Method for eliminating near-surface looseness of turbine blade through brazing and hot isostatic pressing

Abstract

The invention discloses a method for eliminating turbine blade near-surface looseness through brazing and hot isostatic pressing, and relates to the technical field of high-temperature alloy brazing. Through the brazing technology, brazing filler metal powder of a unique formula is used for conducting vacuum brazing and thermal diffusion treatment on the surface of a casting with the loose defect, then hot isostatic pressing treatment is used for eliminating microdefects possibly existing after brazing and diffusion treatment, and then the surface of the blade casting is polished. And finally, the polished blade casting is subjected to solid solution and aging treatment, so that the near-surface looseness of the high-temperature alloy turbine blade is removed.

Description

TECHNICAL FIELD

[0001] The application relates to the field of high-temperature alloy brazing technology, and particularly relates to a method for eliminating near-surface porosity of a turbine blade by brazing and hot isostatic pressing. BACKGROUND

[0002] During the preparation of a precision high-temperature alloy turbine blade, near-surface porosity defects are prone to occur in the blade due to alloy solidification shrinkage, gas precipitation and uneven cooling rate. For such porosity defects, the common removal method is to use a sand belt and a grinding wheel and the like to remove the porosity defects by means of manual or automatic polishing. However, in many cases, the surface porosity region is also accompanied by near-surface porosity deeper from the surface. In the process of removing the surface porosity defects, more and more near-surface porosity is exposed, and even if the surface metal is polished to the lower limit of the size tolerance, the near-surface porosity defects in the related region cannot be eliminated. These porosity defects not only reduce the mechanical properties of the blade, such as strength and fatigue life, but also can become the source of crack initiation and propagation, threatening the safe and stable operation of the equipment. Therefore, researchers have been exploring how to eliminate the near-surface porosity defects of the high-temperature alloy turbine blade.

[0003] A Chinese patent application with the publication number CN109940131A discloses a method for reducing the formation of porosity defects in the interior of a single-crystal high-temperature alloy blade tenon. The steps of the method are as follows: (1) when designing a single-crystal high-temperature alloy seed bar mold, ensure that the size of the seed bar is adapted to the size of the blade tenon; (2) connect the seed bar with the single-crystal high-temperature alloy blade tenon on the tooling mold; (3) after waxing, sanding and dewaxing, sinter the corundum mold shell; and (4) place the corundum mold shell in a directional solidification furnace for solidification to prepare a single-crystal high-temperature alloy blade. The application uses the idea of competitive growth to introduce dendritic crystals on the blade body into the thick tenon part, and uses the competitive growth and self-adaptive adjustment between the dendritic crystals introduced by the seed bar and the dendritic crystals at the tenon to make the dendritic crystals in the thick tenon part of the single-crystal high-temperature alloy blade small, that is, to reduce the primary dendritic arm spacing, thereby reducing the formation of porosity defects.

[0004] However, the method is only applicable to the porosity of the tenon part and relies on the extension of the dendritic crystals on the blade body to the tenon. For the porosity of other parts of the blade (such as the blade body and the rim), the method cannot effectively solve the problem. In addition, the method essentially prevents the formation of porosity by optimizing the solidification process, rather than repairing the porosity that has already been generated. SUMMARY

[0005] In view of the deficiencies of the prior art, the application provides a method for eliminating near-surface porosity of a turbine blade by brazing and hot isostatic pressing. By using a unique brazing powder, the surface of the casting with porosity defects is subjected to vacuum brazing and thermal diffusion treatment, and then the micro defects that may exist after brazing and diffusion treatment are eliminated by using hot isostatic pressing, and then the surface of the blade casting is polished, and finally the polished blade casting is subjected to solid solution and aging treatment, thereby realizing the removal of near-surface porosity of the high-temperature alloy turbine blade. The technical solution can not only prevent the formation of porosity, but also repair the generated porosity, and can significantly improve the utilization rate of the high-temperature alloy turbine blade and save costs.

[0006] In order to achieve the above-mentioned purpose, the application adopts the following technical solution:

[0007] The application provides a method for eliminating near-surface porosity of a turbine blade by brazing and hot isostatic pressing, comprising the following steps:

[0008] The surface of the blade casting is cleaned to expose the surface with porosity defects;

[0009] The nickel-based alloy filler powder is prepared from a nickel-based alloy rod by a rotating electrode method, and then the nickel-based alloy filler powder is mixed with an organic binder to form a paste-like filler;

[0010] After vacuum high-temperature degassing of the blade casting, the surface of the blade casting is coated with the paste-like filler;

[0011] The blade casting coated with the paste-like filler is subjected to vacuum brazing by using a plasma arc welding machine, and then subjected to thermal diffusion treatment;

[0012] The blade casting after the thermal diffusion treatment is subjected to hot isostatic pressing;

[0013] The surface of the blade casting after the hot isostatic pressing is polished;

[0014] The polished blade casting is subjected to solid solution and aging treatment to obtain a high-temperature alloy turbine blade with eliminated near-surface porosity;

[0015] The melting point of the nickel-based alloy filler powder is ≤1250℃, and the melting point of the high-temperature alloy turbine blade is ≥1350℃.

[0016] In a possible implementation manner, in the step of cleaning the surface of the blade casting, sand blasting is used for cleaning, and the surface roughness Ra of the blade casting after cleaning is ≤3.2μm.

[0017] After the above cleaning, the oxide scale, oil stains and porosity layer on the surface of the blade casting can be effectively removed, a clean substrate is provided for subsequent coating of the paste-like filler, and the bonding strength of the filler and the substrate is avoided to be affected by impurities.

[0018] If the roughness is too high, impurities or gas can easily remain in the pits, leading to the formation of pores during brazing. If the roughness is too low, the blade casting surface is too smooth, and the subsequent mechanical interlocking between the paste brazing material and the blade casting surface is insufficient. Keeping the blade casting surface roughness Ra ≤ 3.2μm ensures a sufficiently smooth surface to reduce obstacles to brazing material application, while also enhancing the mechanical interlocking between the brazing material and the substrate through a moderate microscopic concave-convex structure, improving interfacial bonding strength.

[0019] In one possible implementation, the components of the nickel-based alloy rod include nickel, chromium, iron, molybdenum, bismuth, boron, carbon and silicon; the mass ratio of the nickel, chromium, iron, molybdenum, bismuth, boron, carbon and silicon is (60-80): (8-15): (5-10): (2-5): (1-5): (1-5): (0.5-1): (2-5); the nickel-based alloy solder powder is prepared from the nickel-based alloy rod by a rotating electrode method; the particle size of the nickel-based alloy solder powder is 10-80 μm.

[0020] The rotating electrode method uses high-speed rotating electrodes to centrifugally break up molten nickel-based alloys into droplets. The droplets rapidly cool and solidify in an inert atmosphere, forming a 10-80μm powder with a narrow particle size distribution and excellent sphericity. The resulting powder disperses well in an organic binder and can penetrate loose pores when applied. After heating, the powder sinters and densifies, thus filling defects. Nickel, chromium, and iron, which account for the largest proportions of the composition, form the matrix skeleton, ensuring the strength of the brazing layer; molybdenum further enhances the high-temperature strength and corrosion resistance of the brazing layer; bismuth, boron, carbon, and silicon, as low-melting-point components, can form a eutectic phase with the metal components, lowering the melting point of the brazing material to ≤1250°C, allowing it to melt below the melting point of the blade substrate (≥1350°C), achieving a repair effect without damaging the blade substrate.

[0021] In one possible implementation, the components of the organic binder include a binder, a diluent, a thixotropic agent and an antioxidant; the binder includes at least one of ethyl cellulose, cellulose acetate and hydroxypropyl methyl cellulose; the diluent includes at least one of ethanol, ethylene glycol methyl ether and propylene glycol methyl ether; the thixotropic agent includes at least one of colloidal silica and fumed silica; the antioxidant includes a mixture of borax, sodium fluoride and cerium dioxide, wherein the mass ratio of borax, sodium fluoride and cerium dioxide is (50-70):(20-30):(5-15); the mass ratio of the binder, diluent, thixotropic agent and antioxidant is (50-80):(10-30):(5-20):(1-5).

[0022] The binder provides the viscosity of the paste brazing filler metal, ensures that the brazing filler metal does not flow and uniformly adheres when being coated; the diluent can adjust the viscosity of the brazing filler metal, facilitating construction; the thixotropic agent gives the paste brazing filler metal the characteristics of shear thinning and thickening when standing, preventing the paste brazing filler metal from easily falling in the vertical surface when being coated; the antioxidant composed of borax, sodium fluoride and cerium dioxide forms a molten protective layer during heating, which can inhibit the oxidation of the brazing filler metal and the substrate.

[0023] In a possible implementation, the mass ratio of the nickel-based alloy brazing filler metal powder to the organic binder is (70-90):(10-30).

[0024] When the proportion of the binder is too low, the brazing filler metal powder is difficult to be shaped and is easy to fall off when being coated; when the proportion is too high, a large amount of gas is generated during subsequent heating, resulting in pores, and the residual carbide may react with the metal substrate to generate a brittle phase, deteriorating the performance of the prepared blade.

[0025] In a possible implementation, the temperature of the vacuum high-temperature degassing is 120-200℃, the vacuum degree is 0.1-10 Pa, and the degassing time is 1-3 h.

[0026] Degassing in a vacuum environment at 120-200℃ can remove the adsorbed gas and residual organic matter in the surface and loose pores of the blade, avoid the formation of pores due to the escape of gas during brazing, and reduce the gas pressure in the pores, so that the brazing filler metal can penetrate into defects through capillary action in the subsequent preparation process and be fully filled.

[0027] In a possible implementation, during the vacuum brazing, the temperature is 1250-1300℃, the vacuum degree is 1×10 -4 ~ 1×10 -3 Pa, and the brazing time is 10-30 min; during the heat diffusion treatment, the temperature is 1000-1200℃, and the treatment time is 2-4 h.

[0028] After the brazing filler metal is melted at high temperature, the surface tension and capillary action fill the loose pores; and the atomic diffusion coefficient increases at high temperature, so that the components in the brazing filler metal diffuse to the blade substrate, so that the interface between the brazing filler metal and the blade substrate changes from simple mechanical bonding to coexistence of mechanical bonding and metallurgical bonding. In addition, brazing in a vacuum environment can avoid the oxidation of the molten brazing filler metal and the blade substrate, ensuring the purity of the interface.

[0029] In a possible implementation, the temperature of the hot isostatic pressing treatment is 1200-1300℃, the pressure is 100-200 MPa, the holding time is 2-4 h, and the cooling rate is controlled to be 5-20℃ / min.

[0030] The high temperature of 1200-1300 DEG C and the high pressure of 100-200 MPa work together to close the residual loose or micro-channels, promote the grain boundary diffusion and recrystallization, and eliminate the micro-defects possibly existing after brazing and diffusion treatment; meanwhile, the control of the cooling rate can avoid the internal stress in the prepared blade due to rapid cooling, and cause performance degradation.

[0031] In a possible implementation, the temperature of the solid solution treatment is 1150-1250 DEG C, the holding time is 1-3 h, and the furnace cooling is used to cool to room temperature; the temperature of the aging treatment is 700-950 DEG C, the holding time is 4-8 h, and the air cooling is used to cool to room temperature. The solid solution treatment and the aging treatment can further improve the mechanical properties of the prepared blade.

[0032] In a possible implementation, the vacuum brazing and the thermal diffusion treatment are continuously performed in the same vacuum furnace, the heating rate of the vacuum furnace is controlled to be 5-15 DEG C / min, and the cooling rate is controlled to be 10-20 DEG C / min. The continuous performance of the vacuum brazing and the thermal diffusion treatment in the same vacuum furnace can maintain the stability of the structure of the blade substrate, and reduce the generation of the oxide skin and the difficulty of the subsequent surface treatment.

[0033] Beneficial technical effects:

[0034] The method provided in the application can not only effectively eliminate the near-surface loose and micro-channel defects of the high-temperature alloy turbine blade, but also can produce the high-temperature alloy turbine blade according to the method, and directly prevent the near-surface loose of the blade. In the method for eliminating the near-surface loose of the blade provided in the application, the surface roughness Ra of the blade casting is controlled to be less than or equal to 3.2 microns, to provide a clean and mechanically biting substrate for the brazing filler metal; the nickel-based alloy brazing filler metal powder with a specific component and particle size, the organic binder with an optimized component and ratio, uniformly fill the defects and melt into the loose area in a vacuum environment, and form the coexistence of mechanical bonding and metallurgical bonding through thermal diffusion; the hot isostatic pressing treatment further eliminates the residual micro-defects and improves the density under high temperature and high pressure; and finally, the solid solution and aging treatment optimize the substrate structure and strengthen the high-temperature mechanical properties of the obtained blade. The whole process temperature is lower than the melting point of the blade substrate, which can avoid the damage of the blade substrate; in addition, the parameters are quantifiable and controllable, and the process is continuous, which can make the performance of the repaired area close to the original level of the substrate, significantly improve the service reliability of the blade, and reduce the scrap rate and repair cost. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 is a principle schematic diagram of the method for eliminating the near-surface loose of the turbine blade by using brazing and hot isostatic pressing provided in the application;

[0036] Figure 2 is a flow schematic diagram of the method for eliminating the near-surface loose of the turbine blade by using brazing and hot isostatic pressing provided in the application;

[0037] Figure 3 is a metallographic image of the vane cast after hot isostatic pressing in the embodiment 1 of the present application. DETAILED DESCRIPTION

[0038] In order to make the technical problems, technical solutions and beneficial effects of the present application more clearly understood, the present application will be further described in detail below in conjunction with embodiments. However, it should not be understood as limiting the scope of the present application to the following examples. All other embodiments obtained by those skilled in the art without making creative efforts under the premise of not departing from the method idea of the present application belong to the scope of protection of the present application.

[0039] The following will specifically describe a method for eliminating near-surface porosity of a turbine vane by brazing and hot isostatic pressing according to different embodiments.

[0040] Embodiment 1

[0041] As shown in Figure 2 A method for eliminating near-surface porosity of a turbine vane by brazing and hot isostatic pressing, comprising the following steps:

[0042] 1. Sandblasting the surface of the vane cast to expose a clean surface with porosity defects;

[0043] 2. Preparing a nickel-based alloy filler powder from a nickel-based alloy bar by a rotating electrode method, and then mixing the nickel-based alloy powder with an organic binder to form a paste-like filler;

[0044] The mass ratio of the nickel-based alloy filler powder to the organic binder is 70:30;

[0045] The nickel-based alloy bar comprises nickel, chromium, iron, molybdenum, bismuth, boron, carbon and silicon;

[0046] The mass ratio of the nickel, chromium, iron, molybdenum, bismuth, boron, carbon and silicon is 70:10:8:3:2:2:0.5:4.5;

[0047] The components of the organic binder include ethyl cellulose, ethanol, colloidal silicon dioxide and an antioxidant;

[0048] The mass ratio of the ethyl cellulose, ethanol, colloidal silicon dioxide and antioxidant is 50:30:15:5; wherein the antioxidant is a compound of borax, sodium fluoride and cerium dioxide, and the mass ratio of the borax, sodium fluoride and cerium dioxide is 60:25:15;

[0049] 3. The blade casting is subjected to vacuum high-temperature degassing at a temperature of 120°C and a vacuum degree of 0.1 Pa for 3 hours, and then the surface of the blade casting is coated with paste solder;

[0050] 4. The blade casting coated with paste solder is heated at a temperature of 1250℃ and a vacuum degree of 1×10 -4 Vacuum brazing was performed at 1000°C for 4 hours, and then the brazing time was 30 minutes.

[0051] 5. The blade casting after thermal diffusion treatment is subjected to hot isostatic pressing treatment at a temperature of 1200°C and a pressure of 200 MPa. The holding time is 2 hours and the cooling rate is controlled at 20°C / min.

[0052] 6. The surface of the blade casting after hot isostatic pressing (such as Figure 3 As shown in the figure, the red arrow indicates the sealing of loose defects on the casting surface) for grinding;

[0053] 7. The polished blade casting is solution treated at a temperature of 1150°C and a holding time of 3 hours, and then cooled to room temperature by furnace cooling; then it is aged at a temperature of 700°C and a holding time of 8 hours, and then cooled to room temperature by air cooling to obtain a high-temperature alloy turbine blade with eliminated near-surface porosity.

[0054] Step 1 corresponds to the attached Figure 1 (a) in step 3; Figure 1 (b) in the figure; Step 4 corresponds to the attached Figure 1 (c) in the following; Step 5 corresponds to the Figure 1 (d) in the following; Steps 6 to 7 correspond to the attached Figure 1 (e) in .

[0055] Example 2

[0056] like Figure 2 As shown, a method for eliminating near-surface porosity of a turbine blade by brazing and hot isostatic pressing comprises the following steps:

[0057] 1. Sandblast the surface of the blade casting to expose a clean surface with loose defects;

[0058] 2. Prepare nickel-based alloy brazing filler metal powder from nickel-based alloy rods by a rotating electrode method, and then mix the nickel-based alloy powder with an organic binder to prepare a paste-like brazing filler metal;

[0059] The mass ratio of nickel-based alloy brazing filler metal powder to organic binder is 70:30;

[0060] The composition of the nickel-based alloy rod comprises nickel, chromium, iron, molybdenum, bismuth, boron, carbon and silicon;

[0061] The mass ratio of the nickel, chromium, iron, molybdenum, bismuth, boron, carbon and silicon is 60:15:10:2:5:1:1:6;

[0062] The components of the organic binder comprise cellulose acetate, ethylene glycol methyl ether, fumed silica and antioxidant;

[0063] The mass ratio of the cellulose acetate, ethylene glycol methyl ether, fumed silica and antioxidant is 60:25:12:3; wherein the antioxidant is a compound of borax, sodium fluoride and cerium dioxide, and the mass ratio of the borax, sodium fluoride and cerium dioxide is 50:30:20;

[0064] 3. The blade casting is subjected to vacuum high-temperature degassing at a temperature of 150℃ and a vacuum degree of 5Pa for 2h, and then the surface of the blade casting is coated with paste solder;

[0065] 4. The blade casting coated with the paste solder is subjected to vacuum brazing at a temperature of 1270℃ and a vacuum degree of 5x10 -4 Pa for 20min, and then is subjected to thermal diffusion treatment at a temperature of 1100℃ for 3h;

[0066] 5. The blade casting after the thermal diffusion treatment is subjected to hot isostatic pressing at a temperature of 1250℃ and a pressure of 150MPa for 3h, and the cooling rate is controlled at 15℃ / min;

[0067] 6. The surface of the blade casting after the hot isostatic pressing is polished;

[0068] 7. The polished blade casting is subjected to solid solution treatment at a temperature of 1200℃ for 2h, and is cooled to room temperature by furnace cooling; and then is subjected to aging treatment at a temperature of 800℃ for 6h, and is cooled to room temperature by air cooling, to obtain a high-temperature alloy turbine blade with eliminated near-surface porosity.

[0069] Wherein step 1 corresponds to (a) in the accompanying Figure 1 ; step 3 corresponds to (b) in the accompanying Figure 1 ; step 4 corresponds to (c) in the accompanying Figure 1 ; step 5 corresponds to (d) in the accompanying Figure 1 ; and steps 6-7 correspond to (e) in the accompanying Figure 1 .

[0070] Example 3

[0071] As Figure 2As shown, a method for eliminating porosity near the surface of a turbine blade by brazing and hot isostatic pressing, comprising the following steps:

[0072] 1. Sandblasting the surface of the blade casting to expose a clean surface with porosity defects;

[0073] 2. Preparing a nickel-based alloy filler powder from a nickel-based alloy rod by the rotating electrode method, and then mixing the nickel-based alloy powder with an organic binder to form a paste-like filler;

[0074] The mass ratio of the nickel-based alloy filler powder to the organic binder is 75:25;

[0075] The nickel-based alloy rod comprises nickel, chromium, iron, molybdenum, bismuth, boron, carbon, and silicon;

[0076] The mass ratio of the nickel, chromium, iron, molybdenum, bismuth, boron, carbon, and silicon is 65:12:7:4:3:3:0.8:5.2;

[0077] The components of the organic binder include hydroxypropyl methyl cellulose, propylene glycol methyl ether, colloidal silicon dioxide, and an antioxidant;

[0078] The mass ratio of the hydroxypropyl methyl cellulose, propylene glycol methyl ether, colloidal silicon dioxide, and antioxidant is 70:20:8:2; the antioxidant is a compound of borax, sodium fluoride, and cerium dioxide, and the mass ratio of the borax, sodium fluoride, and cerium dioxide is 70:20:10;

[0079] 3. Vacuum high-temperature degassing the blade casting at a temperature of 200℃ and a vacuum degree of 10Pa for 1h, and then coating the surface of the blade casting with the paste-like filler;

[0080] 4. Vacuum brazing the blade casting coated with the paste-like filler at a temperature of 1300℃ and a vacuum degree of 1×10 -3 Pa for 10min, and then performing thermal diffusion treatment at a temperature of 1200℃ for 2h;

[0081] 5. Hot isostatic pressing the blade casting after thermal diffusion treatment at a temperature of 1300℃ and a pressure of 100MPa for 4h, with a cooling rate controlled at 5℃ / min;

[0082] 6. Polishing the surface of the blade casting after hot isostatic pressing;

[0083] 7. The solution treatment is carried out on the polished blade castings under the condition of 1250℃ and 1h, and the blade castings are cooled to room temperature by furnace cooling; then the aging treatment is carried out under the condition of 950℃ and 4h, and the blade castings are cooled to room temperature by air cooling, so as to obtain the high-temperature alloy turbine blade with the near-surface porosity eliminated.

[0084] wherein step 1 corresponds to (a) of the accompanying Figure 1 ; step 3 corresponds to (b) of the accompanying Figure 1 ; step 4 corresponds to (c) of the accompanying Figure 1 ; step 5 corresponds to (d) of the accompanying Figure 1 ; and steps 6-7 correspond to (e) of the accompanying Figure 1 .

[0085] Embodiment 4

[0086] As shown in the accompanying Figure 2 , a method for eliminating the near-surface porosity of a turbine blade by brazing and hot isostatic pressing comprises the following steps:

[0087] 1. The surface of the blade castings is subjected to sandblasting treatment to expose the clean surface with porosity defects;

[0088] 2. The nickel-based alloy filler powder is prepared from a nickel-based alloy bar by the rotating electrode method, and the nickel-based alloy powder is mixed with an organic binder to form a paste-like filler;

[0089] The mass ratio of the nickel-based alloy filler powder to the organic binder is 85:15;

[0090] The nickel-based alloy bar comprises nickel, chromium, iron, molybdenum, bismuth, boron, carbon and silicon;

[0091] The mass ratio of the nickel, chromium, iron, molybdenum, bismuth, boron, carbon and silicon is 65:13:6:5:1:4:0.6:5.4;

[0092] The components of the organic binder include ethyl cellulose, ethanol, fumed silica and an antioxidant;

[0093] The mass ratio of the ethyl cellulose, ethanol, fumed silica and antioxidant is 55:28:14:3; wherein the antioxidant is a compound of borax, sodium fluoride and cerium dioxide, and the mass ratio of the borax, sodium fluoride and cerium dioxide is 65:23:12;

[0094] 3. The blade castings are subjected to vacuum high-temperature degassing under the condition of 130℃ and 2Pa for 2.5h, and then the surface of the blade castings is coated with the paste-like filler;

[0095] 4. The blade castings coated with the paste solder are vacuum brazed at a temperature of 1260 °C, a vacuum degree of 8 x 10 -4 Pa, a brazing time of 25 min, and then subjected to thermal diffusion treatment at a temperature of 1050 °C for 3.5 h;

[0096] 5. The blade castings after the thermal diffusion treatment are subjected to hot isostatic pressing at a temperature of 1220 °C and a pressure of 180 MPa for 2.5 h, and a cooling rate is controlled at 10 °C / min;

[0097] 6. The surface of the blade castings after the hot isostatic pressing is polished;

[0098] 7. The blade castings after the polishing are subjected to solution treatment at a temperature of 1180 °C for 2.5 h, and then cooled to room temperature by furnace cooling, and then subjected to aging treatment at a temperature of 750 °C for 7 h, and then cooled to room temperature by air cooling, to obtain the high-temperature alloy turbine blade with the near-surface porosity eliminated.

[0099] The step 1 corresponds to (a) in the attached Figure 1 Fig. 1; the step 3 corresponds to (b) in the attached Figure 1 Fig. 2; the step 4 corresponds to (c) in the attached Figure 1 Fig. 3; the step 5 corresponds to (d) in the attached Figure 1 Fig. 4; and the steps 6-7 correspond to (e) in the attached Figure 1 Fig. 5.

[0100] Example 5

[0101] As shown in the attached Figure 2 Fig. 6, a method for eliminating the near-surface porosity of a turbine blade by brazing and hot isostatic pressing includes the following steps:

[0102] 1. The surface of the blade castings is subjected to sand blasting treatment to expose a clean surface with porosity defects;

[0103] 2. A nickel-based alloy solder powder is prepared from a nickel-based alloy bar by a rotating electrode method, and then the nickel-based alloy powder is mixed with an organic binder to form a paste solder;

[0104] The mass ratio of the nickel-based alloy solder powder to the organic binder is 78:22;

[0105] The nickel-based alloy bar includes nickel, chromium, iron, molybdenum, bismuth, boron, carbon and silicon;

[0106] The mass ratio of the nickel, chromium, iron, molybdenum, bismuth, boron, carbon and silicon is 66:11:9:3.5:4:1.5:0.7:4.3;

[0107] The components of the organic binder include cellulose acetate, ethylene glycol methyl ether, colloidal silica and antioxidant;

[0108] The mass ratio of the cellulose acetate, ethylene glycol methyl ether, colloidal silica and antioxidant is 75:15:9:1; wherein the antioxidant is a compound of borax, sodium fluoride and cerium dioxide, and the mass ratio of the borax, sodium fluoride and cerium dioxide is 55:28:17;

[0109] 3. The blade casting is subjected to vacuum high-temperature degassing at a temperature of 180℃ and a vacuum degree of 8Pa, and the degassing time is 1.5h, and then the surface of the blade casting is coated with a paste-like filler metal;

[0110] 4. The blade casting coated with the paste-like filler metal is subjected to vacuum brazing at a temperature of 1280℃ and a vacuum degree of 3×10 -4 Pa, and the brazing time is 15min, and then the blade casting is subjected to thermal diffusion treatment at a temperature of 1150℃, and the treatment time is 2.5h;

[0111] 5. The blade casting after the thermal diffusion treatment is subjected to hot isostatic pressing at a temperature of 1280℃ and a pressure of 120MPa, and the holding time is 3.5h, and the cooling rate is controlled at 18℃ / min;

[0112] 6. The surface of the blade casting after the hot isostatic pressing is polished;

[0113] 7. The blade casting after the polishing is subjected to solid solution treatment at a temperature of 1230℃ and a holding time of 1.5h, and then cooled to room temperature by furnace cooling, and then subjected to aging treatment at a temperature of 850℃ and a holding time of 5h, and then cooled to room temperature by air cooling, to obtain a high-temperature alloy turbine blade with the near-surface porosity eliminated.

[0114] Wherein step 1 corresponds to (a) in the accompanying drawings; Figure 1 Step 3 corresponds to (b) in the accompanying drawings; Figure 1 Step 4 corresponds to (c) in the accompanying drawings; Figure 1 Step 5 corresponds to (d) in the accompanying drawings; Figure 1 Steps 6-7 correspond to (e) in the accompanying drawings. Figure 1

[0115] Example 6

[0116] As shown in the accompanying drawings, Figure 2 a method for eliminating near-surface porosity of a turbine blade by brazing and hot isostatic pressing, comprising the following steps:

[0117] 1. The surface of the blade casting is subjected to sand blasting treatment to expose a clean surface with porosity defects;

[0118] ​2. Preparing a nickel-based alloy filler powder from a nickel-based alloy rod by a rotating electrode method, and mixing the nickel-based alloy powder with an organic binder to form a paste-like filler;

[0119] The mass ratio of the nickel-based alloy filler powder to the organic binder is 88:12;

[0120] The nickel-based alloy rod comprises nickel, chromium, iron, molybdenum, bismuth, boron, carbon and silicon;

[0121] The mass ratio of the nickel, chromium, iron, molybdenum, bismuth, boron, carbon and silicon is 68:14:5:4.5:1.5:5:0.9:1.1;

[0122] The organic binder comprises hydroxypropyl methyl cellulose, propylene glycol methyl ether, fumed silica and an antioxidant;

[0123] The mass ratio of the hydroxypropyl methyl cellulose, propylene glycol methyl ether, fumed silica and antioxidant is 80:10:8:2; the antioxidant is a compound of borax, sodium fluoride and cerium dioxide, and the mass ratio of the borax, sodium fluoride and cerium dioxide is 68:22:10;

[0124] 3. Vacuum high-temperature degassing the blade castings at a temperature of 160℃ and a vacuum degree of 0.5Pa for 2.8h, and then coating the surface of the blade castings with the paste-like filler;

[0125] 4. Vacuum brazing the blade castings coated with the paste-like filler at a temperature of 1290℃ and a vacuum degree of 6x10 -4 Pa for 18min, and then performing thermal diffusion treatment at a temperature of 1180℃ for 2.2h;

[0126] 5. Hot isostatic pressing the blade castings after the thermal diffusion treatment at a temperature of 1260℃ and a pressure of 190MPa for 3h, and controlling the cooling rate at 10℃ / min;

[0127] 6. Polishing the surface of the blade castings after the hot isostatic pressing;

[0128] 7. Solution treating the blade castings after the polishing at a temperature of 1200℃ for 2h, and cooling to room temperature by furnace cooling; and then aging treating the blade castings at a temperature of 900℃ for 4.5h, and cooling to room temperature by air cooling, to obtain a high-temperature alloy turbine blade with eliminated near-surface porosity.

[0129] Step 1 corresponds to (a) in FIG. 1; step 3 corresponds to (b) in FIG. 1; and step 5 corresponds to (c) in FIG. 1. Figure 1 Step 1 corresponds to (a) in FIG. 1; step 3 corresponds to (b) in FIG. 1; and step 5 corresponds to (c) in FIG. 1. Figure 1(b) in the method of (a); Step 4 corresponds to Fig. 4 Figure 1 (c) in the method of (a); Step 5 corresponds to Fig. 5 Figure 1 (d) in the method of (a); Steps 6-7 correspond to Fig. 6 Figure 1 (e) in the method of (a).

[0130] Comparative Example 1

[0131] A method for eliminating near-surface porosity of a turbine blade by brazing and hot isostatic pressing, comprising the following steps:

[0132] 1. A sandblasting treatment is performed on the surface of the blade casting to expose a clean surface with porosity defects;

[0133] 2. A nickel-based alloy filler powder is prepared from a nickel-based alloy rod by a rotating electrode method, and then the nickel-based alloy powder is mixed with an organic binder to form a paste-like filler;

[0134] The mass ratio of the nickel-based alloy filler powder to the organic binder is 70:30;

[0135] The nickel-based alloy rod comprises nickel, chromium, iron, molybdenum, bismuth, boron, carbon, and silicon;

[0136] The mass ratio of the nickel, chromium, iron, molybdenum, bismuth, boron, carbon, and silicon is 70:10:8:3:2:2:0.5:4.5;

[0137] The components of the organic binder include ethyl cellulose, ethanol, colloidal silica, and an antioxidant;

[0138] The mass ratio of the ethyl cellulose, ethanol, colloidal silica, and antioxidant is 50:30:15:5; the antioxidant is a compound of borax, sodium fluoride, and cerium dioxide, and the mass ratio of the borax, sodium fluoride, and cerium dioxide is 60:25:15;

[0139] 3. The blade casting is subjected to vacuum high-temperature degassing at a temperature of 120°C and a vacuum degree of 0.1 Pa for 3h, and then the surface of the blade casting is coated with the paste-like filler;

[0140] 4. The blade casting coated with the paste-like filler is subjected to vacuum brazing at a temperature of 1250°C and a vacuum degree of 1×10 -4 Pa for 30min, and then subjected to thermal diffusion treatment at a temperature of 1000°C for 4h;

[0141] 5. The surface of the blade casting after the thermal diffusion treatment is polished;

[0142] 6. The solution treatment of the polished blade castings is carried out at a temperature of 1150℃ for 3h, and the cooling is carried out by furnace cooling to room temperature; then the aging treatment is carried out at a temperature of 700℃ for 8h, and the cooling is carried out by air cooling to room temperature, so as to obtain the high-temperature alloy turbine blade with the near-surface porosity eliminated.

[0143] Comparative Example 2

[0144] A method for eliminating the near-surface porosity of a turbine blade by brazing and hot isostatic pressing, comprising the following steps:

[0145] 1. The surface of the blade castings is subjected to sand blasting treatment to expose the clean surface with porosity defects;

[0146] 2. The iron powder is mixed with the organic binder to prepare the mixed filler metal;

[0147] The mass ratio of the iron powder to the organic binder is 75:25;

[0148] The components of the organic binder include hydroxypropyl methyl cellulose, propylene glycol methyl ether, colloidal silicon dioxide and antioxidant;

[0149] The mass ratio of the hydroxypropyl methyl cellulose, propylene glycol methyl ether, colloidal silicon dioxide and antioxidant is 70:20:8:2; wherein the antioxidant is a compound of borax, sodium fluoride and cerium dioxide, and the mass ratio of the borax, sodium fluoride and cerium dioxide is 70:20:10;

[0150] 3. The blade castings are subjected to vacuum high-temperature degassing at a temperature of 200℃ and a vacuum degree of 10Pa for 1h, and then the surface of the blade castings is coated with the mixed filler metal;

[0151] 4. The blade castings coated with the mixed filler metal are subjected to vacuum brazing at a temperature of 1300℃ and a vacuum degree of 1×10 -3 Pa for 10min, and then subjected to thermal diffusion treatment at a temperature of 1200℃ for 2h;

[0152] 5. The blade castings subjected to the thermal diffusion treatment are subjected to hot isostatic pressing at a temperature of 1300℃ and a pressure of 100MPa for 4h, and the cooling rate is controlled at 5℃ / min;

[0153] 6. The surface of the blade castings subjected to the hot isostatic pressing is polished;

[0154] 7. The blade castings after polishing are subjected to solid solution treatment under the condition of temperature 1250℃ and holding time 1h, and cooled to room temperature by furnace cooling; then subjected to aging treatment under the condition of temperature 950℃ and holding time 4h, and cooled to room temperature by air cooling, to obtain high-temperature alloy turbine blade eliminating near-surface porosity.

[0155] Comparative Example 3

[0156] A method for eliminating near-surface porosity of turbine blade by brazing and hot isostatic pressing, comprising the following steps:

[0157] 1. The surface of the blade castings is subjected to sand blasting treatment to expose the clean surface with porosity defects;

[0158] 2. Iron powder is mixed with organic binder to prepare mixed filler;

[0159] The mass ratio of iron powder to organic binder is 88:12;

[0160] The components of the organic binder include hydroxypropyl methyl cellulose, propylene glycol methyl ether, fumed silica and antioxidant;

[0161] The mass ratio of the hydroxypropyl methyl cellulose, propylene glycol methyl ether, fumed silica and antioxidant is 80:10:8:2; wherein the antioxidant is a compound of borax, sodium fluoride and cerium dioxide, and the mass ratio of borax, sodium fluoride and cerium dioxide is 68:22:10;

[0162] 3. The blade castings are subjected to vacuum high-temperature degassing under the condition of temperature 160℃ and vacuum degree 0.5Pa, and the degassing time is 2.8h, and then the surface of the blade castings is coated with the mixed filler;

[0163] 4. The blade castings coated with the mixed filler are subjected to vacuum brazing under the condition of temperature 1290℃ and vacuum degree 6×10 -4 Pa, and the brazing time is 18min, and then subjected to thermal diffusion treatment under the condition of temperature 1180℃, and the treatment time is 2.2h;

[0164] 5. The surface of the blade castings after thermal diffusion treatment is polished;

[0165] 6. The blade castings after polishing are subjected to solid solution treatment under the condition of temperature 1200℃ and holding time 2h, and cooled to room temperature by furnace cooling; then subjected to aging treatment under the condition of temperature 900℃ and holding time 4.5h, and cooled to room temperature by air cooling, to obtain high-temperature alloy turbine blade eliminating near-surface porosity.

[0166] The high-temperature alloy turbine blades prepared in Examples 1-6 and Comparative Examples 1-3 were subjected to room temperature mechanical property testing and high-temperature durability strength testing at 900℃ for 100h to reflect the performance improvement by eliminating the near-surface porosity. The test results are shown in Table 1.

[0167] Table 1 Test results of high-temperature alloy turbine blades prepared in examples and comparative examples

[0168]

[0169] As shown in Table 1, the test data of the iron-nickel-cobalt alloys prepared in Examples 1-6 are all better than those of Comparative Examples 1-3.

[0170] This is because, in the method for eliminating the near-surface porosity of the blade in Examples 1-6, the surface roughness Ra of the blade casting is controlled to be ≤3.2μm, providing a clean and mechanically biting substrate for the filler metal; the nickel-based alloy filler metal powder with specific composition and particle size, in combination with the organic binder with optimized composition and ratio, uniformly fills the defects and melts into the porosity area under vacuum, and forms coexistence of mechanical bonding and metallurgical bonding through thermal diffusion; the hot isostatic pressing further eliminates residual micro-defects under high temperature and high pressure, and improves the density; and finally, the solid solution and aging treatment optimizes the matrix structure and strengthens the high-temperature mechanical properties of the obtained blade. The entire process temperature is lower than the melting point of the blade matrix, which can avoid damage to the blade matrix; in addition, the parameters are quantifiable and controllable, and the process is continuous, which can make the performance of the repaired area close to the original level of the matrix, significantly improve the service reliability of the blade, and reduce the scrap rate and repair cost.

[0171] Comparative Example 1, without hot isostatic pressing, cannot further eliminate residual micro-defects and improve density, so the mechanical properties and high-temperature durability strength of the obtained high-temperature alloy turbine blade are all decreased.

[0172] Comparative Example 2, without using nickel-based alloy filler metal powder, cannot uniformly fill defects and melt into the porosity area under vacuum, and cannot form coexistence of mechanical bonding and metallurgical bonding through thermal diffusion, so the mechanical properties and high-temperature durability strength of the obtained high-temperature alloy turbine blade are all decreased.

[0173] Comparative Example 3, without hot isostatic pressing and without using nickel-based alloy filler metal powder, has the worst mechanical properties and high-temperature durability strength of the obtained high-temperature alloy turbine blade.

[0174] The above results show and describe the basic principles and main features of the present application, and the advantages of the present application.

[0175] Those skilled in the art should understand that the present application is not limited by the above-mentioned embodiments, the above-mentioned embodiments and descriptions in the specification are only to illustrate the principles of the present application, and various changes and improvements can be made to the present application without departing from the spirit and scope of the present application, and these changes and improvements all fall within the scope of the claimed present application. The scope of protection of the present application is defined by the equivalents of the appended claims.

Claims

1. The melting point of the nickel-based alloy brazing filler metal powder is ≤1250°C, and the melting point of the high-temperature alloy turbine blade is ≥1350°C.

2. The method for eliminating near-surface porosity of turbine blades by brazing and hot isostatic pressing according to claim 1, characterized in that: In the step of cleaning the surface of the blade casting, sandblasting is used for cleaning, and the surface roughness of the blade casting after cleaning is Ra≤3.2μm.

3. The method for eliminating near-surface porosity of turbine blades by brazing and hot isostatic pressing according to claim 1, characterized in that: The components of the nickel-based alloy rod include nickel, chromium, iron, molybdenum, bismuth, boron, carbon and silicon; the mass ratio of the nickel, chromium, iron, molybdenum, bismuth, boron, carbon and silicon is (60-80): (8-15): (5-10): (2-5): (1-5): (1-5): (0.5-1): (2-5); the nickel-based alloy solder powder is prepared from the nickel-based alloy rod by a rotating electrode method; the particle size of the nickel-based alloy solder powder is 10-80 μm.

4. The method for eliminating near-surface porosity of turbine blades by brazing and hot isostatic pressing according to claim 1, characterized in that: The components of the organic binder include a binder, a diluent, a thixotropic agent and an antioxidant; the binder includes at least one of ethyl cellulose, cellulose acetate and hydroxypropyl methyl cellulose; the diluent includes at least one of ethanol, ethylene glycol methyl ether and propylene glycol methyl ether; the thixotropic agent includes at least one of colloidal silicon dioxide and fumed silicon dioxide; the antioxidant includes a compound of borax, sodium fluoride and cerium dioxide, wherein the mass ratio of borax, sodium fluoride and cerium dioxide is (50-70):(20-30):(5-15); the mass ratio of the binder, diluent, thixotropic agent and antioxidant is (50-80):(10-30):(5-20):(1-5).

5. The method for eliminating near-surface porosity of turbine blades by brazing and hot isostatic pressing according to claim 1, characterized in that: The mass ratio of the nickel-based alloy solder powder to the organic binder is (70-90): (10-30).

6. The method for eliminating near-surface porosity of turbine blades by brazing and hot isostatic pressing according to claim 1, characterized in that: The temperature of the vacuum high-temperature degassing is 120-200° C., the vacuum degree is 0.1-10 Pa, and the degassing time is 1-3 hours.

7. The method for eliminating near-surface porosity of turbine blades by brazing and hot isostatic pressing according to claim 1, characterized in that: During the vacuum brazing process, the temperature is 1250-1300°C and the vacuum degree is 1×10 -4 ~1×10 -3 Pa, the brazing time is 10 to 30 minutes; during the thermal diffusion treatment, the temperature is 1000 to 1200° C., and the treatment time is 2 to 4 hours.

8. The method for eliminating near-surface porosity of turbine blades by brazing and hot isostatic pressing according to claim 1, characterized in that: The temperature of the hot isostatic pressing treatment is 1200-1300° C., the pressure is 100-200 MPa, the heat preservation and pressure holding time is 2-4 hours, and the cooling rate is controlled at 5-20° C. / min.

9. The method for eliminating near-surface porosity of turbine blades by brazing and hot isostatic pressing according to claim 1, characterized in that: The temperature of the solid solution treatment is 1150-1250° C., the holding time is 1-3 hours, and the furnace cooling method is used to cool to room temperature; the temperature of the aging treatment is 700-950° C., the holding time is 4-8 hours, and the air cooling method is used to cool to room temperature.

10. The method for eliminating near-surface porosity of turbine blades by brazing and hot isostatic pressing according to claim 1, characterized in that: The vacuum brazing and thermal diffusion treatment are continuously performed in the same vacuum furnace. The heating rate of the vacuum furnace is controlled at 5-15°C / min, and the cooling rate is controlled at 10-20°C / min.

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