Integrated casting method for hollow turbine blade with air film holes

Abstract

The invention relates to the technical field of aero-engine turbine blade casting, in particular to an integrated casting method for a hollow turbine blade with air film holes. The hollow turbine blade and the hollow turbine blade are connected through a mortise and tenon joint structure, a negative hole is formed through nano-imprinting, gradient sintering treatment is conducted, an exhaust micro-channel is formed in a shell, a gas film hole and a self-repairing layer located on the hole wall of the gas film hole are synchronously produced in the pouring process, and chemical etching and aftertreatment are conducted, so that the finally prepared hollow turbine blade is provided with a high-precision gas film. The cooling effect and the interface bonding strength are high, the thermal cycle life is prolonged, the machining period is shortened, and hole wall cracks can be self-repaired.

Description

Technical Field

[0001] This application relates to the field of aero-engine turbine blade casting technology, specifically to an integrated casting method for hollow turbine blades with film vents. Background Technology

[0002] Turbine blades are an important component of the turbine section in a gas turbine engine. The high-speed rotating blades are responsible for drawing high-temperature, high-pressure airflow into the combustor to keep the engine running.

[0003] Currently, hollow turbine blades with film cooling holes are mainly manufactured through casting. The turbine blade mold consists of a core and a shell. Molten metal for manufacturing the hollow turbine blade is poured in, cooled, and solidified. After removing the core and shell, the hollow turbine blade is obtained. Laser / EDM drilling is then performed on the surface of the hollow turbine blade, leading to microcracks in the hole walls, reducing high-temperature fatigue life, and affecting the film cooling effect. Furthermore, laser / EDM machining has a hole diameter error of ±20μm, which is relatively large and cannot meet the precision requirements of film cooling holes. Additionally, drilling efficiency is low, the processing cycle is long, and manufacturing costs are increased.

[0004] CN112916811B discloses a casting method for hollow turbine blades with film cooling holes, in which film cooling holes are directly formed during the casting process. The composition of the hole wall is consistent with the composition of the main body of the hollow turbine blade. During the operation of the gas turbine engine, microcracks are easily generated in the hole wall, which affects the film cooling effect.

[0005] Based on this, a hollow turbine blade with film pores that can be integrally cast and improved in performance is proposed. Summary of the Invention

[0006] The purpose of this invention is to provide an integrated casting method for hollow turbine blades with film cooling holes, which eliminates the need for subsequent machining of the film cooling holes, improves the accuracy of the film cooling holes and the performance of the blades, and solves the problems raised in the prior art.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following solution: An integrated casting method for hollow turbine blades with film-forming pores includes the following steps: S1, Preparation of gradient ceramic core: The core includes an alumina-based main body layer and a sacrificial pillar composed of zirconium silicate and yttrium oxide, and the surface of the sacrificial pillar is pre-formed with negative holes by nanoimprinting technology; S2, the gradient ceramic core is embedded in the wax mold and coated with multiple layers of ceramic. After dewaxing and pre-firing, a casting shell is obtained. S3 involves casting a nickel-based single-crystal superalloy between a cast shell and a gradient ceramic core, and etching the sacrificial pillars through thermal activation during the directional solidification stage to simultaneously produce film pores and a self-healing layer located on the pore wall of the film pores. S4. Gradient ceramics and hollow turbine blades are chemically etched and post-treated to obtain hollow turbine blades with film pores.

[0008] Furthermore, by weight percentage, the alumina-based main body layer is composed of 80-85 wt% alumina, 7-13% zirconium oxide, and 2-8 wt% silica sol, which are mixed to form a main body layer slurry. The main body layer slurry is injected into a photopolymerization 3D printer to obtain a main body layer preform.

[0009] Furthermore, the sacrificial pillar is composed of 90-95 wt% zirconium silicate, 3-8 wt% yttrium oxide, and 2-5 wt% nano-silicon carbide, which are mixed to form a sacrificial pillar slurry. The sacrificial pillar slurry is spin-coated onto the protruding tenon of the main body and subjected to nanoimprinting technology, followed by thermosetting and UV curing to obtain the core preform.

[0010] Furthermore, the bottom end of the sacrificial column is provided with a mortise that matches the tenon.

[0011] Furthermore, the two ends of the negative hole are on two parallel planes, and the surface of one end is in contact with the inner wall of the cast shell.

[0012] Furthermore, during nanoimprinting, the imprinting template is a single-crystal silicon or nickel-based alloy with an array of etched holes on the surface, the imprinting pressure is 5-10 MPa, the vacuum degree is ≤10⁻³ Pa, and the holding time is 3-5 minutes.

[0013] Furthermore, in step S2, the casting shell is provided with multiple exhaust microchannels, and the inlet and outlet of the exhaust microchannels are located on the inner wall and outer wall of the casting shell, respectively. The inlet aperture of the exhaust microchannel is 20 μm; the aperture of the exhaust microchannel is 50 μm.

[0014] Further, in step S3, the process parameters for directional solidification are: temperature gradient ≥100℃ / cm, pulling rate 2~5mm / min; the molten alloy is a nickel-based single crystal high-temperature alloy containing 2.5~3.5wt% aluminum, and the casting superheat ΔT=100-150℃.

[0015] Furthermore, the thermal activation includes: the zirconium silicate in the sacrificial column reacts with aluminum in the nickel-based single-crystal superalloy to generate gaseous SiO2 and solid ZrAl3 / Al2O3 framework; yttrium oxide reacts with aluminum to generate a YAlO3 self-healing oxide layer.

[0016] Further, in step S4, the chemical etching includes the following steps: S41, hydrofluoric acid vapor etching: 20~30% by mass, temperature 80℃, time less than 4h; S41, hydrochloric acid ultrasonic cleaning: molar mass 3~5mol / L, ultrasonic frequency 40kHz, time 1~2h; The post-processing includes the following steps: S42, nitric acid passivation treatment: 30% by mass, 50℃, 10 min; S43, Vacuum Annealing: Vacuum degree ≤10⁻³ Pa, heat to 1000℃ at a rate of 5℃ / min, hold for 2h; cool to room temperature at a rate of 3℃ / min.

[0017] The beneficial effects of this invention are as follows: This invention utilizes a core formed from an alumina-based main body and sacrificial pillars composed of zirconium silicate and yttrium oxide, connected by a tenon-and-mortise structure. It employs nanoimprinting to create negative pores, gradient sintering, and exhaust microchannels in the shell. During the casting process, film pores and a self-healing layer on the pore walls are simultaneously produced. Chemical etching and post-treatment are then used to create hollow turbine blades with high-precision film pores, efficient cooling, an interface bonding strength ≥25MPa, a 5-fold increase in thermal cycle life, and a shortened processing cycle. Furthermore, the self-healing YAlO3 oxide layer within the pore walls repairs microcracks in the pore walls, extending their service life. Attached Figure Description

[0018] Figure 1 This is a process flow diagram of the casting method of the present invention; Figure 2 This is a schematic diagram of the core and casting shell of the present invention; Figure 3 for Figure 1 A magnified schematic diagram of the structure of circle A in the middle.

[0019] Reference numerals: 1-core, 10-main body layer, 100-tenon, 11-sacrificial post, 110-mortise, 111-negative hole, 2-shell, 20-venting microchannel. Detailed Implementation

[0020] 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, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0021] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps described in these embodiments do not limit the scope of the invention.

[0022] At the same time, it should be understood that, for ease of description, the dimensions of the various parts shown in the accompanying drawings are not drawn according to actual scale.

[0023] Furthermore, for clarity and brevity, descriptions of well-known structures, functions, and configurations may have been omitted. Those skilled in the art will recognize that various changes and modifications can be made to the examples described herein without departing from the spirit and scope of this disclosure.

[0024] Techniques, methods, and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and equipment should be considered part of the specification.

[0025] In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values.

[0026] Example 1 Embodiment 1 of this application is an integrated casting method for hollow turbine blades with film-forming holes, referring to... Figure 1 and Figure 2 This includes the following steps: S1, Preparation of gradient ceramic core: The core includes an alumina-based main body layer and a sacrificial pillar composed of zirconium silicate and yttrium oxide, and the surface of the sacrificial pillar is pre-formed with negative holes by nanoimprinting technology; S2, the gradient ceramic core is embedded in the wax mold and coated with multiple layers of ceramic. After dewaxing and pre-firing, a casting shell is obtained. S3 involves casting a nickel-based single-crystal superalloy between a cast shell and a gradient ceramic core, and etching the sacrificial pillars through thermal activation during the directional solidification stage to simultaneously produce film pores and a self-healing layer located on the pore wall of the film pores. S4. Gradient ceramics and hollow turbine blades are chemically etched and post-treated to obtain hollow turbine blades with film pores.

[0027] Current casting processes primarily employ molds consisting of a core and a shell to cast high-temperature alloys for hollow turbine blades. Existing 3D modeling software can be used to directly create 3D models of the core and shell of the hollow turbine blade with film cooling holes, ensuring that the main body and film cooling hole sections of the cast hollow turbine blade match the required dimensions. 3D modeling software includes: Magics, Unigraphics NX, CATIA, Pro / Engineer, and SolidWorks.

[0028] By pre-fabricating a gradient ceramic core and a casting shell, the alumina-based main body layer and the sacrificial pillars composed of zirconium silicate and yttrium oxide form the main body and film cooling pores of the hollow turbine blade, respectively. During the casting of the film cooling pores, a nickel-based single-crystal superalloy undergoes directional solidification during the casting process. This directional solidification utilizes the heat of the molten alloy metal to activate the components within the sacrificial pillars, causing a chemical reaction between the components and the aluminum components within the nickel-based single-crystal superalloy. This dissolves the chemical components within the sacrificial pillars, forming film cooling pores and a self-healing layer, while preserving the supporting structure of the alumina-based main body layer. Specifically, the aluminum components react with the zirconium silicate in the sacrificial pillars to generate gaseous silicon dioxide and a solid ZrAl3 / Al2O3 framework, forming the basic pore structure of the film cooling pores. Simultaneously, the aluminum components react with yttrium oxide to generate a YAlO3 self-healing oxide layer, achieving self-healing of the pore walls within the film cooling pores. After removing the shell, chemical etching was used to remove the core and the solid ZrAl3 / Al2O3 skeleton respectively. Post-treatment was used to form a protective film on the main body of the hollow turbine blade and to densify the YAlO3 self-healing oxide layer in the pore wall of the air film pore.

[0029] This application, based on the specific structure of the core and shell and the use of sacrificial pillars made of specific components, enables the integral formation of film pores during the casting process. Simultaneously, a self-healing oxide layer forms within the pore walls, preventing oxygen penetration and enhancing the high-temperature oxidation and thermal corrosion resistance of the film pores, repairing microcrack propagation, and extending the service life of the hollow turbine blades. This eliminates the need for external machining of the cast hollow turbine blades to drill holes on their surface, thus reducing the precision requirements for the film pores.

[0030] The alumina-based main body layer, by weight percentage, consists of 80-85 wt% alumina, 7-13% zirconium oxide, and 2-8 wt% silica sol, which are mixed to form a main body slurry. The main body slurry is injected into a photopolymerization 3D printer to obtain a main body preform.

[0031] The viscosity of the main layer slurry is 3000~5000 mPas at room temperature. The supporting skeleton for the hollow turbine blade cavity is printed under ultraviolet light at a wavelength of 405 nm and a power of 80 mW / cm². Tenons, or assembly interfaces for sacrificial pillars, are pre-drilled on the surface of the main layer. This supporting skeleton can be a solid structure or a honeycomb-like hollow structure to facilitate subsequent core removal.

[0032] Alumina primarily provides the core's structural strength, withstanding the impact forces during the casting of nickel-based single-crystal superalloys and ensuring high-temperature resistance without deformation. Zirconia enhances crack resistance and fracture toughness through a phase transformation toughening mechanism. Simultaneously, the thermal expansion coefficient of zirconia falls between that of alumina and zirconium silicate in the sacrificial pillars, creating a gradient transition, reducing interfacial thermal stress, and strengthening interfacial bonding. The silica sol, mainly composed of silicon dioxide, possesses excellent fluidity. When combined with photopolymerization 3D printing, it ensures the precision of core forming, meeting the requirements for integrated film pore casting.

[0033] The sacrificial pillar is composed of 90-95 wt% zirconium silicate, 3-8 wt% yttrium oxide, and 2-5 wt% nano silicon carbide, which are mixed to form a sacrificial pillar slurry. The sacrificial pillar slurry is spin-coated onto the protruding tenon of the main body and subjected to nanoimprinting technology, followed by thermosetting and UV curing to obtain the core preform.

[0034] The sacrificial column contains zirconium silicate, which reacts with aluminum to form a solid ZrAl3 / Al2O3 framework, providing temporary support for the gas film pores. Yttrium oxide reacts with aluminum to form a YAlO3 self-healing oxide layer, which covers the pore walls of the gas film pores and has self-healing capabilities at high temperatures, filling microcracks with a width of less than 5 μm. Nano-silicon carbide reacts with aluminum at high temperatures to form Al4C3, which is then removed by acid etching, forming secondary micropores (0.5~5 μm). These secondary micropores enhance the gas film cooling efficiency and reduce the boundary layer temperature gradient. At the same time, the nano-silicon carbide is uniformly dispersed in the sacrificial column, improving the fracture toughness of the sacrificial column during casting.

[0035] The sacrificial column has a mortise at its bottom end that matches the tenon. The negative hole has two parallel surfaces, with one end's surface in contact with the inner wall of the casting shell. One end forms a closed space with the casting shell, while the other end forms an open space, allowing the cast nickel-based single-crystal superalloy to fill from the lower end of the negative hole and stop at the higher end. The nickel-based single-crystal superalloy within the negative hole triggers a chemical reaction with the sacrificial column. The sacrificial column and negative hole employ a specific structure to allow the nickel-based single-crystal superalloy to enter the sacrificial column through the negative hole and trigger the reaction, providing conditions for the subsequent formation of a solid ZrAl3 / Al2O3 framework as temporary support for the gas film pores. The specific dimensions of the negative hole are set according to actual conditions, ensuring that one end contacts the casting shell while the other end does not.

[0036] On the one hand, a mortise and tenon structure, formed by micron-level tenons and mortises between the main body layer and the sacrificial column, serves as a positioning benchmark, ensuring that the sacrificial column and the tenon are coaxial. This prevents core displacement during casting, which could lead to deviations in the final integrally formed air film hole position and reduce the accuracy of the air film hole. On the other hand, it increases the interfacial shear strength between the sacrificial column and the main body layer, preventing cracking at the connection. The specific dimensions of the tenons and mortises are set according to actual needs and will not be elaborated further here; please refer to [reference needed]. Figure 3 .

[0037] At a rotation speed of 3000 rpm, sacrificial pillars are spin-coated to the required thickness over the tenons formed on the surface of the main body preform. After spin-coating, before the sacrificial pillar slurry cures, nanoimprinting is performed. The imprinting template is a single-crystal silicon or nickel-based alloy with an etched hole array on the surface. The imprinting pressure is 5-10 MPa, the vacuum degree is ≤10⁻³ Pa, and the holding time is 3-5 minutes. This ensures high-precision imprinting by the imprinting template, preventing difficulties in high-precision imprinting after the sacrificial pillars have cured.

[0038] After nanoimprinting, the core preform is obtained by thermosetting at 80℃ for 10 minutes and UV curing at 365nm wavelength and 50mW / cm² power for 2 minutes.

[0039] At this point, the core blank still needs to undergo gradient sintering. Through precise control of temperature, time, and atmosphere (argon), the physical-chemical synergistic combination between the main layer and the sacrificial layer is achieved, ensuring the structural stability and functional reliability of the core in a high-temperature casting environment.

[0040] The specific steps are as follows: 1) Degreasing treatment: Heat to 600℃ at 5℃ / min and hold for 1 hour to remove organic binders (such as polyvinyl butyral and polyethylene glycol) from the sacrificial column. 2) Pre-sintering treatment: Heat to 1200℃ at 3℃ / min and hold for 30 minutes to promote the densification of ceramic particles; 3) Gradient sintering treatment: The temperature is increased to 1450℃ at 1℃ / min and held for 2 hours to form an Al2O3-ZrO2-SiC transition layer between the main layer and the sacrificial pillar, realizing interfacial diffusion; the zirconium oxide generated by the decomposition of zirconium silicate reacts with alumina to form ZrAl2O5 spinel phase, which strengthens the interfacial bonding; at the same time, the tenon and mortise structure ensures a high-strength connection and functional transfer between the main layer and the sacrificial pillar.

[0041] More preferably, in step S2, the casting shell is provided with multiple exhaust microchannels, and the inlet and outlet of the exhaust microchannels are located on the inner wall and outer wall of the casting shell, respectively. The inlet aperture of the exhaust microchannel is 20 μm; the aperture of the exhaust microchannel is 50 μm.

[0042] The main purpose of setting up exhaust microchannels is to allow the gaseous SiO2 generated by the reaction of aluminum and zirconium silicate during the casting process of nickel-based single crystal superalloys to escape quickly through the Bernoulli effect, thereby reducing the back pressure inside the casting shell, avoiding insufficient filling of molten metal, ensuring the rapid discharge of this gas, and preventing gas film porosity defects. At the same time, it guides the cooling airflow to be evenly distributed, reduces the temperature gradient on the blade surface, and reduces thermal stress.

[0043] Specifically, the exhaust microchannels are tapered, with the length of the channel matching the thickness of the casting shell, and the distribution density set according to actual conditions. A nano-coating (such as Al2O3) is used to reduce the surface energy of the exhaust microchannels, prevent the nickel-based single-crystal high-temperature alloy from wetting, and avoid impacting the exhaust microchannels, ultimately having no negative impact on the casting of the hollow turbine blades.

[0044] In step S3, the process parameters for directional solidification are: temperature gradient ≥100℃ / cm, pulling rate 2~5mm / min; the molten alloy is a nickel-based single crystal high-temperature alloy containing 2.5~3.5wt% aluminum, and the casting superheat ΔT=100-150℃.

[0045] Directional solidification ensures optimal grain growth along the heat flow direction; controls grain size and microstructure uniformity; achieves high temperature gradients; ensures the fluidity of nickel-based single-crystal superalloys; and reduces casting defects.

[0046] The thermal activation includes: zirconium silicate in the sacrificial column reacts with aluminum in the nickel-based single-crystal superalloy to generate gaseous SiO2 and solid ZrAl3 / Al2O3 framework; the nickel-based single-crystal superalloy enters the negative hole, and yttrium oxide reacts with aluminum to generate a YAlO3 self-healing oxide layer with a thickness of 0.5~2μm.

[0047] The chemical reactions that occur during thermal activation are as follows: ZrSiO4 + 3Al → ZrAl3 + SiO2↑ + Al2O3; the generated gaseous SiO2 escapes directionally through the exhaust microchannels of the cast shell.

[0048] Y2O3 + 2Al → 2YAlO3. The YAlO3 self-healing oxide layer covers the pore walls of the gas film pores and has self-healing ability at high temperatures, which can fill microcracks with a width of less than 5μm.

[0049] Further, in step S4, the chemical etching includes the following steps: S41, hydrofluoric acid vapor etching: 20-30% by mass, temperature 80℃, time less than 4 hours. The corrosion depth is monitored in real time during etching, and samples are taken every 30 minutes for testing. The allowable loss is ≤2μm. Low-concentration hydrofluoric acid vapor is used instead of liquid hydrofluoric acid to selectively etch the alumina support layer in the main body layer, reducing the contact area with the hollow turbine blades, while retaining the YAlO3 self-healing oxide layer as a functional layer. Corrosion inhibitors can be added during the etching process to slow the corrosion rate of the hollow turbine blades.

[0050] S41, hydrochloric acid ultrasonic cleaning: molar mass 3~5mol / L, ultrasonic frequency 40kHz, power 300W, time 1~2h, to accelerate the diffusion of reactants and shorten the treatment time; after rinsing with deionized water, it is dried with nitrogen (pressure 0.2MPa, temperature 60℃), the corrosion depth is <0.5μm, which does not affect the wall thickness tolerance of hollow turbine blades (±10μm), the purpose is to dissolve the ZrAl3 skeleton.

[0051] The post-processing includes the following steps: S42, nitric acid passivation treatment: 30% by mass, 50℃, 10 min, with gentle stirring (50 rpm) to ensure uniform passivation, followed by rinsing with deionized water and drying with nitrogen to rebuild the Cr2O3 protective film.

[0052] S43, Vacuum Annealing: Vacuum degree ≤10⁻³ Pa, heat to 1000℃ at a rate of 5℃ / min, hold for 2h; cool to room temperature at a rate of 3℃ / min to promote further densification of the YAlO3 oxide layer; place titanium powder in the vacuum furnace to adsorb residual oxygen.

[0053] Comparative Example 1 This comparative example uses a core and shell with film-forming holes to prepare hollow turbine blades, and the specific components of the core and shell are aluminum oxide.

[0054] Table 1 Performance comparison data of hollow turbine blades prepared in this application and Comparative Example 1 Comparative Example 2 In this comparative example, hollow turbine blades were fabricated without the use of mortise and tenon structures between the main body layer and the sacrificial column.

[0055] Table 2 Performance comparison data of hollow turbine blades prepared in this application and Comparative Example 2 Comparative Example 3 In this comparative example, hollow turbine blades were prepared without using gradient sintering after nanoimprinting.

[0056] Table 3 Performance comparison data of hollow turbine blades prepared in this application and Comparative Example 3 Comparative Example 4 In this comparative example, hollow turbine blades were prepared without exhaust microchannels inside the cast mold.

[0057] Table 4 Performance comparison data of hollow turbine blades prepared in this application and Comparative Example 4 According to Tables 1-4, the hollow turbine blade with film pores prepared in this application, based on an alumina-based main body layer and a core formed by sacrificial pillars composed of zirconium silicate and yttrium oxide, is connected by a tenon and mortise structure, subjected to gradient sintering, and equipped with exhaust microchannels in the shell, exhibits significantly higher performance than comparative examples 1 to 4.

[0058] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for integrally casting a hollow turbine blade with air film holes, characterized in that: The following steps are involved: S1, preparing a gradient ceramic core: the core comprises an alumina-based main body layer and a sacrificial column composed of zirconium silicate and yttrium oxide, and the surface of the sacrificial column is pre-set with negative holes by nanoimprinting technology; S2, embedding the gradient ceramic core into a wax mold and coating it with multiple layers of ceramics, and obtaining a casting shell after dewaxing and pre-firing; S3, pouring a nickel-based single crystal high-temperature alloy between the casting shell and the gradient ceramic core, etching the sacrificial column by thermal activation during the directional solidification stage, and simultaneously producing the air film pores and the self-repairing layer located on the pore walls of the air film pores; S4, chemically etching and post-processing the gradient ceramic and the hollow turbine blade to obtain a hollow turbine blade with air film holes.

2. The method for integrally casting a hollow turbine blade with air film holes according to claim 1, characterized in that: In terms of weight percentage, the alumina-based main body layer is composed of 80-85wt% alumina, 7-13% zirconium oxide, and 2-8wt% silica sol, which are mixed to form a main body layer slurry, and the main body layer slurry is injected into a light-curing 3D printer to obtain a main body layer embryo.

3. The method for integrally casting a hollow turbine blade with air film holes according to claim 2, characterized in that: The sacrificial column is composed of 90-95wt% zirconium silicate, 3-8wt% yttrium oxide, and 2-5wt% nano-silicon carbide, which are mixed to form a sacrificial column slurry; the sacrificial column slurry is spin-coated on the tenon protruding outward from the main layer embryo body and subjected to nano-imprinting technology, and then thermally cured and UV cured to obtain a core embryo body.

4. The method for integrally casting a hollow turbine blade with air film holes according to claim 3, characterized in that: The bottom end of the sacrificial column is provided with a tenon groove matched with the tenon.

5. The method for integrally casting a hollow turbine blade with air film holes according to claim 3, characterized in that: The two ends of the negative mold hole are located in two parallel planes and the surface of one end is in contact with the inner wall of the casting shell.

6. The method for integrally casting a hollow turbine blade with air film holes according to claim 3, characterized in that: During nanoimprinting, the imprint template is a single crystal silicon or nickel-based alloy with an array of holes etched on the surface. The imprinting pressure is 5-10MPa, the vacuum degree is ≤10⁻³ Pa, and the pressure holding time is 3~5 minutes.

7. The method for integrally casting a hollow turbine blade with air film holes according to claim 3, characterized in that: In step S2, the casting shell is provided with a plurality of exhaust microchannels, and the inlet and outlet of the exhaust microchannels are respectively located on the inner wall and the outer wall of the casting shell; The pore size of the exhaust microchannel inlet is 20 μm; the pore size of the exhaust microchannel is 50 μm.

8. The method for integrally casting a hollow turbine blade with air film holes according to claim 3, characterized in that: In step S3, the process parameters of the directional solidification are: temperature gradient ≥ 100°C / cm, pulling rate 2-5mm / min; the molten alloy is a nickel-based single crystal high-temperature alloy containing 2.5-3.5wt% aluminum, and the pouring superheat ΔT=100-150°C.

9. The method for integrally casting a hollow turbine blade with air film holes according to claim 3, characterized in that: The thermal activation includes: the zirconium silicate in the sacrificial column reacts with the aluminum in the nickel-based single crystal high-temperature alloy to generate gaseous SiO2 and a solid ZrAl3 / Al2O3 skeleton; and the yttrium oxide reacts with the aluminum to generate a YAlO3 self-repairing oxide layer.

10. The method for integrally casting a hollow turbine blade with air film holes according to claim 3, characterized in that: In step S4, the chemical etching comprises the following steps: S41, hydrofluoric acid vapor etching: mass percentage 20-30%, temperature 80°C, time less than 4h; S41, hydrochloric acid ultrasonic cleaning: molar mass 3~5mol / L, ultrasonic frequency 40kHz, time 1~2h; The post-processing comprises the following steps: S42, nitric acid passivation treatment: mass percentage 30%, temperature 50°C, time 10 min; S43, vacuum annealing: vacuum degree ≤10⁻³Pa, heating to 1000℃ at a rate of 5℃ / min, keeping at that temperature for 2h; cooling to room temperature at a rate of 3℃ / min.

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