TC4 titanium alloy is a key material in China’s titanium alloy system, corresponding to Ti-6Al-4V (chemically) and GR5 (under ASTM standards). As a representative α+β dual-phase titanium alloy, it balances high strength, good ductility, corrosion resistance, and processability, making it one of the most widely used titanium alloys in China. Below is a detailed breakdown:
1. Core Identity: TC4 in Chinese Standards
Standard Classification: TC4 is defined by China’s national standard GB/T 3620.1 (titanium and titanium alloy designations) and GB/T 13810 (wrought titanium alloys for medical use).
Alloy Type: α+β dual-phase alloy, containing both α-phase (stable at room temperature, contributes to strength and heat resistance) and β-phase (ductile, enables heat treatment to adjust properties).
2. Chemical Composition (GB/T 3620.1, mass fraction, %)
The composition is strictly regulated to ensure consistent performance:
Element Content Range Role in the Alloy
Titanium (Ti) Balance Matrix element, forming the base structure
Aluminum (Al) 5.5–6.75% Strengthens the α-phase, enhances high-temperature stability and tensile strength
Vanadium (V) 3.5–4.5% Stabilizes the β-phase, improves ductility, toughness, and heat treatability
Iron (Fe) ≤0.30% Controlled impurity (excess impairs corrosion resistance)
Oxygen (O) ≤0.20% Strengthens α-phase but reduces ductility if over 0.2%
Carbon (C) ≤0.08% Prevents brittle carbide formation
Nitrogen (N) ≤0.05% Avoids embrittlement (high levels cause brittleness)
Hydrogen (H) ≤0.015% Critical for preventing hydrogen embrittlement
3. Key Properties
(1) Mechanical Properties (typical values, annealed condition)
Tensile Strength: 900–1100 MPa (significantly higher than pure titanium, comparable to high-strength steel but ~40% lighter).
Yield Strength: 825–930 MPa (resists permanent deformation under load).
Elongation: 10–15% (good ductility for forming processes like forging and rolling).
Hardness: 30–36 HRC (balances wear resistance and machinability).
Fatigue Strength: ~600 MPa (excellent resistance to cyclic loading, critical for dynamic components).
(2) Physical & Chemical Properties
Density: 4.43 g/cm³ (about half the density of steel, ideal for weight-sensitive applications).
Melting Point: ~1668°C (suitable for service temperatures up to 300°C).
Corrosion Resistance: Outstanding—resists seawater, industrial chemicals (e.g., sulfuric acid), and atmospheric corrosion (forms a protective TiO₂ oxide layer that self-repairs).
Thermal Conductivity: 6.7 W/(m·K) (low, requiring careful cooling during machining/welding to prevent overheating).
4. Heat Treatment & Processability
TC4’s properties can be adjusted via heat treatment to meet specific application needs:
Annealing: Heating to 700–800°C, followed by air cooling, improves ductility and machinability (used for general-purpose parts).
Solution Treatment + Aging: Heating to 920–950°C (above the β-transus temperature), quenching in water, then aging at 450–550°C. This increases tensile strength to 1100–1200 MPa (used for high-strength components like aerospace fasteners).
Processability:
Machinable with proper tools (carbide or coated tools) and coolants (to manage low thermal conductivity).
Weldable via TIG, laser, or electron beam welding (welded joints retain ~85–95% of base metal strength).
Compatible with additive manufacturing (3D printing), enabling complex geometries for medical implants and aerospace parts.
5. Applications
TC4 is widely used across industries due to its versatile performance:
Aerospace: Aircraft fuselage components, engine parts (fan blades, casings), rocket structures (balances strength and lightweight requirements).
Medical: Orthopedic implants (hip/knee replacements, bone plates—biocompatible, non-toxic, and matches bone elasticity), dental implants, and surgical instruments.
Marine Engineering: Ship propellers, offshore oil rig components, and seawater pipelines (resists saltwater corrosion).
Automotive & Sports: High-performance vehicle parts (valves, exhaust systems) and sports equipment (golf clubs, bicycle frames) for weight reduction.
6. Why TC4 is a “Workhorse” Alloy?
TC4’s dominance stems from its unique combination of:
Balanced Properties: Strength, toughness, and corrosion resistance rarely matched by other materials.
Cost-Effectiveness: More affordable than specialized high-temperature titanium alloys while outperforming pure titanium.
Process Versatility: Adaptable to forging, machining, welding, and 3D printing, supporting diverse manufacturing needs.
In summary, TC4 (equivalent to Ti-6Al-4V/GR5) is a cornerstone of titanium alloy applications in China, valued for its ability to meet rigorous demands in aerospace, medicine, and beyond.
