Titanium alloy has been widely used in aviation, weapon equipment, naval ships and some light artillery because of its high strength, non-magnetic, good medium temperature, good weldability and corrosion resistance. In recent years, great progress has been made in the application of titanium alloy technology in China. At the same time, there are still some problems to be further studied. It is hoped that there will be greater breakthroughs in the field of processing technology in the future.
Titanium alloys have the characteristics of high temperature resistance, good weldability, high specific strength, easy processing and forming, and have been widely used in aerospace and aerospace fields. In addition, because of its unparalleled corrosion resistance of other materials, it has also been widely used in the ocean and industrial atmosphere. However, titanium alloy has some shortcomings, such as poor formability in cutting, which restricts its application to a certain extent.
CHARACTERISTICS OF TITANIUM ALLOY MATERIALS
Titanium alloys are not only steel in strength, but also light in weight, good corrosion resistance and good thermal stability. In addition to being widely used in aerospace and aerospace fields, titanium alloys are also widely used in biopharmaceutical and petrochemical industries. Titanium alloys have different properties and uses because of their different composition and structure.
(1) Characteristics of Titanium Alloys
Some alloying elements are added to titanium. According to the characteristics of the formed titanium alloys, titanium alloys are usually divided into the following categories:
(1) Alpha phase titanium alloy. This kind of titanium alloy is an alloy with close-packed hexagonal lattice structure. It has strong toughness and strength, and has strong oxidation resistance at high temperature. Its disadvantage is that its formability is poor and it can only be used in high temperature environment.
(2) Titanium alloy with beta phase. This kind of titanium alloy is a body-centered cubic structure alloy with good formability, but it is easy to be damaged in the case of contamination, so its application is not much. It needs to reach a certain aging before its strength can be improved.
(3) Alpha+beta phase alloys. This kind of titanium alloy has good room temperature strength and is easy to form, but its thermal strength is not ideal. After heat treatment and strengthening, it is suitable for parts with high strength requirements. It is not only used in large quantities, but also widely used.
Titanium alloys have good properties at both high and low temperatures, so they can be used in a wide range of applications. It has low density and high strength, so its specific strength is higher. At the same time, titanium alloys have good corrosion resistance in sea water, atmosphere or acidity and alkalinity conditions, which makes titanium alloys become the best choice of corrosion resistant materials in many metal materials. However, its thermal conductivity will be low, and it is generally applicable to all kinds of insulation components.
Titanium alloys also have some disadvantages. That is to say, it lacks good wear resistance, so it is impossible to make some moving parts. The modulus of elasticity is relatively low and lower than that of magnesium and aluminium. Its processing and manufacturing process is more complex, and its production cost will be higher.
- Cutting of Titanium Alloys
Titanium alloys contain a variety of alloying elements, including some high activation energy elements, which are relatively stable in the alloy, so titanium alloys have great energy in plastic deformation, but also have a certain degree of workability. However, the thermal conductivity of titanium alloys is poor. In cutting process, the cutting heat gathers on the tool, unlike in aluminum cutting process, the cutting heat is taken away by chips. As a result, the thermal load of titanium alloy material is large and the cutting tool is damaged. Therefore, the common method to improve production efficiency by increasing the amount of removal per unit time is not suitable for the processing of titanium alloy materials. Therefore, suitable processing methods should be selected for different titanium alloy materials.
(1) Titanium alloys have high strength, toughness and hardness, so the hardening problem in cutting is serious, which needs to be treated with annealing. Especially when there are scratches or notches on the workpiece surface, because they are very sensitive to deformation speed, they are prone to scratches or cracks in the cutting process, so the processing speed must be controlled in order to proceed at a low speed.
(2) In general, titanium alloys have good thermal stability and high temperature resistance. Compared with aluminium alloys, the strength of titanium alloys is much higher. In cutting process, the thermal conductivity of titanium alloy is very low, which is equivalent to a small part of iron and aluminium materials. Its heat is concentrated on the cutting edge. When the temperature exceeds a certain standard, it will produce high chemical activity and react with oxygen and hydrogen in the air, thus reducing its plasticity, and worsening tool wear when it contacts with the cutter face and chips.
(3) In cutting, because there is a certain friction between titanium alloy and cutting tool, with the increase of friction speed, the temperature will be higher, the power will be higher, the tool wear will be faster, and it is easy to bond, thus greatly shortening the service life of the cutting tool. Therefore, the rational selection of cutting tools is also very important. Usually, some cemented carbide materials such as tungsten cobalt cemented carbide tools are selected. This can effectively prevent the generation of bad stress in the process of processing and ensure the processing accuracy of components.
These characteristics of titanium alloy in the cutting process make it very difficult to cut, resulting in lower production efficiency and higher production cost. Therefore, in order to improve the processing quality of titanium alloy, it is necessary to constantly improve the processing plan and adjust the reasonable processing parameters in the cutting process of titanium alloy.
- Welding Processing of Titanium Alloys
In recent years, in addition to some traditional titanium alloy processing technology, there are also some new processing methods, such as low temperature cutting, laser, ultrasonic and electromagnetic cutting. Especially with the development of welding technology, the processing and application of titanium alloys are more extensive. Because of the physical and chemical characteristics of titanium alloy, the weld is easily oxidized and nitrided, which results in pollution, and the joint is sensitive to embrittlement. Therefore, it is a great challenge to weld titanium alloy.
(1) Tungsten Argon Arc Welding
Tungsten Argon Arc Welding is the most common method in Titanium Alloy welding. Under the protection of argon, tungsten pole acts as the electrode and the weld metal is well protected. However, this welding method has low welding production efficiency, large post-weld structural deformation, coarse grain size of welded joint and poor protection, which will seriously affect the welding process. Weld quality. It is only suitable for thin plate welding or bottom welding.
(2) Laser welding is a high energy density welding method. Using this method to weld titanium alloy can not only reduce the defects of traditional processing technology, but also effectively refine the microstructures and grains of the weld and improve the performance of the weld. However, the power of this welding method is small, the laser beam absorbed by the welded workpiece surface is very low, and there are some threshold problems. It is only suitable for special materials or special requirements for processing structure, and is limited to the processing of small and precise parts, so it is more difficult than traditional processing technology.
(3) Friction stir welding (FSW) is a better technology among many new plastic joining processes. When friction stir welding is used, because of the low heating temperature, the defects in the weld zone are the least, and the structure and properties of the joints are good, so the effective welding of titanium alloys can be realized. However, this method has high requirements on the mixer head and its material, and has no good adaptability, and the process is not mature, so it can only be used in the welding of simple components.
(4) Electron beam welding (EBW) is characterized by high welding energy, strong penetration, large depth-width ratio of welds, isolation of atmospheric pollution and good performance of welded joints, which can realize the welding of titanium alloy thick plates. However, this method requires to be carried out in vacuum, limited by the size and shape of the parts processed, can not be produced in batches, and the requirements for equipment are also very high, the production cost is high, which limits its application scope.
(5) Laser-arc hybrid welding is a good welding technology for titanium alloys. It combines the advantages of laser welding and arc welding, with concentrated energy density, stable arc and good weld performance. However, its welding process parameters are too many to be controlled effectively, and its operation process is too complex, so it is only in the research stage at present.
For the welding process of titanium alloy, no matter which new technology or new method, there are some advantages and disadvantages to some extent. With the extensive application of titanium alloy materials in many fields, new welding processes and methods need to be continuously studied to improve the quality of welds and welding production efficiency, to ensure the welding quality of titanium alloy structural parts and meet the requirements of use.
Nowadays, titanium alloys have been widely used for their unique excellent properties, so the processing technology of titanium alloys has become a hot research topic. Compared with some advanced countries, China still has a certain gap in titanium alloy materials and processing technology. With the rapid development of modern technology, the application field of titanium alloy is also expanding year by year. This requires us to strengthen the optimization and innovation of processing technology, and constantly accumulate technical experience. It is of great significance for our country to make full use of titanium alloy materials by high quality products to meet the application requirements in various fields.