Titanium alloy properties and applications

Titanium alloy properties

 

Titanium is a new type of metal, the properties of titanium are related to the content of carbon, nitrogen, hydrogen, oxygen and other impurities contained, the purest titanium iodide impurity content of no more than 0.1%, but its strength is low, high plasticity. 99.5% industrial pure titanium properties are: density ρ = 4.5g/cm³, melting point 172, thermal conductivity λ = 15.24W/(m.K), tensile strength σb = 539MPa, elongation δ=25%, section shrinkage ψ=25%, modulus of elasticity E=1.078×105MPa, hardness HB195.

 

(1) high strength The density of titanium alloy is generally around 4.5g/cm³, only 60% of steel, the strength of pure titanium is close to the strength of ordinary steel, some high-strength titanium alloys exceed the strength of many alloy structural steel. Therefore, the specific strength of titanium alloy (strength / density) is much greater than other metal structural materials, can be produced unit of high strength, good rigidity, lightweight parts and components. At present, the aircraft engine components, skeleton, skin, fasteners and landing gear, etc. are using titanium alloy.

 

(2) high thermal strength, the use of temperature than aluminum alloys a few hundred degrees higher in the medium temperature can still maintain the required strength, can be in the temperature of 450-500 ℃ for long-term work in the two types of titanium alloys in the range of 150 ℃ to 500 ℃ still have a high specific strength, and aluminum alloys at 150 ℃ than the strength of the obvious decline. The working temperature of titanium alloy can reach 500 ℃, aluminum alloy is below 200 ℃.

 

(3) good corrosion resistance Titanium alloy in the humid atmosphere and seawater media, its corrosion resistance is far better than stainless steel; pitting, acid corrosion, stress corrosion resistance is particularly strong; alkali, chloride, chlorine, organic items, nitric acid, sulfuric acid, etc. have excellent corrosion resistance. But titanium has a reducing oxygen and chromium salt media corrosion resistance is poor.

 

(4) Good low-temperature performance Titanium alloy in low temperature and ultra-low temperature, can still maintain its mechanical properties. Good low-temperature performance, the gap element is very low titanium alloy, such as TA7, in -253 ℃ can also maintain a certain degree of plasticity. Therefore, titanium alloy is also an important low temperature structural material.

 

(5) Chemical activity of titanium, titanium's chemical activity, and the atmosphere O, N, H, CO, CO2, water vapor, ammonia, etc. to produce a strong chemical reaction. Carbon content greater than 0.2%, will be formed in the titanium alloy hard TiC; higher temperature, and the role of N will also form a hard surface layer of TiN; above 600 ℃, titanium absorbs oxygen to form a hardened layer of high hardness; the hydrogen content rises, but also the formation of embrittlement layer. Absorption of gas and the resulting hard brittle surface layer depth of up to 0.1 ~ 0.15 mm, the degree of hardening is 20% ~ 30%. Titanium's chemical affinity is also large, easy to produce adhesion with the friction surface.

 

(6) small thermal conductivity, small modulus of elasticity The thermal conductivity of titanium λ = 15.24W / (m.K), titanium alloy products for nickel about 1/4, iron 1/5, aluminum 1/14, and a variety of titanium alloys than the thermal conductivity of titanium thermal conductivity of about 50% down. The modulus of elasticity of titanium alloy is about 1/2 of steel, so its rigidity is poor, easy to deform, not suitable for making slender rods and thin-walled parts, the rebound of the machined surface when cutting is very large, about 2-3 times as much as stainless steel, resulting in sharp friction, adhesion and bonding wear of the tool after the cutter surface.

 

Titanium alloy applications

 

Industrial pure titanium Gr1, Gr2, Gr3: excellent stamping performance. Can be various forms of welding, welding performance is good, welded joints up to 90% of the strength of the base metal. Easy to saw and wheel cutting, good machinability. Excellent corrosion resistance for the following 350 ℃, the force of small parts and stamping into a variety of complex shapes of the parts. Such as thermal power station condenser; marine seawater corrosion of piping systems, valves, pumps; chemical heat exchangers, pumps, distillation towers; seawater desalination systems, platinum-plated anode; aircraft skeletons, skins, engine parts, beams and so on.

Titanium alloy Ti-5Al: good welding performance, high creep strength, but the process plasticity is low, can be deformed in the hot state, Dongri alloy in the bearing axial load, no sensitivity to incision, cutting performance is still good 400 ℃ below the work of the parts and welded parts.

Titanium alloy Gr6: poor stamping performance, thermoplasticity is still good. East can be various forms of welding, good performance, welded joint strength and plasticity can be equal to the base metal. Machinability is the same as industrial pure titanium. Corrosion resistance is good, high temperature thermal stability is good to do 500 ℃ below the long-term work of the structural parts, can do a variety of drop-forged parts.

Titanium alloy Gr16: good thermoplasticity. Dongri can be welded in various forms, weldability is good. Machinability and industrial pure titanium the same. Good oxidation resistance 500 ℃ below the long-term work parts. Dongri can manufacture engine compressor disk and blade.

Titanium alloy Ti-2Al-1.5Mo: good stamping. Dongil can be welded in various forms, weldability is good. Machinability and industrial pure titanium the same. Good oxidation resistance to do 400 ℃ below the work of the parts. Suitable for a variety of plates, stamping and welding parts.

Titanium alloy Ti-4Al-1.5Mo: at 350 ℃, 100h of the enduring strength of more than 400MPa, hot work has good plasticity. Heated to 350-400 ℃, there is no tendency to become brittle, so it can be used to weld the parts working at high temperatures to do 500 ℃ below the work of the parts, weldments, die forging and bending parts.

Titanium alloy Ti 5Al 4V: poor stamping, good thermoplasticity. Various forms of welding can be carried out, welded joint strength up to 90% of the strength of the base metal. Machinability is still good, need to use carbide, large amount of tooling, slow speed, full cooling. Good corrosion resistance and thermal stability. Dongil Metal is one of the most widely used titanium alloys to make parts for long-term work below 400℃.

Titanium alloy Gr5 (Ti 6al 4v): The composition of the material is Ti-6Al-4V, belongs to (a + b) type titanium alloy, has good comprehensive mechanical mechanical properties. Specific strength. Ti 6al 4v properties is strength sb = 1.012MPa, density g = 4.51g/cm³, specific strength sb/g = 23.5, while the specific strength of alloy steel sb/g is less than 18. titanium alloy thermal conductivity is low. The thermal conductivity of titanium alloy is 1/5 of that of iron and 1/10 of that of aluminum, and the thermal conductivity of TC4 l=7.955W/m-K. The coefficient of linear expansion=7.89*10-6℃, and specific heat=0.612cal/g-℃. The modulus of elasticity of titanium alloy is low.The modulus of elasticity of TC4, E=110GPa, is about 1/2 of that of steel, so the titanium alloy is prone to deformation during machining.TC4(Ti-6Al-4V) and TA7(Ti-5Al-2.5Sn) titanium alloys, which have been surface-modified using two injection schemes, have been tested to show that titanium alloys, which have been subjected to ionic injection, have improved the micro-hardness and have significantly lowered the sliding friction coefficient, and effectively improved the wear resistance. In order to explore the mechanism of modification, X-ray photoelectron spectroscopy (XPS) analysis of the injected and uninjected samples was carried out, and satisfactory results were obtained.TC4 titanium alloy has a series of advantages such as excellent corrosion resistance, small density, high specific strength and good toughness and weldability, and has been successfully applied in aerospace, petrochemical, shipbuilding, automotive, mold, medicine and other sectors.

Titanium alloy Ti-662: poor stamping, good thermoplasticity. East can be various forms of welding, welded joint strength up to 90% of the strength of the base metal. Machinability is the same as T alloy. Good corrosion resistance. Thermal stability is good, heat treatment effect is significant, hardenability is good to do 450 ℃ below the long-term work of the parts.