A single crystal casting and a method for producing the same

Abstract

This invention discloses a single-crystal casting and its preparation method. In one aspect of the invention, the single-crystal casting preparation method involves designing the seed crystal and the seed crystal cavity of the mold shell into matching frustoconical shapes, and designing the height of the seed crystal to be greater than the height of the seed crystal cavity. The mold shell equipped with the seed crystal is installed on the quenching base of a vacuum directional solidification furnace. The seed crystal supports the mold shell, preventing it from contacting the quenching base. Because the taper of the seed crystal and the seed crystal cavity are the same, and the entire weight of the mold shell is pressed onto the seed crystal, the seed crystal and the mold shell fit tightly without gaps. Therefore, the poured molten metal will not flow in and form fissures, thus preventing the formation of fissure-related impurities.

Description

Technical Field

[0001] This invention belongs to the field of single crystal preparation technology, and particularly relates to a single crystal casting and its preparation method. Background Technology

[0002] Currently, the main methods for obtaining single crystals are the selection method and the seed crystal method. However, the existing seed crystal method has the following problems: First, when the cylindrical seed crystal 1 is inserted into the cylindrical seed crystal cavity of the mold shell 2, gaps 4 are inevitable. Figure 1 As shown in (a); during casting, the molten metal flows in 5, forming a fissure 6, as shown in (a). Figure 1 As shown in (c), during solidification, it grows into a burr-like impurity 7, as... Figure 1 As shown in (d) in the figure. One method is to directly attach the seed crystal to the bottom of the leaf wax model during the wax model making process. After dipping in slurry and sanding, the seed crystal is seamlessly retained in the mold shell. However, the long baking time (about one day) at about 1000°C after dewaxing will cause the surface of the seed crystal to oxidize, so this method is not practical. The second method is to attach the seed crystal to the mold shell and, during the preheating time (more than an hour) before pouring, the upper surface of the seed crystal 1 will react with the residual gas in the vacuum furnace to produce an oxide film 8, such as Figure 1 As shown in (b), when the molten metal 5 is poured in, this oxide film may remain in place or its position may change. During the subsequent solidification process, it will hinder crystal growth and cause the growth of oxide film impurities 9, such as... Figure 1 As shown in (d) in the figure. Summary of the Invention

[0003] The main objective of this invention is to provide a single-crystal casting and its preparation method, which aims to effectively solve the problem of impurity crystals caused by the gaps between the seed crystal and the mold shell.

[0004] Therefore, one aspect of the present invention provides a method for preparing single crystal castings, comprising: designing the seed crystal and the seed crystal cavity of the mold shell into matching frustoconical shapes, and designing the height of the seed crystal to be greater than the height of the seed crystal cavity; installing the mold shell equipped with the seed crystal on the seed crystal base of the vacuum directional solidification furnace, using the seed crystal to support the mold shell so that the mold shell does not contact the quenching base; since the seed crystal and the seed crystal cavity have the same taper, and the entire weight of the mold shell is pressed on the seed crystal, the seed crystal and the mold shell are tightly fitted without gaps, and the poured molten metal will not flow in to form a burr, thus preventing the formation of burr impurities.

[0005] Specifically, when preparing single-crystal castings using a vacuum directional solidification furnace, the majority of the mold shell is raised into the hot chamber of the directional solidification furnace using a chilling base. After the furnace cavity is evacuated and preheated, the seed crystal cavity along with the seed crystal remains in the cold zone. After the furnace cavity is preheated to the set temperature, the seed crystal cavity of the mold shell is raised into the hot chamber, allowing the seed crystal portion to enter the hot zone. Then, the temperature is maintained and the casting is performed. Finally, the chilling base is slowly lowered, allowing the mold shell to descend into the cold chamber at a set speed, and the seed crystal grows epitaxially upwards to obtain the single-crystal casting.

[0006] Specifically, the mold shell preheating temperature is ≥1500°C, the mold shell preheating time is ≥1 hour, and the seed crystal cavity, together with the seed crystal, is kept at the temperature for 12-18 minutes after entering the hot chamber.

[0007] Specifically, by modifying the vacuum directional solidification furnace, the original chilling base was redesigned into two sets of independently movable mold shell bases and seed crystal bases. During casting, the mold shell base is first used to raise the entire mold shell into the hot chamber of the directional solidification furnace for preheating. During this preheating process, the seed crystal remains in the cold zone of the vacuum directional solidification furnace. Next, the seed crystal base is used to raise the seed crystal into the preheated mold shell and press it firmly, causing the mold shell to slightly rise and separate from the mold shell base. After this, the casting is held at room temperature and then poured. Finally, the seed crystal base and the mold shell base are slowly lowered together, allowing the mold shell to descend into the cold chamber, where the seed crystal undergoes epitaxial growth to produce a single-crystal casting.

[0008] Specifically, the mold base has multiple through holes arranged in a circumferential array, and each through hole corresponds to a seed crystal base. The mold has multiple seed crystal cavities that correspond one-to-one with the seed crystal bases. Each seed crystal cavity is equipped with a seed crystal. Each seed crystal can be epitaxially grown upward to obtain a single crystal casting.

[0009] Specifically, the circumferential axis of the distribution of the multiple through holes coincides with the axis of the mold base.

[0010] Specifically, the mold shell preheating temperature is ≥1500°C, the mold shell preheating time is ≥1 hour, and the seed crystal is kept at the temperature for 4-6 minutes after entering the hot chamber.

[0011] Specifically, the seed crystal is shaped like a frustum conical or a rhomboid frustum conical.

[0012] Another aspect of the present invention provides a single crystal casting prepared by the above-described single crystal casting preparation method.

[0013] Specifically, the single-crystal casting is a single-crystal blade.

[0014] Compared with the prior art, at least one embodiment of the present invention has the following advantages: the seed crystal is made into a frustum shape, and before casting, the seed crystal is matched and installed into the seed crystal cavity from the bottom of the mold shell. Since the seed crystal and the installation cavity have a taper, they will fit tightly. After the mold shell with the seed crystal is installed on the cooling base, the seed crystal supports the mold shell, so that the mold shell does not contact the cooling base. The mold shell is completely seated on the seed crystal. Under the pressure of the mold shell, the contact with the seed crystal is even tighter. After heating and casting, the molten metal will not flow down to form a slit, and thus no impurities will be formed. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a schematic diagram of existing seed crystal technology;

[0017] Figure 2 This is a schematic diagram of one embodiment of the present invention;

[0018] Figure 3 This is a schematic diagram of another embodiment of the present invention;

[0019] Figure 4 This is a top view of the assembly of the mold shell chassis and the seed crystal chassis according to an embodiment of the present invention;

[0020] Figure 5 This is an assembly cross-sectional view of the mold shell chassis and seed crystal chassis according to an embodiment of the present invention;

[0021] Among them: 1. Seed crystal; 2. Mold shell; 3. Cooling base; 4. Gap; 5. Molten metal; 6. Fiber seam; 7. Fiber seam impurity crystal; 8. Oxide film; 9. Oxide film impurity crystal; 10. Seed crystal cavity; 11. Mold shell base; 12. Seed crystal base. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0024] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0025] See Figure 2 A method for preparing single-crystal castings involves designing the seed crystal 1 and the seed crystal cavity 10 of the mold shell 2 into matching frustoconical shapes, and designing the height of the seed crystal 1 to be greater than the height of the seed crystal cavity 10. The mold shell 2, equipped with the seed crystal 1, is installed on the quenching base 3 of a vacuum directional solidification furnace. The seed crystal 1 supports the mold shell 2, preventing the mold shell 2 from contacting the quenching base 3. Since the seed crystal 1 and the seed crystal cavity 10 have the same taper, and the entire weight of the mold shell 2 is pressed on the seed crystal 1, the seed crystal 1 and the mold shell 2 are tightly fitted without gaps. The poured molten metal 5 will not flow in and form a fissure 6, thus preventing the formation of fissure impurities 7.

[0026] In this embodiment, the seed crystal 1 is made into a frustum shape. Before casting, the seed crystal 1 is fitted into the seed crystal cavity 10 from the bottom of the mold shell 2. Since the seed crystal 1 and the seed crystal cavity 10 have a taper, they will fit tightly. After the mold shell 2 with the seed crystal 1 is installed on the cooling base, the seed crystal 1 supports the mold shell 2, so that the mold shell 2 does not contact the cooling base 3. The mold shell 2 sits completely on the seed crystal. Under the pressure of the mold shell 2, the contact with the seed crystal 1 is even tighter. After heating and casting, the molten metal 5 will not flow down to form a burr 6, so no burr impurities will be formed.

[0027] The inventors discovered that, in order to solve the problem of oxide film 8 forming on the upper surface of the preheated seed crystal 1 of the mold shell 2, the casting preparation process can adopt the following solution:

[0028] (1) Shell loading: Before casting, the seed crystal 1 is loaded into the seed crystal cavity 10 of the mold shell 2 from the bottom. Due to the same taper, they will fit tightly. However, because the seed crystal is slightly longer, a small section of the bottom will protrude. The mold shell 2 with the seed crystal is installed on the chilling base 3. The weight of the mold shell 2 presses on the seed crystal and then contacts the chilling base 3. Under the pressure of the mold shell 2, the contact with the seed crystal 1 becomes even tighter, with no gaps 4. The chilling base 3 and the mold shell 2 are raised. Most of the mold shell 2 rises into the hot zone of the directional solidification furnace, leaving only part of the seed crystal 1 in the cold zone.

[0029] (2) Preheating: After vacuuming, the hot zone of the furnace cavity is heated, and the required furnace temperature (above 1500°) is reached after more than an hour. During this period, most of the mold shell 2 is heated in the hot zone, but the seed crystal at the bottom is kept in the cold zone and will not be oxidized.

[0030] (3) Lifting the shell: Lift the shell 2, and the seed crystal 1 part enters the preheated hot zone.

[0031] (4) Heat preservation: After a short heat preservation period (about 15 minutes), the upper part of the seed crystal 1 is rapidly heated to above 1500°C and the upper surface begins to melt. As the high temperature exposure time of the seed crystal 1 is greatly shortened (from more than 1 hour to less than 15 minutes), the oxidation phenomenon is greatly reduced and very little oxide film 8 is produced.

[0032] (5) Casting: The cast molten metal 5 quickly fuses with the molten part on the top of the seed crystal 1. Since the conical seed crystal 1 and the inner cavity of the conical mold shell 2 are fully fitted without gaps, the molten metal 5 will not flow in to form the burr 6, and thus the burr 6 impurity crystal will not be formed.

[0033] (6) Pulling solidification: The mold shell 2 descends into the cold chamber, and the seed crystal 1 grows epitaxially upward. Since there is no impurity crystal 6, there is basically no obstruction of oxide film 8, and it is possible to achieve single crystal directional solidification without impurity crystals.

[0034] In this embodiment, during preheating, the seed crystal cavity 10 of the mold shell 2 is left in the cold zone. After the hot zone of the furnace cavity is heated to a high temperature, it rises to the hot zone. During this period, most of the mold shell 2 has been heated in the hot zone, but the seed crystal at the bottom is left in the cold zone and will not be oxidized. The above method greatly reduces the oxidation phenomenon and produces very little oxide film 8 because the exposure time of the seed crystal at high temperature is greatly shortened.

[0035] Further research by the inventors revealed that due to the poor heat transfer of the mold shell 2, the above method requires a certain holding time (approximately 15 minutes) to ensure that the seed crystal cavity 10 and the seed crystal 1 within the mold shell 2 are sufficiently heated; therefore, oxidation still occurs. To further address the problem of oxide film 8 forming on the upper surface of the seed crystal during preheating of the mold shell 2, the inventors proposed another innovative solution. Specifically, this involves modifying the directional solidification furnace by splitting the original chilling base 3 into two independently movable sets: a mold shell base 11 and a seed crystal base 12. The mold shell base 11 supports the mold shell 2, while the seed crystal base 12 supports the seed crystal 1. See also... Figure 3 The preparation process of the casting is as follows:

[0036] (1) Lifting the shell: First, use the mold base plate 11 to lift the entire mold shell 2 into the hot chamber of the directional solidification furnace.

[0037] (2) Preheating: After vacuuming, the furnace cavity hot zone is heated, and the required furnace temperature (above 1500°) is reached after more than an hour. All the mold shells 2 are heated in the hot zone, but the seed crystals are kept in the cold zone and will not be oxidized.

[0038] (3) Raising the seed crystal: Next, the seed crystal is raised into the heated mold shell 2 using the seed crystal base 12 and pressed tightly, so that the mold shell 2 is slightly raised and separated from the mold shell base 11. The mold shell 2 sits completely on the seed crystal, and the seed crystal is tightly attached to the seed crystal.

[0039] (4) Heat preservation: Heat preservation for about 5 minutes, the seed crystal is rapidly heated and melts from the top. Due to the greatly shortened high temperature exposure time of the seed crystal (only about 5 minutes in total), the oxidation phenomenon is greatly reduced, and there is basically no oxide film.

[0040] (5) Casting: The cast molten metal 5 quickly fuses with the molten part on the top of the seed crystal. Since the cone surface between the seed crystal and the inner cavity of the mold shell 2 is tightly attached without gaps, the molten metal 5 will not flow in to form a burr 6, and thus no burr 6 impurities will be formed. Also, since the exposure time of the seed crystal is greatly shortened, the oxidation phenomenon is greatly reduced, and there is basically no oxide film 8.

[0041] (6) Pull-out solidification: The seed crystal base plate 12 and the mold shell base plate 11 are lowered synchronously, so that the mold shell 2 is lowered into the cold chamber, and the seed crystal 1 is epitaxially grown upward to obtain a single crystal casting. Since there is no appearance of impurity crystals 6 and there is basically no obstruction of oxide film 8, it is possible to achieve impurity-free single crystal directional solidification.

[0042] In this embodiment, the original chilling chassis 3 is designed as two sets of mold shell chassis 11 and seed crystal chassis 12 that can move independently up and down. During preheating, the mold shell chassis 11 is used to heat all the mold shells 2 in the hot zone, but the seed crystal 1 is kept in the cold zone and will not be oxidized. Then, the seed crystal chassis 12 is used to lift the seed crystal 1 into the preheated seed crystal cavity 10 and press it tightly and keep it warm. Since the seed crystal cavity 10 of the mold shell 2 has been preheated, the seed crystal 1 can be heated quickly and melted from the top. The heating and melting time of the upper part of the seed crystal 1 is greatly reduced (about 5 minutes). Therefore, the heating exposure time of the seed crystal 1 is greatly shortened, the oxidation phenomenon is greatly reduced, and there is basically no oxide film 8.

[0043] See Figure 4 and Figure 5 In some embodiments, the mold base 11 is provided with a plurality of through holes arranged in a circumferential array, and each through hole is provided with a seed crystal base 12. The mold 2 is provided with a plurality of seed crystal cavities 10 corresponding one-to-one with the seed crystal base 12. Each seed crystal cavity 10 is equipped with a seed crystal 1. Each seed crystal 1 can be epitaxially grown upward to obtain a single crystal casting. This design allows multiple single crystal castings to be produced in one furnace, with low production cost. The single crystal casting can be a single crystal blade or other castings.

[0044] Understandably, in practical design, to ensure uniform heating, the circumferential axis of the multiple through holes coincides with the axis of the mold base 11. The seed crystal 1 can be designed as a frustum conical or a regular rhomboid frustum, such as a regular triangular or regular tetrahedral frustum. Of course, it can also be designed as other frustum shapes. As for the space gap between the mold shell 2 and the seed crystal base 12 after the mold shell 2 is fully supported by the seed crystal 1, it is usually controlled at 1-2mm. This is because a smaller gap can prevent the seed crystal from being made too long, thus saving material.

[0045] Unless otherwise stated, if any of the technical solutions disclosed in this invention specify a numerical range, then the disclosed numerical range is a preferred numerical range. Anyone skilled in the art should understand that the preferred numerical range is merely one among many feasible numerical values ​​that has a more obvious or representative technical effect. Because there are many numerical values, it is impossible to list them all. Therefore, this invention discloses only some numerical values ​​to illustrate the technical solutions of this invention. Furthermore, the numerical values ​​listed above should not constitute a limitation on the scope of protection of this invention.

[0046] Furthermore, if the present invention discloses or relates to mutually fixedly connected components or structural parts, then unless otherwise stated, a fixed connection can be understood as: a detachable fixed connection (e.g., using bolts or screws), or a non-detachable fixed connection (e.g., riveting, welding). Of course, mutually fixed connections can also be replaced by an integral structure (e.g., manufactured using a casting process) (except where it is obviously impossible to use an integral molding process).

[0047] Furthermore, unless otherwise stated, the terms used to indicate positional relationships or shapes in any of the technical solutions disclosed in this invention include states or shapes that are similar to, analogous to, or close to those states or shapes. Any component provided by this invention can be assembled from multiple individual components or can be a single component manufactured using a one-piece molding process.

[0048] The above embodiments are merely illustrative examples to clearly illustrate the present invention and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all embodiments here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a single-crystal casting, characterized in that, include: The seed crystal cavity (10) of the seed crystal (1) and the mold shell (2) are designed to be a matching frustoconical shape, and the height of the seed crystal (1) is designed to be greater than the height of the seed crystal cavity (10). The mold shell (2) equipped with the seed crystal (1) is installed on the quenching base (3) of the vacuum directional solidification furnace. The seed crystal (1) supports the mold shell (2) so that the mold shell (2) does not contact the quenching base (3). Since the taper of the seed crystal (1) and the seed crystal cavity (10) are the same, and the weight of the entire mold shell (2) is pressed on the seed crystal (1), the seed crystal and the mold shell (2) are tightly fitted without gaps (4). The molten metal (5) will not flow in and form burrs (6), so no burr impurities (7) will be formed. When preparing single crystal castings using a vacuum directional solidification furnace, the mold shell (2) is raised into the hot chamber of the directional solidification furnace by a chilling base (3). The furnace cavity is evacuated and preheated, but the seed crystal cavity (10) and the seed crystal (1) are still kept in the cold zone. After the furnace cavity is preheated to the set temperature, the seed crystal cavity (10) of the mold shell (2) is raised into the hot chamber, so that part of the seed crystal (1) enters the hot zone. Then, it is kept warm and poured. Finally, the chilling base (3) is slowly lowered so that the mold shell (2) is lowered into the cold chamber at the set speed, and the seed crystal (1) grows upward to obtain a single crystal casting.

2. The method for preparing single-crystal castings according to claim 1, characterized in that: The preheating temperature of the mold shell (2) is ≥1500°C, the preheating time of the mold shell (2) is ≥1 hour, and the heat preservation time of the seed crystal cavity (10) and the seed crystal (1) after entering the hot chamber is 12-18 minutes.

3. The method for preparing single-crystal castings according to claim 1, characterized in that: By modifying the vacuum directional solidification furnace, the original chilling base (3) was split into two sets of mold base (11) and seed crystal base (12) that can move independently up and down. When preparing the casting, the mold base (11) is used to raise the entire mold (2) into the hot chamber of the directional solidification furnace for preheating. During the preheating of the mold (2), the seed crystal (1) is still kept in the cold zone of the vacuum directional solidification furnace. Then, the seed crystal base (12) is used to raise the seed crystal (1) into the heated mold (2) and press it tightly, so that the mold (2) is slightly raised and separated from the mold base (11). After that, it is kept warm and poured. Finally, the seed crystal base (12) and the mold base (11) are slowly lowered together, so that the mold (2) is lowered into the cold chamber and the seed crystal (1) grows upward to obtain a single crystal casting.

4. The method for preparing single-crystal castings according to claim 3, characterized in that: The mold base plate is provided with a plurality of through holes arranged in a circular array. Each through hole is provided with a seed crystal base plate (12). The mold (2) is provided with a plurality of seed crystal cavities (10) that correspond one-to-one with the seed crystal base plate (12). Each seed crystal cavity (10) is equipped with a seed crystal (1). Each seed crystal (1) can be epitaxially grown upward to obtain a single crystal casting.

5. The method for preparing single-crystal castings according to claim 4, characterized in that: The circumferential axis of the distribution of the plurality of through holes coincides with the axis of the mold base (11).

6. The method for preparing single-crystal castings according to claim 4, characterized in that: The preheating temperature of the mold shell (2) is ≥1500°C, the preheating time of the mold shell (2) is ≥1 hour, and the heat preservation time of the seed crystal after entering the hot chamber is 4-6 minutes.

7. The method for preparing single-crystal castings according to any one of claims 1-6, characterized in that: The seed crystal is shaped like a frustum or a rhomboid frustum.

8. A single-crystal casting, characterized in that: It is prepared by the single crystal casting preparation method according to any one of claims 1-7.

9. The single-crystal casting according to claim 8, characterized in that: The single-crystal casting is a single-crystal blade.

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