Titanium is a two-phase alloy, has a good overall performance, good organizational stability, good toughness, ductility and high temperature deformation properties, can better thermal pressure processing, can be quenched, aging of the alloy strengthening. Strength after the heat treatment higher than the annealed state of about 50% to 100%; high temperature strength, long-term work at a temperature of 400 ℃ ~ 500 ℃, the thermal stability is inferior α titanium alloy.
The most commonly used three kinds of titanium alloy is α and α + β titanium alloy; α titanium tube stock machinability best, α + β titanium followed, β titanium worst. α titanium codenamed TA, β titanium codenamed TB, α + β titanium codenamed TC.
Titanium can be divided according to use heat-resistant alloys, high-strength alloys, corrosion resistant alloy (Ti - molybdenum, titanium - palladium alloys, etc.), low alloy and alloy special features. Table typical composition and performance of the alloy.
Titanium heat treatment can be obtained by adjusting the heat treatment process and the organization of different phases. Generally considered fine equiaxed has good ductility, thermal stability and fatigue strength; needle tissue has a high rupture strength, creep strength and fracture toughness; equiaxed and needle hybrid organization has good overall performance.
Performance
Titanium is a new type of metal, and the performance of the carbon-containing titanium impurity content of nitrogen, hydrogen, oxygen and so on, the most pure titanium plate iodide impurity content not exceeding 0.1%, but its low strength, high ductility. 99.5% of the performance of industrial pure titanium as: density ρ = 4.5g / cc, a melting point of 1725 ℃, thermal conductivity λ = 15.24W / (mK), the tensile strength σb = 539MPa, elongation δ = 25%, section shrinkage ψ = 25%, the elastic modulus E = 1.078 × 105MPa, the hardness HB195.
High strength
Density of titanium alloys is generally about 4.51g / cc,
Only 60% of steel, titanium density was close to the density of ordinary steel, some high-strength titanium alloy over the strength of the many structural steel. Therefore, the ratio of titanium strength (strength / density) is much larger than other metal structural materials, see Table 7-1, the unit can be made out of high strength, rigidity and lightweight components. Aircraft engine components, skeleton, skin, so the use of titanium fasteners and landing gear.
High heat intensity
Use temperature several hundred degrees higher than aluminum, at moderate temperatures can still maintain the desired strength, long-term work at a temperature of 450 ~ 500 ℃ of these two types of titanium alloys in the range of 150 ℃ ~ 500 ℃ still very high strength, and aluminum at 150 ℃ decreased significantly when compared strength. Titanium alloy operating temperature up to 500 ℃, the aluminum alloy is below 200 ℃.
Good corrosion resistance
Titanium tubing work in humid atmosphere and seawater, which is far superior corrosion resistance of stainless steel; for pitting, etching, stress corrosion resistance is particularly strong; alkali, chloride, chlorine, organic materials, nitric acid, sulfuric acid etc. have excellent corrosion resistance. However, the corrosion resistance of titanium with a reduction of oxygen and chromium salts medium is poor.
Titanium alloys at low and ultra-low temperature, retains its mechanical properties. Low temperature performance, low interstitial elements of titanium alloys, as TA7, at -253 ℃ still maintain a certain plasticity. Thus, low-temperature titanium alloy is also an important structural materials.
Chemical activity of titanium is large, a strong chemical reaction with atmospheric O, N, H, CO, CO2, water vapor, ammonia and the like. Carbon content greater than 0.2%, it will form a hard TiC in the titanium alloy; at higher temperatures, and also the role of N forms TiN hard surface; at above 600 ℃, the high hardness of hardened layer is formed of titanium absorbs oxygen ; hydrogen content increased, brittle layer will form. Absorbing gas produced brittle surface to a depth of 0.1 ~ 0.15 mm, the degree of hardening of 20% to 30%. Chemical affinity of titanium is also large, easy and sticking friction surface.
Small thermal elasticity
Thermal conductivity of titanium λ = 15.24W / (mK) approximately 1/4 of nickel, iron 1/5, 1/14 aluminum, while the thermal conductivity of various titanium alloys decreased by 50% than the thermal conductivity of titanium. Elastic modulus was about 1/2 of the titanium alloy for steel, so the poor rigidity, deformation, and should not be made thin-walled elongated rod member, the machined surface when cutting a large amount of spring back, the stainless steel is about 2 to 3 times, causing severe tool flank friction, adhesion, adhesive wear.
Purpose Editing
Titanium has a high strength and density and small, good mechanical properties, good toughness and corrosion resistance. In addition, poor process performance titanium mesh, machining difficulties in thermal processing, and very easy to absorb carbon hydrogen nitrogen and other impurities. There are poor abrasion resistance, complex production process. Titanium industrial production was started in 1948. Require the development of the aviation industry, the titanium industry with an average annual growth rate of about 8% of the development. World titanium alloy production reached 40,000 tons, nearly 30 kinds of titanium alloys. The most widely used titanium alloy is Ti-6Al-4V (TC4), Ti-5Al-2.5Sn (TA7) and commercially pure titanium (TA1, TA2 and TA3).
Titanium is mainly used for the production of aircraft engine compressor components, followed by structure rockets, missiles and high-speed aircraft. The mid-1960s, titanium and its alloys have been in general industrial applications, electrodes for electrolysis industry production, power plant condensers, oil refining and desalination heater and environmental pollution control devices. Titanium and its alloys have become a corrosion resistant structural materials. In addition, for the production of hydrogen storage materials and shape memory alloys.
Problems editor
Titanium has a light weight, high strength, good corrosion resistance, etc., it is widely used in the automotive industry, the most widely used titanium alloy automotive engine systems. The use of titanium alloy engine parts has many advantages. [1]
Low density titanium ball valves, can reduce the inertial mass of the moving parts, while a titanium valve spring can increase the free vibration, reduced body vibrations, increase engine speed and output power.
Reducing the inertial mass of the moving parts, so that the friction is also reduced, improving engine fuel efficiency. Select titanium can reduce the load of stress-related components, reduce the size of the parts, so that the quality of the engine and the vehicle is reduced. Reduce inertia mass parts, so that the vibration and noise reduction, improved engine performance. Titanium applied to other member may improve comfort and the aesthetics of personnel cars and the like. Applications in the automotive industry, titanium alloys in terms of energy consumption plays an invaluable role.
Although titanium alloy parts has such superior performance, but from titanium and its alloys widely used in the automotive industry there is a great distance, causes include expensive, good formability and weldability and poor.
The most widely used titanium alloy hinder the automotive industry is still the main reason for the high cost.
Heat editor
Commonly used methods of annealing titanium sheet, solution and aging treatment. Annealing is to eliminate stress, improve plasticity and organizational stability, in order to obtain a better overall performance. Typically α alloys and (α + β) alloy annealing temperature selected in the (α + β) ─ → β phase transition point below 120 ~ 200 ℃; solution and aging treatment is rapid cooling from high temperature zone to obtain martensite α 'phase and the metastable β phase, and then incubated in the temperature region of these metastable phase decomposition to obtain compound α phase or the dispersed second phase particles, achieve the purpose of strengthening the alloy. Typically (α + β) quenching the alloy in (α + β) ─ → β phase transition point of 40 ~ 100 ℃ were metastable β quenched alloy in the (α + β) ─ → β phase transition point above 40 ~ 80 ℃ get on. Aging treatment temperature is generally 450 ~ 550 ℃.
