Method for controlling temperature gradient of high-temperature alloy in additive manufacturing

Abstract

The invention relates to the technical field of additive manufacturing high-temperature alloys, in particular to a method for controlling the temperature gradient of an additive manufacturing high-temperature alloy. The method comprises the following steps: (1) designing a water-cooling copper disc with holes; (2) putting the cut seed crystals into a water-cooling copper disc with holes; (3) putting the water-cooled copper disc into additive manufacturing equipment; (4) a laser is started for additive manufacturing; and (6) the water-cooled copper disc moves in the additive manufacturing direction in the additive manufacturing process. Compared with a traditional additive manufacturing method, the method has the advantages that the preparation process is simple, the problems that in the additive manufacturing process, along with additive manufacturing, the temperature of a sample is increased, and the temperature gradient in a molten pool is decreased can be solved, and formation of single crystals is not facilitated. Besides, the powder price of the high-temperature alloy is high, the requirement for the high-temperature alloy powder in the additive manufacturing process can be lowered through movement of the water cooling disc, the cost is low, and therefore the preparation efficiency of the additive manufacturing single-crystal high-temperature alloy can be improved, and the cost can be lowered.

Description

Technical Field:

[0001] The present invention relates to the technical field of preparing superalloy components by additive manufacturing, and specifically to a method for controlling the temperature gradient of superalloys in additive manufacturing. Background Art:

[0002] Superalloy components are key components in aeroengines and industrial gas turbines. With the increasing improvement of engine efficiency, the structure of superalloy components has become more and more complex, making it very difficult to prepare superalloy components by traditional methods. Due to the complex geometric shape of single-crystal components, the influence of different orientations on performance is very significant. Therefore, when designing single-crystal components, it is desired that some special parts have specific crystal orientations to maximize the performance advantages of single-crystal components.

[0003] Currently, the main method for controlling the orientation of single-crystal superalloy components is the seed crystal method. The traditional seed crystal method is to place the prepared seed crystal with a specific orientation at the bottom of the ceramic mold shell, so that the single crystal grown from the seed crystal during directional solidification directly introduces the single-crystal component, making the single-crystal component form a single-crystal structure. Although this method realizes the effective control of the single-crystal orientation, the traditional method uses the wax mold method to prepare the mold shell, and it is very difficult to prepare components with very complex structures under the control of the process.

[0004] Additive manufacturing is a technology that constructs objects by layer-by-layer printing based on digital model files, using powdery metals or plastics and other bondable materials. 3D printing technology has been successfully applied to the manufacture of complex structures of aeroengines and gas turbines, but there are still great difficulties in the control of special orientations. This invention significantly reduces the preparation cost and operation difficulty, and can effectively improve the utilization rate of superalloy powders. Summary of the Invention:

[0005] The purpose of the present invention is to provide a method for controlling the orientation of superalloy components in additive manufacturing. Compared with traditional additive manufacturing, this method flexibly seals the position of the seed crystal with a flexible carbon felt to improve the material utilization rate; at the same time, by using a water-cooled disk and blowing argon at its bottom, it can effectively reduce the deviation of the crystal orientation caused by the reduction of the temperature gradient of the molten pool due to heat accumulation during the additive manufacturing process, and even form polycrystalline defects. This solution can simplify the process, improve the qualification rate of single-crystal components with specific orientations, and is beneficial to reducing the high manufacturing cost of single-crystal components.

[0006] The technical solution of the present invention is (see the claims):

[0007] The design concept of the present invention is:

[0008] The method of the present invention is based on the idea of reducing the heat accumulation of superalloy components during additive manufacturing by means of the circulation of cooling water in the water-cooled plate and the moving cooling of the water-cooled plate during the epitaxial growth process in the directional solidification process. At the same time, this method can also reduce the usage amount of metal powder during additive manufacturing by moving the water-cooled plate, avoid the problem of heat accumulation during additive manufacturing, and the temperature gradient decreases, which is easy to form orientation deviation or even polycrystal, and realize the control of specific orientation.

[0009] Compared with the traditional additive manufacturing method, the present invention has the advantages of simple preparation process, can solve the problem that during additive manufacturing, as the additive manufacturing progresses, the temperature of the sample rises and the temperature gradient in the molten pool decreases, which is not conducive to the formation of single crystals. In addition, the powder price of superalloys is relatively expensive. The present invention can also reduce the demand for superalloy powder during additive manufacturing by moving the water-cooled plate, and has the characteristics of low cost, which is conducive to improving the preparation efficiency of single-crystal superalloys by additive manufacturing and reducing costs.

[0010] The advantages and beneficial effects of the present invention are as follows:

[0011] 1. The process design of the present invention is reasonable. Different from the traditional additive manufacturing method, the present invention has the advantages of simple operation process and low cost.

[0012] 2. The present invention can not only realize the control of the crystal orientation of additive manufacturing, but also realize the flexible movement of the metal powder cylinder with the help of the carbon felt, obtain a variable cylinder volume, significantly reduce the usage amount of superalloy powder during additive manufacturing, and reduce the manufacturing cost.

[0013] 3. The present invention is simple to operate, reasonable in design, strong in operability, can significantly reduce the problem that the orientation of single-crystal superalloy components prepared by additive manufacturing is not easy to control, and is easy to prepare single-crystal superalloy components with better orientation control.

[0014] In summary, the present invention solves the problem of controlling the specific crystal orientation of single-crystal superalloy components by additive manufacturing, and provides a method for additive manufacturing single crystals. Description of the drawings:

[0015] Figure 1 Schematic diagram of the water-cooled plate structure;

[0016] Figure 2 Schematic diagram of the combination of the sample and the water-cooled plate during additive manufacturing

[0017] Figure 3 Orientation of single crystal / directional columnar crystal after additive manufacturing Detailed implementation method:

[0018] In the specific implementation process, the steps of a method for controlling the orientation of single-crystal superalloy components of the present invention are as follows:

[0019] The steps of the method are as follows:

[0020] (1) Design a water-cooled copper disk with a cylindrical through-hole (seed crystal hole) and a sealed cavity inside the ring. There are cooling water inlets and outlets on the sealed cavity.

[0021] (2) Place the cut cylindrical seed crystal (the seed crystal is coaxial with the seed crystal hole of the water-cooled disk) into the seed crystal hole of the water-cooled copper disk.

[0022] (3) Place carbon felt between the inner wall surface of the through-hole in the middle of the water-cooled copper disk and the seed crystal; the carbon felt separates the seed crystal from the inner wall surface of the seed crystal hole of the water-cooled copper disk. The outer surface of the cylindrical carbon felt with openings at both upper and lower ends is in contact with the inner wall surface of the seed crystal hole, and the inner surface of the cylindrical carbon felt is in contact with the surface of the seed crystal, preventing metal powder from flowing along the gap to the bottom of the water-cooled disk during the additive manufacturing process, resulting in waste.

[0023] (4) Place the water-cooled copper disk with the seed crystal in a laser additive manufacturing device to perform additive manufacturing of single-crystal superalloy.

[0024] (5) During the additive manufacturing process, the water-cooled copper disk moves upward along the additive manufacturing direction as the additive manufacturing progresses.

[0025] (6) During the movement of the water-cooled copper disk as the additive manufacturing progresses, cooling water is passed through the water-cooled copper disk, and at the same time, argon gas is passed through the bottom of the water-cooled copper disk facing the lower surface of the water-cooled copper disk for water cooling and gas cooling.

[0026] Example 1

[0027] In this example, nickel-based single-crystal superalloy AM3 is used, and the alloy composition is shown in Table 1.

[0028] Table 1 Weight percentage of alloying elements

[0029] Cr Mo Al W Ti Ta Co Ni 8.0 2.0 5.6 5.0 1.0 4.0 6.0 Balance

[0030] Taking the additive manufacturing of an AM3 single-crystal test bar as an example in this example, the size of the water-cooled disk and the seed crystal hole (the through-hole in the middle of the ring-shaped water-cooled copper disk) are designed according to the additive manufacturing powder chamber (powder bed additive manufacturing). The shape of the hole is a cylinder, and the diameter of the hole is 10 mm larger than the additive manufacturing sample. If it is too large, the gap will be large, which will not only affect the cooling effect but also put higher requirements on the strength of the carbon felt. Design the hole according to the size of the water-cooled disk. The diameter of the hole is 30 mm, and the diameter / height of the hole = 1 / 2. The gap between the seed crystal and the inner wall surface of the seed crystal hole of the water-cooled disk is 5 mm. The material of the seed crystal is nickel-based alloy, and its density is 8.7 g / mm 3 (The density of AM3 single crystal is 8.5 g / mm 3) It can be a single crystal or a directionally solidified alloy. During additive manufacturing, when the water-cooled copper disk moves upward along the additive direction as the additive process progresses, control the distance between the surface of the additive melt pool and the upper surface of the water-cooled disk to be less than 10 mm. The water flow rate into the water-cooled disk is 10 L / min, the water temperature is 25 °C, the argon flow rate is 2 L / min (25 °C), and the distance between the argon pipe outlet (under the carbon felt, facing the carbon felt) and the carbon felt is 1.5 mm. This can not only enhance the cooling effect but also provide a certain supporting force for the carbon felt.

[0031] By using this method, the temperature gradient of the alloy can be effectively increased, the formation of stray grains is inhibited, and a 50-cm-long cylinder is prepared without the generation of stray grains, such as Figure 3 .

[0032] Example 2

[0033] In this example, the nickel-based superalloy SRR99 is used, and the alloy composition is shown in Table 2.

[0034] Table 2 Weight percentages of main alloying elements in SRR99 alloy

[0035] C Cr Co Al Ti W Ta Nb Ni 0.05 9.0 6.0 5.5 1.0 9.5 3.0 1.0 Balance

[0036] Taking the additive manufacturing of SRR99 single crystal test bars as an example in this example, according to the additive manufacturing powder chamber (powder laying additive manufacturing), the size of the water-cooled disk and the seed crystal hole (the central through hole of the annular water-cooled copper disk) are designed. The shape of the hole is a cylinder, and the diameter of the hole is 8 mm larger than the additive manufacturing sample. If it is too large, the gap will be large, which will not only affect the cooling effect but also put higher requirements on the strength of the carbon felt. Design the hole according to the size of the water-cooled disk. The size of the hole is 30 mm in diameter, and the diameter / height of the hole = 1 / 2. The gap between the seed crystal and the inner wall surface of the seed crystal hole of the water-cooled disk is 4 mm. The material of the seed crystal is a nickel-based alloy, and its density is 9.1 g / mm 3 (The density of SRR99 single crystal is 8.7 g / mm 3 ) It can be a single crystal or a directionally solidified alloy. During additive manufacturing, when the water-cooled copper disk moves upward along the additive direction as the additive process progresses, control the distance between the surface of the additive melt pool and the upper surface of the water-cooled disk to be less than 10 mm. The water flow rate into the water-cooled disk is 15 L / min, the water temperature is 25 °C, the argon flow rate is 2 L / min (25 °C), and the distance between the argon pipe outlet (under the carbon felt, facing the carbon felt) and the carbon felt is 4 mm. This can not only enhance the cooling effect but also provide a certain supporting force for the carbon felt.

[0037] By using this method, the temperature gradient of the alloy can be effectively increased, the formation of stray grains is inhibited, and a 50-cm-long cylinder is prepared without the generation of stray grains, such as Figure 3 .

[0038] Example 3

[0039] This embodiment uses a nickel-based superalloy, and the alloy composition is shown in Table 3.

[0040] Table 3 Weight percentages of main alloying elements in the alloy

[0041] Mo Cr Co Al Hf W Ta Re Ni 2.0 7.0 8.0 6.2 0.15 5.0 7.0 3.0 Balance

[0042] Taking the additively manufactured single crystal component as an example, the dimensions of the water-cooled disk and the seed crystal hole (the central through-hole of the annular water-cooled copper disk) are designed according to the powder chamber for additive manufacturing (powder spreading additive manufacturing). The shape of the hole is a cylinder, and the diameter of the hole is 6 mm larger than that of the additively manufactured sample. If it is too large, the gap will be large, which will not only affect the cooling effect but also pose higher requirements for the strength of the carbon felt. Design the hole according to the dimensions of the water-cooled disk. The diameter of the hole is 15 mm, and the ratio of the diameter to the height of the hole is 0.6. The gap between the seed crystal and the inner wall surface of the seed crystal hole of the water-cooled disk is 3 mm. The material of the seed crystal is a nickel-based alloy, and its density is 9.5 g / mm 3 (The density of the single crystal in the embodiment is about 8.7 g / mm 3 ). During additive manufacturing, when the water-cooled copper disk moves upward along the additive manufacturing direction as the additive manufacturing progresses, control the distance between the surface of the additive melting pool and the upper surface of the water-cooled disk to be less than 10 mm. The water flow rate into the water-cooled disk is 10 L / min, the water temperature is 25 °C, the argon flow rate is 2 L / min (25 °C), and the distance between the outlet of the argon pipe (below the carbon felt and facing the carbon felt) and the carbon felt is 1.5 mm. This can not only enhance the cooling effect but also provide a certain supporting force for the carbon felt.

[0043] By using this method, the temperature gradient of the alloy can be effectively increased, the formation of polycrystals is inhibited, and a 50-cm-long cylinder can be prepared without the generation of polycrystals, as shown in Figure 3 .

[0044] In summary, the present invention solves the problem of controlling the specific crystal orientation of additively manufactured single crystal high-alloy components, and provides a method for controlling the orientation of additively manufactured single crystal superalloy components.

Claims

1. A method for controlling the temperature gradient of superalloys in additive manufacturing, characterized in that, the specific steps are as follows: (1) Prepare a water-cooled copper disk with a through-hole (seed crystal hole) and a sealed cavity inside the ring, and a cooling water inlet and outlet are provided on the sealed cavity; (2) Place the seed crystal into the through-hole in the middle of the water-cooled copper disk; (3) Place a carbon felt between the inner wall surface of the through-hole in the middle of the water-cooled copper disk and the seed crystal; (4) Place the water-cooled copper disk with the seed crystal in the additive manufacturing equipment to perform additive manufacturing of single-crystal superalloys; (5) During the additive manufacturing process, the water-cooled copper disk moves upward along the additive manufacturing direction as the additive manufacturing progresses; (6) During the movement of the water-cooled copper disk, cooling water is introduced into the water-cooled copper disk, and at the same time, argon gas is blown onto the lower surface of the water-cooled copper disk facing the lower surface of the water-cooled copper disk for water cooling and air cooling.

2. The method according to claim 1, characterized in that, in step (1), the size of the water-cooled copper disk and the seed crystal hole (the through-hole in the middle of the ring-shaped water-cooled copper disk) are designed according to the additive manufacturing powder chamber (powder bed additive manufacturing) or the sample size (powder feeding additive manufacturing), wherein the shape of the seed crystal hole is columnar with a cylinder (circular cross-section) or a cuboid (rectangular cross-section), and the distance between the inner wall surface of the seed crystal hole and the outer wall surface of the additive manufacturing sample (or the seed crystal) is 2-10 mm. If it is too large, the gap will be large, which will not only affect the cooling effect but also put higher requirements on the strength of the carbon felt.

3. The method according to claim 1, characterized in that, in step (1), the seed crystal hole is designed according to the size of the water-cooled copper disk, wherein the diameter or side length (cross-section) of the seed crystal hole is not more than 30 mm (specific range 5-30 mm), and the hole diameter / height ≤ 1 to prevent large-area melting of the additive manufacturing seed crystal.

4. The method according to claim 1 or 3, characterized in that, in step (3), the carbon felt separates the seed crystal from the inner wall surface of the seed crystal hole of the water-cooled copper disk. The outer surface of the tubular carbon felt with openings at both upper and lower ends is in contact with the inner wall surface of the seed crystal hole, and the inner surface of the tubular carbon felt is in contact with the surface of the seed crystal or has a gap. The gap between the carbon felt and the seed crystal is not more than (less than or equal to) 1 mm (preferably less than or equal to 0.5 mm) to prevent metal powder from flowing to the lower part of the water-cooled disk along the gap during the additive manufacturing process, resulting in waste.

5. The method according to claim 1, characterized in that, in step (2), the material of the seed crystal is a nickel-based alloy, which can be a single crystal or a directionally solidified alloy, and its density is greater than the density of the additive manufacturing superalloy to prevent the formation of polycrystalline defects in the remelting zone.

6. The method according to claim 1, characterized in that, in step (5), when the water-cooled copper disk moves upward along the additive manufacturing direction as the additive manufacturing progresses, the distance between the surface of the additive manufacturing molten pool and the upper surface of the water-cooled disk is controlled to be less than or equal to 10-15 mm.

7. The method according to claim 1, characterized in that, In step (6), the water flow rate into the water-cooling tray is 10 - 15 L / min, the water temperature is ≤ 30°C (usually 20 - 30°C), the argon flow rate is 2 - 4 L / min (usually 20 - 30°C), and the distance between the outlet of the argon pipe and the lower surface of the water-cooling copper tray is not greater than (less than or equal to) 2 mm (preferably less than or equal to 0.5 - 1.5 mm). This can not only strengthen the cooling effect but also provide a certain supporting force for the annular carbon felt.

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