A method of inhibiting recrystallization of a single crystal blade

Abstract

The application discloses a method for inhibiting recrystallization of a single crystal blade. The method controls the primary dendrite orientation of the blade through a seed crystal, so that the primary crystal orientation of the blade is consistent with the direction of the casting stress at the joint of the blade body and the rim plate, thereby achieving the purpose of inhibiting the recrystallization of the blade.

Description

Technical Field

[0001] This invention belongs to the field of single-crystal blade preparation technology, and particularly relates to a method for suppressing recrystallization of single-crystal blades. Background Technology

[0002] As the structure of single-crystal blades becomes increasingly complex, issues such as shrinkage mismatch between the molten metal, core, and shell during blade fabrication can lead to slight plastic deformation. This can easily cause stress concentration at the junction of the blade and the ferrule, resulting in recrystallization defects after subsequent solution heat treatment and reducing the performance of the single-crystal blade. Therefore, employing a reasonable fabrication process to avoid recrystallization during subsequent heat treatment is a problem that must be solved in actual production. Summary of the Invention

[0003] The main objective of this invention is to provide a method for suppressing recrystallization of single-crystal blades. This method controls the primary dendrite orientation of the blades by using seed crystals, so that the primary crystal orientation of the blades and the direction of casting stress at the junction of the blade body and the edge plate are consistent, thereby achieving the purpose of suppressing blade recrystallization.

[0004] Therefore, the present invention provides a method for suppressing recrystallization of single-crystal blades by controlling the primary dendrite orientation of the blades through seed crystals, so that the casting stress of the mold shell at the junction of the blade body and the edge plate during the casting process is consistent with the primary dendrite orientation of the blades, thereby achieving the purpose of suppressing blade recrystallization.

[0005] Specifically, during the blade casting process, after the seed crystal is installed into the seed crystal cavity of the mold shell, the secondary dendrite arm of the seed crystal remains parallel to the tangent normal direction of the tip of the ceramic core where the blade wall is thinner.

[0006] Specifically, before the seed crystal is installed into the mold shell, the bottom of the seed crystal needs to be ground, polished and etched to expose its secondary dendrite arms.

[0007] Specifically, the blades are assembled vertically. During casting, seed crystals are pre-placed at the bottom of the mold shell. The crystal orientation is transmitted to the blades through the epitaxial growth of the seed crystals.

[0008] Principles and advantages

[0009] The inventors discovered that the deviation angles of the primary and secondary dendrite orientations in single-crystal castings have a significant impact on the depth of recrystallization. Furthermore, the recrystallization depth is minimized when the deviation angle is 0 degrees (the dendrite orientation is parallel to the loading direction (force direction)). Therefore, based on these findings, this invention controls the primary dendrite orientation of the blade during blade fabrication by using seed crystals. This ensures that the casting stress on the blade during casting is consistent with the crystal orientation, thereby suppressing blade recrystallization. Attached Figure Description

[0010] 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.

[0011] Figure 1 This is a schematic diagram of the primary crystal orientation deviation angle β and the sample cutting reference plane involved in the embodiments of the present invention;

[0012] Figure 2 These are recrystallization structures of samples with different primary crystal orientation deviation angles β involved in the embodiments of the present invention;

[0013] Figure 3 This is a schematic diagram of the secondary crystal orientation deviation angle α and the sample cutting reference plane involved in the embodiments of the present invention;

[0014] Figure 4 These are recrystallized structures under different secondary crystal orientation deviation angles α involved in the embodiments of the present invention;

[0015] Figure 5 This is a metallographic diagram of a blade prepared using conventional methods when the primary crystal orientation is not effectively controlled.

[0016] Figure 6 This is a metallographic diagram of a blade prepared by effectively controlling the primary crystal orientation using the method described in this embodiment of the invention;

[0017] Figure 7 This is a schematic diagram of the cross-section at the core head of the ceramic blade core;

[0018] Figure 8 This is a metallographic diagram of a blade prepared using conventional methods when the secondary crystal orientation is not effectively controlled.

[0019] Figure 9 This is a metallographic schematic diagram of a hollow blade prepared by effectively controlling the secondary crystal orientation using the method of the present invention. Detailed Implementation

[0020] 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.

[0021] 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.

[0022] 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.

[0023] To clarify the relationship between dendrite orientation and recrystallization, the inventors conducted the following research:

[0024] 1. The effect of grain orientation on recrystallization in single-crystal castings

[0025] (1) The effect of primary crystal orientation on recrystallization

[0026] according to Figure 1 The cutting method shown was used to cut samples with different primary crystal orientations, followed by indentation treatment and solution heat treatment to prepare metallographic samples for observation. (See also...) Figure 2 Metallographic images reveal that the vertical loading applied to the samples created a shallow pit tens of micrometers deep on the upper surface of each sample. Below this pit lies a nearly hemispherical recrystallized layer several hundred micrometers deep. The dashed lines in the images indicate the orientation of the dendrite trunks, i.e., the axial direction of the test specimen. The recrystallization depth H of each sample exhibits a relatively obvious variation pattern: as the primary orientation deviation angle (the angle between the dendrite orientation and the loading direction of the indenter (force direction)) β increases, the recrystallization depth H initially increases gradually, reaching its maximum value at a deviation angle of 45°, and then begins to decrease.

[0027] (2) The effect of secondary crystal orientation on recrystallization

[0028] according to Figure 3 The cutting method shown was used to cut samples with different primary crystal orientations, followed by indentation treatment and solution heat treatment to prepare metallographic samples for observation. (See also...) Figure 4Metallographic images (a)-(d) correspond to photographs with α values ​​of 0°, 15°, 30°, and 45°, respectively. The dashed lines in the images indicate the orientation of the dendrite trunks, i.e., the axial direction of the test specimen. As can be seen from the images, all samples underwent significant recrystallization after heat treatment, and the depth of recrystallization increased with the increase of the deviation angle α.

[0029] The results show that both the primary and secondary dendrite orientations of the casting have a significant impact on its recrystallization depth. Furthermore, the recrystallization depth is minimized when the dendrite orientation is parallel to the direction of stress. Therefore, by controlling the primary dendrite orientation of the blade through seed crystals, ensuring that the casting stress on the blade during casting aligns with the crystal orientation, the blade can withstand greater casting stress, resulting in minimal or no recrystallization after subsequent solution heat treatment.

[0030] This invention provides an innovative method for suppressing recrystallization of single-crystal blades based on the above findings. During blade manufacturing, casting stress often concentrates at the junction of the blade body and the rim plate, which easily leads to recrystallization defects after subsequent solution heat treatment. Therefore, this invention controls the primary dendrite orientation of the blade by using seed crystals, ensuring that the casting stress of the mold shell at the junction of the blade body and the rim plate during casting is consistent with the primary dendrite orientation of the blade, thereby suppressing blade recrystallization.

[0031] In this embodiment, for the guide vane, vertical mold assembly is performed during mold assembly. During casting, a seed crystal is pre-placed at the bottom of the guide vane. Through the epitaxial growth of the seed crystal, the crystal orientation is transmitted to the vane, ensuring that the primary crystal orientation of the vane is consistent with that of the seed crystal. During the directional solidification process, the guide vane shrinks. The mold shell located between the upper and lower edge plates of the guide vane hinders the shrinkage of the vane, thereby generating significant casting stress. The transition R between the blade body and the edge plate is a stress concentration point, where stress concentration occurs. The guide vane body is relatively thin, especially the hollow guide vane, which is even thinner. If the primary crystal orientation of the guide vane is not controlled, the primary crystal orientation of the guide vane will be random, often resulting in varying degrees of recrystallization after solution heat treatment. If the above method is used to effectively control the primary crystal orientation of the guide vane, ensuring that the guide vane body is consistent with its primary crystal orientation, then, according to the above experimental results, recrystallization of the guide vane can be effectively reduced or avoided.

[0032] Figure 5 The figure shows a metallographic diagram of a blade prepared using conventional crystal selection methods without controlling the blade orientation. It can be seen from the figure that a relatively serious recrystallization defect occurred at the junction of the guide vane blade and the edge plate. Figure 6The image shows a metallographic diagram of the blade prepared using the above method. This method effectively controls the primary crystal orientation of the guide vane, ensuring that the primary crystal orientation aligns with the stress direction on the blade body. It can be observed that no recrystallization defects are present at either the blade body or the edge plate. Therefore, the above method can effectively reduce or avoid recrystallization defects in guide vanes.

[0033] See Figure 7 For hollow guide vanes, a ceramic core is added to form the internal cavity. Similarly, the vane shrinks during solidification and cooling, and the ceramic core hinders this shrinkage, resulting in casting stress. This casting stress often concentrates at the tip of the ceramic core, where the casting experiences the greatest stress. When the corresponding blade wall thickness is thin, recrystallization easily occurs in the blade cavity after solution heat treatment.

[0034] Based on the influence of crystal orientation on recrystallization, vertical molding is performed when assembling hollow guide vanes. During casting, a seed crystal is pre-placed at the bottom of the guide vane. Through the epitaxial growth of the seed crystal, the crystal orientation is transmitted to the blade, so that the primary crystal orientation of the guide vane is consistent with the stress direction of the blade. At the same time, before pre-placing the seed crystal, the bottom of the seed crystal is polished and etched to expose its secondary dendrite arm. The direction of the secondary dendrite arm of the seed crystal is the secondary orientation of the seed crystal. Before inserting the seed crystal into the mold shell, the secondary dendrite arm of the seed crystal is aligned with the tangent normal direction of the tip of the ceramic core where the blade wall is thinner (i.e., the stress direction when the casting shrinks). When the grain orientation of the seed crystal grows epitaxially into the blade, the secondary crystal orientation of the blade is consistent with the stress direction of the ceramic core on the blade.

[0035] Figure 8 The image shows the metallographic image of the guide vane obtained when the secondary crystal orientation of the guide vane is randomized using the seed crystal method. It can be seen from the image that a severe recrystallization defect occurred at the core tip (ceramic core tip) of the guide vane. Figure 9 The metallographic image of the guide vane is prepared after effectively controlling the secondary crystal orientation of the guide vane using the above method. It can be seen from the image that no recrystallization defects appeared at the core of the guide vane. It is evident that the above method can effectively reduce or avoid recrystallization defects in the guide vane.

[0036] 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.

[0037] 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).

[0038] 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.

[0039] 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 suppressing recrystallization of single-crystal blades, characterized in that: By controlling the primary dendrite orientation of the blade through seed crystals, the casting stress of the mold shell at the junction of the blade body and the edge plate during the casting process is kept consistent with the primary dendrite orientation of the blade, thereby achieving the purpose of inhibiting blade recrystallization. During the blade casting process, after the seed crystal is installed into the seed crystal cavity of the mold shell, the secondary dendrite arm of the seed crystal remains parallel to the tangent normal direction of the tip of the ceramic core where the blade wall is thinner.

2. The method for suppressing recrystallization of single-crystal blades according to claim 1, characterized in that: Before the seed crystal is installed into the mold shell, the bottom of the seed crystal needs to be ground, polished and etched to expose its secondary dendrite arms.

3. The method for suppressing recrystallization of single-crystal blades according to claim 1, characterized in that: The blades are assembled vertically. During casting, seed crystals are pre-placed at the bottom of the mold shell. The crystal orientation is transmitted to the blades through the epitaxial growth of the seed crystals.

4. The method for suppressing recrystallization of single-crystal blades according to claim 1, characterized in that: The blades are guide blades.

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