TC21 Titanium Alloy
TC21 is a high-performance α+β two-phase titanium alloy independently developed in China. It is renowned for its excellent comprehensive mechanical properties (high strength, high toughness, and good thermal stability) as well as favorable processability, making it widely used in high-end fields such as aerospace. Here is a detailed introduction:
1. Basic Information
Alloy Type: α+β two-phase titanium alloy (can be strengthened by heat treatment).
R&D Background: Developed by institutions like the Northwest Institute for Nonferrous Metal Research, TC21 was designed to meet the demand for high-strength, lightweight structural materials in aerospace, filling the gap in China’s high-end titanium alloy sector.
Core Characteristics:
High room-temperature strength (tensile strength up to 1100-1200 MPa) while maintaining good plasticity and toughness.
Strengthenable via heat treatment (strength improved through solution treatment + aging).
Excellent thermal stability, maintaining stable performance at medium to high temperatures (300-400°C).
Low density (approximately 4.5 g/cm³), with a specific strength (strength/density) much higher than that of steel and aluminum alloys, suitable for lightweight structural design.
2. Chemical Composition (mass fraction, %)
The composition of TC21 balances strength and toughness, with key alloying elements and their contents as follows:
Element Content Range Function
Titanium (Ti) Balance Matrix element
Aluminum (Al) 5.5 – 6.5% Strengthens the α phase, improving strength and heat resistance
Tin (Sn) 2.0 – 3.0% Solid-solution strengthening, enhancing thermal stability
Zirconium (Zr) 1.0 – 2.0% Refines grains, improves high-temperature performance
Molybdenum (Mo) 1.5 – 2.5% Strengthens the β phase, enhancing hardenability and toughness
Chromium (Cr) 1.0 – 2.0% Stabilizes the β phase, improving corrosion resistance and processability
Silicon (Si) 0.05 – 0.30% Refines microstructure, enhances high-temperature creep strength
3. Key Properties
(1) Mechanical Properties (typical values after heat treatment)
Tensile Strength: 1100 – 1200 MPa (far exceeding pure titanium’s 420 MPa, approaching high-strength steel but with lower density).
Yield Strength: 1000 – 1100 MPa.
Elongation: 8 – 12% (excellent among high-strength titanium alloys, balancing strength and toughness).
Impact Toughness: ≥40 J/cm² (strong fracture resistance, suitable for dynamic load-bearing).
Hardness (HRC): 35 – 40.
(2) Other Critical Properties
Density: Approximately 4.5 g/cm³ (only 1/2 that of steel and 1.6 times that of aluminum alloys, offering significant lightweight advantages).
Heat Resistance: Long-term service temperature up to 350 – 400°C (higher than pure titanium and most α-type titanium alloys).
Corrosion Resistance: Stable in atmospheric, seawater, and most non-oxidizing media, better than ordinary steel but weaker than pure titanium and β-type titanium alloys.
Weldability: Can be welded using processes like TIG (tungsten inert gas welding), with welded joint strength reaching over 90% of the base metal, suitable for integral structure manufacturing.
4. Heat Treatment Process
The properties of TC21 can be adjusted through heat treatment, with a typical process as follows:
Solution Treatment: Heat to 880 – 920°C (50-100°C below the β transformation point), hold for 1-2 hours, then water quench to obtain a supersaturated solid solution.
Aging Treatment: Heat to 500 – 550°C, hold for 4-8 hours, then air cool to promote the precipitation of strengthening phases (e.g., Ti₃Al), significantly improving strength.
5. Processability
Forging: Suitable for hot forging (heated to 100-200°C below the β transformation point), can be formed into complex-shaped forgings (e.g., aircraft landing gear, frames).
Rolling/Extrusion: Can be processed into plates, bars, and profiles; cold working requires intermediate annealing to eliminate stress.
Machining: Moderate machinability, requiring cemented carbide tools and sufficient cooling to avoid high-temperature oxidation.
Surface Treatment: Can undergo anodizing, spraying, etc., to improve wear resistance or decoration.
6. Application Fields
With its high strength, lightweight nature, and good comprehensive performance, TC21 is mainly used in:
Aerospace: Aircraft fuselage frames, wing structural parts, landing gear components, engine nacelles (reducing weight while ensuring structural strength).
Weaponry: Missile bodies, armored vehicle protective plates, artillery components (impact-resistant and lightweight).
High-end Equipment: Precision mechanical drive shafts, high-pressure vessels, deep-sea detection equipment (resistant to high pressure and corrosion).
7. Comparison with Similar Alloys
Property TC21 TC4 (Ti-6Al-4V) TB6 (β-type)
Tensile Strength 1100-1200 MPa 900-1100 MPa 1200-1400 MPa
Elongation 8-12% 10-15% 5-8%
Service Temp 350-400°C 300°C 300°C
Cost High Medium Higher
Note: TC21 has higher strength than TC4 and better toughness than TB6, making it a preferred material balancing strength, toughness, and heat resistance.
Summary
As a high-performance α+β titanium alloy independently developed in China, TC21 features high strength, high toughness, lightweight properties, and good thermal stability. It is a key structural material in aerospace, weaponry, and other high-end fields, driving the development of lightweight and high-performance high-end equipment in China.