TC4ELI is the Chinese designation for an extra low interstitial version of the TC4 (Ti-6Al-4V) alloy. The ELI stands for Extra Low Interstitials, meaning the alloy contains significantly reduced levels of oxygen, nitrogen, carbon, and iron compared to standard TC4. This refinement greatly improves fracture toughness and low-temperature ductility while maintaining high strength and excellent corrosion resistance. TC4ELI corresponds to ASTM Grade 23 (Ti-6Al-4V ELI) under international standards.

The nominal chemical composition of TC4ELI is: aluminum 5.5 to 6.5 percent, vanadium 3.5 to 4.5 percent, iron up to 0.15 percent (compared to 0.30 percent in TC4), oxygen up to 0.13 percent (compared to 0.20 percent in TC4), carbon up to 0.08 percent, nitrogen up to 0.03 percent, hydrogen up to 0.012 percent, and the balance titanium. The lower oxygen and iron limits are the key differentiators.

Key mechanical properties (typical for annealed condition):

● Tensile strength: 860 to 965 MPa (minimum 860 MPa)

● Yield strength (0.2% offset): 790 to 900 MPa (minimum 790 MPa)

● Elongation: 12 to 15 percent (slightly lower than standard TC4 due to lower oxygen? Actually lower oxygen increases ductility. Typical ELI elongation is 15-20% vs 10-15% for TC4)

● Fracture toughness: significantly higher than TC4, typically 80–100 MPa√m vs 50–70 MPa√m.

● Density: 4.43 g/cm³

● Modulus of elasticity: 110 GPa

The reduced interstitial content provides:

● Superior fracture toughness and resistance to crack propagation.

● Excellent fatigue performance.

● Enhanced ductility at cryogenic temperatures (down to -196°C), making it suitable for liquid hydrogen and liquid oxygen applications.

● Good weldability with minimal risk of embrittlement.

Common international equivalents:

● ASTM F136 (USA) – Wrought Ti-6Al-4V ELI for surgical implant applications.

● ASTM Grade 23 – General specification for Ti-6Al-4V ELI.

● ISO 5832-3 (for implantable Ti-6Al-4V ELI).

● JIS H4650 (Japan, corresponding grade).

Typical applications of TC4ELI include:

● Medical implants: hip and knee joints, bone plates, spinal fixation devices, dental implants, and pacemaker casings. The alloy’s biocompatibility, high strength, and fatigue resistance make it a standard material for load-bearing implants.

● Aerospace: cryogenic tanks for liquid hydrogen and liquid oxygen (e.g., rocket propellant tanks), airframe structural components requiring high fracture toughness, and fasteners in critical applications.

● Marine: deep-sea submersible pressure housings and components requiring both strength and resistance to brittle fracture at low temperatures.

● Sports equipment: high-end bicycle frames and golf club heads where enhanced toughness is desired.

TC4ELI is available in bar, sheet, plate, wire, forging billet, and tubing. It is typically supplied in the annealed condition. The alloy can be heat treated (solution treated and aged) to increase strength, though this is less common for ELI grades because it may reduce fracture toughness.

Comparison with standard TC4 (Grade 5):

● TC4ELI has slightly lower tensile and yield strength (about 5–10 percent lower) but significantly higher fracture toughness and ductility, especially at low temperatures.

● TC4ELI is more expensive due to tighter composition control and testing requirements.

● For most structural applications not requiring cryogenic toughness or implant certification, standard TC4 is sufficient and more economical.

Selection guidance: Choose TC4ELI for medical implants (per ASTM F136), cryogenic applications (liquid hydrogen tanks), and any application where high fracture toughness and resistance to crack growth are critical. For general high-strength, lightweight components at room temperature, standard TC4 (Grade 5) provides higher strength at lower cost. For simple corrosion-resistant applications, TA2 or TA10 may suffice.