600℃ high-temperature Titanium Alloy, flame-retardant titanium alloy, TiAl alloy, SiCf/Ti composite materials are new high-performance high-temperature titanium alloys, compared with ordinary titanium alloys, their technical maturity is relatively low. For the service characteristics and design requirements of advanced engines, especially for high-temperature environment of the rotating parts, need to carry out a large number of engineering applications, such as high-temperature environment creep-fatigue-environmental interaction, flame retardant properties, microstructure on the fatigue performance of the impact of the surface integrity of the technology, forgings and parts of the analysis of internal and surface residual stresses and their impact on the use of performance, service life prediction and failure analysis, etc., to solve the design of materials related to high temperature titanium alloys. Solve the key technologies of material design, manufacturing and processing technology related to engineering application.
Industrial ingot composition purification and homogenization control technology
TA29, TB12 and TiAl alloys have complex alloying, high content of alloying elements and low plasticity, which makes the preparation of such alloy ingots difficult, mainly in the following aspects: easy to crack due to solidification thermal stress when expanding the ingot, difficult to control the homogeneity of the composition, and easy to produce segregation. Using the traditional vacuum self-consumption electrode arc furnace melting process, should be appropriate to increase the number of times of melting, and control the melting current, shrinkage current, ingot size, crucible cooling mode. For TiAl alloy, plasma cold-bed melting process can be used to produce ingots. The cold hearth melting process can effectively remove inclusions and improve the composition of segregation, which is particularly important for the engine key rotating parts with titanium alloy materials. China has more than one plasma cold-bed melting equipment, with laboratory research, industrialized production capacity and conditions.
Large-size bars and special forgings preparation technology
Aviation forgings of titanium alloy materials are generally used bar, wheel, magazine, the whole blade, fan blades and other large forgings are generally used large-size bar, for small compressor blades, turbine blade forgings, the use of small-size bar. With the advanced engine tends to use the whole leaf disk, the whole leaf ring structure form, the corresponding forging and bar size increase, control the organization of large-size bar uniformity is very important to ensure the quality of forgings, the need to choose the right forging equipment, optimize the design of the forging process. For TB12 and TiAl alloy ingots, due to the cast metal forging deformation resistance, process plasticity is low, sensitive to the deformation temperature, easy to forging cracks, ingots should be used in high-temperature extrusion billet process for the preparation of large-size rods, not only to improve the deformation uniformity, to ensure that there is enough deformation, but also improve the production efficiency of the rods and the stability of the batch.
The microstructure and crystallographic structure of titanium alloys are the main factors affecting the mechanical properties, due to the anisotropy of the α phase. Controlling the morphology of the microstructure of forgings and the homogeneity of microstructure and texture can not only improve the average level of performance, but also improve the creep-fatigue interaction performance of parts, i.e., load-bearing fatigue performance, and reduce the dispersion of performance data of different batches of parts. For these new high-temperature titanium alloys, especially TiAl alloys, the introduction of ordered structure makes the weaving problem more complicated and important, and the influence on the high and low circumferential fatigue performance and load-holding fatigue performance is also more complicated. In the preparation of bars and forgings, the organization and structure should be strictly controlled.
The whole leaf disk and the whole leaf ring parts machining technology
Due to the continuous improvement of the performance level of advanced engines, the whole leaf disk, the whole leaf ring has become the development trend. Integral disc blade structure is complex, poor channel openness, thin blade, bending and twisting, poor rigidity, easy to deform, the design of its geometric accuracy level, the level of comprehensive quality requirements are becoming increasingly high, machining and surface integrity of the guarantee has become more and more difficult. For the smaller blade size of the whole compressor blade disk and the whole leaf ring, leaf generally use high-speed CNC milling method processing, control parts processing deformation, vibration finishing stress relief technology to improve the parts surface residual stress distribution, after the blade part of the surface grinding and abrasive grain flow polishing, leaf size precision, leaf error is less than 0.1mm, blade surface roughness Ra to reach 0.2μm level, to improve the surface of parts. The surface roughness Ra of the blade reaches the level of 0.2μm, which improves the surface quality and surface integrity of the parts. Electrochemical methods should be used to process the profile of TiAl alloy blade.
Material performance evaluation and application design technology
The above four types of materials are still in the engineering research and trial stage, and the accumulated performance data are not sufficient, which affects the design selection and strength calculation of materials and components. Compared with ordinary titanium alloys, these four types of high-temperature titanium alloys have lower plasticity, fracture toughness, impact toughness, large notch sensitivity, and poorer ability to reduce the stress at the tip of the crack through local plastic deformation. Especially TiAl alloys, with a fairly low room temperature tensile plasticity and fatigue crack extension resistance, but in close to 700 ℃ will significantly improve, and the initial creep deformation rate is large. According to the characteristics of such materials, design and develop scientific and reasonable technical specifications, play the thermal strength at the same time, should ensure that there is enough plasticity, pay full attention to the fracture properties of the parts. Engine design selection and strength calculation, need to establish a complete material design performance database. For the low plasticity of TiAl alloy, should be based on the material properties, to determine a reasonable component design and life-span method, as well as cost-effective supply chain. Reasonably control the design stress level of TiAl alloy structures to avoid significant stress concentrations and improve surface integrity. It is also important to scientifically evaluate the flame retardant properties of these titanium alloys. In addition, regardless of the integral leaf disk or integral leaf ring, when used at high temperatures, there is a temperature gradient on the same part, one part of the material will constrain the deformation of the other part of the material, which will cause thermal stresses under the action of the temperature gradient, affecting the fatigue performance of the component and the reliability of the use of the component.
