Title:
Method of plating metal onto titanium
Kind Code:
A1


Abstract:
A method of plating a metal onto a titanium surface comprising a surface cleaning step, an anodic etching step, a cathodic activation step and a plating step.



Inventors:
Radatz, Darrin K. (Westlake, OH, US)
Brain, Ani Yordanova (Worcestershire, GB)
Clouser, Sidney J. (Chardon, OH, US)
Application Number:
12/284813
Publication Date:
04/09/2009
Filing Date:
09/25/2008
Assignee:
Sifco Selective plating
Primary Class:
Other Classes:
204/242, 204/275.1
International Classes:
C25D5/34; C25D17/14
View Patent Images:



Primary Examiner:
COHEN, BRIAN W
Attorney, Agent or Firm:
KUSNER & JAFFE (Mayfield Heights, OH, US)
Claims:
Having described the invention, the following is claimed:

1. A method of plating a metal onto a titanium surface, comprising the steps of: (a) positioning an electrode adjacent to a titanium surface, said electrode having an electrode surface conforming to the shape of said titanium surface and having a porous, abrasive pad positioned thereon, said pad on said electrode completely covering, and being in contact with, said titanium surface, wherein an interface is defined between said pad and said titanium surface and wherein said pad defines a gap between said titanium surface and said electrode surface; (b) etching said titanium surface by applying a positive voltage to said titanium surface and a negative voltage to said electrode while maintaining said relative movement between said titanium surface and said pad and maintaining said wetting of said interface between said pad and said titanium surface with said etching solution; (c) activating said titanium surface by applying a negative voltage to said titanium surface and a positive voltage to said electrode while maintaining said wetting of said interface between said pad and said titanium surface with said etching solution and maintaining said relative movement between said titanium surface and said pad; and (d) plating a metal onto said titanium surface by applying a plating solution to said interface between said pad and said titanium surface while applying a negative voltage to said titanium surface and a positive voltage on said electrode, and while maintaining said relative movement between said titanium surface and said pad, said pad maintaining complete coverage of said titanium surface during said abrading step, said etching step, said activating step and said plating step.

2. A method as defined in claim 1, wherein said etching solution and said plating solution flow through said electrode and through said pad.

3. A method as defined in claim 1, further comprising a support block disposed above said electrode.

4. A method as defined in claim 3, wherein said support block is comprised of a polymer material.

5. A method as defined in claim 3, wherein said support block includes a plurality of fluid supply channels formed therein, wherein said fluid supply channels fluidly communicate with a source of said etching solution and a source of said plating solution.

6. A method as defined in claim 5, further comprising a valve operable to selectively connect said fluid supply channels to said source of said etching solution and said source of said plating solution.

7. A method as defined in claim 1, wherein said titanium surface is stationary.

8. A method as defined in claim 1, wherein said titanium surface is planar.

9. A method as defined in claim 1, wherein said titanium surface is a non-planar surface.

10. A method as defined in claim 1, wherein said pad is made from a material selected from the group consisting of nylon, Dacron and cotton gauze.

11. A method as defined in claim 1, wherein said etching solution is an acid solution.

12. A method as defined in claim 11, wherein said etching solution contains about 10% NaCl, about 7% HCl, about 1% Ni salts and about 0.3% citric acid by weight.

13. A method as defined in claim 1, wherein said plating solution is comprised of an acid nickel sulfate solution.

14. A method as defined in claim 1, further comprising a step of: abrading said titanium surface by producing relative movement between said titanium surface and said pad while simultaneously wetting said interface between said pad and said titanium surface with an etching solution, said abrading step preceding said etching step.

15. A method of plating a surface of a first metal with a second metal, comprising the steps of: (a) positioning an electrode adjacent to a surface of a first metal, said electrode having a porous, abrasive pad positioned thereon, said pad on said electrode completely covering, and being in contact with, said surface of said first metal, wherein an interface is defined between said pad and said surface of said first metal and wherein said pad defines a gap between said surface of said first metal and said electrode surface; (b) etching said surface of said first metal by applying a positive voltage to said surface of said first metal and a negative voltage to said electrode while maintaining said relative movement between said surface of said first metal and said pad and maintaining said wetting of said interface between said pad and said surface of said first metal with said etching solution; (c) activating said surface of said first metal by applying a negative voltage to said surface and a positive voltage to said electrode while maintaining said wetting of said interface between said pad and said surface of said first metal with said etching solution and maintaining said relative movement between said surface of said first metal and said pad; and (d) plating a second metal onto said surface of said first metal by applying a plating solution to said interface between said pad and said surface of said first metal while applying a negative voltage to said surface of said first metal and a positive voltage on said electrode, and while maintaining said relative movement between said surface of said first metal and said pad, said pad maintaining complete coverage of said surface of said first metal during said abrading step, said etching step, said activating step and said plating step.

16. A method as defined in claim 15, wherein said electrode has a surface conforming to the shape of said surface of said first metal.

17. A method as defined in claim 15, wherein said etching solution and said plating solution flow through said electrode and through said pad.

18. A method as defined in claim 15, further comprising a support block disposed above said electrode.

19. A method as defined in claim 18, wherein said support block is comprised of a polymer material.

20. A method as defined in claim 18, wherein said support block includes a plurality of fluid supply channels formed therein, wherein said fluid supply channels fluidly communicate with a source of said etching solution and a source of said plating solution.

21. A method as defined in claim 15, further comprising a valve operable to selectively connect said fluid supply channels to said source of said etching solution and said source of said plating solution.

22. A method as defined in claim 15, wherein said first metal is a quickly oxidizing metal.

23. A method as defined in claim 22, wherein said first metal is titanium.

24. A method as defined in claim 22, wherein said first metal is a titanium alloy.

25. A method as defined in claim 24, wherein said second metal is nickel.

26. A method as defined in claim 15, wherein said pad is made from a material selected from the group consisting of nylon, Dacron and cotton gauze.

27. A method as defined in claim 15, wherein said etching solution is an acid solution.

28. A method as defined in claim 27, wherein said etching solution contains about 10% NaCl, about 7% HCl, about 1% Ni salts and about 0.3% citric acid by weight.

29. A method as defined in claim 15, wherein said plating solution is comprised of an acid nickel sulfate solution.

30. A method as defined in claim 15, further comprising a step of: abrading said surface of said first metal by producing relative movement between said surface of said first metal and said pad while simultaneously wetting said interface between said pad and said surface of said first metal with an etching solution, said abrading step preceding said etching step.

31. A system for plating a metal onto a titanium surface comprised of: an electrode dimensioned to be disposed adjacent to a titanium surface, said electrode having an electrode surface dimensioned to conform to the shape of said titanium surface; a porous abrasive pad disposed on said electrode surface, said pad dimensioned to cover and contact said titanium surface, such that said pad defines a gap between said electrode and said titanium surface; and selective means for selectively supplying an etching solution and a plating solution to said gap between said electrode and said titanium surface such that said titanium surface is covered by said etching solution or said plating solution when said titanium surface is plated and said pad and said titanium surface continuously move relative to each other when said titanium surface is abraded, etched, activated, and plated.

32. A system as defined in claim 31, further comprising: a support block disposed above said electrode, said support block including a plurality of fluid supply channels formed therein, said fluid supply chains fluidly communicating with a source of said etching solution and a source of said plating solutions.

33. A system as defined in claim 32, wherein said selective means is a valve operable to selectively connect said fluid supply channels to said source of said etching solution and said source of said plating solution.

34. A system as defined in claim 31, wherein said pad is made from a material selected from the group consisting of nylon, Dacron and cotton gauze.

Description:

FIELD OF THE INVENTION

The present invention relates to the art of plating, and more particularly to a method of electroplating a metal or metal alloy onto titanium.

BACKGROUND OF THE INVENTION

Because of its high strength and low weight, titanium finds advantageous use in many applications in the aerospace, industrial, and medical fields. The strength, hardness, and working temperature of titanium can further be improved by alloying. An alloy of titanium that is easily available and widely used is 6-4 Titanium (also referred to as “Grade 5 titanium”). 6-4 Titanium consists of 6% by weight aluminum, 4% by weight vanadium and the balance being titanium.

Despite the aforementioned properties, titanium and titanium alloys have found little use in mechanical engineering applications because of their poor tribological properties, namely, poor abrasive wear resistance, poor fretting behavior and high coefficient of friction. These tribological properties relate generally to the tenacious, compact oxide film that readily forms on the surface of titanium. In this respect, titanium is intrinsically very reactive. Whenever the metal is exposed to air or any environment containing available oxygen, the oxide film is formed on the surface thereof. The tribological performance can be improved by applying surface treatments and coatings. Coatings on titanium are also applied for the purposes of heat reflection, emissivity, corrosion resistance in hot acidic environments, conductivity, lubricity, brazing, and resizing.

Electrodeposition is an effective method for applying a coating onto a metal. Preparation of the surface of a titanium part is key to achieving robust adhesion between the titanium and any coating applied thereto.

In order for an electrodeposited coating to have optimal adhesion to titanium, the aforementioned oxide layer should be removed. However, the tenacity of the oxide layer makes its removal problematic. A common method to remove oxide from titanium is by exposure to a fluoride containing electrolyte. However, the toxicity and health hazards associated with fluoride makes such an oxide-removal process undesirable. The rapidity with which the oxide reforms after removal is also a factor to be considered with respect to this method.

Another factor that affects adhesion between two materials is surface area. Surface roughening of titanium is typically carried out by abrasion, grit blasting, and etching. However, as with fluoride cleaning, oxide quickly reforms on the surface of titanium following these cleaning processes and reduces adhesion. In other words, once the area to be plated has been dry-blasted or cleaned using hydrofluoric acid, steps must be taken to prevent titanium oxide from reforming on the surface of the part prior to a plating process.

The present invention overcomes these and other problems and provides a brush plating process for plating metal onto titanium.

SUMMARY OF THE INVENTION

In accordance with a preferred embodiment of the present invention, there is provided a method of plating a metal onto a titanium surface, comprising the steps of:

(a) positioning an electrode adjacent to a titanium surface, the electrode having an electrode surface conforming to the shape of the titanium surface and having a porous, abrasive pad positioned thereon, the pad on the electrode being in contact with the titanium surface, wherein an interface is defined between the pad and the titanium surface and wherein the pad defines a gap between the titanium surface and the electrode surface;

(b) etching the titanium surface by applying a positive voltage to the titanium surface and a negative voltage to the electrode while maintaining the relative movement between the titanium surface and the pad and maintaining the wetting of the interface between the pad and the titanium surface with the etching solution;

(c) activating the titanium surface by applying a negative voltage to the titanium surface and a positive voltage to the electrode while maintaining the wetting of the interface between the pad and the titanium surface with the etching solution and maintaining the relative movement between the titanium surface and the pad; and

(d) plating a metal onto the titanium surface by applying a plating solution to the interface between the pad and the titanium surface while applying a negative voltage to the titanium surface and a positive voltage on the electrode, and while maintaining the relative movement between the titanium surface and the pad, said pad maintaining complete coverage of said titanium surface during said abrading step, said etching step, said activating step and said plating step.

In accordance with another embodiment of the present invention, there is provided a method of plating a surface of a first metal with a second metal, comprising the steps of:

(a) positioning an electrode adjacent to a surface of a first metal, the electrode having a porous, abrasive pad positioned thereon, the pad on the electrode completely covering, and being in contact with, the surface of the first metal, wherein an interface is defined between the pad and the surface of the first metal and wherein the pad defines a gap between the surface of the first metal and the electrode surface;

(b) etching the surface of the first metal by applying a positive voltage to the surface of the first metal and a negative voltage to the electrode while maintaining the relative movement between the surface of the first metal and the pad and maintaining the wetting of the interface between the pad and the surface of the first metal with the etching solution;

(c) activating the surface of the first metal by applying a negative voltage to the surface and a positive voltage to the electrode while maintaining the wetting of the interface between the pad and the surface of the first metal with the etching solution and maintaining the relative movement between the surface of the first metal and the pad; and

(d) plating a second metal onto the surface of the first metal by applying a plating solution to the interface between the pad and the surface of the first metal while applying a negative voltage to the surface of the first metal and a positive voltage on the electrode, and while maintaining the relative movement between the surface of the first metal and the pad, the pad maintaining complete coverage of the surface of the first metal during the abrading step, the etching step, the activating step and the plating step.

In accordance with yet another embodiment of the present invention, there is provided a system for plating a metal onto a titanium surface. An electrode is dimensioned to be disposed adjacent to a titanium surface. The electrode has an electrode surface dimensioned to conform to the shape of the titanium surface. A porous abrasive pad is disposed on the electrode surface. The pad is dimensioned to cover and contact the titanium surface, such that the pad defines a gap between the electrode and the titanium surface. A selective means is provided for selectively supplying an etching solution and a plating solution to the gap between the electrode and the titanium surface such that the titanium surface is covered by the etching solution or the plating solution when the titanium surface is plated and the pad and the titanium surface continuously move relative to each other when the titanium surface is abraded, etched, activated, and plated.

An advantage of the present invention is a method of plating a metal onto a titanium part.

Another advantage of the present invention is a method of electroplating nickel onto a titanium alloy.

Another advantage of the present invention is a method of applying a metal to a titanium alloy using a selective, brush-plating process.

A still further advantage of the present invention is a method of plating as described above that does not use hydrofluoric acid to remove titanium oxide from the surface of the titanium part to be plated.

Another advantage of the present invention is a method of plating as described above that does not require a dry or wet blasting to prepare the surface of the titanium part to be plated.

These and other advantages will become apparent from the following description of a preferred embodiment taken together with the accompanying drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may take physical form in certain parts and arrangement of parts, a preferred embodiment of which will be described in detail in the specification and illustrated in the accompanying drawings which form a part hereof, and wherein:

FIG. 1 is a schematic view of an apparatus for plating metal onto a titanium work piece, illustrating an abrading step in a plating process according to the present invention;

FIG. 2 is a schematic view of the plating apparatus shown in FIG. 1 showing an etching step in a plating process;

FIG. 3 is a schematic view of the plating apparatus shown in FIG. 1 showing an activating step in a plating process;

FIG. 4 is a schematic view of the plating apparatus shown in FIG. 1 showing a plating step in a plating process; and

FIG. 5 is a photomicrograph showing a cross-sectional view of a nickel coating on a titanium surface, formed according to the process schematically illustrated in FIGS. 1-4.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

Referring now to the drawings wherein the showings are for the purpose of illustrating a preferred embodiment of the invention only, and not for the purpose of limiting same, FIG. 1 schematically illustrates an apparatus 10 for brush plating a metal onto a titanium work piece 22. Brush plating is a metallization technique which utilizes a small volume of solution contained in a fabric matrix between the anode and cathode in a plating cell. The small volume of solution and proximity of an anode and cathode enables procedures and techniques to be utilized which are impractical with other electroplating or coating methods.

The present invention shall be described with respect to plating nickel (Ni) onto titanium. However, as will be appreciated by those skilled in the art after reading the specification and claims, the present invention may find advantageous application in plating other metals onto titanium or onto other metals that exhibit similar surface oxidation characteristics. As used herein, the term “titanium” shall refer to titanium and titanium alloys where titanium is the major component.

FIG. 1 shows a rectangular, titanium work piece 22 having a planar, upper surface 22a to be plated. An electrode assembly 32 is disposed above surface 22a. Electrode assembly 32 is comprised of a support block 34 having an electrode 36 attached to the lower surface thereof. Electrode 36 has an electrode surface 36a that is shaped to conform to surface 22a to be plated. In the embodiment shown, electrode surface 36a is planar to match planar surface 22a of work piece 22. In the embodiment shown, support block 34 is rectangular in shape and is formed of a non-conductive polymer material, such as by way of example and not limitation, polypropylene. Electrode 36 is comprised of a sheet of titanium mesh that is plated with a noble metal.

As illustrated in FIG. 1, electrode assembly 32, i.e., support block 34 and electrode 36, is larger than surface 22a to be plated. As shall be described in greater detail below, electrode assembly 32 is designed such that electrode assembly 32 and surface 22a can move relative to each other with electrode assembly 32 maintaining constant contact with surface 22a of work piece 22.

A brush, or pad 42, is disposed between surface 22a of work piece 22 and surface 36a of electrode 36. As shall be described in greater detail below, pad 42 basically forms a uniform gap between surface 22a of work piece 22 and surface 36a of electrode 36. Pad 42 is formed of a fibrous, porous material.

A plurality of fluid supply channels 52 are formed in support block 34. Channels 52 communicate with the lower surface of support block 34 to conduct fluid to electrode 36 and to brush pad 42, as shall be described in greater detail below. A fluid conduit 62 communicates with fluid channels 52. A first branch conduit 64 connects fluid conduit 62 to a source 72 of an acidic, etching solution 74. A second branch conduit 66 connects fluid conduit 62 to a source 76 of a metal plating solution 78. A valve 82 is disposed at the junction where fluid conduit 62 joins first and second branch conduits 64, 66. Valve 82 is operable to control the flow of solution through fluid conduit 62. A pump 84 is provided in fluid conduit 62 to pump either etching solution 74 or plating solution 78 from the respective sources 72, 76, based on the position of valve 82. A motor 86 is provided to drive pump 84.

An electrical power source 92 has a first lead 94 that is electrically connected to electrode 36. A second lead 96 extends from power source 92 and is electrically connected to titanium work piece 22.

As schematically illustrated in FIG. 1, a tank or tray 102 is disposed beneath work piece 22 to collect etching solution 74 and plating solution 78, as shall be described in greater detail below. A drain line 104 is provided at the bottom of tank 102 to direct etching solution 74 and/or plating solution 78 to a location (not shown) for recycling.

The present invention shall now further be described with regard to a method of plating nickel onto titanium. Broadly stated, the method of electroplating nickel onto titanium comprises a surface cleaning step, an anodic etching step, a cathodic activation step and a plating step.

FIG. 1 schematically illustrates a surface cleaning step. Basically, surface area 22a to be plated is abraded to remove surface oxide therefrom. Pad 42, that is attached to electrode 36, is brought into contact with surface 22a of work piece 22. Pad 42 establishes a generally uniform gap or spacing between surface 36a of electrode 36 and surface 22a of work piece 22. In this respect, the thickness of pad (brush) 42 essentially establishes the thickness of the gap. In a preferred embodiment, the gap between electrode 36 and work piece 22 is about 5 mm.

In accordance with the present invention, pad 42 and surface 22a are moved relative to each other. In other words, pad 42 is “brushed” across surface 22a to be plated. As used herein, the term “brushed” refers to moving electrode 36 (having pad 42 on surface 36a thereof) over surface 22a. In a preferred embodiment, work piece 22 is stationary, and electrode 36 with brush pad 42 is reciprocally moved relative thereto. It is also contemplated that electrode 36 with brush pad 42 can remain stationary, while work piece 22 is moved relative thereto.

As indicated above, the cleaning step is intended to remove surface oxides from work piece 22. Accordingly, brush pad 42 is formed of a porous, abrasive material, such as by way of example and not limitation, nylon, Dacron and cotton gauze. In one embodiment, brush pad 42 is comprised of a 3M Scotch-Brite® abrasive pad. An initial period of the surface cleaning step may be comprised of surface 22a of work piece 22 being scoured and abraded by a dry brush pad 42. Preferably, the scouring and abrading of surface 22a occurs while an etching solution is introduced at the interface between brush pad 42 and work piece 22. FIG. 1 schematically illustrates introducing etching solution 74 to the surface of work piece 22 while brush pad 42 is moved thereacross. In this respect, valve 82 is moved to a first position where branch conduit 64 is in fluid communication with fluid line 62 and channel passages 52 in electrode assembly 32. When valve 82 is in this position, flow of plating solution 78 from source 76 is prevented. Motor 86 is energized to cause pump 84 to pump etching solution 74 through support block 34, electrode 36 and brush pad 42 to surface 22a of work piece 22. Pump 84 is dimensioned to maintain sufficient flow to maintain surface 22a immersed in etching solution 74. Etching solution 74 flowing off work piece 22 is collected by tank 102.

Etching solution 74 is basically an acid solution that, together with the scouring of surface 22a caused by the reciprocal motion of brush pad 42 thereon, removes the surface oxidation from surface 22a. As shall be described in greater detail below, acidic etching solution 74 preferably contains a small amount of plating solution. The continuous contact of brush pad 42 against surface 22a and the presence of liquid etching solution 74 within pad 42, basically prevent or significantly retard the reformation of surface oxidation on surface 22a of titanium work piece 22.

Following the aforementioned surface cleaning step, an anodic etch step is performed. During this step, the flow of etching solution 74 to surface 22a and the “brushing” movement of electrode assembly 32 relative to work piece 22 is maintained. During the anodic etch step, a positive voltage is applied by power source 92 to titanium work piece 22 and a negative voltage is applied to electrode 36, as illustrated in FIG. 2. An electrical potential on surface 22a enhances the etching effects of etching solution 74 on surface 22a as surface atoms of titanium and titanium oxide are released from surface 22a. The result of the anodic etch step is to remove small amounts of the titanium surface from surface 22a of work piece 22.

Following the anodic etch step, a cathodic activation step is performed using etching solution 74. During this step, electrode 36 and brush (pad) 42 continuously move across surface 22a to be plated, and etching solution 74 is continuously applied to surface 22a through electrode assembly 32. The polarity of the voltage across electrode 36 and work piece 22 is reversed, such that a negative voltage is applied to work piece 22 and a positive voltage is applied to electrode 36. The reversal of the voltage activates surface 22a of titanium work piece 22. The electrical potential on surface 36a of electrode 36 creates a current density on surface 22a. As indicated above, etching solution 74 preferably includes a small amount of plating solution 78. The metal ions in plating solution 78 and etching solution 74 plate minute amounts of metal onto surface 22a. FIG. 3 schematically illustrates the cathodic activation steps.

Following the cathodic activation step, a metal plating step is performed. During the metal plating step, valve 82 is moved to a second position wherein second branch conduit 66 communicates with fluid conduit 62 to electrode assembly 32 and is pumped thereto by pump 84. Movement of valve 82 to its second position prevents further flow of etching solution 74 to electrode assembly 32. A plating solution 78 is applied to surface 22a of work piece 22 while brush pad 42 is continuously brushed across surface 22a. The voltage to electrode 36 and work piece 22 is increased to a desired plating level to establish a desired current density along surface 22a. As illustrated in FIG. 4, a positive voltage is applied to electrode 36 and a negative voltage is applied to work piece 22. The voltage is maintained across electrode 36 and work piece 22 until a desired thickness of nickel is built up onto surface 22a of titanium work piece 22.

Throughout the foregoing process, brush pad 42 and a solution, either etching solution 74 or plating solution 78, is always in contact with surface 22a of titanium work piece 22 throughout the process. In this respect, the movement of brush pad 42 and the continuous flow of a solution across surface 22a, in addition to surface 22a being kept under electrical potential control, prevents oxide from reforming onto surface 22a. This allows the nickel to be applied to titanium work piece 22 without a titanium oxide layer (that would form if titanium work piece 22 was exposed to oxygen) from interfering with the plating process.

As will be appreciated from the foregoing, it is necessary that brush pad 42 and solutions 74, 78 cover the entire surface 22a, and the same be maintained in contact with surface 22a throughout the plating process.

EXAMPLE I

Using the foregoing process, nickel is brush plated onto a sheet of 6-4 Titanium. The titanium is kept under an electrical potential at all times following the initial surface cleaning step. The plated area is 100% covered by the brush pad 42, and the electrical potential is rapidly switched from anodic to cathodic. No rinsing occurs between steps, and the etching and plating solutions are not reused.

The process for producing nickel coatings on 6-4 Titanium is as follows:

StepOperationMaterialConditions
1Abrading stepRed Scotch BriteWet with etching solution
2Etching stepEtching solutionWet with etching solution,
14 V anodic, 10 seconds
3Activation stepEtching solutionWet with etching solution,
4-8 V cathodic, 1 minute
4Plating stepPlating solutionWet with plating solution,
8-18 V cathodic, 0.078
A * hr/cm2

The etching solution is comprised of 10% NaCl, 7% HCl, 1% Ni salts, 0.3% citric acid by weight. The plating solution is comprised of an acid nickel sulfate solution sold under the trade name SIFCO 2080/5600, manufactured by SIFCO Applied Surface Concepts, 5708 E. Schaaf Road, Independence, Ohio 44131 U.S.A. A SIFCO Model No. SPL-75 rectifier, capable of rapid switching between cathodic and anodic modes, is used.

Adhesion of the plated metal to the titanium substrate is tested following the procedures given in Aerospace Material Specification AMS 2451A and ASTM B571. Adhesion is evaluated using the chisel-knife, tape, and bend tests. The titanium sheets are bent 180° around a diameter equal to the thickness of the sheet in the bend test. The tape is pulled with a quick motion at a 180° angle to the surface. A sharp cold chisel is used to penetrate the coating. The results of a test are considered “good” if no separation of the plated metal from the base metal occurs. The interface between titanium and plating is examined in cross-section.

The aforementioned test provides good nickel deposit adhesion with 6-4 Titanium and Titanium 6-6-2 (6A1-6V-2Sn) alloys.

FIG. 5 shows a cross-section of a brush plated nickel coating on a sheet of 6-4 Titanium. The interface between the titanium and nickel is free of the bulk oxide. FIG. 5 shows that the smooth surface of the original titanium was microetched during pretreatment. Nickel plated readily into the microroughened surface of the titanium. The adhesion is checked by the aforementioned tape and bend tests.

It is believed that several factors contribute to the excellent adhesion exhibited by the structure in FIG. 5, namely, mechanical interlocking, increased surface area, and lack of an oxide film. These three attributes are generated during the brush plating process. Brush plating is particularly suited for generating these three attributes due to (1) the small volumes of electrolyte used, (2) the close contact between the anode and the cathode, and (3) the rapidity with which electrolytes can be switched from activation to strike plating.

The foregoing description is a specific embodiment of the present invention. It should be appreciated that this embodiment is described for purposes of illustration only, and that numerous alterations and modifications may be practiced by those skilled in the art without departing from the spirit and scope of the invention. For example, while the present invention has been described with respect to plating nickel onto titanium, it will be appreciated that the present invention may find advantageous application in plating other metals onto metals having oxide surface coatings. Moreover, while the invention has been described with respect to plating metal onto a planar surface, it will be appreciated by those skilled in the art that the disclosed process may be used in plating internal and external diameters. It is intended that all such modifications and alterations be included insofar as they come within the scope of the invention as claimed or the equivalents thereof.