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Vacuum brazing repair method for cracks

When talking about soldering, everyone will think of using a soldering iron and tin wire to connect electronic component circuits. This is the most common soldering method in soldering connections. Depending on the melting point of the solder, brazing is divided into hard soldering and soft soldering: that is, brazing with the melting point of the solder below 450°C is called soft soldering, and tin soldering is soft soldering; solder Brazing with a melting point temperature greater than 450°C is called brazing. Flame brazing, induction brazing, and vacuum brazing are all brazing.
In the field of aero-engine processing and manufacturing, vacuum brazing technology is widely used because of its incomparable advantages, such as the brazing of engine honeycomb rings, the brazing of turbine guide blade guide tubes, and blade brazing repairs, etc. Many cases.
Some people may ask what are the incomparable advantages of “vacuum brazing”?
First, let’s talk about the principle of vacuum brazing: Vacuum brazing generally uses a vacuum brazing furnace as the heating equipment. The parts to be welded with solder are placed in the vacuum brazing furnace. The vacuum degree in the furnace is less than 2×10-2pa. The furnace heats up at a constant rate until it reaches the brazing temperature point and then keeps it warm. When it reaches the brazing temperature point, the brazing material begins to melt but the base metal does not melt. The liquid metal wets the parts to be welded and fills the entire weld with the molten metal through capillary flow. seam to form a strong brazed joint.
After understanding the principles of brazing, we can find that its biggest advantages include almost no stress deformation, superior welding performance of dissimilar materials, and oxidation resistance. Therefore, it is widely used in components with complex structures, internal channels, and thin-walled features. welding.

After understanding the advantages of vacuum brazing, we found that the existence of vacuum brazing technology has solved many problems in the field of processing and manufacturing of aerospace parts. One typical application is blade crack repair. Cracks are one of the main damage forms that cause engine hot-end components to fail after long-term operation.
Usually we have two ways to repair cracks, one is welding repair, and the other is vacuum brazing repair. Since fusion welding uses local heating during the repair process, the weld and the heat-affected zone will undergo greater deformation, and new cracks may occur in thin-walled parts. Vacuum brazing repair uses overall heating, and the deformation of parts is small. Therefore, the main method used to repair hot-end components is vacuum brazing repair.
The vacuum brazing repair process mainly includes four processes: cleaning, crack filling, vacuum brazing and post-welding treatment.
Parts cleaning methods include pickling to peel off the protective aluminum-silicon coating, fluoride ion cleaning to remove oxides at residual cracks, and high-temperature purification to remove residual carbon deposits on the surface to keep the parts surface clean.
The solder used for crack filling generally uses low melting point alloy powder similar to the blade base material, with strengthening elements such as chromium, tungsten, tantalum and cobalt added and boron element to lower the melting point. Dilute the solder with acetone and assemble it into a syringe. Aim the syringe needle at the crack site and slowly cover the crack surface with the solder.
Then place the assembled parts in the vacuum furnace, and pump the vacuum in the furnace to less than 2×10-2Pa by turning on the mechanical pump, rotary vane pump, and Roots pump in sequence. The furnace body begins to heat up at a constant speed, and the temperature in the furnace reaches vacuum. At the brazing insulation temperature point, the solder metal melts into liquid metal after reaching the liquidus temperature, and fills the entire crack space under the capillary action at the crack site. This process spreads uniformly, allowing the filler metal to diffuse into the high-temperature alloy powder and surrounding base metal, while allowing residual boron to diffuse out of the welding area. After vacuum brazing is completed, it is trimmed by fitter to restore it to the size close to the drawing.
Vacuum brazing repair process for blades made of K447A material. During the repair and development process, Co45NiCrWB filler metal, a brazing temperature of 1180°C, and a heat preservation process of 30 minutes were used. A dense and complete brazed joint was successfully obtained, and the high-temperature durability of the joint part reached More than 60% of the base material.
Vacuum brazing repair process for DZ40 alloy blades. During the repair and development process, a Ni-Cr-Co based brazing material, a brazing temperature of 1170°C, and a heat preservation of 15 minutes were used. A dense and complete brazed joint was successfully obtained and was soldered at 980°C. The durable life of the joint can reach 18h under the condition of 83MPa load at ℃.
The vacuum brazing repair technology of K403 alloy blades uses 3P1 brazing filler metal, the brazing temperature is 1230°C, and the temperature is maintained for 10 minutes. When brazing K403 alloy blades, a defect-free brazed joint similar to the matrix structure can be obtained. At 1000°C The high-temperature tensile strength can reach 90% of the matrix strength, and the high-temperature durable strength can reach more than 70% of the matrix strength.