Shenzhen Wuge Industrial Co., Ltd

The production process of nickel titanium tubes (shape memory alloy tubes) involves multiple processes, requiring precise control of composition, structure, and properties. The following are its core production processes and key points:

1、 Raw material preparation

1. Raw material selection

Main raw materials: high-purity nickel (Ni, purity ≥ 99.5%) and titanium (Ti, purity ≥ 99.6%), mixed in an atomic ratio of approximately 50:50 (or adjusted as needed, such as 55:45) to ensure that the final alloy's phase transition temperature (such as austenite start temperature As, martensite end temperature Mf) meets the design requirements.   

Accessories: Add trace elements (such as Fe, Cr, Cu, etc.) as needed to adjust the performance.

2. Smelting process

acuum melting: Vacuum induction melting (VIM) or vacuum consumable arc melting (VAR) is used to avoid alloy oxidation and contamination.   

Steps:

Place nickel and titanium in a water-cooled copper crucible in proportion and heat and melt them in a vacuum environment (pressure ≤ 10 ⁻³ Pa).   

Multiple remelting (such as 2-3 times) to ensure uniform composition and reduce segregation.   

Ingot forming: The melted alloy liquid is poured into the mold and cooled to form a cylindrical ingot (usually with a diameter of 50-200 mm).

2、 Ingot pretreatment

1. Homogenization annealing

Purpose: To eliminate component segregation and stress inside the ingot and improve its processing performance.   

Process: Heat to 900-1000 ℃, hold for several hours (such as 4-8 hours), and cool with the furnace.

2. Surface treatment

Removing oxide scale and defects on the surface of ingots: through mechanical processing (turning) or chemical acid washing (such as hydrofluoric acid+nitric acid mixture).

3、 Hot processing forming

1. Hot extrusion

Purpose: To process ingots into pipe blanks.   

workmanship

Heat the ingot to 600-900 ℃ (above the recrystallization temperature) and place it in the extruder.   

Use a circular mold to extrude into a hollow tube blank (usually with an outer diameter of 10-50 mm and a wall thickness of 1-5 mm).   

Key: Control the extrusion speed and temperature to avoid cracks or uneven organization.

2. Hot rolling/hot drawing

Further reduce the pipe diameter and wall thickness:

Hot rolling: Rolling at 500-800 ℃ using a pipe mill, suitable for larger size pipes.   

Hot drawing: After heating the tube blank, it is drawn to the target size through a mold, suitable for small and medium-sized pipe diameters (such as outer diameter ≤ 20 mm).   

Intermediate annealing: After each processing, annealing (such as 700-850 ℃, holding for 0.5-2 hours) is required to restore plasticity and refine grain size.

4、 Cold processing finishing

1. Cold drawing/cold rolling

Purpose: To obtain precise dimensions and surface quality, and improve strength and dimensional accuracy.   

Process: Gradually reduce diameter and wall thickness (such as drawing from an outer diameter of 10 mm to less than 1 mm) through multiple passes of drawing or cold rolling at room temperature.   

Key: Control the deformation of the track (usually ≤ 20%) to avoid fracture; Regularly perform intermediate annealing (such as 400-600 ℃, holding for 10-30 minutes) to eliminate work hardening.

2. Straightening and cutting

The pipe is straightened by a straightening machine to eliminate bending and cut into a fixed length (such as 1-3 meters).

5、 Heat treatment (key process)

Regulating the phase transformation behavior and mechanical properties of alloys through heat treatment mainly includes:

1. Solid solution treatment

Purpose: To obtain a single austenite structure in preparation for subsequent aging treatment.   

Process: Heat to 800-1000 ℃ (above the phase transition temperature), hold for 5-30 minutes, and rapidly cool by water (quenching).

2. Timeliness processing (activation of shape memory effect)

Purpose: To precipitate nanoscale second phases, stabilize the martensitic and austenitic transformation temperatures, and endow shape memory function.   

workmanship

Heat to 400-550 ℃ and hold for 0.5-2 hours (time and temperature need to be adjusted according to pipe diameter and performance).   

Air cooling or water cooling allows the alloy to remember a specific shape (such as through mold constraint shaping).

6、 Surface treatment

1. Acid washing

Remove surface oxide scale and oil stains: Use a mixed solution of hydrofluoric acid (HF) and nitric acid (HNO ∝) (such as a volume ratio of 1:3), soak for 5-10 minutes, and then wash with water.

2. Polishing

Mechanical polishing or electrolytic polishing: Improve surface smoothness (roughness Ra ≤ 0.8 μ m) to meet the needs of medical or precision devices.

3. Cleaning and testing

Ultrasonic cleaning to remove residual acid and impurities; Visually inspect surface defects and measure dimensional accuracy (such as outer diameter and wall thickness tolerance ± 0.01 mm).

7、 Performance testing

1. Mechanical properties

Tensile test: Determine tensile strength and elongation to ensure compliance with standards such as ASTM F2063.   

Bending test: Verify shape memory recovery rate (≥ 95% required).

2. Phase transition temperature test

Differential Scanning Calorimetry (DSC): Measure the onset temperature of phase transition (As, Af, Ms, Mf) to ensure compliance with design requirements (such as temperature triggered phase transition of medical stents).

3. Corrosion resistance test

Soak in simulated body fluids (such as physiological saline) to detect corrosion rate and surface integrity.

8、 Finished product packaging and warehousing

Pipes are classified according to specifications, wrapped in plastic film or paper to prevent scratches, and labeled with packing labels (specifications, batch numbers, execution standards, etc.).   

Store in a dry environment, avoiding moisture and chemical corrosion.

Key technical difficulties

1. Composition uniformity: During the melting process, it is necessary to strictly control the nickel titanium ratio to avoid segregation and uneven performance.   

2. Processing cracks: Excessive deformation during cold processing can lead to cracking, which needs to be optimized through intermediate annealing.   

3. Phase change temperature control: The heat treatment process directly affects the shape memory effect and requires precise control of temperature and time.   

4. Precision dimensional accuracy: Medical nickel titanium tubes (such as vascular stents) require extremely high dimensional tolerances (± 0.005 mm), requiring high-precision molds and processing equipment.

application area 

Medical: vascular stents, orthodontic wires, surgical instruments.   

Aerospace: pipeline connectors, thermally driven valves.   

Electronic components: automatic connectors, sensor components.   

Mechanical engineering: temperature control devices, shock absorption components.

Through the above process, nickel titanium tubes with excellent shape memory effect and super elasticity can be produced to meet the stringent requirements of different fields.