One. Properties of titanium
Titanium has a very similar appearance to steel, with a density of 4.51 g/cm 3, less than 60% of steel, making it the least dense metallic element in refractory metals.
Titanium is very stable in air at room temperature.When heated to 400 ~ 550℃, a strong oxidation film is formed on the surface to protect against further oxidation.Titanium has a strong ability to absorb oxygen, nitrogen and hydrogen. This kind of gas is a very harmful impurity to the metal titanium. Even a small amount (0.01% ~ 0.005%) can seriously affect its mechanical properties.
The mechanical properties of titanium, also known as mechanical properties, are closely related to purity.High purity titanium has excellent machining performance, good elongation, reduction of section, but low strength, not suitable for structural materials.Industrial pure titanium contains appropriate impurities, has high strength and plasticity, suitable for making structural materials.
Among the titanium compounds, titanium dioxide (TiO2) has the most practical value.Ti02 is inert and non-toxic to human body. It has a series of excellent optical properties.Ti02 is opaque, high gloss and whiteness, high refractive index and scattering power, strong hiding power, good dispersion, the pigment made of white powder, commonly known as titanium white, widely used.
Two. Application of titanium
1.Application of titanium and its titanium alloy
Because of its light weight and higher strength than aluminum alloy, dense metal titanium is highly valued by the aviation industry for its ability to maintain higher strength than aluminum at high temperatures.In view of the fact that the density of titanium is 57% of that of steel, its specific strength (strength/weight ratio or strength/density ratio are called specific strength) is high, corrosion resistance, oxidation resistance, fatigue resistance are strong, 3/4 of titanium alloy is used as structural material represented by aviation structure alloy, 1/4 is mainly used as corrosion resistance alloy.
Titanium alloy has low strength and high plasticity, medium strength and high strength, 200(low strength) ~ 1300(high strength) mpa, but generally can be regarded as high strength alloy titanium alloy.They are stronger than aluminum alloys, which are considered medium strength, and are strong enough to replace some types of steel.Compared with aluminum alloy, the strength of some titanium alloys can maintain good strength at 600℃.
In addition to strength, according to the use can also be divided into heat, corrosion resistance, low temperature and special functions (such as TiNi shape memory alloy, TiFe hydrogen storage alloy) and other titanium alloys, according to the phase composition can be divided into four types, such as thick, thick and near thick, metastable.Up to now, more than 100 alloy grades have been put into production.Among them, ti-6al-4v, which is used as structural alloy, occupies a dominant position in the whole sales market of titanium alloy, accounting for 60%, followed by ti-5al-2.5sn, whose long-term working temperature can reach 500℃(strength is 780 ~ 980 mpa).
However, there are two main factors that prevent this resource-rich element from becoming a common metal.The first is cost.According to the market price in the United States, us $8 to us $12 per pound (1 pound = 0.45kg) of titanium ingots, us $1.00 to us $1.30 per pound of aluminum ingots and us $0.20 to us $0.40 per pound of carbon steel.But the main factor is that titanium itself is extremely reactive and difficult to handle.Furnace atmosphere must be strictly controlled, welding must be carried out in inert atmosphere.The activity of metal titanium is high, the thermal conductivity is low, the deformation resistance is big, the normal temperature plasticity is poor, in the deformation process not only easy and the mold bond, especially in the machining tool and abrasive bond to the hot processing surface of the tendency, so that the standard structural parts of the manufacture of a large number of scrap titanium, the so-called residual titanium.Generally forged titanium ingots produce 70% residual titanium, sometimes as high as 90%.
In order to reduce the burden caused by excessive cost, on the one hand, the residual titanium treatment technology has been developed, on the other hand, the near-net forming, superplastic forming, precision casting and powder metallurgy, as well as thermal isostatic pressure and diffusion connection and other high and new technologies have been developed.For example, powder metallurgy products processed by powder making, molding, sintering or hot isostatic consolidation are nearly net formed parts, with material utilization rate up to 80%, which not only reduces material consumption, but also significantly reduces the amount of cutting.Another example is the application of large thin-wall precision casting technology in titanium alloy, which makes the performance of titanium casting close to that of titanium forging, and reduces the cost by about 50%.
The main consumption area of titanium and titanium alloys is the aviation industry first.In the 1980s, titanium accounted for 74.8% of the total use of titanium in the us aviation industry, Russia and Britain were also mainly used in the aviation industry, and 90% of the titanium in Japan was used in civil industry.In recent years, the application of titanium in non-aerospace industry is increasing, and aerospace still occupies the "main" position.Ever since 1952, when titanium was used as an engine pod and bulkhead on Douglas dc-7, many aircraft structures have been made of titanium.Titanium components are critical to Boeing 757, supersonic sr-71 blackbird, f-22 fighter jets, space satellites and missiles.Such as the aircraft fan disc, engine blades are made of titanium casting and forging.
The second application of titanium is related to its corrosion resistance.The largest dosage is for the production of chlorine - alkali electrode materials.The service life of the titanium anode is 10 times that of the graphite anode, which increases the production capacity by nearly one time and saves power by 15%.Annual output of 10,000 tons caustic soda, about 5 tons of titanium.
Titanium had its glory days in shipbuilding.Each of the six to seven 3,000-ton nuclear submarines built by the former Soviet union used up to 560 tons of titanium (its alpha-class submarines used more than 908 tons).In recent years, titanium has shown great power in offshore oil and gas exploration and development. From 1997 to 1999 alone, Europe invested $15 billion in north sea oil and gas development, building 21 floating production vessels and 64 platforms.A new platform requires 50 to 500 tons of titanium for life safety systems, 50 to 100 tons of titanium for wedge stress joints, 400 to 1,200 tons of titanium for telescopic lifters, and 1,400 to 4,200 tons of titanium for fixed lifters.
In the energy industry, it is known to use titanium as the condenser and heat exchanger for power generation devices. For example, the generator sets of taizhou power plant, Shanghai jinshan thermal power plant and zhenhai power plant all use titanium tube condenser, with a volume of about 700 tons of titanium.Both qinshan and daya bay nuclear power plants use all-titanium condensers.In recent years, in geothermal development of geothermal Wells, titanium has also demonstrated its ability to resist corrosion.In the hot and corrosive environment of geothermal brine, other materials have to be replaced by titanium because of their short life.The advantage of using titanium is that it can increase the productivity of heat recovery and the life of geothermal Wells.Since the 1990s, the United States has drilled a geothermal well with a temperature of up to 300℃ in the Salton Sea area of southern California, and has used 227 tons of ti-6al-4v-0.1ru alloy hot-rolled seamless tubes.It is estimated that the amount of titanium used in geothermal development worldwide could reach 2,400 tons in the next decade.If the yangbajing power station in Tibet USES titanium, its appearance will be greatly improved.
Golf, biomaterials and automotive manufacturing are three promising new applications of titanium.
In sports and recreation, the use of golf tools has grown dramatically, from titanium, which did not enter the field in 1993, to 4, 000 tons in 1997.This is due to the high strength and light weight of the titanium bat and the average distance of the bat increased by 20-30 yards (1 yard =0.9144 m) or 15%.The advent of titanium bats led to the addition of 448 new pitches in the United States in 1998.The number of players is 25m (nearly half the world's total).Only 500 bats were sold in 1994, which rose to 190,000 in 1995 and jumped to 1.72 million in 1997.Titanium is useful in recreational sports, such as snowboarding, sledding, ice axes, crampons and other climbing facilities.
Titanium has excellent biocompatibility, low coefficient of expansion, high durability and non-magnetic properties, making it an excellent bone support material.The hip implant weighs about half as much as stainless steel, and the bone tissue sticks directly to the titanium implant as it grows.Titanium alloy is also used in knee joint and denture reconstruction.According to statistics, the amount of titanium used in medical implants worldwide is between 600 and 1000 tons per year.
The production of low-cost titanium and the development of titanium powder processing technology have made it possible to extend the application of titanium to the automotive industry.Titanium springs are already being used in formula one cars, racing motorcycles and, most recently, ferraris.
TiFe, made from ilmanite concentrate, is a deoxidizer and stabilizer used in the manufacture of stainless steel. The titanium-iron hydrogen storage anode has different properties from the rare earth hydrogen storage materials in the manufacture of hydrogen storage battery, but the cost is relatively low. It will have a fight with the rare earth in hydrogen storage, transportation, catalysis, fuel cell and other aspects.Ti-ni shape memory alloy is an indispensable high-tech material for medical and military applications.The applications of electronic ceramic functional materials such as barium titanate, strontium titanate, titanium compound catalyst, organic titanium heat resistant paint and titanium epoxy coating are enumerated.