US20210156043A1 - Method for plating a metallic material onto a titanium substrate - Google Patents

Abstract

A method for plating a metallic material onto a titanium substrate, wherein the titanium substrate includes an outer surface and an oxide layer on the outer surface. The method includes chemically etching the outer surface of the titanium substrate to remove at least a portion of the oxide layer, thereby yielding an etched titanium substrate. The method also includes establishing a cathodic protection current through the etched titanium substrate while the etched titanium substrate is immersed in a cathodic electrolyte solution. The method further includes strike plating a bond promoter layer onto the outer surface of the etched titanium substrate after the establishing of the cathodic protection current. The method lastly includes plating the metallic material onto the bond promoter layer.

Description

FIELD
• This application relates to plating a metallic material onto a titanium substrate and, more particularly, to methods for removing a protective oxide layer on the titanium substrate before electroplating the metallic material.
BACKGROUND
• Titanium substrates are plated with metallic materials for various reasons.
• For example, mechanical fasteners are widely used for joining the structural components of the airframe of an aircraft. Such mechanical fasteners are often fabricated from titanium alloys due to the desirable light weight and corrosion resistant qualities of titanium. However, titanium alloys can suffer from poor wear resistance, can be galvanically incompatible with aluminum alloys that are used for major fuselage and wing structure applications, and can be embrittled by elevated temperature phosphate ester hydraulic fluid used in commercial aircraft.
• Many of the drawbacks of titanium alloys can be addressed by plating. However, metallic plating on titanium substrates is often complicated by the extremely stable oxide formation on the surface of the titanium substrate, and also by the fact that very few chemical etchants are capable of attacking the oxide formation.
• Accordingly, those skilled in the art continue with research and development efforts in the field of plating onto titanium substrates.
SUMMARY
• Disclosed are methods for plating metallic materials onto titanium substrates.
• In one example, the disclosed method for plating a metallic material onto a titanium substrate (having an outer surface and an oxide layer on the outer surface) includes chemically etching the outer surface of the titanium substrate to remove at least a portion of the oxide layer, thereby yielding an etched titanium substrate. The method also includes establishing a cathodic protection current through the etched titanium substrate while the etched titanium substrate is immersed in a cathodic electrolyte solution, and then strike plating a bond promoter layer onto the outer surface of the etched titanium substrate after the establishing of the cathodic protection current. The method further includes plating the metallic material onto the bond promoter layer.
• In another example, the disclosed method for plating a metallic material onto a titanium substrate (having an outer surface and an oxide layer on the outer surface) includes abrading the outer surface of the titanium substrate and chemically etching the outer surface of the titanium substrate to remove at least a portion of the oxide layer, thereby yielding an etched titanium substrate. The method also includes rinsing the etched titanium substrate and establishing a cathodic protection current through the etched titanium substrate while the etched titanium substrate is immersed in a cathodic electrolyte solution. The method further includes strike plating a bond promoter layer onto the outer surface of the etched titanium substrate after the establishing of the cathodic protection current. The method lastly includes plating the metallic material onto the bond promoter layer.
• In yet another example, the disclosed method for plating a metallic material onto a titanium substrate (having an outer surface and an oxide layer on the outer surface) includes etching the outer surface of the titanium substrate to yield an etched titanium substrate, wherein the etching includes immersing the titanium substrate in an activation solution and establishing an anodic etching current through the titanium substrate while the titanium substrate is immersed in the activation solution. The method also includes establishing a cathodic protection current through the etched titanium substrate while the etched titanium substrate is immersed in a cathodic electrolyte solution and then strike plating a bond promoter layer onto the outer surface of the etched titanium substrate after the establishing of the cathodic protection current. The method further includes plating the metallic material onto the bond promoter layer.
• Also disclosed are articles manufactured using the disclosed methods for plating a metallic material onto a titanium substrate. Non-limiting examples of such articles include mechanical fasteners, ducts and struts.
• Other examples of the disclosed methods and articles formed therefrom will become apparent from the following detailed description, the accompanying drawings and the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a flow diagram depicting an example of the disclosed method for plating a metallic material onto a titanium substrate;
• FIG. 2 is a schematic illustration of a titanium substrate having an outer surface and an oxide layer on the outer surface;
• FIG. 3 is a schematic illustration of a plated structure manufactured in accordance with the method for plating depicted inFIG. 1;
• FIG. 4 is a flow diagram depicting an example method for etching the outer surface of a titanium substrate in accordance with the method for plating depicted inFIG. 1;
• FIG. 5 is a schematic illustration of a system for activating a titanium substrate in accordance with the method for plating depicted inFIG. 1;
• FIG. 6 is a schematic illustration of an electrochemical cell for establishing an anodic etching current in accordance with the method for plating depicted inFIG. 1;
• FIG. 7 is a flow diagram depicting an example method for establishing a cathodic protection current through a titanium substrate in accordance with the method for plating depicted inFIG. 1;
• FIG. 8 is a schematic illustration of an electrochemical cell for establishing a cathodic protection current in accordance with the method for plating depicted inFIG. 1;
• FIG. 9 is another flow diagram depicting an example of the disclosed method for plating a metallic material onto a titanium substrate;
• FIG. 10 is yet another flow diagram depicting an example of the disclosed method for plating a metallic material onto a titanium substrate;
• FIG. 11 is a cross-sectional view of an article, particularly a mechanical fastener (e.g., a bolt), manufactured in accordance with the method ofFIG. 1;
• FIG. 12 is a cross-sectional view of a portion of the article shown inFIG. 11;
• FIG. 13 is a flow diagram of an aircraft manufacturing and service methodology; and
• FIG. 14 is a block diagram of an aircraft.
DETAILED DESCRIPTION
• The following detailed description refers to the accompanying drawings, which illustrate specific examples described by the disclosure. Other examples having different structures and operations do not depart from the scope of the present disclosure. Like reference numerals may refer to the same feature, element, or component in the different drawings.
• Illustrative, non-exhaustive examples, which may be, but are not necessarily, claimed, of the subject matter according the present disclosure are provided below. Reference herein to “example” means that one or more feature, structure, element, component, characteristic and/or operational step described in connection with the example is included in at least one embodiment and/or implementation of the subject matter according to the present disclosure. Thus, the phrase “an example” and similar language throughout the present disclosure may, but do not necessarily, refer to the same example. Further, the subject matter characterizing any one example may, but does not necessarily, include the subject matter characterizing any other example.
• Referring toFIGS. 1-3, the present disclosure provides examples of amethod100 for plating ametallic material18 onto atitanium substrate10 that includes anouter surface12 and anoxide layer14 on theouter surface12. In performing themethod100, at least a portion of theoxide layer14 may be removed so that themetallic material18 may then be plated onto an etched titanium substrate11 (FIG. 3). Further, an intermediatebond promoter layer16 may be provided between theetched titanium substrate11 and themetallic material18 to promote plating adherence. As such, the resultingplated structure20 may retain the desirable qualities of titanium (e.g., lightweight and corrosion-resistant) while also possessing the bonding and grounding attributes of themetallic material18.
• Themethod100 includes etching (block130) theouter surface12 of thetitanium substrate10 and, atblock160, establishing a cathodic protection current through thetitanium substrate10 that has been etched.Blocks130 and160 may be performed to remove theoxide layer14 on theouter surface13 of theetched titanium substrate11. Following oxide layer removal, themethod100 further includes, atblock180, strike plating the titanium substrate to plate abond promoter layer16 onto thetitanium substrate10 and, atblock190, plating ametallic material18 onto thebond promoter layer16.
• Themethod100 may be performed on anysuitable titanium substrate10 regardless of size, shape and function. In one example, thetitanium substrate10 may be a commercially available one-sided lockbolt mechanical fastener. By performing themethod100 on the mechanical fastener, the plated mechanical fastener may exhibit improved bonding and grounding capabilities. In another example, thetitanium substrate10 may be a custom-machined portion of a fuselage, which may be plated on for similar reasons. Those skilled in the art will appreciate that various other types oftitanium substrates10 may be employed without departing from the scope of the present disclosure.
• The material composition of thetitanium substrate10 may include pure titanium, any suitable titanium alloy and any combination thereof. One suitable titanium material may include, for example, Ti-6Al-4V. Further, thetitanium substrate10 may be homogenous in its composition or contain discrete regions of different titanium materials. For example, thetitanium substrate10 shown inFIGS. 2, 3, 5, 6 and 8 may be formed from a titanium alloy (e.g., Ti-6Al-4V). Those skilled in the art will appreciate that the suitability of any particular titanium alloy may be based, at least in part, on the compatibility of that titanium alloy with thebond promoter layer16 to be strike plated.
• Often, theouter surface12 of atitanium substrate10 may contain debris (e.g., foreign contaminants). This debris obstructs access to theoxide layer14 and, if not removed, may hinder efforts to remove theoxide layer14. Accordingly, themethod100 may begin atblock110 with cleaning theouter surface12 of atitanium substrate10 to remove debris (if any). In an example, the cleaning (block110) may be performed by wiping theouter surface12 of thetitanium substrate10 with a solvent wipe. In an example, the cleaning (block110) may be performed by exposing theouter surface12 to an organic solvent. In an example, the cleaning (block110) may be performed by blasting theouter surface12 with a dry abrasive. In an example, the cleaning (block110) may be performed by vibratory finishing. In an example, the cleaning (block110) may be performed by barrel tumbling. Those skilled in the art will appreciate that various other cleaning methods may be employed without departing from the scope of the present disclosure.
• Themethod100 may include, atblock120, abrading (e.g., roughening) theouter surface12 of atitanium substrate10. In doing so, the abrading (block120) may mechanically remove at least a portion of theoxide layer14, if not most of it. Those skilled in the art will appreciate that abrading (block120) theouter surface12 of thetitanium substrate10 may also increase the overall surface area of theouter surface12, thereby increasing the dissolvability of theoxide layer14.
• A suitable abrasion method may be determined based on, among other things, the number oftitanium substrates10 to be abraded. In one example, batches oftitanium substrates10 may be abraded in a tumbler. Of course, this abrasion method may be preferred for applications involving large numbers oftitanium substrates10. For applications involvingfewer titanium substrates10, blasting thetitanium substrates10 with an abrasive medium may be adequate. In these examples, the blasting may be performed using either wet or dry abrasive mediums, and abrasive mediums of varying grit sizes. In one example, the abrading (block120) may include blasting thetitanium substrate10 with an abrasive medium having a grit size of at least about 60 microns. In another example, the abrading (block120) may include blasting thetitanium substrate10 with an abrasive medium having a grit size of at least about 100 microns. In yet another example, the abrading (block120) may include blasting thetitanium substrate10 with an abrasive medium having a grit size of at least about 140 microns. Those skilled in the art will appreciate that various other abrasive mediums and abrasion methods may be employed without departing from the scope of the present disclosure.
• Referring toFIG. 4, themethod100 includes, atblock130, etching theouter surface12 of atitanium substrate10 to remove at least a portion of theoxide layer14, thereby yielding an etchedtitanium substrate11. Like the abrading (block120), the etching (block130) may be performed to reduce theoxide layer14 in preparation for subsequent plating (block190).
• Referring toFIG. 5, the etching (block130) may be performed by chemical etching (block132) theouter surface12 of thetitanium substrate10. More specifically, asuitable activation solution34 may be prepared (block134 (“preparing an activation solution”)) and the titanium substrate may be immersed (block136 (“immersing the titanium substrate in the activation solution”)) in it for a predetermined duration of time or until a desired amount ofoxide layer14 has been removed. The reason for the etching is to remove the top 0.5-5 micron layer on the surface that is disturbed material and slightly embedded grit (called the Bielby layer) that is detrimental to good plating adhesion.
• While any suitable oxide removal mechanism may be employed, it is generally contemplated that theactivation solution34 should include an oxide removal agent and a complexing agent. The oxide removal agent may remove oxygen ions from theoxide layer14, thereby dissolving theoxide layer14, and the complexing agent may complex with the oxygen ions in solution (e.g., oxygen scavenging) to prevent theoxide layer14 from reforming.
• The oxide removal agent may be fluoride-based (e.g., contains fluoride ions) and may be added to theactivation solution34 as a fluoride salt. For example, theactivation solution34 may include from about 2 grams to about 8 grams of sodium fluoride per liter ofactivation solution34. In another example, theactivation solution34 may include from about 4 grams to about 6 grams of sodium fluoride per liter ofactivation solution34. Those skilled in the art will appreciate that due to the relatively dilute concentration of fluoride in theactivation solution34, theactivation solution34 may be less toxic than most available chemical etchants.
• Any suitable complexing agent (or complexing agents) may be employed to scavenge for oxygen ions in theactivation solution34. For example, reducing agents, such as ascorbic acid, oxalic acid, and bisulfite, can be used. It is generally contemplated, however, that the suitability of a complexing agent may be determined, at least in part, on the compatibility of the complexing agent with the oxide removal agent, and possibly other activation solution components as well (if included). The complexing agent should not interfere/hinder those associated mechanisms (e.g., oxide removal, etc.). One such type of a suitable complexing agent may include, for example, citric acid, or similar organic acids. In one example, theactivation solution34 may include at least about 30 grams of citric acid per liter ofactivation solution34. In another example, theactivation solution34 may include at least about 50 grams of citric acid per liter ofactivation solution34. In another example, theactivation solution34 may include at least about 70 grams of citric acid per liter ofactivation solution34. In another example, theactivation solution34 may include about 30 to about 80 grams of citric acid per liter ofactivation solution34. Those skilled in the art will appreciate that other complexing agents may be employed at various concentrations without departing from the scope of the present disclosure.
• In addition to the oxide removal agent and the complexing agent, in one or more examples, theactivation solution34 may also include a non-oxidizing acid. Those skilled in the art will appreciate that non-oxidizing acids are less likely than oxidizing acids to oxidize thetitanium substrate10, and may be included to help keep the pH of theactivation solution34 relatively low (e.g., pH less than 5). Without being bound by any particular theory, it is believed that by keeping the pH of theactivation solution34 relatively low, the available concentration of hydroxide ions in solution may be suppressed and an optimal environment for oxide removal may be provided. However, it is also generally contemplated that the pH of theactivation solution34 need not be overly acidic (e.g., pH less than 3) or immersed for too long due to the potential of hydrogen ingress into the titanium substrate10 (e.g., hydrogen embrittlement).
• In one example, the non-oxidizing acid may include sulfuric acid. More specifically, theactivation solution34 may include sulfuric acid at concentrations dilute enough such that the reduction of sulfate to SO₂(which is oxidizing) does not occur. For example, theactivation solution34 may include at least about 50 grams of sulfuric acid per liter ofactivation solution34, such about 50 to 150 grams of sulfuric acid per liter ofactivation solution34. In another example, theactivation solution34 may include at least about 90 grams of sulfuric acid per liter ofactivation solution34. In yet another example, theactivation solution34 may include at least about 130 grams of sulfuric acid per liter ofactivation solution34.
• In other examples, the non-oxidizing acid may include phosphoric acid, phosphorous acid, fluoboric acid, or fluosilicic acid if the acid and fluoride sources are combined.
• Referring back toFIG. 4, the etching (block130) may also include anodic etching (block138) thetitanium substrate10 to further remove theoxide layer14. As shown inFIG. 6, the anodic etching (block138) may be performed in a standard two-electrode bath, wherein the titanium substrate10 (e.g., the anode) and asuitable cathode42 is electrically coupled (blocks140 (“electrically coupling the titanium substrate to a current source”) and142 (“electrically coupling the current source to a cathode”)) to acurrent source40, and immersed (block144 (“immersing the titanium substrate in an anodic electrolyte solution”)) in ananodic electrolyte solution44. By establishing an anodic etching current through thetitanium substrate10, as shown inblock146, a reduction reaction may occur on theouter surface12 of thetitanium substrate10, thereby causing the removal of surface-level titanium (e.g., etching). In doing so, at least a portion of theoxide layer14 may be removed as well. The application of anodic current means hydrogen evolution occurs on the cathode and away from the part.
• In one or more examples, the anodic etching (block138) may be performed simultaneously with the chemical etching (block132). More specifically, blocks140-146 may be performed while thetitanium substrate10 is immersed in anactivation solution34. Theactivation solution34 may be formulated to contain charge-carrying electrolytes, thereby completing the electrochemical cell (meaning that a separate anodic electrolyte solution is not needed). Without being bound by any particular theory, it is believed that by performingblocks132 and138 simultaneously, the anodic etching (block138) may enable the use of lesstoxic activation solutions34 at lower temperatures because the anodic etching (block138) compensates for the diminished capability of theactivation solution34 to remove the oxide layer. Thus, theactivation solution34 of the present disclosure may be safer to handle than typical chemical etchants.
• Asuitable activation solution34 for performingblocks132 and138 simultaneously may include an oxide removal agent, a complexing agent and a non-oxidizing acid. The oxide removal agent may be, for example, sodium fluoride at about 2 grams to about 8 grams per liter ofactivation solution34. The complexing agent may be, for example, citric acid at no less than about 30 grams per liter of activation solution34 (e.g., about 30 to about 80 grams of citric acid per liter ofactivation solution34. The non-oxidizing acid may be, for example, sulfuric acid at no less than about 50 grams per liter ofactivation solution34, such as from about 50 to about 150 grams per liter ofactivation solution34. Alternatively, some commercially available solutions may be suitable as well, such as Dipsol 602-AS Power Acid available from Dipsol of America, Inc. of Livonia, Mich. Those skilled in the art will appreciate however, that various other concentrations, reagents and solutions may be employed to performblocks132 and138 simultaneously without departing from the scope of the present disclosure.
• Depending on the size and shape of thetitanium substrate10, the current density of the anodic etching current may be adjusted as needed. For example, it may be appropriate to increase the current density of the anodic etching current to compensate for relativelylarge titanium substrates10 due to their relatively large surface areas. Thus, increasing the current density of the anodic etching current may be required to ensure that an adequate degree of oxide removal is achieved across theouter surface12 of thetitanium substrate10. In one example, the establishing (block146) of the anodic etching current may include establishing an anodic etching current having a current density of at least about 2 amps per square foot. In another example, the establishing (block146) of the anodic etching current may include establishing an anodic etching current having a current density of at least about 4 amps per square foot. In yet another example, the establishing (block146) of the anodic etching current may include establishing an anodic etching current having a current density of at least about 6 amps per square foot.
• The anodic etching current may be maintained for any suitable duration of time. Those skilled in the art will appreciate that it may take longer to remove theoxide layer14 if, among other things, theoxide layer14 is particularly thick and/or thetitanium substrate10 is particularly large. In one example, the establishing (block146) of the anodic etching current includes establishing an anodic etching current through thetitanium substrate10 for at least about 150 seconds. In another example, the establishing (block146) of the anodic etching current includes establishing an anodic etching current through thetitanium substrate10 for at least about 300 seconds. In yet another example, the establishing (block146) of the anodic etching current includes establishing an anodic etching current through thetitanium substrate10 for at least about 450 seconds. The goal is to remove the Bielby layer and not affect part dimensions or modify (smooth out) the mechanically cleaned surface.
• Followingblock130 but beforeblock160, themethod100 may include, atblock150, rinsing thetitanium substrate10 that has been etched (i.e., the etched titanium substrate11) to minimize cross-contamination and remove lingering oxygen ions surrounding the etchedtitanium substrate11. Preferably, the rinsing (block150) may be performed using a solution that contains a low oxygen concentration to minimizeoxide layer14 reformation. In an example, the etchedtitanium substrate11 may be rinsed with theactivation solution34 used inblock132. In an example, the etchedtitanium substrate11 may be rinsed with “dirty water” (e.g., water containing foreign contaminants). In an example, the etchedtitanium substrate11 may be rinsed with thecathodic electrolyte solution62 used in block160 (described below). In an example, the etchedtitanium substrate11 may be rinsed with an aqueous solution having a pH between about 3 and about 5. Those skilled in the art will appreciate that various other solutions maybe employed to rinse the etchedtitanium substrate11, without departing from the scope of the present disclosure.
• A cathodic protection current may be established through the etchedtitanium substrate11 to convert the otherwise activeouter surface13 of the etchedtitanium substrate11 into a passive site for the oxide formation reaction. By supplying free electrons to the etchedtitanium substrate11 and distributing a negative charge across theouter surface13, the cathodic protection current may thereby prevent negatively charged oxygen ions from bonding to theouter surface13. The cathodic protection current may be maintained (e.g., cathodically held) for as long as needed in preparation forblock180, strike plating abond promoter layer16 onto theouter surface13 of the etchedtitanium substrate11. Thus, it is generally contemplated thatblock160 may be performed beforeblock180, but thatblock180 may be performed immediately thereafter.
• Referring toFIGS. 7 and 8, blocks160 and180 may be performed using an electrochemical cell similar to the configuration used for the anodic etching (block138) (e.g., a standard two-electrode bath). Acathodic electrolyte solution62 may first be prepared (block162 (“preparing a cathodic electrolyte solution”)) so that a titanium substrate (e.g., the cathode) and asuitable anode68 may be immersed (block164 (“immersing an etched titanium substrate and an anode in the electrolyte solution”)) in it and electrically coupled (blocks166 (“electrically coupling the etched titanium substrate to a current source”) and168 (“electrically coupling the current source to an anode”)) to a current source. A cathodic protection current may then be established (block170 (“establishing a cathodic protection current through the etched titanium substrate”)) for a duration of time before a strike current is applied (block180) to deposit conductive metal ions in thecathodic electrolyte solution62 onto theouter surface13 of the etchedtitanium substrate11, thereby forming thebond promoter layer16.
• Thecathodic electrolyte solution62 may include, among other things, the conductive metal ions that will later be formed into the bond promoter layer16 (following block180). These conductive metal ions may include, for example, nickel ions, iron atoms, copper ions, and various other conductive metal ions that are suitable for strike plating. These conductive metal ions may be added to theactivation solution34 via any suitable source. For example, nickel sulfate hexahydrate (e.g., a nickel salt) may be added to theactivation solution34 to provide nickel ions. Further, thecathodic electrolyte solution62 may also include various additives such as non-oxidizing acids, reducing agents to prevent oxide formation, and complexing agents. Referring specifically to complexing agents, in one example, thecathodic electrolyte solution62 may include at least one of citric acid and sodium citrate. Reducing agents like ascorbic acid are used, for example, to prevent the ferrous iron from being oxidized to the ferric ion that is not platable. Those skilled in the art will appreciate that various other conductive metal ions and additives may be added to theactivation solution34 without departing from the scope of the present disclosure.
• The cathodic protection current may be applied at any voltage capable of preventing oxygen ions in thecathodic electrolyte solution62 from binding to theouter surface13 of the etchedtitanium substrate11. The voltage may be predetermined prior to the performance ofblock160, but may also be altered at any time if needed. In one example, the establishing (block160) of the cathodic protection current includes applying a constant voltage of at least about 0 volts. In another example, the establishing (block160) of the cathodic protection current includes applying a constant voltage of at least about 2 volts. In one example, the establishing (block160) of the cathodic protection current includes applying a constant voltage of at least about 4 volts. The voltage is high enough to drive the oxide reaction but not so high that the hydrogen evolution reaction predominates.
• The cathodic protection current may be maintained (e.g., “cathodically held”) for a duration of time until the strike current is applied. This duration of time, however, is yet another processing consideration may be varied based on, among other things, the size and shape of the etchedtitanium substrate11, and the time required to remove the oxygen ions surrounding theouter surface13 of the etchedtitanium substrate11. In one example, the establishing (block160) of the cathodic protection current may include establishing a cathodic protection current for at least about 15 seconds. In one example, the establishing (block160) of the cathodic protection current may include establishing a cathodic protection (oxide reduction) current for at least about 120 seconds. In another example, the establishing (block160) of the cathodic protection current may include establishing a cathodic protection current for at least about 480 seconds. In yet another example, the establishing (block160) of the cathodic protection current may include establishing a cathodic protection current for about 30 seconds to about 600 seconds.
• Both the duration and current density of the strike current may be controlled to deposit varying quantities of conductive metal ions on theouter surface13 of the etchedtitanium substrate11. Those skilled in the art will appreciate that by increasing the current density, the density of conductive metal ions across theouter surface13 may increase as well. Accordingly, increasing the current density may be employed as a way to form thicker bond promoter layers16 that cover more of theouter surface13. In one example, the strike plating (block180) may include applying a strike current to the etchedtitanium substrate11, the strike current having a current density of at least about 50 amps per square foot. In another example, the strike plating (block180) may include applying a strike current to the etchedtitanium substrate11, the strike current having a current density of at least about 70 amps per square foot.
• Like the anodic etching current and the cathodic protection (oxide reduction) current, the duration of time that strike current is applied may be varied as needed. However, it is generally contemplated that consideration should be given to the desired physical dimensions of thebond promoter layer16. The longer the strike current is applied, the greater the quantity of conductive metal ions is deposited. In one example, the strike plating (block180) may include applying a strike current for at least about 120 seconds. In another example, the strike plating (block180) may include applying a strike current for at least about 240 seconds.
• Thebond promoter layer16 on theouter surface13 of the etchedtitanium substrate11 provides the etchedtitanium substrate11 with a conductive surface upon which themetallic material18 may be plated. The strike plating (block180) may thus, in effect, render theouter surface13 of the etchedtitanium substrate11 active to the metallic metal, and thereby facilitate titanium-substrate-to-plating adherence. Further, thebond promoter layer16 may also be impermeable to oxygen, thereby “locking in” the whatever remains of the oxide layer14 (if any) and preventing any additional oxygen ions from binding to theouter surface13 of the etchedtitanium substrate11.
• After having been formed, themethod100 includes plating (block190) ametallic material18 onto thebond promoter layer16. Themetallic material18 may cover at least a portion (if not most) of theouter surface13 of the etchedtitanium substrate11, thereby yielding a platedstructure20.
• Variousmetallic materials18 may be plated on the etchedtitanium substrate11. As one example (e.g., for mechanical fastener applications), themetallic material18 can be an electrically conductive and lubricious material, such as an electrically conductive and lubricious material that includes indium and/or tin. As another example (e.g., for corrosion protection), themetallic material18 can be a sacrificial material, such as a sacrificial material that includes cadmium, zinc, and/or nickel. As another example (e.g., for heat reflecting applications), themetallic material18 can be a high reflectivity material, such as a high reflectivity material that includes aluminum and/or gold. As another example (e.g., for sliding applications, such as pistons and actuators), themetallic material18 can be a wear-resistant material, such as a wear-resistant material that includes chromium and nickel (e.g., electroless nickel).
• When selecting ametallic material18, consideration may be given to the compatibility of themetallic material18 with thebond promoter layer16. For example, if thebond promoter layer16 includes nickel, ametallic material18 that may be suitable for plating (block190) may include indium. Those skilled in the art will appreciate, however, that various other combinations of metallic materials and bond promoter layer compositions may be employed without departing from the scope of the present disclosure.
• The plating (block190) may be performed using any suitable method, many of which are well known in the art. For example, at least one of electrodeposition, thin-film deposition and sputter deposition may be employed to perform the plating (block190), among other possible options. Further, the plating (block190) may be performed such that themetallic material18 is of a desired thickness and density. Accordingly, those skilled in the art will appreciate that the physical dimensions of themetallic material18 may vary without departing from the scope of the present disclosure.
• Referring toFIG. 9, the present disclosure provides another example of amethod200 for plating ametallic material18 onto atitanium substrate10, wherein the titanium substrate includes anouter surface12 and anoxide layer14 on theouter surface12. Themethod200 includes, atblock210, abrading theouter surface12 of atitanium substrate10 and, atblock220, chemically etching theouter surface12 of thetitanium substrate10 to remove at least a portion of theoxide layer14, thereby yielding an etchedtitanium substrate11. Themethod200 also includes, atblock230, rinsing the etchedtitanium substrate11 and, at block240, establishing a cathodic protection (oxide reduction) current through the etchedtitanium substrate11 while the etchedtitanium substrate11 is immersed in anelectrolyte solution62. Themethod200 further includes, atblock250, strike plating (block250) abond promoter layer16 onto theouter surface13 of the etchedtitanium substrate11 after the establishing (block240) of the cathodic protection current. Themethod200 lastly includes, atblock260, plating ametallic material18 onto thebond promoter layer16.
• Referring toFIG. 10, the present disclosure provides yet another example of amethod300 for plating ametallic material18 onto atitanium substrate10, wherein thetitanium substrate10 includes anouter surface12 and anoxide layer14 on theouter surface12. Themethod300 includes, atblock310, etching theouter surface12 of atitanium substrate10 to yield an etchedtitanium substrate11, the etching (block310) includes, atblock320, immersing thetitanium substrate10 in anactivation solution34 and, atblock330, establishing an anodic etching current through thetitanium substrate10 while thetitanium substrate10 is immersed in theactivation solution34. Themethod300 also includes, atblock340, establishing a cathodic protection current through the etchedtitanium substrate11 while the etchedtitanium substrate11 is immersed in acathodic electrolyte solution62. Themethod300 further includes, atblock350, strike plating abond promoter layer16 onto theouter surface13 of the etchedtitanium substrate11 after the establishing (block340) of the cathodic protection current, and, atblock360, plating ametallic material18 onto thebond promoter layer16.
• Referring toFIGS. 11 and 12, the present disclosure provides examples of anarticle400 that may be manufactured using any of the previously disclosed methods (e.g.,100,200 and300). Thearticle400 includes atitanium body410, abond promoter layer420 that includes, for example, a nickel-chromium alloy, and plating430 (e.g., indium) on at least a portion of thetitanium body410. For example, theplating430 has a thickness (T) ranging from about 0.2 mils to about 0.5 mils. As shown, thetitanium body410 may be a mechanical fastener, such as a bolt. However, those skilled in the art will appreciate that thetitanium body410 may be fabricated into a variety of shapes including, but not limited to, a tapered pin, a straight pin, a threaded lockbolt, a tapered sleeve bolt, a bushing, a tapered lock, a nut, a screw, and the like.
• Mechanical fasteners are just one application of the disclosed methods for plating a metallic material onto a titanium substrate. For example, aircraft experience electromagnetic effects (EME) from a variety of sources, such as lightning strikes and precipitation static. Metallic aircraft structures are readily conductive and, therefore, are relatively less susceptible to electromagnetic effects. However, composite aircraft structures (e.g., carbon fiber reinforced thermoset and thermoplastic composite structures) do not readily conduct away the significant electrical currents and electromagnetic forces stemming from electromagnetic effects. Therefore, the disclosed methods can be used to direct the current into the mechanical fasteners, such as bolts, screws, rivets, blind fasteners and the like, that connect with metallic layers such as copper foil embedded within the wing.
• Another application of the disclosed methods for plating a metallic material onto a titanium substrate is the use of sacrificial coatings like zinc-nickel to prevent dissimilar metal corrosion. Current practices to prevent corrosion when titanium is mated to aluminum is to prime the titanium surface and seal the joint against moisture intrusion. The problem is sealing is time-consuming and expensive for major subassemblies like a nacelle strut box. By plating the surface with a sacrificial coating, as is disclosed herein, the joint sealing process can be eliminated since the mating surfaces have a similar corrosion potential.
• Yet another application of the disclosed methods for plating a metallic material onto a titanium substrate is plating titanium pneumatic ducts with a nickel coating that prevents damage due to phosphate ester fluid exposure. If the surface is bright (low emissivity) as well then it would prevent radiant heat from damaging aluminum and composite structure. The plating would replace an expensive gold coating that is a challenge to apply.
• Examples of the disclosure may be described in the context of an aircraft manufacturing andservice method1000, as shown inFIG. 13, and anaircraft1002, as shown inFIG. 14. During pre-production, the aircraft manufacturing andservice method1000 may include specification anddesign1004 of theaircraft1002 andmaterial procurement1006. During production, component/subassembly manufacturing1008 andsystem integration1010 of theaircraft1002 takes place. Thereafter, theaircraft1002 may go through certification anddelivery1012 in order to be placed inservice1014. While in service by a customer, theaircraft1002 is scheduled for routine maintenance andservice1016, which may also include modification, reconfiguration, refurbishment and the like.
• Each of the processes ofmethod1000 may be performed or carried out by a system integrator, a third party, and/or an operator (e.g., a customer). For the purposes of this description, a system integrator may include without limitation any number of aircraft manufacturers and major-system subcontractors; a third party may include without limitation any number of venders, subcontractors, and suppliers; and an operator may be an airline, leasing company, military entity, service organization, and so on.
• As shown inFIG. 14, theaircraft1002 produced byexample method1000 may include anairframe1018 with a plurality ofsystems1020 and an interior1022. Examples of the plurality ofsystems1020 may include one or more of apropulsion system1024, anelectrical system1026, ahydraulic system1028, and anenvironmental system1030. Any number of other systems may be included.
• The disclosed methods for plating a metallic material onto a titanium substrate may be employed during any one or more of the stages of the aircraft manufacturing andservice method1000. As one example, the disclosed methods for plating a metallic material onto a titanium substrate may be employed duringmaterial procurement1006. As another example, components or subassemblies corresponding to component/subassembly manufacturing1008,system integration1010, and or maintenance andservice1016 may be fabricated or manufactured using the disclosed methods for plating a metallic material onto a titanium substrate. As another example, theairframe1018 and the interior1022 may be constructed using the disclosed methods for plating a metallic material onto a titanium substrate. Also, one or more apparatus examples, method examples, or a combination thereof may be utilized during component/subassembly manufacturing1008 and/orsystem integration1010, for example, by substantially expediting assembly of or reducing the cost of anaircraft1002, such as theairframe1018 and/or the interior1022. Similarly, one or more of system examples, method examples, or a combination thereof may be utilized while theaircraft1002 is in service, for example and without limitation, to maintenance andservice1016.
• The disclosed methods for plating a metallic material onto a titanium substrate are described in the context of an aircraft; however, one of ordinary skill in the art will readily recognize that the disclosed methods for plating a metallic material onto a titanium substrate may be utilized for a variety of applications. For example, the disclosed methods for plating a metallic material onto a titanium substrate may be implemented in various types of vehicles including, e.g., helicopters, passenger ships, automobiles and the like.
• Although various examples of the disclosed methods for plating a metallic material onto a titanium substrate have been shown and described, modifications may occur to those skilled in the art upon reading the specification. The present application includes such modifications and is limited only by the scope of the claims.

Claims (34)

1. A method for plating a metallic material onto a titanium substrate, said titanium substrate comprising an outer surface and an oxide layer on said outer surface, said method comprising:

chemically etching said outer surface of said titanium substrate to remove at least a portion of said oxide layer, thereby yielding an etched titanium substrate;

establishing a cathodic protection current through said etched titanium substrate while said etched titanium substrate is immersed in a cathodic electrolyte solution;

strike plating a bond promoter layer onto said outer surface of said etched titanium substrate after said establishing said cathodic protection current; and

plating said metallic material onto said bond promoter layer.

2. The method ofclaim 1 wherein said metallic material is an electrically conductive and lubricious material comprising at least one of indium and tin.

3. The method ofclaim 1 wherein said metallic material is a sacrificial material comprising at least one of cadmium, zinc and nickel.

4. The method ofclaim 1 wherein said metallic material is a high reflectivity material comprising at least one of aluminum and gold.

5. The method ofclaim 1 wherein said metallic material is a wear-resistant material comprising at least one of chromium and nickel.

6. The method ofclaim 1 further comprising cleaning said outer surface of said titanium substrate prior to said chemically etching.

7-8. (canceled)

9. The method ofclaim 1 further comprising abrading said outer surface of said titanium substrate prior to said chemically etching.

10. The method ofclaim 9 wherein said abrading comprises blasting said titanium substrate with an abrasive medium having a grit size of at least about 60 microns.

11-13. (canceled)

14. The method ofclaim 1 wherein said chemically etching comprises immersing said titanium substrate in an activation solution.

15. The method ofclaim 14 wherein said activation solution comprises at least one of fluoride ions and sodium fluoride.

16. The method ofclaim 14 wherein said activation solution comprises from about 2 grams to about 8 grams of sodium fluoride per liter of activation solution.

17. The method ofclaim 14 wherein said activation solution comprises at least one of a complexing agent and citric acid.

18. The method ofclaim 14 wherein said activation solution comprises at least about 30 grams of citric acid per liter of activation solution.

19. The method ofclaim 14 wherein said activation solution comprises sulfuric acid.

20. The method ofclaim 14 wherein said activation solution comprises at least about 50 grams of sulfuric acid per liter of activation solution.

21. The method ofclaim 14 further comprising establishing an anodic etching current through said titanium substrate while said titanium substrate is immersed in said activation solution.

22. The method ofclaim 21 wherein said establishing said anodic etching current comprises establishing an anodic etching current having a current density of at least about 2 amps per square foot.

23. The method ofclaim 21 wherein said establishing said anodic etching current comprises establishing said anodic etching current through said titanium substrate for at least about 150 seconds.

24. (canceled)

25. The method ofclaim 1 further comprising rinsing said etched titanium substrate prior to said establishing said cathodic protection current.

26-27. (canceled)

28. The method ofclaim 25 wherein said rinsing comprises rinsing said etched titanium substrate with an aqueous solution having a pH between about 3 to about 5.

29. The method ofclaim 1 wherein said cathodic electrolyte solution comprises at least one of nickel ions and copper ions.

30. The method ofclaim 1 wherein said cathodic electrolyte solution comprises nickel sulfate hexahydrate.

31. The method ofclaim 1 wherein said cathodic electrolyte solution comprises a complexing agent.

32. The method ofclaim 1 wherein said cathodic electrolyte solution comprises at least one of citric acid and sodium citrate.

33. The method ofclaim 1 wherein said establishing said cathodic protection current comprises applying a constant voltage of about 0 volts.

34. The method ofclaim 1 wherein said establishing said cathodic protection current comprises establishing said cathodic protection current for at least about 15 seconds.

35. The method ofclaim 1 wherein said strike plating comprises applying a strike current to said etched titanium substrate, said strike current having a current density of at least about 50 amps per square foot.

36. The method ofclaim 1 wherein said strike plating comprises applying a strike current for at least about 120 seconds.

37. A method for plating a metallic material onto a titanium substrate, said titanium substrate comprising an outer surface and an oxide layer on said outer surface, said method comprising:

abrading said outer surface of said titanium substrate;

chemically etching said outer surface of said titanium substrate to remove at least a portion of said oxide layer, thereby yielding an etched titanium substrate;

rinsing said etched titanium substrate;

establishing a cathodic protection current through said etched titanium substrate while said etched titanium substrate is immersed in a cathodic electrolyte solution;

strike plating a bond promoter layer onto said outer surface of said etched titanium substrate after said establishing said cathodic protection current; and

plating said metallic material onto said bond promoter layer.

38. A method for plating a metallic material onto a titanium substrate, said titanium substrate comprising an outer surface and an oxide layer on said outer surface, said method comprising:

etching said outer surface of said titanium substrate to yield an etched titanium substrate, said etching comprising immersing said titanium substrate in an activation solution and establishing an anodic etching current through said titanium substrate while said titanium substrate is immersed in said activation solution;

establishing a cathodic protection current through said etched titanium substrate while said etched titanium substrate is immersed in a cathodic electrolyte solution;

strike plating a bond promoter layer onto said outer surface of said etched titanium substrate after said establishing said cathodic protection current; and

plating said metallic material onto said bond promoter layer.

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