Titanium rods are widely used in the chemical industry, medical equipment, high-end consumer electronics, and high-temperature resistant structural parts due to their excellent specific strength and biocompatibility. Nevertheless, after conventional forging, heat treatment and mechanical machining, their surfaces will inevitably produce dense oxide layers, nitride films and residual contaminants. Although these spontaneous surface layers provide weak protective effects, they are prone to causing uneven surface texture, dimensional deviation, and poor stability in subsequent welding, anodizing, and precision machining. In severe cases, residual oxides and microdefects will greatly reduce the long-term corrosion resistance of titanium substrates. Therefore, a complete and standardized surface treatment system is essential to remove surface invalid layers, unify surface states, and significantly enhance the overall anti-corrosion performance of titanium rods.
The whole treatment process follows a progressive technical logic of removing defects, leveling surfaces and strengthening performance, mainly including mechanical pretreatment, chemical pickling, precision brightening, stress relief and passivation, as well as optional functional modification.
Mechanical pretreatment is the indispensable foundation of the entire process.
Turning and rough grinding are adopted to remove forging black skin, oxide scale and microcracks, while calibrating the roundness and straightness of titanium rods. Considering the low thermal conductivity and work-hardening tendency of titanium alloys, low linear speed, large feed rate and sufficient cooling are required during cutting to avoid surface burning. On this basis, sandblasting or shot peening can eliminate stubborn hot-processing oxides and form a uniform micro-rough surface, which effectively improves the bonding force of subsequent coatings. It is critical to completely remove embedded abrasive particles after sandblasting to prevent foreign contamination.
As the core procedure, chemical pickling determines the final surface quality and safety of titanium rods.
The mainstream pickling system adopts mixed nitric acid and hydrofluoric acid, with a conventional ratio of 30%–50% nitric acid and 3%–8% hydrofluoric acid. Hydrofluoric acid rapidly dissolves titanium oxide and performs micro-etching on the substrate, while nitric acid inhibits excessive corrosion and promotes the regeneration of passive films. The reaction temperature is controlled at 20–40°C, and the processing time ranges from tens of seconds to several minutes until a uniform silver-gray metallic surface appears. After pickling, thorough deionized water rinsing and alkaline neutralization are required to eliminate residual acid. For high-load components, vacuum dehydrogenation annealing at 650–750°C is necessary to avoid hydrogen embrittlement risks.
Brightening treatment is customized according to product precision standards.
Semi-finish polishing removes tiny surface unevenness to reach Ra 1.6–3.2 μm, providing a consistent base for finishing. High-precision mirror mechanical polishing can achieve ultra-smooth surfaces below Ra 0.2 μm, suitable for high-end watch accessories and precision structural parts. Different from mechanical processing, electrolytic polishing produces no work-hardening layer or residual tensile stress, delivering uniform and flow-mark-free surfaces, which is the optimal process for medical titanium implants such as bone pins and dental components.
Passivation and bright annealing are key steps to enhance corrosion resistance and dimensional stability.
Bright annealing under vacuum or argon protection eliminates machining residual stress while retaining the original metallic luster and restoring material plasticity. Chemical passivation using dilute nitric acid solution generates a dense nano-scale titanium dioxide film on the surface, repairing microscopic defects formed in previous processes and greatly improving the resistance to acid, chloride and salt spray corrosion.
For specialized application scenarios, auxiliary strengthening treatments are available.
Anodization can form controllable oxide films with decorative colors and improved surface hardness, maintaining titanium's biocompatibility. Functional spraying of PTFE, ceramic or DLC coatings effectively enhances the wear resistance, high-temperature stability and insulation performance of industrial titanium rods.
In actual production, process combinations are formulated according to service requirements. Ordinary industrial titanium rods adopt pretreatment, pickling and passivation; medical-grade products apply strict hydrogen-controlled pickling, electrolytic polishing and vacuum annealing; high-end consumer parts use mirror polishing and color anodization; wear-resistant and high-temperature components require sandblasting roughening and ceramic coating. Only by strictly controlling full-process parameters and cleanliness can titanium rods achieve oxide-free, pollution-free and high-corrosion-resistance surface states, giving full play to the superior performance of titanium alloy materials.
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