Method of plating metal onto titanium

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

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.

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.