has an annular shape. Fuel 77 and oxygen 78 are fed into an annular combustion 86 chamber in which combustion occurs. After completing combustion, the hot products enter the central chamber 98, which behaves as a mixing region into which powder is injected. The powder travels down an elongate conduit 102 containing a converging-diverging Laval nozzle 80, and eventually exits the torch at outlet 104. The high-velocity particles in the powder impact a target substrate (not shown) and stick to form a coating such as that illustrated in Figure 5.

Figure 7 shows a further embodiment of the Low Temperature Oxy- Fuel Spray torch in which the inlets 99 and 100 through which powders are fed into the nozzle are inclined at an angle. By introducing powders at an angle, the deposition of powders on the nozzle walls can be minimized. This will also increase the exit velocity of particles.

Figure 8 shows another embodiment of the Low Temperature Oxy- Fuel Spray torch a ceramic porous burner 87. Fuel 76 and oxygen 78 are fed into an annular porous ceramic burner 87. Combustion is completed inside the pores of the burner. The combustion products enter a central chamber 98 which functions as a mixing region. Powder is injected via inlet 74 and travels down the elongate conduit 102, exiting via outlet 104.

Figure 9 shows a preferred embodiment of the Low Temperature Oxy- Fuel Spray torch in which the combustion region is split into a number of subregions. Each subregion is a porous burner 88 with its own inlet for fuel 77 and oxygen 79. Each burner 88 can be individually turned on or off as desired. By varying the number of burners 88, the power supplied to the torch can be controlled, so that the amount of powder fed to the torch and the mass flow rate of gases can be varied as desired. This provides a further degree of control.

In the present invention, there are many possible powder injection locations. Three are shown in the drawings, though more may be used. In Figures 6 through 9, there are three possible powder injection ports: one for axial injection via inlet 74, one for radial injection before the Laval nozzle 82 via inlet 84, and one after the nozzle via inlet 85. By varying the injection location, one has much greater control of the powder temperature and velocity when the particles in the powder exit the torch after travelling through conduit 102. Injecting powder axially via inlet 74 gives the particles in the powder a longer acceleration time, so greater velocities can be achieved. Axial injection via inlet 74 is preferable to radial injection (inlet 84 inlet 85), since particles injected radially follow different trajectories when turning into the flow, depending on their diameter, and therefore are segregated by size when they impact on the substrate.

When powder is injected axially via inlet 74, an inert gas can be added in a co-axial tube 72 around the powder port. Tube 72 forms an inlet with an annular shape in cross-section. Injection of inert gas via tube 72 reduces oxidation of the powder and allows its temperature to be reduced if desired. The axial injection tube 72 provides additional space to accelerate particle powders before they enter the heated zone in the mixing region 98. This further increases particle velocities at the outlet 104 of the spray torch.

To achieve higher particle velocities, they can be suspended in a carrier gas and then accelerated as they flow through the tube used to inject them axially via inlet 74 into the mixing region 98. The tube is made several inches long to give them enough time to reach a significant velocity (between about 100 and about 150 meters per second).

In operation, the combustion process substantially completes within the annular combustion chamber 86. An inert fluid such as compressed nitrogen gas is injected via inlet 80 into the hot combustion products. If combustion has not completed, combustion in the elongate conduit 102 may be quenched by the introduction of inert fluids via inlet 80.

It may be desirable to add powders simultaneously in two different ports. For example, in making abradable seals for the tips of gas turbine blades, a mixture of polymer and metal powders is sprayed to form a soft coating. It is desirable to keep the polymer powders at a lower temperature than the metal powders since they burn at high temperatures. It is possible to inject metal powders upstream of the nozzle throat 82 where temperatures are higher and polymer particles downstream where the gas temperatures are lower.

The LTOF torch was used to prepare copper coatings on a steel substrate. Figures 4(a) and 4(b) are optical micrographs demonstrating copper coatings on a stainless steel substrate. The coatings were produced at a stand-off distance of 50 mm with nitrogen flow rate of 4(a) 100 SLPM and 4(b) 500 SLPM respectively. The coatings made at low nitrogen flow rate show signs of oxidation, as indicated by the dark streaks in Figure 4(a). At high nitrogen flow rates, the gas temperature was much lower and the oxidation was greatly reduced (Figure 4(b)). Figure 5 shows an electron microscope image of a tungsten carbide coating deposited on a stainless steel substrate with the LTOF gun of the present invention.

Figure 10 shows a graph of particle velocity versus distance along the torch axis. Dotted line 202 represents a numerical prediction of a particle with a 6 micron average diameter, solid line 204 represents a numerical prediction of a particle with a 6 micron average diameter, dash-dotted line 206 represents a numerical prediction of a particle with a 25 micron average diameter, and dots 208 represent experimental measurements of a particle with 11.2 micron average diameter. The powder material is WC-12Co, with a mean particle size of 11.2 microns. The powder was injected via the inlet downstream of the throat (inlet 28 in Figure 2). 200 SLPM of nitrogen was injected via cooling fluid inlet 22. The graph demonstrates the particle velocity profile throughout the torch.

In experimentation, particle velocities between about 400 to about 800 meters per second were obtained. The particle diameter has been varied between about 5 and about 50 microns, though larger and smaller sizes can be used. Powders of a very small diameter (between about 1 and about 5 microns) can make dense, pore-free coatings. However, it is difficult to inject small powders of this size into the torch directly since drag forces on them are low and they are not transported effectively by a carrier gas. Small powders can be sprayed by suspending them in a carrier fluid which is a slurry of a volatile liquid such as alcohol or water. A spray of this slurry is injected axially into the torch using an atomizer: the liquid in individual droplets will evaporate in the hot zone and the powders will be carried along the gas flow in the torch. When operating the device, the choice of powder ports, amount of nitrogen injected, and amount of fuel used depends on the powder material. It is an objective of this invention to obtain particles with a temperature just below their melting point.

With metal powders, the important consideration is to avoid oxidation. It does not matter if the particles are heated inside the torch because there is very little oxygen there. However, the particles should have cooled down by the time they emerge from the torch and come in contact with air. With polymer particles it is important to avoid overheating them anywhere since high temperatures may change their chemical composition. Therefore, one can optimize the particle velocity and temperature by configuring the parameters of the present invention such as modifying: the port for injection of the particles, the particle injection rate, the particle material type, the particle carrier fluid, the particle injection angle, the pre-injection particle acceleration rate, the choice of fuel, the source of oxygen, the fuel injection rate, the oxygen injection rate, the combustion chamber size, the number of combustion subregions that are active, the length of barrel, the diameter of barrel, the distance between the outlet of the elongate conduit and the substrate, the shape of nozzle, the rate of non-reactive fluid injection, the type of non-reactive fluid, the rate of cooling fluid flow, and any other physically modifiable property that affects the velocity and temperature of particles as they hit the target substrate.

As used herein, the terms "comprises", "comprising", "includes" and "including" are to be construed as being inclusive and open ended, and not exclusive. Specifically, when used in this specification including claims, the terms "comprises", "comprising", "includes" and "including" and variations thereof mean the specified features, steps or components are included. These terms are not to be interpreted to exclude the presence of other features, steps or components.

The foregoing description of the preferred embodiments of the invention has been presented to illustrate the principles of the invention and not to limit the invention to the particular embodiment illustrated. It is intended that the scope of the invention be defined by all of the embodiments encompassed within the following claims and their equivalents.

Claims

THEREFORE, WHAT IS CLAIMED IS:

1. A method of depositing coatings onto a target location, the method comprising: a) combusting a fuel and oxygen, wherein combustion of the fuel and oxygen is substantially completed, thereby forming a first gas; b) reducing the temperature of the first gas by injecting a cooling fluid into the first gas, thereby forming a second gas; c) directing the second gas into a narrow region such that the flow velocity of the second gas increases to a supersonic velocity, thereby forming a third gas; d) mixing at least one preselected gas with: at least one carrier fluid and a plurality of particles of at least one material, wherein each preselected gas chosen from the group consisting of: the first gas, the second gas, and the third gas; e) directing the third gas against the target location, wherein at least a portion of the plurality of particles stick to the target location.

2. The method of claim 1 wherein each preselected gas is chosen such that a substantial fraction of the plurality particles are substantially not molten when said plurality of particles contact the target location.

3. The method of claim 1 or 2 wherein the cooling fluid is injected in sufficient quantities to reduce the temperature of the first gas such that a substantial fraction of the plurality of particles are substantially not molten when said plurality of particles contact the target location.

4. The method of any one of claims 1 to 3 wherein each preselected gas is chosen such that a substantial fraction of the plurality particles are substantially not molten in steps (a) through (e).

5. The method of any one of claims 1 to 4 wherein the cooling fluid is injected in sufficient quantities to reduce the temperature of the first gas such that a substantial fraction of the plurality of particles are substantially not molten in steps (a) through (e).

6. The method of any one of claims 1 to 5 wherein step (d) is performed by: injection of the carrier fluid into the at least one preselected gas, wherein said injection of the carrier fluid is in a direction substantially the same as a direction of flow of the at least one preselected gas receiving the injected carrier fluid.

7. The method of claim 6 wherein step(d) further comprises: injecting an inert gas into the first gas.

8. The method of claim 7 wherein the inert gas injected into the first gas is injected via an inlet that is substantially annular in cross section.

9. The method of any one of claims 6 to 8 wherein the particles are accelerated prior to injection.

10. The method of any one of claims 1 to 9 wherein the first gas has a direction of flow, and the cooling fluid is injected at an angle to said direction of flow.

11. The method of any one of claims 1 to 9 wherein the first gas has a direction of flow, and the cooling fluid is injected substantially perpendicular said direction of flow.

12. The method of any one of claims 1 to 11, further comprising the step of: providing a cooling system that that has at least one fluid inlet, at least one fluid outlet, and a circulation religion in fluid communication with both the at least one fluid inlet and the at least one fluid outlet; wherein the circulation region is capable of containing and allowing circulation of a fluid; and wherein the cooling system is not in fluid communication any one of: the first gas, the second gas, and the third gas.

13. The method of claim 12 wherein the fluid in the cooling system is selected from the group consisting of: water and air.

14. The method of any one of claims 1 to 13 wherein the carrier fluid is a gas and is selected from the group consisting of: air, helium, argon, nitrogen, and combinations thereof.

15. The method of any one of claims 1 to 13 wherein the carrier fluid is a liquid and is selected from the group consisting of: water, alcohol, oil, and combinations thereof.

16. The method of any one of claims 1 to 15 wherein the cooling fluid does not substantially react with the first gas.

17. The method of any one of claims 1 to 15 wherein the cooling fluid is selected from the group consisting of: air, nitrogen, argon, helium, and carbon dioxide, and combinations thereof.

18. The method of any one of claims 1 to 17 wherein the fuel is selected from the group consisting of: hydrocarbon fuels, combustible gasses, combustible liquids, and combinations thereof.

19. The method of any one of claims 1 to 18 wherein the fuel is selected from the group consisting of: methane, hydrogen, propane, kerosene, propylene, acetylene, and combinations thereof.

20. The method of any one of claims 1 to 19 wherein the oxygen is provided in the form of air.

21. The method of any one of claims 1 to 20 wherein steps (a) through (e) are performed continuously, thereby allowing continuous flow of the third gas.

22. The method of any one of claims 1 to 21 wherein the particles have an average diameter less than about 50 microns.

23. The method of any one of claims 1 to 21 wherein the particles have an average diameter between about 5 and about 50 microns.

24. The method of any one of claims 1 to 23 wherein the third gas has a temperature between about 800 K and about 2300 K.

25. The method of any one of claims 1 to 24 wherein the particles in the third gas have a velocity greater than the speed of sound.

26. The method of any one of claims 1 to 24 wherein the particles in the third gas have a velocity between about 400 and about 800 meters per second.

27. The method of any one of claims 1 to 26, wherein the at least one preselected gas is a first preselected gas and further including a second preselected gas; wherein the plurality of particles mixed with the first preselected gas are of a first material; and wherein the plurality of particles mixed with the second preselected gas are of a second material.

28. The method of claim 27 wherein the first preselected gas and the second preselected gas are not the same.

29. The method of any one of claims 1 to 28 wherein each material of the plurality of particles is selected from the group consisting of: metals, alloys, polymers, cermets, materials that degrade upon heating, tungsten carbide in a metal matrix, and combinations thereof.

30. A thermal spray apparatus for depositing coatings onto a target location, the apparatus comprising: a combustion region having at least one inlet for injection of a fuel and oxygen; an elongate conduit defining a downstream direction and an upstream direction, the elongate conduit having a throat, a first end, and a second end, wherein the first end is in fluid communication with the combustion region and the second end has an outlet; at least one cooling fluid inlet in the elongate conduit for injection of a cooling fluid, where the fluid inlet is upstream of the throat; and at least one particle inlet for injection of particles, where at least one of the at least one particle inlet is upstream of the throat.

31. A thermal spray apparatus as claimed in claim 30 wherein the at least one inlet for injection of a fuel and oxygen includes a fuel inlet and an oxygen inlet.

32. A thermal spray apparatus as claimed in claim 30 further comprising a barrel region in the elongate conduit, downstream from the throat.

33. A thermal spray apparatus as claimed in any one of claims 30 to 32 further comprising a spark plug capable of initiating combustion in the combustion region.

34. A thermal spray apparatus as claimed in any one of claims 30 to 33 wherein the at least one particle inlet is at least two particle inlets, and wherein two of the at least two particle inlets are positioned such that: at least one particle inlet is in the elongate conduit upstream of the throat, and at least one particle inlet is in the elongate conduit downstream of the throat.

35. A thermal spray apparatus as claimed in any one of claims 30 to 34 wherein the combustion region is substantially cylindrical.

36. A thermal spray apparatus as claimed in any one of claims 30 to 35 wherein the combustion region is substantially annular.

37. A thermal spray apparatus as claimed in claim 36 wherein the combustion region further comprises a mixing region in the center of the annular combustion region, wherein said mixing region is in fluid communication with the combustion region and with the elongate conduit, and wherein at least one of the at least one particle inlet is a mixing region particle inlet and is in the mixing region.

38. A thermal spray apparatus as claimed in claim 37, wherein the annular combustion region has a central annular axis passing through the mixing region; and wherein the mixing region particle inlet is capable of injecting particles substantially along said central annular axis.

39. A thermal spray apparatus as claimed in any one of claims 36 to 37 wherein the combustion region further comprises a porous burner.

40. A thermal spray apparatus as claimed in claim 39 wherein the porous burner is ceramic.

41. A thermal spray apparatus as claimed in any one of claims 37 to 40, wherein the combustion region comprises a plurality of combustion subregions, wherein each combustion subregion includes at least one inlet for injection of a fuel and oxygen, and wherein each combustion subregion is in fluid communication with the mixing region.

42. A thermal spray apparatus as claimed in claim 41 wherein the at least one inlet for injection of a fuel and oxygen in each subregion includes a fuel inlet and an oxygen inlet.

43. A thermal spray apparatus as claimed in any one of claims 37 to 41 further comprising means for accelerating particles such that particles are accelerated prior to entering the mixing region.

44. A thermal spray apparatus as claimed in any one of claims 37 to 43 wherein the at least one particle inlet is at least three particle inlets, and wherein three of the at least three particle inlets are positioned such that: at least one particle inlet is in the mixing region, at least one particle inlet is in the elongate conduit upstream of the throat, and at least one particle inlet is in the elongate conduit downstream of the throat.

45. A thermal spray apparatus as claimed in any one of claims 30 to 44 wherein the elongate conduit further comprises a converging region upstream of the throat, and a diverging region downstream of the throat.

46. A thermal spray apparatus as claimed in any one of claims 30 to 45 wherein the lumen of the elongate conduit is substantially circular in cross-section.

47. A thermal spray apparatus as claimed in any one of claims 30 to 46 wherein the elongate conduit is substantially linear.

48. A thermal spray apparatus as claimed in any one of claims 32 to 47 wherein the barrel region in the elongate conduit is substantially cylindrical.

49. A thermal spray apparatus as claimed in any one of claims 46 to 48 wherein the cooling fluid inlet is substantially a radial fluid inlet with respect to the elongate conduit.

50. A thermal spray apparatus as claimed in any one of claims 30 to 49 wherein the cooled fluid injected into the cooled fluid inlet is selected from the group consisting of: air, nitrogen, argon, helium, and carbon dioxide, and combinations thereof.

51. A thermal spray apparatus as claimed in any one of claims 30 to 50 wherein the cooled fluid injected into the cooling fluid inlet is nitrogen.

52. A thermal spray apparatus as claimed in any one of claims 30 to 51 , wherein the thermal spray apparatus further comprises a cooling system that that has at least one fluid inlet, at least one fluid outlet, and a circulation religion in fluid communication with both the at least one fluid inlet and the at least one fluid outlet; wherein the circulation region is capable of containing and allowing circulation of a fluid; and wherein the cooling system is not in fluid communication with the elongate conduit.

53. A thermal spray apparatus as claimed in any one of claims 30 to 52 wherein the fluid in the cooling system is selected from the group consisting of: water and air.

54. The product obtained by the method of any one of claims 1 to 29.

55. A new thermal spray apparatus, substantially as described herein.

56. A new method of depositing coatings onto a target, substantially as described herein.