GB2394479A

GB2394479A - Cold Spray Process for Coating Substrates

Info

Publication number: GB2394479A
Application number: GB0324367A
Authority: GB
Inventors: Jeffrey D Haynes; Karthikeyan Jeganathan
Original assignee: United Technologies Corp
Current assignee: Raytheon Technologies Corp
Priority date: 2002-10-18
Filing date: 2003-10-17
Publication date: 2004-04-28
Anticipated expiration: 2023-10-17
Also published as: RU2003130773A; RU2266978C2; JP2004137602A; FR2845937A1; GB0324367D0; DE10346836C5; CA2444917A1; FR2845937B1; DE10346836B4; GB2394479B; DE10346836A1

Abstract

A process for applying a coating to a substrate 10 comprising the steps of providing metal particles having a size up to 50 microns and passing the metal particles through a spray nozzle 20 at a speed sufficient to plastically deform them on the substrate. The metal particles preferably have a size of between 5-50 microns, and may be chosen from copper alloy, aluminium alloy or nickel alloy particles. The particles are preferably fed to the nozzle using a carrier gas of helium, nitrogen or a mixture of both. The substrate is preferably a stainless steel manifold for a rocket engine, and the coating is applied to at least one of its outer surface 26 or its inner surface 24. The nozzle may deposit a layer 28 between 0.025 - 0.076 mm thick per pass, and the total thickness of the layer may be greater than 1.27mm.

Description

PROCESS FOR APPLYING A COATING TO A SURFACE

FIELD OF THE INVENTION

5 The present invention relates to a process for applying a copper deposit onto surfaces of a substrate, in particular, a manifold to be used in a rocket engine.

Rocket thrust chamber designs include two manifolds that collect and distribute the fuel (typically liquid hydrogen) to the combustion chamber. One of these manifolds is usually located immediately adjacent to the injector assembly where the fuel and oxidizer 10 (typically liquid oxygen) are mixed and ignited. Both manifolds are made from a high strength stainless steel to contain the high pressure cryogenic fuel. The manifold that is located near the injector tends to be exposed to very high temperature combusted gases. As a result, this manifold requires active cooling on the face that is closest to the injector.

Multiple attempts have been made to electroplate pure copper to this manifold face to 15 conduct the coolant across the gap to the injector face. However, the manifold subsequently receives a high temperature braze cycle which in the past has resulted in blistered copper.

Deposit thicker than a few mile is very susceptible to blistering when exposed to heat due to entrapped solutions/impurities expanding.

Plating requires the part to be immersed in acids and plating solutions for long 20 durations to achieve thick build ups on parts. Significant masking is required. Acid exposure is not always permitted on a part and could produce fatigue debits. Another disadvantage is that thickness build up is measured in days.

Thermal spray is another technique for applying a conformal coating to a part.

Thermal spray requires the part to be exposed to very high temperatures locally. Parts with 25 thermal sensitivities and tight dimensional tolerances (distortion from thermals) are limited to this exposure. Oxides are typically formed with thermal spray melting and resolidification in air atmosphere. Oxides reduce ductility of coatings significantly and are difficult to remove.

Vacuum systems are possible but very expensive and difficult to control.

Thus, there is a need for an improved process for applying a copper deposit to the 30 surfaces of a manifold used in a rocket engine.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a process for applying a copper deposit to a substrate which will not blister after receiving a high temperature braze 5 cycle. The foregoing object is attained by the process of the present invention.

In accordance with the present invention, a process for applying a deposit to a substrate comprises the steps of providing metal powder particles having a size in the range of from a size sufficient to avoid getting swept away from the substrate due to a bow shock 10 layer to up to 50 microns and forming a deposit layer on at least one surface of the substrate by passing the metal powder particles through a spray nozzle at a speed sufficient to plastically deform the metal powder particles on the at least one surface.

The present invention also relates to a rocket engine having a stainless steel manifold coated on at least one of an inner surface and/or an outer surface with a copper alloy coating.

15 Other details of the cold sprayed copper for upper stage rocket engines are set forth in the following detailed description and the accompanying drawing wherein like reference

numerals depict like elements.

BRIEF DESCRIPTION OF TlIE DRAWING

20 The figure is a schematic representation of a spray nozzle used to coat the surfaces of a manifold used in a rocket engine.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

In accordance with the present invention, a process is provided for forming a deposit 25 or coating on outer and/or inner surfaces of a substrate 10, such as a manifold formed from a metal alloy material, e.g. stainless steel, used in a rocket engine. The process is a cold gas dynamic spraying (or"cold spray") process. In this process, fine metallic powders are accelerated to supersonic velocities using compressed gas, for example helium and sometimes nitrogen. Helium is a preferred gas in this process due to its low molecular weight 30 and produces the highest velocity at the highest gas cost. The powder which is used to form the deposit is typically a metal powder having particles with a size in the range of from 5 microns to 50 microns. Typical thermal spray powders are usually too large for cold spray.

Smaller particle sizes such as those mentioned above enable the achievement of higher particle velocities. Below 5 microns in diameter, the particles of powder get swept away

from the substrate due to a bow shock layer just above the substrate (insufficient mass to propel through the bow shock). The narrower the particle size distribution, the better the velocity is. This is because if one has large and small particles (hi -modal), the small ones will hit the slower, larger ones and effectively reduce the velocity of both.

5 The bonding mechanism employed by the process of the present invention for transforming the metal powder into a deposit is strictly solid state, meaning that the particles plastically deform. Any oxide layer that is formed is broken up and fresh metal-to -metal contact is made at very high pressures.

The powders used to form the deposit are fed using modified thermal spray feeders.

10 Difficulty in feeding using standard feeders is due to the fine particle sizes and high pressures. One custom designed feeder which 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 are pressurized with either nitrogen 15 or helium. Feeder pressures are usually just above the main gas or head pressures, which head pressures usually range from 250 psi (1.72 mPa) to 500 psi (3.44 mPa), depending on the powder alloy composition. The main gas is heated. Gas temperatures are usually 300 F (148.9 C) to 1200 F (648.9 C), but can go as high as approximately 1250 F (676.7 C) depending on the material being applied to the substrate. The gas is heated to keep it from 20 rapidly cooling and freezing once it expands past the throat of the nozzle. The net effect is a substrate temperature of about 115 F (46.1 C) during deposition (thus cold spray, not warm spray). To form the deposit on the substrate 10, the nozzle 20 of a spray gun 22 must pass over the surface(s) 24 and 26 of the substrate 10 more than once. The number of passes 25 required is a function of the thickness of the deposit to be applied. The process of the present invention is capable of forming a deposit 28 having a thickness of 2 mile (0.05 mm-0.76 mm) per pass. If one wants to form a thick layer, the spray gun 22 can be held stationary and be used to form a deposit layer which is 2 inches (50.8 mm) to 3 inches (76.2 mm) high.

When building a deposit layer, one needs to limit the thickness per pass in order to avoid a 30 quick build up of residual stresses and unwanted debonding between deposit layers. A thickness of 5 mile (0.127 mm) per pass appears to be optimal.

It has been found that if one wanted to apply a copper or copper alloy deposit or coating 28 to a substrate 10, such as a stainless steel manifold, one can use copper powder having particles with a size of up to 50 microns, preferably a particle size in the range of from

5 microns to 30 microns. The main gas may be passed through the nozzle 20 via inlet 30 and/or 32 at a flow rate of from 0.001 SCFM (0.0283 1/min) to 50 SCFM (1416 1/min), preferably in the range of from 15 SCFM (424.8 1/min) to 35 SCFM (991.2 1/min), if helium is used as the main gas. If nitrogen is used by itself or in combination with helium as the 5 main gas, the nitrogen gas may be passed through the nozzle 20 at a flow rate of from 0.001 SCFM (0.0283 1/min) to 30 SCFM (849.6 1/min), preferably from 4.0 SCFM (113.28 1/min) to 30 SCFM (849.6 1/min). The main gas temperature may be in the range of from 600 F (315.6 C) to 1200 F (648. 9 C). The pressure of the spray gun 22 may be in the range of from 200 psi (1.37 mPa) to 350 psi (2.41 mPa), preferably from 250 psi (1.72 mPa) to 350 10 psi (2.41 mPa). The copper powder may be fed into the gun via line 34 at a rate in the range of from 10 grams/mint to 100 grams/min, preferably from 18 grams/mint to 50 grams/mint The copper powder is preferably fed using a carrier gas, introduced via inlet 30 and/or 32, having a flow rate of from 0.001 SCFM (0.0283 1/min) to 50 SCFM (1416 1/min), preferably from 10 SCFM (283.2 1/min) to 35 SCFM (991.2 1/min), for helium and from 0.001 SCFM 15 (0.0283 1/min) to 30 SCFM (849.6 l/min), preferably from 4.0 SCFM (113.28 1/min) to 10 SCFM (283.2 1/min), for nitrogen. Preferably, the spray nozzle 20 is held at a distance away from the surface(s) 24 or 26 of the substrate 10 being coated. This distance is known as the spray distance. Preferably, the spray distance is in the range of from 10 mm. to 50 mm. The deposit thickness per pass may be in the range of 0.001 inch (0.025 mm) to 0.030 inches 20 (0.076 mm).

While the present invention has been described in the context of applying copper powder, the process of the present invention may be used to apply an aluminum based alloy or a nickel based alloy deposit. The harder the alloy, the higher the parameters needed to get close to the as-sprayed density of softer alloys. The parameter ranges mentioned above for 25 forming a copper deposit may also be used to form an aluminum deposit or a nickel deposit.

For example, an aluminum alloy deposit may be formed using a gun head pressure of 300 psi (2.07 mPa), a gas temperature of 600 F (315.6 C), a powder feed rate of 21 grams/mint, a carrier flow rate of 13 SCFM (368.16 1/min) helium, and a main gas flow rate of 34 SCFM helium (962.88 1/min).

30 The process of the present invention has the advantages of eliminating long-lead times and non-environmentally friendly plating processes and can be accomplished in a much shorter time than other plating techniques, which techniques often take weeks.

The process of the present invention has particular utility in applying a thick copper deposit, greater than 0.050 inches (1.27 mm), to internal and outer surfaces of a stainless steel manifold used in rocket engines.

It has been found that deposits formed on stainless steel substrates in accordance with 5 the present invention can undergo heat treatment cycles, such as a 1800 F (982.2 C) heat treatment, without blistering or bond disintegration. Further, the deposits can withstand cryoshock and thermal cycling without bond failure or weakening of coating integrity. Still further, the deposits do not blister or de-bond.

It is apparent that there has been described above a cold sprayed copper for upper 10 stage rocket engines which fully satisfies 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. Accordingly, it is intended to

embrace those alternatives, modifications, and variations as fall within the broad scope of the 15 appended claims.

Claims

1. A process for applying a coating material to a substrate comprising the steps of: providing metal powder particles having a size in the range of from a size sufficient to avoid getting swept away from the substrate due to a bow shock layer to up to 50 microns; and forming a deposit layer on at least one surface of said substrate by passing said metal lO powder particles through a spray nozzle at a speed sufficient to plastically deform the metal powder particles on said at least one surface.

2. A process according to claim 1, wherein said metal powder particles providing step comprises providing metal powder particles having a particle size in the range of from 15 5 microns to 50 microns.

3. A process according to claim 1 or 2, wherein said metal powder particles providing step comprises providing a powder selected from the group consisting of copper alloy particles, aluminum alloy particles and nickel alloy particles.

4. A process according to any preceding claim, wherein said powder providing step comprises feeding said metal powder particles to said nozzle at a feed rate of from 10 grams/mint to 100 grams/min and at a pressure in the range of from 250 psi (1.72 mPa) to 500 psi (3.44 mPa) using a carrier gas selected from the group of helium, nitrogen, 25 and mixtures thereof.

5. A process according to claim 4, wherein said feeding step comprises feeding said metal powder particles to said nozzle at a rate of from 0. 001 gramstmin to 50 grams/mint 30

6. A process according to claim 4 or 5, wherein said carrier gas comprises helium and said feeding step comprises feeding said helium to said nozzle at a flow rate of from 0.001 SCFM to 50 SCFM (0.0283 to 14161/min)

7. A process according to claim 4 or 5, wherein said carrier gas comprises helium and said feeding step comprises feeding said helium to said nozzle at a flow rate of from 10 SCFM to 35 SCFM (283.2 to 991. 21/min).

5

8. A process according to claim 4 or 5, 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 (0.0283 to 849.61/min).

9. A process according to claim 4 or 5, wherein said carrier gas comprises nitrogen and 10 said feeding step comprises feeding said nitrogen to said nozzle at a flow rate of from 4.0 SCFM to 10 SCFM (113. 28 to 283.21/min).

10. A process according to any preceding claim, wherein said forming step further comprises passing said metal powder particles through said nozzle using a main gas 15 selected from the group consisting of helium, nitrogen and mixtures thereof at a main gas temperature in the range of from 600 OF to 1200 F (315.6 to 648.9 C) and at a spray pressure in the range of from 200 psi to 350 psi(1.37 mPa to 2.41 mPa).

11. A process according to claim 10, wherein said passing step comprises passing said 20 metal powder particles through said nozzle at a spray pressure in the range of from 250 psi to 350 psi(1.72 mPa to 2.41 mPa).

12. A process according to claim 10 or 1 1, wherein said main gas comprises helium and wherein said passing step comprises feeding said helium to said nozzle at a rate in the 25 range of from 0.001 SCFM to 50 SCFM (0.0283 to 14161/min).

13. A process according to claim 10 or 11, wherein said main gas comprises helium and wherein said passing step comprises feeding said helium to said nozzle at a rate in the range offrom 15 SCFM to 35 SCFM (424.8 to 991.21/min).

14. A process according to claim 10 or 11, wherein said main gas comprises nitrogen and wherein said passing step comprises feeding said nitrogen to said nozzle at a rate in the range of from 0.001 SCFM to 30 SCFM (0.0283 to 849.61/min).

15. A process according to claim 10 or 11, wherein said main gas comprises nitrogen and wherein said passing step comprises feeding said nitrogen to said nozzle at a rate in the range offrom 4.0 SCFM to 30 SCFM (113.28 to 849.6 1/min).

5

16. A process according to any preceding claim, wherein said substrate comprises a metal alloy manifold for a rocket engine.

17. A process according to claim 16, wherein said substrate comprises a stainless steel, manifold for a rocket engine.

18. A process according to claim 16 or 17 wherein said deposit is applied to at least one of an inner surface (24) and an outer surface (26) of said manifold.

19. A process according to claim 16, 17 or 18, wherein said deposit is formed from copper 15 or a copper alloy.

20. A process according to claim 19, wherein said deposit layer forming step comprises forming a layer of said copper alloy having a thickness in the range of from 0.001 inches to 0.030 inches (0.025 to 0.076 mm) per pass of said nozzle (20) over said at 20 least one of said outer surface (24) and said inner surface (26).

21. A process according to any preceding claim, further comprising maintaining said nozzle (20) at a distance of from 10 mm. to 50 mm. from said at least one surface (24) being coated.

22. A process according to any preceding claim, wherein said deposit has a thickness greater than 0.050 inches (1.27 mm).

23. A rocket engine manifold having a deposit of a copper containing material on at least 30 one surface, said copper deposit being applied by the process of any preceding claim.

24. A process for applying a coating material to a substrate substantially as hereinbefore described with reference to the accompanying drawing.

25. A rocket engine manifold substantially as hereinbefore described with reference to the accompanying drawing.