Because of its excellent specific strength, corrosion resistance, good high temperature performance and biocompatibility, titanium alloys have been widely used in aerospace, military industry, civil industry and other fields. However, the surface hardness of titanium alloy is relatively low and the wear resistance is insufficient, which limits its application in some specific environments. To improve these properties, researchers have developed a variety of surface treatment techniques to enhance the surface properties of titanium alloys.
1. Surface oxidation treatment
An oxide film was formed to enhance the lubricity of the titanium alloy surface and reduce the adhesion during the drawing process.
2. Coating treatment
- Graphite emulsion coating
Applying graphite emulsion before hot drawing not only provides lubrication but also protects the surface of the blank from oxidation. The requirements for graphite emulsion include a graphite content of 20%-25%, a particle size of 1-3um, and a uniform attachment to the surface of the blank.
- Salt lime coating
A specific formulation of a salt lime lubrication layer, such as 12% Na2SO4, 12% CaO, 0.3% Na3PO4, 0.2% NaCl and a margin of water, supplemented by a mixture of 75% soap powder and 25% sulfur powder was used as a solid powder lubricant.
- Fluorophosphate treatment
After cleaning the surface of the metal blank by physical method, a modified coating film is formed on the surface by dipping the coating solution, and then solid lubricant is coated to obtain the lubrication effect of low friction coefficient and high wear resistance.
3. Plating metal film
A metal film such as copper, chromium, nickel or tin is plated on the surface of the titanium alloy to reduce the direct metal contact during the drawing process, thus reducing adhesion.
4. Borylation treatment
Put the titanium alloy wire into the mixed solution containing KFB4, BaCl2 and NH4NO3, heat it to boiling, then soak it, remove it, clean and dry it, and form a layer of fluoroborate on the surface of the wire. It is also necessary to apply a layer of aluminum disulfide on the surface of the wire as a lubricant in the cold pier.
5. Chemical conversion treatment
A dense chemical conversion film is formed on the surface of titanium alloy through chemical conversion treatment. This film can be used as a lubricating coating to adsorb lubricant, so that the surface of the wire is smooth after multiple passes of drawing, without adhesion and slip marks.
6. Lubricant selection
Select the appropriate lubricant, such as industrial soap powder, graphite emulsion and the mixture of soap powder and other materials, should have good infiltration with the coating, good thermal stability.
7. Laser surface treatment
Laser treatment technologies, including laser cladding, laser surface alloying and laser surface quenching, can improve the wear resistance, corrosion resistance and hardness by changing the microstructure of the surface layer. The advantage of laser treatment is that the surface properties can be significantly improved without changing the properties of the titanium alloy matrix.
8. Micro-arc oxidation
This is a technology of in-situ growth of ceramic film on the surface of titanium alloy, which can form a layer of ceramic film with excellent corrosion resistance and wear resistance on the surface of titanium alloy. Micro-arc oxidation technology has the characteristics of green environmental protection, in line with the sustainable development strategy.
9. Ion implantation
By injecting nitrogen, oxygen, carbon and other elements into the surface of titanium alloys, the surface hardness and wear resistance can be improved. The thickness of ion implantation layer is usually in nanometer level, which can significantly improve the surface properties of titanium alloys.
10. Thermal diffusion method
By spreading alloying elements to the surface of titanium alloy at high temperature, an alloying layer is formed, thus improving the hardness and wear resistance of the surface.
