What Kind Of Substance Is Titanium?

Titanium alloys can be divided into three categories according to their organisation . (1 Titanium with elements of aluminium and tin.2 Titanium with alloying elements such as aluminium chromium molybdenum and vanadium.3 Titanium with elements such as aluminium and vanadium.) Titanium alloy has high strength and low density, good mechanical properties, toughness and corrosion resistance is very good. In addition: titanium alloy process performance is poor, cutting and processing difficulties. In thermal processing, very easy to absorb hydrogen, oxygen, nitrogen, carbon and other impurities. There is also poor wear resistance, the production process is complex. titanium alloys to titanium-based alloys composed of other elements. The industrial production of titanium started in 1948. The development of the aviation industry needs, so that the titanium industry to an average annual growth rate of about 8 per cent. At present, the world's annual output of titanium alloy processing materials has reached more than 40,000 tonnes of titanium alloy grades nearly 30 kinds. The most widely used titanium alloy is Ti-6Al-4V (TC4), Ti-5Al-2.5Sn (TA7) and industrial pure titanium (TA1, TA2 and TA3). Titanium alloys are mainly used to make aircraft engine compressor parts, followed by structural parts for rockets, missiles and high-speed aircraft.In the mid-1960s, titanium and its alloys have been used in general industrial applications to make electrodes for the electrolysis industry, condensers for power stations, heaters for petroleum refineries and seawater desalination as well as environmental pollution control devices. Titanium and its alloys have become a corrosion-resistant structural material. It is also used to produce hydrogen storage materials and shape memory alloys. China began research on titanium and titanium alloys in 1956; industrial production of titanium began in the mid-1960s and the TB2 alloy was developed. Characteristics Compared with other metal materials, titanium alloys have the following advantages: ① high specific strength (tensile strength / density) (see chart), tensile strength of up to 100 ~ 140kgf/mm2, while the density of only 60% of steel. ② good strength at medium temperature, the use of temperature than the aluminium alloy a few hundred degrees higher, in the middle of the temperature can still maintain the required strength, can be in the temperature of 450-500 ℃ long-term work. ③ good corrosion resistance, the surface of titanium in the atmosphere immediately form a uniform and dense oxide film, the ability to resist a variety of media erosion. Usually titanium has good corrosion resistance in oxidising and neutral media, and the corrosion resistance in seawater, wet chlorine gas and chloride solution is even better. But in reducing media, such as hydrochloric acid and other solutions, titanium's corrosion resistance is poor. ④ good low-temperature performance, very low gap element titanium alloy, such as TA7, in -253 ℃ can maintain a certain degree of plasticity. ⑤ Low modulus of elasticity, small thermal conductivity, non-ferromagnetic. Alloying elements Titanium has two kinds of homogeneous and heterogeneous crystals: α-titanium with dense hexagonal structure below 882℃, and β-titanium with body-centred cubic structure above 882℃. Alloying elements according to their effect on the phase transition temperature can be divided into three categories: ① stabilisation of the α-phase, to increase the phase transition temperature of the elements for the α-stabilising elements, aluminium, carbon, oxygen and nitrogen and so on. Aluminium is the main alloying element of titanium alloy, which has obvious effects on improving the strength of the alloy at room temperature and high temperature, reducing specific gravity and increasing elastic modulus. ② Stabilisation of β-phase, reduce the phase transition temperature of the elements for the β-stabilising elements, and can be divided into homocrystalline and eutectic type two. The former has molybdenum, niobium, vanadium, etc.; the latter has chromium, manganese, copper, iron, silicon, etc.. ③ The elements that have little effect on the phase transition temperature are neutral elements, such as zirconium and tin. Oxygen, nitrogen, carbon and hydrogen are the main impurities in titanium alloys. Oxygen and nitrogen in the α-phase has a greater solubility, titanium alloy has a significant strengthening effect, but the plasticity is reduced. It is usually stipulated that the content of oxygen and nitrogen in titanium is 0.15-0.2% and 0.04-0.05% respectively. Hydrogen in the α-phase solubility is very small, titanium alloys dissolved in excess of hydrogen will produce hydride, so that the alloy becomes brittle. Normally, the hydrogen content in titanium alloys is controlled to be less than 0.015%. The dissolution of hydrogen in titanium is reversible and can be removed by vacuum annealing. Categories Titanium alloys can be divided into three categories according to the composition of the phase: α-alloys, (α + β) alloys and β-alloys, which are expressed as TA, TC and TB in China respectively. ① α-alloys contain a certain amount of stable α-phase elements, the equilibrium state is mainly composed of α-phase. α-alloys have a small specific gravity, good heat strength, good weldability and excellent corrosion resistance, the disadvantage of room temperature strength is low, usually used as a heat-resistant materials and corrosion-resistant materials. α-alloys can be divided into full-α-alloys (TA7), near-α-alloys (Ti-8Al-1Mo-1V) and a small number of compounds of the α-alloys (Ti-2.0%) and α-alloys (Ti-2.4%). (Ti-2.5Cu). ② (α + β) alloys contain a certain amount of elements that stabilise the α and β phases, and in equilibrium the alloy is organised in the α and β phases. (α + β) alloy has medium strength, and can be heat-treated to strengthen, but the welding performance is poor. (α + β) alloys are widely used, of which the production of Ti-6Al-4V alloy in all of the titanium material accounted for more than half. ③ β alloy contains a large number of stable β phase elements, can be high temperature β phase all retained to room temperature. β alloys can be divided into heat-treatable β alloys (sub-stable β alloys and near-sub-stable β alloys) and heat stabilised β alloys. Heat-treatable β-alloys have excellent plasticity in the quenched condition and can be aged to a tensile strength of 130-140 kgf/mm2. β-alloys are usually used as high-strength, high-toughness materials. The disadvantage is that the ratio of large, high cost, poor welding performance, cutting and processing difficulties. Titanium alloys can be divided into heat-resistant alloys, high-strength alloys, corrosion-resistant alloys (titanium - molybdenum, titanium - palladium alloys, etc.), low-temperature alloys, as well as special function alloys (titanium - iron hydrogen storage materials and titanium - nickel memory alloys) and so on. The composition and properties of typical alloys are shown in the table. Heat treatment Titanium alloys can obtain different phase compositions and organisations by adjusting the heat treatment process. It is generally believed that fine isometric organisation has better plasticity, thermal stability and fatigue strength; needle-like organisation has higher endurance strength, creep strength and fracture toughness; mixed isometric and needle-like organisation has better overall performance. Commonly used heat treatment methods are annealing, solution and aging treatment. Annealing is to eliminate internal stresses, improve plasticity and organisational stability, in order to obtain a better overall performance. Usually α alloy and (α + β) alloy annealing temperature selected in (α + β) - → β phase transition point below 120 ~ 200 ℃; solution and aging treatment is from the high temperature region of the fast cooling, in order to get the martensite α ′ phase and the sub-stable β phase, and then in the medium temperature region to keep warm so that the decomposition of these sub-stable phases, to get the α phase or compounds such as fine dispersion of the second phase of the point, so as to make the alloy to strengthen the purpose. Usually (α + β) alloy quenching in (α + β) - → β phase transition point below 40 ~ 100 ℃, sub-stable β alloy quenching in (α + β) - → β phase transition point above 40 ~ 80 ℃. The aging treatment temperature is generally 450～550℃. In addition, in order to meet the special requirements of the workpiece, the industry also uses double annealing, isothermal annealing, β heat treatment, deformation heat treatment and other metal heat treatment processes.