1. Mechanical Properties
Commercially Pure Titanium
Strength: It has relatively low tensile strength, which increases with the grade. For example, the tensile strength of Grade 1 is approximately 240–370 MPa, and that of Grade 4 can reach 480–620 MPa. It is a typical material with high ductility and low strength.
Ductility & Toughness: It features excellent elongation (up to 20%–30%) and cold-forming performance, enabling easy processing into thin plates, pipes, and complex-shaped components without cracking.
Fatigue Resistance: Its fatigue strength is moderate, and it is prone to fatigue failure under high-cycle alternating loads.
Titanium Alloys
Strength: Alloying elements such as aluminum (Al), vanadium (V), and tin (Sn) are added to significantly improve the strength. For instance, the tensile strength of the common Ti-6Al-4V alloy can exceed 860 MPa, and that of high-strength titanium alloys can reach 1200–1400 MPa, showing high strength and moderate ductility.
Ductility & Toughness: The elongation of titanium alloys is generally lower than that of commercially pure titanium (usually 10%–15%). Some high-strength alloys even have reduced toughness and are prone to brittle fracture at low temperatures.
Fatigue & Creep Resistance: Titanium alloys have excellent fatigue strength and creep resistance, especially at medium-to-high temperatures. They can maintain structural stability for a long time under alternating loads and high-temperature stress, which is far superior to commercially pure titanium.
2. Corrosion Resistance
Commercially Pure Titanium
It has outstanding universal corrosion resistance. Its surface can form a dense, self-healing titanium dioxide (TiO₂) passive film, which can resist the erosion of most organic acids, inorganic acids (except concentrated hydrofluoric acid and hot concentrated sulfuric acid), alkalis, salt solutions, and atmospheric environments.
It performs well in harsh corrosive environments such as seawater, chlorine-containing media, and wet chlorine gas, and is widely used in chemical and marine engineering fields.
Titanium Alloys
The corrosion resistance of titanium alloys is related to the type and content of alloying elements. For example, α-type titanium alloys (e.g., Ti-5Al-2.5Sn) have corrosion resistance close to that of commercially pure titanium, while β-type or α+β-type titanium alloys (e.g., Ti-6Al-4V) have slightly reduced corrosion resistance due to the addition of vanadium and other elements.
Titanium alloys are not suitable for highly corrosive environments such as strong reducing acids and chloride ion-rich media at high temperatures, as alloying elements may cause local pitting corrosion or intergranular corrosion.
3. Thermal Stability
Commercially Pure Titanium
Its long-term service temperature is relatively low, generally not exceeding 315°C. When the temperature exceeds this limit, the oxidation rate accelerates, and the surface oxide film becomes loose, losing its protective effect.
It has excellent low-temperature performance. Taking Grade 1 as an example, it can maintain good toughness at -253°C without brittle fracture, making it suitable for cryogenic applications.
Titanium Alloys
It has excellent high-temperature stability. For example, Ti-6Al-4V can be used for a long time at 400–500°C, and heat-resistant titanium alloys (e.g., Ti-6Al-2Sn-4Zr-2Mo) can withstand temperatures above 600°C.
The low-temperature performance varies by alloy type. α-type titanium alloys have good low-temperature toughness, while some β-type alloys may experience toughness degradation at ultra-low temperatures.
4. Processing Performance
Commercially Pure Titanium
Cold Working: It has excellent cold-forming performance and can be processed through stamping, bending, and drawing without intermediate annealing.
Welding: It has good weldability, and the welded joints have high strength and corrosion resistance, with no strict requirements for welding processes.
Machinability: It has certain machinability, but it is prone to sticking to the tool during processing, requiring the use of tools with high hardness and coolant.
Titanium Alloys
Cold Working: Most titanium alloys have poor cold-forming performance due to high strength and low ductility, and need intermediate annealing treatment to reduce hardness and improve ductility.
Welding: Welding is more difficult than that of commercially pure titanium. Alloying elements are prone to oxidation and segregation during welding, leading to reduced joint performance, so strict protective measures (e.g., argon shielding) are required.
Machinability: It has poor machinability, high cutting resistance, and severe tool wear, requiring the use of specialized cutting processes and tools.
