A method for connecting a single-crystal superalloy with opposite orientations

Abstract

The present invention discloses a method for connecting directionally solidified single crystal superalloys. This connection method uses a low-melting alloy component and a high-melting alloy component directly separated from the composition of the single crystal superalloy base material. After the low-melting alloy component and the high-melting alloy component are combined, a connection material equal to or approximate to the base material composition is formed. During connection, the connection material powder is stirred evenly with an organic solvent to form a paste, which is evenly applied to the surface of the directionally solidified nickel-based single crystal superalloy to be connected. After being fixed with a fixture, it is placed in a vacuum brazing furnace for brazing. After the furnace temperature drops to room temperature, a directionally solidified single crystal superalloy connector with a non-single crystal superalloy connection layer is obtained. Since the connection material in the present invention does not contain melting point depressing elements, there are no brittle compounds or eutectic structures rich in Si and B in the connection layer; the homogenization process of the joint composition belongs to a rapid diffusion mechanism with a large diffusion area and a short diffusion distance, so the kinetics of the connection process can be greatly accelerated.

Description

Technical Field

[0001] The present invention relates to the technical field of nickel-based superalloy material connection, and specifically relates to a method for connecting equiaxed / near-base metal compositions of directionally solidified superalloys. Background Art

[0002] As the heart of an aircraft, an aeroengine is not only the power of the aircraft but also the key thrust for promoting the development of the aviation industry. Currently, the main goal of China's aviation manufacturing industry is to break through the bottlenecks and restrictions of aeroengines.

[0003] To improve the airtightness of aeroengines and reduce aerodynamic losses, thereby enhancing turbine efficiency, aeroengines usually adopt double-walled structure guide vanes. With the increase in the thrust-to-weight ratio of aeroengines, the turbine inlet temperature continues to rise, and the working environment of the turbine guide vanes in the high-temperature gas flow becomes increasingly harsh, with higher requirements for the high-temperature performance of the blade materials. Due to the high high-temperature strength, excellent oxidation resistance, and hot corrosion resistance of nickel-based single-crystal superalloys, the material of turbine guide vanes has entered the era of single-crystal superalloys.

[0004] Single-crystal double-walled guide vanes can be manufactured by two schemes: "double-walled integral casting" or "single-piece casting + welding (connection)". Double-walled integral cast blades have excellent performance, but poor processability and low yield, and can only be used to manufacture small-sized high-pressure turbine guide vanes; with the increase in blade size, changes in the bending and torsion structure, and improvement of the cooling structure, it is difficult to control the temperature field of single-crystal growth during the casting process, and defects such as internal stray crystals gradually increase. The "single-piece casting + welding (connection)" scheme has become the only method for manufacturing large-sized low-pressure turbine guide vanes at present. Single-piece casting of guide vanes usually adopts the spiral grain selection method. Except that the

[001] crystal orientation can be consistent, the other two crystal orientations are random, which means that the crystal orientation at the side position of the flange cannot be determined, and the crystal orientation difference between the two base metals to be welded on both sides is usually greater than 20°. Due to high alloy element (Al, Ti) content, complex structure, and orientation problems, single-crystal guide vanes also belong to a special type of difficult-to-weld materials.

[0005] At present, the main methods for welding (connecting) guide vanes are electron beam welding, brazing, and transient liquid phase diffusion welding (TLP), each having its limitations: As the blade material develops from wrought superalloys to cast superalloys (including single crystal cast superalloys), the content of alloying elements such as Al and Ti in the superalloy composition increases, and the crack sensitivity significantly rises. When electron beam welding single crystal superalloys, not only will polycrystals be formed, but more importantly, a large number of solidification cracks will also be formed. Additionally, when manufacturing double or multi-stage guide vanes by welding (connecting), the cross-section to be welded (connected) is not an equal-thickness structure, and the process adaptability of electron beam welding is not ideal. Therefore, whether from the perspective of material weldability or process adaptability, electron beam welding is no longer an appropriate welding method for manufacturing single crystal guide vanes.

[0006] Brazing is also a commonly used connection technology for manufacturing double-stage blades of non-single crystal (wrought superalloys and equiaxed crystal cast superalloys). The filler metals for brazing superalloys all contain melting point depressing elements Si and B. After brazing, a large amount of brittle compounds of Si and B usually remain in the weld, seriously affecting the joint performance, especially the high-temperature performance. For non-single crystal superalloys, the performance of the base material itself is relatively low, and the performance of the brazed joint can reach 70% or more of the base material performance, which can basically meet the application requirements. However, for single crystal superalloys, due to the significant improvement in the performance of the base material and the absence of grain boundaries as a rapid diffusion channel for melting point depressing elements such as Si and B during brazing, more low-melting-point brittle compounds often remain in the joint after brazing. The brazing performance, especially the high-temperature performance, is generally very poor compared to the base material; although the compounds in the weld can be reduced to a certain extent and the joint performance can be improved by adjusting the process parameters, it is ultimately difficult to achieve a qualitative change (completely eliminate the compounds), and the joint performance is generally below 50% of the base material performance. Ordinary brazing technology is difficult to meet the requirements of single crystal guide vanes for connection performance.

[0007] Transient liquid phase diffusion bonding (TLP) is a bonding method developed specifically for the joining of superalloys and is widely used. Currently, the goal of TLP bonding of single-crystal superalloys is to obtain a single-crystal joint that is identical to the base material in terms of structure and properties. Therefore, related research mainly focuses on the single-crystallization of the joint. Existing research at home and abroad has shown that when there is no crystal orientation difference or the crystal orientation difference is small between the base materials, by using a suitable joining material containing melting-point depressant elements such as Si and B, and through sufficient long-time diffusion homogenization, a single-crystal joint that is identical to the base material in structure and properties can be obtained. However, it has been found that the consistency of the crystal orientation of the base material is the key factor affecting the single-crystallization and properties of the TLP joint of single-crystal superalloys. As the orientation difference of the base material increases, the mechanical properties of the TLP joint decrease very significantly. The fundamental reason is that when the crystal orientation difference of the base material is large, it is difficult for the joint to achieve complete single-crystallization. It has been found that when the orientation difference between the two sides of the base material is greater than 9°-10°, large-angle through-type grain boundaries parallel to the bonding surface will appear in the joint, and carbides and borides will nucleate and grow at the grain boundaries. As the orientation difference increases, the high-temperature tensile strength and creep properties of the joint deteriorate rapidly.

[0008] As is well known, the consistency of the crystal orientation of the base material is precisely a condition that cannot be guaranteed during the welding manufacture of single-crystal guide vanes. The single-crystal guide vane monomers are usually manufactured by the spiral crystal selection method. The other two crystal orientations are not determined except for the

[001] crystal orientation. That is, when using welding technology to manufacture single-crystal double-guide vanes, it is impossible to ensure the same crystal orientation (the orientation difference is usually greater than 20°) of the base materials of the two side flanges to be welded. This means that when using the current method of preparing joining materials by adding melting-point depressant elements such as Si and B for TLP bonding of single-crystal guide vanes, there is often an irreconcilable contradiction: to make the joint single-crystallize through the full diffusion of Si and B, large-angle grain boundaries will inevitably form in the joint, and the joint performance will deteriorate severely; while if Si and B do not diffuse sufficiently, compounds and eutectic phases will remain in the joint, and the joint performance cannot be guaranteed either. Therefore, the existing TLP bonding method cannot meet the requirements of the connection performance for the welding manufacture of single-crystal guide vanes. In addition, during the current TLP bonding process, the homogenization of the joint composition and the single-crystallization of the structure often require dozens of hours or even several days. The slow process kinetics and poor processability are also problems that need to be solved. How to improve the TLP bonding performance of single-crystal superalloys with large orientation differences and enhance the process kinetics of the bonding process is an urgent issue to be solved in the "single-crystal casting + welding" manufacture of single-crystal double-guide vanes, especially low-pressure guide vanes. Summary of the Invention

[0009] The present invention discloses a method for joining dissimilar single-crystal superalloys with equal / approximate base material compositions to solve any of the above and other potential problems of the prior art.

[0010] To solve the above problems, the technical solution of the present invention is as follows: A method for connecting an equiaxed / similar base metal composition of a single-crystal superalloy. This connection method uses a low-melting alloy component and a high-melting alloy component alloy directly separated from the single-crystal superalloy base metal composition to form a connection material with an equiaxed / similar base metal composition for connection. By controlling the volume ratio of the low-melting alloy component to the high-melting alloy component within the range of 1:1 to 4, the volume fraction of the liquid phase during the connection process is controlled not to exceed 50%. During the connection process, isothermal solidification is achieved through the solid-liquid interdiffusion between the liquid phase, high-melting-point component particles, and the base metal, forming a non-single-crystal superalloy connection layer. The specific steps are as follows:

[0011] S1) Select the nickel-based single-crystal superalloy to be connected, prepare it into an anisotropic nickel-based single-crystal superalloy workpiece to be connected, and pre-treat the surface of the workpiece to be connected:

[0012] S2) Stir the connection material powder and organic solvent evenly into a paste, evenly apply it on the surface of the workpiece to be connected after being treated in S1), and fix it with a fixture;

[0013] S3) Place the fixed workpiece to be connected obtained in S2) in a vacuum brazing furnace for brazing. After the furnace temperature drops to room temperature, an anisotropic single-crystal superalloy workpiece with a non-single-crystal superalloy connection layer is obtained.

[0014] Furthermore, the mass percentage of the low-melting alloy component is: Cr 10.0 - 20.0 wt.%, Co 5.0 - 15.0 wt.%, Al 5.0 - 10.0 wt.%, Ti 5.0 - 20.0 wt.%, and the balance is Ni and unavoidable impurities;

[0015] The mass percentage of the high-melting alloy component is: Co 5.0 - 15.0 wt.%, Mo wt.% 1.0 - 5.0, W 5.0 - 15.0 wt.%, Al 5.0 - 6.0 wt.%, Ta 5.0 - 15.0 wt.%, and the balance is Ni and unavoidable impurities.

[0016] Furthermore, the nickel-based single-crystal superalloy to be connected in S1) is a fully heat-treated nickel-based single-crystal superalloy prepared by a directional solidification process.

[0017] Furthermore, the anisotropic nickel-based single-crystal superalloy workpiece to be connected in S1) is oriented parallel to

[001] and deviated from the

[001] orientation on the single-crystal superalloy base metal, and the deviation angle is α, α ≥ 10°.

[0018] Further, the connecting material powder in S2) is a mixture of a low-melting alloy component alloy powder and a high-melting alloy component alloy powder in a volume ratio of 1:1 to 4. The total composition of the mixed powder is equal to / approximate to the composition of the nickel-based single-crystal superalloy. The deviation range of the content of each element in the connecting material and the nickel-based single-crystal superalloy is not more than 15%.

[0019] Further, the particle size of the low-melting alloy component alloy powder in the connecting material is not more than 100 μm, and the melting point is not higher than 1250 °C; the particle size of the high-melting alloy component alloy powder is not more than 100 μm, and the melting point is not lower than the solution heat treatment temperature of the nickel-based single-crystal superalloy.

[0020] Further, the connecting material powder is spherical and / or near-spherical alloy powder with an average particle size range of 5 to 106 μm.

[0021] Further, the vacuum degree of the vacuum environment in S3) is 5×10 -3 Pa, the heating rate is 10 - 15 °C / min, it is heated to 1280 °C, after holding for 30 - 180 min, it is cooled in the furnace, and the cooling rate is 5 - 10 °C / min.

[0022] Further, the pretreatment process in S1) is as follows: the surface to be joined of the nickel-based single-crystal superalloy is polished successively with 400#, 600#, 800#, 1000#, 1200#, 1500#, 2000# sandpapers; then the workpiece to be joined is completely immersed in acetone and ultrasonically cleaned for 10 min; after the cleaning is completed, it is taken out from acetone and put into a vacuum drying oven for drying, the drying temperature is 50 - 80 °C, and the drying time is 20 - 40 min.

[0023] Further, the organic solvent in S2) is ethanol or terpineol; the coating thickness is not less than 0.2 mm.

[0024] The features of the present invention are as follows:

[0025] 1. A connecting method for an equal / approximate base material composition of an anisotropic single-crystal superalloy and its connecting material in the present invention adopt a low-melting alloy component alloy and a high-melting alloy component alloy directly separated from the base material composition of the single-crystal superalloy to form a connecting material with an equal / approximate composition to the base material, without degrading melting elements such as Si and B, and there is no brittle compound or eutectic structure rich in Si and B in the connecting layer. The eutectic reaction between the elements of the separated low-melting alloy component makes its melting point lower than 1250 °C, forming a liquid phase during the connection process, and realizing the connection through the solid-liquid interdiffusion between the low-melting alloy component, the high-melting alloy component and the base material.

[0026] 2. A joining material with the same / approximate base material composition for a directionally solidified single-crystal superalloy of the present invention is composed of two alloy powders, namely a low-melting alloy component and a high-melting alloy component, directly separated from the base material composition of the single-crystal superalloy. The homogenization process of the joint composition belongs to a rapid diffusion mechanism with a large diffusion area and a short diffusion distance, thus greatly accelerating the kinetics of the joining process.

[0027] 3. A joining method with the same / approximate base material composition for a directionally solidified single-crystal superalloy of the present invention and its joining material can obtain a non-single-crystal superalloy joining layer with the same / approximate composition as the base material after joining, avoiding the single-crystallization of the joint to form large-angle through-type grain boundaries parallel to the joining surface, and obtaining high-performance joining joints of single-crystal superalloys with any misorientation.

[0028] 4. A joining method with the same / approximate base material composition for a directionally solidified single-crystal superalloy of the present invention and its joining material can be used for joining single-crystal superalloys and non-single-crystal superalloys with any misorientation, including zero misorientation. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram for preparing the components to be joined of the directionally solidified single-crystal superalloy.

[0030] Figure 2 Schematic diagram for assembling the components of a joining method with the same / approximate base material composition for a directionally solidified single-crystal superalloy of the present invention and its joining material.

[0031] Figure 3 Schematic diagram of the principle of a joining method with the same / approximate base material composition for a directionally solidified single-crystal superalloy of the present invention and its joining material.

[0032] Figure 4 DSC curves of the low- and high-melting alloy powders used in Examples 1 and 2, where (a): alloy powder of the low-melting alloy component, (b): alloy powder of the high-melting alloy component.

[0033] Figure 5 SEM images of the microstructure of the joining layer and the matrix of the directionally solidified DD5 single-crystal superalloy components in Example 1, where (a): misorientation of 0°, (b): misorientation of 45°, (c): misorientation of 90°.

[0034] Figure 6 EBSD analysis results of the microstructure of the joining layer and the matrix of the directionally solidified DD5 single-crystal superalloy components in Example 1, where (a): misorientation of 0°, (b): misorientation of 45°, (c): misorientation of 90°.

[0035] Figure 7 Tensile strength at 980 °C of the joint sample of the directionally solidified DD5 single-crystal superalloy components in Example 2.

[0036] In the figure:

[0037] 1. Nickel-based single crystal superalloy base material, 1-1. The connecting parts to be joined prepared parallel to the

[001] orientation, 1-2. The connecting parts to be joined prepared in a direction deviated from the

[001] orientation by a certain angle, 2. Connecting material layer; 3. Single crystal superalloy base material, 4. Low melting point alloy powder, 5. High melting point alloy powder, 6. Liquid phase formed after melting of the low melting point alloy powder. Specific embodiments

[0038] The present invention will be described in detail below with reference to the accompanying drawings of the specification and embodiments, but the protection scope of the present invention is not limited thereto.

[0039] The present invention proposes a connection method and its connection material with equal / approximate base material composition of anisotropic single crystal superalloys for the connection of nickel-based single crystal superalloy dual-guide vanes. The material to be connected is a fully heat-treated nickel-based single crystal superalloy prepared by a directional solidification process, and the directional solidification direction of the single crystal superalloy is the

[001] direction. In order to simulate the crystal orientation difference between the two base materials to be joined in the connection of nickel-based single crystal superalloy dual-guide vanes, which is usually greater than 20°.

[0040] In the following embodiments, electrical discharge machining technology is used to prepare the connecting parts to be joined along the direction parallel to the

[001] orientation and the direction deviated from the

[001] orientation by a certain angle respectively, and the schematic diagram is as Figure 1 shown.

[0041] The principle of the connection method and its connection material with equal / approximate base material composition of anisotropic single crystal superalloys of the present invention is as Figure 3 shown: A mixed powder of low melting point alloy components and high melting point alloy component alloy powders directly separated from the single crystal superalloy base material is used to form a connection material with equal / approximate base material composition. A vacuum brazing furnace is used to heat and connect under a vacuum condition with a certain pressure applied. During the connection process, the low melting point alloy component alloy powder melts to form a liquid phase, which forms a dense solid-liquid mixed connection layer with the solid high melting point alloy component alloy powder. The connection is achieved by the solid-liquid interdiffusion between the liquid phase and the high melting point component particles and the base material. After further isothermal diffusion for composition homogenization, a non-single crystal superalloy connection layer with equal / approximate composition to the base material is obtained, realizing the high-performance connection of single crystal base materials with any orientation difference.

[0042] A connection method with equal / approximate base material composition of anisotropic single crystal superalloys of the present invention specifically includes the following steps:

[0043] S1) Select the nickel-based single crystal superalloy to be connected, prepare it into anisotropic nickel-based single crystal superalloy connecting parts to be joined, and pre-treat the surfaces of the connecting parts to be joined:

[0044] S2) Stir the joining material powder and the organic solvent evenly into a paste, apply it evenly on the surface of the to-be-joined part after S1) treatment, and fix it with a fixture;

[0045] S3) Place the to-be-joined part with the fixture installed in step S2) into a vacuum brazing furnace for brazing. After the furnace temperature drops to room temperature, take out the anisotropic DD5 single-crystal superalloy joining part.

[0046] The to-be-joined nickel-based single-crystal superalloy in S1) is a fully heat-treated nickel-based single-crystal superalloy prepared by the directional solidification process.

[0047] On the single-crystal superalloy base material in S1), anisotropic nickel-based single-crystal superalloy to-be-joined parts are prepared along the directions parallel to the

[001] orientation and deviated from the

[001] orientation by a certain angle.

[0048] The joining material powder in S2) is a mixture of low-melting alloy component alloy powder and high-melting alloy component alloy powder in a volume ratio of 1:1 to 4. The total composition of the mixed powder is equal / approximate to that of the nickel-based single-crystal superalloy. The deviation range of the content of each element in the joining material and the nickel-based single-crystal superalloy is not more than 15%.

[0049] The particle size of the low-melting alloy component alloy powder in the joining material is not more than 100 μm, and the melting point is not higher than 1250 °C; the particle size of the high-melting alloy component alloy powder is not more than 100 μm, and the melting point is not lower than the solution heat treatment temperature of the nickel-based single-crystal superalloy.

[0050] The mass percentage of the low-melting alloy component in S2) is: Cr 10.0 - 20.0 wt.%, Co 5.0 - 15.0 wt.%, Al 5.0 - 10.0 wt.%, Ti 5.0 - 20.0 wt.%, and the balance is Ni and unavoidable impurities;

[0051] The mass percentage of the high-melting alloy component is: Co 5.0 - 15.0 wt.%, Mo 1.0 - 5.0 wt.%, W 5.0 - 15.0 wt.%, Al 5.0 - 6.0 wt.%, Ta 5.0 - 15.0 wt.%, and the balance is Ni and unavoidable impurities.

[0052] The joining material powder is spherical and / or near-spherical alloy powder with an average particle size range of 5 - 106 μm.

[0053] The vacuum degree of the vacuum environment in S3) is 5×10 -3 Pa, the heating rate is 10 - 15 °C / min, raise the temperature to 1280 °C, hold for 30 - 180 min, then cool down in the furnace, and the cooling rate is 5 - 10 °C / min.

[0054] The pretreatment process in S1) is as follows: successively polish the surface to be joined of the nickel-based single crystal superalloy with 400#, 600#, 800#, 1000#, 1200#, 1500#, and 2000# sandpapers; then completely immerse the component to be joined in acetone and ultrasonically clean it for 10 min; after the cleaning is completed, take it out of the acetone and put it into a vacuum drying oven for drying, the drying temperature is 50 - 80 °C, and the drying time is 20 - 40 min.

[0055] The organic solvent in S2) is ethanol or terpineol; the coating thickness is not less than 0.2 mm.

[0056] Example 1:

[0057] This example is a method for joining an equal / approximate base material composition of a directionally solidified single crystal superalloy of the present invention and its joining material. The nickel-based single crystal superalloy used is the DD5 single crystal superalloy. Using electrical discharge machining technology, blocks to be joined with dimensions of 10×10×2 mm 3 (parallel to the

[001] orientation) and 10×10×2 mm 3 (deviating from the

[001] orientation by 45° and 90°) are prepared on the DD5 single crystal superalloy base material.

[0058] The chemical composition of the alloy powder of the low-melting alloy component in the joining material used in this example is: Cr 10.0 - 20.0 wt.%, Co 5.0 - 15.0 wt.%, Al 5.0 - 10.0 wt.%, Ti 5.0 - 20.0 wt.%, and the rest is Ni; the particle size of the alloy powder of the low-melting alloy component is not greater than 53 μm, and its DSC curve is as Figure 4 shown, and the complete melting temperature is 1218.4 °C; the chemical composition of the alloy powder of the high-melting alloy component is: Co 5.0 - 15.0 wt.%, Mo 1.0 - 5.0 wt.%, W 5.0 - 15.0 wt.%, Al 5.0 - 6.0 wt.%, Ta 5.0 - 15.0 wt.%, and the rest is Ni. The particle size of all alloy powders of the high-melting alloy component is not greater than 50 μm, and its DSC curve is as Figure 5 shown.

[0059] The specific process of this example includes the following steps:

[0060] Step 1, successively polish the surface to be joined of the nickel-based single crystal superalloy with 400#, 600#, 800#, 1000#, 1200#, 1500#, and 2000# sandpapers;

[0061] Step 2: Immerse the polished connector to be joined completely in acetone and ultrasonically clean it for 10 min. After cleaning, take it out of the acetone and put it into a vacuum drying oven for drying. The drying temperature is 60 °C and the drying time is 30 min.

[0062] Step 3: Set the volume ratio of the low-melting alloy component alloy powder to the high-melting alloy component alloy powder as 1:1, and weigh an appropriate amount of the low-melting alloy component alloy powder and the high-melting alloy component alloy powder. The mass fraction of the low-melting alloy component alloy powder in the joining material is 40%; the mass fraction of the high-melting alloy component alloy powder in the joining material is 60%.

[0063] Step 4: Use a planetary ball mill to mix the weighed joining material for 80 min, and set the rotation speed to 240 r / min.

[0064] Step 5: Add an organic solvent to the uniformly mixed joining material and stir it evenly into a paste. Place it between the DD5 single crystal superalloy base materials to be joined and fix it with a fixture.

[0065] Step 8: Put the prepared connector to be joined into a vacuum brazing furnace, and use a mechanical pump and a diffusion pump to evacuate the brazing furnace. When the vacuum degree reaches 5×10 -3 Pa, start heating. The heating rate is 15 °C / min, raise the temperature to 1280 °C, keep it warm for 120 min, and then cool down in the furnace. The cooling rate is about 8 °C / min. When the furnace temperature drops to room temperature, take out the anisotropic DD5 single crystal superalloy connector.

[0066] Step 9: Carry out conventional post-weld heat treatment on the nickel-based single crystal superalloy connector obtained in step (8), including solution heat treatment and aging treatment.

[0067] Cut the anisotropic DD5 single crystal superalloy connector obtained in step 9 along the axial cross-section, mechanically grind and polish the cross-section with sandpaper, and then carry out electro-polishing and electrolytic etching in sequence. The composition of the electro-polishing solution is: 20 vol.% concentrated sulfuric acid + 80 vol.% methanol, and the electro-polishing parameters are: voltage 25 V, time 20 s; the composition of the electrolytic etching solution is: 150 mL phosphoric acid + 10 mL concentrated sulfuric acid + 15 g CrO3, and the electrolytic etching parameters are: voltage 4 V, time 2.5 s. Use a scanning electron microscope to observe the microstructure of the joint layer and the substrate and use the EBSD technology to characterize the grains. As Figure 5 、 Figure 6 shown, the joint layer is a polycrystalline microstructure, and a non-single crystal superalloy joint layer with the same / approximate composition as the base material is obtained.

[0068] Example 2:

[0069] This embodiment is a method for joining a single-crystal superalloy with an equal or approximate base metal composition of the present invention and its joining material. The nickel-based single-crystal superalloy used is the DD5 single-crystal superalloy. The electrical discharge machining technology is used to prepare blocks to be joined with dimensions of 10×10×2 mm 3 (parallel to the

[001] orientation) and 10×10×2 mm 3 (deviating from the

[001] orientation by 45° and 90°) on the DD5 single-crystal superalloy base metal.

[0070] The chemical composition of the alloy powder of the low-melting alloy component in the joining material used in this embodiment is: Cr 10.0 - 20.0 wt.%, Co 5.0 - 15.0 wt.%, Al 5.0 - 10.0 wt.%, Ti 5.0 - 20.0 wt.%, and the rest is Ni; the particle size of the alloy powder of the low-melting alloy component is not more than 53 μm, and its DSC curve is as Figure 4 (shown in (a)), and the complete melting temperature is 1218.4 °C; the chemical composition of the high-melting alloy powder is: the chemical composition of the high-melting alloy powder is: Co 5.0 - 15.0 wt.%, Mo 1.0 - 5.0 wt.%, W 5.0 - 15.0 wt.%, Al 5.0 - 6.0 wt.%, Ta 5.0 - 15.0 wt.%, and the rest is Ni. The particle size of all high-melting alloy powders is not more than 50 μm, and its DSC curve is as Figure 4 (shown in (b)).

[0071] The specific process of this embodiment includes the following steps:

[0072] Step 1, polish the surface to be joined of the nickel-based single-crystal superalloy with 400#, 600#, 800#, 1000#, 1200#, 1500#, and 2000# sandpapers in sequence;

[0073] Step 2, completely immerse the polished parts to be joined in acetone and ultrasonically clean for 10 min; after the cleaning is completed, take them out of acetone and put them into a vacuum drying oven for drying. The drying temperature is 50 °C, and the drying time is 20 - 40 min;

[0074] Step 3, set the volume ratio of the low-melting alloy powder to the high-melting alloy powder to 1:1, weigh an appropriate amount of low-melting alloy powder and high-melting alloy powder, where the mass fraction of the low-melting alloy powder in the joining material is 40%; the mass fraction of the high-melting alloy powder in the joining material is 60% respectively;

[0075] Step 4, use a planetary ball mill to mix the weighed joining material for 120 min, and set the rotation speed to 240 r / min;

[0076] Step 5: Add an organic solvent to the uniformly mixed joining material and stir evenly to form a paste. Place the paste between the DD5 single crystal superalloy base materials to be joined and fix them with a fixture.

[0077] Step 8: Place the prepared components to be joined into a vacuum brazing furnace. Use a mechanical pump and a diffusion pump to evacuate the brazing furnace. When the vacuum degree reaches 5×10 -3 Pa, start heating. The heating rate is 15°C / min. Heat up to 1280°C, hold for 120 min, then cool down in the furnace. The cooling rate is about 10°C / min. After the furnace temperature drops to room temperature, take out the anisotropic DD5 single crystal superalloy joint.

[0078] Step 9: Conduct conventional post-weld heat treatment on the nickel-based single crystal superalloy joint obtained in step (8), including solution heat treatment and aging treatment at high temperature.

[0079] Process the anisotropic DD5 single crystal superalloy joint obtained in step 9 into a standard tensile test sample and conduct tensile testing at 980°C. The test results are as Figure 7 shown. It can be seen that the high-temperature tensile strength of all samples with different orientation differences after joining reaches more than 90% of the single crystal superalloy of the base material. This shows that the high-performance joining of anisotropic single crystal superalloys is achieved by using the method of the present invention.

[0080] A method for joining anisotropic single crystal superalloys with equal / approximate base material composition and its joining material proposed by the present invention adopt a joining material with equal / approximate base material composition formed by mixing two alloy powders, namely a low-melting alloy component alloy and a high-melting alloy component alloy, directly separated from the base material composition of the single crystal superalloy. It can greatly improve the joining kinetics and avoid the formation of brittle compounds of B and Si in the joining layer. After joining, a polycrystalline joining layer is formed, effectively improving the mechanical properties of the joining layer, solving the problem of efficient and high-performance joining of single crystal superalloys with any orientation difference, and can also be used for joining single crystal superalloys with no orientation difference and non-single crystal superalloys.

[0081] The above has introduced in detail a method for joining anisotropic single crystal superalloys with equal / approximate base material composition provided by the embodiments of the present application. The description of the above embodiments is only used to help understand the method and its core idea of the present application; at the same time, for those of ordinary skill in the art, according to the idea of the present application, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present application.

[0082] As used in the specification and claims, certain terms are used to refer to specific components. Those skilled in the art should understand that hardware manufacturers may use different terms to refer to the same component. The specification and claims do not distinguish components by the difference in names, but by the difference in functions of the components. As used throughout the specification and claims, the terms "comprising" and "including" are open-ended terms and should be interpreted as "comprising / including but not limited to". "Substantially" means within an acceptable error range. Those skilled in the art can solve the technical problem within a certain error range and basically achieve the technical effect. The following description in the specification is a preferred embodiment for implementing the present application, but the description is for the purpose of explaining the general principles of the present application and is not used to limit the scope of the present application. The protection scope of the present application shall be determined by the scope defined in the appended claims.

[0083] It should also be noted that the term "including", "comprising" or any other variant thereof is intended to cover non-exclusive inclusion, such that a good or system including a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such good or system. Without further limitation, an element defined by the statement "including one..." does not exclude the existence of another identical element in the good or system including the said element.

[0084] It should be understood that the term "and / or" used herein is only an associative relationship describing associated objects, indicating that three relationships may exist. For example, A and / or B may represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " herein generally represents an "or" relationship between the associated objects before and after.

[0085] The above description shows and describes several preferred embodiments of the present application. However, as mentioned above, it should be understood that the present application is not limited to the form disclosed herein, should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be changed within the scope of the application concept described herein through the above teachings or the technology or knowledge in the relevant field. And the changes and variations made by those skilled in the art that do not depart from the spirit and scope of the present application shall all be within the protection scope of the appended claims of the present application.

Claims

1. A method for connecting single-crystal superalloys with opposite orientations, characterized in that, The connection method uses low-melting alloy components and high-melting alloy components directly separated from the composition of the nickel-based single-crystal superalloy base material. After the components of the low-melting alloy and the high-melting alloy are combined, a connection material equal to or approximate to the base material composition is formed. Then, by regulating the volume ratio between the low-melting alloy component and the high-melting alloy component, the volume fraction of the liquid phase during the connection process is controlled not to exceed 50%. During the connection process, the solid-liquid interdiffusion between the liquid phase formed by the low-melting alloy first and the high-melting point component and the base material is utilized to achieve isothermal solidification, and a non-single-crystal superalloy connection layer is formed between the directionally solidified single-crystal superalloys. It specifically includes the following steps: S1) Select the nickel-based single-crystal superalloy to be connected, prepare it into a directionally solidified nickel-based single-crystal superalloy workpiece to be connected, and pre-treat the surface of the workpiece to be connected: S2) Stir the connection material powder and the organic solvent evenly into a paste, evenly apply it on the surface of the workpiece to be connected after being treated in S1), and fix it with a fixture; S3) Place the fixed workpiece to be connected obtained in S2) in a vacuum brazing furnace for brazing. After the furnace temperature drops to room temperature, a directionally solidified single-crystal superalloy workpiece with a nickel-based non-single-crystal superalloy connection layer is obtained.

2. The connection method according to claim 1, wherein The connection material powder in S2) is spherical and / or near-spherical alloy powder with an average particle size range of 5 - 106 μm.

3. The connection method according to claim 1, characterized in that, The connection material powder in S2) is a mixture of low-melting alloy powder and high-melting alloy powder components in a volume ratio of 1:1 - 4, and the deviation range of the content of each element in the connection material and the nickel-based single-crystal superalloy base material is not more than 15%.

4. The connection method according to claim 3, characterized in that The particle size of the low-melting alloy powder is not more than 100 μm, and the melting point is not higher than 1250 °C; The particle size of the high-melting alloy powder is not more than 100 μm, and the melting point is not lower than the solution heat treatment temperature of the nickel-based single-crystal superalloy base material.

5. The connection method according to claim 4, characterized in that, The mass percentages of the components of the low-melting alloy are: Cr 10.0 - 20.0 wt.%, Co 5.0 - 15.0 wt.%, Al 5.0 - 10.0 wt.%, Ti 5.0 - 20.0 wt.%, and the balance is Ni and inevitable impurities; The mass percentages of the components of the high-melting alloy are: Co 5.0 - 15.0 wt.%, Mo 1.0 - 5.0 wt.%, W 5.0 - 15.0 wt.%, Al 5.0 - 6.0 wt.%, Ta 5.0 - 15.0 wt.%, and the balance is Ni and inevitable impurities.

6. The connection method according to claim 1, wherein The nickel-based single-crystal superalloy to be connected in S1) is a fully heat-treated nickel-based single-crystal superalloy prepared by the directional solidification process.

7. The connection method according to claim 1, characterized in that, The directionally solidified nickel-based single-crystal superalloy workpiece to be connected in S1) is a single-crystal superalloy base material with an orientation parallel to [001] and a deviation from the [001] orientation, and the deviation angle is α, α ≥ 10°.

8. The connection method according to claim 1, characterized in that, The degree of vacuum in the vacuum environment in S3) is 5×10 -3 Pa; during brazing: first, with a heating rate of 10-15 °C / min, raise the temperature to 1280 °C, keep it warm for 30-180 min; then, with a cooling rate of 5-10 °C / min, cool it down in the furnace until it reaches room temperature.

9. The connection method according to claim 1, wherein The pre-treatment process in S1) is: Grind the surface of the nickel-based single-crystal superalloy to be connected with 400#, 600#, 800#, 1000#, 1200#, 1500#, and 2000# sandpapers in sequence; Then completely immerse the ground workpiece to be connected in acetone and ultrasonically clean it for 10 min; After cleaning, take it out of acetone and put it into a vacuum drying oven for drying. The drying temperature is 50-80 °C and the drying time is 20-40 min.

10. The connection method according to claim 1, characterized in that, The organic solvent in the step S2) is ethanol or terpineol; the coating thickness is not less than 0.2 mm.

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