Directional solidification device for single-crystal casting

Abstract

The invention discloses a directional solidification device for a single-crystal casting, and belongs to the technical field of single-crystal material processing and metallurgy. The device comprises a smelting chamber, a crucible, a medium-frequency induction smelting coil, a high-frequency single-turn heating coil, a water-cooling copper disc, a cooling system and a lifting mechanism, the crucible, the medium-frequency induction smelting coil, the high-frequency single-turn heating coil and the water-cooling copper disc are all located in the smelting chamber, and the crucible is placed on the water-cooling copper disc; the lifting mechanism drives the water-cooling copper disc to ascend and descend in the smelting chamber, the medium-frequency induction smelting coil is arranged in the smelting chamber and surrounds the crucible, the high-frequency single-turn heating coil is arranged below the medium-frequency induction smelting coil and surrounds the crucible, and the cooling system is communicated with the water-cooling copper disc. By using the device disclosed by the invention, the single crystal material with relatively uniform crystal growth and consistent growth direction can be prepared, so that the single crystal material has relatively excellent performance.

Description

Technical Field

[0001] The invention belongs to the technical field of single crystal material processing and metallurgy, and relates to a single crystal casting directional solidification device. Background Art

[0002] Single crystal material is a new material with increasingly wide applications. It is composed of a single crystal and its diffraction pattern is a regular lattice. Single crystal materials usually have excellent properties. For example, single crystal aluminum has excellent mechanical, electrical conductivity and corrosion resistance, and is widely used in aerospace and semiconductor fields.

[0003] The excellent performance of single crystal materials comes from their single crystal structure, which can form single crystals growing along a single crystallographic direction. Therefore, if more polycrystalline structures are formed in the single crystal material, it will have a greater negative impact on the performance of the single crystal material. Therefore, in the preparation process of single crystal materials, it is necessary to avoid the formation of polycrystalline structures as much as possible.

[0004] The principle of directional solidification is often used in the preparation of single crystal materials. Directional solidification, also known as directional crystallization, is a technology that uses forced means to establish a temperature gradient along a specific direction in the unsolidified melt during the solidification process, so that the melt nucleates and solidifies in the direction opposite to the heat flow according to the required crystal orientation. In the process of directional solidification to prepare single crystal materials, the direction of the temperature gradient plays an important role as a factor in determining the crystal orientation. If the temperature gradient direction is poorly consistent during the preparation of single crystal materials, it is easy to cause heterogeneous nucleation in the melt, and ultimately lead to crystal growth to form a polycrystalline structure, which has a negative impact on the performance of the single crystal material.

[0005] Therefore, it is necessary to provide a single crystal casting directional solidification device to ensure the consistency of the temperature gradient direction and reduce the generation of non-required temperature gradient directions, thereby reducing the heterogeneous nucleation in the melt and the disorderly growth of crystals to form a polycrystalline structure, thereby preparing a single crystal casting with an excellent single crystal structure. Summary of the invention

[0006] In order to overcome the problems in the background technology, the present invention uses a high-frequency single-turn heating coil to heat the crucible at the solid-liquid interface in the melt, so as to reduce or eliminate the temperature difference between the crucible and the melt during the directional solidification process, reduce the possibility of forming a temperature gradient between the crucible and the melt, reduce the probability of crystals in the melt growing along the direction of the temperature gradient between the crucible and the melt, maintain a good consistency in the direction of the temperature gradient, and thus reduce heterogeneous nucleation and the formation of a polycrystalline structure due to disorderly growth of crystals.

[0007] In order to achieve the above object, the present invention is implemented by the following technical solutions:

[0008] The present invention provides a single crystal casting directional solidification device, which includes a melting chamber 1, a crucible 2, a medium frequency induction melting coil 3, a high frequency single-turn heating coil 4, a water-cooled copper plate 5, a cooling system 6, and a lifting mechanism 7. The crucible 2, the medium frequency induction melting coil 3, the high frequency single-turn heating coil 4, and the water-cooled copper plate 5 are all located in the melting chamber 1, the crucible 2 is placed on the water-cooled copper plate 5, the lifting mechanism 7 drives the water-cooled copper plate 5 to rise and fall in the melting chamber 1, the medium frequency induction melting coil 3 is arranged in the melting chamber 1 and surrounds the crucible 2, the high frequency single-turn heating coil 4 is arranged below the medium frequency induction melting coil 3 and surrounds the crucible 2, and the cooling system 6 is connected to the cooling channel in the water-cooled copper plate 5.

[0009] Preferably, the crucible 2 is made of conductive material.

[0010] Preferably, the medium frequency induction melting coil 3 operates at a frequency of 2-3 kHz, and the high frequency single-turn heating coil 4 operates at a frequency of 60 kHz.

[0011] Preferably, the smelting chamber 1 is connected to a vacuum pump 8 .

[0012] Preferably, an infrared thermometer 9 is installed on the top of the smelting chamber 1 , and the infrared thermometer 9 measures the temperature of the material in the crucible 2 . The infrared thermometer 9 is communicatively connected to the control system, and the control system is communicatively connected to the lifting mechanism 7 .

[0013] Preferably, an observation window 10 is provided on the side wall of the smelting chamber 1 .

[0014] Beneficial effects of the present invention:

[0015] 1. The present invention heats the crucible at the solid-liquid interface of the melt by setting a high-frequency single-turn heating coil, thereby reducing or eliminating the temperature gradient in the non-required direction at the solid-liquid interface of the melt while ensuring the required temperature gradient direction of the melt as a whole, thereby ensuring the consistency of the temperature gradient direction during the directional solidification process, reducing or eliminating the heterogeneous nucleation of the melt and the disorderly growth of crystals during the directional solidification process, reducing or eliminating the polycrystalline structure in the single crystal material, and finally obtaining a single crystal material with a large number of single crystal structures.

[0016] 2. The present invention moves the crucible in a direction opposite to the direction of directional solidification so that the crucible portion at the solid-liquid interface of the melt can be kept within the heating range of the high-frequency single-turn heating coil during the entire directional solidification process, thereby fundamentally reducing or eliminating the heterogeneous nucleation of the melt and the disorderly growth of crystals during the directional solidification process, and reducing or eliminating the polycrystalline structure in the single crystal material. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the structure of the device of the present invention;

[0018] Figure 2 The figures are actual pictures of single crystal aluminum prepared in the embodiments and comparative examples of the present invention, wherein (a) is single crystal aluminum prepared in the embodiments, and (b) is single crystal aluminum prepared in the comparative example.

[0019] 1- melting chamber, 2- crucible, 3- medium frequency induction melting coil, 4- high frequency single turn heating coil, 5- water-cooled copper plate, 6- cooling system, 7- lifting mechanism, 8- vacuum pump, 9- infrared thermometer, 10- observation window. DETAILED DESCRIPTION

[0020] The present invention is further described in detail below in conjunction with specific embodiments.

[0021] In the embodiments and comparative examples of the present invention, the preparation of single crystal aluminum is taken as an example, and all conditions are conditions for preparing single crystal aluminum.

[0022] Example

[0023] like Figure 1 As shown, the directional solidification device includes a melting chamber 1, a crucible 2, a medium frequency induction melting coil 3, a high frequency single-turn heating coil 4, a water-cooled copper plate 5, a cooling system 6, and a lifting mechanism 7. The crucible 2, the medium frequency induction melting coil 3, the high frequency single-turn heating coil 4, and the water-cooled copper plate 5 are all located in the melting chamber 1, the crucible 2 is placed on the water-cooled copper plate 5, the lifting mechanism 7 drives the water-cooled copper plate 5 to move up and down in the melting chamber 1, the medium frequency induction melting coil 3 is arranged in the melting chamber 1 and surrounds the crucible 2, the high frequency single-turn heating coil 4 is arranged below the medium frequency induction melting coil 3 and surrounds the crucible 2, and the cooling system 6 is connected to the cooling channel in the water-cooled copper plate 5.

[0024] The crucible 2 is made of a conductive material, that is, the crucible 2 has a certain conductivity.

[0025] The medium frequency induction melting coil 3 operates at a frequency of 2-3 kHz, and the high frequency single-turn heating coil 4 operates at a frequency of 60 kHz.

[0026] The smelting chamber 1 is connected to a vacuum pump 8 .

[0027] When preparing single crystal aluminum, firstly, a raw material solid block is placed in a crucible 2 (a graphite crucible is used in this embodiment), and then the door of the smelting chamber 1 is closed (the door installed on the smelting chamber 1 belongs to conventional technology and is not shown in the figure), and a closed space is formed inside the smelting chamber 1. The vacuum pump 8 is turned on to evacuate the inside of the smelting chamber 1 into a vacuum space. During the preparation of single crystal aluminum, the vacuum pump 8 is kept turned on to maintain the vacuum degree in the smelting chamber 1 at 10 -3Pa, the water-cooled copper plate 5 is raised or lowered by controlling the lifting mechanism 7 (the lifting mechanism 7 can be an electric push rod, a lifting platform or other existing devices), so that the crucible 2 placed on the water-cooled copper plate 5 is raised and lowered, the bottom surface of the crucible 2 is adjusted to the position of the high-frequency single-turn heating coil 4, and the medium-frequency induction melting coil 3 is turned on. The medium-frequency induction melting coil 3 heats the raw material solid block to melt the raw material solid block into a melt, and then the cooling water output flow rate of the cooling system 6 is set to 5×10 -5 m 3 / s, after the cooling system 6 outputs cooling water at a set flow rate, the cooling water flows into the water-cooled copper plate 5 to cool the water-cooled copper plate 5, so that the water-cooled copper plate 5 maintains a relatively low temperature, the moving speed of the lifting mechanism 7 is set to 0.4mm / min, the lifting mechanism 7 is temporarily kept in a stopped state, and the high-frequency single-turn heating coil 4 is turned on at the same time. The working frequency of the medium-frequency induction melting coil 3 is 2kHz, which heats the aluminum melt (basically does not heat the crucible 2), so that the temperature of the aluminum melt is maintained at 730°C, and the working frequency of the high-frequency single-turn heating coil 4 is 60kHz, which heats the crucible 2 (basically does not heat the aluminum melt), so that the temperature of the crucible 2 is maintained at 660-665°C. At this time, the water-cooled copper plate 5 cools the aluminum melt at the bottom of the crucible 2, while the aluminum melt at the upper part of the crucible 2 is heated to a relatively high temperature. Temperature, a longitudinal temperature gradient is formed inside the aluminum melt. According to the principle of directional solidification, the aluminum melt solidifies in the crystal orientation from the bottom to the top of the crucible 2, that is, in the crucible 2, the solid-liquid interface rises at a relatively stable speed (the directional solidification rate of the single crystal material can be obtained through multiple experiments and other methods, and the directional solidification rate of the same single crystal material under the same temperature gradient is basically the same). During the directional solidification process, the lifting mechanism 7 is set to be lowered, and the lifting mechanism 7 is turned on. The lifting mechanism 7 can be set to reduce the rate. The reduction rate of the lifting mechanism 7 is set to a value that matches the directional solidification rate of the single crystal material. During the directional solidification process, the heating range of the high-frequency single-turn heating coil 4 can cover the crucible 2 at the solid-liquid interface of the melt, eliminate the lateral temperature gradient at the solid-liquid interface, and avoid heterogeneous nucleation in the melt and crystallization in non-required directions.

[0028] An infrared thermometer 9 is installed on the top of the smelting chamber 1 , and the infrared thermometer 9 measures the temperature of the material in the crucible 2 . The infrared thermometer 9 is connected to the control system for communication, and the control system is connected to the lifting mechanism 7 for communication.

[0029] The control system (a conventional PLC control system can be used) can obtain the real-time temperature of the melt by receiving the signal transmitted by the infrared thermometer 9, and adjust the descent rate of the lifting mechanism 7 through a preset program based on the obtained real-time temperature of the melt. For example, when the melt temperature is too high, the control system controls the descent rate of the lifting mechanism 7 to increase. Under normal circumstances, the melt temperature can be maintained in a relatively stable state. Therefore, the control system adjusts the descent rate of the lifting mechanism 7 relatively slightly or infrequently.

[0030] An observation window 10 is arranged on the side wall of the smelting chamber 1 , through which a worker can observe the internal situation of the smelting chamber 1 .

[0031] In this embodiment, the single crystal aluminum ingot produced by the device of the present invention is as follows: Figure 2 (a) shows that the single crystal aluminum ingot has a diameter of 30 mm and a length of 120 mm.

[0032] Comparative Example

[0033] This comparative example uses the same device and the same method as Example 1 to prepare single crystal aluminum. The difference is that during the preparation of single crystal aluminum in this comparative example, the high-frequency single-turn heating coil 4 is kept in a closed state. The single crystal aluminum prepared in this comparative example is as follows: Figure 2 (b) as shown.

[0034] pass Figure 2 From the comparison of (a) and (b), it can be seen that the single crystal aluminum ingot prepared in the embodiment has uniform crystal growth without obvious grain boundaries, while the single crystal aluminum ingot prepared in the comparative example has obvious grain boundaries and its crystal growth direction is disordered, forming a polycrystalline structure.

[0035] In summary, the device of the present invention can effectively avoid the occurrence of heterogeneous nucleation and disorderly crystal growth during the single crystal preparation process, so that the grains can grow stably in the required direction to form a single crystal material with relatively excellent performance.

[0036] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made in form and details without departing from the scope defined by the claims of the present invention.

Claims

1. A single crystal casting directional solidification device, characterized in that: The directional solidification device comprises a melting chamber (1), a crucible (2), a medium frequency induction melting coil (3), a high frequency single turn heating coil (4), a water-cooled copper plate (5), a cooling system (6), and a lifting mechanism (7). The crucible (2), the medium frequency induction melting coil (3), the high frequency single turn heating coil (4), and the water-cooled copper plate (5) are all located in the melting chamber (1). The crucible (2) is placed on the water-cooled copper plate (5). The lifting mechanism (7) drives the water-cooled copper plate (5) to move up and down in the melting chamber (1). The medium frequency induction melting coil (3) is arranged in the melting chamber (1) and surrounds the crucible (2). The high frequency single turn heating coil (4) is arranged below the medium frequency induction melting coil (3) and surrounds the crucible (2). The cooling system (6) is connected to a cooling channel in the water-cooled copper plate (5).

2. The single crystal casting directional solidification device according to claim 1, characterized in that: The crucible (2) is made of conductive material.

3. The single crystal casting directional solidification device according to claim 1, characterized in that: The medium frequency induction melting coil (3) has an operating frequency of 2-3 kHz, and the high frequency single-turn heating coil (4) has an operating frequency of 60 kHz.

4. The single crystal casting directional solidification device according to claim 1, characterized in that: The smelting chamber (1) is connected to a vacuum pump (8).

5. The single crystal casting directional solidification device according to claim 1, characterized in that: An infrared thermometer (9) is installed on the top of the smelting chamber (1), and the infrared thermometer (9) measures the temperature of the material in the crucible (2). The infrared thermometer (9) is connected to the control system for communication, and the control system is connected to the lifting mechanism (7) for communication.

6. The single crystal casting directional solidification device according to claim 1, characterized in that: An observation window (10) is provided on the side wall of the smelting chamber (1).

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