Titanium alloy wire drawing process

1、 Technical features

Titanium alloy wire drawing is the process of reducing the diameter of a rod into wire through plastic deformation, and its special technical requirements stem from the essential characteristics of titanium:

1. Strong temperature dependence

At room temperature, the slip system of titanium is limited (especially in the α - phase HCP structure), and it needs to be drawn in the medium temperature range (400-700 ℃) to improve plasticity.

For example, the German company Hermes uses induction heating temperature control (± 10 ℃) for Ti-6Al-4V, combined with acoustic emission monitoring, to achieve a deformation of 30-50%.

2. Surface high sensitivity

Titanium is easy to bond with molds and requires the use of hard alloy molds and nano lubricating layers (such as water-soluble polymers and graphene).

Patent CN117443979A developed acid free process to avoid surface hydrogen and oxygen pollution through roll die drawing.

3. Complexity of organizational evolution

During the drawing process, the β →α 'phase transformation leads to work hardening, requiring multiple annealing cycles (such as vacuum annealing at 750 ℃/30min).

Difficult to deform alloys (such as TB5) undergo online solution treatment (900 ℃ water quenching) to enhance their cold workability.

2、 Process flow

1. Raw material preparation

• Melting and opening: Three VAR melting processes (oxygen content ≤ 0.15%) → forging and opening (large deformation in the β phase region).

Surface treatment: Sandblasting+chemical milling (HF-HNO ∝ solution) to remove oxide scale.

2. Thermal mechanical treatment

Warm rolling pre deformation: Roll die rolling (400-700 ℃) reduces the diameter of the 20mm billet to 8mm, with a deformation of 10-30% per pass.

• Organization homogenization: Difficult to deform alloys (such as high damping Ti-O alloys) require homogenization treatment in the β phase region (1050 ℃/24h).

3. Cold drawing forming

• Reducing process:

Coarse wire (Φ>1mm): Roller die drawing (deformation 15-20%/pass).

• Fine wire (Φ<1mm): Ultrasonic vibration drawing (frequency 20-40kHz, reducing drawing force by 30%).

Intermediate annealing: Vacuum annealing (700-800 ℃/1h) eliminates stress and controls grain size to ≤ 5 μ m.

4. Finishing and testing

Surface treatment: Electrolytic polishing (voltage 12V, NaCl ethylene glycol solution) to remove microcracks.

Performance testing: Laser caliper (accuracy ± 0.001mm)+online eddy current testing.

3、 Technical difficulties

1. Insufficient plastic deformation ability

Problem: High oxygen titanium alloys (O>0.3%) experience a sudden drop in ductility due to interstitial solution strengthening.

Solution: The Institute of Mechanics, Chinese Academy of Sciences adopts a heterogeneous microstructure design - soft β phase wraps around hard α phase, improving the elongation of high oxygen alloy (Ti-0.5O) to 15%.

2. Difficulties in surface quality control

Problem: Cold welding effect leads to mucosal wire breakage (especially in alloys with low beta stable elements such as CP Ti).

• Innovation:

Rotating mold technology: The worm gear drives the mold core to rotate, transforming sliding friction into rolling friction and reducing wear rate by 60%.

• Coating sleeve drawing: Low carbon steel is coated on the surface of titanium wire → bundled into steel pipe for drawing → acid washing is used to remove the sleeve, which can produce ultra fine wires with a diameter of 5-30 μ m.

3. Organizational performance coordination and regulation

Contradiction: Large deformation refines grain size to enhance strength, but induces residual stress to reduce fatigue life.

• Balance strategy:

Gradient annealing: The axial temperature gradient design of the wire material (700 ℃ → 600 ℃) achieves core strength and surface toughness.

Coupling of deformation heat treatment: cold drawing+short-term annealing (650 ℃/5min), controlling the degree of recrystallization by 50%.

4、 Latest research progress

1. Roller mold ultrasonic collaborative drawing technology

Japan develops a two-piece vibration mold for drawing Ti-6Al-4V:

Reduce the pulling force by 40% and increase the deformation of the pass to 50%

Surface roughness Ra<0.2 μ m, ellipticity ≤ 0.01mm.

Principle: Ultrasonic vibration generates microplastic flow on the surface of titanium wire, repairing surface defects.

2. Induction heating with precise temperature control

German company Hermes achieves continuous production of ultra long wire (8500m) without welding seams:

Diameter stage (mm) Power (kW) Frequency (kHz) Temperature tolerance (± ℃)

8.0~4.0→50-70→40-80→10

4.0~1.6→20-40→300-500→5

Advantages: Uniform grain size (≤ 4 μ m), anisotropy strength difference<5%.

3. New breakthrough in oxygen content control

University of Tokyo develops yttrium metal deoxidation method:

Molten titanium+yttrium → forms Y ₂ O Ⅲ slag phase, with oxygen content reduced to 0.02%

The cost of recycling waste titanium has been reduced by 30%, but residual yttrium (≤ 1%) needs to be removed later.

Sun Yat sen University proposed the Al SiO ₂ coating technology to suppress the precipitation of quartz phase and reduce high-temperature oxygen permeation.

4. Preparation of difficult to deform alloy filaments

Powder metallurgy+hot drawing:

Ti-35Nb-7Zr alloy powder → hot isostatic pressing → multi pass drawing, resulting in a wire with a diameter of 0.1mm (strength of 1.2GPa).

• High oxygen damping titanium alloy: • Chinese Academy of Sciences patent CN119553130A is used to prepare ultrafine wires with a diameter of 0.05mm by adding micro Nb/Y to neutralize oxygen brittleness.

The titanium alloy wire drawing technology is developing towards ultra-fine diameter, low oxygen, and intelligent direction:

Ultra fine diameter: The coating sleeve pulling pushes the wire diameter to exceed 10 μ m, meeting the needs of medical micro implant devices.

Low oxygen control: Yttrium deoxidation+vacuum melting reduces the oxygen content to the 0.01% level, improving the fatigue life of aviation grade wire.