In the field of turbine engines, titanium alloys in turbine engines are widely used in different key components due to their unique performance advantages to meet the requirements of complex and harsh working conditions. The following will introduce in detail the application of titanium alloys in components such as turbine disks, turbine blades, guide vanes, and combustion chambers, and explore the development trends and new technologies of high-temperature alloys.
1. High-temperature titanium alloys for turbine disks
The turbine disk is subjected to uneven heat loads during operation, and the temperature of the rim of the disk is higher than that of the center, resulting in greater thermal stress. In addition, the tenon part is subjected to the greatest centrifugal force, and the stress situation is more complicated. Therefore, there are strict requirements for turbine disk materials: the alloy must have high yield strength and creep strength; have good cold and hot and mechanical fatigue resistance; have a small linear expansion coefficient, no notch sensitivity, and have high low-cycle fatigue performance. High-temperature titanium alloys have become an ideal choice for turbine disk materials due to their excellent performance, which can ensure that the turbine disk operates stably and reliably under high temperature and high stress environments.
2. High-temperature titanium alloys for turbine blades
The turbine blades are one of the most critical components on titanium alloys in turbine engines. Although its operating temperature is slightly lower than that of the guide blade, the force is large and complex, and the working conditions are extremely harsh. Therefore, the following requirements are placed on the material of the turbine blade: high oxidation resistance and corrosion resistance; high creep resistance and long-lasting fracture resistance; good mechanical fatigue and thermal fatigue performance, as well as good high-temperature and medium-temperature comprehensive performance. High-temperature titanium alloys can meet these stringent requirements, ensure the normal operation of turbine blades under complex working conditions, and extend the service life of blades.
3. High-temperature titanium alloys for guide blades
The first stage of the guide blade is one of the parts on the turbine engine that is most subject to thermal shock. However, since it is a stationary part, the mechanical load it is subjected to is relatively small. However, in actual work, the guide blades often fail due to distortion caused by stress, cracks caused by drastic temperature changes, and burns caused by overburning. According to the working conditions of the guide blades, the material is required to have the following properties: sufficient lasting strength and good thermal fatigue performance; high oxidation resistance and corrosion resistance; if a casting alloy is used, it is required to have good casting performance. High-temperature titanium alloys and related casting technologies can meet the material performance requirements of the guide blades and improve the reliability and service life of the guide blades.
4. High-temperature alloys for combustion chambers
Due to the complex structure of gas turbines, the temperature and stress conditions of various parts vary greatly. The mechanical stress of the combustion chamber is small, but the thermal stress is large. The main requirements for combustion chamber materials are: high-temperature oxidation resistance and gas corrosion resistance; sufficient instantaneous and lasting strength; good cold and hot fatigue performance, good process plasticity (lasting, bending performance) and welding performance; long-term structural stability of the alloy at working temperature. By selecting suitable high-temperature alloys, it is possible to ensure that the combustion chamber works stably in a high-temperature environment and reduce failures caused by material problems.
5. Development trend and new technology of high-temperature alloys
In order to meet the needs of the new generation of gas turbines for high-performance materials, in addition to the continuous development of directional solidification casting technology and single crystal casting technology, powder high-temperature titanium alloy technology and new high-temperature oxidation resistance and gas erosion resistance protective coating technology have also been widely used.
(I) Powder high-temperature alloy technology
FGH51 powder high-temperature alloy is a phase precipitation-strengthened nickel-based high-temperature alloy prepared by powder metallurgy. The volume fraction of the γ phase of the alloy is about 5%, and the atomic fraction of its forming elements is about 50%. The manufacturing process of alloy discs is to use vacuum induction melting to make the master alloy, then atomize to make pre-alloyed powder, and then make the part blank. Compared with similar cast and forged high-temperature alloys, it has the advantages of uniform structure, fine grains, high yield and good fatigue performance. It is the highest strength level of high-temperature alloy under the current working conditions of 650℃. This kind of high-temperature alloy is mainly used for rotating parts of high-performance engines, such as turbine discs and bearing rings, which can significantly improve the performance and reliability of engine rotating parts.
(II) New coating technology
To increase the operating temperature of gas turbine turbine blade parts and extend their life, stringent requirements are placed on protective coatings, especially coatings that work under possible thermal corrosion conditions. Traditional diffusion aluminide coatings and aluminum-silicon coatings can no longer meet the working requirements of high-pressure turbine blades to resist high-temperature oxidation and high-temperature gas high-speed erosion, and can only be used to protect the surface of low-pressure turbine guide vanes and rectifier struts.
At present, two new types of coatings - plasma sprayed CoCrAlSiY/ZrO₂ gradient coatings and electron beam CoCrAlSiY/ZrO₂ gradient coatings have been applied on gas turbine turbine blades.
Plasma sprayed CoCrAlSiY/ZrO₂ gradient coating: This coating is a gradient distribution of coating composition, with the ZrO₂ content gradually increasing and the CoCrAlSiY content gradually decreasing along the thickness direction from the high-temperature alloy substrate to the coating surface. There is no obvious composition mutation between the gradient coating layers, and the organization changes continuously, which greatly improves the bonding strength between the coating and the substrate. The maximum thickness of this coating can reach 180μm, which can reduce the operating temperature by 100-150℃, effectively protect the turbine blades and increase their service life.
Electron beam CoCrAlSiY/ZrO₂ gradient coating: This coating is made by preparing a target material of a certain diameter. When the electron beam shoots the target material, the metal Zr and Y atoms are formed on the surface of the CoCrAlY coating into a ZrO₂ coating that is stable in Y₂O₃ by evaporating the elements in the target material and continuously supplying oxygen in the vacuum chamber. The change in coating composition is adjusted by controlling the power of the electron beam spraying equipment. The maximum thickness of this coating can reach 120μm, which can also meet the working conditions of turbine blades, increase the bonding strength between the coating and the blade substrate, and improve the service life of the blade.
The application of titanium alloys in turbine engines and the development of new technologies related to high-temperature alloys have provided important support for the improvement of turbine engine performance and reliability, and promoted technological progress in fields such as aviation and energy.
