Method for eliminating stripe crystal defect of single-crystal high-temperature alloy casting

Abstract

The invention discloses a method for eliminating stripe crystal defects of a single-crystal high-temperature alloy casting. The method comprises the steps that S1, the initial position of the stripe crystal defects is determined; s2, preparing a single-crystal high-temperature alloy casting; wherein in the step S2, when the initial position of the stripe crystal defect on the single-crystal high-temperature alloy casting passes through the thermal radiation baffle between the heating area and the cooling area, the drawing rate of the casting is reduced. According to the method for eliminating the streak crystal defect of the single-crystal high-temperature alloy casting, the initial position of the streak crystal defect on the single-crystal high-temperature alloy casting is determined firstly, during preparation, when the initial position passes through heat radiation baffles of a heating area and a cooling area, the drawing rate is reduced, the temperature gradient can be increased, and the width of a paste area can be reduced; and therefore, the stability of the liquid phase in the pasty area is improved, generation of striped crystals is effectively inhibited, and the single-crystal high-temperature alloy casting without striped crystal defects is prepared.

Description

Technical Field

[0001] The present application relates to the field of single crystal high temperature alloys, and in particular to a method for eliminating streak crystal defects in single crystal high temperature alloy castings. Background Art

[0002] Single crystal superalloy refers to a metal alloy mainly used in high temperature environments, with a single crystal structure (i.e. single crystal structure), usually based on nickel-based or cobalt-based alloys. Single crystal superalloys have good high temperature mechanical properties, including high strength, good creep resistance and good thermal stability, making them ideal for manufacturing high-performance aircraft engine turbine blades. In addition, single crystal superalloys also have high oxidation resistance and corrosion resistance, which further extends their service life and improves the overall efficiency and reliability of aircraft engines.

[0003] Although single crystal high temperature alloys have many advantages, streak crystal defects are a problem that cannot be ignored during their preparation. Especially in components working under high temperature conditions, the formation of streak crystals destroys the single crystal integrity of single crystal high temperature alloy castings and increases the risk of crack initiation, thereby affecting the fatigue life of the material and the safety of long-term use. Therefore, how to effectively control, reduce or even avoid the formation of streak crystals has become an important topic in the research and development and application of single crystal high temperature alloys. At present, the research on streak crystals mainly focuses on the mechanism and influencing factors of the formation of streak crystal defects, focusing on studying the mechanism of streak crystal formation in single crystal high temperature alloy castings, and there is less research on how to avoid or eliminate streak crystal defects in single crystal high temperature alloy castings.

[0004] Therefore, how to eliminate the streak crystal defects of single crystal high-temperature alloy castings has become one of the technical problems that need to be solved in this field. Summary of the invention

[0005] In view of this, the present application proposes a method for eliminating streak crystal defects in single crystal high temperature alloy castings.

[0006] The present application proposes a method for eliminating streak crystal defects in single crystal high-temperature alloy castings, the method comprising: S1. determining the starting position of the streak crystal defect; S2. preparing a single crystal high-temperature alloy casting; wherein, in step S2, when the starting position of the streak crystal defect on the single crystal high-temperature alloy casting passes through a heat radiation baffle between a heating zone and a cooling zone, the pulling rate of the casting is reduced.

[0007] Specifically, the pulling rate of the starting position of the stripe crystal defect when passing through the heat radiation baffle is 1.0 mm / min to 2.0 mm / min.

[0008] Specifically, when the starting position of the stripe crystal defect passes through the heat radiation baffle, the pulling rate decreases within a range of 8 mm to 15 mm above and below the upper edge of the heat radiation baffle.

[0009] Specifically, the step S2 includes: preparing a shell.

[0010] Specifically, the shell is made of zircon powder system or white corundum.

[0011] Specifically, the step S2 further includes: setting the temperatures of the upper heating zone and the lower heating zone to heat and refine the raw material of the single crystal high-temperature alloy casting and preheat the mold shell.

[0012] Specifically, the temperature of the upper heating zone is 1500°C to 1600°C, and the temperature of the lower heating zone is 1500°C to 1600°C.

[0013] Specifically, the step S2 further includes: setting an overall pulling rate during directional solidification of the single crystal high temperature alloy casting, and casting the single crystal high temperature alloy at a casting temperature.

[0014] Specifically, the overall pulling rate is 3.0 mm / min to 7.0 mm / min.

[0015] Specifically, the pouring temperature is 1500°C to 1600°C.

[0016] The present application proposes a method for eliminating streak crystal defects in single crystal high-temperature alloy castings. First, the starting position of the streak crystal defects on the single crystal high-temperature alloy is determined. During preparation, the pulling rate is reduced when the starting position passes through the heat radiation baffles in the heating zone and the cooling zone. This can increase the temperature gradient and reduce the width of the mushy zone, thereby improving the stability of the liquid phase in the mushy zone and effectively inhibiting the generation of streak crystals, thereby preparing a single crystal high-temperature alloy without streak crystal defects.

[0017] Other features and advantages of the present application will be described in detail in the subsequent detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The accompanying drawings constituting a part of the present application are used to provide a further understanding of the present application, and the schematic implementation modes and descriptions of the present application are used to explain the present application. In the accompanying drawings:

[0019] Figure 1 It is a schematic diagram of the starting position of the streak crystal defect on the single crystal high-temperature alloy casting passing through the heat radiation baffle according to the present application.

[0020] Figure 2 This is a picture of a single crystal high-temperature alloy casting with streak crystal defects prepared in a comparative example and the starting position of the streak crystal.

[0021] Figure 3 This is a picture of a single crystal high-temperature alloy casting prepared according to Example 1 in the preferred embodiment of the present application.

[0022] Explanation of the numbers in the accompanying drawings: 1-starting position of the streak crystal defect, 2-heat radiation baffle; 3-mold shell; 4-heating zone; 5-cooling zone; 6-water cooling plate; 7-pulling direction. DETAILED DESCRIPTION

[0023] The technical solution of the present application will be described in detail below with reference to the accompanying drawings and in combination with the implementation modes.

[0024] The streak crystal defect formed in the preparation process of single crystal high temperature alloy castings. During the directional solidification of single crystal high temperature alloys, relatively heavy elements tend to segregate to the dendrite stem area, such as W, Re and other elements, while relatively light elements such as Al, Ti and others tend to segregate to the inter-dendritic area, making the liquid phase density in the mushy zone lower than the density of the liquid phase at the front of the solidification interface during directional solidification, thus forming density inversion. When the density inversion reaches a certain degree, liquid convection will form, which will cause the dendrites in the mushy zone to break or remelt. When the broken dendrites obtain favorable growth conditions and continue to grow in the subsequent cooling process, streak crystal defects will be formed. The formation of streak crystals destroys the single crystal integrity of single crystal high temperature alloy castings, and once formed, it cannot be eliminated by subsequent heat treatment and other processes.

[0025] Therefore, the present application proposes a method for eliminating streak crystal defects in single crystal high-temperature alloy castings, the method comprising: S1. determining the starting position of the streak crystal defect; S2. preparing a single crystal high-temperature alloy casting; wherein, in step S2, when the starting position of the streak crystal defect on the single crystal high-temperature alloy casting passes through the heat radiation baffle between the heating zone and the cooling zone, the pulling rate of the casting is reduced.

[0026] The above step S1 is to determine the position of the streak crystal defect by chemically etching the single crystal high temperature alloy casting cast under the conventional directional solidification process. After chemical etching, the position of the streak crystal defect can be clearly observed (such as Figure 2 As shown), the above chemical corrosion adopts a conventional single crystal high temperature alloy casting corrosion method, such as a mixed solution of hydrochloric acid and hydrogen peroxide or a mixed solution of hydrochloric acid and ferric chloride.

[0027] The single crystal high temperature alloy in the present application is prepared by directional solidification and rapid solidification. The single crystal high temperature alloy is prepared in a directional solidification furnace. The directional solidification furnace is a Brigeman single crystal furnace, which includes an upper heating zone, a lower heating zone and a cooling zone.

[0028] The present application proposes a method for eliminating streak crystal defects in single crystal high-temperature alloy castings. First, the starting position of the streak crystal defects on the single crystal high-temperature alloy is determined. During preparation, the pulling rate is reduced when the starting position passes through the heat radiation baffles in the heating zone and the cooling zone. This can increase the temperature gradient and reduce the width of the mushy zone, thereby improving the stability of the liquid phase in the mushy zone and effectively inhibiting the generation of streak crystals, thereby preparing a single crystal high-temperature alloy without streak crystal defects.

[0029] In order to make the elements evenly distributed in the single crystal high temperature alloy casting during the solidification process and reduce the situation of component segregation, specifically, the pulling rate when the starting position of the stripe crystal defect passes through the heat radiation baffle can be 1.0mm / min~2.0mm / min. Within this pulling rate range, it is helpful to reduce the segregation of solute elements, thereby reducing the formation of stripe crystal defects, improving the uniformity of the crystal structure, reducing thermal stress, optimizing the microstructure of the alloy, and then improving the creep performance and mechanical properties of the alloy. At the same time, this slow pulling can also improve the stability and repeatability of the production process, reduce the defective rate, and reduce the residual stress inside the alloy, improve fatigue life and reduce deformation. However, the realization of these advantages depends on multiple factors such as alloy composition, heat treatment process and equipment conditions, and in actual operation, it is necessary to balance production efficiency and cost, and determine the optimal pulling rate through experiments to obtain the best comprehensive performance.

[0030] In order to ensure that the single crystal high temperature alloy is more stable during the growth process and avoid the generation of streak crystal defects, specifically, when the starting position of the streak crystal defect passes through the heat radiation baffle, the pulling rate is reduced within the range of 8mm-15mm above and below the upper edge of the heat radiation baffle. The crystal growth of the single crystal high temperature alloy within this distance range is at a critical stage, where significant changes in temperature gradients and uneven solute distribution may lead to unstable growth and the formation of defects. By reducing the pulling rate in this area, the solid-liquid interface can be effectively stabilized, solute segregation can be reduced, thermal stress can be relieved, and the flatness and stability of the interface can be ensured, thereby improving the quality of the single crystal high temperature alloy.

[0031] According to a preferred embodiment of the present application, specifically, step S2 may include: preparing a shell. The shell provides a precise casting mold for the single crystal high temperature alloy. In order to make the shell adaptable to high temperature environments, specifically, the shell may be made of zircon powder system or white corundum. These materials have excellent heat resistance and mechanical strength, can withstand the high temperature smelting process of the single crystal high temperature alloy, and ensure the integrity of the casting.

[0032] The above-mentioned shell is prepared according to the method of investment casting, including: preparing a wax mold; immersing the wax mold in ceramic slurry, sprinkling the shell material (zircon powder system or white corundum), and after multiple immersions and powdering, forming a multi-layer ceramic shell to achieve the required thickness; heating to melt the wax mold to leave a hollow ceramic shell; and sintering at high temperature to improve strength and heat resistance.

[0033] Specifically, step S2 further includes: setting the temperature of the upper heating zone and the lower heating zone to preheat the mold shell and heat and refine the raw material of the single crystal high temperature alloy casting. The upper heating zone of the Brigeman single crystal furnace is used to melt the raw material of the single crystal high temperature alloy casting (single crystal high temperature alloy master alloy ingot) and keep it at a constant temperature to avoid premature solidification; the lower heating zone is used to form an appropriate temperature gradient, control the solidification process, and prevent the single crystal high temperature alloy from solidifying too quickly before entering the cooling zone.

[0034] In order to accurately control the temperature gradient. Specifically, the temperature of the upper heating zone can be 1500℃~1600℃, and the temperature of the lower heating zone can be 1500℃~1600℃. It is helpful to form a stable and gentle temperature gradient during the directional solidification process. This temperature control can not only ensure that the molten metal gradually solidifies under appropriate conditions, but also improve the uniformity and directionality of the single crystal structure, reduce grain boundary defects, and improve the mechanical properties of the final material.

[0035] In order to make the crystal solidify quickly, specifically, step S2 further includes: setting the overall pulling rate during directional solidification of the single crystal high temperature alloy casting, and casting the single crystal high temperature alloy at the casting temperature.

[0036] For directional solidification of single crystal high temperature alloy, specifically, the overall pulling rate can be 3.0 mm / min to 7.0 mm / min. In this temperature unit,

[0037] In order to avoid casting defects, specifically, the pouring temperature may be 1500° C. to 1600° C. Within this temperature range, the single crystal high temperature alloy in a molten state has good fluidity and filling properties, which can reduce defects in the preparation process.

[0038] The method for eliminating streak crystal defects in single crystal high-temperature alloy castings proposed in the present application is described below with reference to embodiments.

[0039] 1. Example

[0040] Example 1

[0041] Take the preparation of DD7 high-temperature alloy single crystal castings as an example.

[0042] A1. Use the preliminary experimental method to determine the starting position of the streak crystal defect on the casting;

[0043] A2. Prepare zircon powder system single crystal shell according to the method of investment casting, and obtain single crystal structure by spiral crystal selection method;

[0044] A3. Place the shell into a Brigeman single crystal furnace and obtain a single crystal high temperature alloy casting by HRS (rapid solidification method);

[0045] A4. The upper heater temperature is set to 1500℃, the lower heater temperature is set to 1500℃, and the pouring temperature is controlled at 1500℃;

[0046] A5. Set the variable speed pulling rate. The overall pulling rate is set to 3 mm / min. The starting position of the streak crystal defect on the casting is in the area 8 mm above and below the baffle. The pulling rate is set to 1.5 mm / min.

[0047] A6. Complete the preparation of single crystal high-temperature alloy castings according to the set process to obtain DD7 single crystal high-temperature alloy castings without streak crystal defects.

[0048] Example 2

[0049] The method for eliminating streak crystal defects of single crystal high temperature alloy castings in Example 1 is adopted; taking DD416 single crystal high temperature alloy single crystal castings as an example, wherein:

[0050] A4. The upper heater temperature is set to 1520℃, the lower heater temperature is set to 1530℃, and the pouring temperature is controlled at 1530℃;

[0051] A5. Set the variable speed pulling rate. The overall pulling rate is set to 5 mm / min. The starting position of the streak crystal defect on the casting is within 10 mm above and below the baffle. The pulling rate is set to 1 mm / min.

[0052] Example 3

[0053] The method for eliminating streak crystal defects in single crystal high temperature alloy castings in Example 1 is adopted, taking DD419 single crystal high temperature alloy castings as an example, wherein:

[0054] A4. The upper heater temperature is set to 1550℃, the lower heater temperature is set to 1550℃, and the pouring temperature is controlled at 1550℃;

[0055] A5. Set the variable speed pulling rate. The overall pulling rate is set to 4.5 mm / min. The starting position of the streak crystal defect on the casting is in the area 11.5 mm above and below the baffle. The pulling rate is set to 2 mm / min.

[0056] Example 4

[0057] The method for eliminating streak crystal defects in single crystal high temperature alloy castings in Example 1 is adopted, taking DD476 single crystal high temperature alloy castings as an example, wherein:

[0058] A4. The upper heater temperature is set to 1600℃, the lower heater temperature is set to 1600℃, and the pouring temperature is controlled at 1600℃;

[0059] A5. Set the variable speed pulling rate. The overall pulling rate is set to 7mm / min. The starting position of the streak crystal defect on the casting is in the area 15mm above and below the baffle. The pulling rate is set to 1mm / min.

[0060] Comparative Example

[0061] The method in Example 1 is used to prepare a single crystal high temperature alloy, wherein:

[0062] A1 is not included.

[0063] A5. The overall pulling rate is set to 4 mm / min.

[0064] 2. Stripe crystal defects on the surface of single crystal high temperature alloy castings

[0065] Figure 2 and Figure 3 They are single crystal high-temperature alloys prepared in the comparative example and in Example 1 respectively; it can be seen that obvious streak crystal defects can be seen on the surface of the single crystal high-temperature alloy casting prepared in the comparative example; the surface of the single crystal high-temperature alloy casting prepared in the present application is smooth and free of streak crystal defects.

[0066] The method proposed in this application is applicable to nickel-based single crystal high-temperature alloys, such as DD3, DD476, DD5, DD6, DD7, PWA1483, PWA1484, CMSX-4, RenéN5, CMSX-6, CMSX-10 and other commonly used single crystal high-temperature alloys.

[0067] In summary, the single crystal high temperature alloy surface prepared by the method for eliminating streak crystal defects in single crystal high temperature alloy castings proposed in the present application has no streak crystal defects.

[0068] The preferred embodiments of the present application are described in detail above; however, the present application is not limited to the specific details in the above embodiments. Within the technical concept of the present application, a variety of simple modifications can be made to the technical solution of the present application, and these simple modifications all fall within the protection scope of the present application.

[0069] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, this application will not further describe various possible combinations.

[0070] In addition, the various implementation modes of the present application may be arbitrarily combined, and as long as they do not violate the concept of the present application, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A method for eliminating streak defects in single crystal high temperature alloy castings, characterized in that: The method comprises: S1. determining the starting position of the streak crystal defect; S2. preparing a single crystal high temperature alloy casting; Wherein, in said step S2, when the starting position of the streak crystal defect on the single crystal high temperature alloy casting passes through the heat radiation baffle between the heating zone and the cooling zone, the pulling rate of the casting is reduced.

2. The method for eliminating streak crystal defects in single crystal high temperature alloy castings according to claim 1, characterized in that: The pulling rate of the starting position of the stripe crystal defect when passing through the heat radiation baffle is 1.0 mm / min to 2.0 mm / min.

3. The method for eliminating streak crystal defects in single crystal high temperature alloy castings according to claim 1 or 2, characterized in that: When the starting position of the stripe crystal defect passes through the heat radiation baffle, the pulling rate is reduced within the range of 8mm-15mm above and below the heat radiation baffle.

4. The method for eliminating streak crystal defects in single crystal high temperature alloy castings according to claim 1, characterized in that: The step S2 comprises: preparing a shell mold.

5. The method for eliminating streak crystal defects in single crystal high temperature alloy castings according to claim 4, characterized in that: The shell is made of zircon powder system or white corundum.

6. The method for eliminating streak crystal defects in single crystal high temperature alloy castings according to claim 4, characterized in that: The step S2 further includes: setting the temperatures of the upper heating zone and the lower heating zone to heat and refine the raw material of the single crystal high temperature alloy casting and preheat the mold shell.

7. The method for eliminating streak crystal defects in single crystal high temperature alloy castings according to claim 6, characterized in that: The temperature of the upper heating zone is 1500°C to 1600°C, and the temperature of the lower heating zone is 1500°C to 1600°C.

8. The method for eliminating streak crystal defects in single crystal high temperature alloy castings according to claim 4 or 6, characterized in that: The step S2 further comprises: setting an overall pulling rate during directional solidification of the single crystal high temperature alloy casting, and casting the single crystal high temperature alloy casting at a casting temperature.

9. The method for eliminating streak crystal defects in single crystal high temperature alloy castings according to claim 8, characterized in that: The overall pulling rate is 3.0 mm / min to 7.0 mm / min.

10. The method for eliminating streak crystal defects in single crystal high temperature alloy castings according to claim 8, characterized in that: The pouring temperature is 1500°C to 1600°C.

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