A gravity-aided directional solidification apparatus and method

Abstract

This invention discloses a gravity-directed solidification device and method, belonging to the field of metal casting technology. The gravity-directed solidification device includes a cold chamber, a hot chamber, and a mold shell; the hot chamber is located below the cold chamber; the mold shell has a pouring port communicating with the bottom of the mold shell; the cold chamber is equipped with a pulling mechanism, a water-cooled copper plate, a vacuum component, an air-cooling component, and a water-cooled copper ring; the water-cooled copper plate, vacuum component, air-cooling component, and water-cooled copper ring are arranged sequentially from top to bottom; the upper surface of the water-cooled copper plate is connected to the pulling mechanism, the lower surface is connected to the top of the mold shell, and the pouring port passes through the water-cooled copper plate; in use, the mold shell passes through the vacuum component, air-cooling component, and water-cooled copper ring, and moves vertically between the cold chamber and the hot chamber under the action of the pulling mechanism. This invention breaks through the global homogenization heat dissipation mode of a single water-cooled copper plate by using a combined water-cooling and air-cooling cooling method, realizing targeted enhanced heat dissipation at the solid-liquid interface front and maintaining the stability of the longitudinal temperature gradient during solidification.

Description

Technical Field

[0001] This invention belongs to the field of metal casting technology and relates to a gravity-directed solidification device and method. Background Technology

[0002] Directional solidification is a precision casting process that controls the sequential solidification of alloys along the opposite heat flow direction by establishing a unidirectional temperature gradient. Its core advantage lies in eliminating transverse grain boundaries to obtain excellent longitudinal mechanical properties. Early research found that cracks preferentially initiate at longitudinal grain boundaries in directional solidification structures, leading to the development of single-crystal directional solidification technology. By completely eliminating grain boundaries, it significantly improves the high-temperature performance of high-temperature alloy castings and their high-temperature service capabilities. The current mainstream directional solidification technology in industry is Bridgman directional solidification, which uses a bottom-up anti-gravity solidification method. However, it has two fundamental drawbacks: First, the upward growth of dendrites causes a denser, pasty melt zone to lie above a less dense melt zone, triggering density reversal and heat convection, which can induce freckle defects. Second, the traditional annular module design causes severe transverse bending of the isotherm at the solid-liquid interface, resulting in heat transfer lag in the casting edge region. This manifests as a decrease in temperature gradient, widening of the pasty zone, and increased undercooling, significantly increasing the probability of impurity crystals and freckle defects. To address these bottlenecks, the novel gravity-directed solidification technology alters the dendrite growth direction, allowing the high-density melt to sink naturally and eliminating density inversion at its source. Simultaneously, the innovative design of parallel configuration of single-row modules and flat-plate heaters / coolers enables symmetrical heat exchange on both sides of the casting, effectively eliminating the "hysteresis effect."

[0003] At the microstructure control level, primary dendrite arm spacing (PDAS) refers to the vertical distance between the dendrite trunks of two adjacent dendrites. As a core indicator, it directly affects the microsegregation, secondary phase distribution, and carbide morphology of the alloy. A smaller primary dendrite arm spacing indicates a finer microstructure. Reducing the primary dendrite arm spacing can optimize the as-cast microstructure, effectively reduce the size of the eutectic and γ' phases in the as-cast alloy, and optimize the carbide morphology, thereby improving the alloy's creep retardation properties. Studies have shown that during directional solidification, the primary dendrite arm spacing of the directionally solidified dendritic 5 (DD5) single-crystal superalloy gradually increases with increasing solidification distance, and the rate of increase in primary dendrite arm spacing in the later stages of solidification is significantly greater than that in the early stages. It was found that the primary dendrite arm spacing for different solidification distances ranges from 100 to 600 μm and all exhibit a normal distribution. The distribution probability of primary dendrite spacing is very similar in the early and middle stages of solidification, and the average primary dendrite spacing is also similar. In the later stages of solidification, the distribution probability shifts to the right, and the average primary dendrite spacing increases. This spacing increase stems from the change in heat dissipation mechanism during solidification: in the initial stage of solidification, the heat dissipation of the casting is mainly due to heat exchange between the melt and the water-cooled plate. As the solidification distance increases, the heat dissipation efficiency of the water-cooled plate gradually decreases, which leads to a reduction in the temperature gradient at the solid-liquid interface front, a significant increase in primary dendrite spacing, and a decrease in the performance of the casting.

[0004] like Figure 1 As shown, current directional solidification technology basically uses water-cooled copper rings and water-cooled copper disks for crystallization. This can improve overall heat dissipation from the perspective of enhanced cooling. However, enhanced cooling will lead to the homogenization of the temperature field, which will reduce the local temperature gradient and cause a significant increase in the primary dendrite spacing in the later stage of solidification, which seriously affects the quality of the alloy. Summary of the Invention

[0005] To address the problems existing in the prior art, the present invention provides a gravity-directed solidification apparatus and method, thereby solving the technical problem that the existing gravity-directed solidification technology relies too much on enhanced cooling, which leads to temperature field homogenization, resulting in a significant reduction in the local temperature gradient in the later stage of solidification, causing coarsening of the primary dendrite spacing, and thus deteriorating the microstructure and mechanical properties of the alloy.

[0006] This invention is achieved through the following technical solution:

[0007] A gravity-directed solidification device includes a cold chamber, a hot chamber, and a mold shell; the hot chamber is located below the cold chamber; the mold shell is provided with a pouring gate, and the bottom of the mold shell is connected to the bottom of the pouring gate;

[0008] The cold chamber is equipped with a pull-out mechanism, a water-cooled copper plate, an air extraction assembly, an air-cooling assembly, and a water-cooled copper ring;

[0009] The water-cooled copper plate, the air extraction assembly, the air-cooling assembly, and the water-cooled copper ring are arranged sequentially from top to bottom;

[0010] The upper surface of the water-cooled copper plate is connected to the pulling mechanism, the lower surface is connected to the top of the mold shell, and the pouring gate passes through the water-cooled copper plate.

[0011] In use, the mold shell passes through the air extraction assembly, the air cooling assembly, and the water-cooled copper ring, and moves vertically between the cold chamber and the hot chamber under the pulling action of the pulling mechanism.

[0012] Preferably, the air-cooling assembly includes an air-cooling ring connected to a cooling air source. The air-cooling ring has a rectangular structure and is provided with a plurality of nozzles.

[0013] Preferably, a plurality of the nozzles are located on the inner wall of the air-cooling ring.

[0014] Preferably, the nozzle is trumpet-shaped, and the opening angle of the nozzle is 110°~130°.

[0015] Preferably, the nozzle opening is tilted upwards.

[0016] Preferably, when the mold shell passes through the air-cooling ring, the distance between the nozzle and the mold shell is 15~25 mm.

[0017] Preferably, the air-cooling assembly further includes a main air pipe, and a first branch pipe and a second branch pipe connected to the main air pipe; the free end of the main air pipe is connected to a cooling air source, and the free ends of the first branch pipe and the second branch pipe are respectively connected to the two long sides of the air-cooling ring.

[0018] Preferably, the air extraction assembly includes an air extraction ring and an air extraction power assembly;

[0019] The suction ring is provided with a suction wall, and the suction wall is provided with several through holes.

[0020] Preferably, the suction ring is also provided with a baffle.

[0021] A gravity-directed solidification method, employing the aforementioned gravity-directed solidification apparatus, includes the following steps:

[0022] The mold shell is placed in the hot chamber for preheating. The melt is poured into the mold shell and left to stand. The mold shell is then pulled upward using the pulling mechanism. At the same time, the water-cooled copper plate and water-cooled copper ring are turned on so that the melt in the mold shell is cooled by the action of the water-cooled copper plate and water-cooled copper ring.

[0023] When the mold shell is just pulled into the cold chamber, the suction component and the air cooling component are turned on to continue cooling the melt in the mold shell. After the mold shell is completely pulled into the cold chamber, the suction component and the air cooling component are turned off, and the melt inside the mold shell is completely cooled into solidified material.

[0024] After the heating chamber cools down, the mold containing the solidified material is removed and the mold is taken off, thus completing the gravity-directed solidification.

[0025] Compared with the prior art, the present invention has the following beneficial technical effects:

[0026] This invention provides a gravity-directed solidification apparatus. This apparatus utilizes a gas cooling device and an extraction device mounted on the upper part of a water-cooled copper ring to purge the solidified area with cooling gas, reducing the diffusion of cooled gas after heat exchange into the hot zone, increasing the temperature gradient, and accelerating the cooling rate. This effectively reduces the primary dendrite spacing of single-crystal castings, improving their quality and performance. This invention effectively solves the problems of temperature gradient decay and dendrite coarsening caused by intensified cooling in traditional gravity-directed solidification technology through the following multi-dimensional synergistic mechanisms: First, a water-cooled copper plate and a water-cooled copper ring are set up in the cold chamber to form a basic forced cooling layer. Second, the nozzles of the air-cooling component enable localized dynamic gas convection cooling of the area near the solidification interface. This combined water-cooling and air-cooling cooling method breaks through the global homogenization heat dissipation mode of a single water-cooled copper plate. Directional purging with air cooling achieves targeted enhanced heat dissipation at the solid-liquid interface front, maintaining the stability of the longitudinal temperature gradient during solidification. The forced convection generated by the cooling gas purging significantly improves... The solute diffusion coefficient near the solidification interface, combined with the enhanced temperature gradient, optimizes the critical stability parameter for dendrite growth control to the dendrite refinement range. Rapid gas cooling shortens the duration of the reglow effect of the interdendritic melt, suppresses the coarsening growth of the eutectic phase, and simultaneously reduces the dendrite segregation index. In this device, the gas extraction component and the gas cooling component form a gas circulation system. Through active extraction, the gas that has completed heat exchange is rapidly discharged, blocking the backflow of heat from the cooling medium to the hot chamber. This design creates a clear thermal isolation boundary between the hot zone where the mold shell is located and the cold chamber, raising the temperature gradient and effectively suppressing the gradient decay caused by the decrease in heat dissipation efficiency in the later stages of solidification. This technical solution, through physical field coupling design, transforms the contradictory "overall heat dissipation requirements" and "local gradient maintenance" in traditional processes into a synergistic relationship, providing a new thermodynamic boundary condition control paradigm for the directional solidification of high-temperature alloys.

[0027] Furthermore, the air-cooling ring has a rectangular structure, which is consistent with the structure of the water-cooled copper ring and also matches the structure of the mold shell. Several nozzles are located on the inner wall of the air-cooling ring and are mirror-symmetrically arranged on the long side of the air-cooling ring. This arrangement, in conjunction with the structure of the mold shell, ensures that the cooling gas is evenly covered along both sides of the mold shell, eliminating local temperature gradient fluctuations. Moreover, the symmetrical airflow design can counteract the bending of the solid-liquid interface caused by unilateral cooling, maintain the horizontality of the solid-liquid interface, and avoid impurities and freckle defects.

[0028] Furthermore, the nozzle is trumpet-shaped, which can form a fan-shaped airflow to avoid local "cold spots" or "hot spots". The opening angle of the nozzle is 110°~130°, which balances the airflow diffusion and concentration, and prevents high-speed airflow from directly impacting the mold shell and causing surface defects of the casting.

[0029] Furthermore, when the mold shell passes through the air-cooling ring, the distance between the nozzle and the mold shell is 15~25mm. This distance ensures that the gas diffuses fully before reaching the mold shell, forming a stable convection layer and enhancing heat exchange efficiency. At the same time, it reserves space to prevent the nozzle from colliding with the mold shell during the pulling process, ensuring equipment safety.

[0030] Furthermore, the air-cooling assembly also includes a main air pipe, and a first branch pipe and a second branch pipe connected to the main air pipe; the free end of the main air pipe is connected to a cooling air source, and the free ends of the first branch pipe and the second branch pipe are respectively connected to the two long sides of the air-cooling ring, effectively forming a stable airflow at the nozzle.

[0031] Furthermore, the extraction assembly includes an extraction ring and an extraction power assembly; the extraction ring is provided with an extraction wall, and the extraction wall is provided with several through holes, which are evenly distributed to quickly extract the hot gas after heat exchange, prevent heat from flowing back to the hot chamber, form a "gas cooling-extraction" closed-loop system, strengthen the thermal isolation between the cold chamber and the hot chamber, and stabilize the axial temperature gradient.

[0032] Furthermore, the suction ring is also equipped with a baffle to prevent gas from diffusing into the hot zone, ensuring suction efficiency, reducing thermal pollution, and preventing high-speed suction from interfering with the solidification process of the mold shell surface.

[0033] In addition, this invention also discloses a gravity-directed solidification method, employing the aforementioned gravity-directed solidification apparatus, and comprising the following steps: preheating the mold shell in a hot chamber; pouring the melt into the mold shell; allowing it to stand; pulling the mold shell upwards while simultaneously activating the water-cooled copper plate and water-cooled copper ring, allowing the melt in the mold shell to cool under the action of the water-cooled copper plate and water-cooled copper ring; when the mold shell enters the cold chamber, activating the evacuation assembly and air-cooling assembly to continue cooling the melt in the mold shell; after the mold shell is completely pulled into the cold chamber, closing the evacuation assembly and air-cooling assembly, and cooling the melt inside the mold shell. Complete cooling results in solidified solidified material; after the hot chamber cools, the mold containing the solidified material is removed and the mold is taken out, completing the gravity-driven directional solidification. During this process, water-cooled copper discs and water-cooled copper rings provide basic cooling and initiate directional solidification. When the mold enters the cold chamber, air cooling and evacuation are activated to enhance heat dissipation at the solid-liquid interface. Once the mold is fully inside the cold chamber, air cooling / evacuation is turned off to avoid stress cracks caused by overcooling. This method, through timing control, transforms the "overall heat dissipation requirement" and "local gradient maintenance" into a synergistic relationship, effectively solving the dendrite coarsening caused by temperature field homogenization in traditional processes. Attached Figure Description

[0034] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 This is a schematic diagram of a gravity-directed solidification device in the prior art.

[0036] Figure 2 This is an assembly diagram of the pull-out mechanism, the water-cooled copper plate, and the mold shell;

[0037] Figure 3 This is a schematic diagram of a gravity-directed solidification device according to the present invention;

[0038] Figure 4 This is a schematic diagram of the combined structure of the air extraction component and the air cooling component in this invention;

[0039] Figure 5 This is a schematic diagram of the air-cooling component in this invention;

[0040] Figure 6 This is a schematic diagram of the assembly of the air-cooling component and the mold shell in this invention;

[0041] Figure 7 For the present invention Figure 6 A magnified view of a portion of point a.

[0042] Figure 8 This is a schematic diagram of the air extraction component in this invention;

[0043] Figure 9 Microstructure of a cross-section of a single crystal specimen after directional solidification using a gravity-fed directional solidification device in the prior art;

[0044] Figure 10 This is a cross-sectional microstructure of a single crystal specimen after directional solidification using the gravity-directed solidification device of this invention.

[0045] Figure 11 The solidification structure results of the castings obtained in Examples 4 and 5 and the comparative example of the present invention are shown, wherein (a) is the casting without argon gas, i.e., the comparative example casting, (b) is the casting obtained in Example 4 with argon gas at a pressure of 0.05 MPa, (c) is the casting obtained in Example 5 with argon gas at a pressure of 0.1 MPa, and (d) is the spacing between the primary dendrite arms.

[0046] Figure 12 The eutectic structure distribution results of the castings obtained in Examples 4 and 5 and the comparative example of the present invention are shown. (a) is the casting without argon gas, i.e., the comparative example casting; (b) is the casting obtained in Example 4 with argon gas at a pressure of 0.05 MPa; (c) is the casting obtained in Example 5 with argon gas at a pressure of 0.1 MPa; and (d) is the eutectic content.

[0047] Figure 13 The micro-shrinkage results of the castings obtained in Examples 4 and 5 and the comparative example of the present invention are shown. (a) is the casting without argon gas, i.e., the comparative example casting; (b) is the casting obtained in Example 4 with argon gas at a pressure of 0.05 MPa; and (c) is the casting obtained in Example 5 with argon gas at a pressure of 0.1 MPa.

[0048] The components are as follows: 1. Cold chamber; 2. Water-cooled copper plate; 3. Air-cooled assembly; 301. Air-cooled ring; 302. Nozzle; 303. Gas channel plug; 304. Main gas pipe; 305. Cooling gas source; 306. First branch pipe; 307. Second branch pipe; 4. Air extraction assembly; 401. Through hole; 402. Baffle; 403. Second gas pipe; 404. Flange; 405. Air extraction power assembly; 406. Air extraction ring; 407. Suction wall; 5. Water-cooled copper ring; 6. Heat insulation baffle; 7. Mold shell; 8. Hot chamber; 9. Casting; 10. Pour gate; 11. Crucible; 12. Heating assembly; 13. Pull-out mechanism; 14. Drive mechanism. Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0050] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0051] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0052] In the description of the embodiments of the present invention, it should be noted that if terms such as "upper," "lower," "horizontal," or "inner" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of the invention is in use, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. Furthermore, terms such as "first" and "second" are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0053] Furthermore, the use of the term "horizontal" does not imply that the component must be absolutely horizontal, but rather that it can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0054] In the description of the embodiments of the present invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in the present invention according to the specific circumstances.

[0055] The present invention will now be described in further detail with reference to the accompanying drawings:

[0056] Example 1

[0057] like Figures 1-2 As shown, most current directional solidification technologies employ water-cooled copper rings and water-cooled copper discs for crystallization. This directional solidification device pours the melt into the mold shell 7 through a crucible 11 and a pouring port 10. A heating element 12 is installed in the hot chamber 8 to control its temperature. Under the action of a pulling mechanism 13, the mold shell 7 is pulled into the cold chamber 1. During the pulling process, the melt is solidified using a water-cooled copper disc 2 and a water-cooled copper ring 5. After solidification, a casting 9, such as a blade, is obtained. This technology only improves overall heat dissipation from the perspective of enhanced cooling. However, enhanced cooling leads to a homogenization of the temperature field, which reduces the local temperature gradient and causes a significant increase in the primary dendrite spacing in the later stages of solidification, severely affecting the alloy quality.

[0058] To overcome the above problems, such as Figures 3-4 As shown, this invention discloses a gravity-directed solidification device, including a cold chamber 1, a hot chamber 8, and a mold shell 7; the hot chamber 8 is located below the cold chamber 1; the mold shell 7 is provided with a pouring gate 10, and the bottom of the mold shell 7 is connected to the bottom of the pouring gate 10; the cold chamber 1 is provided with a pulling mechanism 13, a water-cooled copper plate 2, an air extraction component 4, an air cooling component 3, and a water-cooled copper ring 5; the water-cooled copper plate 2, the air extraction component 4, the air cooling component 3, and the water-cooled copper ring 5 are arranged sequentially from top to bottom; the upper surface of the water-cooled copper plate 2 is connected to the pulling mechanism 13, and the lower surface is connected to the mold shell 7; the lower surface is connected to the top of the mold shell 7, and the pouring gate 10 passes through the water-cooled copper plate 2; in use, the mold shell 7 passes through the air extraction component 4, the air cooling component 3, and the water-cooled copper ring 5, and moves vertically between the cold chamber 1 and the hot chamber 8 under the pulling action of the pulling mechanism 13.

[0059] Preferably, the upper surface of the water-cooled copper plate 2 is bolted to the pulling mechanism 13, and the lower surface is bolted to the mold shell 7; the air extraction assembly 4, the air cooling assembly 3, and the water-cooled copper ring 5 can also be bolted together. Preferably, the mold shell 7 and the pouring gate 10 can be integrally formed.

[0060] like Figure 5 As shown, the air-cooling assembly 3 includes an air-cooling ring 301, which is connected to a cooling air source 305. The air-cooling ring 301 has a rectangular structure and is provided with a plurality of nozzles 302. Preferably, the cooling air can be gas loaded in a gas cylinder to form the cooling air source 305.

[0061] In a preferred embodiment, a plurality of the nozzles 302 are located on the inner wall of the air-cooling ring 301 and are arranged in a mirror-symmetrical manner on the long side of the air-cooling ring 301.

[0062] The nozzle 302 is trumpet-shaped, i.e., a fan-shaped nozzle, and the opening angle of the nozzle 302 is 110°~130°, i.e., its spray angle is 110°~130°. Several nozzles 302 are evenly distributed along both sides of the mold shell 7, and the opening of the nozzle 302 is inclined upward, i.e., inclined towards the top of the cold chamber 1, and the inclination angle can be adjusted according to the usage requirements.

[0063] like Figures 6-7 As shown, in a preferred embodiment, when the mold shell 7 passes through the air-cooling ring 301, the distance between the nozzle 302 and the mold shell 7 is 15~25 mm, that is... Figure 7 The diameter of the nozzle is 15~25 mm. A certain distance needs to be left between the nozzle 302 and the mold shell 7 to allow the gas to diffuse, and to prevent the gas flow from being too large or the mold shell from hitting the nozzle during the lifting and lowering process.

[0064] In addition, such as Figure 5 As shown, the air-cooling assembly 3 also includes a main air pipe 304, and a first branch pipe 306 and a second branch pipe 307 connected to the main air pipe 304. The free end of the main air pipe 304 is connected to the cooling air source 305, and the free ends of the first branch pipe 306 and the second branch pipe 307 are respectively connected to the two long sides of the air-cooling ring 301 to realize the delivery of cooling gas in the air-cooling ring 301.

[0065] The main gas pipe 304 is equipped with a flow regulating valve and a flow meter. The flow regulating valve is used to regulate the flow rate of gas entering the square pipe, thereby controlling the pressure of the injected gas. The cooling gas can be high-purity argon, with a gas flow rate of 200~400 L / min; the gas cooling device is made of stainless steel.

[0066] The gas in the cooling gas source 305 is an inert gas, preferably argon. The inert argon gas is sprayed onto the mold shell 7 through the nozzle 302 to cool the mold shell 7 and the alloy inside the mold shell 7.

[0067] The air-cooling ring 301 is also provided with a gas channel plug 303 to prevent air leakage and reduce the gas pressure inside the ring.

[0068] like Figure 8 As shown, the air extraction component 4 includes an air extraction ring 406 and an air extraction power component 405; the air extraction ring 406 is provided with an air suction wall 407, and the air suction wall 407 is provided with a plurality of through holes 401.

[0069] The suction ring 406 is also provided with a baffle 402, which can reduce gas diffusion and allow gas to flow into the suction wall better.

[0070] In addition, the vacuum power assembly 405 and the vacuum ring 406 are connected by a second air pipe 403 and a flange 404.

[0071] like Figure 2 As shown, a heat insulation baffle 6 is provided between the cold chamber 1 and the hot chamber 8. The water-cooled copper plate 2, the air extraction assembly 4, the air-cooling assembly 3, and the water-cooled copper ring 5 are placed sequentially on the heat insulation baffle 6. In addition, the pull-out mechanism 13 also includes a drive mechanism 14, which is located at the top of the cold chamber 1.

[0072] In addition, the mold shell 7 of the present invention is provided with a pouring port 10 for injecting the melt into the mold shell 7.

[0073] Example 2

[0074] In addition, the present invention also discloses a gravity-directed solidification method, which uses the gravity-directed solidification apparatus of the present invention and includes the following steps:

[0075] The mold shell 7 is placed in the hot chamber 8 for preheating. The melt is poured into the mold shell 7 through the pouring port 10. After standing, the mold shell 7 is pulled upward by the pulling mechanism 13. The water-cooled copper plate 2 and the water-cooled copper ring 5 are turned on so that the melt in the mold shell 7 is cooled by the action of the water-cooled copper plate 2 and the water-cooled copper ring 5.

[0076] When the mold shell 7 is just pulled into the cold chamber 1, the pulling distance is about 30~50 mm. The vacuum component 4 and the air cooling component 3 are turned on to continue cooling the melt in the mold shell 7. When the mold shell 7 is completely pulled into the cold chamber 1, the pulling height is about 250~270 mm. The vacuum component 4 and the air cooling component 3 are turned off, and the melt inside the mold shell 7 is completely cooled into solidified solid, i.e., the casting. The above pulling process is realized by the pulling mechanism 13, which also includes a drive mechanism 14 located at the top of the cold chamber 1.

[0077] After the heating chamber 8 cools down, the mold shell 7 containing the solidified material is removed and the mold shell 7 is taken off, thus completing the gravity-directed solidification.

[0078] Example 3

[0079] To further illustrate the gravity-directed solidification method of the present invention, this embodiment is provided:

[0080] A gravity-directed solidification method includes the following steps:

[0081] 1. Preparation and assembly of wax models: The sample and spiral crystal selector are pressed using a pneumatic wax press, and the wax models are assembled according to the designed gating system and module layout.

[0082] In step 1, the raw material for preparing the wax model is polystyrene medium-temperature wax, with a nozzle temperature of 60~65℃, cavity pressure of 0.4~0.6 MPa, and melting temperature of 68~73℃. A release agent is sprayed inside the mold, and after waxing using a pneumatic wax press, the mold is opened after cooling for 4~6 seconds and cooled with cold water. After drying, the surface of the wax model is trimmed, and then the wax model is assembled according to the module arrangement.

[0083] 2. After assembling the mold, use an acetone emulsion diluent to clean the surface of the wax mold components to remove residual silicone oil, wax residue, and dust. After drying, prepare the mold shell.

[0084] 3. Preparation of the mold shell: After processes such as slurry application, sand coating, drying, dewaxing, and firing, the average thickness of the final mold shell is 5~6 mm;

[0085] During the slurry application process, the mold is slowly immersed into the slurry at a 30-35° angle, rotated slowly, and then removed. The slurry is then rotated slowly to ensure that it is evenly distributed on the surface of the wax mold and to remove any surface air bubbles.

[0086] The slurry uses alkaline silica sol as a binder. The first layer of sand coating material is corundum sand with a particle size of 80 mesh; the second and third layers of sand coating material are corundum sand with a particle size of 46 mesh; and the fourth, fifth and sixth layers of sand coating material are corundum sand with a particle size of 24 mesh.

[0087] 4. Place the mold shell obtained in step 3 into the gravity-directed solidification device of the present invention to preheat the mold shell, and then pour the alloy under vacuum conditions. After the melt is poured into the mold shell, it is allowed to stand, and then the mold shell is pulled upward and cooled under the action of the crystallizer.

[0088] The directional solidification furnace hot zone mold shell heater, namely the hot chamber 8 in this invention, is designed with a square structure and adopts a dual-zone temperature control system. The heating element material is CFC (carbon-carbon fiber material), the insulation material is integral graphite hard felt, and the heat insulation baffle material is adhesive graphite felt with a thickness of 5~10 mm.

[0089] The crystallizer assembly consists of a water-cooled copper disc and a water-cooled copper ring, both designed in a rectangular shape to match the square heater structure. The water-cooled copper disc has a double-vortex water channel inside, and a large flow rate and high pressure of cooling water are applied to ensure the cooling effect of the water-cooled copper disc on the casting. The inner surface of the water-cooled ring is first sandblasted and then coated with a high-temperature black paint to enhance the radiative heat transfer effect.

[0090] The preheating temperature is 1500~1530℃, and the mold is allowed to stand for 5~10 minutes after pouring. The square heater and the instant heating chamber are 1500~1530℃, the pouring temperature is 1530~1550℃, and the mold shell pulling speed is 3~6 mm / min.

[0091] 5. After the mold shell is pulled out 110~140 mm, turn on the gas cooling function. The cooling gas can be high-purity argon. Use this cooling gas to cool the upper part of the mold shell. The pressure of the cooling gas is 0.04~0.06 MPa. At the same time, turn on the evacuation function to extract the gas after heat exchange, thereby reducing the gas flow to the hot zone. After the mold shell is pulled out 250~270 mm, turn off the gas cooling and evacuation functions.

[0092] 6. After the drawing process is completed, wait for the furnace temperature to cool to below 100℃, open the furnace and remove the mold shell. Then, remove the mold shell that is easy to peel off from the surface of the casting by the shell vibration method. After that, cut off non-critical parts such as risers and sprues, and perform further sandblasting on the mold shell that is still left on the surface of the casting.

[0093] In this step, the sand used for sandblasting is 60-80 mesh, the sandblasting pressure is 3.5-4.5 bar, and the sandblasting time is determined by the surface quality of the sample. Sandblasting continues until the sample surface is free of ceramic oxide scale and has a bright and uniform appearance.

[0094] This invention utilizes a gas cooling device and a vacuum device installed on the upper part of the water-cooling ring to purge the solidified area with argon gas, reducing the diffusion of argon gas after heat exchange into the hot zone, increasing the temperature gradient, and accelerating the cooling rate. This effectively reduces the primary dendrite spacing of single-crystal castings, thereby improving their quality and performance. The gas pressure, flow rate, and blowing direction can be adjusted according to actual needs. This invention can achieve a finer crystal structure, optimize the as-cast microstructure of the alloy, and thus improve the alloy's creep resistance.

[0095] Example 4

[0096] To further explain the solution of the present invention, this embodiment will be used as an example:

[0097] CMSX-4 alloy was selected as the experimental material, and a single crystal specimen was cast. Its chemical composition by weight percentage was: Cr: 6.4%, Co: 9.6%, W: 6.4%, Mo: 0.61%, Ta: 6.6%, Al: 5.67%, Ti: 1.04%, Hf: 0.1%, Re: 2.9%, Ni - balance.

[0098] The mold shell is placed in the gravity-directed solidification apparatus of this invention for preheating. Then, the alloy is poured under vacuum. After the melt is poured into the mold shell, it is allowed to stand. The mold shell is then pulled upwards and cooled by the crystallizer. The preheating temperature is 1500℃, and the settling time after pouring is 5-10 minutes. The square heater temperature is 1530℃, the pouring temperature is 1550℃, and the pulling rate of the mold shell is 3 mm / min. In this embodiment, the cooling gas pressure is 0.05 MPa.

[0099] Observation of the microstructure of the cross-section of the single-crystal blade reveals that, after process optimization using the method of this invention, the primary dendrite spacing of the single-crystal test rod can be effectively reduced. Figure 9 , Figure 10 Before the process improvement, the primary dendrite spacing of the single-crystal blade was 280~300μm. After process optimization using the method of this invention, the primary dendrite spacing of the single-crystal test rod was 220~230μm.

[0100] Example 5

[0101] The difference between this embodiment and embodiment 4 is that the pressure of the cooling gas is 0.1 MPa.

[0102] Comparative Example

[0103] The difference between this comparative example and Example 4 is that there is no air cooling.

[0104] Figure 11 The figures show the solidification structure results of the castings obtained in Examples 4 and 5 and the comparative example of the present invention. (a) is the casting without argon gas, i.e., the comparative example casting; (b) is the casting obtained in Example 4 with argon gas at a pressure of 0.05 MPa; (c) is the casting obtained in Example 5 with argon gas at a pressure of 0.1 MPa; and (d) is the spacing between the primary dendrite arms. As can be seen from the figures, the application of appropriate pressure cooling gas can reduce the spacing between the primary dendrite arms and refine the higher dendrite arms. However, when the gas pressure is too high, the higher dendrite arms develop and the spacing between the primary dendrite arms increases.

[0105] Figure 12 The figures show the eutectic structure distribution results of the castings obtained in Examples 4 and 5 and the comparative example of the present invention. (a) is the casting without argon gas, i.e., the comparative example casting; (b) is the casting obtained in Example 4 with argon gas at a pressure of 0.05 MPa; (c) is the casting obtained in Example 5 with argon gas at a pressure of 0.1 MPa; and (d) is the eutectic content. As can be seen from the figures, the application of appropriate pressure cooling gas can reduce the eutectic structure content and make the distribution more uniform. However, when the gas pressure is too high, the eutectic content increases and the distribution becomes more uneven.

[0106] Figure 13 The figures show the micro-shrinkage results of castings obtained in Examples 4 and 5 and the comparative example of the present invention. (a) is the casting without argon gas, i.e., the comparative example casting; (b) is the casting obtained in Example 4 with argon gas at a pressure of 0.05 MPa; and (c) is the casting obtained in Example 5 with argon gas at a pressure of 0.1 MPa. As can be seen from the figures, the application of gas cooling conditions reduces the number of micro-shrinkage cavities and refines the size of the micro-shrinkage cavities. However, excessive gas pressure will lead to more micro-shrinkage cavities.

[0107] Therefore, in order to optimize the dendritic structure of the casting, the present invention adds an air cooling component and an air extraction component. The main parameter of this device is the gas pressure. Selecting an appropriate gas pressure ensures that no impurities are generated due to the temperature field tilt during the casting process, and can optimize the dendritic structure. Therefore, the shrinkage porosity content, element segregation degree and primary dendrite spacing of the casting under different pressures were statistically analyzed.

[0108] Example 6

[0109] To further explain the solution of the present invention, this embodiment will be used as an example:

[0110] CMSX-4 alloy was selected as the experimental material, and a single crystal specimen was cast. Its chemical composition by weight percentage was: Cr: 6.4%, Co: 9.6%, W: 6.4%, Mo: 0.61%, Ta: 6.6%, Al: 5.67%, Ti: 1.04%, Hf: 0.1%, Re: 2.9%, Ni - balance.

[0111] The mold shell is placed in the gravity-directed solidification device of this invention for preheating. Then, the alloy is poured under vacuum conditions. After the melt is poured into the mold shell, it is allowed to stand. Then, the mold shell is pulled upward and cooled under the action of the crystallizer. The preheating temperature is 1500℃, and the mold shell is allowed to stand for 5~10 min after pouring. The temperature of the square heater is 1530℃, the pouring temperature is 1550℃, and the pulling speed of the mold shell is 4 mm / min.

[0112] Example 7

[0113] To further explain the solution of the present invention, this embodiment will be used as an example:

[0114] CMSX-4 alloy was selected as the experimental material, and a single crystal specimen was cast. Its chemical composition by weight percentage was: Cr: 6.4%, Co: 9.6%, W: 6.4%, Mo: 0.61%, Ta: 6.6%, Al: 5.67%, Ti: 1.04%, Hf: 0.1%, Re: 2.9%, Ni - balance.

[0115] The mold shell is placed in the gravity-directed solidification device of this invention for preheating. Then, the alloy is poured under vacuum conditions. After the melt is poured into the mold shell, it is allowed to stand. Then, the mold shell is pulled upward and cooled under the action of the crystallizer. The preheating temperature is 1500℃, and the mold shell is allowed to stand for 5~10 minutes after pouring. The temperature of the square heater is 1530℃, the pouring temperature is 1550℃, and the pulling speed of the mold shell is 5 mm / min.

[0116] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A gravity-directed solidification device, characterized in that, It includes a cold chamber (1), a hot chamber (8) and a mold shell (7); the hot chamber (8) is located below the cold chamber (1); the mold shell (7) is provided with a pouring gate (10), and the bottom of the mold shell (7) is connected to the bottom of the pouring gate (10); The cold chamber (1) is provided with a pull-out mechanism (13), a water-cooled copper plate (2), an air extraction component (4), an air-cooling component (3), and a water-cooled copper ring (5); the water-cooled copper plate (2), the air extraction component (4), the air-cooling component (3), and the water-cooled copper ring (5) are arranged sequentially from top to bottom; The upper surface of the water-cooled copper plate (2) is connected to the pulling mechanism (13), the lower surface is connected to the top of the mold shell (7), and the pouring port (10) passes through the water-cooled copper plate (2). In use, the mold shell (7) passes through the air extraction assembly (4), the air cooling assembly (3) and the water-cooled copper ring (5), and moves vertically between the cold chamber (1) and the hot chamber (8) under the pulling action of the pulling mechanism (13).

2. The gravity-directed solidification apparatus according to claim 1, characterized in that, The air-cooling assembly (3) includes an air-cooling ring (301), which is connected to a cooling air source (305); The air-cooling ring (301) has a rectangular structure and is provided with a plurality of nozzles (302).

3. The gravity-directed solidification apparatus according to claim 2, characterized in that, Several of the nozzles (302) are located on the inner wall of the air-cooling ring (301).

4. The gravity-directed solidification apparatus according to claim 2, characterized in that, The nozzle (302) is trumpet-shaped, and the opening angle of the nozzle (302) is 110°~130°.

5. The gravity-directed solidification apparatus according to claim 2, characterized in that, The opening of the nozzle (302) is tilted upward.

6. A gravity-directed solidification apparatus according to claim 2, characterized in that, When the mold shell (7) passes through the air cooling ring (301), the distance between the nozzle (302) and the mold shell (7) is 15~25 mm.

7. The gravity-directed solidification apparatus according to claim 2, characterized in that, The air-cooling assembly (3) also includes a main air pipe (304), and a first branch pipe (306) and a second branch pipe (307) connected to the main air pipe (304); the free end of the main air pipe (304) is connected to a cooling air source (305), and the free ends of the first branch pipe (306) and the second branch pipe (307) are respectively connected to the two long sides of the air-cooling ring (301).

8. The gravity-directed solidification apparatus according to claim 1, characterized in that, The air extraction assembly (4) includes an air extraction ring (406) and an air extraction power assembly (405); The suction ring (406) is provided with a suction wall (407), and the suction wall (407) is provided with several through holes (401).

9. A gravity-directed solidification apparatus according to claim 8, characterized in that, The suction ring (406) is also provided with a baffle (402).

10. A gravity-directed solidification method, characterized in that, The gravity-directed solidification apparatus according to any one of claims 1 to 9 is used, and includes the following steps: The mold shell (7) is placed in the hot chamber (8) for preheating. The melt is poured into the mold shell (7) through the pouring port (10). After standing, the mold shell (7) is pulled upward by the pulling mechanism (13). At the same time, the water-cooled copper plate (2) and the water-cooled copper ring (5) are turned on so that the melt in the mold shell (7) is cooled by the action of the water-cooled copper plate (2) and the water-cooled copper ring (5). When the mold shell (7) is just pulled into the cold chamber (1), the vacuum assembly (4) and the air cooling assembly (3) are turned on to continue cooling the melt in the mold shell (7). After the mold shell (7) is completely pulled into the cold chamber (1), the vacuum assembly (4) and the air cooling assembly (3) are turned off, and the melt inside the mold shell (7) is completely cooled into solidified material. After the heating chamber (8) cools down, the mold shell (7) containing the solidified solids is removed and the mold shell (7) is removed to complete gravity-directed solidification.

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