How To Remove Oxide Scale From Titanium Alloy Surfaces?

Titanium alloys  has excellent performance and are widely used in high-end fields. However, during high-temperature processing and service, they are easy to forming composite oxide scales and brittle α-layers, which impair surface quality and mechanical properties. It might lead to potential workpiece failure. Efficient oxide scale removal while protecting the substrate is crucial for titanium alloy processing.

 

 

 

 

1. Mechanical Methods

• Grinding: Simple operation and low cost, suitable for rough-machined workpieces, but prone to deformation and high surface roughness.
• Polishing: Excellent surface finish, but high cost and potential impact on material properties.
• Sandblasting: Suitable for batch processing of forgings of various specifications with good descaling effect; however, it has limitations in cleaning complex dead corners and needs to be combined with chemical methods.

 

2. Chemical Methods

• Caustic Etching: Molten alkali solution reacts to loosen and strip oxide scales. The NaOH+NaNO₃ system can prevent hydrogen embrittlement, specifically effective for thick oxide scales and α-layers.
• Acid Pickling: Removes residual products. The hydrofluoric acid + nitric acid system controls hydrogen embrittlement; milder systems can also be selected to improve safety, and it can be directly used for thin oxide films.
• Two-Step Alkali-Acid Method: Offers the optimal synergistic descaling effect with low loss and high efficiency. Suitable for complex precision parts, meeting the strict requirements of high-end fields.

 

3. Electrolytic Method

The electrolytic method precisely removes oxide scales through electrochemical reactions. The electrolyte requires additives to protect the substrate, featuring high efficiency, high quality, and minimal damage to the substrate, making it suitable for high-end precision workpieces. However, it requires strict parameter control, guaranteed electrical conductivity, and high equipment investment, limiting its application in ordinary processing.

 

 

1. Mechanical Method

• The core of mechanical methods determines temperature control and cleaning depth control.
• For grinding and polishing, control the speed to prevent high-temperature deformation;
• For sandblasting, strictly control parameters to avoid excessive damage. Preprocessing requires cleaning abrasives to prevent contamination;
• Acid pickling should be performed promptly after sandblasting to eliminate secondary oxidation.

 

2. Chemical Method

The core of chemical methods is the precise matching of reagent ratios, temperature, and time, with strict control of hydrogen embrittlement risks.

 

• Caustic Etching: Formulation: NaOH + NaNO₃. Excessive or insufficient content will increase loss or reduce hydrogen suppression effect. Temperature: excessively high temperature may cause ignition, while excessively low temperature results in low efficiency and increased hydrogen absorption. Time: prolonged time will wrap the surface, stop the reaction, and increase hydrogen embrittlement risk.

 

• Acid Pickling: Formulation: HNO₃ + HF + water; the ratio of nitric acid to hydrofluoric acid ≥5 to prevent hydrogen embrittlement. Temperature: exceeding 60℃ increases hydrogen absorption and corrosion. Time: the acid solution must be replaced when the titanium content exceeds 12g/L.

After acid pickling, wash with hot water, rinse with cold water, and then dry to prevent residual acid corrosion.

 

• Two-Step Alkali-Acid Method: Acid pickling should be performed within 1 hour after caustic etching to prevent secondary oxidation; sandblasting can be carried out before acid pickling to improve efficiency.

 

3. Electrolytic Method

The core of the electrolytic method: Precisely match electrical parameters and electrolyte. Control voltage ,current , temperature and time to ensure electrical conductivity before processing; rinse with deionized water after processing to prevent corrosion.

 

 

• Hydrogen Embrittlement Prevention and Control: Strictly control process parameters to reduce hydrogen absorption; If hydrogen content exceeds the standard, vacuum dehydrogenation annealing is required.

 

• Environmental Protection and Safety: Implement adequate protection and ventilation during acid-base and electrolytic operations; dispose of waste gas, waste water and solid waste in compliance with regulations.

 

• Quality Inspection: Achieve standard removal of oxide scales and α-layers. For aerospace parts, Ra ≤6.3μm; precision parts must be free of surface defects.

 

Ruihang Group strictly controls the surface treatment of semi-finished products to deliver high-quality titanium alloy products. For more details,please contact us via the Email: Sam.Rui@bjrh-titanium.com