Abstract:
A nanophase composite duct assembly and method of fabricating the same are provided that comprise an ultra-high strength nanophase aluminum alloy duct joined with a ceramic particulate reinforced metal matrix fitting, preferably using solid-state friction welding. The nanophase aluminum alloy duct is fabricated by extruding a billet formed by a process of cryogenic milling the alloy, followed by out-gassing, then hot isostatic pressing. The fitting is fabricated by combining a ceramic particulate with a metal matrix, preferably by powder processing or liquid metal infiltration. Further, the solid-state friction welding may comprise inertial welding, friction stir welding, or a combination thereof. As a result, a lightweight duct assembly is provided for high-pressure liquids such as propellants in rocket engines.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 09/945,280 filed on Aug. 31, 2001, presently pending. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to high-pressure ducting and more particularly to high-pressure liquid ducting for propellants in rocket engines. 
     BACKGROUND OF THE INVENTION 
     High-pressure liquid propellant ducts on rocket engines are generally heavy and can represent approximately 10-20 percent of the total weight of the engine. Generally, the ducts comprise a tubular section that is joined to a flange portion at each end thereof to form a section of high-pressure liquid ducting. The section of high-pressure liquid ducting is further joined to another section of ducting or to another component of the rocket engine such as a propellant feed tank or an inlet to the rocket engine of, for example, an aerospace vehicle. 
     In the known art, high-pressure liquid propellant ducts are fabricated from nickel or iron-based superalloys such as 625 or 718, which have relatively high densities and thus contribute significantly to the weight of a rocket engine. To minimize weight, therefore, the ducts are ideally fabricated from materials with high specific strength and toughness for the tubular sections, which generally perform as pressure vessels. Similarly, the flange portions are fabricated from materials with high specific stiffness and hardness, wherein the flange portion performs primarily as a sealing section. 
     At the ambient or cryogenic temperatures of typical liquid propellant ducts, superalloys do not have an ideal high specific strength for the tubular section or an ideal high specific stiffness for the flange portion. For example, when a superalloy tubular section has been designed with sufficient strength to accommodate propellant pressure, the associated stiffness is relatively high such that small misalignments of the flange portions results in high stresses therein after assembly of the duct. Further, the assembly stress can represent approximately 60 percent of the total flange loading. Moreover, welding, weld inspection, and any rework necessary during assembly of high-pressure liquid ducts of the known art adds substantial cost to the rocket engine. 
     High strength aluminum alloys, although approximately one third the density of superalloys, have not been used for propellant ducts for a variety of reasons. Generally, the high strength condition in conventional aluminum alloys is achieved by a solution heat treat, followed by a water quench and age, which introduces constraints on forming, welding, and maximum component section thickness. Unfortunately, the aluminum alloy comprises undesirable residual stresses, anisotropic properties, and susceptibility to stress corrosion as a result of the heat treat, water quenching, and aging processes. 
     Further, conventional aluminum alloys generally have low stiffness, and thus any potential weight benefits of high specific strength in the stiffness-critical flange portions have not been achievable. Moreover, the high coefficient of thermal expansion of conventional aluminum alloys would require an excessively high preload in steel or superalloy bolts that are used to fasten and seal the flange portions to prevent loosening of the bolts during a chill-down process. 
     Accordingly, there remains a need in the art for lightweight high-pressure liquid ducts comprising aluminum alloys to provide significant weight savings over superalloy ducting of the known art. The high-pressure liquid ducts should comprise lightweight tubular sections in addition to lightweight flange portions, which are fabricated and assembled using manufacturing techniques applicable to the particular materials employed throughout the ducting. 
     SUMMARY OF THE INVENTION 
     In one preferred form, the present invention provides a nanophase composite duct assembly that comprises a high pressure liquid duct formed from an ultra-high strength nanophase aluminum alloy, which is joined with a high-pressure liquid ducting flange formed from a ceramic particulate in a metal matrix such as aluminum. Preferably, the duct is joined with the flange using solid-state friction welding such as inertia welding or friction stir welding, among others, as described in greater detail below. 
     The nanophase aluminum alloy duct is preferably formed by synthesizing a nanophase aluminum alloy to form a billet, extruding the billet into a predetermined geometrical shape, followed by bending the extruded billet into a profile to form the high-pressure liquid duct. Further, the extruded billet may be flow formed prior to bending in order to achieve a precise wall thickness with relatively tight tolerances for a particular application. 
     Generally, the nanophase aluminum alloy is synthesized by a powder processing sequence of cryogenic milling, out-gassing, and hot isostatic pressing (HIP) to form the billet. The billet is then extruded into a predetermined geometrical shape such as a cylindrical tube for use in many ducting applications for rocket engines. Further, in order to meet the dimensional requirements of rocket engine and other applications, the extruded billet is further flow formed to reduce the wall thickness of the duct to a desired dimension prior to bending, wherein relatively tight tolerances are maintained along the entire length of the extruded billet. (Generally, flow forming is a manufacturing technique that is used for high precision, high tolerance net shape component fabrication). 
     In preparation of the extrusion process, a center hole is machined through the center of the billet and an internal liner is secured within the center hole, along with an extrusion mandrel. A leader is then positioned at one end of the billet and a follower is positioned at another end of the billet, and an extrusion jacket is placed over the billet, the leader, and the follower. The billet is then extruded through an extrusion die, along with the internal liner, the extrusion jacket, the leader, and the follower, to form an extruded billet having a predetermined geometrical shape. Furthermore, other extrusion methods commonly known in the art may be employed in accordance with the teachings of the present invention. Accordingly, the preferred extrusion method as described herein shall not be construed as limiting the scope of the present invention. 
     The high-pressure liquid ducting flange comprising a ceramic particulate in a metal matrix is preferably formed by powder processing or by a liquid metal infiltration process. Further, the metal matrix is preferably aluminum in one form of the present invention. The high-pressure liquid ducting flange in one form comprises a series of radial holes wherein bolts are used to secure the flange to another flange portion or to another component within the systems of, for example, a rocket engine. In another embodiment, the high-pressure liquid ducting flange is a two-piece component comprising a nanophase flange joined to a discontinuously reinforced aluminum (DRA) base, preferably using inertia welding, wherein the nanophase flange is then joined to the high-pressure liquid duct. 
     The high-pressure liquid duct is joined to the high-pressure liquid ducting flange preferably using solid-state friction welding. The solid-state friction welding may comprise inertia welding or friction stir welding, or a combination of both inertia welding and friction stir welding, among others. Furthermore, the nanophase composite duct assembly may also comprise a collar between the high-pressure liquid duct and the high-pressure liquid ducting flange to further seal and secure the interface therebetween. Similarly, the collar is preferably welded to the high-pressure liquid duct and the high-pressure liquid ducting flange using solid-state friction welding. 
     Although the present invention is directed to a high-pressure liquid duct within a rocket engine, the invention may also be applicable to other high-pressure ducting applications. Accordingly, the reference to rocket engines throughout the description of the invention herein should not be construed as limiting the scope of the present invention. 
     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is an orthogonal view of a nanophase composite duct assembly in accordance with the present invention; 
         FIG. 2  is an exploded view of a nanophase aluminum alloy billet, an internal sleeve, an extrusion mandrel, a leader, a follower, and an extrusion jacket in accordance with the present invention; 
         FIG. 3  is a side view of a nanophase aluminum alloy billet, an internal sleeve, an extrusion mandrel, a leader, a follower, and an extrusion jacket in accordance with the present invention; 
         FIG. 4  is a side view of an extruded billet in accordance with the present invention; 
         FIG. 5  is an orthogonal view of a high-pressured liquid ducting flange in accordance with the present invention; 
         FIG. 6  is a side view of a high-pressure liquid duct joined with a high-pressure liquid ducting flange in accordance with the present invention; and 
         FIG. 7  is a side view of a collar around a high-pressure liquid duct and a high-pressure liquid ducting flange in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
     Referring to the drawings, a nanophase composite duct assembly according to the present invention is illustrated and generally indicated by reference numeral  10  in FIG.  1 . As shown, the nanophase composite duct assembly  10  generally comprises a high-pressure liquid duct  12  joined to a high-pressure liquid ducting flange  14 . Preferably, the high-pressure liquid duct  12  is an ultra-high strength nanophase aluminum alloy and the high-pressure liquid ducting flange  14  is formed from a ceramic particulate in a metal matrix, wherein the metal matrix is preferably aluminum. Accordingly, the nanophase composite duct assembly  10  provides significant weight and cost savings over superalloy high-pressure ducting of the known art. 
     The high-pressure liquid duct  12  is preferably formed by first synthesizing the nanophase aluminum alloy using powder processing. More specifically, the nanophase aluminum alloy is milled in a cryogenic high-energy ball mill while submerged in liquid nitrogen. After cryogenic milling, the nanophase aluminum alloy is out-gassed and pressed into a billet using hot isostatic pressing (HIP). As a result, a nanophase aluminum alloy billet is produced that is then preferably extruded into predetermined geometrical shape as described in greater detail below. Alternately, the nanophase aluminum alloy billet may be formed into the desired geometrical shape using other methods commonly known in the art such as machining, pultrusion, and die forming, among others. Accordingly, the extrusion process as described herein shall not be construed as limiting the scope of the present invention. 
     Referring to  FIGS. 2 and 3 , a nanophase aluminum alloy billet  16  is illustrated along with an internal sleeve  18 , an extrusion mandrel  20 , a leader  22 , a follower  24 , and an extrusion jacket  26 , which are used to contain and extrude the nanophase aluminum alloy billet  16  during the extrusion process. As further shown, a center hole  28  is created through the nanophase aluminum alloy billet  16 , preferably by machining, and the internal sleeve  18  along with the extrusion mandrel  20  are placed within the center hole  28 . Further, the leader  22  is placed at one end of the nanophase aluminum alloy billet  16 , and the follower  24  is placed at another end thereof as shown. Generally, the leader  22  and the follower  24  are employed to increase the yield of the extrusion process and to provide consistent material properties. 
     The mandrel  20  further comprises a collar  21  as shown, which is preferably larger in diameter than the extrusion jacket  26 . Further, the mandrel  20  and the internal sleeve  18  extend through the extrusion jacket  26  as illustrated. Accordingly, the internal sleeve  18  is preferably split to form ears  29 , which prevent the internal sleeve  18  from slipping during the extrusion process. 
     As further shown, the extrusion jacket  26  is placed over the nanophase aluminum alloy billet  16 , the leader  22 , and the follower  24 . Generally, the extrusion jacket  26  is provided to encapsulate the nanophase aluminum alloy billet  16  during the extrusion process. Preferably, the extrusion jacket  26 , along with the internal sleeve  18 , are a copper material, and the leader  22  and the follower  24  are preferably an aluminum material such as 6061-T6. 
     The extrusion jacket  26 , the nanophase aluminum alloy billet  16  with the internal sleeve  18  and the extrusion mandrel  20 , the leader  22 , and the follower  24  are then placed in an extrusion die (not shown), wherein the mandrel  20  is activated to force the aluminum alloy billet  16  with the internal sleeve  18 , along with the extrusion jacket  26 , the leader  22 , and the follower  24  through the die to form an extruded billet having a predetermined geometrical shape. Preferably, the nanophase aluminum alloy billet  16 , the leader  22 , and the extrusion jacket  26  are preheated prior to extrusion, while the follower  24  remains at approximately room temperature. Further, the internal sleeve  18  is also preheated, however, at temperatures somewhat higher than the nanophase aluminum alloy billet  16 , the leader  22 , and the extrusion jacket  26 . 
     In one form of the present invention, a nanophase aluminum alloy billet having a diameter of approximately 9.125 inches is extruded at an area reduction ratio of approximately 20:1. The nanophase aluminum alloy billet  16 , the leader  22 , and the extrusion jacket  26  are preheated to approximately 400° F., the follower  24  remains at approximately room temperature, the internal sleeve  18  is preheated to approximately between 550° F. and 610° F., and the die temperature is approximately between 350° F. and 500° F. with an extruder having approximately a 5,000 ton capacity. Accordingly, a high-pressure liquid duct is extruded in one form of the present invention that has an outer diameter of approximately 3.35 inches and an inner diameter of approximately 2.80 inches. Additionally, alternate dimensions according to specific applications may also be achieved in accordance with the teachings of the present invention. 
     Referring to  FIG. 4 , an extruded billet  30  is illustrated, which is a result of the extrusion process as described herein. The geometrical shape in one form is tubular as shown, however, other geometrical shapes may also be created according to specific application requirements, including constant and non-constant cross sections. As shown, the extruded billet  30  comprises an outer diameter  32 , an inner diameter  34 , and a wall thickness  36 , wherein the outer diameter  32  is significantly smaller than the diameter of the nanophase aluminum alloy billet  16  (not shown) prior to the extrusion process. 
     Once the nanophase aluminum alloy billet  16  is extruded into the predetermined geometrical shape to form the extruded billet  30 , the extruded billet  30  is preferably flow formed to further reduce the wall thickness  36  to a desired dimension. Generally, flow forming produces precise and consistent dimensions along the entire length of the extruded billet  30  within relatively tight tolerances. Accordingly, for applications requiring tighter dimensional control, flow forming is employed after the extrusion process as described herein. 
     To complete the high-pressure liquid duct  12 , the extruded billet undergoes a bending operation to form a profile that corresponds with the final shape of the nanophase composite duct assembly  10 . In one form, the geometry of the high-pressure liquid duct  12  is tubular as shown, and thus tube bending operations as commonly known in the art are employed to create the desired profile. Accordingly, further forming methods known in the art may also be employed in accordance with the teachings of the present invention. 
     The high-pressure liquid duct  12  may also be formed using other methods commonly known in the art such as die forming, pultrusion, or blow forming, among others. Accordingly, the description of extrusion and bending processes herein to form the high-pressure liquid duct  12  shall not be construed as limiting the scope of the present invention. 
     Referring to  FIG. 5 , the high-pressure liquid ducting flange  14  is illustrated, wherein a plurality of radial holes  40  are formed therethrough for bolts (not shown) that secure the high-pressure liquid ducting flange  14  to other portions of rocket engine systems. The high-pressure liquid ducting flange  14  generally comprises ceramic particulates in a metal matrix and is preferably formed by powder processing or liquid metal infiltration. In one form, the ceramic particulate comprises B 4 C (boron carbide) in an A356 (aluminum) matrix, wherein the percent by volume of B 4 C is approximately 52 percent. Additional materials for the ceramic particulates and the metal matrix, further in various percentages, may also be employed in accordance with the teachings of the present invention. For example, in one form of the present invention, a SiC (silicon carbide) particulate is employed at a volume by percent of approximately 18 percent within an aluminum matrix. 
     In another form of the present invention, the high-pressure liquid ducting flange  14  is a two-piece component comprising a nanophase flange joined to a discontinuously reinforced metal matrix base (not shown). Preferably, the nanophase flange is joined to the discontinuously reinforced metal matrix base using inertia welding to form the completed high-pressure liquid ducting flange  14 . Further, the nanophase flange portion of the high-pressure liquid ducting flange  14  is joined to the high-pressure liquid duct, while the discontinuously reinforced metal matrix base portion is joined to other portions of rocket engine systems as previously described. Accordingly, the nanophase flange portion defines a tapered outer surface that generally transitions from the diameter of the high-pressure liquid duct  12  to the larger diameter of the discontinuously reinforced metal matrix base portion. Preferably, the metal matrix is aluminum for the discontinuously reinforced metal matrix base portion. 
     Referring now to  FIG. 6 , the high-pressure liquid duct  12  is joined to the high-pressure liquid ducting flange  14  along an interface  41  as shown. Preferably, the high-pressure liquid duct  12  and the high-pressure liquid ducting flange  14  are joined using solid-state friction welding along the interface  41 . The solid-state friction welding may comprise inertia welding, friction stir welding, or a combination of both inertia welding and friction stir welding, among others commonly known in the art. 
     As shown in  FIG. 7 , a collar  42  may also be employed around the joint between the high-pressure liquid duct  12  and the high-pressure liquid ducting flange  14  to further secure and seal the interface therebetween. Similarly, the collar  42  is preferably secured to the high-pressure liquid duct  12  and the high-pressure liquid ducting flange  14  along interfaces  43  using solid-state friction welding as described herein. 
     Accordingly, a lightweight, low cost composite duct assembly is provided in accordance with the teachings of the present invention. The composite duct assembly comprises a lightweight nanophase aluminum alloy duct that is joined with a lightweight ceramic particulate reinforced aluminum matrix flange, which together with the joining methods as described herein provide significant weight savings over superalloy ducting of the known art. 
     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the substance of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.