In recent years, the rapid development of domestic aviation and aerospace industry has promoted the production of various new materials, and various new fasteners have also been continuously developed and applied.
These new fasteners generally use new and stable high-performance titanium alloys and high-temperature alloy materials. Through advanced processing technology and surface treatment methods, they have very good surface quality and performance. High-strength titanium alloy materials TB8 and high-temperature alloy materials GH4169 The manufactured fasteners are a typical representative among them.
1. Material characteristics
TB8 is a new type of metastable B-type titanium alloy material, corresponding to the foreign material β21S. It is a new type of titanium alloy material developed in China in recent years, and it is also the highest strength titanium alloy material in China.
Inconel 718 materials solid solution state internal grain structure GH4168 material tensile state grain structure
TB8 materials are generally delivered in a solid solution or hot rolled state, and then processed and used. In the solid solution state, the internal structure of the material is B equiaxed grains, this state has good ductility and deformability, the plasticity of the material is very good, and the upsetting ratio can exceed 15. In the hot-rolled state, the internal structure of the material is very fine β-phase grains. In this state, the plasticity of the material is poor and it is not easy to be cold-formed.
GH4169-Inconel 718 materials solid solution state internal grain structure GH4169 material tensile state grain structure is a new type of high-temperature alloy material, belonging to the stainless steel material, is currently the highest strength stainless steel material, the corresponding imported material grades are Inconel 718 (USA), NC19FeNb (France). GH4169 is a nickel-based superalloy with body-centered tetragonal γ” and face-centered cubic γ’phase precipitation strengthening. It is generally delivered in a solid solution or cold drawn state. This material is a deformed superalloy and can be obtained by cold working deformation. The shape and structure.
Both TB8 material and GH4169-Inconel 718 materials solid solution state internal grain structure GH4169 material tensile state grain structure are high-strength materials, and the processed products are generally aged. In order to verify the difference in strength levels between the two, the typical φ10 specification TB8 material and GH4169 material are taken and their strength is actually tested. The results are shown in Table 1. Shown.
rate of reduction in area
solution + aging
GH4169-φ10 solution + aging
Cold drawn + aging
2. Molding characteristics
TB8 material and GH4169 two kinds of materials are quite different in organization and performance. When manufacturing fasteners, there are also big differences in forming methods.
2.1 Upsetting performance
TB8 material is a near β-type titanium alloy, which has good ductility and deformability in the solid solution state. It can be produced by cold heading in the process of manufacturing fasteners. The material also has very high thermal stability. And thermal corrosion resistance, it is not easy to overheat and burn during thermal processing. For hot-rolled materials with poor plasticity, they can be formed by warm upsetting.
GH4169 is a deformed superalloy. Its yield strength below 650C ranks first among deformed superalloys. It has very good plasticity and deformability at room temperature. However, due to its relatively high strength, it has an impact on equipment tonnage and molds when manufacturing fasteners. The requirements are relatively high, and it is easy to upset, and the blanks are generally formed by warm upsetting.
2.2 Machining performance
TB8 material is mainly used to manufacture 1300MPa grade high-strength fasteners. Due to the very high requirements for surface quality, in the process of manufacturing fasteners, precision machining methods such as CNC lathes and CNC centerless grinding are required to ensure it.
From the current processing situation, the turning machining performance of this material is relatively poor. In the case of large turning volume and high processing speed, problems such as material sintering and sticking are prone to occur. Therefore, the turning processing parameters should be selected as small as possible. The volume and lower turning speed; the problem of sticking the grinding wheel also exists in the grinding process and the processing process is also more difficult. The machining efficiency of TB8 material fasteners is very low, and special machining tools need to be developed to solve the problems in the machining process.
Fasteners made of GH4169 material have a strength of more than 1600MPa, turning processing is difficult, and the problem of tool chipping often occurs during processing, but its grinding performance is relatively good. Therefore, for GH4169 material, turning processing should be avoided as much as possible. Choose the grinding process to meet the requirements.
3. Fastener structure and performance characteristics
TB8 material has been successfully developed in a relatively short time. It is mainly used to manufacture high-lock bolt fasteners, and has been installed and tested on a certain model in China. As the material continues to be promoted and applied, there will be more new types of fasteners Manufactured with TB8 material. Fasteners made of TB8 material are generally designed according to the 1300MPa strength level, and the shear strength is designed according to the 750MPa level. The fatigue high load value is controlled at 35% of the tensile load. It is reasonable. From the material itself, the TB8 material The biggest advantage is its small weight and high strength. It can greatly reduce its own weight under the premise of satisfying the maximum performance.
The GH4169 material has been successfully developed for a relatively long time. It has been widely used in the manufacture of various types of fasteners, such as high-strength bolts, nuts, screw and screw sleeve road parts, etc. It can be divided into two strength levels of 1275MPa and 1512MPa. , The shear strength is only 860MPa, and the fatigue high load value can reach up to 60% of the tensile load. The biggest advantage of GH4169 material is that it can still maintain high strength at a certain high temperature, and its superiority is obvious.
4. Application of fasteners
Fasteners made of TB8 material, in addition to the excellent performance of general titanium alloy fasteners such as light weight and high strength, also have high corrosion resistance and good high temperature oxidation resistance, and can be used in aircraft with temperature requirements Or engine structural parts, fasteners, etc. The foreign material B2IS corresponding to the TB8 material has been applied to F-22 aircraft and C-17 models, mainly for the wings and the middle and rear fuselage parts. The domestic TB8 material is a new research material. Although it has not been widely promoted and applied, its superior performance will enable it to be applied to more types of aircraft and equipment.
Fasteners made of CH4169 material have very good comprehensive performance. The product can be used in the temperature range of -253C-700C. It still has good fatigue resistance, radiation resistance, oxidation resistance and corrosion resistance at high temperatures, and can guarantee long-term Organizational stability has been widely used in aviation, aerospace, nuclear energy, petroleum and other fields.
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