The welding methods often used in superalloy structural parts include argon arc welding, electron beam welding, brazing and friction welding. In recent years, transient liquid phase diffusion welding (TLP) has gradually developed and applied. my country’s superalloys have experienced 50 years of development. The research on the weldability and welding processes of superalloys has developed simultaneously with the research on superalloy materials. With the complication of superalloy components, the weldability is getting worse and worse, from the widely used argon arc welding to electron beam welding, brazing, transient liquid phase diffusion welding and friction welding. These welding methods have been successfully used in advanced aerospace engines. This chapter will briefly introduce the above welding processes based on practical applications.
40.1 Argon arc welding
40.1.1 The principle and characteristics of argon arc welding
Welding is performed using an inert gas argon shielded arc. Using a tungsten rod as the electrode is called tungsten arc welding (TIG welding), and using a welding wire as the electrode is called melting arc welding (MIG welding). Argon tungsten arc welding is widely used. It is a welding method that uses the arc heat generated between the tungsten electrode and the workpiece to melt the base material and filler wire under the protection of argon gas. Tungsten argon arc welding can be divided into two types according to the operation mode: manual argon arc welding and automatic argon arc welding.
Due to the full protection of inert gas, argon tungsten arc welding has good weld quality, no slag on the surface, concentrated heat, and small heat-affected zone; less investment in equipment, easy operation, and low cost; open arc operation is easy to realize automatic welding.
40.1.2 Determination of argon arc welding process parameters
1. Welding current. Welding current is the most important process parameter of tungsten argon arc welding. On the premise of ensuring welding penetration, try to use as small a welding current as possible. Select from the welding standard according to the part material, the thickness of the joint to be welded and the form of the weld.
2. Wire material and diameter. The selection is based on the material, thickness and welding current of the parts to be welded. For welding solid-solution strengthened superalloys and precipitation-strengthened superalloys with low strengthening phase quantity, the welding wire with the same or similar chemical composition as the base metal can be selected to make the performance of the welded joint similar to that of the base metal. For welding nickel-based or iron-based superalloys with high phase number, Ni-Cr-Mo welding wire (HGH3533) containing aluminum and titanium can be selected to ensure that the welded joint has good crack resistance. At the same time, through aging treatment Improve the mechanical properties of joints. Cobalt-based superalloys can use the same welding wire as the base metal or Ni-Cr-Mo alloy welding wire.
The national standard GB/T14992-2005 released a total of 28 high-temperature alloy wire grades for welding, see Table 40-1[1]. It can be selected according to the composition of the alloy to be welded.
3. Type and diameter of tungsten electrode. Generally choose cerium tungsten electrode (WCe20). Pure tungsten electrodes and thoriated tungsten electrodes (WTh15) are not as good as cerium tungsten grades. Cerium tungsten electrodes have strong electron emission ability, low arc ignition voltage and good arc stability. The tungsten electrode diameter is selected according to the allowable current and welding current.
4. Argon flow rate. It is selected according to the diameter of the nozzle of the welding torch to ensure that the flow of the shielding gas is laminar without turbulence.
5. Welding speed. Welding speed is also an important welding parameter. Choose according to the requirements of the geometric dimensions of the weld. If the required penetration depth and width are larger, the welding speed must be slower, otherwise it should be faster. During manual argon arc welding, everyone’s welding speed is different, and it is often based on experience, mainly based on penetration.
6. Welding joint design. Due to the poor fluidity of the molten pool and the small penetration depth during argon arc welding of superalloys, the design of the joint requires a large groove angle, a reduced height of the blunt edge, and an increased root gap [3].
40.1.3 Application of argon arc welding to aeroengines or gas turbines
Argon arc welding of superalloys is relatively mature and widely used. Such as combustor flame tube, afterburner adjustable nozzle, rear mounting edge, casing, turbine blade wear-resistant layer and so on. The GH2135 alloy developed by the author of this book [4] has been used successively as a turbine disk, turbine blade and flame tube.
In 1970, the Institute of Metal Research, Chinese Academy of Sciences, Harbin Steam Turbine Factory and Harbin Railway Bureau jointly trial-produced the GH2135 alloy flame tube, which replaced the nickel-based alloy GH3030, and installed it on the gas turbine of my country’s first 3,000 horsepower “Long March No. 1″ locomotive. The GH2135 flame tube was installed in July 1970, and passed the test of more than 300 hours of operation in 1972, with good results. The flame tube is one of the important parts of the gas turbine or aero-engine. The material of the flame tube requires good high temperature strength and thermal fatigue performance, excellent oxidation resistance and corrosion resistance, good formability and weldability. The wall surface temperature of the locomotive gas turbine flame tube is in the range of 800-900 ℃, and the service life is long. Using heavy oil fuel, the wall surface is prone to carbon deposition and gas corrosion, and the working conditions are relatively harsh. The appearance of GH2135 flame tube for locomotive is shown in Figure 40-1. In order to solve the welding and forming problems of GH2135 alloy aging plates for locomotive gas turbine flame tubes, the weldability and forming of GH2135 alloy plates were studied.
Tianjin Anton Metal Manufacture Co., Ltd. is a company specializing in the production of various nickel-based alloys, Hastelloy alloys and high-temperature alloy materials. The company was established in 2001 with a registered capital of 16.8 million, specializing in the production and sales of alloy materials. Anton Metal’s products are widely used in aerospace, chemical industry, electric power, automobile, nuclear energy and other fields, and can also provide customized alloy material solutions according to customer needs. If you need to know the price consultation of alloy materials or provide customized alloy material solutions, please feel free to contact the sales staff.
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Post time: Sep-02-2023
