Key technologies for the design, processing, and use of advanced high-temperature titanium alloy materials!

Release time：2023-07-17 12:26:52 丨 Number of visits：

600 ℃ high-temperature titanium alloy, flame-retardant titanium alloy, TiAl alloy, and SiCf/Ti composite material are new high-performance high-temperature titanium alloys with lower technological maturity compared to ordinary titanium alloy materials. A large amount of engineering application research is needed to address the service characteristics and design requirements of advanced engines, especially for rotating components used in high-temperature environments, such as creep fatigue environment interaction, flame retardancy, the impact of micro texture on fatigue performance, surface integrity technology, analysis of residual stresses inside and on the surface of forgings and parts and their impact on service performance, service life prediction and failure analysis, etc, Solve key technologies such as material design and manufacturing processes related to engineering applications.

High Purification and Homogenization Control Technology for Industrial Ingot Composition

The alloying of TA29, TB12, and TiAl alloys is complex, with high alloying element content and low plasticity. The preparation of ingots for these alloys is difficult, mainly manifested in: cracking is easy to occur due to solidification thermal stress when the ingot mold is expanded, and the control of composition uniformity is difficult, leading to segregation. Adopting the traditional vacuum consumable electrode arc furnace melting process, it is necessary to increase the melting frequency appropriately, and control the melting current, shrinkage current, ingot size, crucible cooling method, etc. For TiAl alloys, the plasma cold furnace bed melting process can be used to produce ingots. The use of cold furnace bed melting process can effectively remove inclusions and improve component segregation, which is particularly important for titanium alloy materials used in key rotating parts of engines. China has multiple plasma cold furnace bed melting equipment, which has the ability and conditions for laboratory research and industrial production.

Preparation Technology for Large Size Bars and Special Forgings

The titanium alloy raw materials used for aviation forgings are generally bars. Large sized bars are generally used for large forgings such as wheel disks, casings, Blisk, fan blades, and small sized bars are used for small compressor blades and turbine blades. As advanced engines tend to adopt the structural form of Blisk and integral bladed ring, the corresponding size of forgings and bars is increased. It is important to control the organizational uniformity of large bars to ensure the quality of forgings. It is necessary to select appropriate forging equipment and optimize the design of forging process. For TB12 and TiAl alloy ingots, due to the high forging deformation resistance, low process plasticity, sensitivity to deformation temperature, and susceptibility to forging cracking of the as cast metal, it is advisable to use high-temperature extrusion and blooming technology to prepare large-sized bars. This not only improves the uniformity of deformation, ensures sufficient deformation, but also improves the production efficiency and batch stability of the bars.

The microstructure and Crystallography texture of titanium alloy are the main factors affecting the mechanical properties, because α Anisotropy of phases. Controlling the morphology of the microstructure of forgings and the uniformity of microstructure and texture can not only improve the average performance level, but also enhance the creep fatigue interaction performance of components, i.e. load holding fatigue performance, and reduce the dispersion of performance data for different batches of components. For these new high-temperature titanium alloys, especially TiAl alloys, due to the introduction of ordered structures, the texture problem is more complex and important, and the impact on high and low cycle fatigue properties and load holding fatigue properties is more complex. Strictly control the microstructure and texture during the preparation of bars and forgings.

Machining technology of Blisk and blisk parts

Due to the continuous improvement of advanced engine performance, Blisk and blisk have become the development trend. The structure of Blisk blades is complex, the channel openness is poor, the blades are thin, the bending and twisting are large, the rigidity is poor, and the deformation is easy. The geometric accuracy level and the comprehensive quality level are required to be higher and higher during the design, and the guarantee of machining and surface integrity becomes more and more difficult [30]. For compressor Blisk and integral bladed ring with small blade size, the blade profile is generally processed by high-speed CNC milling method to control the machining deformation of parts, and the vibration light finishing stress relief technology is used to improve the residual stress distribution on the surface of parts. After that, some blade profiles are grinded and polished by abrasive flow. The blade profile size accuracy is high, the profile error is less than 0.1mm, and the blade surface roughness Ra reaches 0.2 μ Improve the surface quality and integrity of parts at the level of m. Electrochemical methods should be used to machine the profile of TiAl alloy blades.

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 is insufficient, which affects the design, material selection, and strength calculation of materials and components. Compared with ordinary titanium alloys, these four types of high-temperature titanium alloy materials have lower plasticity, fracture toughness, and impact toughness, greater notch sensitivity, and poorer ability to reduce stress at the crack tip through local plastic deformation. Especially TiAl alloys have relatively low room temperature tensile plasticity and fatigue crack propagation resistance, but they significantly improve near 700 ℃ [31], and have a high initial creep deformation rate. Based on the characteristics of this type of material, scientific and reasonable technical indicators should be designed and developed to maximize thermal strength while ensuring sufficient plasticity and fully valuing the fracture performance of the workpiece. When selecting materials and calculating strength for engine design, it is necessary to establish a complete material design performance database. For low plasticity TiAl alloys, reasonable component design and life determination methods should be determined based on the characteristics of the material, as well as a cost-effective supply chain [32]. Reasonably control the design stress level of TiAl alloy parts to avoid obvious stress concentration and improve surface integrity [31]. Scientific evaluation of the flame retardancy of these titanium alloys is also crucial. In addition, no matter whether the Blisk or blisk is used at high temperature, 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 stress under the effect of the temperature gradient, affecting the fatigue performance and use reliability of the components.