α titanium alloy refers to titanium alloys primarily composed of the α phase. Titanium (Ti) has two main crystal structures: α phase and β phase, which can change depending on temperature and chemical composition.
• α Phase: The α phase has a hexagonal close-packed (HCP) structure, characterized by high strength, hardness, excellent high-temperature resistance, and corrosion resistance. α titanium alloys are highly stable and perform well under high temperatures and harsh environments.
• β Phase: The β phase has a body-centered cubic (BCC) structure, offering better ductility, but lower high-temperature strength compared to the α phase.
Elements that dissolve preferentially in the α phase, increase the allotropic transformation temperature, and expand the α-phase region are called α-stabilizing elements. These include substitutional elements such as aluminum (Al) and interstitial elements like oxygen (O), nitrogen (N), and carbon (C).
Among these, aluminum is the primary alloying element in titanium alloys, significantly enhancing strength, high-temperature performance, and reducing density.
Since α titanium alloys rely on the stability of the α phase, they exhibit excellent high-temperature performance. While their room-temperature strength is lower than that of β-type and α+β-type titanium alloys, they provide the highest strength at 500–600°C among all titanium alloy categories.
Additionally, α titanium alloys feature structural stability, oxidation resistance, excellent weldability, high corrosion resistance, and good machinability. They also perform well at room temperature, extremely low temperatures, and high temperatures. However, their ductility is low, and their pressure processing ability is relatively poor.
Near-α Titanium Alloys
These titanium alloys contain a small amount of β-stabilizing elements, forming an annealed microstructure with less than 10% β phase or intermetallic compounds at room temperature. Some examples include:
• Ti-8Al-1Mo-1V – A high-temperature titanium alloy developed in the United States. However, its high aluminum content may lead to hot salt stress corrosion issues.
• Ti-6.5Al-1Mo-1V-2Zr (BT20) – A titanium alloy developed in Russia, similar to Ti-8Al-1Mo-1V, but with reduced aluminum content and the addition of zirconium (Zr), which maintains heat resistance while improving resistance to hot salt stress corrosion.
• α + Intermetallic Compound Alloy (Ti-2.5Cu) – The IMI230 alloy developed in the United Kingdom.
Applications of α Titanium Alloys
α titanium alloys are widely used in the chemical, petrochemical, and processing industries, where corrosion resistance, formability, and high-temperature stability are key considerations.
