Titanium and titanium alloys are widely used in aerospace, medical implants, chemical equipment, and other fields due to their excellent properties, such as high strength, low density, and corrosion resistance. However, during processing and use, titanium plate surfaces are prone to discoloration, which not only affects appearance quality but also may reduce corrosion resistance and mechanical properties. This article, combining Titanium Home research data with industry practices, systematically describes a comprehensive technical solution to address titanium plate discoloration, providing a practical reference for the industry.
Surface Treatment Technology: Building a Protective Barrier
Titanium plate discoloration is often caused by damage or contamination of the surface oxide layer. Surface treatment can significantly improve its discoloration resistance:
1. Anodizing
A dense oxide film (1-30μm thick) is formed on the titanium plate surface through electrolysis, effectively isolating it from environmental media. For example, micro-arc oxidation of medical-grade titanium alloy increases its surface hardness by three times and its corrosion resistance by 50%. It also forms a colorful oxide layer, combining aesthetics with protective properties.
2. Coating Spraying
Plasma spraying technology is used to deposit alumina and zirconia ceramic coatings, which can withstand temperatures of 1200°C and are suitable for use in extreme environments such as aircraft engine blades. Experimental data show that the corrosion resistance of coated titanium plates in salt spray tests is extended to over 2000 hours.
3. Electroplating Protection
Nickel- or chromium-based electroplating can increase the surface hardness of titanium plates (HV 800-1200) while reducing the coefficient of friction. Electroplating of titanium plates for automotive connecting rods improves wear resistance by 40% and reduces discoloration risk by 70%.
Process Control: Precise Parameter Management
Thermal stress and mechanical damage during machining are the main causes of discoloration, requiring process optimization to achieve controllable processing:
1. Dynamic Temperature Control
When cutting titanium plates, the tool temperature must be kept below 400°C. Using low-temperature cutting fluids (such as water-based emulsions) in conjunction with carbide-coated cutting tools can reduce cutting zone temperatures by 30%, stabilize surface roughness Ra values within 0.8μm, and minimize thermal oxidation discoloration.
2. Structural Stress Relief
Finite element analysis was used to optimize the titanium plate surface welding sequence, and a staged annealing process (500°C/2h) was employed to eliminate residual stress. Experimental results showed that the optimized titanium plate exhibited a 65% reduction in deformation at 350°C and an 80% reduction in discoloration.
3. High-Speed Machining Technology
Using five-axis high-speed milling (12,000 rpm, 0.1 mm/min feed) can reduce machining time by 40% and minimize heat buildup. In a case study of aviation parts machining, high-speed processing reduced surface discoloration from 15% to below 2%.
Environment and Protection System: Full-Lifecycle Management
A systematic protection plan must be established from storage to use:
1. Environmental Parameter Control
Storage warehouses must maintain a stable temperature and humidity of 25°C ± 5°C and 40%-60% relative humidity, equipped with a dehumidifier and air filtration system. A chemical equipment manufacturer has demonstrated that environmental control can reduce the discoloration rate of titanium plates from 8% to 0.5% during storage.
2. Specialized Packaging Design
Titanium plates are wrapped with a VCI vapor phase anti-rust film and sealed with a desiccant to create an inert gas protective layer. This packaging method has been verified in ASTM B117 salt spray testing to extend the corrosion resistance of titanium plates to 1500 hours.
3. Application Scenario Adaptation
For high-temperature friction environments (such as aircraft engines), a MoS₂ coating containing a solid lubricant has been developed. This coating can reduce the friction coefficient to 0.05 and increase the operating temperature to 600°C. The service life of a titanium alloy blade on a certain engine has been extended by 2.3 times after treatment.
Quality Monitoring System: Data-Driven Improvement
Establish a full-process traceability system from raw materials to finished products:
1. Online Inspection Technology
Laser-induced breakdown spectroscopy (LIBS) is used to monitor the elemental composition of titanium plate surfaces in real time, with an automatic alarm if the deviation exceeds 0.5%. After implementing this technology on a medical implant production line, the product qualification rate increased to 99.8%.
2. Nondestructive Testing Standards
Penetrant testing is performed according to ASTM E165, capable of identifying surface cracks as small as 0.01mm. The aviation industry requires a 100% defect detection rate for titanium plates to ensure structural safety.
3. Supplier Evaluation Mechanism
Establish a supplier evaluation system encompassing 20 indicators, including melting process, purity control, and surface treatment capabilities. After using this system to screen suppliers, an automobile manufacturer reduced the discoloration defect rate of incoming titanium plate material from 3.2% to 0.1%.
Industry Practice Case Studies
1. Medical Implants
An orthopedic device company used a micro-arc oxidation + polytetrafluoroethylene coating composite process to reduce the surface friction coefficient of titanium alloy joint prostheses to 0.03. Ten years of clinical follow-up showed zero discoloration.
2. Aerospace
The C919 engine's titanium alloy blades used a plasma spraying + gradient heat treatment process to maintain an intact surface oxide layer at 650°C, achieving 5,000 hours of service without discoloration or failure.
Solving the discoloration problem in titanium plate surface requires a comprehensive approach throughout the entire lifecycle, from material design, processing, and manufacturing to maintenance. The synergistic effects of surface protection technology, process parameter optimization, environmental control systems, and quality traceability systems can achieve long-term stability in the appearance quality and performance of titanium plates. When selecting suppliers, companies should focus on their process control capabilities, testing equipment accuracy, and historical quality data to ensure highly reliable titanium products. With the advancement of digital manufacturing technology, AI-based process parameter prediction and adaptive control will become core areas of next-generation titanium processing technology.
