Patent Publication Number: US-2021180675-A1

Title: High strength vibration damping components

Description:
TECHNICAL FIELD 
     The present disclosure relates techniques for forming mechanical components, such as aerospace components. 
     BACKGROUND 
     Mechanical components may expose to a variety of stresses or other factors during operation, such as, for example, bending forces, compression forces, shear forces, tensile forces, thermal cycling stress, vibration, erosion, and corrosion, and the like. The exposure of the mechanical components to the variety of stresses and other factors may impact the lifespan of the component, such as leading to early fatigue or failure. In some examples, mechanical components have been developed that exhibit higher strength and durability using high density metals or metal alloys. However, some high-density metals or metal alloys may be relatively heavy, difficult to manufacture, and expensive making their use non-ideal for some applications. 
     SUMMARY 
     In some examples, the disclosure describes a mechanical component that includes a core substrate and a nano-crystalline coating on at least a portion of the core substrate. The core substrate defines a resonance damping cavity. The resonance damping cavity is configured to damp a vibration in the component at a selected frequency or range of frequencies. 
     In some examples, the disclosure describes a gear that includes a core substrate and a nano-crystalline coating on at least a portion of the core substrate. The core substrate is formed in the shape of the gear. The gear includes a body and gear teeth extending from the body. A portion of the body adjacent the gear teeth defines a resonance damping cavity configured to damp a vibration in the gear at a selected frequency or range of frequencies. 
     In some examples, the disclosure describes a method for forming an aerospace mechanical component that includes forming a core substrate defining a resonance damping cavity, the resonance damping cavity configured to damp a vibration in the component at a selected frequency or range of frequencies, and depositing a nano-crystalline coating on at least a portion of the core substrate. 
     The details of one or more examples are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1A  is a conceptual plan view of an example component defining a resonance damping cavity. 
         FIG. 1B  is a conceptual partial cross-sectional view of the example component, along line A-A as indicated in  FIG. 1A , that illustrates the core substrate and the nano-crystalline coating of the component. 
         FIG. 2  is a conceptual partial cross-sectional view of an example component including core substrate and plurality of nano-crystalline layers. 
         FIG. 3  is a conceptual partial cross-sectional view of an example component that includes a metal-polymer laminate on a portion of a core substrate. 
         FIG. 4  is a conceptual diagram illustrating a portion of a spur gear under an applied load. 
         FIGS. 5A-5C  are heat maps illustrating stresses applied to a coating top layer, a coating intermediate layer, and a core substrate of the spur gear of  FIG. 4 . 
         FIG. 6  is a heat map illustrating static structural equivalent stress applied to the spur gear pf  FIG. 4  under an applied load. 
         FIG. 7  is a flow diagram illustrating an example technique for forming an example component that includes a nano-crystalline coating on a core substrate that defines a resonance damping cavity. 
     
    
    
     DETAILED DESCRIPTION 
     In general, the disclosure describes components and techniques for making components that include a core substrate defining a resonance damping cavity and a nano-crystalline material applied to at least a portion of the core substrate. The techniques described herein may be used to form, via additive manufacturing methods such as three-dimensional printing, components that exhibit improved strength and reduced weight characteristics compared to conventional metal components. Additionally, or alternatively, the described techniques may be used to form components with improved noise and vibrational damping characteristics which may result in an increased service life for the component. In some examples, the components may be constructed such that the resonance damping cavity is shaped and/or is filled with a vibration damping material to damp a vibration in the component at a selected frequency or frequency range (e.g., frequencies to which the component is exposed during operation). 
     In some examples, a design of the component formed by additive manufacturing, such as by three-dimensional printing, may be topologically optimized. Constrains of the topological optimization may include, for example, reduced weight, reduced cost, substantially similar safety margins, substantially similar bending strength, substantially similar impact strength, substantially similar compressive or pitting strength, and substantially similar scoring resistance, compared to a similar component formed by other techniques or other materials. Additionally, or alternatively, forming the component using additive manufacturing may enable forming the resonance damping cavity to have a selected shape (e.g., tuned) to damp a vibration in the component at a selected frequency or frequency range. Additionally, or alternatively, forming the component using additive manufacturing may enable forming structures, such as webs or slots, configured to reduce the weight and/or material cost of the component. 
     In some examples, the component may include a gear, such as a spur gear. The gear may include a core material defining a web extending from an inner rim to an outer rim with radially protruding gear teeth. The gear may be three-dimensionally printed from any suitable material. In some examples, the material may include light weight, moderately inexpensive, high performance metallic alloys, such as, for example, titanium, aluminum, or alloys thereof. In other examples, the material may include one or more plastics or one or more performance ceramic metallics. In the example of a gear, the resonance damping cavity may include an annular hollow chamber within the outer rim a selected distance from the gear teeth. 
       FIG. 1A  is a conceptual plan view of an example component  10  defining a resonance damping cavity  12  (“cavity  12 ”). In some examples, cavity  12  may be partially or completely filled with a vibration damping material  14 . Component  10  is formed from a core substrate  16  that is coated with a nano-crystalline coating  18 .  FIG. 1B  is a conceptual partial cross-sectional view of component  10 , along line A-A as indicated in  FIG. 1A , that reveals core substrate  16  and nano-crystalline coating  18 . 
     In some examples, the conditions in which component  10  is typically operated (e.g., mechanical system applications) may exert forces on component  10  that cause component  10  to vibrate. Depending on the structure and natural resonance frequency of component  10 , the applied forces may be similar to the natural resonance frequency of component  10 , thereby causing component  10  to resonate. The resonance of component  10  may lead to increased noise and, over an extended period of time, may cause early fatigue of component  10 . The applied forces are a particular concern for aerospace components, such as turbine engine components, accessory gearbox components, gears, driveshafts, or the like. In such instances, it may be desirable for component  10  to possess a natural resonance frequency outside the range of operational frequencies or otherwise damp the vibrational frequencies anticipated to be experienced by the component during operation. 
     Cavity  12  is configured to damp a vibration in component  10  at a selected frequency or frequency range (e.g., the vibrational frequencies experienced by on component  10  during operation). For example, cavity  12  may inhibit, slow, or otherwise disrupt vibrational waves traveling through component  10  in such a way so as to alter a natural resonance frequency of component  10 . In some examples, a shape and/or a position of cavity  12  may be selected to damp a vibration at the selected frequency or frequency range. In some examples, the selected frequency or range of frequencies may be within a range from about 50 Hz to about 50,000 Hz, such as about 500 Hz to about 5,000 Hz. In examples in which component  10  includes a gear, cavity  12  may include an annular cavity positioned within a body of the gear. For example, the body of the gear may include outer rim  20 , web  24 , and inner rim  26 . Inner rim  26  may include spline teeth  23 . Spline teeth  23  may be configured to mechanically couple component  10  to another mechanical component, such as a driveshaft or the like. Outer rim  20  may include teeth  22  and define cavity  12 . In some examples, a position of cavity  12  closer to teeth  22  may improve vibration damping relative to a cavity positioned farther from teeth  22 . A position of cavity  12  may be determined based on a selected mechanical strength of a root  21 , e.g., where teeth  22  meet rim  20 , and a selected quantity of vibration damping. 
     In some examples, cavities  12  may be filled with a vibration damping material  14 . Vibration damping material  14  may absorb or otherwise dissipate at least a portion of the energy of vibrational waves traveling through component  10  in such a way so as to alter a natural resonance frequency of component  10 . Vibration damping material may include any material or combination of materials suitable to disrupt vibration travelling from teeth  22 , through web  24 , toward inner rim  24 . For example, vibration damping material may include a material that is different than a material of core substrate  12 . In some examples, the vibration damping material may include a polymer, rubber, polyurethane, polyvinyl chloride, or a metal or alloy. In some examples, the vibration damping material may include a material having a selected damping coefficient. 
     Core substrate  16  may include any suitable material. The material of core substrate  16  may be selected based on selected mechanical properties of the material, such as modulus of elasticity, tensile strength, elongation, hardness, and fatigue limit. In some examples, core substrate  16  may include a metal, such as, for example, aluminum, titanium, alloys thereof, one or more metals suitable for three-dimensional printing, or the like. In some examples, core substrate may include a polymeric material, such as, for example, polyether ether ketone (PEEK), polyamide (PA), polyimide (PI), bis-maleimide (BMI), epoxy, phenolic polymers (e.g., polystyrene), polyesters, polyurethanes, silicone rubbers, nylons, copolymers, polymeric blends, one or more polymers suitable for three-dimensional printing, or the like. In some examples, the polymeric material may be combined with one or more optional additives including, for example, binders, hardeners, plasticizers, antioxidants, and the like. In some examples, core substrate  12  may include a combination of two or more materials, such as a polymeric material and a metal or alloy. 
     In examples in which core substrate includes a polymeric material, core substrate  16  may also include one or more reinforcement fibers or reinforcing materials such as, for example, carbon fibers, carbon nano-tubes, and the like embedded in the polymeric material. The reinforcement fibers or reinforcing materials may increase the relative strength of polymeric material, thereby increasing the strength of the resultant core substrate  16 . In some examples, core substrate  16  may include between about 10% to about 40% reinforcement fibers/materials (e.g., carbon fibers) mixed with polymeric material and the one or more optional additives. In other examples, core substrate  16  may consist essentially of polymeric material. 
     Core substrate  16  may be formed using any suitable additive manufacturing technique. In addition, the technique may include one or more processing steps, such as, for example, machining holes in cavity  12  to subsequently inject liquid (e.g., melted, molten, or otherwise flowable) vibrational damping material  14  into cavity  12 . In some examples, the one or more processing steps may include machining one or more portions of component  10  to define a final shape of component  10 . For example, machining may include removing material to define at least a portion of web  24 , such as windows  28  of framed by trusses  30  of web  26 . In some examples, web  24  of core substrate  16  in conjunction with nano-crystalline coating  18  may allow for significant weight reduction of component  10  without significantly reducing the strength and durability properties of component  10 . 
     Nano-crystalline coating  18  of component  10  may include one or more layers of metals or metal alloys that defines an ultra-fine-grained microstructure with an average grain size less than about 50 nanometers (nm), such as less than about 20 nm or less than about 5 nm. Nano-crystalline coating  18  may be disposed on a surface of substrate  16 , such as, for example, on a surface of substrate  16  defining one or more of outer rim  20 , teeth  22 , spline teeth  23 , web  24 , and/or inner rim  26 . In some examples, the reduced grain size of nano-crystalline coating  18  may increase the relative tensile strength of the resultant layer as well as the overall hardness of the layer. In this way, nano-crystalline coating  18  may be significantly stronger and more durable compared to a conventional metallic coating (e.g., coarse grain coating) of the same composition and thickness. In some examples, the increased strength and hardness of nano-crystalline coating  18  may allow for the layer to remain relatively thin (e.g., between about 0.025 millimeters (mm) and about 0.15 mm) without sacrificing the desired strength and hardness characteristics of the layer. Additionally, or alternatively, depositing a relatively thin layer of nano-crystalline coating  18  on core substrate  16  may help reduce the overall weight of component  10  by reducing the volume of denser metals or metal alloys. The combination of the relatively light weight core substrate  16  and nano-crystalline coating  18  may result in a relatively high strength, relatively low weight component ideal for aerospace applications. In some examples, reducing an amount of metal used to form component  10  and/or increasing sizes of windows  28  may improve stealth capabilities of component  10 . 
     Nano-crystalline coating  18  may include one or more pure metals or metal alloys including, for example, cobalt, nickel, copper, iron, cobalt-based alloys, nickel-based alloys, copper-based alloys, iron-based alloys, or the like deposited on at least a portion of core substrate  16 . In some examples, nano-crystalline coating  18  may include a nickel-cobalt alloy, such as a nickel-cobalt superalloy, e.g., a Ni/Co layer. In some examples, nano-crystalline coating  18  may include cobalt and phosphorus, e.g., a Co/P layer. 
     In some examples, nano-crystalline coating  18  may include a plurality of layers. For example, nano-crystalline coating  18  may include at least one Ni/Co layer and at least one Co/P layer. The thickness of each layer of the plurality of layers may be the same or different. For example, nano-crystalline coating  18  may include a Ni/Co layer having a thickness of about 0.075 mm (e.g., about 0.003 inches) to about 1 mm (e.g., about 0.04 inches), such as about 0.381 mm (e.g., about 0.015 inches), and a Co/P layer having a thickness of about 0.025 mm (e.g., about 0.001 inches) to about 0.33 mm (e.g., about 0.013 inches), such as about 0.127 mm (e.g., about 0.005 inches). 
     Nano-crystalline coating  18  may be formed using suitable plating techniques, such as electro-deposition. For example, core substrate  16  may be suspended in suitable electrolyte solution that includes the selected metal or metal alloy for nano-crystalline coating  18 . A pulsed or direct current (DC) may then be applied to core substrate  16  to plate the substrate with the fine-grained metal to form nano-crystalline coating  18  to a desired thickness and average grain size. In some examples, a pulsed current may be utilized to obtaining an average grain size less than about 20 nm. 
     In some such examples, core substrate  16  may be initially metalized in select locations with a base layer of metal to facilitate the deposition process of forming nano-crystalline coating  18  on core substrate  16  using electro-deposition. In some examples, the metalized base layer on core substrate  16  may be produced using, for example, electroless deposition, physical vapor deposition (PVD), chemical vapor deposition (CVD), cold spraying, gas condensation, and the like. The layer formed using metallization may include one or more of the metals used to form nano-crystalline coating  18 . 
     In some examples, nano-crystalline coating  18  may be configured to exhibit improved barrier protection against erosion or corrosion compared to traditional materials used for mechanical system components, such as aerospace components. For example, nano-crystalline coating  18  may include a layer of nano-crystalline cobalt. The layer of nano-crystalline cobalt may impart anti-corrosion properties to component  10  as well as increased friction resistance and wear resistance to nano-crystalline coating  18  compared to traditional materials used for mechanical system components. 
     Additionally, or alternatively, nano-crystalline coating  18  may be configured to contribute to the durability of component  10  to resist compression stress and/or bending stress. For example, to improve compression stress resistance and/or bending stress resistance, mechanical system components have traditionally been formed with high strength metals, case hardened, carburized, and/or nitrided. Such techniques, however, may suffer from increased costs associated with processing and raw materials. Additionally, components formed from high strength metals may result in relatively dense and heavy components which may be less desirable in some applications, such as aerospace applications. Forming component  10  to include core substrate  16  and nano-crystalline coating  18  (e.g., nano-crystalline nickel) may significantly reduce the weight of the component compared to those formed with traditional high strength metals while also obtaining comparable or even improved compression stress resistance and/or bending stress resistance characteristics. Additionally, or alternatively, portions of component  10  may have improved micro-shear, micro-abrasion resistance, and/or micro-fretting resistance, such as, for example, spline teeth  23 . 
     In some examples, the thickness  18  of nano-crystalline coating  18  may be between about 0.025 mm and about 0.15 mm. In some examples, nano-crystalline coating  18  may be about 0.13 mm (e.g., about 0.005 inches). In some examples, the overall thickness of nano-crystalline coating  18  may be selectively varied on different portions of core substrate  16  to withstand various mechanical loads that component  10  may be subjected to during operation. For example, in areas where increased compression stress resistance is desired, e.g., the face or the flank of teeth, the relative thickness of nano-crystalline coating  18  may be increased to impart greater strength properties in that region. Similarly, in areas where increased bending stress resistance is desired, e.g., the root fillet of teeth, the relative thickness of nano-crystalline coating  18  may be increased to impart greater strength properties in that region. Additionally, or alternatively, thickness  18  of nano-crystalline coating  18  in regions where mechanical stress resistance is less desired, the thickness of the coating may be reduced or removed from component  10 , such as, for example, portions of outer rim  20 , web  24  (e.g., trusses  30 ), or inner rim  26 . In some examples, the relative thickness of nano-crystalline coating  18  may vary over a portion of component  10 . For example, the relative thickness of nano-crystalline coating  18  may be thicker where trusses  30  meet outer rim  20  and/or inner rim  26  relative to other portions of trusses  30 . 
     As shown in  FIG. 1A , in some examples, component  10  may be in the form of a mechanical system component such as a spur gear. However, component  10  may include any number of mechanical system components that may benefit from the described strength characteristic, reduced weight, or vibrational damping features. Other mechanical system components may include, for example, aerospace components, housings, brackets, air ducts, manifolds, tubes, chevron ventilation outlets, vane box plume tabs, variable vane actuator arms, nose cones, transition duct seals, actuation rings, airfoils, flaps, casing, frames, accessory gear, drive shafts, rotors, discs, panels, tanks, covers, flow surfaces, turbine engine components, and the like. In some examples, component  10  may exhibit complex three-dimensional geometries. In other examples, component  10  may be in the form of a sheet or a shaped-sheet component. 
     In some examples, nano-crystalline coating  18  may include a plurality of nano-crystalline layers.  FIG. 2  is a conceptual cross-sectional view of an example component  40  including core substrate  46  (e.g., similar to core substrate  16  as described above) and a nano-crystalline coating  48  that includes a first nano-crystalline layer  47  and a second nano-crystalline layer  49 . Component  40  may be the same as or substantially similar to component  10  describe above in reference to  FIGS. 1A and 1B , except for the differences described herein. For example, component  40  may include a resonance damping cavity. 
     In some examples, first and second nano-crystalline layers  47  and  49  may be selectively tailored to produce a nano-crystalline coating  48  with desired physical, thermal, and chemical (e.g., corrosion resistance) characteristics. For example, first nano-crystalline layer  47  may include nano-crystalline nickel or nickel-based alloy which may impart high tensile strength properties to nano-crystalline coating  48  to contribute to the overall durability of component  40 . In some examples, first nano-crystalline layer  47  may include a nano-crystalline nickel-cobalt alloy. Second nano-crystalline layer  49  may include nano-crystalline cobalt or a cobalt-based alloy, which may impart anti-corrosion properties to nano-crystalline coating  48  as well as friction resistance and wear resistance. In some examples, second nano-crystalline layer  49  may include a nano-crystalline cobalt-phosphorus alloy. 
     In some examples, the relative thicknesses of first and metallic second nano-crystalline layers  47  and  49  may be substantially the same (e.g., the same or nearly the same within common nano-crystalline coating application tolerances) or may be different depending on the composition of the respective layer and intended application of component  40 . In some examples in which first nano-crystalline layer  47  includes nickel or a nickel-based alloy and second nano-crystalline layer  49  includes cobalt or a cobalt-based alloy, the relative thicknesses of the layers may be selected such that first nano-crystalline layer  47  is about three times thicker than second nano-crystalline layer  49  (e.g., producing a thickness ratio of about 3:1 nickel-based layer to cobalt-based layer). For example, first nano-crystalline layer  47  (which may include nickel or a nickel-based alloy) may have a thickness of about 0.075 mm (e.g., about 0.003 inches) to about 1 mm (about 0.04 inches), such as about 0.381 mm (e.g., about 0.015 inches), and second nano-crystalline layer  49  (which may include cobalt or a cobalt-based alloy) may have a thickness of about 0.025 mm (e.g., about 0.001 inches) to about 0.33 mm (e.g., about 0.013 inches), such as about 0.127 mm (e.g., about 0.005 inches). 
     Additionally, or alternatively, a component may be constructed with a multi-layered metal-polymer laminate structure.  FIG. 3  is a conceptual cross-sectional view of an example component  50  including core substrate  56  (e.g., similar to core substrate  16  as described above) and a metal-polymer laminate  58  on a portion of core substrate  56 . Component  50  may be the same as or substantially similar to components  10  and  40  discussed above in reference to  FIGS. 1A-2 , except for the differences described herein. For example, component  50  may include a resonance damping cavity. 
     Metal-polymer laminate  58  may include one or more polymer-based layers  55  and one or more nano-crystalline layers (e.g., first nano-crystalline layer  57  and second nano-crystalline layer  59 ) applied on core substrate  56  in an alternating fashion such that the outermost layer (e.g., layer  59 ) includes a nano-crystalline layer. In some examples, the alternating configuration of the one or more nano-crystalline layers  57  and  59  with one or more polymer-based layers  55  may impart additional vibrational-damping properties to component  50  by allowing for additional relative motion between one or more of the adjacent layers (e.g., between polymer-based layer  34  and first nano-crystalline layer  57 , between polymer-based layer  34  and second nano-crystalline layer  59 , or both). 
     In some examples, first nano-crystalline layer  57  and/or second nano-crystalline layer  59  may include the substantially the same (e.g., the same or nearly the same) composition of metals. In other examples, first nano-crystalline layer  57  and/or second nano-crystalline layer  59  may include different compositions of metals to impart different characteristics to component  50 . For example, second nano-crystalline layers  59  may include nano-crystalline cobalt or cobalt-based alloy, which may impart anti-corrosion properties to metal-polymer laminate  58  as well as contribute friction resistance and wear resistance to the laminate structure, and first nano-crystalline layers  57  may include nano-crystalline nickel or nickel-based alloy, which may impart high tensile strength properties to the laminate structure to improve the overall durability of component  50 . In some examples, the thicknesses of first and second nano-crystalline layers  57  and  59  may be between about 0.025 mm (e.g., about 0.001 inches) to about 1 mm (e.g., about 0.04 inches). The thickness selected for a respective layer may depend on a variety of factors including, for example, the composition of the respective layer, the purpose of the respective layer, and the total number of layers in metal-polymer laminate  58 . In some examples, metal-polymer laminate  58  may define an overall thickness of about 0.075 mm to about 2.15 mm. 
     The one or more polymer-based layers  55  may be formed using any suitable polymeric material. In some examples, one or more of polymer-based layers  55  may include substantially the same (e.g., the same or nearly the same) polymeric material or include a composition substantially the same (e.g., the same or nearly the same) as core substrate  56 . Each respective layer of polymer-based layers  55  may be formed using any suitable technique including, for example, injection molding, dip coating, and the like. The thickness of each respective layer of polymer-based layers  55  may be between about 0.025 mm and about 0.15 mm. 
       FIG. 4  is a conceptual diagram illustrating a portion of an example spur gear  60  under an applied load. The direction of rotation of spur gear  60  is illustrated as arrow  61 . The pitchline is illustrated as dashed line  62 . Force on tooth  63  is illustrated as opposing force arrows  64 A and  64 B. 
     Spur gear  60  included a core substrate (e.g., the same as or similar to core substrate  12 ) formed from a titanium-aluminum alloy (e.g., α 2 Ti 3 Al or equivalent). Spur gear  60  also included a nano-crystalline coating including two layers (e.g., the same as or similar to nano-crystalline coating  48 ). A first layer included a nickel-cobalt alloy intermediate shell encasing the core substrate. The first layer had a thickness of several thousandths of an inch (e.g., 15 mil). A second layer included a cobalt-phosphorus alloy outer shell (e.g., encasing the first layer. The second layer had a thickness of a few thousandths of an inch (e.g., 5 mil). 
     A uniform pitchline loading model was used to evaluate compressive stress and bending stress on spur gear  60 .  FIGS. 5A-5C  are heat maps illustrating stresses applied in the uniform pitchline loading model to a coating top layer of gear  60  ( FIG. 5A ), a coating intermediate layer of gear  60  ( FIG. 5B ), and a core substrate of gear  60  ( FIG. 5C ). The maximum compressive stress on tooth  63  was located on face  65  at pitchline  62 . The maximum bending stress of tooth  63  was located at root fillet  66 . 
       FIG. 6  is a heat map illustrating static structural equivalent stress applied to gear  60  under an applied load using ANSYS 30 Finite Element Analysis. A maximum stress of about 2.1661×105 is located near the root fillet  66 . The results illustrate that spur gear  60  was equivalent in bending stress and compression stress to a standard AMS6265 case carburized spur gear. However, spur gear  60  was lighter and cost less to produce based on cost index. 
       FIG. 7  is a flow diagram illustrating an example technique for forming an example component that includes a nano-crystalline coating on a core substrate that defines a resonance damping cavity. While the techniques of  FIG. 7  are described with concurrent reference to the conceptual diagrams of  FIGS. 1-6 , in other examples, the techniques of  FIG. 7  may be used to form other components and aerospace components, the components and components of  FIGS. 1-6  may be formed using a technique different than that described in  FIG. 7 , or both. 
     The technique of  FIG. 7  includes forming core substrate  16  that defines a resonance damping cavity  12  ( 72 ). As described above, core substrate  16  may include a polymeric material, a metal, or an alloy. In some examples, forming core substrate  16  ( 72 ) may include additive manufacturing of core substrate  16 , such as three-dimensional printing core substrate  16 . In some examples, forming core substrate  16  ( 72 ) may include three-dimensional printing the core substrate in the shape of a gear. In some examples, forming core substrate  16  ( 72 ) may include introducing a vibration damping material into the resonance damping cavity. As discussed above, the vibration damping material may include a polymer, a metal, or an alloy. 
     The technique of  FIG. 7  also includes depositing a nano-crystalline coating  18  on at least a portion of the core substrate  16  ( 74 ). As described above, nano-crystalline coating  18  may include one or more layers of nano-crystalline metal (e.g., nickel, cobalt, copper, iron, or the like) or metal alloy (e.g., nickel-based alloy, cobalt-based alloy, copper-based alloy, iron-based alloy, or the like) that defines an ultra-fine-grained microstructure with an average grain size less than about 20 nanometers (nm). The nano-crystalline coating  18  may be applied using an electro-deposition process (e.g., pulse electro-deposition using an electrolyte bath). In some examples, core substrate  16  may be initially metalized to aid in the deposition of nano-crystalline coating  18 . 
     In examples in which nano-crystalline coating  18  includes a plurality of nano-crystalline coatings (e.g., layers  47  and  49 ), depositing nano-crystalline coating  18  ( 74 ) may include first layer  47  and depositing second layer  49 . In some examples, first layer  47  may include a nano-crystalline nickel-cobalt alloy and define a first thickness. Second layer  49  may include a nano-crystalline cobalt-phosphorus alloy and define a second thickness. In some examples, the first thickness may be greater than the second thickness. 
     Additionally, or alternatively, the nano-crystalline coating may be deposited ( 74 ) as a metal-polymer laminate  58  that includes alternating layers of one or more nano-crystalline layers  57  and  59  with one or more polymer-based layers  55 . In some such examples, the nano-crystalline layers  57  and  59  and polymer-based layers  55  may be selectively applied to allow for improved strength, wear and corrosion resistance, and additional relative motion between adjacent layers for increased vibrational-damping properties. 
     Various examples have been described. These and other examples are within the scope of the following claims.