Patent Publication Number: US-2021178511-A1

Title: Transient liquid phase bonding of surface coatings and metal-covered materials

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Patent Application Ser. No. 61/844,118 filed on Jul. 9, 2013 and to U.S. Provisional Patent Application Ser. No. 61/844,032 filed on Jul. 9, 2013. 
    
    
     FIELD OF DISCLOSURE 
     The present disclosure generally relates to methods for joining metal-coated materials, and to methods for producing customized metallic coatings. More specifically, this disclosure relates to the use of transient liquid phase (TLP) for joining metal-coated materials and for the production of customized metallic coatings on metallic substrates. 
     BACKGROUND 
     Technological advances in metal-covered non-metallic materials such as metal-plated polymers and metal-plated composites (collectively referred to herein as “plated polymers”) provide for their use in gas turbine engines. Plated polymers can be substituted for gas turbine engine components previously composed of metals, alloys and traditional composites. 
     However, due to the presence of polymers and/or composite materials, plated-polymer components cannot be joined to other metal components by many conventional methods. Polymers tend to flow or outgas at relatively low temperatures. Thus, welding and brazing, techniques commonly used for joining two metal components, require temperatures that can cause deformation or destruction of the polymer or composite substrate of a plated polymer component. As a result, few methods can be used to join plated polymer components to themselves or to other metal structures. Hardware and assembly devices such as bolts and rivets can be used, but these forms of fastening have disadvantages and limitations. Clearly, there is a need for improved methods for joining plated polymer components to other metal components, including metal-covered components. 
     In addition, many metallic structures employed in industries such as, but not limited to, aerospace and automotive industries may derive substantial beneficial properties from the application of metallic coatings to their surfaces. Modifications of the exterior surfaces of metallic structures with metallic coatings may occur without altering the interior of the metallic structures. Depending on the industrial use of the metallic structure, metallic coatings may be selected based on their ability to impart the surfaces of the metallic structure with one or more desired properties such as, but not limited to, enhanced hardness, wear resistance, oxidation resistance, or conductivity. Although conventional coating application methods, such as cold spraying, may provide a metallic interlock between the metallic substrate and the coating, in some cases it may be desirable to form a more robust and thermally stable bond between the metallic substrate and the coating. Furthermore, current metallic coating application methods typically do not provide surface coatings which have a blend of the microstructural and physical properties of both the metallic substrate and the metallic coating(s). In this regard, methods which allow an engineer to select and combine metallic coatings to provide customized coatings having a mixture of desired properties are wanting. Clearly, there is also a need for methods which provide more thermally stable bonds between metallic substrates and the metallic coating(s) and which result in a customized surface coating having a mixture of the properties of the metallic substrate and the metallic coating(s). 
     SUMMARY 
     In accordance with one aspect of the present disclosure, a method of bonding components is disclosed. The method can include positioning an interlayer between a first metallic component and a metal-plated non-metallic component at a bond region, heating the bond region to a bonding temperature to produce a liquid at the bond region, and maintaining the bond region at the bonding temperature until the liquid produced at the bond region has solidified to form a bond between the first metallic component and the metal-plated non-metallic component at the bond region. The interlayer can include an element selected from the group consisting of gallium, indium, selenium, tin, bismuth, iodine, polonium, cadmium, and combinations thereof. 
     The method of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     A further embodiment of the foregoing method can further include homogenizing the bond. 
     A further embodiment of any of the foregoing methods can further include homogenizing the bond at a temperature substantially equivalent o the bonding temperature. 
     A further embodiment of any of the foregoing methods can further include homogenizing the bond at a temperature lower than the bonding temperature. 
     A further embodiment of any of the foregoing methods can further include that the first metallic component is selected from the group consisting of metal-plated polymers and metal-plated composites. 
     A further embodiment of any of the foregoing methods can further include that one of the first metallic component and the metal-plated non-metallic component are selected from the group consisting of ribs, bosses, flanges, channels, clamps, covers, ducts and brackets. 
     A further embodiment of any of the foregoing methods can further include that the interlayer has a thickness between about 0.00127 mm (0.00005 inches) and about 1.27 mm (0.050 inches). 
     A further embodiment of any of the foregoing methods can further include that the interlayer has at least 50% by weight of an element selected from the group consisting of gallium, indium, selenium, tin, bismuth, iodine, polonium, cadmium, and combinations thereof. 
     A further embodiment of any of the foregoing methods can further include an interlayer having a first layer with a first thickness, a second layer adjacent the first layer with a second thickness greater than the first, and a third layer adjacent the second layer on a side generally opposite the first layer. 
     A further embodiment of any of the foregoing methods can further include that the first layer has an element selected from the group consisting of gallium, indium, selenium, tin, bismuth, iodine, polonium, cadmium, and combinations thereof. 
     A further embodiment of any of the foregoing methods can further include that the second layer has an element selected from the group consisting of refractory metals nickel, iron, cobalt, gold, magnesium, silver, copper, antimony, manganese, palladium, strontium, tellurium, ytterbium, aluminum, calcium, europium, gadolinium, germanium, platinum, rhodium, thulium, vanadium, and combinations thereof. 
     A further embodiment of any of the foregoing methods can further include that the third layer has an element selected from the group consisting of gallium, indium, selenium, tin, bismuth, iodine, polonium, cadmium, and combinations thereof. 
     A further embodiment of any of the foregoing methods can further include that the second thickness is between about 0.00254 mm (0.0001 inches) and about 1.27 min (0.050 inches). 
     A further embodiment of any of the foregoing methods can further include that the first thickness is between about 0.2% and about 20% of the second thickness. 
     A further embodiment of any of the foregoing methods can further include that the metal-plated non-metallic component is a metal-plated polymer having a polymer component having a polymer selected from the group consisting of polyphenylene sulfides, polyamides, polyvinylchloride (PVC), polystyrene (PS), polyethylene (PE), polypropylene (PP), styrene-acrylonitrile (SAN), polycarbonate (PC), acrylonitrile styrene acrylate (ASA), acrylonitrile butadiene styrene (ABS), ethylene tetrafluoroethylene fluoropolymer (ETFE), high impact polystyrene (HIPS), polyamide (PA), polybutylene terephthalate (PBT), polyetherimide (PEI), perchloroethylene (PCE), polyether sulfone (PES), polyethylene terephthalate (PET), polysulfone (PSU), polyurethane (PUR), polyvinylidene fluoride (PVDF), polyether ether ketone (PEEK), polyetherimide (PEI), thermoplastic polyimide, condensation polyimide, addition polyimide, polyether ketone ketone (PEKK), polysulfone, polyphenylsulfide, polyester, epoxy cured with aliphatic and/or aromatic amines and/or anhydrides, cyanate esters, phenolics, polyacrylates, polymethacrylates, silicones (thermoset), and combinations thereof; and a metallic layer covering at least a portion of the polymer component such that the metallic layer is located at the bond region of the second component. 
     A further embodiment of any of the foregoing methods can further include that the metallic layer has an element selected from the group consisting of nickel, cobalt, iron, gold, silver, copper, alloys of nickel, cobalt, iron, gold, silver, and copper, and combinations thereof. 
     A further embodiment of any of the foregoing methods can further include that the metallic layer has a thickness between about 0.127 mm (0.005 inches) and about 2.54 mm (0.100 inches). 
     A further embodiment of any of the foregoing methods can further include that the polymer component has an average thickness between about 1.27 mm (0.050 inches) and about 12.7 mm (0.500 inches). 
     A further embodiment of any of the foregoing methods can further include that the metal-plated non-metallic component is a metal-plated composite having a composite component with an average thickness between about 1.27 mm (0.050 inches) and about 12.7 mm (0.500 inches) and a metallic layer covering at least a portion of the composite component such that the metallic layer is located at the bond region of the second component. 
     A further embodiment of any of the foregoing methods can further include that the metallic layer has a thickness between about 0.127 mm (0.005 inches) and about 2.54 mm (0.100 inches). 
     A further embodiment of any of the foregoing methods can further include that the metal-plated non-metallic component is a metal-plated composite having a composite component; and a metallic layer covering at least a portion of the composite component such that the metallic layer is located at lite bond region of the second component. 
     In accordance with another aspect of the present disclosure, a bonded component is disclosed. The bonded component can include one of a polymer component or a composite component, a first metal layer covering the polymer component or composite component, a second metal layer, and a solidified layer located between the first and second metal layers that bonds the first metal layer to the second metal layer. The solidified layer can include an element selected front the group consisting of gallium, indium, selenium, tin, bismuth, iodine, polonium, cadmium, and combinations thereof. 
     The bonded component of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     A further embodiment of the foregoing bonded component can further include that the polymer component comprises a polymer selected from the group consisting of polyphenylene sulfides, polyamides, polyvinylchloride (PVC), polystyrene (PS), polyethylene (PE), polypropylene (PP), styrene-acrylonitrile (SAN), polycarbonate (PC), acrylonitrile styrene acrylate (ASA), acrylonitrile butadiene styrene (ABS), ethylene tetrafluoroethylene fluoropolymer (ETFE), high impact polystyrene (HIPS), polyamide (PA), polybutylene terephthalate (PBT), polyetherimide (PEI), perchloroethylene (PCE), polyether sulfone (PES), polyethylene terephthalate (PET), polysulfone (PSU), polyurethane (PUR), polyvinylidenc fluoride (PVDF), polyether ether ketone (PEEK), polyetherimide (PEI), thermoplastic polyimide, condensation polyimide, addition polyimide, polyether ketone ketone (PEKK), polysulfone, polyphenylsulfide, polyester, epoxy cured with aliphatic and/or aromatic amines and/or anhydrides, cyanate esters, phenolics, polyacrylates, polymethacrylates, silicones (thermoset), and combinations thereof. 
     A further embodiment of any of the foregoing bonded components can further include that the second metal layer covers a second polymer component or composite component. 
     A further embodiment of any of the foregoing bonded components can further include that the solidified layer further has an element selected from the group consisting of refractory metals, nickel, iron, cobalt, gold, magnesium, silver, copper, antimony, manganese, palladium, strontium, tellurium, ytterbium, aluminum, calcium, europium, gadolinium, germanium, platinum, rhodium, thulium, vanadium, and combinations thereof. 
     A further embodiment of any of the foregoing bonded components can further include that the polymer component or composite component has an average thickness between about 1.27 mm (0.050 inches) and about 12.7 mm (0.500 inches), and wherein the first metal layer has a thickness between about 0.127 mm (0.005 inches) and about 2.54 mm (0.100 inches). 
     In accordance with another aspect of the present disclosure, a bonded component can include a first polymer or composite component, a first metal layer covering the first polymer or composite component, a second polymer or composite component, a second metal layer covering the second polymer or composite component, and a solidified layer located between the first and second metal layers that bonds the first metal layer to the second metal layer, the solidified layer comprising an element selected from the group consisting of gallium, indium, selenium, tin, bismuth, iodine, polonium, cadmium, and combinations thereof. 
     The bonded component of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     A further embodiment of the foregoing bonded component can further include that the solidified layer further contains an element selected from the group consisting of refractory metals, nickel, iron, cobalt, gold, magnesium, silver, copper, antimony, manganese, palladium, strontium, tellurium, ytterbium, aluminum, calcium, europium, gadolinium, germanium, platinum, rhodium, thulium, vanadium, and combinations thereof. 
     A further embodiment of any of the foregoing bonded components can further include that the first and second polymer or composite components have a material selected from the group consisting of polyphenylene sulfides, polyamides, polyvinylchloride (PVC), polystyrene (PS), polyethylene (PE), polypropylene (PP), styrene-acrylonitrile (SAN), polycarbonate (PC), acrylonitrile styrene acrylate (ASA), acrylonitrile butadiene styrene (ABS), ethylene tetrafluoroethylene fluoropolymer (ETFE), high impact polystyrene (HIPS), polyamide (PA), polybutylene terephthalate (PBT), polyetherimide (PEI), perchloroethylene (PCE), polyether sulfone (PES), polyethylene terephthalate (PET), polysulfone (PSU), polyurethane (PUR), polyvinylidene fluoride (PVDF), polyether ether ketone (PEEK), polyetherimide (PEI), thermoplastic polyimide, condensation polyimide, addition polyimide, polyether ketone ketone (PEKK), polysulfone, polyphenylsulfide, polyester, epoxy cured with aliphatic and/or aromatic amines and/or anhydrides, cyanate esters, phenolics, polyacrylates, polymethacrylates, silicones (thermoset), and combinations thereof. 
     In accordance with another aspect of the present disclosure, a method for providing a part having a customized coating is disclosed. The method may comprise applying a metallic coating on a surface of a metallic substrate to provide a coated substrate, and bonding the metallic coating to the substrate by a transient liquid phase bonding process to provide the part having the customized coating. 
     In another refinement, the customized coating may have a set of properties different than those of the metallic substrate and the metallic coating. 
     In another refinement, the transient liquid phase bonding process may comprise progressively heating the coated substrate to a bonding temperature. 
     In another refinement, progressively heating the coated substrate to the bonding temperature may cause at least a portion of the metallic coating to melt and form a liquid interlayer, the liquid interlayer to expand in thickness and dissolve a portion of a material forming the metallic substrate, and the liquid interlayer to undergo an isothermal solidification process. 
     In another refinement, the bond between the customized coating and the metallic substrate may have a inching temperature that exceeds the bonding temperature. 
     In another refinement, heating the coated substrate to the first temperature may cause the metallic coating to melt by direct melting. 
     In another refinement, heating the coated substrate to the first temperature may cause a portion of the metallic coating to melt by eutectic melting, and the liquid interlayer may be formed between the metallic substrate and an un-melted portion of the metallic coating. 
     In another refinement, the method may further comprise heating the part past the bonding temperature to increase a fraction of the material forming the metallic substrate in the customized coating. 
     In accordance with another aspect of the present disclosure, a method for providing a part having a customized coating is disclosed. The method may comprise: 1) applying a first metallic coating on a surface of a metallic substrate, 2) applying a second metallic coating on the first metallic, coating to provide a coated substrate, and 3) bonding the first metallic coating and the second metallic coating to the metallic substrate by a transient phase bonding process to provide the part having the customized coating. 
     In another refinement, the first metallic coating and the second metallic coating may each have a thickness ranging from less than about 0.001 millimeters up to about 0.5 millimeters. 
     In another refinement, the transient liquid phase bonding process may comprise progressively heating the coated substrate to a bonding temperature. 
     In another refinement, progressively heating the coated substrate to the bonding temperature may comprise: 1) heating the coated substrate to a first temperature that is lower than the bonding temperature to cause at least a portion of at least one of the first metallic coating and the second metallic coating to melt and form at least one liquid interlayer, 2) heating the coated substrate past the first temperature to cause the at least one liquid interlayer to expand in thickness, and 3) heating the coated substrate to the bonding temperature to cause the at least one liquid interlayer to undergo an isothermal solidification process. 
     In another refinement, a bond between the customized coating and the metallic substrate may have a melting temperature that exceeds the bonding temperature. 
     In another refinement, heating the coated substrate to the first temperature may cause the first metallic coating to melt by direct melting. 
     In another refinement, heating the coated substrate to the first temperature may cause a portion of the second metallic coating to melt by eutectic melting, and the at least one liquid interlayer may be formed between an un-melted portion of the first metallic coating an un-melted portion of the second metallic coating. 
     In another refinement, the method may further comprise heating the part past the bonding temperature to increase a fraction of a material forming the metallic substrate in the customized coating. 
     In accordance with another aspect of the present invention, a metallic part having a customized metallic coating is disclosed. The metallic part may be formed by a method comprising applying one or more, metallic coatings to a surface of a metallic substrate to provide a coated substrate, and bonding the one or more metallic coatings to the metallic substrate by a transient liquid phase bonding process. The transient liquid phase bonding process may comprise progressively heating the coated substrate to a bonding temperature to cause: 1) at least a portion of the at least one metallic coating to melt and form a liquid interlayer, 2) the liquid interlayer to expand in thickness, and 3) the liquid interlayer to undergo an isothermal solidification process and provide the part with the customized coating. 
     In another refinement, a bond between the customized metallic coating and the metallic substrate may have a melting temperature that exceeds the bonding temperature. 
     These and other aspects and features of the present disclosure will be more readily understood when read in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic showing a plated polymer component and a metal substrate prior to TLP bonding. 
         FIG. 2A  is a block diagram showing one embodiment of a TLP bonding method. 
         FIG. 2B  is a block diagram showing another embodiment of a TLP bonding method. 
         FIG. 3  is a schematic showing a plated polymer component and a metal substrate prior to PTLP bonding. 
         FIG. 4  is a cross section view of a nosecone and its internal ribbing connected by TLP bonding. 
         FIG. 5  is a cross section view of a tube having a flange joined by TLP bonding and an O-ring channel joined by TLP bonding. 
         FIG. 6  is a schematic representation illustrating a transient liquid phase (TLP) bonding process for forming a bond between a substrate and a coating in accordance with the present disclosure. 
         FIG. 7  is a schematic representation illustrating the TLP bonding process for forming a bond between the substrate and two coatings in accordance with the present disclosure. 
         FIG. 8  is a block diagram illustrating the steps involved in bonding the substrate to one or more coatings by the TLP bonding process, in accordance with a method of the present disclosure. 
       It should be understood that the drawings are not necessarily drawn to scale and that the disclosed embodiments are sometimes illustrated diagrammatically and in partial views. In certain instances, details which are not necessary for an understanding of this disclosure or which render other details difficult to perceive may have been omitted. It should be understood, of course, that this disclosure is not limited to the particular embodiments disclosed herein. 
     
    
    
     DETAILED DESCRIPTION 
     Transient Liquid Phase Bonding of Metal-Covered Materials 
     The term “plated polymer” as used herein refers to a metal-covered non-metallic material, including, but not limited to, polymers having a metal covering formed by electroplating, electroless plating, electroforming, spray coating, physical vapor deposition, and other metal deposition methods and composite materials having a metal covering formed by electroplating, electroless plating, electroforming, spray coating, physical vapor deposition, and other metal deposition methods. “Composite materials” include, but are not limited to, carbon- or glass-fiber-reinforced polymers (thermoplastics and thermosets). 
     Transient liquid phase (TLP) bonding is a bonding process that joins materials using an interlayer. On heating, the interlayer melts and the interlayer element diffuses into the substrate materials, causing isothermal solidification. The result of this process is a bond that has a higher melting point than the bonding temperature (i.e. the temperature at which the interlayer is melted and isothermally solidifies). According to embodiments of the present invention, TLP bonding is used to join a plated polymer component with a metal component. TLP bonding allows plated polymer components to be joined with metal components without the use of the aforementioned destructive welding or brazing and without the physical limitations presented by bolts, rivets and other mechanical joining methods. TLP bonding of plated polymer components can also eliminate weak or thin areas in the plating formed as a result of pitting or recesses formed during the plating process. 
       FIG. 1  is a schematic view showing a plated polymer component and a metal substrate prior to TLP bonding. Plated polymer component  10  includes a non-metallic core  12  and metal layer  14 . In some embodiments, non-metallic core  12  is formed from a thermoplastic and/or thermoset material, forming a polymer component. Suitable thermoplastic and thermoset materials for non-metallic core  12  include, but are not limited to, polyphenylene sulfides, polyamides, polyvinylchloride (PVC), polystyrene (PS), polyethylene (PE), polypropylene (PP), styrene-acrylonitrile (SAN), polycarbonate (PC), acrylonitrile styrene acrylate (ASA), acrylonitrile butadiene styrene (ABS), ethylene tetrafluoroethylene fluoropolymer (ETFE), high impact polystyrene (HIPS), polyamide (PA), polybutylene terephthalate (PBT), polyetherimide (PEI), perchloroethylene (PCE), polyether sulfone (PES), polyethylene terephthalate (PET), polysulfone (PSU), polyurethane (PUR), polyvinylidene fluoride (PVDF), polyether ether ketone (PEEK), polyetherimide (PEI), thermoplastic polyimide, condensation polyimide, addition polyimide, polyether ketone ketone (PEKK), polysulfone, polyphenylsulfide, polyester, epoxy cured with aliphatic and/or aromatic amines and/or anhydrides, cyanate esters, phenolics, polyacrylates, polymethacrylates, silicones (thermoset), any of the foregoing with fiber reinforcement (e.g., carbon-fiber or glass-fiber) and combinations thereof. 
     In some embodiments, non-metallic core  12  is solid. In other embodiments, non-metallic core  12  is a hollow body. In some embodiments, non-metallic core  12  has an average wall thickness between about 1.27 mm (0.050 inches) and about 12.7 mm (0.500 inches). Non-metallic core  12  can be formed by injection molding, resin transfer molding, vacuum-assisted resin transfer molding, composite layup (autoclave, compression, or liquid molding), compression molding, extrusion, thermoforming, weaving (2D or 3D), braiding, vacuum-forming, machining, laminating, additive manufacturing (liquid bed, powder bed, deposition processes), and other manufacturing techniques. 
     Metal layer  14  is formed over at least a portion of non-metallic core  12  and joined to non-metallic core  12 . Metal layer  14  can be formed from any metal having a melting temperature above about 150° C. (302° F.). In some embodiments, metal layer  14  contains nickel, cobalt, iron, gold, silver, and copper, alloys of nickel, cobalt, iron, gold, silver, and copper, and combinations thereof. Metal layer  14  can be formed on and joined to non-metallic core  12  by electroplating, electroless plating, electroforming, spray coating, physical vapor deposition, or any other metal deposition method capable of joining metal layer to non-metallic core  12 . In some embodiments, metallic layer  14  has a thickness between about 0.0254 mm (0.001 inches) and about 2.54 mm (0.100 inches). 
     Together, non-metallic core  12  and metal layer  14  make up plated polymer component  10 . Plated polymer component  10  can be any of a number of gas turbine engine components. Suitable components include spinners/nose cones, airfoils, tubes, connectors, covers, ducts, platforms, eases, nacelle components, cascade reversers, brackets, struts, tubes. FADECs, and housings. 
       FIG. 1  also illustrates metal substrate  16 . Metal substrate  16  can be formed from any metal having a melting temperature above about 150° C. (302° F.). In some embodiments, metal substrate  16  contains nickel, cobalt, iron, gold, silver, and copper, alloys of nickel, cobalt, iron, gold, silver, and copper, and combinations thereof. In some embodiments, metal substrate  16  is a structural component to which plated polymer component  10  will be bonded. In some particular embodiments, metal substrate  16  is a rib, boss or flange. Metal substrate  16  can also be a metal-plated polymer component as described above. 
       FIG. 1  further illustrates interlayer  18 . As described in greater detail below, interlayer  18  is used to TLP bond plated polymer component  10  to metal substrate  16 . Interlayer  18  is located in bond region  20  between metal substrate  16  and metal layer  14  of plated polymer component  10 . Interlayer  18  can be composed of a single element, an alloy or a multi-layer combination of elements and/or alloys. In some embodiments, interlayer  18  includes elements selected from the group consisting of gallium, indium, selenium, tin, bismuth, iodine, polonium, cadmium, and combinations thereof. In some embodiments, interlayer  18  includes other components in addition to the elements listed above. In these cases, interlayer  18  generally includes at least 50% of gallium, indium, selenium, tin, bismuth, iodine, polonium, cadmium, and combinations thereof by weight. In some embodiments, interlayer  18  has a thickness between about 0.00127 mm (0.00005 inches) and about 1.27 mm (0.050 inches). 
       FIG. 2A  is a block diagram showing the steps of one embodiment of a TLP bonding method for bonding a plated polymer component to a metal substrate. According to  FIG. 2A , TLP bonding method  30  includes setting up the bond (step  32 ), heating the bond region to liquefy the interlayer (step  34 ) and maintaining the bond region at the bonding temperature to allow isothermal solidification of the bond (step  36 ). 
     In step  32 , the bond is set up. Polymer component  10  and metal substrate  16  are positioned adjacent one another at bond region  20  as shown in  FIG. 1 . Interlayer  18  is positioned between metal layer  14  of polymer component  10  and metal substrate  16 . Depending on its form, interlayer  18  can be positioned at bond region  20  in different ways. In some embodiments, interlayer  18  is a thin foil, a powder, a powder compact or a paste. In these embodiments, interlayer  18  is typically positioned, spread or brushed on either metal layer  14  or metal substrate  16 . In other embodiments, interlayer  18  is deposited on either metal layer  14  or metal substrate  16  by physical vapor deposition, sputtering, electroplating, electroforming or applying interlayer  18  as a solution and vaporizing the solvent. 
     Once interlayer  18  has been positioned between metal layer  14  and metal substrate  16 , metal layer  14 , metal substrate  16  and interlayer  18  are held in place at bond region  20 . In some embodiments, pressure is applied to bond region  20  to maintain alignment of polymer component  10  and metal substrate  16  and promote bonding. In some embodiments, a fixture is used to maintain alignment of polymer component  10  and metal substrate  16  (the bond can be formed with little or no pressure). 
     Once the bond has been set up in step  32 , bond region  20  is heated to liquefy interlayer  18  in step  34 . Bond region  20  can be heated using radiation (visible or infrared), conduction, induction, resistance heating or a laser. Depending on the type of metal layer  14 , metal substrate  16  and interlayer  18  chosen, step  34  (and subsequent steps) can be carried out under vacuum conditions, in an inert atmosphere or ambient atmospheric conditions. Inert atmospheres include, but are not limited to, argon, nitrogen, hydrogen and a mixture of nitrogen and hydrogen. 
     Bond region  20  is heated to a bonding temperature greater than or equal to either (1) the melting temperature of interlayer  18  or (2) the minimum eutectic reaction temperature between interlayer  18  and (a) metal layer  14  or (b) metal substrate  16 . The melting temperature of interlayer  18  depends on the particular makeup of interlayer  18 . In some embodiments, the bonding temperature used in step  34  is substantially equal to the melting temperature (direct or eutectic) of interlayer  18 . In other embodiments, the bonding temperature is between about 11.1° C. (20° F.) and about 33.3° C. (60° F.) greater than the melting temperature of interlayer  18 . Once the inciting point of interlayer  18  is reached, interlayer  18  begins to liquefy. Typically, the bonding temperature is greater than the melting point of interlayer  18  to ensure complete melting of interlayer  18  and to increase the rate at which interlayer  18  diffuses into metal layer  14  and metal substrate  16  at bond region  20 . 
     At the bonding temperature, liquefied interlayer  18  dissolves (or “melts hack”) metal layer  14  and metal substrate  16  at bond region  20 . Once interlayer  18  has been completely liquefied, the temperature at bond region  20  is maintained at the bonding temperature to allow isothermal solidification of the bond. At the bonding temperature, interlayer  18  diffuses into metal layer  14  and metal substrate  16  at bond region  20 . In step  36 , bond region  20  is kept at the bonding temperature while this diffusion occurs. Because the diffusion occurs isothermally, the liquid region of interlayer  18  contracts to maintain equilibrium and interlayer  18  solidifies with metal layer  14  and metal substrate  16  at bond region  20 . Once interlayer  18  has isothermally solidified, the TLP bond is complete. 
     In some embodiments, the bond formed in steps  32 ,  34  and  36  is further homogenized as shown in  FIG. 2B . Method  30 A includes homogenization step  38  following isothermal solidification step  36 . Homogenization increases the melting temperature of the resulting bond formed at bone region  20 . Homogenization step  38  includes heating bond region  20 . Homogenization can be performed at or near the bonding temperature used in steps  34  and  36  or at a temperature lower than the bonding temperature. Homogenization can be performed immediately after step  36 , where bond region  20  is held at an elevated temperature for an extended time. Alternatively, homogenization can be performed at a later time as a post-bonding treatment. After homogenization, the resulting bond formed at bond region  20  between metal layer  14  and metal substrate  16  can have a remelting temperature hundreds of degrees Celsius above the initial melting temperature of interlayer  18 . 
     Partial transient liquid phase (PTLP) bonding is a variant of TLP bonding that is typically used to join ceramics. PTLP bonding can also be used to join metal layer  14  and metal substrate  16 . PTLP requires an interlayer composed of multiple layers. In some embodiments, PTLP is performed using an interlayer having a relatively thick refractory core sandwiched by thin, lower-melting layers on each side.  FIG. 3  is a schematic view showing a plated polymer component and a metal substrate prior to PTLP bonding including interlayer  18 A having first layer  18 B, second (middle) layer  18 C and third layer  18 D.  FIG. 3  is not drawn to scale in order to show the distinct layers of interlayer  18 A. In some embodiments, middle layer  18 C of interlayer  18 A used in PTLP bonding includes elements selected from the group consisting of refractory metals nickel, iron, cobalt, gold, magnesium, silver, copper, antimony, manganese, palladium, strontium, tellurium, ytterbium, aluminum, calcium, europium, gadolinium, germanium, platinum, rhodium, thulium, vanadium and combinations thereof and has a thickness between about 0.00254 mm (0.0001 inches) and about 1.27 mm (0.050 inches). In some embodiments, interlayer  18  includes other components in addition to the elements listed above. In these cases, interlayer  18  generally includes at least 50% of nickel, iron, cobalt, gold, magnesium, silver, copper, antimony, manganese, palladium, strontium, tellurium, ytterbium, aluminum, calcium, europium, gadolinium, germanium, platinum, rhodium, thulium, vanadium, and combinations thereof by weight. In some embodiments, the thinner outer layers ( 18 B and  18 D) of interlayer  18  include elements selected from the group consisting of gallium, indium, selenium, tin, bismuth, iodine, polonium, cadmium, and combinations thereof, and have thicknesses between about 0.2% and about 20% of the thickness of middle layer  18 C. In some embodiments, interlayer  18  includes other components in addition to the elements listed above. In these cases, interlayer  18  generally includes at least 50% of gallium, indium, selenium, tin, bismuth, iodine, polonium, cadmium, and combinations thereof by weight. PTLP bonding is performed as described above with respect to TLP bonding. In the case of PTLP bonding, different bonding temperatures can be utilized and the rate at which interlayer  18 A melts and diffuses may differ due to the multi-layer nature of interlayer  18 A. 
       FIG. 4  illustrates one example of TLP or PTLP bonding between a plated polymer component and a metal substrate.  FIG. 4  is a cross-section view of a nosecone and its internal ribs. In one embodiment, nosecone  40  is a metal-plated polymer component having a polymer or composite core and a metal layer covering the core. As shown in  FIG. 4 , nosecone  40  includes outer shell  42 . Circular ribs  44 A and  44 B and axial ribs  46  are structures that provide support to nosecone  40 . In one embodiment, one or more of circular ribs  44 A and  44 B and axial ribs  46  are metal-plated polymers. Bonding interlayer  48  is positioned between outer shell  42  and circular ribs  44 A and  44 B and axial ribs  46 , and can be a single layer or a multi-layer interlayer o produce a TLP or PTLP bond, respectively, as described above.  FIG. 4  is not drawn to scale to better illustrate the layers of the cross-section view of nosecone  40 . Circular ribs  44 A and  44 B and axial ribs  46  are TLP or PTLP bonded to inner surface  50  of nosecone  40  and the external surfaces of ribs  44 A,  44 B, and  46  as described above with respect to  FIGS. 2A and 2B . In another embodiment, one or more of circular ribs  44 A and  44 B and axial ribs  46  are Ni-based alloys. 
       FIG. 5  illustrates another example of TLP bonding between a plated polymer component and a metal substrate.  FIG. 5  is a cross-section view of a tube having a flange joined to the tube by TLP or PTLP bonding and an O-ring channel joined to the tube by TLP or PTLP bonding. Tube  52  is generally cylindrical and includes wall  54  having outer surface  56 . In some embodiments, tube  52  is a metal-plated polymer component having a polymer or composite core and a metal layer at outer surface  56 . In other embodiments, outer surface  56  is metallic. Attached to tube  56  along outer surface  56  are flange  58  and O-ring channel  60 . Flange  58  and O-ring channel  60  are metal-plated polymer components or have an outer metallic surface and are TLP or PTLP bonded to outer surface  56  of tube  52  as described above with respect to  FIGS. 2A and 2B . TLP and PTLP bonding allows the formation of a typical component using easily molded or machined parts. While  FIGS. 4 and 5  illustrate just two particular embodiments of metal-plated polymer components or features that are TIP bonded to other structures, many other examples are possible such as ducts, covers, brackets, clamps, bosses, flanges, ribs, and channels. 
     TLP bonding allows plated polymer components to be bonded to metal components without deforming or destroying the polymer core of the plated polymer. TLP bonding provides a strong bond that can be used above the bonding temperature and TLP bonded parts do not possess the disadvantages and limitations of conventional hardware and assembly devices such as bolts and rivets. 
     Transient Liquid Phase Bonded Alloyed Surface Coatings 
     Turning now to  FIG. 6 , the bonding of a first coating  70  to a substrate  72  by a TLP bonding process  74  is depicted. The first coating  70  may consist of any metallic material and it may be applied by any suitable method apparent to those of ordinary skill in the art. Such methods may include, but are not limited to, chemical vapor deposition, physical vapor deposition, plating, cold spraying, or plasma spraying. The substrate  72  may be any metallic structure, such as, but not limited to, a pure metal, an alloy, an intermetallic, or a metal matrix composite. The first coating  70  may be applied to one or more surfaces of the substrate  72  and it may be capable of imparting the substrate  72  with one or more properties favorable to its operation and use, such as, but not limited to, enhanced hardness, wear resistance, oxidation resistance, thermal conductivity, and/or electrical conductivity. The first coating  70  may have a thickness from less than about one (1) micron (about 0.001 mm) to up to about 500 microns (about 0.5 mm). 
     Following the application of the first coating  70  to one or more exterior surfaces of the substrate  72 , the coated substrate may be progressively heated (symbolized by Δ) to a bonding temperature (T 2 ) which is selected based on the composition of the first coating  70 . Upon reaching a suitable temperature (T 1 ) during the heating process, and prior to reaching the bonding temperature (T 2 ), a liquid interlayer  76  may form at the interface between the coating  70  and the substrate  72  by either direct melting  73  of the first coating  70  or by eutectic melting  75  between the first coating  70  and the substrate  72 , as shown in  FIG. 6 . Direct melting  73  of the first coating  70  may result if the first coating  70  is heated beyond its melting point such tat the entire first coating  70  liquefies and forms the interlayer  76 . In contrast, eutectic melting  75  of the first coating  70  may result if the substrate  72  and the first coating  70  form a eutectic product at the interface of the first coating  70  and the substrate  72  and the eutectic product has a melting temperature lower than the melting temperatures of the first coating  70  and the substrate  72 . Accordingly, the interlayer  76  formed by eutectic melting  75  may be a thin liquid located between the substrate  72  and an un-melted layer of the first coating  70 , as shown in  FIG. 1 . With continued heating past T 1 , dissolution may occur in which the solid-liquid boundaries of the interlayer  76  may expand and dissolve some of the material of the substrate  72  (and an un-melted layer of the first coating  70 , if present), as shown. During this dissolution/expansion process  77 , the interlayer  76  may expand up to several times its original thickness. 
     Upon reaching the bonding temperature (T 2 ), the liquid interlayer  76  may diffuse into the substrate  72  and undergo an isothermal solidification process  78  until all of the liquid of the interlayer  76  has solidified and a custom coating  82  is formed at the outer surface of the substrate  72 . For the case of eutectic melting, the liquid of the interlayer  76  migrates towards the surface by solidifying at the interface with substrate  72  and liquefying material at the interface with the first coating  70 . This process continues until the first coating  70  is completely consumed and solidification of interlayer  76  proceeds as described previously to yield the custom coating  82 , as shown. At this stage, the custom coating process may be terminated. The custom coating  82  may compositionally resemble a gradient of the first coating  70  material in the substrate  72  material and may have a smooth transition of grain boundaries and properties between the outer surface and the substrate  72 . Alternatively, the custom coating  82  may be diffused in with continued heating to form different gradients having increasing proportions of the substrate  72  with increased heating. In any event, whether the custom coating  82  undergoes homogenization after the TLP bonding process or not, the completion of the TLP bonding process  74  will provide a part  85  having a custom coating  82  with a functionally graded structure having microstructural, mechanical, and physical properties different than those of the substrate  72  and the first coating  70 . For example, if the substrate  72  is formed from nickel and the first coating  70  is formed from aluminum, the custom coating  82  may have properties of an intermetallic material composed of nickel and aluminum. In addition, the custom coating  82  may have a melting temperature that exceeds the bonding temperature (T 2 ) used to join the substrate  72  and the first coating.  70  and may therefore exhibit enhanced thermal stability. 
     The bonding of multiple coatings (a first coating  70  and a second coating  90 ) to the outer surface of the substrate  72  by the TLP bonding process  74  is depicted in  FIG. 7 . The second coating  90  may be a metallic coating which differs in composition from the first coating  70  and may impart one or more selected properties to the substrate  72  which may differ from the properties provided by the first coating  70 . The first coating  70  and the second coating  90  may be deposited sequentially on one or more surfaces of the substrate  72  by any deposition method apparent to those of ordinary skill in the art (e.g., chemical vapor deposition, physical vapor deposition, plating, cold spraying, plasma spraying, etc.). The second coating  90  may also have a thickness from less than about one (1) micron (about 0.001 mm) to up to about 500 microns (about 0.5 mm). The coated substrate may then be progressively heated (symbolized by T 1 ) to a bonding temperature (T 2 ), as shown. Upon reaching a suitable temperature (T 1 ) during the heating process, melting of all of the first coating  70  may occur by direct melting  73  to form an interlayer  76  between the second coating  90  and the substrate  72 . Alternatively, if a eutectic product is formed between the substrate  72  and the first coating  70  and/or between the first coating  70  and the second coating  90 , the eutectic product may melt by eutectic melting  75  to form a thin interlayer  76  between the substrate  72  and the first coating  70  and/or between the first coating  70  and the second coating  90 , as shown. 
     With continued heating above T 1  and prior to reaching the bonding temperature T 2 , the interlayer(s)  76  may expand in thickness by a dissolution/expansion process  77 , as explained above. Once the bonding temperature T 2  is reached, the interlayer(s)  76  may diffuse and isothermally solidify into the substrate  72  (and any solid portions of the first coating  70  and second coating  90 ) to form a custom coating  82  between the substrate  72  and the first coating  70 . In this way, a multi-layered custom coating may also be formed of the first coating  70  and the second coating  90  as the liquid interfaces migrate towards the surface, as described above. If the TLP process is ceased after completion of the isothermal solidification  78 , the custom coating  82  may be a gradient of the composition of the substrate  72  and the first coating  70  and may have microstructural and physical properties between those of the substrate  72  and the first coating  70 . Similarly, if a custom coating is formed between the first coating  70  and the second coating  90 , it may compositionally resemble a gradient of the first coating  70  and the second coating  90  and have microstructural and physical properties resembling both coatings. Homogenization of the custom coating  82  may be achieved, if desired, with further heating as described above. The resulting part  92  may exhibit any advantageous properties provided by the first coating  70  and/or the second coating  90 . In this way, multiple coatings may be bonded to one or more surfaces of the substrate  72  and one may select and combine coatings according to desired combinations of physical properties. In addition to the embodiments described above, more than two coatings can be utilized to further enhance the custom coatings that can be produced by TLP bonding in this manner. Furthermore, one or more coatings may be utilized in different sections of the component to produce locally customized coatings. 
       FIG. 8  illustrates steps which may be involved in bonding one or more metallic coatings to one or more exterior surfaces of the substrate  72  by the TLP bonding process  74 . According to a first block  94 , one or more coatings (such as the first coating  70 ) may be applied to one or more surfaces of the substrate  72  by any conventional deposition process selected by a skilled artisan. The coated substrate may then be heated to a first temperature (T 1 ) which may cause a liquid interlayer  76  to form between the surface of the substrate  72  and the coating by direct or eutectic melting according to a block  96  and a block  98 , as shown. In this way, interlayer(s)  76  may also be formed between each of the coatings as illustrated in  FIG. 7 . According to a next block  100 , the coated substrate may be further heated past T 1  which causes expansion of the liquid interlayer(s)  76 . Further heating of the coated substrate to the bonding temperature (T 2 ) may cause the diffusion and isothermal solidification of the interlayer(s)  76  into the substrate  72  (and adjacent coatings which remain in a solid state) according to a block  102  and a block  104 , as shown. At this stage, the customized coating  82  may be formed between the substrate  72  and the coating(s), and the customized coating  82  may have microstructural and physical properties between those of the substrate  72  and the coating(s) (block  106 ). To further homogenize the customized coating  82 , optional continued heating may be employed according to a block  106 . The part having a customized coating  82  bonded to the substrate  72  may then be provided according to a block  108 , as shown. 
     From the foregoing, it can therefore be seen that TLP bonding of one or more metallic coatings to metallic substrates can find applicability in many situations, including, but not limited to, the production of metallic components having specialized or customized coatings. The TLP bonding process forms a strong bond or joint between the metallic substrate and the coating(s) which has microstructural and physical properties between those of the substrate and the coating materials. Moreover, one may select and combine coatings having varying desirable properties to form specialized coatings by the TLP bonding process. Although some conventional coating methods for metals (e.g., cold spraying) may provide a mechanical interlock between the metallic substrate and the coating, TLP bonding may provide a more robust and thermally stable bond between the substrate and coating. More specifically, the resulting bond between the metallic substrate and the coating may have a melting temperature in excess of the bonding temperature used for TLP bonding, such that the formed bond may operate at temperatures well above the bonding temperature. This feature may be advantageous, for example, when joining temperature-sensitive materials whose micro-structures could be damaged by too much thermal energy input. It is expected that the technology as disclosed herein may find wide industrial applicability for component fabrication in various industries including, but to limited to, aerospace and automotive industries.