The invention belongs to a metal surface crack repair method, specifically a gas turbine high-pressure turbine blade tip crack repair method. The specific method is to first grind the opening to completely remove the crack according to the crack situation at the tip of the high-pressure turbine blade of the gas turbine, and then use a low heat input welding process to perform overlay welding in the repair welding area, and heat treat the repaired blade. The advantages of this invention are: the process method is simple, no vacuum and preheating are required, the damage to the blade base material is small, the non-destructive repair of high-pressure turbine blade tip cracks is achieved, and the repair cost is reduced. The method of the invention can not only be used to repair high-pressure turbine blade tip cracks in gas turbines but can also be used to repair high-pressure and low-pressure blade tip cracks in steam turbines, flue gas turbines, and other turbine mechanisms. The high-pressure turbine blades of aerospace engines repaired using this process have passed the 368-hour long-term bench test assessment.

1. A gas turbine high-pressure turbine blade tip crack repair method, which is characterized in that according to the gas turbine high-pressure turbine blade tip crack situation, the corresponding micro-grinding mechanical opening is used to completely remove the crack; and then a low heat input welding process is used under gas protection. The blade tip is polished and the opening area is surfacing; then the repaired blade is heat treated to restore performance.
2. The gas turbine high-pressure turbine blade tip crack repair method according to claim 1, is characterized in that the size of the opening is: the depth does not exceed 15% of the height of the blade body, and the width is enough to completely remove the crack with minimal loss of the base material. It is appropriate.
3. The gas turbine high-pressure turbine blade tip crack repair method according to claim 1, is characterized in that the repair material is domestic or foreign solid solution strengthening or age hardening that has a composition similar to that of the base material, a comparable thermal expansion coefficient, and good weldability. A high-temperature alloy whose performance is better than or similar to the material to be repaired.
4. The gas turbine high-pressure turbine blade tip crack repair method according to claim 3, is characterized in that the repair material is one or two forms of electrode and powder used simultaneously, and the electrode composition and the powder composition are the same or different.
5. The gas turbine high-pressure turbine blade tip crack repair process according to claim 1, is characterized in that the low heat input welding process includes: laser welding or high-energy micro-arc spark deposition or laser welding/high-energy micro-arc spark deposition composite Craftsmanship.
6. The gas turbine high-pressure turbine blade tip crack repair method according to claims 1, 3, 4, or 5, is characterized in that the material placement method is: under gas protection, using a laser to directly irradiate powder or high-energy micro-arc Spark deposition electrode; or a combination of the two for overlay welding in the repair welding area. First, use a high-energy micro-arc spark deposition electrode to pre-position the bottom layer, and then laser weld overlay welding layer by layer in the repair welding area until the entire repair welding area is filled.
7. The gas turbine high-pressure turbine blade tip crack repair method according to claim 1, is characterized in that the protective gas is: nitrogen, helium, argon, or a mixed gas thereof.
8. The gas turbine high-pressure turbine blade tip crack repair method according to claim 1, is characterized in that the heat treatment is: 9 0 0 ℃ ~ 1 3 0 0 ℃, heat preservation for 0 ~ 1 0 0 hours, and air cooling.

Technical field: The present invention belongs to a metal surface crack repair method, specifically a gas turbine high-pressure turbine blade tip crack repair method.

Background technology: Modern gas turbines are widely used in aero-engines and ground electric gas turbines. With the improvement of engine efficiency, the gas temperature of the engine is getting higher and higher. At the same time, the high-temperature gas generated by engine combustion is also highly corrosive and oxidizing. The high-pressure turbine blades are located in the turbine part of the gas turbine. The highest-temperature gas discharged from the combustion chamber directly acts near the turbine blade tips. Due to the start and stop of the engine or sudden state changes, the blade tips will generate high thermal stress, and the blades will creep at high temperatures. The tips of the variable elongation blades and the outer casing are worn. Coupled with the corrosion and oxidation of high-temperature gas, the blade tips of gas turbines, especially the high-pressure turbine blades of aero-engines, will undergo early cracking. As the working time increases, blade tip cracks will occur. Showing a growing trend, many blades are scrapped early due to excessive cracks. Since blades are expensive to manufacture, it makes sense to repair and reuse blades that have not yet reached their design life.
On the other hand, because high-pressure turbine blades are nickel-based high-temperature alloys with high Al and Ti content, they have high sensitivity to hot cracks during welding and post-weld heat treatment. They are usually non-weldable materials, which creates problems for high-pressure turbine blades. The repair brought great difficulties.
The early failures of high-pressure turbine blade tips are mainly wear and cracks. In terms of failure forms, the longer the service time, the more prominent the wear, and the higher the operating temperature, the more prominent the cracks. For the repair of high-pressure turbine blade tip wear, fusion welding methods such as argon arc welding and laser welding and non-fusion welding methods such as brazing and diffusion welding are generally used. There are literature and patent reports in this regard at home and abroad, but high-pressure turbine blades There are few published literature reports on the repair of sharp cracks at home and abroad.

Summary of the invention: Given the above problems, the present invention proposes a gas turbine high-pressure turbine blade tip crack repair method, which can repair the tip cracks of high-Al, Ti high-temperature alloy turbine blades, so that the original blades can reach a level that can be reused normally.
The technical solution of the present invention is implemented as follows:
A gas turbine high-pressure turbine blade tip crack repair method. According to the crack condition of the gas turbine high-pressure turbine blade tip, the corresponding micro-grinding mechanical opening is used to completely remove the crack; then a low heat input welding process is used under gas protection to grind the blade tip opening area. Overlay welding; then perform heat treatment on the repaired blades to restore performance.
The size of the opening is: the depth does not exceed 15% of the height of the blade body, and the width is suitable to completely remove the cracks and minimize the loss of the base material.
The repair material of the present invention adopts domestic or foreign solid-solution strengthened or age-hardened high-temperature alloys with a similar composition to the base material, comparable thermal expansion coefficient, and good weldability. Its performance is better than or similar to the material to be repaired.
The repair material is one or two forms of electrode and powder used simultaneously, and the electrode composition and powder composition are the same or different.
The low heat input welding process includes: laser welding or high-energy micro-arc spark deposition or laser welding/high-energy micro-arc spark deposition composite process.
The material placement method of the present invention is: under gas protection, use laser to directly irradiate powder or high-energy micro-arc spark deposition electrode; or combine the two for surfacing in the repair welding area, first use high-energy micro-arc spark deposition electrode to pre-position the bottom layer, and then Laser welding builds up welding layer by layer in the repair welding area until the entire repair welding area is filled.
The protective gas in the present invention is: nitrogen, helium, argon or their mixed gases.
The heat treatment is: 900°C to 1300°C, heat preservation for 0 to 100 hours, and air cooling.

Advantages of the invention:
1. The present invention grinds the opening to completely remove the crack according to the crack situation at the tip of the high-pressure turbine blade of the gas turbine, and then uses a low heat input welding process to perform overlay welding in the repair welding area, and heat-treats the repaired blade. The process method is simple, does not require vacuum and preheating, causes little damage to the blade base material, realizes non-destructive repair of high-pressure turbine blade tip cracks, and reduces repair costs.
2. The present invention uses high-temperature alloy fillers, high-energy micro-arc sparks (also called electric sparks), and laser beams at room temperature, and repairs the cracks at the tip of the high-pressure turbine blades of the gas turbine under gas protection and through a complete set of processes such as heat treatment. Repair method, the process method is simple and the operation is easy.
3. The present invention has little thermal damage to high-temperature alloys and has a narrow or no heat-affected zone, which effectively avoids the occurrence of interface cracks between the repair welding material and the base material, and makes unweldable high-temperature alloy materials weldable. Moreover, in this method No preheating is required.
4. The method of the present invention can not only be used to repair high-pressure turbine blade tip cracks in gas turbines but can also be used to repair high-pressure and low-pressure blade tip cracks in steam turbines, flue gas turbines, and other turbine mechanisms. The high-pressure turbine blade of an aviation engine repaired by this process has passed the 368-hour long-term bench test test.

Description of the drawings
Figure 1 is a schematic diagram of a high-pressure turbine blade and its tip crack; in the figure, 1-high-pressure turbine blade; and 2-tip crack.
Figure 2 is a schematic diagram of the main process of crack repair welding. The process includes crack → grinding opening → filler welding → heat treatment.
Figure 3(a)-(b) shows the actual crack repair structure. The repair welding area is completed by high-energy micro-arc spark deposition and laser welding composite surfacing; Figure 3 (a) shows the filler welding structure, and Figure 3 (b) shows the heat treatment Post-organization.

Detailed ways
There are various forms of out-of-tolerance cracks in aircraft engines and ground electric power gas turbines, ranging from single cracks to dense cracks. The feature of this invention is that it can repair cracks whose tip length is not greater than 15% of the blade body height of high-pressure turbine blades. The cracks pass through the opening. It is removed by grinding. The filling of the grinding opening area is completed by laser welding, high-energy micro-arc spark, or a combination of the two processes. The repair area and the matrix are metallurgically bonded without cracks. The materials used in the repair area are compatible with the matrix and have good high-temperature mechanical properties. For high-temperature alloys, the blades after repair welding must be heat treated to restore the structure. The process method is:
1. According to the length and density of cracks on the high-pressure turbine blade tip, use an opening to grind and remove the cracks. The depth of the opening should not exceed 15% of the height of the blade body, and the width should be such that the cracks can be completely removed with minimal loss of the base material.
2. Repair materials: Repair materials are made from domestic or foreign solid solution-strengthened or age-hardened high-temperature alloys with similar composition to the base material, comparable thermal expansion coefficient, and good weldability. Their performance is better than or similar to the material to be repaired.
3. Under gas protection, use a laser to directly irradiate powder or high-energy micro-arc spark deposition electrodes or a combination of the two to build up welding layer by layer in the repair welding area until the entire repair welding area is filled with a polishing margin.
4. Modify, polish and shoot blast the repair welding area of the high-pressure turbine blades.
5. Perform heat treatment on the leaves to restore tissue, with a temperature of 900°C to 1300°C, heat preservation for 0 to 100 hours, and air cooling.
6. No preheating is required before blade repair.
7. The metal electrode material used for repair needs to be descaled and machined to fit the size of the repair welding area. Metal powder materials for repair need to be dried and sieved, and the particle size should not be larger than 200 mesh. The repaired area needs to be cleaned and scaled to make the surface bright.

Example 1
Repairing the tip crack of a high-pressure turbine blade of an aerospace engine. The material is K465 alloy. The specific steps are as follows:
1. According to the length and density of cracks on the high-pressure turbine blade tip, grind and remove the cracks in the form of openings. The maximum opening depth is 5mm and the width is suitable to completely remove the cracks and minimize the loss of the base material. 2. Under the protection of argon gas, the 3H-ES-6 metal surface strengthening repair machine developed by the Institute of Metal Research, Chinese Academy of Sciences is used to perform high-energy micro-arc spark (electrical spark) deposition. The electrode diameter is Φ1mm, and the electrode is cladded layer by layer in the repair welding area. Until the entire repair welding area is filled and there is a grinding allowance.
3. The high-energy micro-arc spark deposition material is GH44.
4. Modify, polish and shoot blast the repair welding area of the high-pressure turbine blades.
5. Heat-treat the blades at a temperature of 900°C, keep warm for 2 hours, and air-cool.
6. No preheating is required before blade repair.
7. The metal electrode material used for repair needs to be descaled and machined to fit the size of the repair welding area. The high-pressure turbine blades repaired by this process meet the repair technical standards through X-ray and fluorescence inspection.

Example 2
The differences from Example 1 are: The blade tip cracks of a high-pressure turbine blade of an aerospace engine are repaired. The blade material is Rene80, and open filler welding is used for repair. The maximum opening depth is 7 mm. The repair material is IN 6 2 5 powder, and the average particle size is About 270 mesh. Under helium protection, the laser welding process is used to build up welding layer by layer in the repair welding area until the entire repair welding area is filled with a polishing allowance. Afterward, grinding, testing, polishing, and shot blasting are carried out. Finally, the blades are heat treated at 1050°C for 80 hours to restore performance.
The high-pressure turbine blades repaired by this process meet the repair technical standards through X-ray and fluorescence inspection.

Example 3
The differences from Example 1 are: The blade tip cracks of a high-pressure turbine blade of an aerospace engine are repaired. The blade material is K24, and open filler welding is used for repair. The maximum opening depth is 5mm. Under the protection of helium, the 3H-ES-6 metal surface strengthening repair machine developed by the Institute of Metal Research, Chinese Academy of Sciences is first used to perform high-energy micro-arc spark deposition to pre-set the bottom layer (the electrode diameter is Φ3mm, the height of the bottom layer is 100um), and then the metal powder is used Carry out laser welding, build-up welding layer by layer in the repair welding area until the entire repair welding area is filled and leave a polishing margin. The electrode and powder are both Haynes 230. Afterwards, grinding, inspection, polishing, and shot blasting are carried out. Finally, the blades are heat treated at 1180℃ for 10 hours to restore performance.
In this embodiment, high-energy micro-arc spark deposition electrodes are used to pre-position the bottom layer, and then laser welding is performed layer by layer in the repair welding area until the entire repair welding area is filled, which can minimize thermal damage to the base material.
The high-pressure turbine blades repaired by this process meet the repair technical standards through X-ray and fluorescence inspection.

Example 4
The difference from Example 1 is: that the blade tip crack of a high-pressure turbine blade of a ground electric gas turbine is repaired. The blade material is IN738, and open filler welding is used for repair. The repair material is IN625 powder, the average particle size is about 320 mesh, and the opening depth is the largest. 10mm. Under the protection of a mixed gas of helium and argon, laser irradiation is used to build up IN625 powder layer by layer until 90% of the entire repair welding area is filled, and then 3H-ES-D3000 developed by the Institute of Metal Research, Chinese Academy of Sciences is used to strengthen the metal surface for repair. The machine performs high-energy micro-arc spark deposition of NiCrAlY on the surface of the IN625 deposition layer and leaves a polishing allowance. Afterward, grinding, inspection, polishing, and shot blasting are carried out. Finally, the blades are heat treated at 1210°C and kept for 24 hours to restore performance.
This embodiment first uses a combination of high-energy micro-arc spark and laser welding. Because NiCrAlY has high hot crack sensitivity, high-energy micro-arc spark deposition is required to improve surface oxidation resistance.
Figure 3(a)-(b) shows the microstructure after actual crack repair. The repair welding area is completed by high-energy micro-arc spark deposition and laser welding composite surfacing. The repair layer has no cracks or obvious metallurgical defects and is well metallurgically bonded with the substrate. The quality of the gas turbine blades repaired by this process meets the repair technical standards through X-ray and fluorescence inspection.

Example 5
The difference from Embodiment 1 is: that the blade tip crack of a high-pressure turbine blade of a ground electric power gas turbine is repaired. The blade material is K24, and open filler welding is used for repair. The maximum opening depth is 12mm. The repair material is a K24 electrode, and the electrode diameter is Φ5mm. Under the protection of helium gas, the 3H-ES-D3000 metal surface strengthening repair machine developed by the Institute of Metal Research, Chinese Academy of Sciences is used to perform high-energy micro-arc spark deposition, and the repair welding area is cladded layer by layer until the entire repair welding area is filled and polishing is left. margin. Afterward, grinding, inspection, polishing, and shot blasting are carried out. Finally, the blades are heat treated at 1210℃ for 50 hours to restore performance.
The gas turbine blades repaired by this process meet the repair technical standards through X-ray and fluorescence inspection.