Usually, electroless nickel processing makes it excellent at achieving a good bond to the titanium, making it widely used to coat titanium as an initial coating. Although not used as the initial layers for metalizing on top of titanium, copper, gold, and silver serve as subsequent plating finishes coated onto the nickel layer. Plating on the titanium offers nearly the same resistance to corrosion as platinum. Not only has that, but it also limits the negative impacts of chemical elements such as hydrochloric acid (HCL), chlorine gas (Cl2), and many organic acids.
Uses for Plating on Titanium
Titanium usage has grown non-stop throughout the next half-century. With countless industrial and manufacturing applications, here are the prime examples.
Aerospace
With wide usage for its lightweight, titanium can be found in several different types of aircraft. Essentially, the metal increases the aircraft’s aerodynamics and improves fuel efficiency. Apart from that, the titanium also has excellent fatigue and great crack and corrosion resistance. Moreover, it can also withstand high temperatures. Besides aircraft, titanium is used to develop and manufacture missiles and spacecraft, as mentioned earlier.
Marine
Titanium’s resistance to corrosion from seawater makes it a frequent choice for marine applications and the manufacture of parts used in marine applications. An example of this application is manufacturing underwater devices, such as surveillance cameras on boats and submarines.
Jewelry
The physical properties of titanium, including durability, light-in-weight, and corrosion resistance, make it a frequently opted choice to manufacture designer jewelry and watch cases. Because titanium can be colored effortlessly, it is prevalent in smaller jewelry articles like body piercings.
Medical
Ball and socket joints utilized in hip replacements require lightweight and superior strength, undoubtedly achieved through titanium. The metal is one of the few biocompatible materials, making titanium non-toxic and non-hazardous for the human body. Titanium is also used to manufacture crutches, wheelchairs, and surgical instruments.
Automotive
Titanium’s aerodynamic, lightweight, and super-strength properties, along with its alloys, make them ideal for manufacturing automotive parts, such as race car bodies and other elements.
Need for Titanium Electroplating
Titanium is an excellent metal with extraordinary properties ideal for manufacturing several parts and industrial applications. Nevertheless, there are several reasons for plating on titanium and its alloys. Plating, in general, will further enhance the properties already existing in titanium, thus further enhancing the metal finishing and the metal’s ability to withstand surface fatigue, fretting, and anti-galling properties. Plating on titanium further increases corrosion resistance in hot and acidic environments. Furthermore, it can increase and decrease electrical conductivity, add lubricity, reflect heat, and repair or resize applications.
Issues with Plating on Titanium
The process of plating with titanium has long been considered a complicated process to perfect, if not entirely impossible. It is because titanium remains a highly reactive metal. Titanium essentially reacts with oxygen produced in the plating process to form a passive film on the substrate. This film acts as a hindrance in the bonding of the metal coating during plating, making the process inefficient. The solution is to pick the electroplating process to promote the metal coating and substrate adhesion. The native oxide must be eradicated, isolating it from the rest of the plating process. Without question, it can only be accomplished by employing a plating-on-titanium company to achieve each of these objectives efficiently and cost-effectively.
Surface Preparation Tips
The most initial process is to prepare the titanium substrate surface properly. Several methods can be utilized for the surface preparation process, which usually includes:
- Conventional methods like grinding, vapor degreasing, blasting, and alkaline cleaning.
- Activation by electrochemical etching, without implementing heat treatment.
- Activation via liquid abrasive blasting.
These processes are practical and applicable to titanium metal and several titanium alloys. What’s more, these processes also meet the compliance requirements by fulfilling standards set by the ASTM (American Society for Testing and Materials) International in terms of the promotion of adhesion while plating different metals on titanium.
Nickel Plating on Titanium
Nickel is one of the more commonly used materials for plating on titanium due to its high success rate. Thanks to nickel plating, the titanium underneath becomes more resistive to corrosion and less likely to wear out. The process, in general, contains the following steps:
- Use a solvent to reduce the grease on the substrate.
- Use pumice powder paste to scrub the surface in water.
- Clean the substrate thoroughly with an alkaline cleaner.
- Rinse the substrate by submerging it into a solution of 500ml of HCL with 500ml of water.
- Thoroughly rinse the substrate by immersing it into a solution of 120ml of Hydrofluoric acid (48%), 400ml of Nitric acid, and 1 liter of water.
- Again, thoroughly rinse in a solution of 130ml of Hydrofluoric acid (70%), 830ml of Acetic acid, and 40ml of water for anodic treatment.
- Rinse the substrate while applying a 15-30ASF current density at room temperature.
- Now rinse the substrate thoroughly in a sulfamate nickel plating bath that contains a retaining temperature of 145°F and an electric current density of 1000 ASF.
- Heat-treat in an atmosphere that involves inert gas at 480 degrees centigrade for 2 hours to increase adhesion between titanium and nickel.
Electroless Nickel Plating as Undercoating
Electroless nickel plating is another method, which is often used for plating nickel onto titanium. As the name suggests, in electroless plating, contrary to electroplating, you don’t involve an electric current in the plating bath. In the replacement of the current, you use an autocatalytic chemical reaction in which you deposit an alloy of nickel-phosphorous on the surface of the substrate.
The electroless nickel plating proves advantageous over electroplating as it provides a better uniformity in the thickness and an even coating. When titanium is considered substrate, electroless nickel plating usually is not used for the finishing coat on titanium. Instead of being the finishing coat, it is used as a base coat for other metals to increase their adhesive strength. Other valuable benefits of electroless nickel plating on titanium include better thermal conductivity, improved brazing and soldering, and heightened high-temperature oxidization.
Gold Plating on Titanium
Gold is uncommonly used as a plating material for titanium to improve the substrate’s exterior look and appearance. However, due to the cost of gold being relatively high, only a thin layer of it is used to plate the titanium surface. To succeed in plating gold onto titanium, firstly, you need to remove the titanium dioxide entirely and then start the plating process to guarantee an even, uniform, and continuous coating on the whole surface of the titanium.A general problem with electroplating gold onto titanium is the formation of minor surface flaws and imperfections. These might incorporate cracks or holes forming the substrate’s surface. But then again, this issue can be resolved by first coating the titanium using electroless nickel coating then applying the gold using electroplating over it.
Gold plating over titanium is not only done using electro-deposition. However, some other methods also exist. For example, chemical displacement is a frequently used process in the jewelry industry. In chemical displacement, an element switches positions with another element of a compound during a chemical reaction. Similarly, chemical displacement happens in gold plating. When titanium is kept in a solution containing gold ions, the gold ions start displacing the titanium ions and form a layer of gold on the surface of the titanium.
The bath utilized to envelop the titanium during chemical displacement consists of:
- Fluoride ions for dissolving the titanium oxide (already present as a layer on the titanium).
- Monovalent gold ions for forming a coating over the titanium.
- Citrate ions for complexing of the monovalent gold.
Furthermore, hydrogen ions are added to the batch to acquire the preferred acidic state, and tungsten ions can likewise be implemented to conserve the batch.
The ideal amount of each material mentioned above has been listed below. Suppose the bath is prepared and applied according to these specifications. In that case, it will produce a uniform coating without any faults present on the surface of the substrate.
- Monovalent gold: 25 grams/liter
- Citrate: 50 grams/liter
- Fluoride: 10-20 grams/liter
- Hydrogen: Amount enough to obtain a pH level of 5-6
Copper Plating on Titanium
For increasing titanium’s electrical conductivity, copper can be plated over it. Like gold plating onto titanium, to avoid getting a lousy coating or having defects in the layer, it is advised to first create an electroless nickel coating over the titanium. To further improve the result of the coat, it is also necessary to remove the titanium oxides layer already present on the surface of the titanium. The process commonly used for plating copper onto titanium is as follows:
- Use a solvent to remove grease, debris, and other contaminants from the substrate.
- Clean the substrate using an alkaline solution.
- Rinse the substrate with deionized water.
- With a water abrasive slurry, blast the substrate.
- Again, rinse the substrate with deionized water.
- Perform an electroless nickel coating on the titanium with the optimum thickness.
- Clean the substrate with deionized water.
- Perform electroplating of copper onto titanium in an acid-based copper bath.
- Clean the substrate with deionized water.
Finally, it is suggested to bake during the plating of the copper onto the titanium to increase the adhesive property. In a reducing atmosphere, heat-treating should last about one hour.