Surface Treatment Technology Of Titanium Forgings

Titanium forgings serve in harsh environments in the aerospace engine, chemical, and medical fields, requiring extremely high surface quality. Surface defects of blanks are prone to cause failure. Scientific surface treatment can strengthen and modify the surface, improve quality and extend service life, and ensure safety under extreme working conditions.

 

 

It refers to modifying the chemical composition, organizational structure, or morphological characteristics of the material surface through physical, chemical, electrochemical, or other methods. It can achieve functional goals such as enhanced corrosion resistance, improved wear resistance, and optimized biocompatibility.

 

 

 

(I) Chemical Passivation: Low Cost

Chemical passivation involves immersing titanium forgings in a chemical solution to form a dense TiO₂ passivation film that isolates corrosion. The industrial mainstream process uses 20-30% nitric acid for immersion for 30 minutes, forming a 5-15nm film. It boasts the advantages of simplicity, low cost, and high efficiency, with minimal impact on dimensions. Suitable for batch protection of titanium forgings under conventional working conditions, it is widely used in chemical flanges and ordinary energy components.

 

However, the film is relatively thin, unable to withstand strong corrosion and high stress, and is not applicable to extreme working conditions.

 

(II) Anodizing: Precision Scenarios

Anodizing is an electrochemical process. Titanium forgings are treated with a sulfuric acid electrolyte under 20-60V voltage to form a 10-30μm oxide film. Its corrosion resistance is more than 50% higher than that of chemical passivation. The film color is adjustable, combining functional and decorative properties, and its porous structure can optimize biocompatibility. It is suitable for medical orthopedic implants and precision electronic titanium components.

 

The disadvantage is that the film is brittle, unable to withstand strong impacts, and should be used with caution under high-wear and high-fatigue working conditions.

 

(III) Microarc Oxidation : Extreme Working Conditions

Microarc Oxidation (MAO) is a high-end electrochemical technology. High-voltage (300-600V) induced microarc discharge generates a 50-100μm TiO₂/Al₂O₃ composite ceramic film on the surface of titanium forgings. The film-substrate bonding is tight, featuring excellent corrosion resistance, high-temperature resistance (>500℃), high hardness, and wear resistance. It is the core protection solution for titanium components under extreme working conditions, suitable for key components of aerospace engines and marine engineering.

 

The drawbacks are increased surface roughness and high cost, limiting its application to high-end scenarios only.

 

(IV) Shot Peening: Components Under High Fatigue Stress

Shot peening is a physical modification process. High-speed projectiles impact titanium forgings to form a 0.1-0.3mm compressive stress layer with a coverage rate of ≥200%. It can inhibit fatigue cracks, improve fatigue resistance by more than 30%, and extend the service life of components under high stress, specifically designed for key parts subjected to alternating loads.

 

Note: The surface roughness slightly increases, and subsequent polishing is required for ultra-high-precision components.

 

(V) Physical Vapor Deposition (PVD): Precision Coating Technology

PVD is a vacuum coating technology with ultra-hard coating . It reduces friction and wear without damaging the substrate performance, and its parameters are adjustable to support customization. It is suitable for high-wear components such as titanium gears and bearings.

 

Limitations: The coating is thin and unable to withstand impacts, and the preparation cost is high.

 

(VI) Electropolishing: Biomedical Field

Electropolishing uses a phosphoric acid-based electrolyte for electrochemical leveling and purification, resulting in a titanium surface with Ra ≤ 0.1μm. It eliminates microcrack defects and offers excellent biocompatibility, mainly used for medical implants and also applicable to high-purity scenarios such as semiconductors.

 

Disadvantages: High energy consumption, low efficiency, strict parameter control, and inability to perform batch conventional processing.

 

 

The selection of surface treatment processes for titanium forgings should follow the principles of "working condition adaptation, performance priority, and cost control," considering material properties, service environment, functional requirements, and economic efficiency comprehensively.

• For compressor blades of aero-engines requiring temperature resistance and corrosion fatigue resistance, the composite process of "microarc oxidation + shot peening" is adopted.
• For agitator paddles of chemical reactors requiring resistance to strong corrosion, the low-cost anti-corrosion combination of "chemical passivation + PTFE coating" is selected.
• For medical artificial joints needing both biocompatibility and wear resistance, "electropolishing + anodizing" is used to ensure cleanliness and osseointegration.
• For valve stems of marine engineering valves requiring resistance to seawater corrosion and erosion, the mainstream solution is microarc oxidation + sacrificial anode protection.

 

Material properties also affect process selection:

Commercial pure titanium (Gr1/Gr2) is suitable for conventional corrosive environments, with chemical passivation as the preferred option.

Gr5 (Ti-6Al-4V) serves at high temperatures requires thermal barrier coatings.

β-type titanium alloys need to avoid processes involving hydrogen-containing media to prevent hydrogen embrittlement.

 

Ruihang, as a professional manufacturer of titanium and titanium alloy products, supply high-quality titanium and titanium alloy forgings,plates,bars,pipes,wires,sections etc. For the details,please contact us via email: Sam.Rui@bjrh-titanium.com