1. Industrial pure titanium
This kind of material is not an alloy, but titanium containing a small amount of oxygen, iron and other impurities.
Example: CP Grade 1, Grade 2, Grade 3, Grade 4 (the larger the number, the higher the intensity)
Main features：
Low strength: The strength is the lower of all titanium materials, which is comparable or slightly lower than ordinary steel.
Good corrosion resistance: especially in oxidizing environments (such as seawater and chlorine environments), its corrosion resistance is better than that of most titanium alloys.
Good plasticity: easy to cold process and form.
Application scenario：
It is mainly used in situations where strength requirements are not high, but high corrosion resistance is required, such as certain non-load-bearing structural parts of chemical equipment and marine platforms.
It is not commonly used in the manufacture of high-strength structural screws.
2. α-type and near-α-type titanium alloys
The main characteristics of this type of alloy are stable organization, good heat resistance, and excellent welding performance.
Example: Ti-5Al-2.5Sn, Ti-0.3 Mo-0.8Ni
Main features：
It cannot be strengthened by heat treatment, and is usually used in an annealed state.
It has good high temperature performance and creep strength.
Moderate strength.
Application scenario：
It is mainly used for high-temperature components (such as engine compressor housings) in the aerospace field.
It is not common in screw applications, unless there are special high temperature resistance or welding requirements.
3. (α+β) titanium alloy
This is the main material category commonly used in the manufacture of high-strength titanium alloy screws. They can be significantly strengthened by solution and aging treatment to achieve high strength.
3.1 Universal (α+β) alloy
Example: Ti-6Al-4V (Grade 5)
This is because the use of titanium alloy screws accounts for more than 90% of all titanium alloy fasteners.
Features: It has excellent overall performance, high strength, good fatigue performance, good corrosion resistance, and mature technology.
Application: From aerospace, industry to high-end bicycles, racing cars, medical implants, etc., it is widely used.
Example: Ti-6Al-4V ELI (low clearance)
Features: It is a high-purity version of Ti-6Al-4V, which reduces the content of gap elements such as oxygen and nitrogen, and has better toughness and plasticity, especially at low temperatures.
Application: Mainly used in fields with high fracture toughness requirements, such as medical implants (artificial joints, bone plate screws), and low-temperature pressure vessels.
3.2 Heat-treatable reinforced (α+β) alloy
Such alloys can retain more metastable β phases after quenching, thereby obtaining high strength during aging.
Example: Ti-5Al-2Sn-2Zr-4Mo-4Cr (Ti-17)
Features: It has a combination of high strength and good toughness, and good deep hardenability.
Application: Mainly used for high-strength structural parts of aviation engines, but also for the manufacture of screws with high requirements.
3.3 High-strength and high-toughness (α+β) alloy
Example: Ti-6Al-2Sn-2Zr-2Mo-2Cr-0.25Si (Ti-62222S)
Features: It maintains good toughness and stress corrosion resistance at a higher strength level.
Application: Aerospace main bearing structural parts, high-strength screws in environments sensitive to stress corrosion.
4. β-type titanium alloy
This kind of alloy contains a large number of β-stable elements, and all β-phase tissues can be obtained after quenching. It has good plasticity and is easy to cold process.Through aging treatment, fine α phases can be precipitated and high strength can be obtained.
Example: Ti-3Al-8V-6Cr-4Mo-4Zr (Beta C), Ti-15V-3Cr-3Sn-3Al (Ti-15-3), Ti-13V-11Cr-3Al
Main features：
Good cold formability: it is very soft in the solid solution state, and can be directly cold-headed, and the cost of manufacturing screws is low.
High strength: after aging treatment, the strength can reach 1100-1400 MPa or even higher.
Good corrosion resistance: especially the corrosion resistance to reducing acids is better than that of Ti-6Al-4V.
Application scenario：
It is mainly used in the manufacture of high-performance aerospace fasteners, as well as fields with high requirements for strength and weight loss.
In the medical field, certain β alloys are used in the manufacture of bone screws because of their low elastic modulus (closer to human bone) and good biocompatibility.
Conventional applications: Ti-6Al-4V (Grade 5) is preferred, which is cost-effective and has balanced performance.
Medical implantation: Ti-6Al-4V ELI or β alloy with better biocompatibility is preferred.
High-strength/weight-loss requirements: Consider high-strength (α+β) alloys (such as Ti-62222S) or β alloys (such as Beta C).
Consider cost for mass production: consider cold-heading β alloys (such as Ti-15-3), which can save processing costs.
