A method for controlling the defects of abrupt cross-section of single crystal high-temperature alloy castings by secondary orientation

Abstract

The present invention provides a method for controlling the defects of impure crystals in a sudden cross section of a single crystal high-temperature alloy casting with secondary orientation, and relates to the technical field of preparation of single crystal high-temperature alloy castings. The present invention can effectively shorten the time for the dendrite branches of the blade to grow to the corners of the sudden cross section by controlling the growth direction of the secondary dendrite orientation relative to the sudden cross section based on the position, shape and placement of the sudden cross section of the single crystal high-temperature alloy casting where impure crystals are likely to appear, thereby effectively suppressing the impure crystals generated by supercooled nucleation at the corners of the sudden cross section of the blade. Compared with the prior art, the process of the present invention is simple and easy to implement, does not require the addition of new equipment or the modification of the original directional solidification equipment, does not introduce other solidification defects, does not affect subsequent heat treatment, and can greatly improve the yield of single crystal high-temperature alloy castings.

Description

Technical Field

[0001] The present invention relates to the technical field of preparation of single crystal high temperature alloy castings, and in particular to a method for controlling the abrupt cross-section miscellaneous crystal defects of single crystal high temperature alloy castings through secondary orientation. Background Art

[0002] Single crystal high temperature alloy blades are key components of aircraft engines. As engine service conditions become more stringent, thrust-to-weight ratios, and operating temperatures continue to increase, higher requirements are placed on the temperature-bearing capacity and performance of single crystal high temperature alloy blades. Single crystal turbine blades are developing in the direction of alloying with high refractory elements, larger sizes, and more complex structures to meet the development requirements of advanced aircraft engines. Specifically, a large amount of refractory elements such as W and Ta and rare and precious metal elements such as Re and Ru are added to the new single crystal high temperature alloys, which makes it easy to produce defects such as impurities during the casting process of the single crystal high temperature alloys. In addition, in order to enhance the air cooling effect and reduce the actual temperature that the single crystal blades are subjected to, the new single crystal turbine blades have a complex appearance and a variable cross-sectional shape. The interior is a hollow multi-channel air-cooled structure. Such a complex internal and external structure further induces an increased tendency for defects to form during the single crystal preparation process. In particular, the cross-section at the connection between the blade body and the edge plate suddenly expands significantly, and the dendrite growth here presents a complex three-dimensional growth pattern. During this process, the liquid at the front of the solidification interface is often in an overcooled state and the temperature gradient is negative at the edge corners of the edge plate, and there is a great tendency for defects such as stray crystals to form; especially when preparing single-crystal blade molds, due to the extremely uneven temperature distribution on the positive and negative surfaces, defects such as stray crystals are very likely to occur in the sudden change section on the negative side of the casting close to the inside of the furnace body, which greatly reduces the qualified rate of single-crystal blades and sharply increases the difficulty and cost of production and preparation.

[0003] In order to eliminate the formation of stray crystals on the edge of a single crystal blade, scholars at home and abroad have proposed various methods. Among them, the invention with the publication number CN106270392A discloses a method for preventing the formation of stray crystals on the edge of a single crystal blade by variable speed pulling, but this method causes the dendrite scales at the blade body position, the position near the edge plate, and the edge plate position to be different, which affects the subsequent heat treatment time. The invention with the publication number CN105108061A discloses the use of a seeding bar to connect the bottom end of the blade with the edge corner of the edge plate, so that the dendrites grown from the crystal selector enter the edge corner of the edge plate through the seeding bar, and then merge with the dendrites at the blade body, avoiding the supercooling nucleation at the edge corner of the edge plate to produce stray crystals, but this method is prone to the formation of small-angle grain boundary defects when the dendrites in the seeding bar merge with the dendrites from the blade body. There is also a method of inserting a graphite heat conductor into the mold shell of the thermal barrier area at the variable cross-section of the blade (publication number CN108097877A) or inserting a heat-insulating body into the mold shell at the edge of the edge plate (publication number CN102166643B), which improves the temperature distribution at the edge plate during directional solidification, thereby suppressing the occurrence of supercooling nucleation at the edge plate. However, it brings problems such as a long mold shell preparation process and a complicated process. The invention of publication number CN113279049A also discloses a method of using a strong magnetic field to change the supercooling degree of melt nucleation and control the formation of stray crystals at the variable cross-section. However, this method requires the modification of the original directional solidification equipment, and there are problems such as complex process and high cost. Therefore, the current methods for suppressing stray crystals at the edge plate of single crystal blades are subject to certain limitations in actual production. Finding an efficient and easy method to suppress the formation of stray crystals at the edge plate is of great scientific significance for obtaining single crystal blades with excellent performance in actual industrial production. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for secondary orientation control of the mixed crystal defects of the sudden cross-section of single crystal high-temperature alloy castings, which can solve the mixed crystal problem caused by the sudden change of geometric shape during the directional solidification process of single crystal high-temperature alloy castings. The process is simple and easy, and there is no need to add new equipment or modify the original directional solidification equipment. It will not introduce other solidification defects and will not affect the subsequent heat treatment.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a method for controlling the abrupt cross-section defects of single crystal high-temperature alloy castings through secondary orientation, comprising the following steps:

[0007] A single crystal casting mold shell is provided; the single crystal casting mold shell includes a seeding section; a corundum tube is pre-installed in the seeding section;

[0008] Mark the secondary dendrite orientation on any end face of the

[001] -oriented seed crystal to obtain a marked seed crystal;

[0009] The marked seed crystal is placed in the corundum tube at a predetermined angle to obtain a mold shell for pre-setting the seed crystal with a specific three-dimensional orientation; the method for determining the placement angle of the marked seed crystal includes: determining the growth direction of the secondary dendrite orientation relative to the shape mutation section based on the structure, size and position of the shape mutation section of the single crystal high-temperature alloy casting and the principle of the shortest path of dendrite branch growth;

[0010] A high-temperature alloy melt is cast into the mold shell with the preset specific three-dimensional oriented seed crystals, and directionally solidified to obtain a single crystal high-temperature alloy casting.

[0011] Preferably, the inner diameter of the corundum tube is 6.96-11.98 mm; the length of the corundum tube is 30-45 mm.

[0012] Preferably, the method for obtaining the

[001] -oriented seed crystal comprises: determining the orientation of a single crystal test rod for the seed crystal, and directionally cutting the

[001] -oriented seed crystal.

[0013] Preferably, the

[001] oriented seed crystal is polished to be smooth with sandpaper before marking.

[0014] Preferably, the

[001] oriented seed crystal has a diameter of 6.66 to 11.94 mm and a length of 29 to 44 mm.

[0015] Preferably, the

[001] orientation of the

[001] -oriented seed crystal deviates from its axial direction by 0 to 5°.

[0016] Preferably, the method of marking the secondary dendrite orientation on any end face of the

[001] oriented seed crystal comprises: polishing and etching any end face of the

[001] oriented seed crystal in sequence, obtaining a "cross" pattern on the end face of the seed crystal after etching; and taking a line parallel to any side of the "cross" pattern as the secondary dendrite orientation.

[0017] Preferably, the gap between the marking seed crystal and the inner wall of the corundum tube is 0.02-0.48 mm.

[0018] Preferably, the angle between the secondary dendrite orientation and the edge of the cross section with a sudden change in shape is less than 45°.

[0019] Preferably, the casting is performed in a directional solidification furnace.

[0020] The present invention provides a method for controlling stray crystal defects in abrupt cross-sections of single-crystal superalloy castings through secondary orientation. Based on the location and shape of the abrupt cross-sections in single-crystal superalloy castings where stray crystals are most likely to form, and their placement within the furnace, the method effectively shortens the time it takes for blade dendrites to branch and grow to the corners of the abrupt cross-sections, thereby effectively suppressing stray crystals generated by undercooling nucleation at the corners of the blade's abrupt cross-sections. Compared to existing technologies, the present invention offers a simple and easy process, requiring no new equipment or modification to existing directional solidification equipment. It also avoids introducing other solidification defects and does not affect subsequent heat treatment. Furthermore, it significantly improves the yield of single-crystal superalloys.

[0021] The present invention adopts the "seed crystal + crystal selection" method to prepare single crystal high-temperature alloy castings, which can greatly improve the yield of single crystal high-temperature alloy castings; uses a pre-embedded corundum tube in the mold shell of the seeding section to effectively control the gap between the seed crystal and the inner wall of the seeding section, reduce the surface roughness of the mold shell of the seeding section, which is beneficial to avoid the formation of miscellaneous crystals in the seed crystal remelting zone, realize three-dimensional orientation precise control, and further improve the yield of single crystal high-temperature alloy castings. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A schematic diagram of a single crystal blade simulation component used in an embodiment of the present invention;

[0023] Figure 2 This is a schematic diagram of a wax mold chassis used in an embodiment of the present invention;

[0024] Figure 3 The wax model of the single crystal blade simulation part with the corundum tube pre-embedded in the seeding section and the base after bonding in the embodiment of the present invention;

[0025] Figure 4 The end face of a

[001] -oriented cylindrical seed crystal test rod, with the straight line in the figure marking the secondary dendrite orientation;

[0026] Figure 5 Schematic diagram of the growth direction of secondary dendrites relative to the rectangular mutation cross section in Example 1 of the present invention;

[0027] Figure 6 : is a cross-sectional microstructure diagram of the bottom surface of the rectangular mutation section of the blade simulation component when the angle θ between the secondary dendrite orientation and the edge of the rectangular mutation section is 0° in Example 1 of the present invention;

[0028] Figure 7 Schematic diagram of the growth direction of secondary dendrites relative to the rectangular mutation cross section in Comparative Example 1 of the present invention;

[0029] Figure 8 : is a cross-sectional microstructure diagram of the bottom surface of the rectangular mutation section of the blade simulation part when the angle θ between the secondary dendrite orientation and the edge of the rectangular mutation section is 45° in Comparative Example 1;

[0030] Figure 9 Schematic diagram of the path of dendrite branches from the blade body growing to the corner of the rectangular mutation section when the angle θ between the secondary dendrite orientation and the edge of the rectangular mutation section is 0°, and the bold line is the path;

[0031] Figure 10 Schematic diagram of the path of dendrite branches from the blade body growing to the corner of the rectangular mutation section when the angle θ between the secondary dendrite orientation and the edge of the rectangular mutation section is 45°, and the bold line is the path;

[0032] Figures 1 to 10 In the figure, 1—riser; 2—rectangular sudden cross-section; 3—support column; 4—blade body; 5—spiral crystal selection section; 6—seeding section; 7—wax mold of the seeding section of the outer corundum tube; 8—end face of the

[001] oriented cylindrical seed crystal test rod; 9—secondary dendrite marking line; 2D—secondary dendrite; 3D—tertiary dendrite; 4D—quaternary dendrite; 5D—quintadecrite; HD—higher-order dendrite with more than five branches;

[0033] Figure 11 Schematic diagram of the structure of the directional solidification furnace. DETAILED DESCRIPTION

[0034] The present invention provides a method for controlling the abrupt cross-section defects of single crystal high-temperature alloy castings through secondary orientation, comprising the following steps:

[0035] A single crystal casting mold shell is provided; the single crystal casting mold shell includes a seeding section; a corundum tube is pre-installed in the seeding section;

[0036] Mark the secondary dendrite orientation on any end face of the

[001] -oriented seed crystal to obtain a marked seed crystal;

[0037] The marked seed crystal is placed in the corundum tube at a predetermined angle to obtain a mold shell for pre-setting the seed crystal with a specific three-dimensional orientation; the method for determining the placement angle of the marked seed crystal includes: determining the growth direction of the secondary dendrite orientation relative to the shape mutation section based on the structure, size and position of the shape mutation section of the single crystal high-temperature alloy casting and the principle of the shortest path of dendrite branch growth;

[0038] A high-temperature alloy melt is cast into the mold shell with the preset specific three-dimensional oriented seed crystals, and directionally solidified to obtain a single crystal high-temperature alloy casting.

[0039] The present invention provides a single crystal casting mold. The mold comprises a seeding section, wherein a corundum tube is pre-installed within the seeding section. The inner diameter of the corundum tube is preferably 6.96 to 11.98 mm, and the length of the corundum tube is preferably 30 to 45 mm.

[0040] The present invention marks the secondary dendrite orientation on any end face of a

[001] -oriented seed crystal to obtain a marked seed crystal. In the present invention, the method for obtaining the

[001] -oriented seed crystal preferably includes: determining the orientation of a single crystal test rod for the seed crystal, and directionally cutting the

[001] -oriented seed crystal. The present invention preferably uses a high-precision X-ray crystal orientation instrument to determine the orientation of the single crystal test rod for the seed crystal, and fixes the single crystal test rod with a fixture provided by the instrument, places the fixture on the guide rail of a wire cutting machine, and directionally cuts the

[001] -oriented seed crystal using a wire electric discharge machine.

[0041] In the present invention, the

[001] oriented seed crystal has a diameter of 6.66 to 11.94 mm and a length of 29 to 44 mm.

[0042] In the present invention, the

[001] orientation of the

[001] oriented seed crystal deviates from its axial direction by 0 to 5°.

[0043] In the present invention, the

[001] -oriented seed crystal is preferably polished to a smooth surface using sandpaper before marking. In the present invention, the sandpaper is preferably water-abrasive sandpaper. The present invention polishes the surface of the seed crystal to a smooth surface.

[0044] In the present invention, the method of marking the secondary dendrite orientation on any end face of a

[001] -oriented seed crystal preferably includes: sequentially grinding and etching any end face of the

[001] -oriented seed crystal, thereby forming a cross pattern on the etched seed crystal end face; and defining a line parallel to any side of the cross pattern as the secondary dendrite orientation. In the present invention, the cross pattern is a secondary dendrite. In the present invention, the grinding and polishing preferably includes: sequentially grinding with 80#, 220#, 400#, 800#, 1000#, 1500#, and 2000# water-abrasive sandpaper, followed by polishing on a polishing machine. In the present invention, the etching agent is preferably a mixture of nitric acid solution, hydrofluoric acid solution and glycerol; the concentration of the nitric acid solution is preferably 65-68wt.%; the concentration of the hydrofluoric acid solution is preferably ≥40wt.%; the volume ratio of the nitric acid solution, hydrofluoric acid solution and glycerol is preferably 1:2:2.7-3.5, more preferably 1:2:3.

[0045] In the present invention, one line of the "cross" pattern is regarded as a group, and the directions of two groups of secondary dendrites are perpendicular to each other.

[0046] After obtaining the marked seed crystal, the present invention places the marked seed crystal in the corundum tube at a predetermined angle to obtain a mold shell with a predetermined three-dimensionally oriented seed crystal. In the present invention, the gap between the marked seed crystal and the inner wall of the corundum tube is 0.02 to 0.48 mm.

[0047] In the present invention, the method for determining the placement angle of the marker seed crystal includes determining the growth direction of secondary dendrites relative to the cross-section with a sudden change in shape based on the structure, size, and position of the cross-section with a sudden change in shape in the single crystal superalloy casting, in conjunction with the principle of the shortest path for dendrite branch growth. In the present invention, the shortest path for dendrite branch growth refers to the shortest path along which secondary dendrites from the blade body grow to the cross-section with the greatest likelihood of generating stray crystal corners.

[0048] In a specific embodiment of the present invention, the angle between the secondary dendrite orientation and the edge of the cross-section with a sudden change in shape is preferably less than 45°, and more preferably 0°.

[0049] After obtaining a mold shell pre-installed with seed crystals in a specific three-dimensional orientation, the present invention casts a high-temperature alloy melt into the mold shell pre-installed with seed crystals in a specific three-dimensional orientation, performs directional solidification, and obtains a single crystal high-temperature alloy casting. In a specific embodiment of the present invention, the casting is performed in a directional solidification furnace. The present invention has no special requirements for the specific casting process, and a casting process familiar to those skilled in the art can be used. In the present invention, the withdrawal rate of the mold shell during the directional solidification is preferably 50 to 200 μm / s.

[0050] In a specific embodiment of the present invention, the casting and directional solidification are carried out as follows Figure 11 The process is carried out in the directional solidification furnace shown in the figure. The present invention places the bottom surface of the mold shell with the preset specific three-dimensional oriented seed crystal on the water-cooled copper plate of the directional solidification furnace, so that the lower surface of the mold shell chassis is in close contact with the upper surface of the water-cooled copper plate, and the mold shell is raised to a position where the upper surface of the mold shell chassis is 5 to 22 mm away from the lower surface of the radiation baffle.

[0051] In the present invention, the single crystal high temperature alloy has a face-centered cubic structure, and the crystal grows in the form of dendrites. The primary dendrite direction of the dendrite is the same as that of the <001> direction is parallel to the secondary dendrite direction. <010> or <100> The directions are parallel, so the crystallographic orientation of the single crystal high-temperature alloy can be determined according to the dendrite growth direction. Based on this, the three-dimensional orientation of the single crystal high-temperature alloy casting can be precisely controlled.

[0052] In a specific embodiment of the present invention, the solidification interface of multiple sudden changes in the external structure of a single crystal blade is concave during the directional solidification process, and independent undercooling zones are easily formed at the edges and corners, resulting in undercooling nucleation and ultimately the formation of mixed crystal defects. The present invention is based on the "seed crystal + crystal selection" method for preparing single crystal high-temperature alloy castings. By controlling the orientation of secondary dendrites relative to the growth direction of the sudden change in shape section, the path of dendrite branch growth to the corner of the sudden change in shape section can be reduced. Before the melt at the corner of the sudden change in shape section reaches the critical nucleation supercooling of the alloy, the dendrites from the blade body preferentially fill the corner of the sudden change in shape section, thereby suppressing heterogeneous nucleation at the sudden change in shape section and preventing the formation of mixed crystals.

[0053] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0054] Example 1

[0055] This embodiment takes a single crystal high temperature alloy blade simulation as an example. The structure of the blade simulation is as follows: Figure 1 As shown, it includes a riser 1, a blade body 4 (symmetrical crescent shape, total length 70mm, width 30mm), a sudden change section 2 (rectangular, length 40mm, width 20mm), a spiral grain selection section 5, and a seeding section 6. This embodiment uses DD91, a domestically produced fourth-generation nickel-based single crystal superalloy with very low nucleation undercooling (extremely prone to generating stray crystals), to produce the single crystal blade simulation.

[0056] The specific steps of this embodiment are as follows:

[0057] The first step is to make a blade simulation mold with a pre-embedded corundum tube in the seeding section:

[0058] One-piece molding using 3D printing wax model technology Figure 1 The wax molds of the riser, blade body, rectangular sudden change section, crystal selection section and seeding section of the blade simulation part shown are as follows. The diameter of the seeding section is 6.92 mm and the length is 40 mm.

[0059] The wax model base is prepared using 3D printing wax model technology, such as Figure 2 As shown, the wax mold base is disc-shaped, with a diameter equal to the diameter of the water-cooled copper disk of the directional solidification equipment used, and a height less than or equal to the height of the water-cooled copper disk of the directional solidification equipment used. In this embodiment, the wax mold base has a diameter of 72 mm and a height of 15 mm.

[0060] The length of the corundum tube 7 is the same as that of the wax mold seeding section 6, and the corundum tube is sleeved on the outside of the seeding section wax mold 6; the inner diameter of the corundum tube is 6.98 mm, the wall thickness is 1.0 mm, and the length is 40 mm.

[0061] The bottom surface of the seeding section wax mold of the corundum tube of the seeding section is bonded to the plane of the wax mold base, and the bottom surface of the two support columns 3 is bonded to the plane of the wax mold base. The structure after bonding with the wax mold chassis is as follows Figure 3 The connection between the wax mold base, the wax mold of the outer corundum tube of the seeding section, and the two support rods is trimmed to make them smooth to obtain a shell wax mold.

[0062] In the shell wax mold, the connection between the seeding section wax mold of the outer corundum tube and the wax mold base is a right-angle transition, and the connection between the two support column wax molds and the wax mold base is a rounded transition.

[0063] By using the investment casting technology, the ceramic mold shell for casting blade simulation parts is made by hanging slurry and pouring sand on the surface of the shell wax mold, dewaxing and sintering.

[0064] The second step is to make

[001] oriented seed crystals and polish the surface of the seed crystals to a bright finish:

[0065] A single crystal test rod is prepared by a crystal selection method, and a single crystal test rod for seed crystal is cut from the nickel-based single crystal high-temperature alloy test rod; the single crystal test rod for seed crystal has a diameter of 15 mm and a length of 45 mm.

[0066] The orientation of the single crystal test rod for the seed crystal is determined by using a high-precision X-ray crystal orientation instrument, and the single crystal test rod is fixed using the fixture provided by the instrument. The

[001] orientation of the single crystal cut by the instrument deviates from the axial direction by less than 5°.

[0067] The fixture is placed on the guide rails of a wire-cutting machine, and a

[001] -oriented single crystal cylinder is cut from the seed crystal single crystal test rod using a wire-cutting machine as a seed crystal. The directionally cut seed crystal is cylindrical and has a

[001] orientation that deviates from the axial direction by 0°.

[0068] The surface of the seed crystal was polished with 1000# water-abrasive sandpaper until smooth.

[0069] The final

[001] oriented seed crystal had a diameter of 6.96 mm and a length of 35 mm.

[0070] The third step is to mark the secondary dendrite orientation on either end face of the

[001] oriented seed crystal:

[0071] Standard metallographic preparation steps were used to polish any end face of the

[001] oriented seed crystal, and the end face was chemically etched. Polishing conditions: 80#, 220#, 400#, 800#, 1000#, 1500#, and 2000# water-abrasive sandpaper was used to polish one end face of the seed crystal, and then polished on a polishing machine. Subsequently, the end face was etched with an etchant consisting of a mixture of nitric acid solution (concentration of 65-68wt.%), hydrofluoric acid solution (concentration ≥40wt.%), and propylene glycol (volume ratio of 1:2:3) for 20-60 seconds. After etching, a regular "cross" pattern appeared on the end face. The "cross" pattern was the secondary dendrite. When observed from the end face, the directions of the two groups of secondary dendrites were perpendicular to each other.

[0072] A secondary dendrite marking line 9 is drawn on the end face 8 of the seed crystal that has been metallographically chemically etched. The marking line is parallel to the direction of one of the secondary dendrites, such as Figure 4shown.

[0073] The fourth step is to place the

[001] oriented seed crystal in a specific three-dimensional orientation in the corundum tube of the seeding section of the mold shell according to the shape, size and position of the sudden change section of the blade simulation part:

[0074] According to the shape and size of the variable cross-section of the blade simulation used in this embodiment, the angle θ between the secondary dendrite marking line and the edge of the rectangular mutation cross-section 2 is set to 0°, even if the growth direction of the secondary dendrite is parallel to the two vertical sides of the rectangular mutation cross-section. The schematic diagram is as follows: Figure 5 shown.

[0075] Mark a line on the mold base that is parallel to any side of the rectangular cross-section.

[0076] Place the above-mentioned

[001] oriented seed crystal into the corundum tube of the mold shell seeding section, with the end face marked with the secondary dendrite direction facing downward (i.e., close to the side of the mold shell bottom plate), and ensure that the secondary dendrite marking line marked on the end face of the seed crystal is parallel to the line marked on the mold shell bottom plate that is parallel to one side of the rectangular mutation section.

[0077] Use high-temperature tape to secure the seed crystal in place.

[0078] Step 5: Complete the casting and obtain the single crystal blade simulation:

[0079] The blade simulation mold equipped with the controlled three-dimensional orientation seed crystal is placed on a water-cooled copper plate in a directional solidification furnace, so that the lower surface of the mold chassis is in close contact with the upper surface of the water-cooled copper plate.

[0080] The fourth generation nickel-based single crystal high temperature alloy DD91 master alloy block is placed in the electromagnetic melting crucible on the upper part of the furnace body.

[0081] Lift the ceramic mold into the hot zone so that the upper surface of the mold chassis is 10 mm away from the lower surface of the radiation baffle.

[0082] The furnace door was closed, vacuum was applied, the heater was turned on, and the temperature of the directional solidification furnace was raised to 1550° C. at a rate of 10° C. / min to melt the seed crystal for three-dimensional orientation control near the heating body of the directional solidification furnace.

[0083] The power of the electromagnetic melting crucible was increased to 10 kW to completely melt the high-temperature alloy master alloy ingot in the crucible to obtain a high-temperature alloy melt. Under the condition of a directional solidification furnace with a vacuum degree of 0.01 to 5 Pa, the high-temperature alloy melt was poured into a ceramic mold at a pouring temperature of 1450°C, and the mold was filled with the high-temperature alloy melt.

[0084] Keep warm for 5 minutes until the temperature is basically constant, and pull the casting system and the bottom water-cooled copper plate from the hot zone to the cold zone of the directional solidification furnace at a pulling speed of 100 μm / s, so that the alloy melt in the mold shell undergoes directional solidification from bottom to top to form a single crystal structure.

[0085] After the drawing is completed, wait for the temperature of the heating furnace to cool down to below 300°C, release the vacuum in the directional solidification furnace, open it, take it out and shell it, and obtain a single crystal high-temperature alloy casting.

[0086] The microstructure of the single crystal high temperature alloy casting prepared in this embodiment at the bottom of the rectangular cross section is as follows: Figure 6 shown.

[0087] Comparative Example 1

[0088] The preparation method is basically the same as that of Example 1, except that the angle θ between the secondary dendrite and the side of the rectangular mutation section is 45°, that is, the growth direction of the secondary dendrite is 45° to the side of the rectangular mutation section. Figure 7 The microstructure of the final casting at the bottom of the rectangular cross section is shown as follows: Figure 8 As shown, the curves are marked as grain boundaries.

[0089] Comparing Example 1 and Comparative Example 1, it can be seen that at the same pulling speed, no stray crystals are produced in the casting blade. Figure 6 It can be seen that when the angle θ between the secondary dendrite and the edge of the rectangular mutation section is 0°, no stray crystals are generated at the rectangular mutation section of the casting, and a uniform single crystal structure is obtained; Figure 8 It can be seen that when the angle θ between the secondary dendrite and the edge of the rectangular mutation section is 45°, a large number of stray crystals are generated at the corners of the rectangular mutation section of the casting.

[0090] Combine Figure 9 and Figure 10 In the schematic diagram, when the angle between the secondary dendrite growth direction and the rectangular mutation section is 0° and 45°, the path of the dendrite branches from the blade body growing to the rectangular mutation section can be seen. Compared with the case where the angle between the secondary dendrite growth direction and the rectangular mutation section is 45°, when the angle between the secondary dendrite growth direction and the rectangular mutation section is 0°, the path of the dendrite branches from the blade body growing to the corners of the rectangular mutation section is significantly shorter. Therefore, before the melt at the corners of the shape mutation section reaches the critical nucleation supercooling of the alloy, the dendrites from the blade body can preferentially fill the corners of the shape mutation section, thereby inhibiting heterogeneous nucleation at the mutation section and preventing the formation of impurity crystals.

[0091] In summary, the present invention effectively shortens the path of dendrites from the blade body to grow to the corners of the rectangular mutation section by precisely controlling the growth direction of secondary dendrites relative to the rectangular mutation section according to the shape, size and position of the mutation section of the blade simulation part. Before the melt at the corners of the rectangular mutation section reaches the critical nucleation supercooling of the alloy, the dendrites from the blade body preferentially fill the corners of the rectangular mutation section, which can effectively suppress the formation of miscellaneous crystal defects at the mutation section of the blade simulation part, demonstrating the feasibility and effectiveness of the present invention. The process of the present invention is simple and easy to implement, and does not require the addition of new equipment or the modification of the original directional solidification equipment; it will not introduce other solidification defects, nor will it affect subsequent heat treatment; and it can greatly improve the yield of single crystals. Its technical advantages are very obvious, and its market application prospects are very broad.

[0092] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for controlling the sudden cross-section defects of single crystal high-temperature alloy castings by secondary orientation, comprising the following steps: A single crystal casting mold shell is provided; the single crystal casting mold shell includes a seeding section; a corundum tube is pre-installed in the seeding section; Mark the secondary dendrite orientation on any end face of the [001]-oriented seed crystal to obtain a marked seed crystal; Placing the marked seed crystal in the corundum tube at a predetermined angle to obtain a mold shell with a preset specific three-dimensional oriented seed crystal; The method for determining the placement angle of the marked seed crystal includes: determining the growth direction of the secondary dendrite orientation relative to the shape mutation section based on the structure, size and position of the shape mutation section of the single crystal high-temperature alloy casting and the principle of the shortest path of dendrite branch growth; the angle between the secondary dendrite orientation and the edge of the shape mutation section is 0°; A high-temperature alloy melt is cast into the mold shell with the preset specific three-dimensional oriented seed crystals, and directionally solidified to obtain a single crystal high-temperature alloy casting.

2. The method according to claim 1, characterized in that The inner diameter of the corundum tube is 6.96-11.98 mm; the length of the corundum tube is 30-45 mm.

3. The method according to claim 1, characterized in that The method for obtaining the [001]-oriented seed crystal comprises: measuring the orientation of a single crystal test rod for the seed crystal, and directionally cutting the [001]-oriented seed crystal.

4. The method according to claim 1, wherein The [001] oriented seed crystal is further polished with sandpaper to be smooth before marking.

5. The method according to claim 1 or 2, characterized in that The [001] oriented seed crystal has a diameter of 6.66 to 11.94 mm and a length of 29 to 44 mm.

6. The method according to claim 1, characterized in that The [001] orientation of the [001] oriented seed crystal deviates from its axial direction by 0 to 5 degrees.

7. The method according to claim 1, characterized in that The method for marking the secondary dendrite orientation on any end face of the [001]-oriented seed crystal comprises: polishing and etching any end face of the [001]-oriented seed crystal in sequence, obtaining a "cross" pattern on the seed crystal end face after etching; and taking a line parallel to any side of the "cross" pattern as the secondary dendrite orientation.

8. The method according to claim 1 or 2, characterized in that The gap between the marking seed crystal and the inner wall of the corundum tube is 0.02-0.48 mm.

9. The method according to claim 1, characterized in that The casting is carried out in a directional solidification furnace.

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