Titanium and titanium alloys have many excellent properties such as high strength, low density, and good corrosion resistance. They are widely used in aviation, aerospace, shipbuilding, automobiles, nuclear power, and other fields. However, titanium and titanium alloys are not wear-resistant, have poor conductivity and weldability, and have poor high-temperature resistance. For this reason, it is necessary to use surface modification or Titanium alloy surface treatment (such as physical method, chemical method, electrochemical method, etc.) to improve the surface properties of titanium and titanium alloys.
Surface oxidation treatment
1. Chemical oxidation method
This method is simple to operate, and the oxide film layer has good adsorption capacity. It can be used as a paint base or intermediate layer to improve surface durability. However, the oxide film is thin and has poor corrosion resistance, so it is not suitable to be used alone.
2. Electrochemical oxidation method
The oxide film obtained by this method is thicker than the chemical oxide film, has better corrosion resistance, and has good high-temperature lubricity, adhesion, and durability. The power supplies used are DC power supply, AC power supply, and pulse power supply, among which the film thickness obtained by the AC and pulse power supply is greater than that of DC power supply. The main uses of electrochemical oxidation film are as follows: as a wear-resistant and corrosion-resistant film layer to improve the wear resistance and corrosion resistance of the Titanium alloy surface treatment; as the bottom layer of the coating layer to improve the bonding strength between the film layer and the substrate; good insulation, as a capacitor dielectric film; adding colorants to the oxidation solution to change the color of the coating as a decorative layer; used for functional film layers, such as depositing magnetic alloys in porous films as memory elements, solar absorption panels and ultra-high hard films, dry lubrication films, and catalyst films.
3. Micro-arc oxidation method
The electrochemical method is used to generate tiny sparks on the surface, and an oxide film grows in situ on the surface under the action of thermochemistry, plasma chemistry, and electrochemistry. This method converts the base metal into oxide ceramics through instant high temperature and high-pressure sintering in the micro-arc discharge zone to obtain a thicker oxide film layer. This method has the following advantages: thick film layer, low porosity, good corrosion resistance; strong operability, easy to control thickness; good bonding between the film layer and the substrate; high hardness of the film layer, wear resistance, and high-temperature resistance; simple operation, high efficiency, low environmental pollution, suitable for automated production.
Surface chemical deposition and electrodeposition
The process flow of chemical deposition and electrodeposition on titanium surface is usually: degreasing → purification and roughening → corrosion → activation and active film treatment → chemical plating, electroplating or composite plating, etc. → heat treatment. The above process is complicated and the bonding strength of the coating is not ideal. When titanium is placed in oxygen-containing media such as air or aqueous solution, an oxide film is quickly formed on the surface, which causes great difficulties for subsequent electroplating, chemical plating, and conversion film treatment. The poor bonding strength between the film layer and the substrate is the main problem of electrochemical Titanium alloy surface treatment, and plating pretreatment becomes a key step. The key to pretreatment is activation film formation, which directly affects the bonding strength of the coating. Compared with industrial pure titanium, titanium alloy surface pretreatment is more difficult.
After degreasing, roughening, and corrosion of the titanium surface, active film treatment should be carried out. Activation is the key to ensuring the quality of titanium surface coating. Its purpose is to remove the surface oxide film and form an active film that is well bonded to the substrate and has a certain activity so that it will not be re-oxidized before electroplating. The active film (such as hydrogenated film, or fluorinated film) has a good bonding strength with the substrate and the coating. The Titanium alloy surface treatment after activation treatment can be chemically deposited or electro-deposited to obtain a coating with excellent bonding strength.
Surface electrophoretic coating
Electrophoretic coating is a coating method that uses an external electric field to make particles such as resins and pigments suspended in the electrophoretic liquid migrate in a directional manner and deposit on the electrode surface. The reaction process includes electrophoresis, electrodeposition, electroosmosis, electrolysis, etc. Electrophoretic coating has the advantages of high efficiency, low energy consumption, high quality, safety, and economy. It is widely used in titanium surface corrosion protection, decoration, and functional coating. In addition, electrophoretic coating can replace some electroplating processing and painting processing with greater pollution.
Surface nano-treatment
By preparing a certain thickness of a nanostructured surface layer on the surface of titanium and titanium alloys, surface nano-treatment is achieved, thereby improving surface hardness, wear resistance, corrosion resistance, ductility, photosensitivity, and high-temperature stability. There are many nano-treatment methods, such as chemical methods, electrochemical methods, physical methods, and mechanical methods. Electrochemical nano-deposition can be used to obtain nano-single metal layers, nano-alloy layers, and nano-composite coatings, which greatly improve and improve the properties of titanium surfaces. The methods are divided into DC electrodeposition, AC electrodeposition, pulse electrodeposition, composite electrodeposition, jet electrodeposition, and ultrasonic electrodeposition.
Titanium and Titanium alloy surface treatment must undergo appropriate nano-pretreatment before nano-electrodeposition can be performed to obtain single metal nanocrystals (such as nickel, copper, zinc, gold, silver, platinum, etc.), nano-alloys (such as zinc-nickel, zinc-cobalt, nickel-iron, cobalt-nickel, tin-nickel, tin-cobalt, etc.), and nano-composite coatings of various single metals or alloys.
