Titanium is a versatile metal used in many industries due to its unique combination of properties. It has an exceptional strength-to-weight ratio, excellent corrosion resistance, and biocompatibility, making it an attractive option for medical devices, aircraft, automotives, and marine vessels.
To broaden the usability of Titanium, manufacturers often combine pure titanium with other elements. This introduces desirable properties such as flexibility and malleability. There are different titanium alloys, each with unique traits and uses. In this article, we’ll discuss the common types of titanium alloys, their properties, and applications.
What Are Titanium Alloys?
A titanium alloy is a combination of pure titanium and other elements, such as vanadium, copper, aluminum, molybdenum, iron, cobalt, nickel, and manganese. Adding another element to titanium changes its mechanical and physical properties, resulting in the formation of an alloy with specific traits for specialized applications.
For example, a vanadium-titanium alloy exhibits enhanced strength and heat resistance. On the other hand, nickel-titanium alloys are known for their shape memory effect and superelasticity.
What Are Titanium Alloys Made Of?
Pure titanium is often combined with other metals or chemical elements to form titanium alloys. Some of the most common alloying elements in the titanium industry include:
Aluminum: Improves strength and corrosion resistance, and reduces plasticity.
Vanadium: Increases the yield and tensile strength of titanium alloys, and also improves thermal stability.
Molybdenum: Enhances strength, wear resistance, and corrosion resistance. It also leads to a lower elastic modulus, suitable for biomedical applications.
Silicon: Boosts high-temperature strength, creep resistance, and oxidation resistance.
Chromium: Enhances corrosion resistance and tensile properties.
Zirconium: Improves mechanical strength, corrosion resistance, and biocompatibility.
Niobium: Increases hardness, fracture toughness, and biocompatibility.
Titanium Alloy Material Properties
Adding another element to titanium modifies its traits. Here are some of the material properties of titanium alloys:
Low density and high strength:
Despite being hard and strong, titanium alloys have a relatively low density, approximately 4.5g/cm3. Their high specific strength (strength/density ratio) allows for the fabrication of lightweight parts with high unit strength.
High-temperature performance:
Titanium alloys can operate in temperatures as high as 500ºC while maintaining their strength. For comparison, aluminum alloys are limited to temperatures below 200ºC.
Excellent corrosion resistance:
Titanium alloys will naturally form a passive layer that shields against corrosion and oxidation. For this reason, they can withstand aggressive chemicals, acids, and marine environments without degradation.
Tensile strength:
The tensile strength of titanium alloys ranges from about 600 MPa to 1200 MPa for very high-strength alloys.
Good biocompatibility:
Titanium alloys are biocompatible, meaning they are non-toxic and readily accepted by the human body. This has led to their widespread use in medical implants and devices.
High fatigue and crack resistance:
Titanium alloys can withstand stress cycles and repeated vibrations without fatigue or cracking.
Common Types Of Titanium (Ti) Alloys
Titanium alloys are classified into three distinct categories based on their structure: alpha alloys, beta alloys, and alpha-beta alloys. Each of these lightweight alloys is designed to have unique characteristics that address specific performance requirements.
Titanium material undergoes a phase change from its hexagonal close-packed alpha phase to a body-centered cubic beta phase at around 890ºC. These phases are stabilised using different alloying elements.
Alpha alloys
Alpha titanium alloys consist entirely of alpha (α) phase structure. Aluminum is typically the primary alloying agent stabilizing the α-phase.
These alloys are non-heat treatable and are usually easy to weld. They offer good fracture toughness, exceptional corrosion resistance, and ductility. Alpha alloys also exhibit excellent mechanical properties at cryogenic and elevated temperatures.
Near alpha titanium alloys consist mostly of α-phase with a small amount of beta (β) phase. In addition to the α-phase stabilizer (aluminum), these alloys also feature a small amount of β-phase stabilizers (such as molybdenum or silicon).
Near-α alloys may be heat treatable since they contain beta phase. They offer good creep resistance and moderate strength at elevated temperatures, making them suitable for demanding applications.
Beta alloys
Beta titanium alloys are a versatile class of materials. They use beta stabilisers such as molybdenum, vanadium, chromium, or silicon to stabilize the beta phase and achieve desired properties.
Near-beta alloys consist mostly of the β-phase with a small amount of the α-phase. Beta and near-beta titanium grades are collectively known as metastable alloys. They are readily heat treatable and can be solution treated and aged to achieve higher strengths. These titanium alloys also offer good formability before heat treatment procedures.
Metastable alloys are widely adopted in medical applications since they exhibit good biocompatibility and enhanced corrosion resistance due to the presence of a stable titanium oxide layer formed with beta stabilisers. Other applications of these materials include aerospace components and high-performance motorsport systems.
Alpha-Beta alloys
Alpha-beta (α-β) titanium alloys combine the best characteristics of alpha and beta phases to achieve a balance of properties. They contain both alpha and beta stabilizers and are, therefore, heat treatable through solution treatment and aging.
These alloys also offer good mechanical strength, high corrosion resistance, formability, and excellent fatigue resistance, making them suitable for a wide range of applications. α-β alloys typically have lower creep resistance compared to alpha alloys.
A common example of an α-β titanium alloy is Ti 6Al-4V (Grade 5).
Titanium Alloy Grades
Commercially pure titanium and titanium alloys can be placed into different grades, depending on their chemical composition and mechanical properties. Below is an overview of the most common titanium grades.
Commercially Pure Titanium (Grades 1-4)
With unalloyed titanium, commercially pure grades will vary primarily based on the oxygen and nitrogen content. This affects mechanical properties such as strength, formability, and corrosion resistance.
The strength increases significantly for higher grade numbers compared to the lower grades. As such, Grade 4 (Ti 65A) titanium is very strong with applications in airframe components, heat exchangers, and chemical processing equipment.
On the other hand, Grade 1 (Ti 35A) titanium has the highest corrosion resistance and formability, but also the lowest mechanical strength.
Grade 5 Titanium (Ti-6Al-4V)
This is the most common titanium alloy, and accounts for over half of the titanium usage globally (approximately 70% of alloy grades melted are a sub-grade of Ti-6Al-4V. For this reason, it is often referred to as the “workhorse” alloy.
The alloying elements in Ti-6Al-4V are 6% aluminum and 4% vanadium. This titanium grade can be heat-treated to enhance its strength, and it has good corrosion resistance in both oxidizing and reducing environments.
The desirable properties of Grade 5 titanium make it a popular choice for applications that prioritize weight reduction and corrosion resistance. It is commonly used in aerospace applications, marine, and power generation industries.
Grade 7 Titanium (Ti-0.15Pd)
Grade 7 titanium is formed by adding a small amount of palladium (0.12 to 0.25%) to commercially pure titanium. This results in significantly higher corrosion resistance, making this alloy particularly suited to saltwater, acidic environments, and those rich in chlorides.
Ti-0.15Pd is also easy to weld and offers moderate strength and ductility. This alloy can be readily heat-treated and is commonly used in desalination equipment, hydrocarbon processing, and the chemical industry.
Grade 9 Titanium (Ti-3Al-2.5V)
Grade 9 titanium contains about 3% aluminum and 2.5% vanadium. This alloy has improved strength and corrosion resistance. It can also be cold-formed and is easy to weld, which makes it beneficial for many applications.
Like other titanium alloys, Ti-3Al-2.5V has a low density, which is crucial for fabricating lightweight parts. Grade 9 titanium is used in applications such as aircraft frames, performance bicycles, golf clubs, and components for jet engines.
Grade 23 Titanium (Ti-6Al-4V ELI)
Titanium grade 23 is essentially the more pure version of Grade 5. It has lower levels of interstitials, such as oxygen, nitrogen, iron, and carbon, hence the “ELI” designation.
Grade 23, with its high purity and hypoallergenic properties, offers superior biocompatibility, making it ideal for bone screws, medical implants, and orthodontic appliances. The reduced levels of interstitial elements also contribute to improved fracture toughness and ductility.
Ti-6Al-4V ELI is also lightweight and exhibits excellent resistance to corrosion. Its low elastic modulus allows for medical implants to bond effectively with the surrounding bone tissue.
Ti-6Al-2Sn-4Zr-2Mo
Ti-6Al-2Sn-4Zr-2Mo, or Ti-6-2-4-2, is an alpha-beta alloy that is known for its high mechanical strength, weldability, formability, and high temperature creep strength. The elemental composition of Ti-6-2-4-2 is as follows: 6% aluminum, 2% tin, 4% zirconium, and 2% molybdenum.
This titanium alloy is often used in gas turbine compressor components and high-temperature jet engines.
Applications of Titanium Alloys
Aerospace Industry
Titanium alloys are favored in aerospace applications due to their outstanding strength-to-weight ratio, heat resistance, and corrosion resistance. These properties allow aircraft designers to avoid unnecessary weight while maintaining structural integrity and durability.
Titanium alloys are often used in the manufacture of aircraft fuselages, wings, engines, compressor blades, landing gear, and fasteners. For example, the Boeing 777, 787, and the Airbus 350 utilize titanium alloys in crucial structural components.
Medical Industry
Titanium alloys excel in terms of biocompatibility. It is non-reactive, and the human body can handle it with no impact. Also, its density is comparable to that of human bone, which supports fusing and bonding. Due to these properties, titanium alloys are perfect for surgical implants such as hip replacements, knee replacements, dental implants, and heart stents.
Titanium is the preferred material for surgical instruments and other medical devices due to its corrosion resistance and high strength-to-weight ratio. It is used in the manufacture of wheelchairs, surgical tools, and MRI-compatible medical devices.
Marine Industry
Titanium alloys are known for their corrosion resistance, which makes them highly suited to marine environments. They can withstand prolonged exposure to saltwater and other corrosive agents without degradation.
Titanium alloys are, therefore, the material of choice for ship hulls, propeller shafts, cooling systems, and submarine components. They are also common in desalination plants and offshore oil rigs, where they provide long-term reliability with minimal maintenance.
Consumer Products
There is a growing demand for titanium in the production of consumer goods. Its durability and biological inertness make it a popular choice for jewellery. It does not react with the skin, unlike copper and nickel-based accessories.
In addition to jewellery, titanium alloys are also used in sunglasses, high-end watches, cookware, camping gear, and computer cases. For example, Apple’s PowerBook line utilizes this metal to achieve a light weight frame.
Sports Equipment
Titanium alloys are used in a growing range of sporting goods. Their high strength-to-weight ratio allows them to deliver higher performance and durability while keeping equipment lightweight. The stiffness of the material is beneficial for energy transfer in sports such as golf and tennis. Also, the good corrosion resistance of these alloys ensures the durability of equipment in various conditions.
Some sporting goods that utilize titanium alloys include golf clubs, bicycle frames, climbing gear, ski poles, ice skates, and tennis rackets.
Industrial Applications and Chemical Processing
Titanium alloys are widely used in industrial manufacturing and chemical processing, where exposure to high temperatures, corrosive chemicals, and pressure is the norm. Their inert ceramic layer and excellent high-temperature stability make them suited to such environments.
In chemical plants and refineries, titanium heat exchangers, pumps, and valves withstand extreme temperatures and harsh chemical environments, ensuring durability. Titanium alloys are also commonly used in industrial piping and geothermal energy production lines.
Art and Architecture
Titanium alloys are seeing increased use in artistic and architectural structures. With rates of thermal expansion that are similar to glass and concrete, these alloys can be successfully used with these materials.
The protective oxide film that forms naturally on the metal surface gives the appearance of various colors depending on its thickness. Also, being corrosion-resistant reduces the lifetime cost of structures.
Other reasons titanium is used in architecture are its flexibility, which allows for complex designs, and a high-tech image, which contributes to a modern and futuristic aesthetic.
Important architectural works that incorporate titanium and its alloys include:
Guggenheim Museum (Bilbao, Spain)
Denver Art Museum (Denver, USA)
National Grand Theater (Beijing, China)