A method for controlling porosity defects of an equiaxed crystal high-temperature alloy casting
By adding high thermal conductivity silicon nitride whiskers to the mold shell and preparing spiral cooling channels, combined with partitioned cotton wrapping technology, the problem of porosity defects at hot spots in high-temperature alloy castings was solved, and sequential solidification and high yield production of castings were achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- RED SILVER METAL CO LTD
- Filing Date
- 2026-07-01
- Publication Date
- 2026-08-04
AI Technical Summary
How to effectively control and eliminate porosity defects at hot spots in high-temperature alloy castings, especially in areas with complex blade shapes, thin walls, curved surfaces, and complex internal cavities, where the liquidus and solidus temperatures are wide and the flow resistance of liquid metal between dendrites is high, leading to difficulties in feeding, the formation of porosity zones, and affecting the overall strength of the casting.
By adding high thermal conductivity silicon nitride whiskers to the mold shell to prepare spiral cooling channels and performing zoned cotton wrapping, the casting solidifies sequentially, and the timing and rate of the cooling medium are controlled to improve the solidification rate at hot spots.
It achieves the control of porosity defects in equiaxed superalloy castings, is simple to operate, reduces production costs, improves casting qualification rate, and avoids stress concentration and crack initiation caused by porosity defects.
Smart Images
Figure CN122500128A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of high-temperature alloy precision casting technology, specifically relating to a method for controlling porosity defects in equiaxed high-temperature alloy castings. Background Technology
[0002] High-temperature alloys are a class of alloys used in high-temperature environments above 650℃, possessing excellent mechanical properties and surface stability. High-temperature alloys are not only key metallic materials for manufacturing aerospace engines, but they are also widely used in the chemical industry, energy and power, and transportation sectors. Therefore, the development level of high-temperature alloys is a marker of a country's defense capabilities and industrial level. Nickel-based high-temperature alloys have been widely used due to their excellent comprehensive properties. However, nickel-based high-temperature alloys are complex alloy systems composed of more than ten elements, and are prone to porosity defects in metallurgy, which seriously affect the quality of castings and the final yield rate.
[0003] During the solidification process of high-temperature alloys from liquid to solid, volume shrinkage occurs. The density of liquid metal is typically lower than that of solid metal. In areas with complex blade shapes (thin walls, curved surfaces, complex internal cavities) far from gating systems or feeding channels, insufficient liquid metal to fill the spaces left by shrinkage during final solidification can lead to shrinkage cavities or porous regions. Many high-temperature alloys have a wide temperature range (solidification zone) between their liquidus and solidus. Within this range, the alloy solidifies in a "paste-like" manner, containing numerous dendrites. The extremely high resistance to liquid metal flow between dendrites makes feeding extremely difficult and facilitates the formation of porosity between dendrites. Porosity defects disrupt the continuity of the matrix. Under tensile and bending loads, severe stress concentration occurs at the edges of these cavities, becoming preferred sites for crack initiation and leading to a significant decrease in overall strength, particularly tensile strength and yield strength.
[0004] Therefore, how to effectively control and eliminate porosity defects at hot spots in high-temperature alloy castings has become an urgent problem to be solved. Summary of the Invention
[0005] The technical problem to be solved by the present invention is to provide a method for controlling porosity defects in equiaxed crystal superalloy castings, which addresses the shortcomings of the prior art. This method reduces the porosity tendency of equiaxed crystal superalloy castings, is simple to operate, easy to implement, and greatly reduces production costs.
[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for controlling porosity defects in equiaxed superalloy castings, the method being as follows: S1. Preparation of wax mold assembly: Wax is injected into the product mold and cooled to obtain a wax mold; the wax mold is combined with the gating system to obtain a wax mold assembly. S2. Preparation of the shell: S201. After cleaning the wax model assembly obtained in S1, apply the surface slurry to the surface of the cleaned wax model assembly, sprinkle sand on the surface, and dry it to form a first layer on the surface of the wax model assembly, thus obtaining a wax model assembly with the first layer. S202. Apply the transition layer slurry to the surface of the wax model assembly with the first layer obtained in S201, sprinkle sand on the surface, and dry it to form a transition layer on the outside of the first layer, thus obtaining a wax model assembly with a second transition layer. S203. The first back layer slurry is applied to the surface of the casting blade, casting edge plate, casting tenon and casting root of the wax mold assembly with the second transition layer obtained in S202. After the surface is sprinkled with sand, it is dried to form the first back layer and obtain the wax mold assembly with the first back layer. The first back layer slurry of the casting blade is a mixture of mullite powder, silica sol and silicon nitride whiskers; S204. Apply the remaining back layer slurry to the surfaces of the casting blade, casting edge plate, casting tenon, and casting root of the wax mold assembly with the first back layer obtained in S203. After sprinkling sand on the surface, dry it. Repeat this step multiple times to form a total of n-1 remaining back layers, and finally obtain a shell with n back layers; 6≥n≥3, where n is a natural number. The remaining back layer slurry of the casting blade is a mixture of mullite powder, silica sol and silicon nitride whiskers; S3. Dewaxing the shell with n back layers obtained in S204. After dewaxing, calcining is performed to obtain the calcined shell. S4. Test the leak of the calcined shell obtained in S3, and print spiral cooling channels on the outer layer of the calcined shell that has passed the leak test to obtain a shell containing spiral cooling channels. S5. Wrap cotton around the riser and the middle section of the blade of the shell with spiral cooling channel obtained in S4. After preheating the shell, the shell to be cast is obtained. S6. Pour molten metal into the mold shell obtained in S5. After cooling and solidification, remove the mold shell and perform heat treatment to obtain an equiaxed high-temperature alloy casting.
[0007] Preferably, the surface slurry in S201 is a mixture of corundum powder and silica sol; the viscosity of the surface slurry is 35s to 45s; and the sprinkled sand is corundum sand with a particle size of 80 to 100 mesh.
[0008] Preferably, the transition layer slurry in S202 is a mixture of EC95 powder and silica sol; the viscosity of the transition layer slurry is 25s to 35s; and the sand sprinkled is corundum sand with a particle size of 60 to 80 mesh.
[0009] Preferably, the first backing slurry for the casting edge plate, casting tenon, and casting root in S203 is a mixture of mullite powder and silica sol; the viscosity of the first backing slurry is 10s to 15s; and the sprinkled sand is mullite with a particle size of 40 to 50 mesh.
[0010] Preferably, in S204, the remaining backing slurry for the casting edge plate, casting tenon, and casting root is a mixture of mullite powder and silica sol; the viscosity of the remaining backing slurry is 10s to 15s, and the sprinkled sand is mullite with a particle size of 16 to 30 mesh.
[0011] Preferably, the dewaxing method in S3 is as follows: dewaxing is performed using a dewaxing kettle at a temperature of 180℃~200℃, a pressure of 7.9bar~8.5bar, and a holding time of 16min~20min.
[0012] Preferably, the calcination temperature in S3 is 900℃~1000℃ and the time is 1.5h~2.5h.
[0013] Preferably, the diameter of the spiral cooling channel in S4 is 1.5mm to 3mm.
[0014] Preferably, in S5, the riser is wrapped with a double layer of aerogel felt; the middle section of the blade is wrapped with a single layer of ceramic fiber blanket; and the preheating temperature of the shell is 950℃~1200℃ for 4h~8h.
[0015] Compared with the prior art, the present invention has the following advantages: 1. This invention achieves good feeding effect and reduces porosity by adding high thermal conductivity silicon nitride whiskers to the shell, preparing spiral cooling channels on the outer layer of the shell, and partitioning the cotton.
[0016] 2. The method for controlling porosity defects in equiaxed superalloy castings provided by this invention is simple to operate and easy to implement, which greatly reduces production costs and improves the qualification rate of castings.
[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 - (a) is a fluorescence penetrant detection image of an isometric high-temperature alloy casting in Embodiment 1 of the present invention.
[0019] Figure 1 - (b) is the fluorescence penetrant detection image of the alloy casting in Comparative Example 1 of the present invention. Detailed Implementation
[0020] Example 1
[0021] This embodiment describes a method for controlling porosity defects in equiaxed superalloy castings. The method is as follows: S1. Preparation of wax model assembly: Wax is injected into the product mold and cooled in a constant temperature and humidity environment for 30 minutes to obtain a wax model, so as to avoid deformation of the wax model and affect the size of the casting; the wax model is combined with the gating system to obtain a wax model assembly. S2. Preparation of the shell: S201. Clean the wax model obtained in S1 to facilitate the application of slurry. The cleaning time is 5 minutes. Apply the surface slurry to the surface of the cleaned wax model. Sprinkle 100-mesh corundum sand on the surface and dry it at 23°C for 4 hours to form the first layer on the surface of the wax model, thus obtaining a wax model with the first layer. The surface slurry is a mixture of corundum powder (Guizhou Qingzhen Jincheng Abrasive Mold Factory) and silica sol (Nalco Environmental Protection Technology Service Co., Ltd.) in a ratio of 3.6g:1ml; the corundum powder has a particle size of 320 mesh. The viscosity of the surface slurry is 45s; Using corundum powder instead of EC95 powder in the surface slurry and corundum sand in the sand spreading material can improve the strength of the shell and at the same time avoid some special alloys from reacting with the EC95 powder in the surface layer during the pouring process to form chemical sand adhesion and reactive pores, which would affect the metallurgical quality of the casting. S202. Apply the transition layer slurry to the surface of the wax model module with the first layer obtained in S201, sprinkle corundum sand with a particle size of 80 mesh on the surface, and dry it at a temperature of 23℃ for 4 hours to form a transition layer on the outside of the first layer, thus obtaining a wax model module with a second transition layer. The transition layer slurry is a mixture of EC95 powder (Guizhou Qingzhen Jincheng Abrasive Mold Factory) and silica sol in a ratio of 3g:1ml. The viscosity of the transition layer slurry is 35s; Using EC95 powder as the transition layer slurry and corundum sand as the sand spreading material can effectively improve the strength of the shell and prevent the shell from cracking. S203. The first back layer slurry is applied to the surface of the casting blade, casting edge plate, casting tenon and casting root of the wax mold assembly with the second transition layer obtained in S202. After sprinkling the surface with mullite with a particle size of 46, it is dried at a temperature of 23°C for 6 hours to form the first back layer and obtain the wax mold assembly with the first back layer. The first back layer slurry of the casting blade is a mixture of mullite powder, silica sol, and silicon nitride whiskers in a ratio of 1.1g:1ml:0.05g; the silicon nitride whiskers were purchased from Nangong Harbin Institute of Technology New Materials Technology Co., Ltd., and have a diameter of 15μm; the first back layer slurry of the casting edge plate, casting tenon, and casting root are all a mixture of mullite powder and silica sol in a ratio of 1.15g:1ml. The viscosity of the first back layer slurry is 10s; The use of mullite powder in the first backing slurry and mullite in the sand spreading material can effectively improve the air permeability of the shell, prevent gas from being unable to escape during the casting process, form pores, and affect metallurgical quality. S204. Apply the remaining back layer slurry to the surface of the casting blade, casting edge plate, casting tenon and casting root of the wax mold assembly with the first back layer obtained in S203. Sprinkle the surface with mullite with a particle size of 24 and dry at a temperature of 23°C for 6 hours. Repeat this step multiple times to form a total of 3 remaining back layers, and finally obtain a shell with 4 back layers. The remaining back layer slurry of the casting blade is a mixture of mullite powder, silica sol, and silicon nitride whiskers in a ratio of 1.1g:1ml:0.05g; the remaining back layer slurry of the casting edge plate, casting tenon, and casting root is a mixture of mullite powder and silica sol in a ratio of 1.15g:1ml; the mullite powder was purchased from Jincheng Abrasive Mold Factory in Qingzhen City, Guizhou Province. The viscosity of the remaining back layer slurry is 10s; The first back layer and the remaining back layers of the blade all use mullite powder, silica sol and silicon nitride whiskers. Silicon nitride whiskers can improve the cooling rate. The first back layer uses 46-mesh mullite as the sanding material, which is intended to connect the transition layer and the remaining back layers and avoid the sanding particle size range being too large, which would reduce the bonding strength. The remaining back layers use mullite powder, which can improve the air permeability of the shell and facilitate gas discharge. S3. Dewaxing the shell with 4 back layers obtained in S204. After dewaxing, calcining at 950℃ for 2 hours to obtain the calcined shell. The dewaxing method is as follows: dewaxing is carried out in a dewaxing kettle at a temperature of 190℃ and a pressure of 8.2 bar; the holding time is 18 minutes. S4. Use a mixed solution of methylene blue and alcohol with a volume ratio of 1:1500 to test the leak of the calcined shell obtained in S3. Then, use a 3D printer to print spiral cooling channels on the outer layer of the calcined shell that has passed the leak test to obtain a shell containing spiral cooling channels. The diameter of the spiral cooling channel is 2mm; the spiral cooling channel is located on the blade and at the junction of the blade and the edge plate. S5. Wrap cotton around the riser and the middle section of the blade of the shell with spiral cooling channel obtained in S4. After preheating the shell, the shell to be cast is obtained. The riser is wrapped with a double-layer aerogel felt with low thermal conductivity (0.02 W / m·K, purchased from Hebei Hegao Insulation Materials Co., Ltd.); the middle section of the blade is wrapped with a single-layer ceramic fiber blanket (0.1 W / m·K, purchased from Shandong Hongyang High Temperature Energy Saving Materials Co., Ltd.); the shell is preheated at 1000℃ and the heat preservation time is 6 hours. Before pouring, the mold shell is wrapped with cotton in sections to allow the casting to solidify sequentially, achieving a good feeding effect and reducing the tendency to porosity. S6. A vacuum induction melting furnace is used for casting. The weight of the casting material is 18 kg. To ensure the uniformity of the molten metal, the refining temperature is 1520℃, and the refining time is 3 minutes. The resulting molten metal is poured into the mold shell obtained in S5 at a pouring temperature of 1480℃. During the filling period of the pouring stage, from the start of pouring, argon gas is preheated through a spiral cooling channel within 0-30 seconds to prevent premature solidification of the metal. During the feeding period, liquid nitrogen is atomized and injected within 30-120 seconds of pouring to cool the hot spots. During the solid-state phase transformation period, after 120 seconds of pouring, the casting is allowed to cool naturally. This reduces porosity at hot spots while preventing the casting from solidifying during the solid-state phase transformation period. Rapid cooling leads to excessive residual stress and cracks. After complete cooling and solidification, the riser is hammered to remove the surface shell of the part, followed by heat treatment. The heat treatment process consists of one solution treatment followed by three aging treatments. A vacuum high-pressure gas quenching furnace is used for heat treatment, with argon cooling. The solution temperature is 1300℃ and the solution time is 120 min. The first aging temperature is 1120℃ and the holding time is 240 min. The second aging temperature is 1080℃ and the holding time is 240 min. The third aging temperature is 900℃ and the holding time is 240 min. After heat treatment, polishing and sandblasting are performed to remove the oxide scale from the surface of the casting, resulting in an equiaxed crystal high-temperature alloy casting.
[0022] Fluorescent penetrant testing was performed on the obtained equiaxed superalloy castings to observe porosity defects, such as... Figure 1 As shown in (a), the porosity defect is significantly reduced.
[0023] During the solidification process of high-temperature alloys from liquid to solid, the volume undergoes solidification shrinkage. The density of liquid metal is usually lower than that of solid metal. For areas with complex blade shapes (thin walls, curved surfaces, complex internal cavities) far from the gating system or feeding channels, if there is insufficient liquid metal to fill the space left by shrinkage during the final solidification, shrinkage cavities or porous areas will form. Many high-temperature alloys have a wide temperature range (solidification zone) between the liquidus and solidus. Within this range, the alloy solidifies in a "paste" manner, with a large number of dendrites. The flow resistance of liquid metal between dendrites is extremely high, making feeding extremely difficult and making it easier for porosity to form between dendrites. Porosity defects disrupt the continuity of the matrix. When subjected to tensile, bending, or other loads, severe stress concentration will occur at the edges of the pores, becoming a preferred location for crack initiation, resulting in a significant decrease in overall strength, especially tensile strength and yield strength.
[0024] By adding high thermal conductivity silicon nitride whiskers to the thinner blade section of the mold shell, the heat dissipation rate is increased, allowing the casting to solidify sequentially along the direction of gravity, resulting in a good feeding effect. Simultaneously, by creating cooling channels in the outermost layer of the mold shell and controlling the timing of the cooling medium introduction, the solidification rate at hot spots is increased, improving the overall feeding effect of the casting. Using materials with different thermal conductivity for zoned insulation, the combined effect of these three methods ensures sequential solidification of the equiaxed casting, reducing the tendency for porosity at hot spots. The provided method for controlling porosity defects in equiaxed superalloy castings is simple to operate, easy to implement, significantly reduces production costs, and improves the casting yield. Based on existing technologies, the cooling timing and rate at hot spots are controlled, overcoming the shortcomings of existing technologies in controlling shrinkage defects at hot spots and significantly solving the metallurgical problem of shrinkage defects easily occurring at hot spots.
[0025] Comparative Example 1 This comparative example illustrates the preparation method of alloy castings without adding silicon nitride whiskers, without adding spiral cooling channels to the outer shell, and with the shell uniformly wrapped with aluminum silicate cotton.
[0026] The alloy casting method in this comparative example is the same as in Example 1, except that in step S203, the first back layer slurry is a mixture of mullite powder and silica sol with a ratio of 1.15g:1ml; in step S4, the shell obtained in step S3 after calcination is tested for leaks using a mixed solution of methylene blue and alcohol with a volume ratio of 1:1500, and a shell that passes the leak test is obtained; in step S5, the riser and the middle section of the blade of the shell that passes the leak test are uniformly wrapped with aluminum silicate cotton (Suzhou Carford Materials Technology Co., Ltd.) with a conventional thickness of 20mm.
[0027] Fluorescent penetrant testing was performed on the alloy castings prepared in this comparative example to observe porosity defects, such as... Figure 1 As shown in (b), the degree of porosity defect is significantly more severe compared to Example 1.
[0028] Example 2
[0029] This embodiment describes a method for controlling porosity defects in equiaxed superalloy castings. The method is as follows: S1. Preparation of wax model assembly: Wax is injected into the product mold and cooled in a constant temperature and humidity environment for 30 minutes to obtain a wax model, so as to avoid deformation of the wax model and affect the size of the casting; the wax model is combined with the gating system to obtain a wax model assembly. S2. Preparation of the shell: S201. Clean the wax model obtained in S1 to facilitate the application of slurry. The cleaning time is 5 minutes. Apply the surface slurry to the surface of the cleaned wax model. Sprinkle 80-mesh corundum sand on the surface and dry it at 22°C for 5 hours to form the first layer on the surface of the wax model, thus obtaining a wax model with the first layer. The surface slurry is a mixture of corundum powder and silica sol in a ratio of 3g:1ml; the corundum powder has a particle size of 320 mesh. The viscosity of the surface slurry is 35s; S202. Apply the transition layer slurry to the surface of the wax model module with the first layer obtained in S201, sprinkle corundum sand with a particle size of 60 mesh on the surface, and dry it at a temperature of 22℃ for 5 hours to form a transition layer on the outside of the first layer, thus obtaining a wax model module with a second transition layer. The transition layer slurry is a mixture of EC95 powder and silica sol in a ratio of 2.5g:1ml; The viscosity of the transition layer slurry is 25s; S203. The first back layer slurry is applied to the surface of the casting blade, casting edge plate, casting tenon and casting root of the wax mold assembly with the second transition layer obtained in S202. After sprinkling the surface with mullite with a particle size of 40 mesh, it is dried at a temperature of 22℃ for 7 hours to form the first back layer and obtain the wax mold assembly with the first back layer. The first back layer slurry of the casting blade is a mixture of mullite powder, silica sol, and silicon nitride whiskers in a ratio of 1.4g:1ml:0.06g; the silicon nitride whiskers were purchased from Nangong Harbin Institute of Technology New Materials Technology Co., Ltd., and have a diameter of 15μm; the first back layer slurry of the casting edge plate, casting tenon, and casting root is a mixture of mullite powder and silica sol in a ratio of 1.45g:1ml. The viscosity of the first back layer slurry is 15s; S204. Apply the remaining back layer slurry to the surface of the wax mold with the first back layer obtained in S203, sprinkle the surface with mullite with a particle size of 16, and dry at a temperature of 22°C for 7 hours. Repeat this step multiple times to form a total of 2 remaining back layers, and finally obtain a shell with 3 back layers. The remaining back layer slurry of the casting blade is a mixture of mullite powder, silica sol and silicon nitride whiskers in a ratio of 1.3g:1ml:0.06g; the remaining back layer slurry of the casting edge plate, casting tenon and casting root is a mixture of mullite powder and silica sol in a ratio of 1.35g:1ml. The viscosity of the remaining back layer slurry is 13s; S3. Dewaxing the shell with 3 back layers obtained in S204. After dewaxing, calcining at 900℃ for 2.5h to obtain the calcined shell. The dewaxing method is as follows: dewaxing is carried out in a dewaxing kettle at a temperature of 180℃, a pressure of 8.5 bar, and a holding time of 20 minutes. S4. Use a mixed solution of methylene blue and alcohol with a volume ratio of 1:1500 to test the leak of the calcined shell obtained in S3. Then, use a 3D printer to print spiral cooling channels on the outer layer of the calcined shell that has passed the leak test to obtain a shell containing spiral cooling channels. The diameter of the spiral cooling channel is 1.5 mm; the spiral cooling channel is located on the blade and at the junction of the blade and the edge plate. S5. Wrap cotton around the riser and the middle section of the blade of the shell with spiral cooling channel obtained in S4. After preheating the shell, the shell to be cast is obtained. The riser is wrapped with a double-layer aerogel felt with low thermal conductivity; the middle section of the blade is wrapped with a single-layer ceramic fiber blanket; the shell is preheated to 950℃ and kept warm for 8 hours; S6. A vacuum induction melting furnace is used for casting. The weight of the casting material is 18 kg. To ensure the uniformity of the molten metal, the refining temperature is 1520℃, and the refining time is 3 minutes. The resulting molten metal is poured into the mold shell obtained in S5 at a pouring temperature of 1480℃. During the filling period of the pouring stage, from the start of pouring, argon gas is preheated through a spiral cooling channel within 0-30 seconds to prevent premature solidification of the metal. During the feeding period, liquid nitrogen is atomized and injected within 30-120 seconds of pouring to cool the hot spots. During the solid-state phase transformation period, after 120 seconds of pouring, the casting is allowed to cool naturally. This reduces porosity at hot spots while preventing the casting from solidifying during the solid-state phase transformation period. Rapid cooling leads to excessive residual stress and cracks. After complete cooling and solidification, the riser is hammered to remove the surface shell of the part, followed by heat treatment. The heat treatment process consists of one solution treatment followed by three aging treatments. A vacuum high-pressure gas quenching furnace is used for heat treatment, with argon cooling. The solution temperature is 1300℃ and the solution time is 120 min. The first aging temperature is 1120℃ and the holding time is 240 min. The second aging temperature is 1080℃ and the holding time is 240 min. The third aging temperature is 900℃ and the holding time is 240 min. After heat treatment, polishing and sandblasting are performed to remove the oxide scale from the surface of the casting, resulting in an equiaxed crystal high-temperature alloy casting.
[0030] Example 3
[0031] This embodiment describes a method for controlling porosity defects in equiaxed superalloy castings. The method is as follows: S1. Preparation of wax model assembly: Wax is injected into the product mold and cooled in a constant temperature and humidity environment for 30 minutes to obtain a wax model, so as to avoid deformation of the wax model and affect the size of the casting; the wax model is combined with the gating system to obtain a wax model assembly. S2. Preparation of the shell: S201. Clean the wax model obtained in S1 to facilitate the application of slurry. The cleaning time is 5 minutes. Apply the surface slurry to the surface of the cleaned wax model. Sprinkle 90-mesh corundum sand on the surface and dry it at 21°C for 6 hours to form the first layer on the surface of the wax model, thus obtaining a wax model with the first layer. The surface slurry is a mixture of corundum powder and silica sol in a ratio of 3.3g:1ml; the corundum powder has a particle size of 320 mesh. The viscosity of the surface slurry is 40s; S202. Apply the transition layer slurry to the surface of the wax model module with the first layer obtained in S201, sprinkle corundum sand with a particle size of 70 mesh on the surface, and dry it at a temperature of 21℃ for 6 hours to form a transition layer on the outside of the first layer, thus obtaining a wax model module with a second transition layer. The transition layer slurry is a mixture of EC95 powder and silica sol in a ratio of 2.8g:1ml; The viscosity of the transition layer slurry is 30s; S203. The first back layer slurry is applied to the surface of the casting blade, casting edge plate, casting tenon and casting root of the wax mold assembly with the second transition layer obtained in S202. After sprinkling the surface with 50-mesh mullite, it is dried at 23°C for 6 hours to form the first back layer and obtain the wax mold assembly with the first back layer. The first back layer slurry of the casting blade is a mixture of mullite powder, silica sol, and silicon nitride whiskers in a ratio of 1.2g:1ml:0.07g; the silicon nitride whiskers were purchased from Nangong Harbin Institute of Technology New Materials Technology Co., Ltd., and have a diameter of 20μm; the first back layer slurry of the casting edge plate, casting tenon, and casting root are all a mixture of mullite powder and silica sol in a ratio of 1.25g:1ml. The viscosity of the first back layer slurry is 12s; S204. Apply the remaining back layer slurry to the surface of the casting blade, casting edge plate, casting tenon and casting root of the wax mold assembly with the first back layer obtained in S203. Sprinkle the surface with mullite with a particle size of 30 mesh and dry at a temperature of 21℃ for 8 hours. Repeat this step multiple times to form a total of 5 remaining back layers, and finally obtain a shell with 6 back layers. The remaining back layer slurry of the casting blade is a mixture of mullite powder, silica sol and silicon nitride whiskers in a ratio of 1.4g:1ml:0.07g; the remaining layers of slurry of the casting edge plate, casting tenon and casting root are a mixture of mullite powder and silica sol in a ratio of 1.45g:1ml. The viscosity of the remaining back layer slurry is 15s; S3. Dewaxing the shell with 6 back layers obtained in S204. After dewaxing, calcining at 1000℃ for 1.5h to obtain the calcined shell. The dewaxing method is as follows: dewaxing is carried out in a dewaxing kettle at a temperature of 200℃, a pressure of 7.9 bar, and a holding time of 16 minutes. S4. Use a mixed solution of methylene blue and alcohol with a volume ratio of 1:1500 to test the leak of the calcined shell obtained in S3. Then, use a 3D printer to print spiral cooling channels on the outer layer of the calcined shell that has passed the leak test to obtain a shell containing spiral cooling channels. The diameter of the spiral cooling channel is 3mm; the spiral cooling channel is located on the blade and at the junction of the blade and the edge plate. S5. The riser and the middle section of the blade of the shell with spiral cooling channel obtained in S4 are wrapped with cotton, and after being fired again, the shell to be cast is obtained. The riser is wrapped with a double-layer aerogel felt with low thermal conductivity; the middle section of the blade is wrapped with a single-layer ceramic fiber blanket; the shell is preheated at 1200℃ and kept warm for 4 hours. S6. A vacuum induction melting furnace is used for casting. The weight of the casting material is 18 kg. To ensure the uniformity of the molten metal, the refining temperature is 1520℃, and the refining time is 3 minutes. The resulting molten metal is poured into the mold shell obtained in S5 at a pouring temperature of 1480℃. During the filling period of the pouring stage, from the start of pouring, argon gas is preheated through a spiral cooling channel within 0-30 seconds to prevent premature solidification of the metal. During the feeding period, liquid nitrogen is atomized and injected within 30-120 seconds of pouring to cool the hot spots. During the solid-state phase transformation period, after 120 seconds of pouring, the casting is allowed to cool naturally. This reduces porosity at hot spots while preventing the casting from solidifying during the solid-state phase transformation period. Rapid cooling leads to excessive residual stress and cracks. After complete cooling and solidification, the riser is hammered to remove the surface shell of the part, followed by heat treatment. The heat treatment process consists of one solution treatment followed by three aging treatments. A vacuum high-pressure gas quenching furnace is used for heat treatment, with argon cooling. The solution temperature is 1300℃ and the solution time is 120 min. The first aging temperature is 1120℃ and the holding time is 240 min. The second aging temperature is 1080℃ and the holding time is 240 min. The third aging temperature is 900℃ and the holding time is 240 min. After heat treatment, polishing and sandblasting are performed to remove the oxide scale from the surface of the casting, resulting in an equiaxed crystal high-temperature alloy casting.
[0032] In summary, the equiaxed superalloy castings prepared by this invention improve heat dissipation by adding high thermal conductivity silicon nitride whiskers to the thinner blade section of the mold shell, allowing the casting to solidify sequentially along the direction of gravity, thus achieving a good feeding effect. Simultaneously, by creating cooling channels in the outermost layer of the mold shell and controlling the timing of the cooling medium introduction, the solidification rate at the hot joint is increased, improving the overall feeding effect of the casting. The use of materials with different thermal conductivity for zoned insulation, combined with these three factors, ensures sequential solidification of the equiaxed casting, significantly reducing the tendency for shrinkage porosity at the blade-blade transition R (hot joint). The castings prepared in Examples 1-3 showed no obvious shrinkage porosity defects at the hot joint, or only a small amount of shallow shrinkage porosity, which can be completely removed by polishing within the allowable tolerance range. In contrast, the casting in Comparative Example 1 showed obvious shrinkage porosity defects, with larger dimensions and greater depth, exceeding the allowable tolerance range, and could not be removed by polishing. Through comparison, this invention significantly improves casting quality, reduces metallurgical defects, and increases the casting yield.
[0033] 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 porosity defects in equiaxed superalloy castings, characterized in that, The method is as follows: S1. Preparation of wax mold assembly: Wax is injected into the product mold and cooled to obtain a wax mold; the wax mold is combined with the gating system to obtain a wax mold assembly. S2. Preparation of the shell: S201. After cleaning the wax model assembly obtained in S1, apply the surface slurry to the surface of the cleaned wax model assembly, sprinkle sand on the surface, and dry it to form a first layer on the surface of the wax model assembly, thus obtaining a wax model assembly with the first layer. S202. Apply the transition layer slurry to the surface of the wax model assembly with the first layer obtained in S201, sprinkle sand on the surface, and dry it to form a transition layer on the outside of the first layer, thus obtaining a wax model assembly with a second transition layer. S203. The first back layer slurry is applied to the surface of the casting blade, casting edge plate, casting tenon and casting root of the wax mold assembly with the second transition layer obtained in S202. After the surface is sprinkled with sand, it is dried to form the first back layer and obtain the wax mold assembly with the first back layer. The first back layer slurry of the casting blade is a mixture of mullite powder, silica sol and silicon nitride whiskers; S204. Apply the remaining back layer slurry to the surfaces of the casting blade, casting edge plate, casting tenon, and casting root of the wax mold assembly with the first back layer obtained in S203. After sprinkling sand on the surface, dry it. Repeat this step multiple times to form a total of n-1 remaining back layers, and finally obtain a shell with n back layers; 6≥n≥3, where n is a natural number. The remaining back layer slurry of the casting blade is a mixture of mullite powder, silica sol and silicon nitride whiskers; S3. Dewaxing the shell with n back layers obtained in S204. After dewaxing, calcining is performed to obtain the calcined shell. S4. Test the leak of the calcined shell obtained in S3, and print spiral cooling channels on the outer layer of the calcined shell that has passed the leak test to obtain a shell containing spiral cooling channels. S5. The riser and the middle section of the blade of the shell with spiral cooling channel obtained in S4 are wrapped with cotton respectively. After the shell is preheated, the shell to be cast is obtained. S6. Pour molten metal into the mold shell obtained in S5. After cooling and solidification, remove the mold shell and perform heat treatment to obtain an equiaxed high-temperature alloy casting.
2. The method for controlling porosity defects in equiaxed superalloy castings according to claim 1, characterized in that, The surface slurry described in S201 is a mixture of corundum powder and silica sol; the viscosity of the surface slurry is 35s to 45s; and the sand sprinkled is corundum sand with a particle size of 80 to 100 mesh.
3. The method for controlling porosity defects in equiaxed superalloy castings according to claim 1, characterized in that, The transition layer slurry in S202 is a mixture of EC95 powder and silica sol; the viscosity of the transition layer slurry is 25s to 35s; and the sand sprinkled is corundum sand with a particle size of 60 to 80 mesh.
4. The method for controlling porosity defects in equiaxed superalloy castings according to claim 1, characterized in that, The first backing slurry for the casting edge plate, casting tenon, and casting root described in S203 is a mixture of mullite powder and silica sol; the viscosity of the first backing slurry is 10s to 15s; and the sand sprinkled is mullite with a particle size of 40 to 50 mesh.
5. The method for controlling porosity defects in equiaxed superalloy castings according to claim 1, characterized in that, The remaining backing slurry for the casting edge plate, casting tenon, and casting root described in S204 is a mixture of mullite powder and silica sol; the viscosity of the remaining backing slurry is 10s to 15s, and the sprinkled sand is mullite with a particle size of 16 to 30 mesh.
6. The method for controlling porosity defects in equiaxed superalloy castings according to claim 1, characterized in that, The dewaxing method in S3 is as follows: dewaxing is carried out using a dewaxing kettle at a temperature of 180℃~200℃, a pressure of 7.9bar~8.5bar, and a holding time of 16min~20min.
7. The method for controlling porosity defects in equiaxed superalloy castings according to claim 1, characterized in that, The roasting temperature in S3 is 900℃~1000℃ and the time is 1.5h~2.5h.
8. The method for controlling porosity defects in equiaxed superalloy castings according to claim 1, characterized in that, The diameter of the spiral cooling channel described in S4 is 1.5mm to 3mm.
9. The method for controlling porosity defects in equiaxed superalloy castings according to claim 1, characterized in that, The riser in S5 is wrapped with a double layer of aerogel felt; the middle section of the blade is wrapped with a single layer of ceramic fiber blanket; the preheating temperature of the shell is 950℃~1200℃ and the time is 4h~8h.