Titanium alloys, with their excellent properties of lightweight, high strength, and corrosion resistance, have shown irreplaceable application value in many fields such as aerospace, biomedicine, and high-end equipment. However, it also has fatal shortcomings such as poor wear resistance, easy adhesion to metal, and monotonous surface color. To overcome these shortcomings, it is often necessary to use titanium metal surface treatment technologies such as electroplating, micro-arc oxidation, electrophoretic coating, and anodizing. The following is a detailed introduction to these four "black technologies".
1. Electroplating: Wear a "protective suit" for titanium metal
Principle
Electroplating is like "painting" metal. It relies on electrolysis to coat a layer of metal film on the surface of titanium metal. This film can not only prevent rust, but also enhance wear resistance, making the appearance of titanium metal more beautiful.
Function
1. Improved wear resistance: After the surface of Ti6Al4V titanium alloy is plated with nano-pure nickel, its hardness and wear resistance are significantly enhanced.
2. High temperature anti-stuck: After the titanium blade is silver-plated, even if it is rubbed at a high temperature of 500℃, there will be no "welding" phenomenon, which effectively solves the "bite problem" of aircraft engines.
Difficulties and solutions
titanium metal surface treatment is easy to combine with oxygen, and an oxide film will form on the surface, which will interfere with the electroplating process. To solve this problem, there are two
ways:
1. Use nickel sulfate electrolyte and add activator. First, use an electric pulse to "activate" the titanium metal surface treatment, and then perform nickel plating.
2. Use hydrofluoric acid + dimethylformamide solution to corrode the titanium surface, and then directly plate copper, which can also make the coating firmly adhere.
2. Micro-arc oxidation: Let the titanium surface "grow" ceramic armor
Principle
Micro-arc oxidation technology relies on high-voltage electric sparks to "burn" a ceramic film on the titanium surface. The main component of the ceramic film is titanium oxide.
Function
1. Strong bonding: The ceramic film and the titanium substrate are as tightly bonded as tree roots in the soil. Even if they are pressed to 200 MPa by a hydraulic press, they will not fall off.
2. Excellent performance: The film thickness can reach several hundred microns, the hardness is comparable to that of ceramics, and it has excellent corrosion resistance, wear resistance, and heat resistance.
3. Customized gameplay
Adding potassium permanganate to the electrolyte can produce a titanium film that is both corrosion-resistant and antibacterial to meet special application requirements.
3. Electrophoretic coating: Give titanium a "colorful bath"
Principle
Put the titanium parts in charged paint water, and the paint particles will "queue" and adhere to the titanium metal surface treatment under the action of the electric field to form a layer of paint film.
Advantages
1. Environmentally friendly and safe: Electrophoretic coating uses non-toxic, water-soluble paint, which is more environmentally friendly than traditional spray painting.
2. High automation: The process has a high degree of automation, and 90% of the primer coating of automobile bodies uses this method.
3. Good biocompatibility: For example, TA4 titanium alloy can be used in the medical field after being coated with polyurethane, and has good biocompatibility.
Tips
Cathode electrophoresis has more advantages than anodic electrophoresis in terms of corrosion resistance and coverage.
4. Anodic oxidation: engrave "nano fingerprints" on titanium metal
Principle
Anodic oxidation is equivalent to the reverse operation of 3D printing on metal. It uses titanium as the anode to energize and grow an oxide film on its surface in the electrolyte. The oxide film is divided into two forms:
1. Dense type: The thickness is between tens and hundreds of nanometers, the surface is smooth and dense, and the biocompatibility is good. It is suitable for anti-corrosion and medical fields.
2. Porous type: It can grow into a TiO₂ nanotube array in a fluorine-containing electrolyte, just like countless nanostraws arranged neatly.
Magical application
1. Photocatalysis and solar energy: Nanotubes have a large specific surface area and can be used as photocatalytic materials to decompose pollutants, and can also be used in solar panels.
2. Hydrogen sensitive sensing: The hydrogen sensitive sensor is extremely sensitive to hydrogen, with fast and stable response speed.
3. Lithium battery application: It can be used in lithium batteries to prevent corrosion and improve the charging and discharging efficiency of the battery.
