A method for controlling orientation deviation of a nickel-based single crystal superalloy casting

Abstract

The application provides a control method for orientation deviation of a nickel-based single crystal superalloy casting, which comprises steps of wax mold preparation, shell preparation, casting pouring and heat treatment, etc., a positioning and locking mechanism is arranged on a wax mold base plate, the shell can be ensured to be in a correct center position during pouring, heat radiation of a hot zone and a cold zone is uniformly distributed around the shell, and orientation deviation is reduced; different heights and numbers of heat insulation sleeves are prepared according to different heights of the casting, heat radiation of the casting is isolated or reduced, and dendrite growth is improved; and the temperature of water cooling disc cooling water is adjusted, so that the temperature gradient and the solidification rate are changed, solidification stress and dendrite deflection are reduced, the dendrites grow vertically upward, and a casting with good orientation is obtained. The control method for orientation deviation of the nickel-based single crystal superalloy casting is simple to operate and easy to realize, production cost is reduced, the qualified rate of the casting is improved, and is especially suitable for a large mold group combination scheme.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature alloy precision casting technology, specifically relating to a method for controlling orientation deviation in nickel-based single-crystal high-temperature alloy castings. Background Technology

[0002] Nickel-based single-crystal superalloys are widely used in hot-end components of aero-engines and ground-based gas turbines due to their excellent high-temperature mechanical properties, and their development level has become one of the important indicators for measuring the development level of materials. The development of high-performance aero-engines has placed higher demands on the temperature resistance and mechanical properties of nickel-based single-crystal superalloys. Optimizing alloy composition design and preparation process is currently the main method to improve and enhance the performance of superalloys. A significant characteristic of changes in alloy composition is the increase in the content of refractory elements. By adding a large amount of refractory elements, the temperature resistance and high-temperature mechanical properties of the alloy can be effectively improved. However, the addition of refractory elements leads to a sharp increase in the tendency of casting defects, such as impurities, striations, and orientation deviations. These defects can adversely affect the performance of single-crystal castings and even directly lead to the scrapping of blades.

[0003] Nickel-based single-crystal superalloys have a face-centered cubic structure, and their preferred crystallographic growth direction is... <001> Crystal orientation, <001> It has the lowest directional elastic modulus and the best high-temperature mechanical properties. Since turbine blades primarily bear axial loads, when... <001> When the primary dendrites of a single-crystal blade grow in a direction-preferred manner and are parallel to the blade axis, the blade can better exert its advantages. However, during the growth of a single crystal, the orientation can be slightly deviated due to the influence of temperature field, solute field, etc., causing the crystal growth direction to be different from the direction of the blade. <001> Significant deviations, especially when dendrites deviate inconsistently, can lead to the formation of small-angle grain boundaries between dendrite rows. This orientation deviation significantly reduces the alloy's creep resistance, peristaltic properties, and fatigue performance. Therefore, controlling the orientation of single-crystal superalloy crystals and reducing crystal density is crucial. <001> The deviation of the direction from the blade axis is crucial. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for controlling orientation deviation of nickel-based single crystal high-temperature alloy castings, which effectively reduces the tendency of orientation deviation of single crystal high-temperature alloy castings, and is particularly suitable for large module (module with chassis diameter not less than 300mm) combination schemes.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for controlling orientation deviation of nickel-based single-crystal superalloy castings, comprising the following steps: S1. Wax Model Preparation The pressing wax mold includes a base, a central column, a gating system, and a positioning and locking mechanism. A metal aluminum disc is pre-embedded in the base to ensure that the base is flat. The positioning and locking mechanism is located on the edge of the base and is an integral structure with the base, and is pressed out together with the base during pressing. The central column is connected to the center of the base. After the wax model has completely cooled, it is assembled. A circular heat insulation sleeve is prepared using wax paper according to the size of the casting, and the heat insulation sleeve is assembled onto the central column to obtain the wax model module. S2, Shell Preparation The wax model obtained from S1 is subjected to multiple processes of slurry application, sanding, and drying to prepare the surface layer, transition layer, and back layer of the shell. Finally, the shell is sealed and dried to obtain the shell. S3, Casting pouring The shell obtained in S2 is placed in a vacuum melting furnace for casting. The positioning and locking mechanism on the chassis is installed on the water cooling plate of the vacuum melting furnace and works with the water cooling plate to ensure that the shell is in the center of the vacuum melting furnace. The temperature of the cooling water is controlled during the casting process and gradually decreases as the crystal pulling process proceeds. S4, Heat Treatment After the S3 casting is completed, the mold shell is cleaned and then heat-treated. After completion, orientation samples are cut from the excess parts of the casting and orientation analysis is performed using EBSD.

[0006] Preferably, the thickness of the wax paper in S1 is 1.5mm to 2mm.

[0007] Preferably, the total number of heat insulation sleeves in S1 is adjusted according to the height of the casting, and the total height of the heat insulation sleeves is equivalent to the height of the casting; the height of a single heat insulation sleeve is 40mm~50mm. If the number of heat insulation sleeves is not less than two, a gap of 10mm~15mm is maintained between two adjacent heat insulation sleeves.

[0008] Preferably, when applying the slurry in S2, the composition of the surface slurry is as follows by mass ratio: corundum powder: silica sol: wetting agent: defoamer = (3.5~4.0):1.0:0.003:0.01, the viscosity of the surface slurry is 40s~45s, and the sanding material for the surface layer is 100# corundum sand; The composition of the transition layer slurry by mass ratio is: EC95 powder: silica sol: wetting agent: defoamer = (2.5~3.0):1.0:0.003:0.003; the viscosity of the transition layer slurry is 30s~35s, and the sand spreading material of the transition layer is 60# corundum sand; The composition of the backing slurry by mass ratio is: EC95 powder: silica sol: wetting agent: defoamer = (1.5~2.0):1.0:0.003:0.003. The viscosity of the backing slurry is 15s~20s. The backing sand material is 24# corundum sand.

[0009] Preferably, in S2, the total number of shell layers is between 6 and 8, depending on the size of the wax model module.

[0010] Preferably, during the casting process described in S3, the initial temperature of the cooling water in the water-cooling pan is 20℃~25℃; when the crystal pulling height exceeds the crystal-drawing transition section and the crystal stabilizes, the temperature of the cooling water is reduced to 10℃~15℃; when the crystal pulling height is located at half the height of the casting, the temperature of the cooling water is reduced to 0℃~5℃.

[0011] Preferably, the heat treatment process described in S4 is determined according to the technical requirements of different alloy grades.

[0012] Preferably, the size of the detection surface of the orientation sample cut in S4 is (3±0.5mm)×(2±0.5mm).

[0013] Compared with the prior art, the present invention has the following significant technical effects: 1. This invention provides a method for controlling orientation deviation in nickel-based single-crystal superalloy castings. By setting a positioning and locking mechanism at the edge of the chassis, adding a heat-insulating sleeve to the inner ring of the casting, and adjusting the cooling water temperature of the water-cooling plate, the tendency of orientation deviation in nickel-based single-crystal superalloy castings is reduced. This method is simple to operate, easy to implement, reduces production costs, and improves the casting qualification rate. It is especially suitable for large module (chassis diameter not less than 300mm) combination schemes.

[0014] 2. The positioning and locking mechanism of this invention is pressed out as a whole with the chassis during the chassis pressing process, eliminating the need for post-processing. Furthermore, a metal aluminum disc is pre-embedded in the chassis, reducing the risk of breakage during large module fabrication. During the casting process, a certain gap exists between the heat insulation baffle and the mold shell between the hot and cold zones in the vacuum furnace, resulting in heat radiation between the hot and cold zones. The positioning and locking mechanism designed in this invention is installed on the water-cooling plate during casting, cooperating with the water-cooling plate to ensure the mold shell is centered. This maintains a consistent gap between the heat insulation baffle and the perimeter of the mold shell, thereby ensuring that heat radiation from the hot and cold zones is evenly distributed around the mold shell, reducing orientation deviation.

[0015] 3. For large modules with a large number of castings in each group, the heat radiation between castings is significant, which can easily lead to inconsistent temperature fields in different parts of the casting, resulting in orientation deviation. This invention prepares different numbers of heat-insulating sleeves according to the different heights of the castings, ensuring that the total height of the sleeves is comparable to the height of the castings. This effectively isolates or reduces the heat radiation from the castings, improving dendrite growth. Furthermore, a gap of 10mm to 15mm is maintained between adjacent sleeves to allow the slurry and corundum sand to be evenly coated across the entire module during shell preparation, preventing insufficient strength that could lead to shell failure. The gaps between the sleeves can be completely connected during subsequent shell coating processes as the number of shell layers increases, thus achieving better heat insulation.

[0016] 4. This invention adjusts the temperature of the cooling water in the water-cooling pan, thereby appropriately changing the temperature gradient and solidification rate, reducing solidification stress and dendrite deflection, and causing the dendrites to grow vertically upward, resulting in castings with good orientation.

[0017] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. Attached Figure Description

[0018] Figure 1 The following is a schematic diagram of the structure of the wax mold module for controlling the orientation deviation of nickel-based single-crystal superalloy castings in Embodiment 1 of the present invention: (a) a three-dimensional schematic diagram, and (b) a two-dimensional schematic diagram. Figure 2 This is a schematic diagram of the three usage states of the positioning and locking mechanism in Embodiment 1 of the present invention; Figure 3 These are photographs of the chassis and right-angled groove of Embodiment 1 of the present invention; Figure 4 This is a photograph of the combined heat insulation sleeve of Embodiment 1 of the present invention; Figure 5 This is a photograph of the shell of Embodiment 1 of the present invention; Explanation of reference numerals in the attached figures: 1-Central column; 2-Insulation sleeve; 3-Base plate; 4-Positioning and locking mechanism; 5-Furnace body water cooling plate; 6-Positioning pin; 7-Right-angled groove. Detailed Implementation

[0019] Example 1 Figure 1 This is a schematic diagram of the wax mold module for controlling the orientation deviation of nickel-based single-crystal superalloy castings in this embodiment. (a) is a three-dimensional schematic diagram, and (b) is a two-dimensional schematic diagram. The wax mold module includes a central column 1, a heat insulation sleeve 2, a base 3, and a positioning and locking mechanism 4. The number of heat insulation sleeves 2 and the number of casting parts in each group can be adjusted according to the actual situation. Figure 2 This is a schematic diagram of three usage states of the positioning and locking mechanism 4 in this embodiment, from left to right: (a) the chassis 3 and the furnace water-cooling plate 5 are separated, and the positioning and locking mechanism 4 is not used; (b) the chassis 3 and the furnace water-cooling plate 5 are aligned, and the positioning and locking mechanism 4 is in a positioning state; (c) the chassis 3 and the furnace water-cooling plate 5 are locked together using the positioning and locking mechanism 4. The positioning and locking mechanism 4 includes a positioning pin 6 and a right-angled groove 7. The positioning pin 6 is fixed to the side of the furnace water-cooling plate 5 by bolts, and the right-angled groove 7 is located on the side of the chassis 3.

[0020] This embodiment describes a method for controlling orientation deviation in nickel-based single-crystal superalloy castings. The casting is made from DD98M master alloy, approximately 180mm high and 50mm wide. The method includes the following steps: S1. Wax Model Preparation First, wax molds are pressed according to the process parameters. F28 type part wax is used, with a melting point of approximately 70℃. After pressing, the molds are cooled for 30 minutes. The right-angled groove 7 of the positioning and locking mechanism 4 is located on the edge of the chassis 3 and is an integral structure with the chassis 3. During the pressing of the chassis 3, the right-angled groove 7 is pressed out as a whole along with the chassis 3. The chassis 3 has a diameter of 400mm, and a metal aluminum disc is pre-embedded in the chassis 3 to reduce the risk of breakage during the fabrication of large modules. Photos of the pressed chassis 3 and the right-angled groove 7 can be found below. Figure 3 .

[0021] After cooling, the wax molds are assembled. First, the gating system is assembled, then heat-insulating sleeves 2 are prepared using wax paper. These sleeves are fixed to the central column 1. The wax paper is 2mm thick and 50mm high, with a total of 3 sleeves. A 15mm gap is maintained between each sleeve. A photograph of the assembled heat-insulating sleeves can be seen below. Figure 4 Next, the castings are assembled, ensuring they are completely perpendicular to the base plate 3. Each group consists of 10 parts, resulting in a wax model assembly. The assembled models are then cleaned for 5 minutes to facilitate slurry application, and then air-dried for later use.

[0022] S2, Shell Preparation The wax model obtained from S1 is subjected to slurry coating, sanding, and drying to prepare the surface layer, transition layer, and back layer of the mold shell. Finally, it is sealed and dried to obtain the mold shell; the mold shell photograph is shown below. Figure 5 As shown.

[0023] Preparation of the first layer: The module is immersed in the surface layer slurry for coating. The composition of the surface layer slurry by mass ratio is corundum powder: silica sol: wetting agent: defoamer = 3.8:1.0:0.003:0.01. The viscosity of the surface layer slurry is 45s. Then, the coated module is placed in a sand-spraying machine for sanding. The sanding material is 100# corundum sand. The surface layer drying time is 4 hours, the drying temperature is 23±2℃, and the drying humidity is 70±10%RH.

[0024] Preparation of the second transition layer: The module after the preparation of the first layer is completed is immersed in the transition layer slurry for coating. The composition of the transition layer slurry by mass ratio is EC95 powder: silica sol: wetting agent: defoamer = 3.0:1.0:0.003:0.003. The viscosity of the transition layer slurry is 35s. Then, the coated module is placed in a sand-spraying machine for sanding. The sand-spraying material is 60# corundum sand. The drying time is 4 hours, the drying temperature is 23±2℃, and the drying humidity is 70±10%RH.

[0025] Preparation of the third back layer: The module after the preparation of the second transition layer is completed is immersed in the back layer slurry for coating. The composition of the back layer slurry is EC95 powder: silica sol: wetting agent: defoamer = 1.8:1.0:0.003:0.003 by mass ratio. The viscosity of the back layer slurry is 20s. Then, the coated module is placed in a sand spraying machine for sanding. The back layer sanding material is 24# corundum sand. The drying time is 6 hours, the drying temperature is 23±2℃, and the drying humidity is 50±10%RH.

[0026] The process of applying slurry, sprinkling sand, and drying the backing layer was repeated five times, resulting in a total of six backing layers. After the last backing layer was completely dry, a sealing treatment was performed, i.e., another layer of backing slurry was applied, but without sprinkling sand. Finally, the backing layer was dried for 48 hours. After drying, the backing layer was dewaxed and fired. The dewaxing temperature was 170℃, the dewaxing time was 15 minutes, and the dewaxing pressure was 8.2 bar. The firing temperature was 950℃, and the firing time was 2 hours. After firing, the backing layer was cooled to room temperature in the furnace to obtain the desired shell.

[0027] S3, Casting pouring The mold shell prepared by S2 is placed in a vacuum induction melting furnace for casting. For example... Figure 2As shown, the locating pin 6 is fixed to the side of the furnace water-cooling plate 5 by bolts, and the right-angled groove 7 is located on the side of the wax model shell base. During casting, the mold shell is first aligned with the locating pin 6, and then the mold shell is rotated to move the locating pin 6 within the right-angled groove 7, achieving mechanical locking. In reality, the locating pin 6 will not extend beyond the edge of the right-angled groove 7; the extension beyond the edge in the diagram is for better illustration and understanding. The positioning and locking mechanism 4 works in conjunction with the furnace water-cooling plate 5 to ensure that the mold shell is in the exact center of the vacuum melting furnace, keeping the gap between the heat insulation baffle and the mold shell consistent, thereby ensuring that the heat radiation from the hot and cold zones is evenly distributed around the mold shell, reducing orientation deviation. Five groups of castings were prepared, totaling 50 pieces, with a casting material weight of 9.5 kg. The refining temperature was 1580℃, and the casting temperature was 1550℃. The casting rate was 3 mm / min, and the initial cooling water temperature of the water-cooling pan was 20℃. This ensured a sufficiently large but not excessive temperature gradient at the solid-liquid interface, guaranteeing a good competitive growth and elimination process for the crystals while minimizing solidification stress and dendrite deflection. This resulted in stable, vertically growing crystals in the initial stage. When the crystal pulling position was 80 mm, the cooling water temperature was reduced to 10℃; when the crystal pulling position was 170 mm, the cooling water temperature was reduced to 1℃ until the crystal pulling was completed. This ensured that the entire casting maintained a relatively uniform and sufficiently large temperature gradient during the crystal pulling process, reducing the stress generated during solidification and thus reducing dendrite deflection. (Regarding the crystal pulling position in this embodiment: the crystal selector plus the transition section is about 80mm, the casting body height is 180mm, and half of the casting height is 90mm. Therefore, when the crystal pulling height is located at half the casting height, it is 80mm plus 90mm, which is 170mm. The other embodiments follow the same principle.)

[0028] S4, Heat Treatment After the S3 casting assembly is air-cooled for 5 hours, the casting is cleaned, cut, and then placed into a vacuum heat treatment furnace for heat treatment. The heat treatment process is as follows: 1300℃±10℃×4h / AC+1080℃±10℃×6h / AC+870℃±10℃×24h / AC.

[0029] After heat treatment, orientation samples were prepared. Excess portions of the casting were cut from the orientation samples, with a size of 3mm × 2mm. After grinding, polishing, and electrolytic treatment, EBSD analysis was performed on 50 orientation samples. The orientation deviation results were all less than 10°, and all met the technical requirements.

[0030] Comparative Example 1 The alloy casting is the same as in Example 1, except that the chassis in this comparative example does not have a positioning and locking mechanism, the heat insulation sleeve is not added to the module, and the cooling water temperature remains unchanged.

[0031] S1. Wax Model Preparation First, wax molds are pressed according to the process parameters. F28 type part wax is used, with a melting point of approximately 70℃. After pressing, the molds are cooled for 30 minutes. The chassis diameter is 400mm, and an aluminum disc is pre-embedded in the chassis to reduce the risk of breakage during the fabrication of large modules.

[0032] After cooling, the wax models are assembled, ensuring the castings are completely perpendicular to the base. Each group consists of 10 parts, resulting in a wax model assembly. The assembled assemblies are then cleaned for 5 minutes to facilitate the application of the slurry, and then allowed to air dry for later use.

[0033] S2, Shell Preparation The wax model obtained in S1 is coated with slurry, sanded and dried to prepare the surface layer, transition layer and back layer of the shell. Finally, the shell is sealed and dried to obtain the shell. Preparation of the first layer: The module is immersed in the surface layer slurry for coating. The composition of the surface layer slurry by mass ratio is corundum powder: silica sol: wetting agent: defoamer = 3.8:1.0:0.003:0.01. The viscosity of the surface layer slurry is 45s. Then, the coated module is placed in a sand-spraying machine for sanding. The sand-spraying material is 100# corundum sand. The surface layer drying time is 4 hours; the drying temperature is 23±2℃; and the drying humidity is 70±10%RH.

[0034] Preparation of the second transition layer: The module after the preparation of the first layer is completed is immersed in the transition layer slurry for coating. The composition of the transition layer slurry by mass ratio is EC95 powder: silica sol: wetting agent: defoamer = 3.0:1.0:0.003:0.003. The viscosity of the transition layer slurry is 35s. Then, the coated module is placed in a sand-spraying machine for sanding. The sand-spraying material is 60# corundum sand. The drying time is 4 hours; the drying temperature is 23±2℃; and the drying humidity is 70±10%RH.

[0035] Preparation of the third back layer: The module after the preparation of the second transition layer is completed is immersed in the back layer slurry for coating. The composition of the back layer slurry is EC95 powder: silica sol: wetting agent: defoamer = 1.8:1.0:0.003:0.003 by mass ratio. The viscosity of the back layer slurry is 20s. Then, the coated module is placed in a sand spraying machine for sanding. The back layer sanding material is 24# corundum sand. The drying time is 6 hours, the drying temperature is 23±2℃, and the drying humidity is 50±10%RH.

[0036] Repeat the above process of applying slurry, sprinkling sand, and drying the backing layer, applying a total of 6 layers. After the last layer of the backing layer is completely dry, a sealing treatment is performed, i.e., another layer of backing slurry is applied, but without sprinkling sand. Finally, the layer is dried for 48 hours. After drying, the layer is dewaxed and fired. The dewaxing temperature is 170℃, the dewaxing time is 15 minutes, and the dewaxing pressure is 8.2 bar. The firing temperature is 950℃, and the firing time is 2 hours. After firing, the layer is cooled to room temperature in the furnace to obtain the desired shell.

[0037] S3, Casting pouring The shells prepared by S2 were placed in a vacuum induction melting furnace for casting. Five sets of castings were made, totaling 50 pieces. The weight of the casting material was 9.5 kg. The refining temperature was 1580℃. The casting temperature was 1550℃. The pulling speed during casting was 3 mm / min. The cooling water temperature of the water-cooling plate was 20℃ until the crystal pulling was completed.

[0038] S4, Heat Treatment After the S3 casting assembly is air-cooled for 5 hours, the casting is cleaned, cut, and then placed into a vacuum heat treatment furnace for heat treatment. The heat treatment process is as follows: 1300℃±10℃×4h / AC+1080℃±10℃×6h / AC+870℃±10℃×24h / AC.

[0039] After heat treatment, orientation specimens were prepared. Excess portions of the casting were cut from the specimens, with dimensions of 3mm × 2mm. Following grinding, polishing, and electrolytic treatment, EBSD analysis was performed on 50 orientation specimens, of which 30 showed orientation deviations within... Between, 8 items smaller It meets the technical requirements, and the orientation deviation of 12 pieces is greater than [a certain value]. This does not meet the technical requirements.

[0040] Example 2 This embodiment describes a method for controlling orientation deviation in nickel-based single-crystal superalloy castings. The castings are made from DD5 master alloy, approximately 75mm high and 30mm wide, with two castings connected together for a total height of 160mm. The method includes the following steps: S1. Wax Model Preparation First, wax molds are pressed according to the process parameters. F28 type part wax is used, with a melting point of approximately 70℃. After pressing, the molds are cooled for 30 minutes. During chassis pressing, the positioning and locking mechanism is pressed out as a whole along with the chassis. The chassis diameter is 400mm, and a metal aluminum disc is pre-embedded in the chassis to reduce the risk of breakage during the fabrication of large modules.

[0041] After cooling, the wax models are assembled. First, the gating system is assembled, then heat-insulating sleeves are prepared using wax paper. These sleeves are fixed to the central column. The wax paper is 1.5mm thick and 45mm high, with a total of three sleeves, each with a 13mm gap between them. Next, the castings are assembled, ensuring they are completely perpendicular to the base. Each group consists of 40 parts, resulting in a wax model assembly. The assembled models are then cleaned for 5 minutes to facilitate slurry application, and then air-dried for later use.

[0042] S2, Shell Preparation The wax model obtained in S1 is coated with slurry, sanded and dried to prepare the surface layer, transition layer and back layer of the shell. Finally, the shell is sealed and dried to obtain the shell. Preparation of the first layer: The module is immersed in the surface layer slurry for coating. The composition of the surface layer slurry by mass ratio is corundum powder: silica sol: wetting agent: defoamer = 3.5:1.0:0.003:0.01. The viscosity of the surface layer slurry is 40s. Then, the coated module is placed in a sand-spraying machine for sanding. The sand-spraying material is 100# corundum sand. The surface layer drying time is 4 hours, the drying temperature is 23±2℃, and the drying humidity is 70±10%RH.

[0043] Preparation of the second transition layer: The module after the preparation of the first layer is completed is immersed in the transition layer slurry for coating. The composition of the transition layer slurry by mass ratio is EC95 powder: silica sol: wetting agent: defoamer = 2.5:1.0:0.003:0.003. The viscosity of the transition layer slurry is 30s. Then, the coated module is placed in a sand-spraying machine for sanding. The sand-spraying material is 60# corundum sand. The drying time is 4 hours, the drying temperature is 23±2℃, and the drying humidity is 70±10%RH.

[0044] Preparation of the third back layer: The module after the preparation of the second transition layer is completed is immersed in the back layer slurry for coating. The composition of the back layer slurry is EC95 powder: silica sol: wetting agent: defoamer = 1.5:1.0:0.003:0.003 by mass ratio. The viscosity of the back layer slurry is 15s. Then, the coated module is placed in a sand spraying machine for sanding. The back layer sanding material is 24# corundum sand. The drying time is 6 hours, the drying temperature is 23±2℃, and the drying humidity is 50±10%RH.

[0045] Repeat the above process of applying slurry, sprinkling sand, and drying the backing layer, applying a total of 4 layers. After the last layer of the backing layer is completely dry, a sealing treatment is performed, i.e., another layer of backing slurry is applied, but without sprinkling sand. Finally, the layer is dried for 48 hours. After drying, the layer is dewaxed and fired. The dewaxing temperature is 170℃, the dewaxing time is 15 minutes, and the dewaxing pressure is 8.2 bar. The firing temperature is 950℃, and the firing time is 2 hours. After firing, the layer is cooled to room temperature in the furnace to obtain the desired shell.

[0046] S3, Casting pouring The mold shell prepared by S2 is placed in a vacuum induction melting furnace for casting. The positioning and locking mechanism is designed to cooperate with the water cooling plate to ensure that the mold shell is in the center of the vacuum melting furnace, and to keep the gap between the heat insulation baffle and the mold shell consistent. This ensures that the heat radiation from the hot and cold zones is evenly distributed around the mold shell, reducing orientation deviation. Two groups of castings were completed, totaling 80 pieces, with a casting material weight of 9.0 kg. The refining temperature was 1550℃, and the casting temperature was 1520℃. The casting rate was 3 mm / min, and the initial cooling water temperature of the water-cooling pan was 25℃. This ensured a sufficiently large but not excessive temperature gradient at the solid-liquid interface, guaranteeing a good competitive growth and elimination process for the crystals while minimizing solidification stress and dendrite deflection. This resulted in stable, vertically growing crystals in the initial stage. When the crystal pulling position reached 80 mm, the cooling water temperature was reduced to 15℃; when the crystal pulling position reached 160 mm, the cooling water temperature was reduced to 5℃ until the crystal pulling was completed. This ensured that the entire casting maintained a relatively uniform and sufficiently large temperature gradient during the crystal pulling process, reducing the stress generated during solidification and thus reducing dendrite deflection.

[0047] S4, Heat Treatment After the S3 casting assembly is air-cooled for 5 hours, the casting is cleaned, cut, and then placed in a vacuum heat treatment furnace for heat treatment. The heat treatment process is as follows: 1300℃±10℃×3h / AC+1120℃±10℃×4h / AC+1080℃±10℃×4h / AC+900℃±10℃×4h / AC.

[0048] After heat treatment, orientation specimens were prepared. Excess portions of the casting were cut from the specimens, with dimensions of 3.5 mm × 2.5 mm. Following grinding, polishing, and electrolytic treatment, EBSD analysis was performed on 80 orientation specimens. 77 specimens met the technical requirements, while only 3 were larger than the specified values. The pass rate was 96%.

[0049] Example 3 This embodiment describes a method for controlling orientation deviation in nickel-based single-crystal superalloy castings. The casting is made from DD32 master alloy, approximately 220mm high and 28mm in diameter. The method includes the following steps: S1. Wax Model Preparation First, wax molds are pressed according to the process parameters. F28 type part wax is used, with a melting point of approximately 70℃. After pressing, the molds are cooled for 30 minutes. During chassis pressing, the positioning and locking mechanism is pressed out as a whole along with the chassis. The chassis diameter is 400mm, and a metal aluminum disc is pre-embedded in the chassis to reduce the risk of breakage during the fabrication of large modules.

[0050] After cooling, the wax models are assembled. First, the gating system is assembled, then heat-insulating sleeves are prepared using wax paper. These sleeves are fixed to the central column. The wax paper is 1.5mm thick and 45mm high, with a total of four sleeves, each with a 15mm gap between them. Next, the castings are assembled, ensuring they are completely perpendicular to the base. Each group consists of 12 parts, resulting in a wax model assembly. The assembled models are then cleaned for 5 minutes to facilitate slurry application, and then air-dried for later use.

[0051] S2, Shell Preparation The wax model obtained in S1 is coated with slurry, sanded and dried to prepare the surface layer, transition layer and back layer of the shell. Finally, the shell is sealed and dried to obtain the shell. Preparation of the first layer: The module is immersed in the surface layer slurry for coating. The composition of the surface layer slurry by mass ratio is corundum powder: silica sol: wetting agent: defoamer = 4.0: 1.0: 0.003: 0.01. The viscosity of the surface layer slurry is 45s. Then, the coated module is placed in a sand-spraying machine for sanding. The sand-spraying material is 100# corundum sand. The surface layer drying time is 4 hours, the drying temperature is 23±2℃, and the drying humidity is 70±10%RH.

[0052] Preparation of the second transition layer: The module after the preparation of the first layer is completed is immersed in the transition layer slurry for coating. The composition of the transition layer slurry by mass ratio is EC95 powder: silica sol: wetting agent: defoamer = 2.8:1.0:0.003:0.003. The viscosity of the transition layer slurry is 33s. Then, the coated module is placed in a sand-spraying machine for sanding. The sand-spraying material is 60# corundum sand. The drying time is 4 hours, the drying temperature is 23±2℃, and the drying humidity is 70±10%RH.

[0053] Preparation of the third back layer: The module after the preparation of the second transition layer is completed is immersed in the back layer slurry for coating. The composition of the back layer slurry is EC95 powder: silica sol: wetting agent: defoamer = 2.0:1.0:0.003:0.003 by mass ratio. The viscosity of the back layer slurry is 20s. Then, the coated module is placed in a sand spraying machine for sanding. The back layer sanding material is 24# corundum sand. The drying time is 6 hours, the drying temperature is 23±2℃, and the drying humidity is 50±10%RH.

[0054] Repeat the above process of applying backing slurry, sprinkling sand, and drying, applying a total of 5 backing layers. After the last backing layer is completely dry, a sealing treatment is performed, i.e., another layer of backing slurry is applied, but without sprinkling sand. Finally, the material is dried for 48 hours. After drying, dewaxing and firing are performed. The dewaxing temperature is 170℃, the dewaxing time is 15 minutes, and the dewaxing pressure is 8.2 bar. The firing temperature is 950℃, and the firing time is 2 hours. After firing, the material is cooled to room temperature in the furnace to obtain the desired shell.

[0055] S3, Casting pouring The mold shell prepared by S2 is placed in a vacuum induction melting furnace for casting. The positioning and locking mechanism is designed to cooperate with the water cooling plate to ensure that the mold shell is in the center of the vacuum melting furnace, and to keep the gap between the heat insulation baffle and the mold shell consistent. This ensures that the heat radiation from the hot and cold zones is evenly distributed around the mold shell, reducing orientation deviation. Five groups of castings were completed, totaling 60 pieces, with a casting material weight of 18.5 kg. The refining temperature was 1550℃, and the casting temperature was 1520℃. The casting rate was 3 mm / min, and the initial cooling water temperature of the water-cooling pan was 22℃. This ensured a sufficiently large but not excessive temperature gradient at the solid-liquid interface, guaranteeing a good competitive growth and elimination process for the crystals while minimizing solidification stress and dendrite deflection. This resulted in stable, vertically growing crystals in the initial stage. When the crystal pulling position reached 80 mm, the cooling water temperature was reduced to 12℃. When the crystal pulling position reached 190 mm, the cooling water temperature was reduced to 3℃ until the crystal pulling was completed. This ensured that the entire casting maintained a relatively uniform and sufficiently large temperature gradient during the crystal pulling process, reducing the stress generated during solidification and thus reducing dendrite deflection.

[0056] S4, Heat Treatment After the S3 castings were air-cooled for 5 hours, the castings were cleaned, cut, and then placed in a vacuum heat treatment furnace for heat treatment. The heat treatment process was as follows: 1290℃±10℃×4h / AC+1280℃±10℃×4h / AC+1150℃±10℃×4h / AC+870℃±10℃×24h / AC.

[0057] After heat treatment, orientation samples were prepared. Excess portions of the casting were cut from the samples, with dimensions of 2.5 mm × 1.5 mm. Following grinding, polishing, and electrolytic treatment, EBSD analysis was performed on 60 orientation samples. The orientation results for 59 samples met the technical requirements, with only one sample exceeding the acceptable range. The pass rate was 98%.

[0058] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. A method for controlling orientation deviation in nickel-based single-crystal superalloy castings, characterized in that, Includes the following steps: S1. Wax mold preparation: The pressing wax mold includes a base, a central column, a gating system, and a positioning and locking mechanism. A metal aluminum disc is pre-embedded in the base to ensure that the base is flat. The positioning and locking mechanism is located on the edge of the base and is an integral structure with the base, and is pressed out together with the base during pressing. The central column is connected to the center of the base. After the wax model has completely cooled, it is assembled. A circular heat insulation sleeve is prepared using wax paper according to the size of the casting, and the heat insulation sleeve is assembled onto the central column to obtain the wax model module. S2. Shell preparation: The wax model obtained from S1 is subjected to multiple processes of slurry application, sanding, and drying to prepare the surface layer, transition layer, and back layer of the shell. Finally, the shell is sealed and dried to obtain the shell. S3. Casting: The shell obtained in S2 is placed in a vacuum melting furnace for casting. The positioning and locking mechanism on the chassis is installed on the water cooling plate of the vacuum melting furnace and works with the water cooling plate to ensure that the shell is in the center of the vacuum melting furnace. During the casting process, the temperature of the cooling water is controlled. The initial temperature of the cooling water in the water cooling plate is 20℃~25℃. When the crystal pulling height exceeds the crystal pulling transition section and the crystal stabilizes, the temperature of the cooling water is reduced to 10℃~15℃. When the crystal pulling height is half the height of the casting, the temperature of the cooling water is reduced to 0℃~5℃. S4. Heat treatment: Clean the shell of the casting after S3 casting is completed, and then perform heat treatment. After completion, take orientation samples from the excess parts of the casting and perform orientation analysis using EBSD. The positioning and locking mechanism (4) includes a positioning pin (6) and a right-angled groove (7). The positioning pin (6) is fixed to the side of the furnace water cooling plate (5) by bolts, and the right-angled groove (7) is located on the side of the base plate (3). When casting, the mold shell is first aligned with the positioning pin (6) and then the positioning pin (6) is moved in the right-angled groove (7) by rotating the mold shell to achieve mechanical locking.

2. The method according to claim 1, characterized in that, The thickness of the waxed paper described in S1 is 1.5mm to 2mm.

3. The method according to claim 1, characterized in that, The total number of heat insulation sleeves mentioned in S1 is adjusted according to the height of the casting, and the total height of the heat insulation sleeves is equivalent to the height of the casting; the height of a single heat insulation sleeve is 40mm~50mm.

4. The method according to claim 3, characterized in that, If there are at least two heat insulation sleeves, a gap of 10mm to 15mm should be maintained between two adjacent heat insulation sleeves.

5. The method according to claim 1, characterized in that, When applying slurry in S2, the composition of the surface slurry by mass ratio is: corundum powder: silica sol: wetting agent: defoamer = (3.5~4.0):1.0:0.003:0.01, the viscosity of the surface slurry is 40s~45s, and the sanding material for the surface layer is 100# corundum sand. The composition of the transition layer slurry by mass ratio is: EC95 powder: silica sol: wetting agent: defoamer = (2.5~3.0):1.0:0.003:0.003; the viscosity of the transition layer slurry is 30s~35s, and the sand spreading material of the transition layer is 60# corundum sand; The composition of the backing slurry by mass ratio is: EC95 powder: silica sol: wetting agent: defoamer = (1.5~2.0):1.0:0.003:0.

003. The viscosity of the backing slurry is 15s~20s. The backing sand material is 24# corundum sand.

6. The method according to claim 1, characterized in that, Depending on the size of the wax model module, the total number of shell layers in S2 ranges from 6 to 8.

7. The method according to claim 1, characterized in that, The size of the test surface for cutting the orientation sample as described in S4 is (3±0.5mm)×(2±0.5mm).

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