How is the Tensile Strength of Black Tungsten Wire?

The tensile strength of black tungsten wire ranges between 1,000–2,000 MPa at room temperature, depending on purity, processing, and temperature. Its primary advantage lies in high-temperature stability rather than absolute strength. For enhanced strength or high-temperature performance, doping (e.g., thoriated or lanthanated tungsten) or alloying can further optimize its properties.

1. Basic Tensile Strength Range
   • At Room Temperature: Pure tungsten wire typically has a tensile strength of 1,000–2,000 MPa, varying based on wire diameter and processing conditions.
   • At High Temperatures: Tensile strength decreases significantly due to creep and recrystallization tendencies at elevated temperatures.
2. Key Factors Affecting Tensile Strength
   • Purity:
     • High-purity tungsten wire (>99.95%) exhibits higher tensile strength. Impurities (e.g., oxygen, carbon) reduce strength by forming brittle phases or grain boundary defects, leading to fracture.
   • Processing Techniques:
     • Cold Drawing: Multiple cold-drawing cycles (plastic deformation) refine the grain structure, increasing strength, but excessive cold drawing may increase brittleness.
     • Annealing: Proper annealing relieves internal stresses, but over-annealing can reduce strength.
   • Wire Diameter:
     • Thinner wires, due to their larger surface area, are more affected by surface defects, potentially lowering strength. However, stricter processing controls for fine wires can result in higher actual strength.
   • Temperature:
     • Tungsten’s strength decreases with rising temperature, particularly above the recrystallization temperature (approximately 1,000–1,200°C), where strength drops sharply.
3. Comparison with Other Materials
   • Metals:
     • Tungsten wire’s tensile strength surpasses that of common metals like steel (400–1,000 MPa) but is lower than some alloys (e.g., titanium alloys at 1,000–1,500 MPa).
     • Tungsten’s advantage lies in its high-temperature stability, maintaining higher strength at elevated temperatures compared to steel, which softens rapidly.
   • Ceramics:
     • Ceramics (e.g., silicon carbide) may have higher tensile strength (>3,000 MPa) but are highly brittle. Tungsten wire offers a balance of toughness and high-temperature performance.
4. Performance in Practical Applications
   • Light Bulb Filaments: Black tungsten wire operates at 2,500–3,000°C, where doping (e.g., with potassium or aluminum) increases recrystallization temperature and creep resistance. Tensile strength may drop to 500–1,000 MPa but remains sufficient for the application.
   • Electronic Devices: Fine tungsten wire is used in electron tubes and X-ray tubes, requiring high strength and conductivity, achieved through optimized processing techniques.

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