Titanium is an allotrope with a melting point of 1668°C. Below 882°C, it exhibits a hexagonal close-packed crystal structure, known as α-titanium; above 882°C, it has a body-centered cubic crystal structure, known as β-titanium. By utilizing the distinct characteristics of these two structures in titanium, adding appropriate alloying elements, and gradually altering the phase transformation temperature and phase content, different titanium alloys (titanium alloys) with various microstructures can be obtained. At room temperature, titanium alloys have three basic microstructures, leading to the following three categories: α alloys, (α+β) alloys, and β alloys. In China, they are respectively represented by TA, TC, and TB.
Titanium is a new type of metal, with its properties being related to the content of impurities such as carbon, nitrogen, hydrogen, and oxygen. The purest titanium iodide has an impurity content of no more than 0.1%, yet it has low strength and high plasticity. The properties of 99.5% industrial pure titanium are as follows: density ρ = 4.5 g/cm³, melting point 1725°C, thermal conductivity λ = 15.24 W/(m·K), tensile strength σb = 539 MPa, elongation δ = 25%,断面收缩率 ψ = 25%, modulus of elasticity E = 1.078×10^5 MPa, hardness HB 195.
High strength
Titanium alloys typically have a density of around 4.51 g/cm³, which is only 60% of steel's density. Pure titanium has a density close to that of ordinary steel, and some high-strength titanium alloys exceed the strength of many alloy structural steels. Therefore, the specific strength (strength/density) of titanium alloys is much greater than that of other metal structural materials, as shown in Table 7-1. They can be used to manufacture components with high unit strength, good rigidity, and light weight. Titanium alloys are used in aircraft engine components, frames, skins, fasteners, and landing gears.
High thermal intensity
These titanium alloys can operate at temperatures several hundred degrees higher than aluminum alloys, maintaining the required strength at moderate temperatures and can work continuously at temperatures between 450°C and 500°C. They exhibit high specific strength within the range of 150°C to 500°C, whereas aluminum alloys show a significant decrease in specific strength at 150°C. Titanium alloys can operate up to 500°C, while aluminum alloys are limited to below 200°C.
Good resistance to etching
Titanium alloys excel in corrosive environments like humid atmospheres and seawater, boasting superior corrosion resistance compared to stainless steel; they have exceptional resistance to pitting, acid, and stress corrosion; and exhibit excellent corrosion resistance against alkalis, chlorides, organic chloride compounds, sulfuric acid, etc. However, titanium is less resistant to corrosion in environments containing reducing oxygen and chromium salts.
Four, excellent low-temperature performance
Titanium alloys maintain their mechanical properties at both low and ultra-low temperatures. Alloys with excellent low-temperature properties and extremely low interstitial elements, such as TA7, can still retain a certain degree of plasticity at -253℃. Therefore, titanium alloys are also an important low-temperature structural material.
Five, High chemical activity
Titanium has a high chemical reactivity, reacting strongly with atmospheric O, N, H, CO, CO2, and water vapor. Carbon content above 0.2% forms hard TiC in titanium alloys; at higher temperatures, reaction with N also forms TiN, creating a hard surface layer in titanium alloy products. Above 600°C, titanium absorbs oxygen to form a highly hardening layer; an increase in hydrogen content can also lead to a brittle layer. The depth of the hard, brittle surface layer formed by absorbing gases can reach 0.1-0.15 mm, with a hardening degree of 20%-30%. Titanium also exhibits a high chemical affinity, easily causing adhesion to friction surfaces.
Six, Low thermal elasticity
Titanium has a thermal conductivity λ of approximately 15.24 W/(m.K), which is about 1/4 that of nickel, 1/5 of iron, and 1/14 of aluminum. The thermal conductivity of various titanium alloys is about 50% lower than that of pure titanium. The elastic modulus of titanium alloys is about 1/2 that of steel, making them less rigid and more prone to deformation. They are not suitable for making slender rods and thin-walled parts. During cutting, the amount of workpiece bounceback on the machined surface is significantly high, about 2 to 3 times that of stainless steel, leading to severe friction, adhesion, and adhesive wear on the cutting tool's back face.
Reaction vessels are widely used in the petrochemical, rubber, pesticide, dye, pharmaceutical, and food industries. They serve as pressure vessels for processes such as sulfonation, nitration, hydrogenation, hydrocarbonation, polymerization, and condensation. The design structures and parameters of reaction vessels vary according to different production processes and operating conditions, making them non-standard equipment with different structural styles. Materials commonly used include carbon manganese steel, stainless steel, zirconium, titanium, nickel-based (Hastelloy, Inconel, Monel) alloys, and other composite materials. Heating/cooling methods include electric heating, hot water heating, thermal oil circulating heating, steam heating, far-infrared heating, external/internal coil heating, and electromagnetic induction heating, among others. Cooling methods include jacket cooling and internal coil cooling. The choice of heating method is primarily related to the required heating/cooling temperature for the chemical reaction and the amount of heat required. Agitators are available in anchor, frame, paddle, turbine, scraper, and multi-layer composite blade designs, and are designed and manufactured according to the process requirements of different working environments.
