A seed crystal oxidation structure to prevent single-crystal superalloys during directional solidification

Abstract

This invention discloses a seed crystal oxidation structure to prevent oxidation of single-crystal superalloys during directional solidification, aiming to effectively suppress surface oxidation of the seed crystal during directional solidification. To this end, the seed crystal oxidation structure provided by this invention includes a ceramic mold shell, in which a seed crystal is fitted into the seed crystal cavity of the ceramic mold shell. The top of the seed crystal is covered by an alloy spacer, the melting point of which is lower than that of the seed crystal.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature alloy directional solidification technology, and particularly relates to a seed crystal oxidation structure to prevent single-crystal high-temperature alloys during directional solidification. Background Technology

[0002] In the preparation of single-crystal superalloys, seed crystal casting is a commonly used technique. However, when using the seed crystal method, the seed crystal is directly exposed to a high-temperature vacuum environment. Due to the limitations of the vacuum furnace environment, a severe oxidation reaction occurs on the surface of the seed crystal, forming an oxide film. The presence of this oxide film can lead to orientation transfer failure, resulting in problems such as impurities, banding, and seed crystal detachment, which seriously restricts the improvement of the quality and performance of single-crystal superalloys. For example, in the manufacturing of single-crystal superalloys for aero-engine turbine blades, the oxide film problem causes unstable blade performance and makes it difficult to improve the yield rate. Therefore, there is an urgent need to innovate the seed crystal structure to solve these technical problems. Summary of the Invention

[0003] The main purpose of this invention is to provide a seed crystal structure that prevents oxidation of the seed crystal during the directional solidification of single-crystal high-temperature alloys, thereby effectively suppressing oxidation of the seed crystal surface during directional solidification.

[0004] To address this, the present invention provides a structure for preventing seed crystal oxidation during the directional solidification of single-crystal high-temperature alloys, comprising a ceramic mold shell, wherein a seed crystal is fitted into the seed crystal cavity of the ceramic mold shell, and the top of the seed crystal is covered by an alloy spacer. The melting point of the alloy spacer is lower than that of the seed crystal, and the alloy spacer is an Al3Ni alloy spacer, an Al3Ni2 alloy spacer, or an AlNi alloy spacer.

[0005] Specifically, the top surface of the seed crystal is provided with a positioning groove, and the bottom of the alloy gasket is provided with a positioning post that cooperates with the positioning groove.

[0006] Specifically, the ceramic mold shell is placed on a water-cooled copper plate in a directional solidification furnace, and a transition pad is provided between the ceramic mold shell and the water-cooled copper plate.

[0007] Specifically, the transition pad is a stainless steel pad or a copper alloy pad.

[0008] Compared with the prior art, the present invention has the following beneficial effects: By adding an alloy gasket with strong anti-oxidation capabilities above the seed crystal, and taking advantage of its characteristic of melting before the seed crystal, a protective layer is formed on the upper part of the seed crystal, which effectively avoids the formation of an oxide film on the surface of the seed crystal and improves the bonding quality between the seed crystal and the casting.

[0009] 2. Adding a transition pad to the water-cooled copper plate keeps the seed crystal at a higher temperature, reduces the temperature difference stress and temperature gradient between the seed crystal and the alloy liquid, and reduces the risk of seed crystal detachment and impurity crystal formation. Attached Figure Description

[0010] To more clearly illustrate the technical solutions in the embodiments of this utility model, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0011] Figure 1 This is a schematic diagram of the seed crystal oxidation structure provided by an embodiment of the present invention for preventing the directional solidification of single-crystal high-temperature alloys; The components include: 1. Ceramic mold shell; 2. Seed crystal cavity; 3. Seed crystal; 4. Alloy gasket; 5. Positioning groove; 6. Positioning post; 7. Water-cooled copper plate; 8. Transition pad. Detailed Implementation

[0012] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0013] In the description of this utility model, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this utility model 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, and therefore should not be construed as a limitation of this utility model.

[0014] 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 utility model, "a plurality of" means two or more, unless otherwise explicitly specified.

[0015] See Figure 1 A seed crystal oxidation structure for preventing the directional solidification of single-crystal high-temperature alloys includes a ceramic mold shell 1, a seed crystal 3 inserted into the seed crystal cavity 2 of the ceramic mold shell 1, and an alloy spacer 4 covering the top of the seed crystal 3. The alloy spacer 4 is made of Al3Ni alloy, Al3Ni2 alloy or AlNi alloy.

[0016] In this embodiment, by adding an alloy gasket 4 with strong oxidation resistance above the seed crystal 3, and utilizing its characteristic of melting before the seed crystal, a protective layer is formed on the upper part of the seed crystal 3, effectively preventing the formation of an oxide film on the surface of the seed crystal and improving the bonding quality between the seed crystal 3 and the casting. At the same time, the selected NiAl alloy has a composition close to that of high-temperature alloys, and the presence of the alloy will not adversely affect the composition of the poured high-temperature alloy liquid.

[0017] Specifically, a positioning groove 5 is provided on the top surface of the seed crystal 3, and a positioning post 6 that cooperates with the positioning groove 5 is provided on the bottom of the alloy gasket 4. When installing the seed crystal 3, the positioning post 6 is first inserted into the positioning groove 5 to fix the alloy gasket 4 on the seed crystal and make close contact with the upper surface of the seed crystal 3. Then, the seed crystal 3 is inserted into the seed crystal cavity 2. The positioning post 6 and the positioning groove 5 are used to fix the alloy gasket 4 on the seed crystal, which can effectively prevent the alloy gasket 4 from flipping over during the installation of the seed crystal 3 and causing protection failure.

[0018] See Figure 1 In other embodiments, the ceramic mold shell 1 is placed on the water-cooled copper plate 7 of the directional solidification furnace, and a transition pad 8 is provided between the ceramic mold shell 1 and the water-cooled copper plate 7. The transition pad 8 can be made of stainless steel or copper alloy. In this embodiment, adding the transition pad 8 to the water-cooled copper plate keeps the seed crystal at a higher temperature, reduces the temperature difference stress and temperature gradient between the seed crystal and the alloy liquid, and lowers the risk of seed crystal detachment and the formation of impurities.

[0019] A casting method using the above structure includes the following steps: Before casting a single-crystal superalloy, prepare the seed crystal and the mold for casting.

[0020] Based on the NiAl phase diagram, we can find an alloy composition with a melting point of approximately 1000℃, which has a composition range of 30-40 wt% Ni.

[0021] An alloy spacer 4 is added above the seed crystal 3. The cylindrical section of the spacer is 2mm high and has a 1mm high positioning post 6. During casting, a 1mm deep positioning groove 5 is cut into the top of the seed crystal, and then the positioning post 6 is inserted into the positioning groove 5 of the seed crystal, so that the spacer and the seed crystal are tightly bonded, preventing the spacer from flipping and shifting during the seed crystal installation process and losing its protective function. The melting point of the alloy spacer 4 is lower than that of the seed crystal, so that it melts before the seed crystal during the casting process. According to phase diagram analysis, Al3Ni alloy, Al3Ni2 alloy or AlNi alloy has good compatibility with single crystal high-temperature alloys during melting and solidification, and can form a stable protective layer.

[0022] A transition pad 8 is added to the water-cooled copper plate 7. The transition pad 8 is used to keep the seed crystal at a high temperature during the casting process to avoid impurities and thermal stress caused by the large temperature difference between the seed crystal and the alloy liquid. During the casting of single-crystal high-temperature alloys, the alloy spacer 4, due to its lower melting point, melts before the seed crystal, forming a protective layer on top of the seed crystal. This protective layer effectively prevents the seed crystal surface from contacting air, avoiding the formation of an oxide film. Simultaneously, the transition spacer 8 maintains a higher temperature for the seed crystal, ensuring a good bonding interface between the seed crystal and the subsequently solidified casting.

[0023] As the pouring process proceeds, the molten alloy gradually solidifies. The protective layer formed by the gasket prevents the formation of an oxide film on the surface of the seed crystal, allowing the seed crystal and the casting to bond tightly together, thereby achieving high-quality transfer of crystal orientation.

[0024] This method can achieve high-quality transfer of crystal orientation, reduce the generation of defects such as impurities and banding, and significantly improve the quality and performance of single-crystal superalloys, with good economic benefits and application prospects.

[0025] Application examples The shell is made by assembling the test bar mold according to the normal investment casting process, with 6 shell layers.

[0026] DD419 alloy is used for casting, and the seed crystal material is also DD419 alloy with a length of 50mm. A 2mm thick NiAl alloy shim is placed on top of the seed crystal, and the positioning post is 1mm thick. The surfaces of the seed crystal and the NiAl alloy shim are all pre-polished clean.

[0027] The ceramic mold shell 1 was kept at a temperature of 1550℃ and a pulling rate of 3mm / min. Casting was performed using conventional directional solidification methods, followed by etching. The test specimen surface was observed to have intact single crystals, free from defects such as banding, freckles, and impurities. The seed crystals were tightly bonded to the casting, with no seed crystal detachment observed.

[0028] A seed crystal sample was taken and longitudinally cut using wire cutting, followed by metallographic treatment. The metallographic images show that the dendrites are well grown and no oxide film was found.

[0029] Unless otherwise stated, if any of the technical solutions disclosed in this utility model discloses 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 utility model discloses only some numerical values ​​to illustrate the technical solutions of the invention. Furthermore, the numerical values ​​listed above should not constitute a limitation on the scope of protection of this invention.

[0030] Meanwhile, if the present invention discloses or relates to mutually fixedly connected parts or structural components, then unless otherwise stated, the 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 by casting) (except where it is obviously impossible to use an integral forming process).

[0031] Furthermore, unless otherwise stated, the terms used to indicate positional relationships or shapes in any of the technical solutions disclosed in this utility model include states or shapes that are similar to, analogous to, or close to those states or shapes. Any component provided by this utility model can be assembled from multiple individual components or can be a single component manufactured using a one-piece molding process.

[0032] 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 can make other variations or modifications 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 protection scope of this invention.

Claims

1. A structure for preventing seed crystal oxidation during the directional solidification of single-crystal superalloys, comprising a ceramic mold shell, characterized in that: A seed crystal is inserted into the seed crystal cavity of the ceramic mold shell. The top of the seed crystal is covered by an alloy spacer. The melting point of the alloy spacer is lower than that of the seed crystal. The alloy spacer is an Al3Ni alloy spacer, an Al3Ni2 alloy spacer, or an AlNi alloy spacer.

2. The seed crystal oxidation structure for preventing directional solidification of single-crystal superalloys according to claim 1, characterized in that: The top surface of the seed crystal is provided with a positioning groove, and the bottom of the alloy gasket is provided with a positioning post that cooperates with the positioning groove.

3. The seed crystal oxidation structure for preventing directional solidification of single-crystal superalloys according to claim 1 or 2, characterized in that: The ceramic mold shell is placed on the water-cooled copper plate of the directional solidification furnace, and a transition pad is provided between the ceramic mold shell and the water-cooled copper plate.

4. The seed crystal oxidation structure for preventing directional solidification of single-crystal superalloys according to claim 3, characterized in that: The transition pad is a stainless steel pad or a copper alloy pad.

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