Preparation method for accurately controlling secondary orientation of single-crystal high-temperature alloy bicrystal plate

Abstract

The invention relates to the technical field of high-temperature alloy investment precision casting, and discloses a preparation method for accurately controlling the secondary orientation of a single-crystal high-temperature alloy bicrystal plate, which comprises the following steps: cutting two cylindrical seed crystals from a complete single-crystal test bar, and grinding and polishing the surfaces of the two cylindrical seed crystals; pressing a plurality of simple wax molds in a wax injection press, and combining and connecting the plurality of simple wax molds with the cylindrical seed crystals to obtain a double-crystal plate module structure; after coating, sand hanging and drying are conducted on the bicrystal plate module structure, dewaxing and roasting are conducted, and a bicrystal plate module shell is obtained; carrying out a directional solidification process on the double-crystal-plate module shell to obtain a double-crystal-plate sample; and determining the small-angle grain boundary angle of the double-crystal plate sample after macroscopic corrosion. According to the method, the secondary orientation angle of the small-angle grain boundary in the nickel-based single-crystal high-temperature alloy twin-crystal plate can be accurately controlled, so that the influence of the small-angle grain boundary on the performance of the nickel-based single-crystal high-temperature alloy under a certain service condition can be quantitatively evaluated, and the qualification rate of the single-crystal high-temperature alloy blade is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of investment precision casting of superalloys, and particularly to a preparation method for precisely controlling the secondary orientation of a double crystal plate of a single crystal superalloy. Background Art

[0002] Nickel-based single crystal superalloys have excellent high-temperature strength, oxidation resistance and corrosion resistance, and are widely used as materials for advanced aeroengines. With the continuous increase in the demand for the thermal efficiency of aeroengines, the refractory elements in advanced single crystal alloys are continuously increasing and their geometric structures are becoming more complex, resulting in various casting defects that are difficult to avoid during the directional solidification of single crystal blades, especially small-angle grain boundary defects, which greatly increase the production cost of single crystal blades. Therefore, the industrial community often adds trace elements to improve the damage caused by small-angle grain boundaries to single crystal blades. How to quantitatively determine the allowable small-angle grain boundary angle of a certain alloy under a specific service condition has become a common topic of concern among researchers. In recent years, designing a double crystal plate with controllable secondary orientation to simulate the influence of small-angle grain boundaries on single crystal superalloys has become the main method for studying such problems.

[0003] Currently, the preparation of double crystal plates uses the method of post-placing the seed crystal and the method of prefabricating the seed crystal groove in the mold. The method of post-placing the seed crystal is to leave a space with corresponding size and position for the subsequent insertion of the seed crystal during the preparation of the double crystal plate wax mold. After the double crystal plate wax mold is prepared, the seed crystal is inserted and adjusted to the target secondary orientation angle by manual rotation, and then fixed with EC95 powder slurry. After drying, it can be poured to obtain the double crystal plate. However, there is a dimensional tolerance between the seed crystal and the reserved space in this method. During the pouring process, the molten metal flows into the surrounding of the seed crystal and nucleates rapidly due to rapid cooling, resulting in polycrystalline defects in the double crystal plate. In addition, there is a risk that the seed crystal will fall into the cavity during the installation process of the seed crystal, and the two seed crystals will rotate freely during the installation process of the casting shell, which will lead to the failure of the preparation of the double crystal plate. The method of prefabricating the seed crystal groove is to prepare several independent seed crystal inserts with fixed angles during the processing of the mold. During the preparation of the wax mold, different secondary orientation arrangements of the seed crystals are realized by replacing the seed crystal inserts, and then double crystal plates with different small-angle grain boundaries are prepared. The mold processing cost of this method is relatively high, the working efficiency is low, and due to the tolerance between the seed crystal insert and the mold, the matching accuracy between the double crystal plate and the seed crystal is reduced.

[0004] Therefore, it is urgent to develop a preparation method for precisely controlling the secondary orientation of a nickel-based single crystal superalloy double crystal plate to solve the problems existing in the prior art, which is of great significance for studying the small-angle grain boundary damage tolerance of nickel-based single crystal superalloys under a certain service condition. Summary of the Invention

[0005] The present invention provides a preparation method for precisely controlling the secondary orientation of a twin plate of a single crystal superalloy, which can precisely control the secondary orientation angle of the small-angle grain boundary in the twin plate of a nickel-based single crystal superalloy, so as to quantitatively evaluate the influence of the small-angle grain boundary on the performance of the nickel-based single crystal superalloy under a certain service condition, and has important guiding significance for improving the qualified rate of single crystal superalloy blades.

[0006] The present invention provides a preparation method for precisely controlling the secondary orientation of a twin plate of a single crystal superalloy, comprising:

[0007] S1. Using a wire electrical discharge machining (WEDM) machine in combination with a Laue single crystal diffractometer, cutting two cylindrical seeds with a deviation from the primary orientation direction of less than 3° from a complete single crystal test bar, polishing the surfaces of the two cylindrical seeds, and marking the secondary orientation angle between the two cylindrical seeds;

[0008] S2. Pressing a plurality of simple wax patterns in a wax pressing machine using a simple mold, and combining and connecting the plurality of simple wax patterns with the cylindrical seeds obtained in step S1 to obtain a twin plate module structure; wherein, the plurality of simple wax patterns include a twin plate wax pattern, a sprue cup wax pattern, a fixed wax rod, a connecting wax rod, and a chill plate wax pattern;

[0009] S3. After coating, sand hanging, and drying the twin plate module structure, dewaxing and roasting to obtain a twin plate module shell;

[0010] S4. Obtaining a twin plate specimen from the twin plate module shell by using a directional solidification process;

[0011] S5. Determining the small-angle grain boundary angle of the twin plate specimen.

[0012] Further, step S1 specifically includes:

[0013] S101. Cutting of nickel-based single crystal superalloy seeds: Using the measurement results of a Laue single crystal diffractometer, adopting a matching fixture, and cutting a single crystal bar with a wire electrical discharge machining (WEDM) machine to make the axial orientation of the single crystal bar deviate from

[001] by less than 3° to obtain two cylindrical seeds with a diameter of 8-16 mm; wherein, the primary orientation direction is set as

[001] ;

[0014] S102. Reconfirm the primary orientation and secondary orientation of the seed crystal through grinding, polishing and etching: Use 50# sandpaper to grind the surface of each seed crystal until it has a metallic luster. In addition, use 320#, 800#, 1000#, 1500#, 2000# to finely mechanically grind and polish the crystal plane in the

[001] direction of the seed crystal. Use a metallographic etchant to etch the surface of the seed crystal. The metallographic etchant is a mixture of equal amounts of hydrogen peroxide and hydrochloric acid. Reconfirm the dendrite orientation, and then place the seed crystal in alcohol and clean it in an ultrasonic cleaner for 10 minutes for standby;

[0015] S103. Mark the included angle of the secondary orientation of the seed crystal: Use a metallographic etchant to etch until a very clear cross appears on the crystal plane in the

[001] direction of the seed crystal. Use a marker pen to draw lines on this plane, including marking the direction of the secondary orientation of the seed crystal and the direction deviating from the secondary orientation by 12°, so as to determine the usage positions of the two seed crystals subsequently.

[0016] Further, the step S2 specifically includes:

[0017] S201. Simple wax mold pressing: Use a simple mold to prepare a twin plate wax mold, a sprue cup wax mold, a fixed wax rod, a connecting wax rod, a chill plate wax mold, and a twin plate transition section wax mold in a wax press;

[0018] S202. Combined connection of some simple wax molds and the cylindrical seed crystal: Use an electric soldering iron to melt the wax material to connect the sprue cup wax mold and the twin plate wax mold to obtain a twin plate module wax mold; Melt part of the wax material of the block bonding wax and evenly apply it on the crystal plane in the unmarked

[001] direction of the cylindrical seed crystal. Connect the connecting wax rods to the two cylindrical seed crystals coated with bonding wax respectively to obtain a seed crystal module wax mold; Finally, connect the twin plate module wax mold and the seed crystal module wax mold to form an initial module;

[0019] S203. Connection of the fixed wax rod and the chill plate wax mold: First, evenly connect three of the fixed wax rods to the sprue cup wax mold of the initial module obtained in step S202, and connect the bottom end of the fixed wax rod to the chill plate wax mold. The height of the fixed wax rod needs to ensure that the cylindrical seed crystal is 3 mm away from the chill plate wax mold. Then, evenly connect the remaining three fixed wax rods to the sprue cup wax mold and the chill plate wax mold; Finally, use wax material to fill the gap between the cylindrical seed crystal and the chill plate wax mold, and stack the wax material around the cylindrical seed crystal to obtain a twin plate module structure.

[0020] Further, in step S201, the height of the twin plate transition section wax mold is 1 / 5 of the total height of the twin plate wax mold. Use an electric soldering iron to perform a smooth transition treatment on all right-angle areas in the twin plate wax mold and the twin plate transition section wax mold.

[0021] Further, in step S202, visually check that the axial directions of the seed crystal module wax mold and the twin crystal plate module wax mold are parallel, the secondary orientation direction of the first seed crystal is parallel to the horizontal direction of the twin crystal plate wax mold, fix the first seed crystal with wax, and fix the second seed crystal with wax; then rotate the second seed crystal and use a measuring scale to keep the secondary orientation direction of the first seed crystal and the direction where the second seed crystal deviates from the secondary orientation by 12° on the same horizontal line, and then completely fix the connections of the first seed crystal, the second seed crystal and the twin crystal plate module wax mold with wax, and air dry for 10 min.

[0022] Further, in step S203, the whole of the twin crystal plate module wax mold is perpendicular to the chill plate wax mold.

[0023] Further, step S3 specifically includes:

[0024] S301. Prepare the facing layer slurry and the fixing layer slurry: The raw materials of the slurry are high-purity corundum powder, silica sol 1430, wetting agent JFC and defoaming agent n-octanol; among them, the weight ratio of silica sol to high-purity corundum powder in the facing layer slurry is 1:4.5, the volume of the wetting agent accounts for 0.2% of the volume of the silica sol, and the volume of the defoaming agent accounts for 0.2% of the volume of the silica sol; the weight ratio of silica sol to high-purity corundum powder in the fixing layer slurry is 1:2.5, the volume of the wetting agent accounts for 0.2% of the volume of the silica sol, and the volume of the defoaming agent accounts for 0.2% of the volume of the silica sol;

[0025] S302. Perform a coating and sanding operation on the twin crystal plate module structure: Apply 8 layers of coating and sanding to the twin crystal plate module; for the first layer, apply the facing layer slurry, then send it into a sand spraying machine to spray sand and then air dry naturally; for the second layer, apply the fixing layer slurry, then send it into a sand spraying machine to spray sand and then hang it on a closed rail suspension conveyor to dry; for the third layer, apply the fixing layer slurry, operate in the same way as the second layer, and the sand spraying requirement is 70# EC95 type sand; for the fourth layer, apply the fixing layer slurry, operate in the same way as the third layer, and the sand spraying requirement is 55# EC95 type sand; for the fifth to eighth layers, apply the fixing layer slurry, operate in the same way as the fourth layer, and the sand spraying requirement is 30# EC95 type sand;

[0026] S303. Perform dewaxing treatment on the twin crystal plate module structure: Dewax the twin crystal plate module structure with a high-pressure dewaxing kettle, control the pressure at 0.6 - 0.7 MPa, the temperature at 160 - 165 °C, the dewaxing time is 15 - 20 min, and after dewaxing, perform ventilation and drying;

[0027] S304. Perform roasting treatment on the twin crystal plate module structure: Perform roasting treatment in a heating furnace, the roasting temperature is 950 °C, the heat preservation time is 3 h, cool it in the furnace to 100 °C and then take it out, and air cool it to room temperature to obtain the twin crystal plate module shell.

[0028] Further, in step S302,

[0029] Layer 1: The viscosity requirement for the surface coating slurry is 25 - 30 s. Hold the handle or the sprue cup of the twin crystal plate module structure and slowly immerse it into the surface coating slurry. After 10 - 15 s, take out the module, let the excess slurry drip into the slurry bucket, gently blow the surface bubbles with a spray gun, so that each part of the module is evenly covered with a layer of slurry. Then send the module into the sand spraying machine to spray sand. The sand spraying time is 10 seconds. The sand spraying requirement is 90# EC95 molding sand. Then hang the module on the module rack and let it dry naturally for about 10 - 12 hours;

[0030] Layer 2: The viscosity requirement for the fixing layer slurry is 15 - 20 s. The sand spraying requirement is 90# EC95 molding sand. First, gently blow off the floating sand on the surface coating with a spray gun and then immerse it into the silica sol. Immerse it in the silica sol for 2 seconds and quickly take it out. After draining off the excess silica sol, immerse it into the second - layer slurry. The operation is the same as that of the surface layer. After spraying sand, hang the module on the closed - track suspension conveyor and dry it for 8 - 10 hours.

[0031] Further, step S4 specifically includes:

[0032] S401. Pouring preparation: Cut off 4 of the fixed wax rods, keep the left - most and right - most fixed wax rods, and block the gaps with 30# EC95 powder slurry. Use a high - pressure air gun to blow out the residues inside the twin crystal plate module shell;

[0033] S402. Directional solidification process: The upper - zone temperature is 1520 °C, the lower - zone temperature is 1550 °C, the pouring temperature is 1550 °C, the refining temperature is 1580 °C, the refining time is 4 min, the static time is 5 min, the drawing rate is 3 mm / min. Before pouring, the shell is kept at 1550 °C in the furnace for 30 min. After pouring according to the above process, a nickel - based single - crystal superalloy twin crystal plate specimen is obtained.

[0034] Further, step S5 specifically includes:

[0035] S501. Preparation work: After cutting the riser, perform sand - blasting treatment on the twin crystal plate specimen, and use a belt sander and 800# sandpaper to mechanically grind the cross - section of the twin crystal plate specimen;

[0036] S502. Macroscopic corrosion: Use a mixed solution of hydrogen peroxide and hydrochloric acid with equal volumes to conduct macroscopic corrosion on the twin crystal plate specimen. The corrosion time is 20 min, and wash it with tap water until the primary orientation seed crystal and the secondary orientation cross - shaped pattern can be clearly observed;

[0037] S503. Optical microscope observation: Take a photo of the small - angle grain boundary structure of the twin crystal plate specimen under an optical microscope, and then measure the small - angle grain boundary angle.

[0038] The beneficial effects of the present invention are:

[0039] 1. The present invention is applicable to the preparation of nickel-based single-crystal superalloy bicrystal plate specimens with small-angle grain boundary defects at precise target angles, thereby quantitatively evaluating the small-angle grain boundary damage tolerance of nickel-based single-crystal superalloys under a specific service condition, which has important guiding significance for guiding the production efficiency of industrial single-crystal blades and reducing costs.

[0040] 2. The present invention is suitable for the preparation of nickel-based single-crystal superalloy bicrystal plates of each generation, especially for high-generation nickel-based single-crystal superalloys with extremely small critical nucleation undercooling, and has a qualified rate of more than 90%.

[0041] 3. In the present invention, the requirement for the size of the seed crystal is small, which avoids the waste of seed crystal rods with a large deviation angle of the primary orientation from

[001] , and greatly saves the preparation cost.

[0042] 4. The present invention can precisely control the small-angle grain boundary angle and can achieve any angle within the range of 0 - 90°.

[0043] 5. The process of the present invention is simple and controllable, without the need for a mold, and has low requirements for equipment, reducing the problem of large defect tendencies brought by the post-seed crystal method and the prefabrication method of the seed crystal groove in the mold, reducing the preparation cost of nickel-based single-crystal superalloy bicrystal plate sample preparation, and is widely applicable to the preparation of various types and angles of small-angle grain boundaries. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is a schematic structural diagram of a nickel-based single-crystal alloy bicrystal plate model containing small-angle grain boundary defects in the present invention.

[0045] Figure 2 It is a schematic diagram of obtaining a seed crystal rod with a primary orientation deviation from the

[001] direction of less than 3° and the installation of the seed crystal in the present invention.

[0046] Figure 3 It is a front view of the module structure for preparing a nickel-based single-crystal superalloy bicrystal plate containing small-angle grain boundaries by the double-seed crystal prefabrication method provided by the present invention.

[0047] Figure 4 It is a left view of the module structure for preparing a nickel-based single-crystal superalloy bicrystal plate containing small-angle grain boundaries by the double-seed crystal prefabrication method provided by the present invention.

[0048] Figure 5 It is a physical diagram of the bicrystal plate after macroscopic corrosion in the present invention.

[0049] Figure 6 It is a schematic diagram of the small-angle grain boundary morphology of the

[001] crystal plane of a nickel-based single-crystal superalloy bicrystal plate containing small-angle grain boundaries in the present invention.

[0050] The realization, functional characteristics and advantages of the object of the present invention will be further described with reference to the embodiments and the accompanying drawings.

[0051] In the attached drawings, there are a sprue cup wax mold 1, a fixed wax rod 2, a twin crystal plate wax mold 3, a twin crystal plate transition section wax mold 4, a connecting wax rod 5, a bonding wax 6, a seed crystal 7, a chill plate wax mold 8, a twin crystal plate module wax mold 9, and a seed crystal module wax mold 10. Detailed implementation manners

[0052] It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0053] As Figure 1 shown, the present invention provides a preparation method for precisely controlling the secondary orientation of a twin crystal plate of a single crystal superalloy, which can precisely control the secondary orientation angle of small-angle grain boundaries in the twin crystal plate of a nickel-based single crystal superalloy, so as to be able to quantitatively evaluate the influence of small-angle grain boundaries on the performance of nickel-based single crystal superalloys under a certain service condition, and has important guiding significance for improving the qualified rate of single crystal superalloy blades; the fourth-generation nickel-based single crystal superalloy is selected as the object for description, and the small-angle grain boundary angle of 12° is taken as an example for illustration.

[0054] Specifically, the following steps are included:

[0055] S1. Using a wire electrical discharge machining (EDM) machine in combination with a Laue single crystal diffractometer, cut two cylindrical seed crystals 7 with a primary orientation of

[001] and the same size from a single crystal test bar. The primary orientation of the two cylindrical seed crystals 7 deviates from the

[001] direction by less than 3°. Grind the surfaces of the two cylindrical seed crystals 7, and after carefully grinding the cross-section of the seed crystal 7, etch a cross-shaped dendrite pattern. Confirm the primary orientation of the seed crystal 7, and use a marker pen to mark the secondary orientation direction and the deviation angle, so as to adjust the secondary orientation angle between the two seed crystals 7, that is, the small-angle grain boundary angle.

[0056] Specifically,

[0057] S101. Cutting of the nickel-based single crystal superalloy seed crystal 7: Use a wire electrical discharge machining (EDM) machine to cut a part from a complete single crystal test bar. Using the measurement results of the Laue single crystal diffractometer, adopt a matching fixture, and use a wire electrical discharge machining (EDM) machine to cut the single crystal bar so that the axial orientation of the single crystal bar deviates from

[001] by less than 3° to obtain two cylindrical seed crystals 7 with a diameter of 8-16 mm; among them, the primary orientation direction is set as

[001] ; in this example, the diameter of the single crystal bar used is 16 mm and the height is 50 mm, and the diameter of the cut seed crystal 7 is 10 mm and the height is 35 mm, as Figure 2 (a).

[0058] S102. Reconfirm the primary orientation and secondary orientation of the seed crystal 7 through grinding, polishing, and etching: Use 50# sandpaper to grind the surface of each seed crystal 7 until it has a metallic luster. Additionally, use 320#, 800#, 1000#, 1500#, and 2000# to finely mechanically grind and polish the crystal plane in the

[001] direction of the seed crystal. Use a metallographic etchant to etch the surface of the seed crystal 7. The metallographic etchant is a mixed solution of equal amounts of hydrogen peroxide and hydrochloric acid. Reconfirm the dendrite orientation, and then place the seed crystal 7 in alcohol and clean it in an ultrasonic cleaner for 10 minutes for standby. In addition, a chemical etchant can also be used: hydrochloric acid: nitric acid: glycerol volume ratio = 1:2:3.

[0059] S103. Mark the included angle of the secondary orientation of the seed crystal 7: Use a metallographic etchant to etch until a very clear cross is visible on the crystal plane in the

[001] direction of the seed crystal. Use a marker pen to draw lines on this plane, including marking the secondary orientation direction of the seed crystal 7 and the direction deviated 12° from the secondary orientation, so as to determine the usage positions of the two seed crystals 7 later, as Figure 2 (b).

[0060] S2. Use a simple mold to press multiple simple wax molds in a wax press, and combine and connect the multiple simple wax molds with the cylindrical seed crystal 7 obtained in step S1, ensuring that the primary orientation directions of the two seed crystals 7 are parallel to the twin plate; the deviation directions of the secondary orientations of the two seed crystals 7 are ensured to be in the same straight line direction through a measuring scale; use fixed wax rods 2 as support columns around the obtained twin plate module wax mold 9, and finally obtain a twin plate module structure; among them, the multiple simple wax molds include a twin plate wax mold 3, a sprue cup wax mold 1, fixed wax rods 2, connecting wax rods 5, and a chill plate wax mold 8; all vertical chamfers of the twin plate wax mold 3 must be smoothly transitioned.

[0061] Specifically,

[0062] S201. Pressing of simple wax molds: Use a simple mold to prepare a twin plate wax mold 3, a sprue cup wax mold 1, fixed wax rods 2, connecting wax rods 5, a chill plate wax mold 8, and a twin plate transition section wax mold 4 in a wax press; the height of the twin plate transition section wax mold 4 is 1 / 5 of the total height of the twin plate wax mold 3. Use an electric soldering iron to smoothly transition all right-angle areas in the twin plate wax mold 3 and the twin plate transition section wax mold 4, as Figure 1 shown.

[0063] S202. Combined connection of some simple wax patterns and the cylindrical seed crystal 7: Use a soldering iron to melt the wax material to connect the sprue cup wax pattern 1 and the twin plate wax pattern 3 and place them aside to dry naturally for 10 minutes to obtain the twin plate module wax pattern 9; then melt part of the wax material of the block bonding wax 6 and evenly apply it on the crystal plane of the

[001] direction of the unmarked cylindrical seed crystal 7. Cut out two connecting wax rods 5 with a diameter of 8 mm and a height of 20 mm and connect them to the two cylindrical seed crystals 7 coated with the bonding wax 6 respectively, and dry naturally for 10 minutes. Among them, under the condition of ensuring its own strength, the diameter of the connecting wax rod 5 should be 2 mm smaller than the diameter of the seed crystal 7; and the bonding wax 6 with stronger bonding force is used for the connection between the connecting wax rod 5 and the seed crystal 7 to avoid the breakage of the seed crystal 7 and the wax rod during the coating and sand hanging process, and finally obtain the seed crystal module wax pattern 10; a smooth transition needs to be made between the seed crystal 7 and the connecting wax rod 5, and between the connecting wax rod 5 and the twin plate transition section wax pattern 4 with the bonding wax 6. Finally, connect the twin plate module wax pattern 9 and the seed crystal module wax pattern 10 to form the initial module.

[0064] Visually check that the axial directions of the seed crystal module wax pattern 10 and the twin plate module wax pattern 9 are parallel, the secondary orientation direction of the first seed crystal (1) is parallel to the horizontal direction of the twin plate wax pattern 3, and fix the first seed crystal (1) with wax material, and fix the second seed crystal (2) with a small amount of wax material; then rotate the second seed crystal (2) and use a measuring scale to keep the secondary orientation direction of the first seed crystal (1) and the direction deviated from the secondary orientation of the second seed crystal (2) by 12° on the same horizontal line, and then completely fix the connections of the first seed crystal (1), the second seed crystal (2) and the twin plate module wax pattern 9 with a small amount of wax material, and dry naturally for 10 minutes.

[0065] S203. Connection of the fixing wax rods 2 and the chill plate wax pattern 8: There are a total of 6 fixing wax rods 2, which are evenly distributed around the twin plate, with a diameter of 16 - 30 mm, and their size selection is determined according to the thickness and height of the twin plate to achieve the stability of the overall twin plate module.

[0066] First, evenly connect three of the fixing wax rods 2 to the sprue cup wax pattern 1 of the initial module obtained in step S202, and connect the bottom ends of the fixing wax rods 2 to the chill plate wax pattern 8. The height of the fixing wax rods 2 needs to ensure that the cylindrical seed crystal 7 is 3 mm away from the chill plate wax pattern 8, and then evenly connect the remaining three fixing wax rods 2 to the sprue cup wax pattern 1 and the chill plate wax pattern 8. This process needs to ensure that the overall twin plate module wax pattern 9 is approximately perpendicular to the chill plate wax pattern 8. In this example, the diameter of the connecting wax rod 5 as the fixed support column is 16 mm; finally, use a small amount of wax material to fill the gap between the cylindrical seed crystal 7 and the chill plate wax pattern 8, and stack the wax material around the cylindrical seed crystal 7 to avoid breakage between the seed crystal 7 and the chill plate wax pattern 8 during the coating process, and obtain the twin plate module structure, the front view of which is as Figure 3 shown in, and the left view is asFigure 4 。

[0067] In this embodiment, medium-temperature die wax is selected for all the wax patterns, and all the wax parts are fixed by welding.

[0068] S3. After coating, sand hanging, and drying the twin crystal plate module structure, dewaxing and roasting are performed to obtain the shell of the twin crystal plate module. The coating slurry and the particle size of the sand for sand hanging are carried out according to the industry standards. Specifically,

[0069] S301. Prepare the surface layer slurry and the fixing layer slurry: The raw materials of the slurry are high-purity corundum powder (325 mesh), silica sol 1430, wetting agent JFC, and defoaming agent n-octanol; among them, in the surface layer slurry, the weight ratio of silica sol to high-purity corundum powder (325 mesh) is 1:4.5, the volume of the wetting agent accounts for 0.2% of the volume of silica sol, and the volume of the defoaming agent accounts for 0.2% of the volume of silica sol; in the fixing layer slurry, the weight ratio of silica sol to high-purity corundum powder is 1:2.5, the volume of the wetting agent accounts for 0.2% of the volume of silica sol, and the volume of the defoaming agent accounts for 0.2% of the volume of silica sol.

[0070] S302. Perform the coating and sand hanging operation on the twin crystal plate module structure: The twin crystal plate module is coated and sanded in 8 layers.

[0071] For the first layer, coat the surface layer slurry with a viscosity requirement of 25 - 30 s. Hold the handle or sprue cup of the module and slowly immerse it in the surface layer slurry. After 10 - 15 s, take out the module, let the excess slurry drip into the slurry bucket, gently blow the surface bubbles with a spray gun, so that each part of the module is evenly covered with a layer of slurry. Then send the module into a sanding machine (manual sand hanging) for sand hanging. The sand hanging time is about 10 seconds. The sanding requirement is 90# EC95 sand. Then hang the module on the module rack and dry it naturally for about 10 - 12 hours.

[0072] For the second layer, coat the fixing layer slurry with a viscosity requirement of 15 - 20 s. The sanding requirement is 90# EC95 sand. First, gently blow off the floating sand on the surface layer coating with a spray gun and then immerse it in silica sol. Immerse it in silica sol for about 2 seconds and then quickly take it out. After draining the excess silica sol, immerse it in the second layer slurry. The operation is the same as that of the surface layer. After sand hanging, hang the module on the closed rail suspension conveyor and dry it for 8 - 10 hours.

[0073] For the third layer, coat the fixing layer slurry. The operation is the same as that of the second layer. The sanding requirement is 70# EC95 sand.

[0074] For the fourth layer, coat the fixing layer slurry. The operation is the same as that of the third layer. The sanding requirement is 55# EC95 sand.

[0075] For the 5th - 8th layers, coat the fixing layer slurry. The operation is the same as that of the fourth layer. The sanding requirement is 30# EC95 sand.

[0076] S303. Dewax the twin-plate module structure: Dewax the twin-plate module structure using a high-pressure dewaxing kettle. During dewaxing, the riser of the investment shell should face downwards to ensure the stable removal of the wax liquid from the investment shell. The pressure is controlled at 0.6 - 0.7 MPa, the temperature is 160 - 165 °C, and the dewaxing time is 15 - 20 min. After dewaxing, conduct ventilation and drying.

[0077] S304. Roast the twin-plate module structure: Conduct roasting treatment in a heating furnace. The roasting temperature is 900 - 1000 °C, and the holding time is 2 - 4 h. Load the furnace at a temperature below 300 °C. After reaching the holding time, open the furnace door to cool down, and cool with the furnace to 100 °C before taking out, then air-cool to room temperature to obtain the investment shell of the twin-plate module. After taking out the investment shell, four of the fixed support columns need to be cut off, and two symmetrically arranged fixed support columns on the side of the twin-plate should be retained.

[0078] S4. Obtain twin-plate specimens from the investment shell of the twin-plate module using the directional solidification process. Specifically,

[0079] S401. Pouring preparation: Cut off 4 of the fixed wax rods 2, retain the leftmost and rightmost fixed wax rods 2, and block the gaps with 30# EC95 powder slurry. Use a high-pressure air gun to blow out the residues inside the investment shell of the twin-plate module to ensure the inside of the investment shell is smooth and clean.

[0080] S402. Directional solidification process: For the directional solidification process of twin-plate casting, the upper zone temperature is 1520 °C, the lower zone temperature is 1550 °C, the pouring temperature is 1550 °C, the refining temperature is 1580 °C, the refining time is 4 min, the standing time is 5 min, and the pulling rate is 3 mm / min. Before pouring, the investment shell is subjected to secondary roasting in a directional furnace at a roasting temperature of 1550 °C and a holding time of 30 min. After pouring according to the above process, a nickel-based single-crystal superalloy twin-plate specimen is obtained.

[0081] S5. Determine the small-angle grain boundary angle of the twin-plate specimen. Specifically,

[0082] S501. Preparation work: After cutting off the riser, conduct sandblasting on the twin-plate specimen, and use a belt sander and 800# sandpaper to mechanically grind the cross-section of the twin-plate specimen.

[0083] S502. Macroscopic corrosion: Use a mixed solution of equal volumes of hydrogen peroxide and hydrochloric acid to conduct macroscopic corrosion on the twin-plate specimen for 20 min, and wash it with tap water until the primary orientation seed crystal 7 and the secondary orientation cross pattern can be clearly observed, as Figure 5 shown.

[0084] S503. Optical microscopy observation: Take a photo of the small-angle grain boundary structure of the twin-plate specimen under an optical microscope, and then measure the small-angle grain boundary angle to be 11.5°, asFigure 6 as shown

[0085] As can be seen from the above embodiments, the present invention can accurately control the secondary orientation angle of the small-angle grain boundary in the twin plate of the nickel-based single crystal superalloy, so as to quantitatively evaluate the influence of the small-angle grain boundary on the performance of the nickel-based single crystal superalloy under a certain service condition, which has important guiding significance for improving the qualified rate of the single crystal superalloy blade.

[0086] It should be noted that in this text, the term "comprising", "including" or any other variant thereof is intended to cover a non-exclusive inclusion, such that a process, apparatus, article or method comprising a series of elements includes not only those elements but also other elements not expressly listed, or further includes elements inherent to such process, apparatus, article or method. Without further limitation, an element defined by the statement "comprising a..." does not exclude the presence of additional identical elements in the process, apparatus, article or method comprising the element.

[0087] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent structure or equivalent process transformation made by using the content of the specification and drawings of the present invention, or directly or indirectly applied in other related technical fields, shall be similarly included in the patent protection scope of the present invention.

Claims

1. A preparation method for precisely controlling the secondary orientation of a single crystal superalloy twin plate, characterized in that include: S1. Using a wire-cut electric discharge machine combined with a Laue single crystal diffractometer, two cylindrical seed crystals with a deviation from the primary orientation direction of less than 3° are cut from a complete single crystal test rod, and the surfaces of the two cylindrical seed crystals are ground and polished, and the secondary orientation angles of the two cylindrical seed crystals are marked; S2, using a simple mold to press out a plurality of simple wax molds in a wax press, and combining and connecting the plurality of simple wax molds with the cylindrical seed crystal obtained in step S1 to obtain a dual crystal plate module structure; wherein the plurality of simple wax molds include a dual crystal plate wax mold, a pouring cup wax mold, a fixed wax rod, a connecting wax rod, and a chill plate wax mold; S3, coating, sanding and drying the twin-crystal plate module structure, dewaxing and baking to obtain a twin-crystal plate module shell; S4, obtaining a twin crystal plate sample by using a directional solidification process on the twin crystal plate module shell; S5. Determine the low-angle grain boundary angle of the twin crystal plate sample.

2. The preparation method for precisely controlling the secondary orientation of the single crystal superalloy twin plate according to claim 1, wherein, The step S1 specifically includes: S101. Cutting of nickel-based single crystal high-temperature alloy seed crystals: using the measurement results of a Laue single crystal diffractometer, using a fixture matched therewith, and using an electric spark wire cutting machine to cut the single crystal rod, so that the axial orientation of the single crystal rod deviates from [001] by less than 3°, thereby obtaining two cylindrical seed crystals; wherein the primary orientation direction is set to [001]; S102, reconfirming the primary orientation and secondary orientation of the seed crystal by grinding, polishing and etching: using 50# sandpaper to grind the surface of each seed crystal until it has a metallic luster, and using 320#, 800#, 1000#, 1500#, 2000# sandpaper to finely mechanically grind and polish the crystal surface in the [001] direction of the seed crystal, and using a metallographic etchant to etch the surface of the seed crystal, the metallographic etchant is a mixture of equal amounts of hydrogen peroxide and hydrochloric acid, and the dendrite orientation is reconfirmed, and then the seed crystal is placed in alcohol and cleaned in an ultrasonic cleaner for 10 minutes for use; S103, marking the secondary orientation angle of the seed crystal: using a metallographic etchant to etch until a very clear cross is observed on the crystal plane in the [001] direction of the seed crystal, and using a marker to draw lines on the surface, including marking the secondary orientation direction of the seed crystal and the direction that deviates from the secondary orientation by 12°, so as to subsequently determine the positions of the two seed crystals to be used.

3. The preparation method for precisely controlling the secondary orientation of the single crystal superalloy twin plate according to claim 2, wherein, The step S2 specifically includes: S201, simple wax mold pressing: using a simple mold to prepare a wax mold of a twin crystal plate, a pouring cup wax mold, a fixed wax rod, a connecting wax rod, a quenching plate wax mold, and a wax mold of a transition section of a twin crystal plate in a wax pressing machine; S202, combining and connecting part of the simple wax mold and the cylindrical seed crystal: using an electric soldering iron to melt the wax material to connect the pouring cup wax mold and the twin crystal plate wax mold to obtain a twin crystal plate module wax mold; melting part of the block adhesive wax and evenly applying it on the unmarked [001] direction crystal surface of the cylindrical seed crystal, connecting the connecting wax rod to the two cylindrical seed crystals coated with adhesive wax, respectively, to obtain a seed crystal module wax mold; finally, connecting the twin crystal plate module wax mold and the seed crystal module wax mold to form an initial module; S203. Connection of the fixed wax rods and the chill plate wax mold: First, evenly connect three of the fixed wax rods to the sprue cup wax mold of the initial mold obtained in step S202, and connect the bottom ends of the fixed wax rods to the chill plate wax mold. The height of the fixed wax rods should ensure that the cylindrical seed crystal is 3 mm away from the chill plate wax mold. Then, evenly connect the remaining three fixed wax rods to the sprue cup wax mold and the chill plate wax mold. Finally, fill the gap between the cylindrical seed crystal and the chill plate wax mold with wax material, and stack the wax material around the cylindrical seed crystal to obtain a twin crystal plate mold structure.

4. The preparation method for precisely controlling the secondary orientation of the single crystal superalloy twin plate according to claim 3, characterized in that, In step S201, the height of the twin crystal plate transition section wax mold is 1 / 5 of the total height of the twin crystal plate wax mold. Use an electric soldering iron to smooth the transition of all right-angle areas in the twin crystal plate wax mold and the twin crystal plate transition section wax mold.

5. The preparation method for precisely controlling the secondary orientation of the single crystal superalloy twin plate according to claim 3, characterized in that, In step S202, visually check that the axial directions of the seed crystal mold wax mold and the twin crystal plate mold wax mold are parallel, and the secondary orientation direction of the first seed crystal is parallel to the horizontal direction of the twin crystal plate wax mold. Fix the first seed crystal with wax material, and fix the second seed crystal with wax material. Then rotate the second seed crystal and use a measuring scale to keep the secondary orientation direction of the first seed crystal and the direction where the second seed crystal deviates from the secondary orientation by 12° on the same horizontal line. Then completely fix the connections of the first seed crystal, the second seed crystal, and the twin crystal plate mold wax mold with wax material, and let it dry naturally for 10 min.

6. The preparation method for precisely controlling the secondary orientation of the single crystal superalloy twin plate according to claim 3, wherein In step S203, the entire twin crystal plate mold wax mold is perpendicular to the chill plate wax mold.

7. The preparation method for precisely controlling the secondary orientation of the single crystal superalloy twin plate according to claim 3, characterized in that Step S3 specifically includes: S301. Prepare the surface layer slurry and the fixing layer slurry: The raw materials of the slurry are high-purity corundum powder, silica sol 1430, wetting agent JFC, and defoaming agent n-octanol. Among them, in the surface layer slurry, the weight ratio of silica sol to high-purity corundum powder is 1:4.5, the volume of the wetting agent accounts for 0.2% of the volume of silica sol, and the volume of the defoaming agent accounts for 0.2% of the volume of silica sol. In the fixing layer slurry, the weight ratio of silica sol to high-purity corundum powder is 1:2.5, the volume of the wetting agent accounts for 0.2% of the volume of silica sol, and the volume of the defoaming agent accounts for 0.2% of the volume of silica sol. S302. Perform a coating and sanding operation on the twin crystal plate mold structure: Apply 8 layers of coating and sanding to the twin crystal plate mold. For the first layer, apply the surface layer slurry, then send it into a sand spraying machine to spray sand and let it dry naturally. For the second layer, apply the fixing layer slurry, then send it into a sand spraying machine to spray sand and hang it on a closed rail suspension conveyor to dry. For the third layer, apply the fixing layer slurry, and the operation is the same as the second layer. The sand spraying requirement is 70# EC95 type sand. For the fourth layer, apply the fixing layer slurry, and the operation is the same as the third layer. The sand spraying requirement is 55# EC95 type sand. For the fifth to eighth layers, apply the fixing layer slurry, and the operation is the same as the fourth layer. The sand spraying requirement is 30# EC95 type sand. S303. Perform a dewaxing treatment on the twin crystal plate mold structure: Dewax the twin crystal plate mold structure with a high-pressure dewaxing kettle, control the pressure at 0.6 - 0.7 MPa, the temperature at 160 - 165 °C, and the dewaxing time at 15 - 20 min. After dewaxing, perform ventilation and drying. S304. Bake the twin-plate module structure: Bake it in a heating furnace at a temperature of 950 °C for 3 hours of heat preservation, then cool it in the furnace to 100 °C and take it out, and air-cool it to room temperature to obtain the shell of the twin-plate module.

8. The preparation method for precisely controlling the secondary orientation of a single crystal superalloy twin plate according to claim 7, characterized in that, In the step S302, Layer 1: The viscosity requirement of the surface layer slurry is 25 - 30 s. Hold the handle or sprue cup of the twin-plate module structure and slowly immerse it in the surface layer slurry. Take out the module after 10 - 15 s, let the excess slurry drip into the slurry bucket, gently blow the surface bubbles with a spray gun to evenly cover a layer of slurry on each part of the module, and then send the module into a sand spraying machine to spray sand for 10 seconds. The sand spraying requirement is 90# EC95 molding sand. Then hang the module on the module rack and let it dry naturally for about 10 - 12 hours; Layer 2: The viscosity requirement of the fixing layer slurry is 15 - 20 s, and the sand spraying requirement is 90# EC95 molding sand. First, gently blow off the floating sand on the surface layer coating with a spray gun and then immerse it in the silica sol for 2 seconds and quickly take it out. After draining the excess silica sol, immerse it in the second-layer slurry. The operation is the same as that of the surface layer. After spraying sand, hang the module on a closed-rail suspension conveyor and dry it for 8 - 10 hours.

9. The preparation method for precisely controlling the secondary orientation of the single crystal superalloy twin plate according to claim 7, wherein The step S4 specifically includes: S401. Pouring preparation: Cut off 4 of the fixed wax rods, keep the leftmost and rightmost fixed wax rods, and block the gaps with 30# EC95 powder slurry. Use a high-pressure air gun to blow out the residues inside the shell of the twin-plate module; S402. Directional solidification process: The upper zone temperature is 1520 °C, the lower zone temperature is 1550 °C, the pouring temperature is 1550 °C, the refining temperature is 1580 °C, the refining time is 4 min, the standing time is 5 min, the pulling rate is 3 mm / min. The shell is kept at 1550 °C in the furnace for 30 min before pouring. After pouring according to the above process, a nickel-based single crystal superalloy twin-plate sample is obtained.

10. The preparation method for precisely controlling the secondary orientation of the single crystal superalloy twin plate according to claim 9, wherein The step S5 specifically includes: S501. Preparation work: After cutting the riser, perform sand blasting on the twin-plate sample, and use a belt sander and 800# sandpaper to mechanically grind the cross-section of the twin-plate sample; S502. Macroscopic corrosion: Use a mixed solution of hydrogen peroxide and hydrochloric acid with equal volumes to conduct macroscopic corrosion on the twin-plate sample for 20 min, and clean it with tap water until the primary orientation seed crystal and the secondary orientation cross pattern are clearly observed; S503. Optical microscope observation: Take a photo of the small-angle grain boundary structure of the twin-plate sample under an optical microscope, and then measure the small-angle grain boundary angle.

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