Method for controlling dendritic crystal spacing in growth process of multi-layer module single-crystal high-temperature alloy

Abstract

The invention relates to the technical field of single-crystal high-temperature alloys, in particular to a control method for dendritic crystal spacing in the growth process of a multi-layer module single-crystal high-temperature alloy. The method comprises the following steps: fixing a pre-prepared multi-layer module single crystal alloy ceramic shell with a graphite center column on a water-cooling copper disc of a liftable bracket of multi-layer module directional solidification equipment; after the mother alloy is smelted, standing is conducted, and the smelting furnace is controlled to pour alloy liquid into the multi-layer module single crystal alloy ceramic shell; and the multi-layer module single crystal alloy ceramic shell filled with the alloy liquid is pulled into the solidification cavity under the driving of the transmission device, so that directional solidification is realized, and the small-dendrite-spacing single crystal high-temperature alloy test bar is obtained. According to the method, under the condition of not changing the casting process, the problems of overlarge dendritic crystal spacing and isotherm inclination caused by the shadow effect of radiation heat dissipation in the directional solidification process of the multi-layer module single crystal high-temperature alloy are solved, and the qualified rate of large-batch production of single crystal blades is effectively increased.

Description

Technical field:

[0001] The present invention relates to the technical field of single crystal high temperature alloys, and in particular to a method for controlling the dendrite spacing during the growth of a multi-layer module single crystal high temperature alloy. Background technology:

[0002] In the process of development and progress of aero-engine technology, single-crystal high-temperature alloy turbine blades have occupied a core position. With the development of processes and technologies, the size specifications and complexity of single-crystal high-temperature alloy blades have continued to increase. This has become an effective way to improve the overall performance of key hot-end components of the engine and an inevitable trend. At present, directional solidification technology is usually used to prepare such high-performance single-crystal high-temperature alloy turbine blades. Among them, the high-speed solidification (HRS) method using a water-cooled copper disk at the bottom of the module is simple to operate and does not pollute the alloy composition. It is widely used in industrial production in China. However, the traditional HRS process faces many challenges. First, during the directional solidification process, as the solid-liquid interface gradually rises away from the water-cooled copper disk, the dominant heat dissipation mechanism of the entire module gradually changes from heat conduction inside the shell to radiation heat dissipation outside the shell, which causes the temperature gradient at the front of the solid-liquid interface to drop rapidly. Secondly, conventional HRS single crystal furnaces primarily heat and cool the entire single crystal superalloy module via radial radiation from heating elements mounted on the furnace wall and a water-cooling ring. This results in faster heating and cooling rates in the module's area closer to the furnace body, resulting in a higher temperature gradient, while areas farther from the furnace body heat and cool more slowly, resulting in a lower temperature gradient and a significant shadowing effect. This leads to various defects in the finished single crystal superalloys produced by the HRS method, especially those produced in multi-layer module single crystal alloys. Coarse dendrites are a primary concern, leading to performance fluctuations and shortened blade life. Therefore, to address these issues, it is necessary to optimize the temperature field distribution during directional solidification of multi-layer module single crystal superalloys, increase the temperature gradient at the solid-liquid front interface, and thus control the spacing between dendrites. These measures are crucial for improving the quality and performance of single crystal blades and represent a key focus for future research. Summary of the invention:

[0003] The purpose of the present invention is to provide a method for controlling the dendrite spacing during the growth process of a multi-layer module single crystal high-temperature alloy. The method effectively regulates the temperature field distribution during the solidification process by adding a central column of a graphite heat conductor in the center of the multi-layer module single crystal high-temperature alloy ceramic shell, thereby solving the problems of isothermal line inclination and dendrite coarsening caused by slow internal heat dissipation due to the shadow effect during the directional solidification of the multi-layer module single crystal high-temperature alloy, reducing the formation of single crystal blade casting defects and effectively improving the production qualification rate of single crystal blades.

[0004] The technical solution of the present invention is:

[0005] A method for controlling the dendrite spacing during the growth of a multi-layer module single crystal high-temperature alloy comprises the following steps:

[0006] Step 1: Fix a pre-prepared multi-layer module single crystal alloy ceramic shell with a graphite center column on a water-cooled copper plate of a liftable bracket of a multi-layer module directional solidification equipment;

[0007] Step 2: Add the master alloy raw material into the melting furnace above the melting chamber of the multi-layer module directional solidification equipment, and melt the master alloy while maintaining a sealed vacuum in all working areas within the equipment. Simultaneously, the multi-layer module single crystal alloy ceramic shell will be preheated. The master alloy raw material of the single crystal alloy is DD5 nickel-based single crystal high-temperature alloy.

[0008] Step 3: After the master alloy is smelted, it is allowed to stand, and the smelting furnace is controlled to pour the molten alloy into the multi-layer module single crystal alloy ceramic shell to complete the pouring and filling, and then keep it warm;

[0009] Step 4: The multi-layer module single crystal alloy ceramic shell filled with alloy liquid is pulled into the solidification chamber by the transmission device to achieve directional solidification. After the directional solidification process is completed, the vacuum state in the furnace is released and the multi-layer module single crystal alloy ceramic shell is removed;

[0010] Step 5: remove the ceramic shell, cut off the top injection plate and the spiral crystal selector seeding section, and obtain a single crystal high-temperature alloy test rod with a small dendrite spacing.

[0011] The method for controlling the dendrite spacing during the growth of a multi-layer module single crystal high-temperature alloy is described. In step 1, the multi-layer module directional solidification equipment is a directional solidification furnace having an annular heating component and a water cooling device. The directional solidification furnace includes two upper and lower annular heating components vertically arranged in the melting chamber, a water-cooled ring cooling component located in the solidification chamber, a liftable bracket and an insulating baffle; wherein the upper and lower annular heating components and one water-cooled ring cooling component are respectively located at the upper and lower parts of the initial position of the liftable bracket, and are blocked by the annular insulating baffle to achieve separation of the melting chamber and the solidification chamber.

[0012] In the method for controlling the dendrite spacing during the growth of a multi-layer module single crystal high-temperature alloy, the temperatures of the two annular heating components vertically arranged in the melting chamber are 1470℃±20℃ in the upper zone and 1520℃±20℃ in the lower zone, respectively.

[0013] In the method for controlling the dendrite spacing during the growth of a multi-layer module single crystal high-temperature alloy, in step 1, the size of the graphite center column is φ40-60 mm, and the multi-layer module single crystal alloy ceramic shell reserves a circular opening with a diameter larger than the size of the graphite center column at the bottom center for installing the graphite center column.

[0014] The method for controlling the dendrite spacing during the growth of a multi-layer module single crystal high-temperature alloy is described. The pouring cup of the multi-layer module single crystal alloy ceramic shell and the water-cooled copper disk are connected by a graphite center column, and the graphite center column is located at the central axis of the pouring cup and the water-cooled copper disk.

[0015] In the method for controlling the dendrite spacing during the growth of a multi-layer module single crystal high-temperature alloy, in step 2, the vacuum treatment condition during the smelting process is that the air pressure in the smelting chamber is lower than 7Pa.

[0016] In the method for controlling the dendrite spacing during the growth of a multi-layer module single crystal high-temperature alloy, in step 2, the mother alloy melting temperature is 1520°C ± 20°C, and the preheating temperature of the multi-layer module single crystal alloy ceramic shell is consistent with the mother alloy melting temperature.

[0017] In the method for controlling the dendrite spacing during the growth of a multi-layer module single crystal high-temperature alloy, in step 3, after the mother alloy is smelted, the standing time is 1 to 3 minutes.

[0018] In the method for controlling the dendrite spacing during the growth of a multi-layer module single crystal high-temperature alloy, in step 3, after the alloy liquid is poured, the holding time is 4 to 6 minutes.

[0019] In the method for controlling the dendrite spacing during the growth of a multi-layer module single crystal high-temperature alloy, in step 4, the pulling speed is 4 to 6 mm / min.

[0020] The design concept of the present invention is:

[0021] In order to solve the problem of coarse dendrites in single crystal alloy blades prepared by multi-layer modules, which leads to fluctuations in blade performance and shortened life, the present invention aims to optimize the temperature field distribution of multi-layer module single crystal high-temperature alloy during directional solidification, increase the temperature gradient of the solid-liquid front interface, control the spacing between dendrites, and improve the quality and performance of single crystal blades. By using a graphite column as the central column in the center of the Ni-based single crystal high-temperature alloy shell of the multi-layer module, the heat dissipation capacity of the multi-layer module single crystal shell is improved, the lateral temperature field during directional solidification is regulated to increase the temperature gradient at the solid-liquid interface front, and a single crystal high-temperature alloy casting with a smaller dendrite spacing is obtained.

[0022] The advantages and beneficial effects of the present invention are:

[0023] 1. The present invention improves the problems of excessive dendrite spacing and isothermal tilt caused by the shadow effect of radiation heat dissipation during the directional solidification process of multi-layer module single crystal high-temperature alloy without changing the casting process, effectively improving the qualification rate of large-scale production of single crystal blades.

[0024] 2. Furthermore, the pulling rate is 4 to 6 mm / min. A pulling rate that is too fast will cause the isotherm to tilt, and a pulling rate that is too slow will cause the dendrite spacing to increase. Therefore, the pulling rate is limited to 4 to 6 mm / min.

[0025] 3. Furthermore, during pouring, the vacuum degree in the melting chamber is ensured to be lower than 7Pa, the melting temperature is 1520℃, and the preheating temperature of the multi-layer module single crystal alloy ceramic mold shell is consistent with the melting temperature of the master alloy; at the same time, a graphite center column is added to the center of the mold shell, which can make the inner and outer layers of the single crystal alloy module test rods more evenly heated, and the excellent thermal conductivity of the graphite column improves the heat dissipation capacity of the ceramic mold shell, thereby increasing the temperature gradient at the front of the solid-liquid interface, thereby controlling the dendrite spacing. This improvement measure has a positive impact on improving the metallurgical quality and service performance of single crystal alloys. Description of the drawings:

[0026] Figure 1 Schematic diagram of the ceramic shell of a multi-layer module single crystal alloy test rod; (a) without graphite central column, (b) with graphite central column.

[0027] Figure 2 The dendrite morphologies of single crystal alloy test rods under different experimental conditions; among them, (a) test rod without outer layer of graphite central column, (b) test rod without inner layer of graphite central column, (c) test rod 1 with outer layer of graphite central column, (d) test rod 1 with inner layer of graphite central column, (e) test rod 2 with outer layer of graphite central column, and (f) test rod 2 with inner layer of graphite central column.

[0028] Figure 3 The primary dendrite spacing statistics at different height positions of the inner and outer single crystal alloy test rods cast in ceramic shells with or without a graphite central column.

[0029] Figure 4 Schematic diagram of the structure of the multi-layer module directional solidification equipment in the embodiment.

[0030] Explanation of the accompanying reference numerals: 1 pouring cup, 2 top pouring tray, 3 single crystal alloy test rod, 4 graphite center column, 5 spiral crystal selector, 6 seeding section, 7 water-cooled copper plate, 8 melting furnace, 9 upper heating assembly, 10 lower heating assembly, 11 water-cooled ring cooling assembly, 12 thermal insulation baffle, 13 lifting bracket, 14 melting chamber, 15 solidification chamber. Specific implementation method:

[0031] In order to better enable those skilled in the art to understand the present invention, the following is a clear and complete description of the embodiments of the present invention in conjunction with the accompanying drawings. It should be understood that the described embodiments only represent a portion of the embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work should fall within the scope of protection of the present invention.

[0032] like Figure 1 To investigate the influence of dendrite growth patterns on blade dendrite spacing, two multi-layer ceramic shells with and without graphite cores were designed. Each shell was divided into two layers, one inside and one outside, for casting 24 single-crystal alloy test rods: 16 on the outer layer and 8 on the inner layer. The inner and outer layers of the test rods did not obstruct each other, and the spacing between the test rods was consistent across all layers. The shell diameter was 300 mm for both layers. The master alloy used for casting was DD5 nickel-based single-crystal superalloy.

[0033] Below, the present invention is further described in detail by examples.

[0034] Example 1:

[0035] In this embodiment, a method for controlling the dendrite spacing during the growth of a multi-layer module single crystal high-temperature alloy includes the following steps:

[0036] Step 1: Fix the pre-prepared multi-layer module single crystal alloy ceramic shell with a graphite center column on the water-cooled copper plate of the multi-layer module directional solidification equipment; wherein the size of the graphite center column is φ60mm, and the multi-layer module single crystal alloy ceramic shell reserves a circular opening with a diameter of 64mm at the center of the bottom for installing the graphite center column.

[0037] like Figure 1 As shown in (b), the ceramic shell of the single crystal alloy test rod is an integrated structure in which a pouring cup 1, a top pouring plate 2, a single crystal alloy test rod 3, a spiral crystal selector 5, a seeding section 6, and a water-cooled copper plate 7 are connected in sequence from top to bottom. The vertical single crystal alloy test rod 3 is divided into an inner and outer layer and is evenly distributed along the circumference at the bottom of the top pouring plate 2. The upper end of each single crystal alloy test rod 3 is connected to the top pouring plate 2 through a riser, and the lower end is connected to the water-cooled copper plate 7 through a spiral crystal selector 5 and a seeding section 6. The pouring cup 1 and the water-cooled copper plate 7 are connected through a graphite center column 4, and the graphite center column 4 is located at the central axis of the pouring cup 1 and the water-cooled copper plate 7.

[0038] like Figure 4As shown, the multi-layer module directional solidification equipment is a large-scale directional solidification furnace with an annular heating component and a water cooling device, which includes a water-cooled copper plate 7, a smelting furnace 8 placed above the smelting chamber 14, an upper heating component 9 and a lower heating component 10 arranged vertically on the inner wall of the smelting chamber 14, a water-cooled ring cooling component 11 located in the solidification chamber 15, a heat insulation baffle 12 and a liftable bracket 13; wherein the smelting chamber 14 and the solidification chamber 15 correspond to each other up and down, and the ceramic shell is cooled by the water-cooled copper plate 7. The plate 7 is placed on top of a liftable support 13. The annular heating assembly (upper heating assembly 9 and lower heating assembly 10) and the water-cooled ring cooling assembly 11 are respectively located above and below the initial position of the liftable support 13 and separated by an annular heat-insulating baffle 12 to isolate the melting chamber 14 (hot zone) from the solidification chamber 15 (cold zone). The liftable support 13 drives the water-cooled copper plate 7 and the ceramic shell on it through the center hole of the heat-insulating baffle 12, and reciprocates between the melting chamber 14 and the solidification chamber 15.

[0039] Step 2: Add the master alloy raw material into the melting furnace of the multi-layer module directional solidification equipment, and melt the master alloy at 1520° C. while maintaining a closed vacuum in all working areas inside the equipment. Simultaneously, preheat the multi-layer module single crystal alloy ceramic mold shell (the temperatures of the two annular heating components vertically arranged in the melting chamber are 1470° C. in the upper zone and 1520° C. in the lower zone, respectively). The preheating temperature of the multi-layer module single crystal alloy ceramic mold shell is consistent with the melting temperature of the master alloy. The master alloy raw material of the single crystal alloy is DD5 nickel-based single crystal high-temperature alloy.

[0040] Step 3: After the master alloy raw material is completely melted, let it stand for 3 minutes, pour the alloy liquid into the multi-layer module single crystal alloy ceramic shell, complete the pouring and filling, and keep it warm for 5 minutes;

[0041] Step 4: The multi-layer module single crystal alloy ceramic shell filled with alloy liquid is slowly moved downward into the solidification chamber at a pulling speed of 5 mm / min under the drive of the pull-down transmission device to achieve directional solidification. After the directional solidification process is completed, it is cooled, the vacuum state in the furnace is released, and the multi-layer module single crystal alloy ceramic shell is removed;

[0042] Step 5: Remove the ceramic shell, cut off the pouring riser and seeding section, and obtain a single crystal high-temperature alloy test rod with a small dendrite spacing. Figure 2 As shown in (c) and (d).

[0043] Example 2:

[0044] In this embodiment, a method for controlling the dendrite spacing during the growth of a multi-layer module single crystal high-temperature alloy includes the following steps:

[0045] Step 1: Fix the pre-prepared multi-layer module single crystal alloy ceramic shell with a graphite center column on the water-cooled copper plate of the multi-layer module directional solidification equipment; wherein the size of the graphite center column is φ60mm, and the multi-layer module single crystal alloy ceramic shell reserves a circular opening with a diameter of 64mm at the center of the bottom for installing the graphite center column.

[0046] like Figure 1 As shown in (b), the ceramic shell of the single crystal alloy test rod is an integrated structure in which a pouring cup 1, a top pouring plate 2, a single crystal alloy test rod 3, a spiral crystal selector 5, a seeding section 6, and a water-cooled copper plate 7 are connected in sequence from top to bottom. The vertical single crystal alloy test rod 3 is divided into an inner and outer layer and is evenly distributed along the circumference at the bottom of the top pouring plate 2. The upper end of each single crystal alloy test rod 3 is connected to the top pouring plate 2 through a riser, and the lower end is connected to the water-cooled copper plate 7 through a spiral crystal selector 5 and a seeding section 6. The pouring cup 1 and the water-cooled copper plate 7 are connected through a graphite center column 4, and the graphite center column 4 is located at the central axis of the pouring cup 1 and the water-cooled copper plate 7.

[0047] like Figure 4 As shown, the multi-layer module directional solidification equipment is a large-scale directional solidification furnace with an annular heating component and a water cooling device, which includes a water-cooled copper plate 7, a smelting furnace 8 placed above the smelting chamber 14, an upper heating component 9 and a lower heating component 10 arranged vertically on the inner wall of the smelting chamber 14, a water-cooled ring cooling component 11 located in the solidification chamber 15, a heat insulation baffle 12 and a liftable bracket 13; wherein the smelting chamber 14 and the solidification chamber 15 correspond to each other up and down, and the ceramic shell is cooled by the water-cooled copper plate 7. The plate 7 is placed on top of a liftable support 13. The annular heating assembly (upper heating assembly 9 and lower heating assembly 10) and the water-cooled ring cooling assembly 11 are respectively located above and below the initial position of the liftable support 13 and separated by an annular heat-insulating baffle 12 to isolate the melting chamber 14 (hot zone) from the solidification chamber 15 (cold zone). The liftable support 13 drives the water-cooled copper plate 7 and the ceramic shell on it through the center hole of the heat-insulating baffle 12, and reciprocates between the melting chamber 14 and the solidification chamber 15.

[0048] Step 2: Add the master alloy raw material into the melting furnace of the multi-layer module directional solidification equipment, and melt the master alloy at 1520° C. while maintaining a closed vacuum in all working areas inside the equipment. Simultaneously, preheat the multi-layer module single crystal alloy ceramic mold shell (the temperatures of the two annular heating components vertically arranged in the melting chamber are 1470° C. in the upper zone and 1520° C. in the lower zone, respectively). The preheating temperature of the multi-layer module single crystal alloy ceramic mold shell is consistent with the melting temperature of the master alloy. The master alloy raw material of the single crystal alloy is DD5 nickel-based single crystal high-temperature alloy.

[0049] Step 3: After the master alloy raw material is completely melted, let it stand for 2 minutes, pour the alloy liquid into the multi-layer module single crystal alloy ceramic shell, complete the pouring and filling, and keep it warm for 4 minutes;

[0050] Step 4: The multi-layer module single crystal alloy ceramic shell filled with alloy liquid is slowly lowered by the pull-down transmission device at a pulling speed of 4 mm / min into the solidification chamber to achieve directional solidification. After the directional solidification process is completed, it is allowed to cool, the vacuum state in the furnace is released, and the multi-layer module single crystal alloy ceramic shell is removed;

[0051] Step 5: Remove the ceramic shell, cut off the pouring riser and seeding section, and obtain a single crystal high-temperature alloy test rod with a small dendrite spacing. Figure 2 As shown in (e) and (f).

[0052] Example 3:

[0053] In this embodiment, a method for controlling the dendrite spacing during the growth of a multi-layer module single crystal high-temperature alloy includes the following steps:

[0054] Step 1: Fix the pre-prepared multi-layer module single crystal alloy ceramic shell with a graphite center column on the water-cooled copper plate of the multi-layer module directional solidification equipment; wherein the size of the graphite center column is φ40mm, and the multi-layer module single crystal alloy ceramic shell reserves a circular opening with a diameter of 44mm at the center of the bottom for installing the graphite center column.

[0055] like Figure 1 As shown in (b), the ceramic shell of the single crystal alloy test rod is an integrated structure in which a pouring cup 1, a top pouring plate 2, a single crystal alloy test rod 3, a spiral crystal selector 5, a seeding section 6, and a water-cooled copper plate 7 are connected in sequence from top to bottom. The vertical single crystal alloy test rod 3 is divided into an inner and outer layer and is evenly distributed along the circumference at the bottom of the top pouring plate 2. The upper end of each single crystal alloy test rod 3 is connected to the top pouring plate 2 through a riser, and the lower end is connected to the water-cooled copper plate 7 through a spiral crystal selector 5 and a seeding section 6. The pouring cup 1 and the water-cooled copper plate 7 are connected through a graphite center column 4, and the graphite center column 4 is located at the central axis of the pouring cup 1 and the water-cooled copper plate 7.

[0056] like Figure 4As shown, the multi-layer module directional solidification equipment is a large-scale directional solidification furnace with an annular heating component and a water cooling device, which includes a water-cooled copper plate 7, a smelting furnace 8 placed above the smelting chamber 14, an upper heating component 9 and a lower heating component 10 arranged vertically on the inner wall of the smelting chamber 14, a water-cooled ring cooling component 11 located in the solidification chamber 15, a heat insulation baffle 12 and a liftable bracket 13; wherein the smelting chamber 14 and the solidification chamber 15 correspond to each other up and down, and the ceramic shell is cooled by the water-cooled copper plate 7. The plate 7 is placed on top of a liftable support 13. The annular heating assembly (upper heating assembly 9 and lower heating assembly 10) and the water-cooled ring cooling assembly 11 are respectively located above and below the initial position of the liftable support 13 and separated by an annular heat-insulating baffle 12 to isolate the melting chamber 14 (hot zone) from the solidification chamber 15 (cold zone). The liftable support 13 drives the water-cooled copper plate 7 and the ceramic shell on it through the center hole of the heat-insulating baffle 12, and reciprocates between the melting chamber 14 and the solidification chamber 15.

[0057] Step 2: Add the master alloy raw material into the melting furnace of the multi-layer module directional solidification equipment, and melt the master alloy at 1520° C. while maintaining a closed vacuum in all working areas inside the equipment. Simultaneously, preheat the multi-layer module single crystal alloy ceramic mold shell (the temperatures of the two annular heating components vertically arranged in the melting chamber are 1470° C. in the upper zone and 1520° C. in the lower zone, respectively). The preheating temperature of the multi-layer module single crystal alloy ceramic mold shell is consistent with the melting temperature of the master alloy. The master alloy raw material of the single crystal alloy is DD5 nickel-based single crystal high-temperature alloy.

[0058] Step 3: After the master alloy raw material is completely melted, let it stand for 3 minutes, pour the alloy liquid into the multi-layer module single crystal alloy ceramic shell, complete the pouring and filling, and keep it warm for 5 minutes;

[0059] Step 4: The multi-layer module single crystal alloy ceramic shell filled with alloy liquid is slowly lowered by the pull-down transmission device at a pulling speed of 5 mm / min into the solidification chamber to achieve directional solidification. After the directional solidification process is completed, it is allowed to cool, the vacuum state in the furnace is released, and the multi-layer module single crystal alloy ceramic shell is removed;

[0060] Step 5: Remove the ceramic shell, cut off the pouring riser and seeding section, and obtain a single crystal high-temperature alloy test rod with a small dendrite spacing. Figure 2 As shown in (g) and (h).

[0061] Comparative Example

[0062] In this embodiment, a multi-layer module single crystal alloy ceramic shell without a graphite central column was prepared as described in Example 1.

[0063] Step 1: Fixing a pre-prepared multi-layer module single crystal alloy ceramic shell without a graphite center column on a water-cooled copper plate of a multi-layer module directional solidification device;

[0064] like Figure 1 As shown in (a), the ceramic shell of the single crystal alloy test rod is an integrated structure in which a pouring cup 1, a top pouring plate 2, a single crystal alloy test rod 3, a spiral crystal selector 5, a seeding section 6, and a water-cooled copper plate 7 are connected in sequence from top to bottom. The vertical single crystal alloy test rods 3 are evenly distributed along the circumference at the bottom of the annular top pouring plate 2. The upper end of each single crystal alloy test rod 3 is connected to the top pouring plate 2 through a riser, and the lower end is connected to the water-cooled copper plate 7 through a spiral crystal selector 5 and a seeding section 6.

[0065] Other conditions are the same as in Example 1.

[0066] The dendrite morphology of the single crystal alloy test rod prepared by using a multi-layer module single crystal alloy ceramic shell without a graphite center column is as follows: Figure 2 As shown in (a) and (b).

[0067] like Figure 2 As shown in Figure 1, under the condition of unchanged directional solidification process, with the addition of graphite center column, the dendrite spacing of the single crystal alloy test rods in the inner and outer layers of the module is significantly reduced. The cross sections of 50mm, 100mm and 150mm above the spiral crystal selector in the single crystal alloy test rods of Example 1 and the comparative example were selected to measure the dendrite spacing. The results are shown in Figure 1. Figure 3 As shown in the figure, after adding the graphite central pillar, the primary dendrite spacing at various locations in the outer single crystal alloy test rod decreased from 361μm, 373μm, and 386μm to 351μm, 358μm, and 341μm, while the primary dendrite spacing at various locations in the inner single crystal alloy test rod decreased from 560μm, 574μm, and 646μm to 434μm, 462μm, and 528μm. Therefore, by adding the graphite central pillar to the multi-layer module single crystal alloy ceramic shell, the purpose of controlling the dendrite spacing can be achieved.

[0068] The implementation results show that the present invention adds a graphite central column to the multi-layer module single crystal alloy shell. Due to the excellent thermal conductivity of graphite, the overall heat dissipation capacity of the graphite central column shell is improved, especially the heat dissipation conditions on the inner side of the graphite central column shell are greatly improved, which effectively regulates the lateral temperature field distribution during the solidification process and increases the temperature gradient at the solid-liquid interface front.

Claims

1. A method for controlling the dendrite spacing during the growth of a multi-layer module single crystal high-temperature alloy, characterized in that: The following steps are involved: Step 1, fixing a pre-prepared multi-layer module single crystal alloy ceramic shell with a graphite center column on a water-cooled copper plate of a liftable bracket of a multi-layer module directional solidification equipment; Step 2, adding the master alloy raw material into the melting furnace at the upper part of the melting chamber of the multi-layer module directional solidification equipment, melting the master alloy while keeping all working areas inside the equipment in a closed vacuum state, and at the same time, the multi-layer module single crystal alloy ceramic shell will be preheated synchronously, and the master alloy raw material of the single crystal alloy is DD5 nickel-based single crystal high temperature alloy; Step 3, after the master alloy is smelted, it is allowed to stand, and the smelting furnace is controlled to pour the alloy liquid into the multi-layer module single crystal alloy ceramic shell to complete the pouring and filling, and keep it warm; Step 4, the multi-layer module single crystal alloy ceramic shell filled with alloy liquid is pulled into the solidification chamber under the drive of the transmission device to achieve directional solidification. After the directional solidification process is completed, the cooling is completed, the vacuum state in the furnace is released, and the multi-layer module single crystal alloy ceramic shell is taken out; Step 5, remove the ceramic shell, cut off the top injection plate and the spiral crystal selector seeding section, and obtain a single crystal high-temperature alloy test rod with a small dendrite spacing.

2. The method for controlling the dendrite spacing during the growth of a multi-layer module single crystal high-temperature alloy according to claim 1, characterized in that: In step 1, the multi-layer module directional solidification equipment is a directional solidification furnace with an annular heating assembly and a water cooling device, which includes two upper and lower annular heating assemblies vertically arranged in the melting chamber, a water-cooled ring cooling assembly located in the solidification chamber, a liftable bracket and an insulating baffle; wherein the upper and lower two annular heating assemblies and one water-cooled ring cooling assembly are respectively located at the upper and lower parts of the initial position of the liftable bracket, and are blocked by the annular insulating baffle to achieve separation of the melting chamber and the solidification chamber.

3. The method for controlling the dendrite spacing during the growth of a multi-layer module single crystal high-temperature alloy according to claim 2, characterized in that: The temperatures of the two annular heating assemblies arranged vertically in the smelting chamber are 1470°C ± 20°C in the upper zone and 1520°C ± 20°C in the lower zone respectively.

4. The method for controlling the dendrite spacing during the growth of a multi-layer module single crystal high-temperature alloy according to claim 1, characterized in that: In step 1, the size of the graphite center column is φ40-60 mm, and the multi-layer module single crystal alloy ceramic shell reserves a circular opening with a diameter larger than the size of the graphite center column at the bottom center for installing the graphite center column.

5. The method for controlling the dendrite spacing during the growth of a multi-layer module single crystal high-temperature alloy according to claim 4, characterized in that: The pouring cup and the water-cooled copper disk of the multi-layer module single crystal alloy ceramic shell are connected by a graphite center column, and the graphite center column is located at the center axis of the pouring cup and the water-cooled copper disk.

6. The method for controlling the dendrite spacing during the growth of a multi-layer module single crystal high-temperature alloy according to claim 1, characterized in that: In step 2, the vacuum treatment condition during the smelting process is that the air pressure in the smelting chamber is lower than 7Pa.

7. The method for controlling the dendrite spacing during the growth of a multi-layer module single crystal high-temperature alloy according to claim 1, characterized in that: In step 2, the melting temperature of the master alloy is 1520°C ± 20°C, and the preheating temperature of the multi-layer module single crystal alloy ceramic shell is consistent with the melting temperature of the master alloy.

8. The method for controlling the dendrite spacing during the growth of a multi-layer module single crystal high-temperature alloy according to claim 1, characterized in that: In step 3, after the master alloy is smelted, the standing time is 1 to 3 minutes.

9. The method for controlling the dendrite spacing during the growth of a multi-layer module single crystal high-temperature alloy according to claim 1, characterized in that: In step 3, after the alloy liquid is poured, the insulation time is 4 to 6 minutes.

10. The method for controlling the dendrite spacing during the growth of a multi-layer module single crystal high-temperature alloy according to claim 1, characterized in that: In step 4, the pulling speed is 4 to 6 mm / min.

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