Laser enhancements of cold sprayed deposits
A process for depositing a powder metal onto a substrate is performed by providing a substrate, depositing at least one layer of powder metal onto a surface of the substrate using a non-oxidizing carrier gas so that the powder metal plastically deforms without melting and bonds to a surface upon impact with the surface, and subjecting the at least one powder metal deposited layer to a treatment to improve density and/or raise a temperature of the at least one powder metal deposited layer. In a preferred embodiment of the present invention, the treatment to improve density and/or raise a temperature of the at least one powder metal deposited layer is a laser treatment.
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(1) Field of the Invention
The present invention relates to a process and an apparatus for applying localized improvements to cold sprayed deposited materials.
(2) Prior Art
Cold gas dynamic spraying or “cold spray” has been recently introduced as a new metallization spray technique to deposit powder metal with or without inclusions onto a substrate. A supersonic jet of helium and/or nitrogen is formed by a converging/diverging nozzle and is used to accelerate the powder particles toward the substrate to produce cold spray deposits or coatings. Deposits adhere to the substrate and previously deposited layers through plastic deformation and bonding. U.S. Pat. Nos. 5,302,414 and 6,502,767 illustrate cold gas dynamic spraying techniques.
Despite the existence of cold spray techniques improvements are needed.
SUMMARY OF THE INVENTIONAccordingly, it is an object of the present invention to provide a process which improves the density of deposited materials and/or raise the coating temperature.
It is a further object of the present invention to provide an apparatus which improves the density of deposited materials and/or raise the coating temperature.
The foregoing objects may be attained using the process and apparatus of the present invention.
In accordance with the present invention, a process for depositing a powder metal onto a substrate is provided. The process broadly comprises the steps of providing a substrate, depositing at least one layer of powder metal onto a surface of the substrate using a non-oxidizing carrier gas so that the powder metal plastically deforms without melting and bonds to a surface upon impact with the surface, and subjecting the at least one powder metal deposited layer to a treatment to improve density and/or raise a temperature of the at least one powder metal deposited layer. In a preferred embodiment of the present invention, the treatment to improve density and/or raise a temperature of the at least one powder metal deposited layer is a laser treatment.
Further in accordance with the present invention, an apparatus for depositing a powder metal onto a substrate is provided. The apparatus broadly comprises means for depositing at least one layer of powder metal onto a surface of the substrate using a non-oxidizing carrier gas so that the powder metal plastically deforms without melting and bonds to a surface upon impact with the surface, and means for subjecting the at least one powder metal deposited layer to a treatment to improve density and/or raise a temperature of the at least one powder metal deposited layer.
Other details of the laser enhancements of cold sprayed deposits of the present invention, as well as other objects and means attendant thereto, are set forth in the following detailed description and the accompanying drawings wherein like reference numerals depict like elements.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention relates to a process and an apparatus for applying localized improvements to cold sprayed deposited materials. The localized improvements may be density improvements and/or raising the temperature of the deposited material high enough for short durations to recover ductility without significant heat input to the substrate material or any underlying prior cold sprayed deposits.
The cold spray process for depositing powder metal materials onto substrates is advantageous in that it provides sufficient energy to accelerate particles to high enough velocities such that, upon impact, the particles plastically deform and bond to the surface of the substrate or onto a previously deposited layer. The process allows the build up of a relative dense coating or structural deposit. Cold spray does not metallurgically transform the particles from their solid state.
Referring now to
In the process of the present invention, the material to be deposited is a powdered metal material. The powdered metal material may be of the same composition as the substrate 10 is made from or it may be a compatible composition. For example, the powder metal material may be a nickel based alloy such as IN 718, IN 625, IN 100, WASPALOY, IN 939, or GATORIZED WASPALOY. The powder metal material may also be another metallic material such as a copper based alloy or an aluminum based alloy. The powdered metal materials that are used to form the deposit on the surface 24 preferably have a diameter in the range of from about 5.0 microns to 50 microns (0.2 mils to 2.0 mils). Smaller particle sizes enable the achievement of higher particle velocities. Below 5 microns in diameter, the particles risk getting swept away from the surface 24 due to a bow shock layer above the surface 24, i.e. insufficient mass to propel the particle through the bow shock. The narrower the particle size distribution, the more uniform the particle velocity will be. This is because the smaller particles in the spray/plume will hit the slower, larger ones and effectively reduce the velocity of both.
The particles to be deposited may be accelerated to supersonic velocities using compressed gas, such as a gas selected from the group consisting of helium, nitrogen, another inert gas, and mixtures thereof. Helium is a preferred gas because it produces the highest velocity due to its low molecular weight.
The bonding mechanism employed by the process of the present invention for transforming the powdered metal material into a deposit is strictly solid state, meaning that the particles plastically deform but do not melt. Any oxide layer that is formed on the particles, or is present on the surface 24, or is present in a previously deposited layer, is broken up and fresh metal-to-metal contact is made at very high pressures.
The powdered metal material used to form the deposit may be fed to the spray gun 22 using any suitable means known in the art, such as modified thermal spray feeders. One custom designed feeder that may be used is manufactured by Powder Feed Dynamics of Cleveland, Ohio. This feeder has an auger type feed mechanism. Fluidized bed feeders and barrel roll feeders with an angular slit may also be used.
In the process of the present invention, the feeders may be pressurized with a gas selected from the group consisting of helium, nitrogen, another inert gas, and mixtures thereof. Feeder pressures are generally 15 psi above the main gas or head pressures, which pressures are usually in the range of from 200 psi to 500 psi, depending on the powder metal material composition. The main gas is preferably heated so that gas temperatures are in the range of from 600 degrees Fahrenheit to 1200 degrees Fahrenheit. If desired, the main gas may be heated as high as approximately 1250 degrees Fahrenheit depending on the material being deposited. The gas may be heated to keep it from rapidly cooling and freezing once it expands past the throat of nozzle 20. The net effect is a surface temperature on the substrate 10 of about 115 degrees Fahrenheit during deposition. Any suitable means known in the art may be used to heat the gas.
To deposit the powdered metal material, the nozzle 20 may pass over the surface 24 of the substrate 10 being repaired on multiple occasions. The number of passes is a function of the thickness of the material to be applied. The process of the present invention is capable of forming a deposit having any desired thickness. Cold spray can produce thin layers ranging from 0.002 inches to 0.020 inches per single pass.
The main gas that is used to deposit the powdered metal particles onto the surface 24 may be passed through the nozzle 20 via inlet 30 at a flow rate of from 0.001 SCFM to 50 SCFM, preferably in the range of from 15 SCFM to 35 SCFM. The foregoing flow rates are preferred if helium is used as the main gas. If nitrogen is used by itself or in combination with helium as the main gas, the nitrogen may be passed through the nozzle 20 at a flow rate of from 0.001 SCFM to 30 SCFM, preferably from 4.0 SCFM to 30 SCFM.
The main gas temperature may be in the range of from 600 degrees Fahrenheit to 1200 degrees Fahrenheit, preferably from 700 degrees Fahrenheit to 1000 degrees Fahrenheit, and most preferably from 725 degrees Fahrenheit to 900 degrees Fahrenheit.
The pressure of the spray gun 22 may be in the range of from 200 psi to 500 psi, preferably from 200 psi to 400 psi, and most preferably from 275 psi to 375 psi. The powdered metal material is preferably fed from a hopper, which is under a pressure of 10 to 50 psi higher than the specific main gas pressure, preferably 15 psi higher, to the spray gun 22 via line 34 at a rate in the range of from 10 grams/min to 100 grams/min, preferably from 15 grams/min to 50 grams/min.
The powdered metal material is fed to the spray gun 22 using a non-oxidizing carrier gas. The carrier gas may be introduced via inlet 30 at a flow rate of from 0.001 SCFM to 50 SCFM, preferably from 8.0 SCFM to 15 SCFM. The foregoing flow rate is useful if helium is used as the carrier gas. If nitrogen by itself or mixed with helium is used as the carrier gas, a flow rate of from 0.001 SCFM to 30 SCFM, preferably from 4.0 to 10 SCFM, may be used.
The spray nozzle 20 is held at a distance from the surface 24. This distance is known as the spray distance and may be in the range of from 10 mm. to 50 mm.
The velocity of the powdered metal particles leaving the spray nozzle 20 may be in the range of from 825 m/s to 1400 m/s, preferably from 850 m/s to 1200 m/s.
As mentioned before, the powdered metal material may be deposited onto the surface 24 so as to form a coating having one or more layers. It has been discovered that the deposited layer(s) could receive localized improvements from laser processing. With proper settings, a laser could be passed directly over a deposited layer to improve density (sintering) and/or raise the coating temperature high enough, for a short duration, to recover ductility without significant heat input to the substrate material or underlying prior cold sprayed layer (small thermal gradient). To this end, the system 8 includes a laser 60 which may be movable to allow the laser beam to apply heat to the entire powder metal material deposit. The laser 60 may comprise any suitable laser known in the art such as a YAG laser. The laser processing may be performed after each successive cold sprayed layer deposit.
As shown in
Cold spray coatings are highly cold worked due to the extreme impact velocity and the nature of the bonding mechanism. This degree of cold work results in very low tensile ductility of the deposited material. Also, some high hardness materials produce fairly porous deposits even at the highest possible spray parameters. The use of the laser 60 helps improve the ductility of the deposited material. It can also increase the density or reduce the porosity of deposited material.
The cold spray process offers many advantages over other metallization processes. Since the powders are not heated to high temperatures, no oxidation, decomposition, or other degradation of the feedstock materials occurs. Powder oxidation during deposition is also controlled since the particles are contained within the oxygen-free accelerating gas stream. Other potential advantages include the formation of compressive residual surface stresses and retaining the microstructure of the feedstock. Also, because relatively low temperatures are used, thermal distortion of the substrate will be minimized. Because the feedstock is not melted, cold spray offers the ability to deposit materials that cannot be sprayed conventionally due to the formation of brittle intermetallics or a propensity to crack upon cooling or during subsequent heat treatments.
It is apparent that there has been provided in accordance with the present invention laser enhancements of cold sprayed deposits which fully satisfy the objects, means, and advantages set forth hereinbefore. While the present invention has been described in the context of specific embodiments thereof, other alternatives, modifications, and variations will become apparent to those skilled in the art having read the foregoing description. Therefore, it is intended to embrace those alternatives, modifications, and variations which fall within the broad scope of the appended claims.
Claims
1. A process for depositing a powder metal onto a substrate comprising the steps of:
- providing a substrate;
- depositing at least one layer of powder metal onto a surface of said substrate using a non-oxidizing carrier gas so that said powder metal plastically deforms without melting and bonds to a surface upon impact with said surface; and
- subjecting said at least one powder metal deposited layer to a treatment to improve density and/or raise a temperature of said at least one powder metal deposited layer.
2. The process according to claim 1, wherein said subjecting step comprises utilizing a laser to improve said density and/or raise said temperature.
3. The process according to claim 1, wherein said depositing step comprises depositing multiple layers of said powder metal.
4. The process according to claim 3, wherein said subjecting step is performed after each said layer is deposited.
5. The process according to claim 4, wherein each said subjecting step comprises utilizing a laser to improve said density and/or raise said temperature.
6. The process according to claim 1, wherein said depositing step comprises depositing multiple layers of said powder metal and said subjecting step is performed after said multiple layers have been deposited.
7. The process according to claim 1, wherein said depositing step comprises providing said powder metal in particle form having a particle size in the range of from 5 microns to 50 microns and accelerating said particles to a speed in the range of from 825 m/s to 1400 m/s.
8. The process according to claim 7, wherein said accelerating step comprises accelerating said particles to a speed in the range of from 850 m/s to 1200 m/s.
9. The process according to claim 7, wherein said depositing step further comprises feeding said powder metal to a spray nozzle at a feed rate of from 10 grams/min to 100 grams/min using a carrier gas selected from the group consisting of helium, nitrogen, another inert gas, and mixtures thereof.
10. The process according to claim 9, wherein said feeding step comprises feeding said metal powder to said spray nozzle at a feed rate of from 15 grams/min to 50 grams/min.
11. The process according to claim 9, wherein said carrier gas is helium and said feeding step comprises feeding helium to said nozzle at a flow rate of from 0.001 SCFM to 50 SCFM.
12. The process according to claim 11, wherein said feeding step comprises feeding said helium to said nozzle at a flow rate in the range of from 8.0 SCFM to 15 SCFM.
13. The process according to claim 9, wherein said carrier gas comprises nitrogen and said feeding step comprises feeding said nitrogen to said nozzle at a flow rate of from 0.001 SCFM to 30 SCFM.
14. The process according to claim 13, wherein said feeding step comprises feeding said nitrogen to said nozzle at a flow rate of from 4.0 SCFM to 10 SCFM.
15. The process according to claim 7, wherein said depositing step comprises passing said metal powder particles through said nozzle using a main gas selected from the group consisting of helium, nitrogen, another inert gas, and mixtures thereof at a main gas temperature in the range of from 600 degrees Fahrenheit to 1200 degrees Fahrenheit and at a spray pressure in the range of from 200 psi to 500 psi.
16. The process according to claim 15, wherein said passing step comprising passing said metal powder particles through said nozzle at a main gas temperature in the range of from 700 degrees Fahrenheit to 1000 degrees Fahrenheit at a spray pressure in the range of from 200 psi to 400 psi.
17. The process according to claim 15, wherein said main gas temperature is in the range of from 725 degrees Fahrenheit to 900 degrees Fahrenheit at a spray pressure in the range of from 275 psi to 375 psi.
18. The process according to claim 15, wherein said main gas comprises helium and said passing step comprises feeding said helium to said nozzle at a flow rate in the range of from 0.001 SCFM to 50 SCFM.
19. The process according to claim 18, wherein said helium feeding step comprises feeding said helium to said nozzle at a flow rate in the range of from 15 SCFM to 35 SCFM.
20. The process according to claim 15, wherein said main gas comprises nitrogen and said passing step comprises feeding said nitrogen to said nozzle at a feed rate in the range of from 0.001 SCFM to 30 SCFM.
21. The process according to claim 20, wherein said nitrogen feeding step comprises feeding said nitrogen to said nozzle at a feed rate in the range of from 4.0 to 8.0 SCFM.
22. The process according to claim 1, wherein said depositing step comprises depositing each layer at a thickness of from 0.002 inches to 0.020 inches.
23. An apparatus for depositing a powder metal onto a substrate comprising:
- means for depositing at least one layer of powder metal onto a surface of said substrate using a non-oxidizing carrier gas so that said powder metal plastically deforms without melting and bonds to a surface upon impact with said surface; and
- means for subjecting said at least one powder metal deposited layer to a treatment to improve density and/or raise a temperature of said at least one powder metal deposited layer.
24. An apparatus according to claim 23, wherein said subjecting means comprises a laser.
25. An apparatus according to claim 23, wherein said depositing means comprises:
- a source of powder metal; and
- means for delivering said powder metal to a convergent-divergent spray nozzle so that said powder metal exits said nozzle at a speed of from 825 m/s to 1400 m/s.
26. An apparatus according to claim 25, wherein said delivering means comprises means for supplying a carrier gas selected from the group consisting of helium, nitrogen, another inert gas, and mixtures thereof.
27. An apparatus according to claim 25, wherein said subjecting means comprises a laser attached to said spray nozzle.
Type: Application
Filed: Dec 21, 2004
Publication Date: Jun 22, 2006
Applicant:
Inventors: Andrew DeBiccari (North Branford, CT), Jeffrey Haynes (Stuart, FL)
Application Number: 11/019,751
International Classification: B22F 7/00 (20060101);
