GR5 Ti-6Al-4V Titanium Alloy

Ti-6Al-4V, also known as Grade 5 titanium or TC4, is an α+β titanium alloy renowned for its exceptional combination of strength, corrosion resistance, and versatility. This alloy is extensively utilized across various industries, including aerospace, medical, marine, and chemical processing.

Chemical Composition and Alloy Design

The primary constituents of Ti-6Al-4V are:

• Titanium (Ti): Balance

• Aluminum (Al): 5.5% to 6.75%

• Vanadium (V): 3.5% to 4.5%

• Iron (Fe): ≤ 0.3%

• Oxygen (O): ≤ 0.2%

• Carbon (C): ≤ 0.08%

• Nitrogen (N): ≤ 0.05%

• Hydrogen (H): ≤ 0.015%

• Yttrium (Y): ≤ 0.005%

• Other elements: Each ≤ 0.1%, total ≤ 0.3%

Aluminum acts as an α-phase stabilizer, enhancing strength and reducing density, while vanadium stabilizes the β-phase, improving ductility and toughness.

Physical and Mechanical Properties

Physical Properties:

• Density: Approximately 4.43 g/cm³, providing a significant weight advantage over steel.

• Melting Point: Between 1,600°C and 1,660°C, indicating excellent high-temperature performance.

• Thermal Conductivity: Around 6.6 W/m·K, lower than that of many metals, which can be advantageous in certain applications.

• Elastic Modulus: Approximately 113 GPa, lower than steel, contributing to better flexibility.

Mechanical Properties:

• Tensile Strength: Typically ranges from 895 to 930 MPa in the annealed condition; can exceed 1,000 MPa with heat treatment.

• Yield Strength: Around 880 MPa in the annealed state.

• Elongation: Approximately 10% to 15%, indicating good ductility.

• Hardness: Typically about Rockwell C 36.

• Fatigue Strength: Exhibits excellent fatigue resistance, making it suitable for cyclic load applications.

Notably, Ti-6Al-4V maintains its mechanical properties at elevated temperatures up to 400°C, retaining a tensile strength of approximately 675 MPa at this temperature.

Heat Treatment and Processing

Ti-6Al-4V can undergo various heat treatment processes to optimize its microstructure and mechanical properties:

• Annealing: Heating between 730°C and 850°C to relieve internal stresses and improve ductility.

• Solution Treatment and Aging: Solution treating at approximately 955°C to 1010°C, followed by aging at 480°C to 650°C, enhances strength and hardness.

• Stress Relief Annealing: Conducted at 538°C to 649°C for 1 to 8 hours, then air or furnace cooled, to reduce residual stresses without significantly altering mechanical properties. 

In terms of processing, Ti-6Al-4V is typically hot worked at temperatures between 500°C and 700°C to minimize work hardening. Cold working is challenging due to the alloy's high strength and low thermal conductivity. Additionally, additive manufacturing techniques, such as laser-based methods, have been employed to produce complex components, with subsequent heat treatments applied to optimize the microstructure. 

Corrosion Resistance and Biocompatibility

Ti-6Al-4V forms a stable, continuous oxide layer upon exposure to oxygen, providing excellent corrosion resistance in various environments, including seawater and chemical processing settings. 

The alloy also exhibits superior biocompatibility, making it a preferred material for medical implants and prostheses. However, its poor shear strength and wear resistance necessitate careful consideration in load-bearing applications. 

Applications

Due to its favorable properties, Ti-6Al-4V is employed in a wide range of applications:

• Aerospace: Utilized in aircraft turbine engine components, structural parts, and fasteners. 

• Medical: Commonly used for orthopedic implants, dental implants, and surgical instruments. 

• Automotive: Employed in high-performance automotive parts. 

• Sports Equipment: Used in the manufacturing of high-end bicycles and other sports gear.