A method for controlling the three-dimensional crystal orientation of a single crystal blade by a universal seed crystal

Abstract

The application discloses a method for precisely controlling three-dimensional crystal orientation of a single crystal blade by using a universal seed crystal, which comprises the following steps: seed crystal preparation, mold preparation and assembly, shell preparation, smelting and pouring, etc. The method realizes the precise control of the three-dimensional crystal orientation of the single crystal blade by regulating the positional relationship between the seed crystal and the wax mold of the blade casting, and the seed crystal with any orientation can be used, so that the method has the characteristics of the universal seed crystal, the process difficulty of the seed crystal preparation is greatly simplified, and the cost of the seed crystal preparation is reduced. By limiting the size of the seed crystal, a better remelting ratio can be formed between the seed crystal and the cooling plate even without contact during the single crystal preparation, the technical requirement that the seed crystal is strictly limited to be attached to the bottom plate during the mold assembly is avoided, and the mold assembly difficulty is reduced. When the last layer of the molding material is coated and hung, only the lower part of the mold assembly from the bottom plate wax mold to the pouring cup is coated and hung, the strength of the shell is ensured, the thickness of the shell as a whole is reduced, the temperature field evolution process in the directional solidification process is improved, and the single crystal blade preparation success rate is improved.

Description

Technical Field

[0001] This invention relates to the field of precision casting technology for single-crystal blades, and specifically to a method for controlling the three-dimensional crystal orientation of single-crystal blades using a universal seed crystal. Background Technology

[0002] Nickel-based single-crystal superalloys are widely used in the manufacture of blades for aero-engines and ground-based gas turbines due to their excellent high-temperature comprehensive performance. With the increasing demands on the thrust-to-weight ratio of aero-engines and the continuous rise in turbine inlet temperatures, hollow and ultracooled blades with more complex structures and lower minimum wall thicknesses are gradually becoming the development trend. The mechanical properties of nickel-based single-crystal superalloys exhibit significant anisotropy, and the increasing complexity of blade structures leads to a more pronounced dependence on crystal orientation. Currently, aero-engine design and application units have explicitly stipulated in the production requirements of some single-crystal blades that the crystal orientation should be controlled within a narrow range to improve their service performance.

[0003] Directional solidification investment casting combined with selective crystal or seed crystal technology is the main method for preparing single-crystal superalloys. Compared with selective crystal casting, seed crystal casting can precisely control the crystal orientation of single-crystal castings in three dimensions, which has significant advantages in preparing advanced single-crystal blades. However, solidification defects such as impurities are prone to appear in the early stage of directional solidification, leading to single-crystal preparation failure. In recent years, through research on the formation mechanism and control technology of solidification defects, various methods have been proposed and applied to the seed crystal method for preparing single-crystal blades, such as "variable speed pulling", "pre-placed seed crystal in the mold shell", "seed crystal and selective crystal combination method", "setting thermal resistance material in the seed crystal section of the mold shell", and "applying a strong static magnetic field", reducing the formation of solidification defects. Chinese inventions CN114618993A and CN114622270A have proposed a method using... <001> The method for preparing single-crystal superalloys using oriented seed crystals improves the versatility of seed crystals. Meanwhile, <001> Oriented seed crystals are easy to obtain and their orientation deviations are easy to detect, which is conducive to promoting the widespread application of the seed crystal method in industrial production. However, precise control of the three-dimensional crystal orientation of single-crystal blades still faces problems such as high process control difficulty, low success rate, and poor economic efficiency. Summary of the Invention

[0004] To address the technical problems of existing methods for precisely controlling the three-dimensional crystal orientation of single-crystal blades, such as high process control difficulty, low success rate, and poor economic efficiency, this invention provides a universal seed crystal method for precisely controlling the three-dimensional crystal orientation of single-crystal blades, which features simple process, high success rate, and low overall cost.

[0005] The technical solution of this invention is: A method for controlling the three-dimensional crystal orientation of a single-crystal blade using a general seed crystal includes the following steps: S1. Preparation of seed crystals Seed crystal specimens are cut from bulk single crystals. Based on the shape, structure and size characteristics of the seed crystal specimens, a reference plane and reference direction are established. The reference plane is parallel to the existing plane on the seed crystal specimens. Using the reference direction and reference plane as a reference system, the three-dimensional crystal orientation of the seed crystal specimens is determined. The seed crystal specimens are then ground or polished to remove oxide scale, oil stains, etc. from the surface and cleaned for later use. S2. Molding and assembly Based on the principle that the crystallographic orientation of the seed crystal and the single crystal blade are completely consistent after directional solidification, the orientation relationship between the seed crystal and the blade casting wax model is designed. The blade casting wax model, pouring cup wax model, sprue wax model, base plate wax model, and central column tube wax model are pressed according to the casting process requirements. Then, the blade casting wax model, pouring cup wax model, sprue wax model, base plate wax model, central column tube wax model and seed crystal are welded together to form a module. S3. Shell making Apply a 5-15mm layer of molding material (using commonly used materials in existing technologies, such as EC95 powder, corundum powder, etc.) to the surface of the module, then dewax it at 100-180℃, and then bake the shell at 800-1000℃ for 2-4 hours to obtain the shell. S4. Melting and Casting The mold shell is placed in a directional solidification furnace, and the corresponding melting process parameters are set. The temperature is heated to 1480-1550℃ and held for 3-15 minutes. The molten master alloy is then poured into the mold shell and allowed to stand for 3-15 minutes. After the crystal pulling is completed, the mold shell is cooled in the furnace for 5-10 minutes and then removed from the vacuum to obtain the blade casting blank.

[0006] Furthermore, in S1, the height of the seed crystal is 25-60mm; the maximum lateral dimension in the vertical height direction is 1-7mm, preferably 2-4mm.

[0007] Furthermore, in S2, the assembly welding is selected from one of the following processes: ① Place the seed crystal into the mold for pressing the blade casting wax model, and directly connect and form the blade casting wax model during pressing; ② First, press the blade casting wax model, and then weld the blade casting wax model directly to the seed crystal to form the shape; ③ First, press the blade casting wax model and the seed crystal connection wax model, and then directly connect the blade casting wax model and the seed crystal welding wax model to form the shape.

[0008] Furthermore, in S2, after the seed crystal is connected to the wax model of the blade casting, the depth of the seed crystal inserted into the wax model is 3-10mm, and the abrupt change in the cross-sectional dimensions of the transition zone between the seed crystal and the wax model does not exceed 10mm.

[0009] Furthermore, in S2, the cross-sectional dimensions of the transition zone between the seed crystal and the wax mold are gradually transitioned.

[0010] Furthermore, in S2, after the mold is assembled, the seed crystal is located above the base plate, and the distance between the two is 0-5mm.

[0011] Furthermore, in S3, when applying the final layer of the molding material, only the lower part of the mold assembly from the base plate wax model to the pouring cup is coated, including the base plate wax model, seed crystal, partial blade casting wax model, and central column tube.

[0012] Compared with the prior art, the beneficial effects of the present invention are: First, this invention achieves precise control of the three-dimensional crystal orientation of single-crystal blades by adjusting the orientation relationship between the seed crystal and the wax model of the blade casting. It can use seed crystals with arbitrary orientations, has the characteristics of universal seed crystals, and can greatly simplify the process difficulty of making seed crystals and reduce the cost of making seed crystals.

[0013] Secondly, by limiting the size of the seed crystal, the present invention enables a better remelting ratio to be formed even if there is no contact between the seed crystal and the cooling plate during the single crystal preparation process. This avoids the technical requirement of strictly limiting the fit between the seed crystal and the base plate during mold assembly and reduces the difficulty of mold assembly.

[0014] Third, when applying the last layer of the molding material in this invention, only the lower part of the module from the base plate wax model to the pouring cup is coated. This reduces the overall thickness of the shell while ensuring the strength requirements of the shell, improves the temperature field evolution process during directional solidification, and helps to increase the success rate of single crystal blade preparation. Attached Figure Description

[0015] Figure 1 Schematic diagrams of several seed crystal structures provided by this invention; Figure 2 This is a schematic diagram showing the connection between the wax model and the seed crystal of the blade casting. Figure 3 This is a schematic diagram of the seed crystal connecting to the wax mold; Figure 4 This is a schematic diagram of the module.

[0016] In the figure, 1. Seed crystal; 101. Reference direction; 102. Reference plane; 2. Wax model of blade casting; 201. Transition zone between seed crystal and wax model; 3. Paraffin wax; 4. Wax model of pouring cup; 5. Wax model of sprue; 6. Wax model of central column tube; 7. Wax model of base plate. Detailed Implementation

[0017] The present invention will be further described in detail below with reference to specific embodiments, but the present invention is not limited thereto. Example 1

[0018] Preparation of primary orientation <001> Secondary orientation is <010> Single-crystal turbine blades in the direction of rotation.

[0019] Step 1: Preparation of seed crystals A square-prism-shaped seed crystal specimen was cut from a bulk single crystal. Based on the shape, structure, and size characteristics of the seed crystal specimen, the axis of the square-prism-shaped seed crystal specimen was used as the reference direction, and the side surface of the square-prism-shaped seed crystal specimen was used as the reference plane. The crystallographic orientation of the seed crystal specimen was detected using X-ray diffraction, and the results were as follows: <001> The direction is parallel to the reference direction, and <010> The orientation is perpendicular to the reference plane. Grind or polish the seed crystal test block to remove the oxide scale, oil stains, etc. from the surface, and clean it for later use; the height of the seed crystal test block is 60mm; the side length of the bottom surface of the square prism seed crystal test block is 3mm.

[0020] Step 2: Mold making and assembly Based on the principle that the crystallographic orientation of the seed crystal and the single-crystal blade is completely consistent after directional solidification, the orientational relationship between the seed crystal and the blade casting wax model is designed, resulting in the seed crystal's reference direction being parallel to the blade axis and its reference plane being perpendicular to the blade basin direction. According to the casting process requirements, the blade casting wax model, pouring cup wax model, sprue wax model, base plate wax model, and central column tube wax model are pressed together. These components, along with the seed crystal, are then welded together to form a module. The seed crystal is placed into the mold used to press the blade casting wax model, and the pressing process directly connects and shapes the wax model.

[0021] After the seed crystal is connected to the wax model of the blade casting, the seed crystal is inserted into the wax model to a depth of 3mm. The cross-section of the transition zone between the seed crystal and the wax model is abruptly changed by 5mm. After the mold is assembled, the seed crystal is located above the base plate, and the distance between the two is 5mm.

[0022] Step 3, Shell Making A molding material, corundum powder, is applied to the surface of the mold. The final layer of molding material is applied only to the lower part of the mold, from the base plate wax model to the pouring cup, including the base plate wax model, seed crystal, some blade casting wax models, and the central column tube. The overall thickness of the molding material is 5mm. The mold is then dewaxed at 100℃, and the shell is fired at 1000℃ for 2 hours to obtain the final shell.

[0023] Step 4, Melting and Casting The mold shell is placed in a directional solidification furnace, and the corresponding melting process parameters are set. The furnace is heated to a holding temperature of 1480℃ and held for 3 minutes. Then, the molten master alloy is poured into the mold shell and allowed to stand for 15 minutes before crystal pulling at a speed of 9 mm / min. After crystal pulling is completed, the mold shell is cooled in the furnace for 5 minutes and then removed from the furnace after the vacuum is broken to obtain the blade casting blank with the required orientation. Example 2

[0024] Preparation of primary orientation <011> A single-crystal turbine blade with a secondary orientation in the <01-1> direction.

[0025] Step 1: Preparation of seed crystals A cylindrical seed crystal specimen with a plane parallel to the axis was cut from a bulk single crystal. Based on the shape, structure, and size characteristics of the seed crystal specimen, the axis of the cylindrical seed crystal specimen was used as the reference direction, and the plane parallel to the axis of the cylindrical seed crystal specimen was used as the reference plane. The crystallographic orientation of the cylindrical seed crystal specimen was detected using X-ray diffraction. The results are as follows: <011> The direction is parallel to the reference direction, and the <01-1> direction is perpendicular to the reference plane. Grind or polish the cylindrical seed crystal test block to remove the oxide scale, oil stains, etc. on the surface, and clean it for later use; the height of the cylindrical seed crystal test block is 25mm; the diameter of the cylindrical seed crystal test block is 1mm.

[0026] Step 2: Mold making and assembly Based on the principle that the crystallographic orientation of the seed crystal and the single-crystal blade is completely consistent after directional solidification, the orientational relationship between the seed crystal and the blade casting wax model is designed, resulting in the seed crystal's reference direction being parallel to the blade axis and the seed crystal's reference plane being parallel to the blade basin direction. According to the casting process requirements, the blade casting wax model, pouring cup wax model, sprue wax model, base plate wax model, and central column tube wax model are pressed together. These wax models, along with the seed crystal, are then welded together to form a module. Finally, the blade casting wax model is directly welded to the seed crystal to form the final shape.

[0027] After the seed crystal is connected to the wax model of the blade casting, the seed crystal is inserted into the wax model to a depth of 3mm, and the cross-sectional dimensions of the transition zone between the seed crystal and the wax model are gradually changed. After the mold is assembled, the seed crystal is located above the base plate, and the distance between the two is 2mm.

[0028] Step 3, Shell Making EC95 molding compound powder is applied to the surface of the mold. The final layer of molding compound is applied only to the lower part of the mold from the base plate wax model to the pouring cup, including the base plate wax model, seed crystal, some blade casting wax models, and the central column tube. The overall thickness of the molding compound is 8mm. The mold is then dewaxed at 180℃, and the shell is fired at 800℃ for 4 hours to obtain the final shell.

[0029] Step 4, Melting and Casting The mold shell is placed in a directional solidification furnace, and the corresponding melting process parameters are set. The furnace is heated to a holding temperature of 1550℃ and held for 15 minutes. The molten master alloy is then poured into the mold shell and allowed to stand for 3 minutes before crystal pulling at a speed of 1 mm / min. After crystal pulling is completed, the mold shell is cooled in the furnace for 10 minutes and then removed from the furnace after the vacuum is broken to obtain the blade casting blank with the required orientation. Example 3

[0030] Preparation of primary orientation <001> Single-crystal turbine blades with secondary orientation in the <1-10> direction.

[0031] Step 1: Preparation of seed crystals A cubic seed crystal specimen was cut from a bulk single crystal. Based on the shape, structure, and size characteristics of the cubic seed crystal specimen, the major axis of the specimen was used as the reference direction, and the largest plane parallel to the major axis was used as the reference plane. The crystallographic orientation of the cubic seed crystal specimen was detected using X-ray diffraction. The results are as follows: <112> The direction is parallel to the reference direction, and the <1-10> direction is perpendicular to the reference plane. Grind or polish the seed crystal test block to remove the oxide scale, oil stains, etc. on the surface, and clean it for later use; the height of the square seed crystal test block is 50mm; the side lengths of the square seed crystal test block are 2mm and 3mm respectively.

[0032] Step 2: Mold making and assembly Based on the principle that the crystallographic orientation of the seed crystal and the single-crystal blade is completely consistent after directional solidification, the orientation relationship between the seed crystal and the blade casting wax model is designed. This results in the seed crystal's reference direction being inclined at 35.3° to the blade axis, the seed crystal's base plane normal being parallel to the blade direction, and the seed crystal's reference plane being inclined at 35.3° to the blade basin direction. According to the casting process requirements, wax models of the blade casting, pouring cup, sprue, base plate, central column tube, and seed crystal connection are pressed. These wax models are then welded together to form a module.

[0033] After the seed crystal is connected to the wax model of the blade casting, the seed crystal is inserted into the wax model to a depth of 7mm. The cross-section of the transition zone between the seed crystal and the wax model is abruptly changed, with an abrupt change amount of 10mm. After the mold is assembled, the seed crystal is located above the base plate, and the distance between the two is 0mm.

[0034] Step 3, Shell Making The molding material, corundum powder, is applied to the surface of the mold. When applying the final layer of molding material, only the lower part of the mold, from the base plate wax model to the pouring cup, is coated, including the base plate wax model, seed crystal, some blade casting wax models, and the central column tube. The overall thickness of the molding material is 15mm. The mold is then dewaxed at 150℃, and the shell is fired at 900℃ for 3 hours to obtain the final shell.

[0035] Step 4, Melting and Casting The mold shell is placed in a directional solidification furnace, and the corresponding melting process parameters are set. The temperature is heated to 1500℃ and held for 10 minutes. Then, the molten master alloy is poured into the mold shell and allowed to stand for 10 minutes before crystal pulling at a speed of 6 mm / min. After crystal pulling is completed, the mold shell is cooled in the furnace for 7 minutes and then removed from the furnace after the vacuum is broken to obtain the blade casting blank with the required orientation.

Claims

1. A method for controlling the three-dimensional crystal orientation of a single-crystal blade using a universal seed crystal, characterized in that, The steps include the following: S1. Preparation of seed crystals Seed crystal specimens are cut from bulk single crystals. Based on the shape, structure and size characteristics of the seed crystal specimens, a reference plane and reference direction are established. The reference plane is parallel to the existing plane on the seed crystal specimens. The three-dimensional crystal orientation of the seed crystal specimens is determined using the reference direction and reference plane as a reference system. Grind or polish the seed crystal test block, clean the surface and wash it thoroughly for later use; S2. Molding and Assembly Based on the principle that the crystallographic orientation of the seed crystal and the single crystal blade are completely consistent after directional solidification, the orientation relationship between the seed crystal and the blade casting wax model is designed. The blade casting wax model, pouring cup wax model, sprue wax model, base plate wax model, and central column tube wax model are pressed according to the casting process requirements. Then, the blade casting wax model, pouring cup wax model, sprue wax model, base plate wax model, central column tube wax model and seed crystal are welded together to form a module. S3. Shell making Apply 5-15mm of molding material to the surface of the module, then dewax it at 100-180℃, and then bake the shell at 800-1000℃ for 2-4 hours to obtain the shell. S4. Melting and Casting The mold shell is placed in a directional solidification furnace and heated to a holding temperature of 1480-1550℃. After holding for 3-15 minutes, the molten master alloy is poured into the mold shell. After standing, crystal pulling is performed. After the crystal pulling is completed, the mold shell is removed after the furnace is cooled and the vacuum is broken to obtain the blade casting blank. In S3, when applying the final layer of molding material, only the lower part of the mold assembly from the base plate wax model to the pouring cup is coated, including the base plate wax model, seed crystal, some blade casting wax models, and central column tube.

2. The method for controlling the three-dimensional crystal orientation of a single-crystal blade using a universal seed crystal according to claim 1, characterized in that, In S1, the height of the seed crystal is 25-60mm; the maximum lateral dimension in the vertical height direction is 1-7mm.

3. The method for controlling the three-dimensional crystal orientation of a single-crystal blade using a universal seed crystal according to claim 1, characterized in that, In S2, the assembly welding is selected from one of the following processes: ① Place the seed crystal into the mold for pressing the blade casting wax model, and directly connect and form the blade casting wax model during pressing; ② First, press the blade casting wax model, and then weld the blade casting wax model directly to the seed crystal to form the shape; ③ First, press the blade casting wax model and the seed crystal connection wax model, and then directly connect the blade casting wax model and the seed crystal welding wax model to form the shape.

4. The method for controlling the three-dimensional crystal orientation of a single-crystal blade using a universal seed crystal according to claim 1, characterized in that, In S2, after the seed crystal is connected to the wax model of the blade casting, the depth of the seed crystal inserted into the wax model is 3-10mm, and the abrupt change in the cross-sectional size of the transition zone between the seed crystal and the wax model does not exceed 10mm.

5. The method for controlling the three-dimensional crystal orientation of a single-crystal blade using a universal seed crystal according to claim 1, characterized in that, In S2, the cross-sectional dimensions of the transition zone between the seed crystal and the wax mold are gradually transitioned.

6. The method for controlling the three-dimensional crystal orientation of a single-crystal blade using a universal seed crystal according to claim 1, characterized in that, In S2, after the mold is assembled, the seed crystal is located above the base plate, and the distance between the two is 0-5mm.

7. The method for controlling the three-dimensional crystal orientation of a single-crystal blade using a universal seed crystal according to claim 1, characterized in that, In S4, the settling time is 3-15 min, the crystal pulling speed is 1-9 mm / min, and the cooling time is 5-10 min.

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