EH-10789(03-550) ~ 02444917 2003-10-15 COLD SPRAYED COPPER FOR ROCKET ENGINE APPLICATIONS
CROSS-REFERENCE TO RELATED APPLICATION S
[0001 ~ The present application claims the benefit of U.S. Provisional Patent Application No.
(~() 419,~t03, entitled COLD SfRA~'ED COPPER FOR UPPER STAGE ROCKET
I-'\CINES. !il:cl October 1S. 2002.
FIELD OF THE INVENTION
(0002) 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.
[0003) Rocket thmst 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 (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.
[0004) Multiple attempts have been made to electroplate pure copper to this manifold face to 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 mils is very susceptible to blistering when exposed to heat due to entrapped solutions/impurities expanding.
(0005) Plating requires the part to be immersed in acids and plating solutions for long durations to achieve thick build ups on parts. Significant masking is required. Acid exposure is not always pernnitted on a part and could produce fatigue debits. Another disadvantage is that thickness build up is measured in days.
(0006] Thermal spray is another technique for applying a con.formal coating to a part.
Thermal spray requires the part to be exposed to very high temperatures locally. Parts with 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.
(0007) Thus, there is a need for an improved process for applying a copper deposit to the surfaces of a manifold used in a rocket engine.
EH-10789(03-550) CA 02444917 2003-10-15 SUMMARY OF THE INVENTION
[0008] 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 cycle.
[0009) The foregoing object is attained by the process of tllc present inv:a:tio::.
(0010( In accordance with tltc prcscm invention. at process fur applying a ~icposit ;it 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 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.
[0011) 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.
[0012] Other details of the cold sprayed copper for upper stage rocket engines, as well as other objects and advantages attendant thereto, are set forth in the following detailed description and the accompanying drawing wherein like reference numerals depict like elements.
BRIEF DESCRIPTION OF THE DRAWII~TG
[0013] 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 EMBODIMENTS) [0014] In accordance with the present invention, a process is provided for forming a deposit 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 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 Eli~10789(03-fJ50) ~ 02444917 2003-10-15 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 panicle size distribution, the better the velocity is. This is because if one has large and small particles (bi-modal), the small ones will hit the slower, larger ones and effectively reduce the velocity of both.
~Q015i Tlle bOtld117g 111eChat11St17 etllplp\'etl by tl7C pl-OCCSS Of the p1'CSellt 111VCIltlOtl for 11'E117Sf01'lllill~ the metal powder into a deposit is strictly solid state, lneanin;~ th<It tile yarticics plastically defonll. Any oxide layer that is formed is broken up and fresh metal-to-metal contact is made at very high pressures.
[0016] The powders used to form the deposit are fed using modified thermal spray feeders.
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.
[0017] In the process of the present invention, the feeders are pressurized with either nitrogen or helium. Feeder pressures are usually just above the main gas or head pressures, which head pressures usually range from 250 psi to 500 psi, depending on the powder alloy composition. The main gas is heated. Gas temperatures are usually 300°F
to 1200°F, but can go as high as approximately 1250°F depending on the material being applied to the substrate.
The gas is heated to keep it from rapidly cooling and freezing once it expands past the throat of the nozzle. The net effect is a substrate temperature of about 1 I
5°F during deposition {thus cold spray, not warm spray).
(0018] 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 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 - 30 mils 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 to 3 inches high. When building a deposit layer, one needs to limit the thickness per pass in order to avoid a quick build up of residual stresses and unwanted debonding between deposit layers. A thickness of S mils per pass appears to be optimal.
(0019] 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 Eli-10789(03-550) CA 02444917 2003-10-15 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 to 50 SCFM, preferably in the range of from 1S
SCFM to 35 SCFM, 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 gas may be passed through the nozzle 20 at a tow rate of from 0.001 SCFl~t to 30 SC.'FM, preferably from 4.0 SCFM
to 30 SCFM.
ThL main 'gas tcmpcrature may be in the ran'~c of from 600 "F to 1200 "F. The pressure of the spray 'gun ?? may be in the rany~c oi~ iiwm 2uu psi to ;ou psi, preferably from 250 psi to s50 psi. 'I-he copper powder may be fed into the gun via line 34 at a rate in the range of from 10 grams/min. to 100 gramslmin, preferably from 18 gramshnin. to 50 grams/min.
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 to 50 SCFM, preferably from 10 SCFM to 35 SCFM, for helium and from 0.001 SCFM to 30 SCFM, preferably from 4.0 SC.FM to 10 SCFM, for nitrogen.
Preferably, the spray nozzle 20 is held at a distance away from the surfaces) 24 or 2G of the substrate 10 being coated. This distance is known as the spray distance.
Preferably, the spray distance is in the range of from l0 mm. to 50 mm. The deposit thickness per pass may be in the range of 0.001 inch to 0.030 inches.
[0020] 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 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, a gas temperature of 600°F, a powder feed rate of 21 grams/min., a carrier flow rate of 13 SCFM helium, and a main gas flow rate of 34 SCFM helium.
[0021] 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.
[0022] The process of the present invention has particular utility in applying a thick copper deposit, greater than 0.050 inches, to internal and outer surfaces of a stainless steel manifold used in rocket engines.
[0023] It has been found that deposits formed on stainless steel substrates in accordance with the present invention can undergo heat treatment cycles, such as a 1800°F heat treatment, without blistering or bond disintegration. Further, the deposits can withstand cryoshock and EH-10789(03-$Sfl~ ~ 02444917 2003-10-15 thernial cycling without bond failure or weakening of coating integrity. Still further, the deposits do not blister or de-bond.
[0024] It is apparent that there has been provided in accordance with the present invention a cold sprayed copper for upper stage rocket engines which fully satisfies the objects. means, and adv,.nta~~es sei forth hereinbefore. While the present invention has been described in the ro;~text ol'snecific embociin~ents thereof, other <rlternatives, modifications, anti variations mill f~econw ahparcnt to those skilled in the art having read the fore~~oin'~
description.
:accordingly, it is intended to embrace-those alternatives, modifications, and variations as tall within the broad scope of the appended claims.