A turbine blade shroud crack classification brazing repair method

Abstract

The present application relates to the technical field of aero-engine parts repair, and discloses a turbine blade rim plate crack classification brazing repair method. The method comprises the following steps: performing visual inspection on the blade and removing the thermal barrier coating layer; classifying the cracks through fluorescence detection, into micro cracks with a width of less than 0.2 mm and wide cracks with a width of more than 0.2 mm; prepositioning a flow resistance agent in the film hole after removing the thermal barrier coating bottom layer; prepositioning a low-melting-point and high-wetting 1st nickel-based filler for micro cracks, and prepositioning a high-strength and high-toughness 2nd nickel-based filler for wide cracks, and prepositioning a crack flow resistance agent around the brazing material; then, preheating and brazing heat treatment are performed in a vacuum furnace; finally, the flow resistance agent is cleaned, polished, and subjected to fluorescence detection. The present application has small deformation and low residual stress after repair, precisely controls the filler flow by combining the flow resistance agent, reduces the film hole blockage rate, has consistent strength in the repair area and the matrix, and realizes high-quality remanufacturing of damaged blades.

Description

Technical Field

[0001] This invention relates to the field of aero-engine component repair technology, and discloses a brazing repair method for classifying and repairing turbine blade edge plate cracks. Background Technology

[0002] High-pressure turbine guide vanes are typically manufactured using directionally solidified or single-crystal alloys, resulting in high material costs. Furthermore, the complex manufacturing process, stringent dimensional accuracy requirements, high machining difficulty, long production cycles, and low yield further increase blade costs. During actual service, cracks easily develop in the blade rim. Directly replacing damaged blades with new ones would result in enormous material waste and is economically unsustainable. Therefore, there is an urgent need to develop efficient, high-precision, and high-quality crack repair and remanufacturing technologies to restore the aerodynamic shape, microstructure, and mechanical properties of damaged blades, enabling them to continue operating.

[0003] However, in the field of high-pressure turbine guide vane maintenance for aero-engines, no complete repair process has been found specifically for blade edge cracks. Existing repair methods often face problems such as uneven heating during the repair process, large blade deformation after repair, and high residual stress when dealing with such cracks. At the same time, due to the lack of classification repair strategies for different crack types, it is difficult to simultaneously ensure the penetration and filling of microcracks and the weldability and mechanical properties of wide cracks. In addition, during the brazing process, the molten filler metal is prone to spread under capillary action, leading to blockage of the film cooling pores and contamination of the non-repair area surface by the filler metal, making it difficult to meet the stringent maintenance standards of aero-engines. Summary of the Invention

[0004] To address the problems in existing turbine blade rim crack repair processes, such as uneven heating leading to large deformation and high residual stress after repair; inability to balance permeability and post-weld mechanical properties for cracks of different widths; and disordered brazing filler metal flow causing blockage of film pores and surface contamination in non-repair areas, this invention provides a classified brazing repair method for turbine blade rim cracks.

[0005] To address the aforementioned technical problems, this invention provides a brazing repair method for classifying and repairing cracks in turbine blade rim plates, comprising the following steps: Step 1, Visual inspection: Perform a macroscopic inspection of the surface condition of the blade samples after the coating has been removed, conduct preliminary screening, and exclude blades that cannot be repaired; Step 2, removal of thermal barrier coating: The guide vane edge plate to be treated is sandblasted to remove the surface thermal barrier coating. Step 3: Crack classification based on fluorescence detection: Perform fluorescence detection on the blades, conduct secondary screening based on the detection results, and for repairable blades, mark the crack distribution locations and record the crack sizes, classifying them according to crack width; Step 4, Thermal barrier coating underlayer removal: Remove the surface thermal barrier coating underlayer and cracked oxides; Step 5, Pre-apply flow-blocking agent to the air film pores: Coat the air film pores with flow-blocking agent to prevent blockage; Step 6, Pre-apply brazing material: Pre-apply matching brazing material for different types of cracks; Step 7, Pre-apply crack resistant agent: Apply a resistant agent around the pre-applied brazing material; Step 8, Preheating treatment before brazing: Place the blade in a vacuum brazing furnace for preheating treatment; Step 9, Brazing heat treatment: After the preheating treatment, continue to raise the temperature for brazing heat treatment, and after holding at the temperature, cool down with the furnace and remove from the furnace. Step 10, Cleaning the choke and post-weld polishing: Clean the blades to remove the choke and polish them to remove excess brazing material. Step 11, Fluorescence detection: Perform fluorescence detection on the repaired blades, and repair the defective blades by welding.

[0006] Furthermore, in steps one and two of the above technical solution, when inspecting the surface macroscopic condition of the sample after removing the coating, an unrepairable fault description sheet is issued for the unrepairable sample according to the corresponding standard, and the samples are stored and recycled in a unified manner; when sandblasting the guide blade edge plate to be treated, the sandblasting process parameters are controlled to completely remove the surface thermal barrier coating layer, while avoiding damage to the blade substrate material, so as to provide a clean surface basis for subsequent fluorescence detection and crack classification.

[0007] Furthermore, in step three of the above technical solution, fluorescence detection is performed on the blades that have passed the preliminary screening and had their surface layer removed, and a blade pre-welding fault description form is generated. According to the location of the crack distribution, the inner and outer sides of the upper and lower edge plates are marked in sections, and the length, width, and height of the cracks are recorded in detail. The cracks are classified according to their width: Class A cracks are micro-cracks with a width of less than 0.2 mm, and Class B cracks are wide cracks with a width of more than 0.2 mm. The blade pre-welding fault description form number corresponds to the blade number, which facilitates the subsequent pre-brazing treatment.

[0008] Furthermore, in step four of the above technical solution, a fluoride ion cleaning process is adopted to remove the surface thermal barrier coating and crack oxides. Through the chemical reaction between fluoride ions and the underlying adhesive and oxides, the oxide impurities inside the cracks are thoroughly removed, thereby exposing a fresh metal substrate surface. This effectively ensures the wettability and penetration ability of the subsequent brazing material inside the cracks, and improves the bonding strength and quality of the brazed joint.

[0009] Furthermore, in step five of the above technical solution, when coating the air film pores with a flow-blocking agent, a high-temperature resistant organosilicon-based composite flow-blocking agent formulation is selected. This flow-blocking agent can remain stable during high-temperature brazing and does not react adversely with the brazing filler metal and the blade substrate. It effectively prevents the molten brazing filler metal from flowing into and blocking the air film pores under capillary action, ensuring the normal ventilation function of the air film pores after blade repair and guaranteeing the cooling effect of the blade during service.

[0010] Furthermore, in step six of the above technical solution, for type a microcracks with a width of less than 0.2 mm, No. 1 nickel-based high-sensitivity brazing filler metal is used. This filler metal contains Cr, B, and Si elements, has a low melting point of less than or equal to 450°, and has high wettability and a contact angle of less than 15°, thus exhibiting strong penetration ability into microcracks. For type b wide cracks with a width greater than 0.2 mm, No. 2 nickel-based brazing filler metal is used. This filler metal contains Cr, Fe, and Si elements, and has good high-temperature creep resistance, high strength, and toughness to ensure the mechanical properties and weld penetration of the welded area.

[0011] Furthermore, in step seven of the above technical solution, a flow-blocking agent is coated around the pre-placed brazing material. A high-temperature resistant organosilicon-based composite flow-blocking agent formula is selected. This flow-blocking agent can form a dense inert isolation film within the brazing temperature range, effectively blocking the capillary spread of the brazing filler metal along the non-repair area metal surface, preventing the brazing filler metal from overflowing into the repair area after melting and causing contamination or damage to other parts of the blade, thereby achieving precise control of the brazing filler metal flow area.

[0012] Furthermore, in step eight of the above technical solution, to alleviate the thermal stress concentration during the wide crack repair process, the blade is preheated, and the vacuum degree of the brazing furnace is controlled at 1×10⁻⁶. -3 Pa, the brazing preheating temperature is set to 650~850°C, the holding time is set to 5~10min, and the heating rate is controlled at 10~15°C / min. This preheating process effectively reduces the thermal shock and thermal stress of the blade during the subsequent high-temperature brazing process, and reduces the deformation and residual stress after repair.

[0013] Furthermore, in step nine of the above technical solution, after the preheating and holding process, the temperature continues to rise, with the rising rate controlled at 10~15℃ / min, and the vacuum degree of the brazing furnace maintained at 1×10⁻⁶. -3 Pa, the brazing temperature is set to 975~1175°C, the holding time is set to 15~30min, and after the holding time is completed, the brazing filler metal is cooled to below 80~100°C and then removed from the furnace. The overall vacuum heating ensures that the brazing filler metal is fully melted and fills the crack defects by using capillary action, thus avoiding uneven heating.

[0014] Furthermore, in steps ten and eleven of the above technical solution, the polished blades are ultrasonically cleaned at a temperature of 50-80℃ for 15-30 minutes. After cleaning, they are blown clean with compressed air. Then, pneumatic polishing is performed, with appropriate speed and force selected according to different parts to remove excess brazing material and ensure the flatness of the blade surface. Finally, the repaired blades are subjected to fluorescence detection and the results are recorded. For unqualified blades, the corresponding steps are repeated for re-welding, and the re-welding is not performed more than twice.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. By placing the brazing filler metal and the blade edge plate in a vacuum chamber for overall heating, the wetting and capillary action of the melted brazing filler metal is used to fill the crack defects, which effectively avoids uneven heating during the repair process. After repair, the blade has small deformation and low residual stress.

[0016] 2. A repair strategy based on crack classification using fluorescence detection is adopted. For Class A microcracks with a width <0.2mm, No. 1 nickel-based brazing filler metal with low melting point and high wettability is used to ensure strong penetration into the microcracks. For Class B wide cracks with a width >0.2mm, No. 2 nickel-based brazing filler metal with good high-temperature creep performance, high strength and toughness is used to ensure the weld penetration of the wide cracks and the mechanical properties of the welded parts.

[0017] 3. By coating the air film pores and surrounding the pre-placed brazing material with a high-temperature resistant silicone-based composite flow-blocking agent, a dense, inert isolation film is formed within the brazing temperature range, effectively preventing the brazing filler metal from spreading capillarily along the non-repaired metal surface. The customized pre-placed brazing filler metal technology combined with the flow-blocking agent controls flow, reducing the air film pore blockage rate to 0.5%, ensuring normal ventilation and cooling function of the air film pores after blade repair.

[0018] 4. Fluorine ion cleaning is used in the thermal barrier coating underlayer removal step, which effectively removes the surface thermal barrier coating underlayer and cracked oxides, exposing the fresh metal substrate surface, and further improving the bonding strength and quality of the brazed joint. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the following detailed description of a method for classifying and brazing repairing cracks in turbine blade rim plates, in conjunction with specific embodiments, provides a further explanation. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of the invention.

[0020] This invention provides a classification and brazing repair process for cracks in the rim plates of equiaxed high-pressure turbine guide vanes. The overall process flow is as follows: visual inspection → removal of the thermal barrier coating top layer → crack classification based on fluorescence detection → removal of film pores from the thermal barrier coating bottom layer → pre-application of brazing material → pre-application of crack flow barrier agent → preheating treatment before brazing → brazing heat treatment → cleaning of flow barrier agent → post-weld grinding → fluorescence detection.

[0021] The specific implementation steps are as follows: Step S1, Visual Inspection: Perform a macroscopic surface condition inspection on the samples after coating removal to preliminarily screen and exclude irreparable blades. Based on the corresponding standards, issue an irreparable fault description form for the irreparable samples, and store and recycle the samples uniformly.

[0022] Step S2, thermal barrier coating removal: The guide vane edge plate to be treated is sandblasted to remove the surface thermal barrier coating, providing a clean surface for subsequent inspection and treatment.

[0023] Step S3: Crack classification based on fluorescence detection: For blades that have passed the initial screening and had their surface layer removed, fluorescence detection is performed. Based on the detection results, a second screening is conducted to exclude unrepairable blades, and step S1 is repeated for description and recovery. For repairable blades, a pre-welding fault description form is issued. Based on the crack distribution location, the inner and outer sides of the upper and lower edge plates are marked, and the length, width, and height of the cracks are recorded in detail. Cracks are classified according to their width: Class A cracks are microcracks with a width < 0.2 mm, and Class B cracks are wide cracks with a width > 0.2 mm. The blade pre-welding fault description form number corresponds to the blade number to facilitate subsequent pre-brazing treatment.

[0024] Step S4, removal of the thermal barrier coating underlayer: Fluorine ion cleaning is used to remove the surface thermal barrier coating underlayer and cracked oxides, exposing the fresh metal substrate to ensure the wettability and penetration of subsequent brazing materials.

[0025] Step S5, Pre-applying air film pore choke agent: Coating the air film pore with a choke agent, using a high-temperature resistant organosilicon-based composite choke agent formulation to prevent air film pore blockage during subsequent brazing.

[0026] Step S6, Pre-apply brazing material: For Class a microcracks less than 0.2 mm, pre-apply No. 1 nickel-based (containing Cr, B, Si) high-sensitivity brazing filler metal. This filler metal has a low melting point (≤450℃) and high wettability (contact angle <15°), and strong penetration ability to microcracks. For Class b wide cracks greater than 0.2 mm, considering the weld penetration and ensuring the mechanical properties of the welded part, pre-apply No. 2 nickel-based (containing Cr, Fe, Si) brazing filler metal. This filler metal has good high-temperature creep performance and high strength and toughness.

[0027] Step S7, Pre-applying crack resistant agent: Apply a resistant agent around the pre-applied brazing material, using a high-temperature resistant silicone-based composite resistant agent formulation. The resistant agent forms a dense, inert isolation film within the brazing temperature range, effectively preventing the brazing filler metal from spreading capillarily along the non-repair area metal surface.

[0028] Step S8, Preheating Treatment Before Brazing: To alleviate thermal stress concentration during the wide crack repair process, the blades are preheated. The vacuum level of the brazing furnace is controlled at 1×10⁻⁶. -3 Pa, brazing temperature 650~850°C, holding time 5~10min, heating rate 10~15°C / min.

[0029] Step S9, Brazing heat treatment: After the preheating and holding period, continue heating at a rate of 10~15℃ / min, with a vacuum degree of 1×10⁻⁶ in the brazing furnace. -3 Pa, brazing temperature 975~1175°C, holding time 15~30min, after holding, cool with furnace to below 80~100°C before removing from furnace.

[0030] Step S10, Cleaning the anti-flow agent and post-weld grinding: After grinding, the blades are ultrasonically cleaned at a temperature of 50~80℃ for 15min~30min. After cleaning, they are blown clean with compressed air. Then, pneumatic grinding is performed. Depending on the different parts, the appropriate speed and force are selected to grind away excess brazing material and ensure the flatness of the blade surface.

[0031] Step S11, Fluorescence detection: Perform fluorescence detection on the repaired blades and record the detection results. For unqualified blades, describe the defects and repeat steps S3 to S10. The welding should not be done more than twice.

[0032] The technical solution of the present invention will be further described below with reference to two specific embodiments: Example 1: Repair of crack in the rim plate of guide vane #1 Visual inspection: After removing the coating, the surface of the #1 guide blade was inspected to check its macroscopic condition and conduct a preliminary screening to confirm its repairability.

[0033] Thermal barrier coating removal: The edge plate of guide vane #1 is sandblasted to remove the surface thermal barrier coating.

[0034] Cracks were classified based on fluorescence detection: a pre-welding fault description sheet was issued for blade #1, and the inner and outer sides of the upper and lower edge plates were marked and their dimensions recorded. Inspection revealed 17 cracks requiring repair on blade #1, including 3 on the inner side of the upper edge plate (2 in category A, 1 in category B); 5 on the outer side of the upper edge plate (2 in category A, 3 in category B); 4 on the inner side of the lower edge plate (2 in category A, 2 in category B); and 5 on the outer side of the lower edge plate (1 in category A, 4 in category B).

[0035] Removal of thermal barrier coating bond layer: Fluoride ion cleaning is adopted to remove the underlying thermal barrier coating bond layer and crack oxides on the surface.

[0036] Pre-placement of gas film hole flow resisting agent: A high temperature resistant silicone-based composite flow resisting agent is coated inside the gas film holes.

[0037] Pre-placement of brazing material: No.1 nickel-based (containing Cr, B, Si) highly sensitive brazing filler metal is used for type a microcracks; No.2 nickel-based (containing Cr, Fe, Si) brazing filler metal is used for type b wide cracks.

[0038] Pre-placement of crack flow resisting agent: A high temperature resistant silicone-based composite flow resisting agent is coated around the pre-placed brazing material.

[0039] Preheating treatment before brazing: The vacuum degree of the brazing furnace is 1×10 -3 Pa, the brazing temperature is 700°C, the holding time is 7min, and the heating rate is 10°C / min.

[0040] Brazing heat treatment: After preheating, continue heating at a heating rate of 10°C / min, and the vacuum degree of the brazing furnace is 1×10 -3 Pa, the brazing temperature is 975~1100°C, the holding time is 15min. After the holding period, cool down in the furnace to below 80°C before taking out the workpiece.

[0041] Flow resisting agent removal and post-weld grinding: The ultrasonic cleaning temperature is 60°C for 15min. After blowing clean with compressed air, pneumatic grinding is adopted to remove excess brazing filler metal.

[0042] Fluorescent inspection: The repaired blade is qualified with no blockage of gas film holes. Through tensile, hardness and 850°C thermal cycle tests, the strength of the repaired area is consistent with the matrix, and no secondary cracks are found.

[0043] Example 2: Crack repair for the platform of No.2 guide vane Visual appearance inspection: Perform macroscopic surface condition inspection on the No.2 guide vane after coating removal, conduct preliminary screening to confirm the repairability of the vane.

[0044] Removal of thermal barrier coating top layer: Sand blasting is performed on the platform of the No.2 guide vane to remove the top layer of the surface thermal barrier coating.

[0045] Crack classification based on fluorescent inspection: Issue a pre-brazing fault description sheet for the No.2 vane, mark the inner and outer sides of the upper and lower platforms in zones and record the dimensions. After inspection, there are 11 cracks to be repaired on the No.2 vane, including 3 cracks on the inner side of the upper platform (1 type a, 2 type b); 2 cracks on the outer side of the upper platform (1 type a, 1 type b); 2 cracks on the inner side of the lower platform (2 type a); 4 cracks on the outer side of the lower platform (1 type a, 3 type b).

[0046] Removal of thermal barrier coating bond layer: Fluoride ion cleaning is adopted to remove the surface thermal barrier coating bond layer and crack oxides.

[0047] Pre-plugging of gas film holes with flow-resisting agent: A high-temperature resistant silicone-based composite flow-resisting agent is applied inside the gas film holes.

[0048] Pre-placement of brazing filler material: No.1 nickel-based (containing Cr, B, Si) high-sensitivity brazing filler is used for type a microcracks; No.2 nickel-based (containing Cr, Fe, Si) brazing filler is used for type b wide cracks.

[0049] Pre-placement of crack flow-resisting agent: A high-temperature resistant silicone-based composite flow-resisting agent is applied around the pre-placed brazing filler material.

[0050] Preheating treatment before brazing: The vacuum degree of the brazing furnace is 1×10 -3 Pa, the brazing temperature is 680°C, the holding time is 8min, and the heating rate is 10°C / min.

[0051] Brazing heat treatment: After preheating, the temperature is continuously increased at a heating rate of 10°C / min, the vacuum degree of the brazing furnace is 1×10 -3 Pa, the brazing temperature is 1075°C, the holding time is 15min, and after the holding period ends, the component is cooled in the furnace to below 80°C before being taken out of the furnace.

[0052] Flow-resisting agent cleaning and post-brazing grinding: The ultrasonic cleaning temperature is 60°C for 15min, after being blown clean with compressed air, pneumatic grinding is adopted to remove excess brazing filler.

[0053] Fluorescent inspection: The repaired blade is qualified, with no gas film hole blockage. Through tensile, hardness and 850°C thermal cycle tests, the strength of the repaired area is consistent with the substrate, with no secondary cracks.

[0054] The above descriptions are merely specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any variations or replacements that can be easily conceived by a person skilled in the art within the technical scope disclosed by the present invention shall be covered within the protection scope of the present invention.

Claims

1. A method for brazing and repairing cracks in turbine blade rim plates, characterized in that, Includes the following steps: Step 1, Visual inspection: Perform a macroscopic inspection of the surface condition of the blade samples after the coating has been removed, conduct preliminary screening, and exclude blades that cannot be repaired; Step 2, removal of thermal barrier coating: The guide vane edge plate to be treated is sandblasted to remove the surface thermal barrier coating. Step 3: Crack classification based on fluorescence detection: Perform fluorescence detection on the blades, conduct secondary screening based on the detection results, and for repairable blades, mark the crack distribution locations and record the crack sizes, classifying them according to crack width; Step 4, Thermal barrier coating underlayer removal: Remove the surface thermal barrier coating underlayer and cracked oxides; Step 5, Pre-apply flow-blocking agent to the air film pores: Coat the air film pores with flow-blocking agent to prevent blockage; Step 6, Pre-apply brazing material: Pre-apply matching brazing material for different types of cracks; Step 7, Pre-apply crack resistant agent: Apply a resistant agent around the pre-applied brazing material; Step 8, Preheating treatment before brazing: Place the blade in a vacuum brazing furnace for preheating treatment; Step 9, Brazing heat treatment: After the preheating treatment, continue to raise the temperature for brazing heat treatment, and after holding at the temperature, cool it out of the furnace. Step 10, Cleaning the choke and post-weld polishing: Clean the blades to remove the choke and polish them to remove excess brazing material. Step 11, Fluorescence detection: Perform fluorescence detection on the repaired blades, and repair the defective blades by welding.

2. The method for classifying and brazing repair of turbine blade rim cracks according to claim 1, characterized in that, In steps one and two, when inspecting the surface macroscopic condition of the sample after removing the coating, an unrepairable fault description form is issued for the irreparable sample according to the corresponding standard, and the samples are stored and recycled in a unified manner. When sandblasting the guide blade edge plate to be treated, the sandblasting process parameters are controlled to completely remove the surface thermal barrier coating layer, while avoiding damage to the blade substrate material, so as to provide a clean surface basis for subsequent fluorescence detection and crack classification.

3. The method for classifying and brazing repair of turbine blade rim cracks according to claim 1, characterized in that, In step three, the blades that have passed the initial screening and had their surface layer removed are subjected to fluorescence detection, and a blade pre-welding fault description form is generated. According to the location of the crack distribution, the inner and outer sides of the upper and lower edge plates are marked in sections, and the length, width, and height of the cracks are recorded in detail. The cracks are classified according to their width: Class A cracks are micro-cracks with a width of less than 0.2 mm, and Class B cracks are wide cracks with a width of more than 0.2 mm. The blade pre-welding fault description form number corresponds to the blade number, which facilitates the subsequent pre-brazing process.

4. The method for classifying and brazing repair of turbine blade rim cracks according to claim 1, characterized in that, In step four, a fluoride ion cleaning process is used to remove the surface thermal barrier coating and crack oxides. Through the chemical reaction between fluoride ions and the underlying adhesive and oxides, oxide impurities inside the cracks are thoroughly removed, thereby exposing a fresh metal substrate surface. This effectively ensures the wettability and penetration ability of the subsequent brazing material inside the cracks, and improves the bonding strength and quality of the brazed joint.

5. The method for classifying and brazing repair of turbine blade rim cracks according to claim 1, characterized in that, In step five, when coating the air film pores with a flow-blocking agent, a high-temperature resistant organosilicon-based composite flow-blocking agent formulation is selected. This flow-blocking agent can remain stable during high-temperature brazing and does not react adversely with the brazing filler metal and the blade substrate. It effectively prevents the molten brazing filler metal from flowing into and clogging the air film pores under capillary action, ensuring that the air film pores have normal ventilation function after the blade is repaired and guaranteeing the cooling effect of the blade during service.

6. The method for classifying and brazing repair of turbine blade rim cracks according to claim 1, characterized in that, In step six, for type a microcracks with a width less than 0.2 mm, No. 1 nickel-based high-sensitivity brazing filler metal is used. This filler metal contains Cr, B, and Si elements, has a low melting point of less than or equal to 450°C, and has high wettability and a contact angle of less than 15°, thus exhibiting strong penetration ability into microcracks. For type b wide cracks with a width greater than 0.2 mm, No. 2 nickel-based brazing filler metal is used. This filler metal contains Cr, Fe, and Si elements, and has good high-temperature creep resistance, high strength, and toughness to ensure the mechanical properties and weld penetration of the welded area.

7. The method for classifying and brazing repair of turbine blade rim cracks according to claim 1, characterized in that, In step seven, a flow retardant is coated around the pre-placed brazing material. A high-temperature resistant organosilicon-based composite flow retardant formulation is selected. This flow retardant can form a dense inert isolation film within the brazing temperature range, effectively blocking the capillary spread of the brazing filler metal along the non-repair area metal surface, preventing the brazing filler metal from overflowing into the repair area after melting and causing contamination or damage to other parts of the blade, thus achieving precise control of the brazing filler metal flow area.

8. The method for classifying and brazing repair of turbine blade rim cracks according to claim 1, characterized in that, In step eight, to alleviate thermal stress concentration during the wide crack repair process, the blade is preheated, and the vacuum level of the brazing furnace is controlled at 1×10⁻⁶. -3 Pa, the brazing preheating temperature is set to 650~850°C, the holding time is set to 5~10min, and the heating rate is controlled at 10~15°C / min. This preheating process effectively reduces the thermal shock and thermal stress of the blade during the subsequent high-temperature brazing process, and reduces the deformation and residual stress after repair.

9. The method for classifying and brazing repair of turbine blade rim cracks according to claim 1, characterized in that, In step nine, after the preheating and holding period, the temperature continues to rise at a rate controlled at 10-15°C / min, while maintaining the vacuum level of the brazing furnace at 1×10⁻⁶. -3 Pa, the brazing temperature is set to 975~1175°C, the holding time is set to 15~30min, and after the holding time is completed, the brazing filler metal is cooled to below 80~100°C and then removed from the furnace. The overall vacuum heating ensures that the brazing filler metal is fully melted and fills the crack defects by using capillary action, thus avoiding uneven heating.

10. A method for classifying and brazing repairing turbine blade rim cracks according to claim 1, characterized in that, In steps ten and eleven, the polished blades are ultrasonically cleaned at a temperature of 50-80°C for 15-30 minutes. After cleaning, they are blown clean with compressed air. Then, pneumatic polishing is performed, with appropriate speed and force selected according to different parts to remove excess brazing material and ensure the flatness of the blade surface. Finally, the repaired blades are subjected to fluorescence detection and the results are recorded. For unqualified blades, the corresponding steps are repeated for re-welding, and the re-welding is not performed more than twice.