An integrated casting method for a hollow turbine blade with air film holes

Abstract

This application relates to the technical field of aviation engine turbine blade casting, and specifically relates to an integrated casting method for a hollow turbine blade with air film holes. By using a core formed based on an alumina-based main body layer and sacrificial columns composed of zirconium silicate and yttrium oxide, a mortise and tenon structure is used for connection between the two, nanoimprinting is used to form negative holes, gradient sintering treatment is carried out, and exhaust microchannels are provided in the mold shell. During the pouring process, air film holes and a self-healing layer located on the pore wall of the air film holes are synchronously produced, and chemical etching and post-treatment are used to make the finally prepared hollow turbine blade have high-precision air films, high cooling effects, interface bonding strength, and thermal cycle life, shorten the processing cycle, and enable self-healing of pore wall cracks.

Description

Technical Field

[0001] The present application relates to the technical field of casting technology for aeroengine turbine blades, and particularly relates to an integrated casting method for a hollow turbine blade with film holes. Background Art

[0002] Turbine blades are important components in the turbine section of a gas turbine engine. The high-speed rotating blades are responsible for sucking high-temperature and high-pressure airflows into the combustor to maintain the operation of the engine.

[0003] Currently, hollow turbine blades with film holes are mainly manufactured by casting. The mold for the turbine blade includes a core and a shell. The molten metal for manufacturing the hollow turbine blade is poured, and after cooling and solidifying, the core and the shell are removed to obtain the hollow turbine blade. Then, laser / electrical discharge machining is used to drill holes on the surface of the hollow turbine blade, resulting in microcracks on the hole wall, reducing the high-temperature fatigue life and affecting the film cooling effect. At the same time, the aperture error of laser / electrical discharge machining is ±20μm, which is relatively large and cannot meet the precision requirements of the film holes; at the same time, the drilling efficiency is low, the processing cycle is long, and the manufacturing cost is increased.

[0004] CN112916811B, a casting method for a hollow turbine blade with film holes, discloses directly forming film holes during the casting process. The composition of the hole wall of the film hole is consistent with that of the main part of the hollow turbine blade. During the operation of the gas turbine engine, microcracks are likely to occur on the hole wall, affecting the film cooling effect.

[0005] Based on this, an integrated casting method for a hollow turbine blade with film holes and improved performance is proposed. Summary of the Invention

[0006] The purpose of the present invention is to provide an integrated casting method for a hollow turbine blade with film holes, which does not require subsequent processing of the film holes, improves the precision of the film holes and the performance of the blade, and solves the problems raised in the prior art.

[0007] To solve the above technical problems, the present invention adopts the following solutions:

[0008] An integrated casting method for a hollow turbine blade with film holes, comprising the following steps:

[0009] S1, preparing a gradient ceramic core: the core includes an alumina-based main layer and sacrificial columns, and negative-type holes are pre-set on the surface of the sacrificial columns by nanoimprinting technology; the sacrificial columns are composed of 90-95wt% zirconium silicate, 3-8wt% yttrium oxide, and 2-5wt% nano-silicon carbide, and are mixed to form a sacrificial column slurry;

[0010] S2, embedding the gradient ceramic core into a wax mold and coating multiple layers of ceramics, and obtaining a casting shell after dewaxing and pre-firing;

[0011] S3. Pour a nickel-based single-crystal superalloy between the investment casting shell and the gradient ceramic core, and etch the sacrificial posts through thermal activation during the directional solidification stage to simultaneously produce air film holes and a self-healing layer on the pore walls of the air film holes;

[0012] S4. Chemically etch and post-treat the gradient ceramic and the hollow turbine blade to obtain a hollow turbine blade with air film holes.

[0013] Further, by weight percentage, the alumina-based main layer is composed of 80-85 wt% alumina, 7-13% zirconia, and 2-8 wt% silica sol, which are mixed to form a main layer slurry. The main layer slurry is injected into a photocuring 3D printer to obtain a main layer embryo.

[0014] Further, spin-coat the sacrificial post slurry on the tenons protruding outward from the main layer embryo and use nanoimprint technology, and then obtain a core embryo after thermal curing and UV curing.

[0015] Further, a mortise groove adapted to the tenon is provided at the bottom end of the sacrificial post.

[0016] Further, both ends of the negative-type hole are in two parallel planes and the surface of one end is in contact with the inner wall of the investment casting shell.

[0017] Further, during nanoimprinting, the imprint template is single-crystalline 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 pressure holding time is 3-5 minutes.

[0018] Further, in step S2, the investment casting shell is provided with a plurality of exhaust microchannels, and the inlets and outlets of the exhaust microchannels are respectively located on the inner wall and the outer wall of the investment casting shell;

[0019] The aperture of the inlet of the exhaust microchannel is 20 μm; the aperture of the exhaust microchannel is 50 μm.

[0020] Further, in step S3, the process parameters of the directional solidification are: the temperature gradient ≥100 °C / cm, the pulling rate is 2-5 mm / min; the molten alloy is a nickel-based single-crystalline superalloy containing 2.5-3.5 wt% aluminum, and the pouring superheat ΔT = 100-150 °C.

[0021] Further, the thermal activation includes: zirconium silicate in the sacrificial post reacts with aluminum in the nickel-based single-crystalline superalloy to generate gaseous SiO 2 and solid ZrAl 3 / Al 2 O 3 skeleton; yttrium oxide reacts with aluminum to generate YAlO 3 self-healing oxide layer.

[0022] Further, in step S4, the chemical etching includes the following steps:

[0023] S41, etching with hydrofluoric acid vapor: mass percentage 20 - 30%, temperature 80 °C, time less than 4 h;

[0024] S41, ultrasonic cleaning with hydrochloric acid: molar mass 3 - 5 mol / L, ultrasonic frequency 40 kHz, time 1 - 2 h;

[0025] The post - treatment includes the following steps:

[0026] S42, passivation treatment with nitric acid: mass percentage 30%, temperature 50 °C, time 10 min;

[0027] S43, vacuum annealing: vacuum degree ≤ 10⁻³ Pa, heating to 1000 °C at a rate of 5 °C / min, holding for 2 h; cooling to room temperature at a rate of 3 °C / min.

[0028] The beneficial effects of the present invention are as follows:

[0029] In the present invention, through the core formed based on the alumina - based main layer and the sacrificial posts, the sacrificial posts are composed of 90 - 95 wt% zirconium silicate, 3 - 8 wt% yttrium oxide, and 2 - 5 wt% nano - silicon carbide, and the sacrificial post slurry is formed by mixing; the connection between the two adopts a mortise - and - tenon structure, nano - imprinting to form a negative - type hole, gradient sintering treatment, and exhaust micro - channels are provided in the mold shell. During the pouring process, gas film holes and a self - repair layer located on the pore wall of the gas film holes are synchronously produced, and chemical etching and post - treatment are used, so that the finally prepared hollow turbine blade has high - precision gas film holes, efficient cooling, interface bonding strength ≥ 25 MPa, the thermal cycle life is increased by 5 times, the processing cycle is shortened, and at the same time, the micro - cracks on the pore wall are repaired under the self - repair oxide layer of YAlO 3 to extend the service life. Description of the Drawings

[0030] Figure 1 is the process flow chart of the casting method of the present invention;

[0031] Figure 2 is the structural schematic diagram of the core and the casting mold shell of the present invention;

[0032] Figure 3 is Figure 1 the partial enlarged structural schematic diagram of circle A in

[0033] Reference numerals: 1 - core, 10 - main layer, 100 - tenon, 11 - sacrificial post, 110 - mortise, 111 - negative - type hole, 2 - mold shell, 20 - exhaust micro - channel. Detailed Embodiments

[0034] 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 in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the described embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0035] Unless otherwise specifically stated, the relative arrangements, numerical expressions, and numerical values of the components and steps set forth in these embodiments do not limit the scope of the present invention.

[0036] Meanwhile, it should be understood that, for the sake of convenience of description, the dimensions of the various parts shown in the drawings are not drawn in actual proportional relationships.

[0037] In addition, for the sake of clarity and conciseness, the descriptions of well-known structures, functions, and configurations may be omitted. Those of ordinary skill 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 the present disclosure.

[0038] The techniques, methods, and devices known to those of ordinary skill in the relevant art may not be discussed in detail, but where appropriate, the said techniques, methods, and devices should be regarded as part of the authorization specification.

[0039] In all the examples shown and discussed here, any specific value should be construed as merely exemplary and not as a limitation. Therefore, other examples of the exemplary embodiments may have different values.

[0040] Embodiment 1

[0041] Embodiment 1 of the present application is an integrated casting method for a hollow turbine blade with air film holes. Referring to Figure 1 and Figure 2 , the method includes the following steps:

[0042] S1. Prepare a gradient ceramic core: The core includes an alumina-based main body layer and sacrificial columns. Negative holes are pre-set on the surface of the sacrificial columns by nanoimprinting technology; the sacrificial columns are composed of 90-95 wt% zirconium silicate, 3-8 wt% yttrium oxide, and 2-5 wt% nano silicon carbide, and are mixed to form a sacrificial column slurry.

[0043] S2. Embed the gradient ceramic core into a wax mold and coat it with multiple layers of ceramics. After dewaxing and pre-firing, a casting shell is obtained.

[0044] S3. Pour a nickel-based single crystal superalloy between the investment casting shell and the gradient ceramic core. During the directional solidification stage, etch the sacrificial posts through thermal activation to synchronously produce air film holes and a self-repairing layer on the pore walls of the air film holes.

[0045] S4. Chemically etch and post-process the gradient ceramic and the hollow turbine blade to obtain a hollow turbine blade with air film holes.

[0046] Currently, the existing casting processes mainly use molds composed of cores and shells to pour and prepare hollow turbine blades from superalloys. Use 3D modeling software in the existing technology to directly establish 3D models of the cores and shells of hollow turbine blades with air film holes, so that the main part and the air film hole part of the cast hollow turbine blade are consistent with the required dimensions. The 3D modeling software includes: Magics software, Unigraphics NX software, CATIA software, Pro / Engineer software, SolidWorks software, etc.

[0047] By prefabricating a gradient ceramic core and an investment casting shell, the alumina-based main layer and the sacrificial posts respectively form the main part and the air film hole part of the hollow turbine blade. When casting the air film holes, directional solidification mainly occurs during the pouring process of the nickel-based single crystal superalloy. Directional solidification mainly uses the heat of the molten alloy metal to activate the components in the sacrificial posts to chemically react with the aluminum components in the nickel-based single crystal superalloy, so that the chemical components in the sacrificial posts dissolve and form air film holes and a self-repairing layer, while retaining the support structure of the alumina-based main layer. The specific chemical reaction is: the aluminum component reacts with zirconium silicate in the sacrificial post to generate gaseous silicon dioxide and solid ZrAl 3 / Al 2 O 3 skeleton, which constitutes the basic pore frame structure of the air film hole; at the same time, the aluminum component reacts with yttrium oxide to generate YAlO 3 self-repairing oxide layer to achieve self-repair of the pore walls in the air film holes. After continuing to remove the shell, chemically etch the core, solid ZrAl 3 / Al 2 O 3 skeleton for removal; use post-processing to form a protective film on the main part of the hollow turbine blade respectively, and densify the YAlO 3 self-repairing oxide layer inside the pore walls of the air film holes.

[0048] Based on the specific structures of the core and the shell mold and the sacrificial posts made of specific components, this application enables the integrated formation of gas film holes during the casting process. Meanwhile, a self-repairing oxide layer is formed within the pore walls of the formed gas film holes, preventing oxygen penetration, enhancing the high-temperature oxidation resistance, thermal corrosion resistance, and the repair of microcrack propagation of the gas film holes, and extending the service life of the hollow turbine blade. There is no need to perform external machining on the surface of the cast hollow turbine blade again to punch holes, thus reducing the precision requirements for the gas film holes.

[0049] Among them, by weight percentage, the alumina-based main layer is composed of 80 - 85 wt% alumina, 7 - 13% zirconia, and 2 - 8 wt% silica sol. They are mixed to form the main layer slurry, and the main layer slurry is injected into a stereolithography 3D printer to obtain the main layer embryo.

[0050] The viscosity of the main layer slurry is 3000 - 5000 mPas at room temperature. Under the conditions of an ultraviolet light wavelength of 405 nm and a power of 80 mW / cm², a support skeleton for the inner cavity of the hollow turbine blade is printed, and an assembly interface for the sacrificial posts, i.e., a tenon, is reserved on the surface of the main layer. The support skeleton here can be a solid structure or a honeycomb hollow structure to facilitate the subsequent removal of the core.

[0051] Alumina mainly provides the strength of the core body, withstands the impact force during the pouring of nickel-based single-crystal superalloy, and ensures no deformation at high temperatures; zirconia enhances the crack resistance and the fracture toughness of the core through the transformation toughening mechanism. At the same time, the thermal expansion coefficient of zirconia is between that of alumina and zirconium silicate in the sacrificial posts, forming a gradient transition, reducing the interfacial thermal stress, and enhancing the interfacial bonding strength. Among them, silica sol is mainly silicon dioxide, which has good fluidity. When combined with the stereolithography 3D printing process, it ensures the precision during the forming of the core and meets the requirements for the integrated casting of gas film holes.

[0052] The sacrificial post slurry is spin-coated on the tenon protruding from the main layer embryo and then processed by nanoimprint technology, and then thermally cured and UV cured to obtain the core embryo.

[0053] Among them, the zirconium silicate contained in the sacrificial post reacts with aluminum to generate a solid ZrAl 3 / Al 2 O 3 skeleton, providing a temporary supporting effect for the gas film holes; yttrium oxide reacts with aluminum to generate YAlO 3 self-repairing oxide layer, covering the pore walls of the gas film holes, having self-repairing ability at high temperatures, and capable of filling microcracks with a width less than 5 μm; nano silicon carbide reacts with aluminum at high temperatures to generate Al 4 C 3, and then removed by acid etching to form secondary micropores (0.5 - 5 μm). The secondary micropores enhance the gas film cooling efficiency and reduce the boundary layer temperature gradient. At the same time, nano - silicon carbide is uniformly dispersed in the sacrificial posts, improving the fracture toughness during the casting of the sacrificial posts.

[0054] A mortise groove adapted to the tenon is provided at the bottom end of the sacrificial post. The two ends of the negative - type hole are in two parallel planes, and the surface of one end is in contact with the inner wall of the investment shell. One end forms a closed space with the investment shell, and the other end forms an open space, enabling the nickel - based single - crystal superalloy for pouring to fill from the negative - type hole with a lower height and stop at the end of the negative - type hole with a higher height. The nickel - based single - crystal superalloy in the negative - type hole triggers a chemical reaction with the sacrificial post. The sacrificial post and the negative - type hole adopt a specific structure to allow the nickel - based single - crystal superalloy to enter the sacrificial post through the negative - type hole and trigger a reaction, for the subsequent formation of the solid - state ZrAl 3 / Al 2 O 3 skeleton to provide conditions for the temporary support of the gas film holes. The specific specifications of the negative - type hole here are set according to the actual situation, ensuring that one end is in contact with the investment shell and the other end is not.

[0055] On the one hand, a mortise - tenon structure formed by setting micron - level tenons and mortise grooves between the main body layer and the sacrificial post is used as a positioning reference to ensure the coaxiality of the sacrificial post and the tenon, thereby preventing the displacement of the core during the pouring process, which may cause deviation in the position of the finally integrally formed gas film holes and avoid the reduction of the gas film hole accuracy. On the other hand, it improves the interfacial shear strength between the sacrificial post and the main body layer, preventing cracking at the connection between the two. The specific dimensions of the tenon and the mortise groove are set according to actual requirements and will not be elaborated here. Refer to Figure 3 .

[0056] Under the condition of a rotational speed of 3000 rpm, the sacrificial post is spin - coated above the tenon formed on the surface of the main body layer embryo to the required thickness. After spin - coating, before the sacrificial post slurry solidifies, nano - imprinting is carried out. 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 pressure - holding time is 3 - 5 minutes. Ensure that the imprinting template achieves high - precision imprinting to prevent difficult high - precision imprinting after the sacrificial post solidifies.

[0057] After nano - imprinting, through thermal curing at 80 °C for 10 min and UV curing at a wavelength of 365 nm and a power of 50 mW / cm² for 2 min, the core embryo is obtained.

[0058] At this time, the core embryo still needs to undergo gradient sintering. Through precise control of temperature, time, and atmosphere (argon gas), physical - chemical synergistic bonding between the main body layer and the sacrificial layer is achieved, ensuring the structural stability and functional reliability of the core in a high - temperature casting environment.

[0059] The specific steps are as follows:

[0060] 1) Degreasing treatment: Heat up to 600 °C at a rate of 5 °C / min and hold for 1 hour to remove the organic binders (such as polyvinyl butyral and polyethylene glycol, etc.) in the sacrificial columns;

[0061] 2) Pre-sintering treatment: Heat up to 1200 °C at a rate of 3 °C / min and hold for 30 minutes to promote the densification of ceramic particles;

[0062] 3) Gradient sintering treatment: Heat up to 1450 °C at a rate of 1 °C / min and hold for 2 hours to form an Al 2 O 3 -ZrO 2 -SiC transition layer between the main body layer and the sacrificial columns to achieve interfacial diffusion; The zirconia generated by the decomposition of zirconium silicate reacts with alumina to generate ZrAl 2 O 5 spinel phase to strengthen the interfacial bonding; At the same time, through the mortise and tenon structure, ensure the high-strength connection and function transfer between the main body layer and the sacrificial columns.

[0063] Further preferably, in step S2, the investment shell is provided with a plurality of exhaust micro-channels, and the inlets and outlets of the exhaust micro-channels are respectively located on the inner wall and the outer wall of the investment shell;

[0064] The aperture of the inlet of the exhaust micro-channel is 20 μm; The aperture of the exhaust micro-channel is 50 μm.

[0065] Setting the exhaust micro-channels mainly enables the gaseous SiO 2 generated by the reaction of aluminum and zirconium silicate during the casting of nickel-based single-crystal superalloy to escape. The exhaust micro-channels accelerate the gas escape through the Bernoulli effect, reduce the back pressure inside the investment shell, avoid insufficient filling of the molten metal, ensure the rapid discharge of this gas, and prevent the defect of gas film holes; At the same time, guide the cooling air flow to be evenly distributed, reduce the surface temperature gradient of the blade, and reduce the thermal stress.

[0066] Specifically, the exhaust micro-channels are in a conical structure, the length of the channels is the same as the thickness of the investment shell, and the distribution density is set according to the actual situation; Use a nano-coating (such as Al 2 O 3 ) to reduce the surface energy of the exhaust micro-channels, prevent the nickel-based single-crystal superalloy from wetting and avoid impacting the exhaust micro-channels, and finally will not have a negative impact on the casting of the hollow turbine blade.

[0067] In step S3, the process parameters of the directional solidification are: temperature gradient ≥ 100 °C / cm, pulling rate 2 - 5 mm / min; The molten alloy is a nickel-based single-crystal superalloy containing 2.5 - 3.5 wt% aluminum, and the pouring superheat ΔT = 100 - 150 °C.

[0068] Directional solidification ensures that grains preferentially grow along the heat flow direction; controls grain size and tissue uniformity; achieves a high temperature gradient; ensures the fluidity of nickel-based single crystal superalloys and reduces casting defects.

[0069] The thermal activation includes: zirconium silicate in the sacrificial column reacts with aluminum in the nickel-based single crystal superalloy to generate gaseous SiO 2 and solid ZrAl 3 / Al 2 O 3 skeleton; the nickel-based single crystal superalloy enters the negative mold hole, and yttrium oxide reacts with aluminum to generate YAlO 3 self-healing oxide layer with a thickness of 0.5 - 2 μm.

[0070] In the thermal activation, the chemical reactions that occur are as follows:

[0071] ZrSiO 4 +3Al → ZrAl 3 +SiO 2 ↑ + Al 2 O 3 ; the generated gaseous SiO 2 is directionally escaped through the exhaust microchannels of the casting shell.

[0072] Y 2 O 3 +2Al → 2YAlO 3 , YAlO 3 The self-healing oxide layer covers the pore walls of the gas film holes and has self-healing ability at high temperatures, and can fill microcracks with a width less than 5 μm.

[0073] Furthermore, in step S4, the chemical etching includes the following steps:

[0074] S41, hydrofluoric acid vapor etching: mass percentage 20 - 30%, temperature 80 °C, time less than 4 h. During the etching process, the corrosion depth is monitored in real time and samples are taken for detection every 30 min. The allowable loss ≤ 2 μm. Using low-concentration hydrofluoric acid vapor to replace liquid hydrofluoric acid, selectively etching the alumina in the main layer as the support layer and reducing the contact area with the hollow turbine blade, and retaining the YAlO 3 self-healing oxide layer as the functional layer. A corrosion inhibitor can be added during the etching process to relieve the corrosion rate of the hollow turbine blade.

[0075] S41, Hydrochloric acid ultrasonic cleaning: molar mass 3 - 5 mol / L, ultrasonic frequency 40 kHz, power 300 W, time 1 - 2 h, accelerating the diffusion of reactants and shortening the treatment time; after rinsing with deionized water, drying with nitrogen (pressure 0.2 MPa, temperature 60 °C), the corrosion depth < 0.5 μm, not affecting the wall thickness tolerance of the hollow turbine blade (±10 μm), aiming to dissolve the ZrAl 3 skeleton.

[0076] The post - treatment includes the following steps:

[0077] S42, Nitric acid passivation treatment: mass percentage 30%, temperature 50 °C, time 10 min, gently stirring (rotation speed 50 rpm) to ensure uniform passivation, then rinsing with deionized water and drying with nitrogen, reconstructing the Cr 2 O 3 protective film.

[0078] S43, Vacuum annealing: vacuum degree ≤ 10⁻³ Pa, heating to 1000 °C at a rate of 5 °C / min and holding for 2 h; cooling to room temperature at a rate of 3 °C / min, promoting the further densification of the YAlO 3 oxide layer; placing titanium powder in the vacuum furnace to adsorb residual oxygen.

[0079] Comparative Example 1

[0080] This comparative example uses a core and shell with gas film holes to prepare hollow turbine blades, and the specific components of the core and shell are alumina.

[0081] Table 1 Performance comparison data table of the hollow turbine blades prepared in this application and Comparative Example 1

[0082]

[0083] Comparative Example 2

[0084] This comparative example prepares hollow turbine blades without using a mortise - and - tenon structure between the main layer and the sacrificial columns.

[0085] Table 2 Performance comparison data table of the hollow turbine blades prepared in this application and Comparative Example 2

[0086]

[0087] Comparative Example 3

[0088] This comparative example prepares hollow turbine blades without using a gradient sintering process after nano - imprinting.

[0089] Table 3 Performance comparison data table of the hollow turbine blades prepared in this application and Comparative Example 3

[0090]

[0091] Comparative Example 4

[0092] In this comparative example, a hollow turbine blade was prepared without arranging an exhaust microchannel in the investment shell mold.

[0093] Table 4 Performance comparison data table of the hollow turbine blades prepared in this application and Comparative Example 4

[0094]

[0095] It can be concluded from Tables 1 - 4 that for the core formed by the alumina-based main layer and sacrificial columns in this application, the sacrificial columns are composed of 90 - 95 wt% zirconium silicate, 3 - 8 wt% yttrium oxide, and 2 - 5 wt% nano silicon carbide, and are mixed to form a sacrificial column slurry; the two are connected by a mortise and tenon structure, gradient sintering treatment is carried out, and exhaust microchannels are arranged in the shell mold. Finally, the performance of the hollow turbine blade with air film holes prepared is significantly higher than that of Comparative Examples 1 to 4.

[0096] The above are only preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to the above-disclosed technical content to be equivalent change equivalent embodiments within the scope of the technical solution of the present invention. However, as long as it does not depart from the technical solution of the present invention, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention still fall within the scope of the technical solution 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, and a 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; The alumina-based main body layer is composed of 80-85wt% alumina, 7-13% zirconium oxide, and 2-8wt% silica sol by weight, 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; 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-imprint technology, and then thermally cured and UV cured to obtain a core embryo body; 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, one end and the casting shell form a closed space, and the other end forms an open space; In step S2, the casting shell is provided with a plurality of exhaust microchannels, the inlet and outlet of the exhaust microchannels are respectively located on the inner wall and the outer wall of the casting shell; the aperture of the inlet of the exhaust microchannel is 20 μm; the aperture of the exhaust microchannel is 50 μm; 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; 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.

2. The method for integrally casting a hollow turbine blade with air film holes according to claim 1, characterized in that: The bottom end of the sacrificial column is provided with a tenon groove matched with the tenon.

3. The method for integrally casting a hollow turbine blade with air film holes according to claim 1, 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.

4. The method for integrally casting a hollow turbine blade with air film holes according to claim 1, 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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