A method for repairing the tip of a single crystal superalloy turbine rotor blade of a gas turbine

Abstract

The invention discloses a method for repairing the tip of a single-crystal superalloy turbine rotor blade of a gas turbine, belonging to the technical field of rotor blade tip repair. The fast-frequency pulse mode of a DC fast-frequency pulse welding machine is used to reduce the heat input during the repair process and avoid the occurrence of tissue recrystallization. The directionally solidified superalloy welding wire used ensures that the tensile strength and high-temperature creep performance reach more than 85% of those of single-crystal DD5. The method of water-cooling the blade tenon and heating the blade tip is adopted. On the one hand, it ensures that the growth direction of the surfacing structure is parallel to the <001> orientation, eliminates the transverse grain boundaries perpendicular to the stress axis direction, and at the same time avoids the formation of grains with large orientation differences and abnormal grains, ensuring the overall thermal fatigue resistance of the blade. On the other hand, the surfacing layer at the blade tip is in a high-temperature state, effectively reducing the residual stress and improving the service life of the blade.

Description

Technical Field

[0001] The present invention belongs to the technical field of rotor blade tip repair, and in particular relates to a method for repairing the tip of a combustion engine single crystal high-temperature alloy turbine rotor blade. Background Art

[0002] Single crystal blades are key technologies and components of modern aircraft engines. An important indicator of aircraft engines is the temperature before the turbine. The higher this indicator, the greater the engine thrust. However, the temperature of the gas coming out of the combustion chamber is as high as thousands of degrees, which has exceeded the melting point of steel. Under such high temperature, high speed, and high pressure gas impact, the high-pressure turbine must also rotate at high speed to drive the high-pressure compressor. Therefore, the requirements for materials and processes are extremely high. Single crystal blades are the most ideal material for high-pressure turbine blades. The so-called single crystal blade refers to a blade with only one crystal material. The grain boundary is parallel to the stress direction, eliminating voids and cracks. Only in this way can the blade withstand the impact of engine gas and have higher reliability. Therefore, single crystal blades have become the mainstream material for high-pressure turbine blades of modern aircraft engines.

[0003] Aircraft engines and ground-based gas turbines are known as the "crown" of modern industry and a key indicator of a nation's comprehensive strength. Turbine blades, owing to their location at the highest temperatures, most complex stresses, and harshest environments, are considered the most critical components and are often called the "crown jewels."

[0004] Because gas turbine OEMs (original equipment manufacturers) maintain a monopoly on turbine blade repair technology, repairs must be sent to the OEM. Complete external reliance leads to uncontrolled cycles and costs, which in turn creates maintenance cycle risks (and significant foreign exchange expenditures). Therefore, advanced and reliable repair technologies are urgently needed to repair locally damaged turbine rotor blades.

[0005] Due to their harsh service environments, single-crystal blades are susceptible to localized damage, including tip wear, cracks, and ablation. Developing reliable blade repair technology is crucial for extending aero-engine life and reducing costs. A single single-crystal blade can cost between 300,000 and 800,000 yuan. Repairing single-crystal blades requires specialized processes. While maintaining the performance of the repaired area is crucial, high-angle grain boundaries and stray crystals are prone to forming, which can lead to cracks during service. Furthermore, recrystallization of the blade matrix, which can degrade high-temperature performance, must be prevented. Therefore, the selection of repair materials and heat input control during the repair process require strict control. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method for repairing the tip of a gas turbine single crystal high temperature alloy turbine rotor blade in response to the shortcomings of the background technology. The method uses the fast frequency pulse mode of a DC fast frequency pulse welding machine to reduce the heat input during the repair process and avoid the occurrence of tissue recrystallization. The directionally solidified high temperature alloy welding wire used ensures that the tensile strength and high temperature endurance performance reach 85% of the single crystal DD5. The blade tenon is water-cooled and the blade tip is preheated. On the one hand, it avoids the generation of cracks at the repair site, and on the other hand, it ensures that the tissue growth direction is consistent with the <001> parallel to the direction, forming a directionally solidified structure.

[0007] The present invention adopts the following technical solutions to solve the above technical problems:

[0008] A method for repairing a tip of a gas turbine single crystal high temperature alloy turbine rotor blade comprises the following steps:

[0009] Step 1, inspection and recording of blades: Inspect the blades for cracks, wear, ablation, pits and other defects, and record the type, quantity, size and location;

[0010] Step 2: Blade size inspection, flow rate test, and weighing: Use a 3D optical scanner or a three-dimensional coordinate measuring machine to scan or inspect each blade piece by piece, and record the blade tip size deviation; measure the flow rate of each blade and each cooling channel. The blade flow rate before repair must meet the requirement of 7±1L / min. If not, check whether the air film holes are blocked. If blocked, clear them.

[0011] Step 3, sand blasting and cleaning:

[0012] Step 3.1: Use 60-120 mesh quartz sand or corundum sand to perform dry powder sandblasting on the surface of the single crystal blade to remove the carbon deposit layer and oxide film on the surface until the carbon deposit and oxide film on the surface are completely removed. The sandblasting time for the same part shall not exceed 1 minute. After the blade is sandblasted, use compressed air to remove the sand and dust on the blade surface and inspect the appearance.

[0013] Step 3.2, immerse the leaves in a 3% to 5% (by mass) water-based degreasing agent aqueous solution, clean them in an ultrasonic cleaner for 5 to 10 minutes, and then rinse them with running cold water;

[0014] Step 3.3, drying the cleaned leaves in a drying oven at a temperature of 60°C to 100°C for 20 to 60 minutes;

[0015] Step 4: Remove the blade coating;

[0016] Step 4.1, use a brush to apply the protective agent to the uncoated blade tenon part;

[0017] Step 4.2: Immerse the blade in the acidic solution with corrosion inhibitor added. Check the peeling of the surface coating of the blade every 10 minutes. After complete peeling, neutralize it with an alkaline solution, then rinse it with running water and dry it.

[0018] Step 4.3: Finally, place the single-crystal blade in a drying oven for drying at a temperature of 60°C to 100°C for a duration of 30 minutes to 60 minutes.

[0019] Step 4.4: Use acetone to remove the tenon and the protective agent, and then perform dry powder blasting on the surface of the single-crystal blade with 60 - 120 mesh quartz sand or corundum sand.

[0020] Step 5: Defect inspection: Use a magnifying glass with a magnification of 3 - 5 times to check the surface of the blade and perform fluorescence inspection according to HB / Z61. Mark the cracks, lengths, and positions. For cracks, ablation, etc. that appear at the blade tip and the airfoil surface 1 mm higher than the adjacent cover plate, repair by surfacing is allowed. If there are cracks at other positions, it shall be scrapped. Grind the area to be surfaced before surfacing.

[0021] Step 6: Blade tip surfacing:

[0022] Step 6.1: Use a tenon water-cooled fixing tooling, which also serves as a machining and inspection tooling, to perform plug-in fixing on the tenon of the single-crystal blade. The water flow rate in the flow channel of the tenon water-cooled fixing tooling is 5 - 10 L / min. Use an induction heating device with a conforming copper tube coil at the blade tip for heating. The distance between the coil and the blade tip is 5 - 10 mm, and the temperature at the blade tip is 450 - 550°C (measured and controlled by an infrared temperature control gun).

[0023] Step 6.2: Perform GTAW surfacing 5 - 10 s after preheating to the appropriate temperature. Use a DC fast-frequency pulsed welding machine for the equipment. The tungsten electrode diameter is 1.2 mm - 1.6 mm, the nozzle diameter is 8 mm, welding mode: fast-frequency pulsed mode, fast-frequency current is 20 - 30 A, frequency f = 20000 Hz, main current = 30 A, duration 0.1 s, secondary current 10 A, duration 0.01 - 0.05 s, argon gas flow rate is 10 L / min - 12 L / min; the width of the blade tip is 0.8 - 2.0 mm, the height of the blade tip defect is 1 - 2 mm, and the surfacing height is 3 - 4 mm. After surfacing, first turn off the water flow, and then reduce the temperature of the induction heating device at a rate of 20°C / min until it reaches 100°C and then turn off the induction heating device.

[0024] Step 7: Stress relief annealing: Use a vacuum heat treatment furnace to start heating under the condition that the vacuum degree is better than 10 Pa, heat to 950 - 1050°C, hold for 1 h, and quickly cool to room temperature with argon.

[0025] Step 8, perform non-destructive testing on the surfacing area at the blade tip and the nearby areas, including visual inspection, X-ray inspection, and fluorescent inspection; if unqualified, return to Step 6 for repair welding until there are no defects in the surfacing area at the blade tip, and the repair welding at the same surfacing area shall not exceed 3 times; Step 9, blade tip profile machining: fix and position the blade using a tooling fixture, and then use a numerically controlled machine tool to machine the blade tip of the surfaced blade according to the digital model of the blade, leaving a 0.2 mm margin on both sides of the blade tip; after machining, use tools such as a file and an oilstone to polish the blade tip, and the final machined blade tip profile shall be smooth and seamless with the original airfoil profile;

[0026] Step 10, restore the coating: restore the coating on the blade surface, with a coating thickness of 30 - 70 μm;

[0027] Step 11, final inspection: including visual inspection, dimensional inspection, weighing inspection, flow inspection, and fluorescent inspection.

[0028] As a further preferred solution of a method for repairing the blade tip of a single-crystal superalloy turbine rotor blade for a gas turbine of the present invention, in Step 6, the blade material is DD5 single crystal, and the welding wire is a directionally solidified superalloy, and its composition is: C 0.08 - 0.15, Cr 6.00 - 7.50, Co 11.00 - 12.00, W 4.50 - 5.00, Mo 1.00 - 2.00, Al 5.00 - 6.00, Ta 6.00 - 6.50, Re 2.50 - 3.50, Hf 1.30 - 1.70, B 0.01 - 0.02, Ni 60.00 - 65.00.

[0029] As a further preferred solution of a method for repairing the blade tip of a single-crystal superalloy turbine rotor blade for a gas turbine of the present invention, the role of Ta: promotes the dissolution of Cr into the γ-phase matrix, causes lattice distortion, improves the strength of the solid solution, enhances the oxidation resistance and high-temperature corrosion resistance of the nickel-based superalloy, and at the same time, has an impact on the tensile strength and yield strength;

[0030] Cr: simultaneously combines with O to form Cr2O3, which is resistant to high temperature and corrosion;

[0031] Co: increases the solubility of Cr, Mo, W, and C in the γ-phase matrix, improves the morphology of carbides at the grain boundaries, strengthens the grain boundaries, and at the same time plays a role in solid solution strengthening and improves the hot corrosion resistance;

[0032] The role of C: a dendrite-interstitial and grain boundary strengthening element, forms discontinuous granular carbides, such as MC, M7C3, M6C, M23C6, etc., to prevent grain boundary sliding;

[0033] The role of Re: refines the structure of the γ′ phase, controls the content at 2.5% - 3.5%, improves the creep properties of the superalloy, and excessive content will lead to the precipitation of TCP phase and a serious reduction in the creep life;

[0034] The role of Ni: a stabilizing element of the austenite phase, forming a solid solution with elements such as Cr, Co, Mo, Al, C, and B, and at the same time being pro-O and promoting the formation of oxide film;

[0035] The role of W: causing significant lattice expansion, forming a long-range stress field, preventing dislocation movement, and thus increasing yield strength;

[0036] The role of Mo is basically the same as that of W, which is solid solution strengthening and improves the passivation and reduction resistance of the alloy. However, the content must be controlled below 2%. Too high a content can easily cause structural segregation.

[0037] Function of B: Microalloying element, enriched at the grain boundaries, eliminating the precipitation of harmful phases at the grain boundaries, and improving the durability and creep properties;

[0038] The role of Al: It forms γ′-Ni3Al with Ni, which improves the strength and also improves the oxidation resistance and corrosion resistance;

[0039] The role of Hf: improve the high-temperature durable plasticity of high-temperature alloys, eliminate high-temperature notch sensitivity, increase the amount of γ′, and improve the stability of MC-type carbides.

[0040] As a further preferred embodiment of the present invention's method for repairing the tip of a gas turbine single-crystal high-temperature alloy turbine rotor blade, the tip microstructure after surfacing welding is all small-angle grain boundaries, wherein the phase difference between adjacent grains is less than 10°, and there are no stray crystals; the hardness of the surfacing layer is 460HV-475HV, while the hardness of the DD5 matrix is about 440HV; the room temperature tensile strength of the joint tensile specimen is more than 90% of that of the DD5 matrix, which is 900-950MPa, and the high-temperature endurance performance is more than 85% of that of the DD5 matrix.

[0041] As a further preferred embodiment of the method for repairing a tip of a combustion engine single crystal high temperature alloy turbine rotor blade of the present invention, in step 6,

[0042] The tenon water-cooled fixing fixture, which is both a machining and testing fixture, is printed using laser selective melting technology. The material is GH4169, and then the tenon mating surface is machined to ensure a positioning accuracy of 0.01mm and an inner flow channel diameter of φ6mm.

[0043] As a further preferred embodiment of the method for repairing a tip of a combustion engine single crystal high temperature alloy turbine rotor blade of the present invention, in step 11,

[0044] Visual inspection: The blade surface must not be bumped or scratched; the coating surface must not have defects such as warping, bubbling, and cracking, and the tenon area must not be coated; the air film holes on the exhaust side of each blade must be visually and probe-checked, and the air film holes must not be blocked;

[0045] Dimensional inspection: Use the inspection tooling and measure the profile tolerance of the tip surface of the repaired part with a coordinate measuring machine. A deviation of ±0.1 mm is considered qualified.

[0046] Weight inspection: A deviation of ±5 g from the weight of the new part is considered qualified.

[0047] Flow rate inspection: A main channel flow rate of 6 - 8 L / min is considered qualified.

[0048] Fluorescent inspection: Conduct fluorescent inspection in accordance with HB / Z61. Cracks, pores, inclusions, and lack of fusion defects are not allowed.

[0049] Compared with the prior art, the present invention adopts the above technical solutions and has the following technical effects:

[0050] 1. The present invention uses the fast frequency pulse mode of a DC fast frequency pulse welder, reducing the heat input during the repair process and avoiding the occurrence of recrystallization of the microstructure.

[0051] 2. The directionally solidified superalloy welding wire used in the present invention ensures that the tensile strength and high-temperature creep properties reach 85% of those of single crystal DD5.

[0052] 3. The present invention uses the method of water cooling the blade tenon and heating the tip. On the one hand, it ensures that the growth direction of the surfacing microstructure is parallel to the <001> orientation, eliminating the transverse grain boundaries perpendicular to the stress axis direction, and at the same time avoiding the formation of grains with large orientation differences and abnormal grains, ensuring the overall thermal fatigue resistance of the blade. On the other hand, the surfacing layer at the tip is in a high-temperature state, effectively reducing the residual stress and increasing the service life of the blade. Description of the Drawings

[0053] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention, and those of ordinary skill in the art can also obtain other drawings based on these drawings without creative efforts.

[0054] Figure 1 It is a schematic diagram of a single crystal superalloy turbine rotor blade, a water-cooled fixing tooling, and a heating device of the present invention;

[0055] Figure 2 It is a schematic diagram of the tenon water-cooled fixing tooling (serving as a machining and inspection tooling) of the present invention;

[0056] Figure 3 It is a schematic diagram of the internal flow channel of the tenon water-cooled fixing tooling of the present invention;

[0057] Figure 4 It is the morphology after surfacing at the tip of the present invention

[0058] Figure 5 It is a schematic diagram of the morphology of the blade tip after processing according to the present invention;

[0059] Figure 6 It is a schematic diagram of the surfacing directional solidification structure (low magnification and high magnification) of the blade tip of a single crystal superalloy turbine rotor blade according to the present invention. Specific implementation manners

[0060] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings:

[0061] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0062] Embodiment 1

[0063] As Figures 1 to 6 shown, a method for repairing the blade tip of a single crystal superalloy turbine rotor blade of a gas turbine includes the following steps:

[0064] Step 1: Inspection and recording of the blade. Inspect the types, quantities, sizes and positions of defects such as cracks, wear, ablation, pits, etc. on the blade and record them;

[0065] Step 2: Dimension inspection, flow rate test and weighing of the blade. Scan each blade one by one using a three-dimensional optical scanner, record the dimensional deviation of the blade tip, and the blade tip is defective by 1.8 mm. Measure the flow rate of the blade and each cooling channel. The flow rate of the blade before repair is 7.7 L / min;

[0066] Step 3: Blasting and cleaning. Use 60-120 mesh quartz sand or corundum sand to perform dry blasting treatment on the surface of the single crystal blade to remove the surface carbon deposit layer and oxide film until all the surface carbon deposits and oxide films are removed. The blasting time for the same part does not exceed 1 min. After the blade is blasted, use compressed air to remove the sand and dust on the blade surface and check the appearance. Immerse the blade in an aqueous solution of 3%-5% water-based degreaser (mass ratio), clean it with an ultrasonic cleaner for 5 min-10 min, and then rinse it thoroughly with flowing cold water. Place the cleaned blade in a drying oven for drying, the drying temperature is 60°C-100°C, and the drying process time is 20 min-60 min;

[0067] Step 4: Remove the blade coating. Apply the protective agent to the uncoated blade tenon part with a brush; Immerse the blade in an acidic solution added with a corrosion inhibitor, check the peeling of the blade surface coating every 10 minutes. After complete peeling, neutralize it with an alkaline solution, then rinse with running water and dry; Finally, place the single crystal blade in a drying oven for drying, at a temperature of 60°C - 100°C for a duration of 30 minutes - 60 minutes; Use acetone to remove the tenon and the protective agent, and then perform dry powder blasting treatment on the surface of the single crystal blade with 60 - 120 mesh quartz sand or corundum sand;

[0068] Step 5: Defect inspection. Use a magnifying glass with a magnification of 3 - 5 times to check the blade surface and perform fluorescence inspection according to HB / Z61, mark the cracks, lengths, and positions. For cracks, ablation, etc. that appear at the blade tip and the airfoil surface 1 mm higher than the cover plate adjacent to it, surfacing repair is allowed. If there are cracks in other positions, it shall be scrapped. Grind the area to be surfaced before surfacing;

[0069] Step 6: Blade tip surfacing. Use the device shown in Figure 1 to fix the tenon of the single crystal blade of the gas turbine by plugging and unplugging, and the water flow rate in the flow channel of the tenon water-cooled fixing tooling is 5 - 10 L / min. Use an induction heating device with a conforming copper tube coil to heat the blade tip, and the distance between the coil and the blade tip is 5 - 10 mm, and the temperature at the blade tip is 450 - 550°C (measured and controlled by an infrared temperature control gun); After preheating to the specified temperature, perform argon arc surfacing after 5 - 10 s. The equipment uses a DC fast frequency pulse welding machine, with a tungsten electrode diameter of 1.2 mm - 1.6 mm, a nozzle diameter of 8 mm, welding mode: fast frequency pulse mode, fast frequency current of 20 - 30 A, frequency f = 20000 Hz, main current = 30 A, duration 0.1 s, secondary current 10 A, duration 0.01 - 0.05 s, and argon gas flow rate of 10 L / min - 12 L / min. The width of the blade tip is 0.8 - 2.0 mm, the height of the blade tip defect is 1.8 mm, and the surfacing height is 3.5 mm. After surfacing, first close the water flow, and then reduce the temperature of the induction heating device at a rate of 20°C / min until it is reduced to 100°C and then turn off the induction heating device;

[0070] As shown in Figure 6 the blade material is DD5 single crystal, and the welding wire is a directionally solidified superalloy, with its composition: C 0.10%, Cr 6.50%, Co 11.00%, W 5.00%, Mo 1.50%, Al 5.20%, Ta 6.48%, Re 2.8%, Hf 1.5%, B 0.01%, Ni 60.91%.

[0071] The microstructure of the blade tip after surfacing is as shown in Figure 5As shown, the structure is composed of small-angle grain boundaries (the phase difference between adjacent grains is less than 10°), and there are no abnormal grains. The hardness of the surfacing layer is about 470 HV, the DD5 substrate is 440 HV, the tensile strength of the joint tensile specimen at room temperature reaches 92% of the DD5 substrate, which is 920 MPa, and the high-temperature creep rupture property is 87% of the DD5 substrate.

[0072] Step 7: Stress relief annealing. Use a vacuum heat treatment furnace to start heating under the condition that the vacuum degree is better than 10 Pa, heat to 1000 °C ± 10 °C, hold for 1 h, and quickly cool to room temperature with argon.

[0073] Step 8: Nondestructive testing is carried out on the surfacing area at the blade tip and the nearby area, including visual inspection, X-ray inspection, and fluorescence inspection. If it is unqualified, return to Step 6 for repair welding until there are no defects in the surfacing area at the blade tip. The repair welding at the same surfacing area shall not exceed 3 times. Visual inspection: There shall be no defects such as lack of material, cracks, and pores. X-ray inspection: Cracks, inclusions, lack of fusion, etc. are not allowed in accordance with HB / Z60. Fluorescence inspection is carried out in accordance with HB / Z61, and cracks, pores, inclusions, lack of fusion, etc. are not allowed.

[0074] Step 9: Machining of the blade tip profile. Use the Figure 2 tooling shown to fix and position the blade, and then use a numerical control machine tool to machine the blade tip after surfacing according to the digital model of the blade, leaving a margin of 0.2 mm on both sides of the blade tip. After machining, use tools such as files and oilstones to polish the blade tip. The final machined blade tip profile shall be smooth and seamless with the original airfoil profile.

[0075] Step 10: Restoration of the coating. Restore the coating on the blade surface, and the coating thickness is 30 - 50 μm.

[0076] Step 11: Final inspection. It includes visual inspection, dimensional inspection, weighing inspection, flow inspection, and fluorescence inspection.

[0077] Visual inspection: There shall be no bumps and scratches on the blade surface; there shall be no defects such as peeling, blistering, and cracking on the coating surface, and there is no coating in the tenon area. Visually and with a probe, check the film holes on the exhaust side of each blade one by one, and the film holes are not allowed to be blocked.

[0078] Dimensional inspection: Use the Figure 2 detection tooling, and then use a coordinate measuring machine to measure the profile tolerance of the blade tip profile at the repaired part. A deviation of ±0.06 mm is considered qualified.

[0079] Weighing inspection: A weight deviation of 1.5 g from the new part is considered qualified.

[0080] Flow inspection: A main channel flow rate of 7.5 L / min is considered qualified.

[0081] Fluorescent inspection: Conduct fluorescent inspection in accordance with HB / Z61, and there are no defects such as cracks, pores, inclusions, lack of fusion, etc.

[0082] Step 12: Package and ship.

[0083] Example 2

[0084] A method for repairing the tip of a single crystal superalloy turbine rotor blade of a gas turbine, comprising the following steps:

[0085] Step 1: Inspection and recording of the blade. Inspect the types, quantities, sizes and positions of defects such as cracks, wear, ablation, pits, etc. on the blade and record them;

[0086] Step 2: Dimension inspection, flow rate test and weighing of the blade. Use a coordinate measuring machine to scan or detect the blade, record the tip dimension deviation, and the tip defect height is about 1.4 mm. Measure the flow rate of the blade and each cooling channel, and the flow rate of the blade before repair meets 7.1 L / min;

[0087] Step 3: Blasting and cleaning. Use 60-120 mesh quartz sand or corundum sand to conduct dry powder blasting on the surface of the single crystal blade to remove the carbon deposit layer and oxide film on the surface until all the carbon deposits and oxide films on the surface are removed. The blasting time for the same part does not exceed 1 min. After the blade is blasted, use compressed air to remove the sand and dust on the blade surface and check the appearance. Immerse the blade in an aqueous solution of 3%-5% water-based degreaser (mass ratio), clean it with an ultrasonic cleaner for 5-10 min, and then rinse it thoroughly with flowing cold water. Place the cleaned blade in a drying oven for drying, the drying temperature is 60°C-100°C, and the drying process time is 20 min-60 min;

[0088] Step 4: Remove the blade coating. Use a brush to apply a protective agent to the tenon part of the blade without coating; Immerse the blade in an acidic solution added with a corrosion inhibitor, check the peeling of the blade surface coating every 10 min. After complete peeling, use an alkaline solution for neutralization treatment, then rinse with running water and dry; Finally, place the single crystal blade in a drying oven for drying, the temperature is 60°C-100°C, and the duration is 30 min-60 min; Use acetone to remove the protective agent from the tenon, and then use 60-120 mesh quartz sand or corundum sand to conduct dry powder blasting on the surface of the single crystal blade;

[0089] Step 5: Defect inspection. Use a 3-5 times magnifying glass to inspect the blade surface and conduct fluorescent inspection in accordance with HB / Z61, and mark the cracks, lengths and positions. For cracks, ablation, etc. that appear at the tip and the airfoil surface 1 mm higher than the cover plate adjacent to it, repair by surfacing is allowed. If there are cracks in other positions, it shall be scrapped. Grind the area to be surfaced at the tip before surfacing;

[0090] Step 6: Tip surfacing. Use Figure 1The device shown fixes the tenon of the single crystal blade of the gas turbine by plugging, and the water flow rate in the flow channel of the tenon water-cooling fixing tooling is 5 - 10 L / min. An induction heating device with a conformal copper tube coil is used for heating at the blade tip, the distance between the coil and the blade tip is 5 - 10 mm, and the temperature at the blade tip is 450 - 550 °C (measured and controlled by an infrared temperature control gun); after preheating to the set temperature, argon arc surfacing is carried out after 5 - 10 s. The equipment uses a DC high-frequency pulsed welding machine, the tungsten electrode diameter is 1.2 mm - 1.6 mm, the nozzle diameter is 8 mm, the welding mode: high-frequency pulsed mode, the high-frequency current is 20 - 30 A, the frequency f = 20000 Hz, the main current = 30 A, the duration is 0.1 s, the secondary current is 10 A, the duration is 0.01 - 0.05 s, and the argon gas flow rate is 10 L / min - 12 L / min. The surfacing height is 3.0 mm. After surfacing, first turn off the water flow, and then control the temperature of the induction heating device to decrease at 20 °C / min until it reaches 100 °C and then turn off the induction heating device;

[0091] Among them, the blade material is DD5 single crystal, and the welding wire is a directionally solidified superalloy, and its composition: C 0.12%, Cr 6.30%, Co 11.50%, W 4.50%, Mo 1.50%, Al 5.20%, Ta 6.48%, Re 3.2%, Hf 1.3%, B 0.01%, Ni 60.71%.

[0092] The microstructure at the blade tip after surfacing is as Figure 5 shown. The microstructure is all small-angle grain boundaries (the phase difference between adjacent grains is less than 10°), and there are no abnormal grains. The hardness of the surfacing layer is about 465 HV, the DD5 matrix is 440 HV, the room temperature tensile strength of the joint tensile specimen reaches 91% of the DD5 matrix, which is 910 MPa, and the high-temperature creep rupture performance is 86% of the DD5 matrix.

[0093] Step 7: Stress relief annealing. Use a vacuum heat treatment furnace, start heating under the condition that the vacuum degree is better than 10 Pa, heat to 1020 °C ± 10 °C, hold for 1 h, and quickly cool to room temperature with argon;

[0094] Step 8: Nondestructive testing is carried out on the surfacing area and the nearby area at the blade tip, including visual inspection, X-ray inspection, and fluorescent inspection. If it is unqualified, return to step six for repair welding until there are no defects in the surfacing area at the blade tip, and the repair welding at the same surfacing place does not exceed 3 times; Visual inspection: no defects such as lack of meat, cracks, pores, etc.; X-ray inspection: no cracks, inclusions, lack of fusion and other defects are allowed in accordance with HB / Z60; Fluorescent inspection is carried out in accordance with HB / Z61, and there are no cracks, pores, inclusions, lack of fusion and other defects.

[0095] Step 9: Machining of the blade tip profile. Use Figure 2The shown tooling fixture fixes and positions the blade, and then uses a numerical control machine tool to machine the tip of the blade after surfacing according to the digital model of the blade, leaving a margin of 0.2 mm on both sides of the tip. After machining, use tools such as a file and an oilstone to polish the tip. The final machined tip surface should be smooth and seamless with the original airfoil surface;

[0096] Step 10: Restore the coating. Restore the coating on the blade surface, with the coating thickness being 30 - 70 μm;

[0097] Step 11: Final inspection. Include visual inspection, dimensional inspection, weighing inspection, flow inspection, and fluorescent inspection.

[0098] Visual inspection: There shall be no bumps or scratches on the blade surface; there shall be no defects such as peeling, blistering, or cracking on the coating surface, and there is no coating in the tenon area; visually and with a probe, inspect each blade's film cooling holes on the exhaust side one by one, and the film cooling holes shall not be blocked;

[0099] Dimensional inspection: Use Figure 2 the inspection tooling fixture, and then use a coordinate measuring machine to measure the profile tolerance of the tip surface of the repaired part, with a deviation of ±0.05 mm being qualified;

[0100] Weighing inspection: A weight deviation of 1.2 g from the new part is qualified;

[0101] Flow inspection: A main channel flow rate of 7.2 L / min is qualified;

[0102] Fluorescent inspection: Conduct fluorescent inspection according to HB / Z61, with no defects such as cracks, pores, inclusions, or lack of fusion.

[0103] Step 12: Pack and ship.

[0104] Those skilled in the art of this technology can understand that, unless otherwise defined, all terms (including technical terms and scientific terms) used here have the same meaning as the general understanding of those of ordinary skill in the art to which this invention belongs. It should also be understood that terms defined in general dictionaries should be understood to have a meaning consistent with their meaning in the context of the prior art, and will not be interpreted with idealized or overly formal meanings unless defined as such here.

[0105] The above embodiments are only for illustrating the technical idea of the present invention, and cannot be used to limit the protection scope of the present invention. Any modification made on the basis of the technical solution according to the technical idea proposed by the present invention falls within the protection scope of the present invention. The above has made a detailed description of the embodiments of the present invention, but the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those of ordinary skill in the art, various changes can be made without departing from the gist of the present invention.

Claims

1. A method for repairing the tip of a single crystal superalloy turbine rotor blade of a gas turbine, characterized in that: Specifically, it includes the following steps: Step 1, inspection and recording of the blade: Inspect the crack, wear, ablation, pit defect type, quantity, size and position of the blade and record them; Step 2, dimension inspection, flow rate test and weighing of the blade: Use a three-dimensional optical scanner or a coordinate measuring machine to scan or detect each blade one by one, and record the tip dimension deviation; Measure the flow rate of each blade and each cooling channel. The flow rate of the blade before repair should meet the requirement of 7±1 L / min. If not, check whether the film cooling holes are blocked. If blocked, they need to be dredged; Step 3, sandblasting and cleaning: Step 3.1, conduct dry sandblasting treatment on the surface of the single crystal blade with 60-120 mesh quartz sand or corundum sand to remove the carbon deposition layer and oxide film on the surface until all the carbon deposition and oxide film on the surface are removed. The sandblasting time for the same part does not exceed 1 minute. After sandblasting the blade, use compressed air to remove the sand and dust on the blade surface and check the appearance; Step 3.2, immerse the blade in an aqueous solution with a mass ratio of 3%-5% water-based degreasing agent, and clean it with an ultrasonic cleaner for 5-10 minutes, and then rinse it thoroughly with flowing cold water; Step 3.3, place the cleaned blade in a drying oven for drying. The drying temperature is 60℃-100℃, and the drying process time is 20-60 minutes; Step 4: Remove the blade coating; Step 4.1, apply the protective agent on the blade tenon part without coating with a brush; Step 4.2, immerse the blade in an acidic solution added with an inhibitor, check the peeling situation of the blade surface coating every 10 minutes. After complete peeling, perform neutralization treatment with an alkaline solution, and then rinse and dry it with running water; Step 4.3, finally place the single crystal blade in a drying oven for drying, the temperature is 60℃-100℃, and the duration is 30-60 minutes; Step 4.4, use acetone to remove the protective agent at the tenon, and then conduct dry sandblasting treatment on the surface of the single crystal blade with 60-120 mesh quartz sand or corundum sand; Step 5: Defect inspection: Use a 3-5 times magnifying glass to inspect the blade surface and conduct fluorescence inspection according to HB / Z61, and mark the crack, length and position; For cracks and ablation at the blade tip and the airfoil surface 1 mm higher than the cover plate adjacent to it, repair by surfacing is allowed. If there are cracks at other positions, it shall be scrapped. Grind the area to be surfaced before surfacing; Step 6: Blade tip surfacing: Step 6.1, use a tenon water-cooled fixing tooling, which also serves as a machining and inspection tooling, to fix the single crystal blade tenon in a plug-and-play manner. The water flow rate in the flow channel of the tenon water-cooled fixing tooling is 5-10 L / min. Use an induction heating device with a conforming copper tube coil to heat the blade tip. The distance between the coil and the blade tip is 5-10 mm, and the temperature at the blade tip is 450-550℃; Step 6.2, after preheating to the appropriate temperature, perform argon arc surfacing within 5 - 10 s. The equipment uses a DC high-frequency pulsed welder. The tungsten electrode diameter is 1.2 mm - 1.6 mm, the nozzle diameter is 8 mm. Welding mode: high-frequency pulsed mode, high-frequency current 20~30 A, frequency f = 20000 Hz, main current = 30 A, duration 0.1 s, secondary current 10 A, duration 0.01~0.05 s, argon gas flow rate 10 L / min~12 L / min; the width of the blade tip is 0.8~2.0 mm, the height of the tip defect is 1~2 mm, and the surfacing height is 3~4 mm; after surfacing, first turn off the water flow, and then reduce the temperature of the induction heating device at a rate of 20 °C / min until it reaches 100 °C and then turn off the induction heating device; Step 7, stress relief annealing: Use a vacuum heat treatment furnace to start heating under the condition that the vacuum degree is better than 10 Pa, heat to 950 - 1050 °C, hold for 1 h, and quickly cool to room temperature with argon; Step 8, perform non-destructive testing on the surfacing area at the blade tip and the nearby area, including visual inspection, X-ray inspection, and fluorescence inspection; if unqualified, return to Step 6 for repair welding until there are no defects in the surfacing area at the blade tip, and the repair welding at the same surfacing area does not exceed 3 times; Step 9, blade tip profile machining: Use a fixture to fix and position the blade, and then use a numerically controlled machine tool to machine the blade tip after surfacing according to the digital model of the blade, leaving 0.2 mm allowance on both sides of the blade tip; after machining, use a file and an oilstone tool to polish the blade tip. The finally machined blade tip profile should be smooth and conform to the original airfoil profile; Step 10, restore the coating: Restore the coating on the blade surface, and the coating thickness is 30 - 70 μm; Step 11, final inspection: Include visual inspection, dimensional inspection, weighing inspection, flow inspection, and fluorescence inspection; In Step 6, the blade material is DD5 single crystal, and the welding wire is a directionally solidified superalloy, with its composition: C 0.08 - 0.15, Cr 6.00 - 7.50, Co 11.00 - 12.00, W 4.50 - 5.00, Mo 1.00 - 2.00, Al 5.00 - 6.00, Ta 6.00 - 6.50, Re 2.5 - 3.5, Hf 1.3 - 1.7, B 0.01 - 0.02, Ni 60.00 - 65.00; After surfacing, the microstructure at the blade tip is all small-angle grain boundaries. Among them, the phase difference between adjacent grains is less than 10°, and there are no abnormal grains; the hardness of the surfacing layer is 460 HV - 475 HV, the DD5 matrix is about 440 HV, the room temperature tensile strength of the joint tensile specimen reaches more than 90% of the DD5 matrix, which is 900 - 950 MPa, and the high-temperature creep rupture performance is more than 85% of the DD5 matrix.

2. A method for repairing the tip of a single-crystal superalloy turbine rotor blade of a gas turbine according to claim 1, characterized in that: In Step 6, The tenon water-cooled fixing fixture, which also serves as a machining and inspection fixture, is printed by laser selective melting forming technology, made of GH4169, and then perform machining on the mating surface of the tenon of the tenon to ensure the positioning accuracy of 0.01 mm, and the inner flow channel diameter is φ6 mm.

3. A method for repairing the tip of a single crystal superalloy turbine rotor blade of a gas turbine according to claim 1, characterized in that: In Step 11, Visual inspection: There shall be no bumps or scratches on the blade surface; there shall be no peeling, blistering or cracking defects on the coating surface, and there is no coating in the tenon area; Visually and with a probe, check the film cooling holes on the exhaust edge of each blade one by one. The film cooling holes shall not be blocked; Dimensional inspection: Use the inspection tooling and a coordinate measuring machine to measure the profile tolerance of the blade tip surface of the repaired part. A deviation of ±0.1 mm is qualified; Weight inspection: A deviation of ±5 g from the weight of the new part is qualified; Flow inspection: A main channel flow rate of 6 - 8 L / min is qualified; Fluorescent inspection: Conduct fluorescent inspection according to HB / Z61. Cracks, pores, inclusions and lack of fusion defects are not allowed.

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