Mechanical Properties of Titanium Alloys

Titanium alloys occupy a unique niche in engineering with an exceptional combination of mechanical performance, corrosion resistance, and biocompatibility. These properties make them invaluable in aerospace, medical implants, automotive, and energy applications.

Mechanical Strength & Ductility

Commercially pure Ti (CP-Ti grades 1–4) exhibit tensile strength between 240–590 MPa, with yield strength from ~170–483 MPa; elongation typically ranges from 15–35%.

Alloyed grades, such as Ti-6Al-4V (Grade 5), offer higher strength—ultimate tensile strength (UTS) around 900–950 MPa, yield ~880 MPa, and elongation ≈14%. High-strength alloys like Ti-10V-2Fe-3Al reach UTS up to 1,200–1,250 MPa.

Elasticity & Modulus

Titanium’s Young’s modulus is approximately 105–120 GPa, about half that of steel, which helps reduce stress shielding in medical implants.

Poisson’s ratio varies: ~0.31 for Ti-6Al-4V and ~0.36 for CP-Ti.

Fatigue & Creep Strength

Fatigue strength (at 10⁷ cycles) typically falls between 40–60% of UTS. Notably, titanium offers excellent fatigue resistance—even in seawater—due to its stable oxide layer.

For temperatures up to ~300 °C, CP-Ti retains strength. Alloys like Ti-6Al-4V maintain integrity up to ~500 °C, while specialized near-α and β alloys are tailored for creep resistance up to 600 °C.

Fracture Toughness

Fracture toughness in titanium alloys spans 28–108 MPa·√m, with higher-strength alloys often exhibiting slightly lower toughness. Microstructure engineering helps maximize both toughness and strength.

Hardness

Hardness increases with alloying and heat treatment. Vickers hardness for Ti-6Al-4V is typically ~349 HV, correlating with higher tensile strength.

Phase-Structure Interplay

Titanium alloys are categorized as:

α-alloys: hcp structure, good weldability, moderate strength.

α+β alloys (e.g., Ti-6Al-4V): offer balanced strength and ductility through heat treatment.

β and metastable β alloys: bcc structure, very high strength after aging.

Near-α and duplex microstructures: achieve optimized creep and toughness.

Effect of Alloying Elements

α-stabilizers: Al, O, N raise the α→β transformation temperature.

β-stabilizers: V, Mo, Nb lower it.

Alloying refines phase balance, enabling heat treatments that enhance strength, fatigue life, and creep resistance.

Additive Manufacturing (SLM/EBM)

Titanium alloys processed via SLM (Selective Laser Melting) or EBM (Electron Beam Melting) often show improved mechanical properties:

Example: β-Ti alloy made by SLM showed UTS ≈ 630 MPa, ~15% elongation, and modulus ~81 GPa—ideal for biomedical implants.

Superplasticity

Alloys like Ti-6Al-4V exhibit superplastic behavior, enabling the fabrication of complex shapes in aerospace using thermoforming techniques.

Summary Table

Key Takeaways

High Specific Strength: Titanium alloys offer high strength-to-weight ratio, typically outperforming steels and aluminum.

Excellent Corrosion Resistance: Stable oxide layer ensures durability in harsh environments.

Manufacturability: Microstructure control via alloying and heat treatment enables design flexibility between ductility, strength, creep resistance, and toughness.

Tech Innovations: Additive manufacturing unlocks tailored properties for biomedical and aerospace applications.

Cost-Performance Trade-off: Despite high processing costs, titanium alloys excel in applications demanding long life, low mass, and extreme durability.