Comprehensive Research Report On Titanium And Titanium Alloys: Basic Characteristics, Research Progress And Future Challenges

1 Basic physical and chemical properties of titanium and titanium alloys
Titanium, as a strategic light metal, occupies an irreplaceable position in the high-end industrial field with its excellent specific strength (strength/density ratio) and all-environment corrosion resistance. The density of titanium is only 4.51 g/cm³ (about 57% of steel), but its strength is equivalent to that of high-strength steel, making it the highest specific strength among metal materials. The crystal structure of titanium is hexagonal close-packed (HCP, α phase) below 882℃ and body-centered cubic (BCC, β phase) above 882℃. This phase change characteristic provides rich possibilities for alloy design.

 

1.1 Mechanical and environmental adaptability High and low temperature performance: Titanium alloys still maintain good strength in the range of 450-600℃, such as Ti-6Al-4V, which maintains a yield strength of more than 500 MPa at 400℃. The low temperature performance is even more outstanding. The elongation of TA7 alloy at -253℃ liquid hydrogen temperature is greater than 12%, making it the preferred material for aerospace cryogenic fuel containers. Corrosion resistance mechanism: A dense TiO₂ passivation film (thickness 5-20 nm) is instantly formed on the surface of titanium, making its corrosion rate in seawater, chlorine-alkali and acidic media lower than 0.001 mm/a. Its resistance to pitting and stress corrosion cracking (SCC) is significantly better than that of stainless steel, and it is known as "ocean metal". Biocompatibility: The self-corrosion current density of pure titanium in simulated body fluids is as low as 2.24×10⁻⁸ A/cm², and the lack of metal ion release makes it a core material for artificial joints and dental implants.

 

1.2 Inherent processing challenges Thermal conductivity defects: The thermal conductivity is only 17 W/m·K (1/14 of aluminum), and the temperature in the cutting zone is as high as over 1000°C, which accelerates tool wear. High chemical activity: It reacts with O, N, and H at high temperatures to generate a 50-200 μm hardened layer, which requires inert atmosphere protection for processing. Low elastic modulus: about 110 GPa (1/2 of steel), resulting in severe processing springback and difficulty in controlling the forming accuracy of thin-walled parts.