A method for homogenizing nickel-based single crystal superalloys using pulsed current

Abstract

The application belongs to the field of metal material processing, and discloses a method for homogenizing nickel-based single crystal superalloy by using pulse current, wherein a gradient pulse current with two or more stages is applied to the as-cast nickel-based single crystal superalloy. The single crystal superalloy can be quickly homogenized by applying the gradient pulse current, and the gamma / gamma prime eutectic structure and carbide can be eliminated, and the dendritic segregation can be obviously improved.

Description

Technical Field

[0001] This invention belongs to the field of metal material processing, and specifically relates to a method for homogenizing nickel-based single-crystal superalloys using pulsed current. Background Technology

[0002] The fabrication of single-crystal hollow blades with complex cooling structures is one of the major technological bottlenecks in the research and development of advanced aero-engines in my country. The directional solidification process for single-crystal blades is complex, the alloy contains excessively high levels of refractory elements, and the melting points and diffusion rates of these elements vary significantly. Homogenization heat treatment, as a key process for achieving product homogenization, plays a crucial role in the entire high-temperature alloy production process: by eliminating dendritic segregation and low-melting-point harmful phases, it improves the hot working properties of the ingot.

[0003] Existing methods for homogenizing single-crystal superalloys involve heat treatment. Chinese patent CN115747687A discloses a method for homogenizing second-generation single-crystal superalloys using a multi-stage heat treatment process; Chinese patent CN113528993B discloses a method for expanding the solution heat treatment window of the alloy and improving the homogenization degree of various elements in DD476 alloy through a three-stage heat treatment process. While traditional heat treatment can achieve homogenization, it also has limitations and risks. For example, excessively high homogenization temperatures may lead to the initial melting of the alloy's eutectic phase. Furthermore, heat treatment suffers from drawbacks such as expensive equipment, complex operation, long cycles, and high operating temperatures, which does not align with current industrial green development plans. Therefore, there is an urgent need for an efficient, energy-saving, and environmentally friendly treatment method to rapidly achieve homogenization of single-crystal superalloys.

[0004] Chinese patent CN 100432245 C discloses a method and apparatus for DC current remelting treatment of single-crystal superalloys. Clearly, it uses direct current, favoring the utilization of the thermal effect of the current, resulting in a relatively long processing time. Pulsed current is a special instantaneous high-energy treatment method that can improve the properties of metallic materials. How to utilize pulsed current to achieve homogenization of nickel-based single-crystal superalloys is one of the key problems urgently needing to be solved in this field, especially since the nickel-based single-crystal superalloys targeted in this invention not only exhibit dendritic segregation but also have γ / γ′ eutectic structures and carbides, making them even more difficult to remove effectively. Summary of the Invention

[0005] The purpose of this invention is to address the problems of long cycles, complex operations, and expensive equipment associated with traditional heat treatment and DC current treatment methods. It provides an unconventional treatment method, namely, a method for homogenizing nickel-based single-crystal superalloys using pulsed current. This method can not only improve dendrite segregation but also eliminate the γ / γ′ eutectic structure and carbides in the cast alloy, thereby improving the high-temperature performance of the ingot.

[0006] To achieve the above objectives, the present invention adopts the following technical solutions.

[0007] This invention provides a method for homogenizing nickel-based single-crystal superalloys using pulsed current, by applying two or more levels of gradient pulsed current to the as-cast nickel-based single-crystal superalloy.

[0008] Furthermore, a gradient pulse current with gradually increasing levels of 2 to 4 is applied to the as-cast nickel-based single-crystal superalloy.

[0009] Furthermore, the parameters of the gradient pulse current are: frequency 100~2000Hz, pulse width 200μs~10ms, and current density 10~100A / mm². 2 The action time is 10 minutes to 3 hours.

[0010] Furthermore, the current density of the applied gradient pulse current increases stepwise.

[0011] Furthermore, for as-cast nickel-based single-crystal superalloys, the dimensions of the single-crystal superalloy are first determined, and the pulse current parameters are determined based on the sample dimensions. When the method is applied to actual as-cast single-crystal superalloys, the larger the size, the lower the frequency, the wider the pulse width, the larger the current, and the longer the action time.

[0012] Furthermore, for a 30mm×5mm×1.5mm nickel-based single-crystal superalloy, the applied pulse current parameters are in the range of 1000~2000Hz, pulse width 100ms~200ms, and current density 30~40A / mm. 2 The action time is 10 min to 3 h; the current density of the applied gradient pulse current increases step by step.

[0013] Furthermore, at room temperature, two or more levels of gradient pulse current were applied to the as-cast nickel-based single-crystal superalloy.

[0014] This invention utilizes pulsed current to accelerate atomic diffusion and achieve homogenization of single-crystal superalloys, a principle entirely different from that of traditional annealing heat treatment. This invention can achieve homogenization at temperatures lower than traditional heat treatment, consuming less energy and achieving "green manufacturing." The pulsed current treatment time used in this invention is only 10 minutes to 3 hours, far shorter than traditional heat treatment, significantly reducing the time required for homogenization. By precisely controlling the pulsed current parameters and treatment method, this invention improves dendritic segregation in as-cast alloys, simultaneously dissolving coarse γ′ phases and γ / γ′ eutectic structures in the as-cast microstructure, eliminating carbides, and improving compositional uniformity.

[0015] Therefore, compared with the prior art, the method for homogenizing nickel-based single-crystal superalloys using pulsed current provided by the present invention has the following beneficial effects:

[0016] 1. This invention can rapidly homogenize single-crystal superalloys by applying gradient pulsed current, eliminating γ / γ′ eutectic structure and carbides, and can also significantly improve dendrite segregation;

[0017] 2. This invention can also reduce the temperature required for homogenization of nickel-based single-crystal high-temperature alloys to a certain extent, without the need for additional heat source assistance, thus saving energy and achieving green manufacturing. Attached Figure Description

[0018] Figure 1 SEM image of the original cast nickel-based single-crystal superalloy sample;

[0019] Figure 2 This is a SEM image of the nickel-based single-crystal superalloy sample from Example 1 after processing with a crystal pulse current.

[0020] Figure 3 This is a SEM image of the nickel-based single-crystal superalloy sample from Example 2 after processing with a crystal pulse current.

[0021] Figure 4 This is a SEM image of the nickel-based single-crystal superalloy sample from Example 3 after pulsed current processing. Detailed Implementation

[0022] The principles and features of the present invention are described below. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0023] In the following embodiments, the devices used for pulse current processing are all pulse power supplies.

[0024] The as-cast nickel-based single-crystal superalloy samples used in the following examples were obtained using traditional preparation processes, see ([1] Tang Guoxing, Mao Weimin, Liu Yongfeng. Development and application of directional solidification technology [J]. China Foundry Equipment and Technology, 2007(02):11-16.). The mass fractions of the main elements in the samples were: Cr 4.97%; W 8.58%; Re 4.04%; Ta 3.96%; Al 5.97%, with the balance being Ni. The original as-cast nickel-based single-crystal superalloy samples were subjected to SEM testing, and the results are as follows. Figure 1 As shown, the original sample exhibits a distinct dendritic morphology and contains a large amount of black blocky γ / γ′ eutectic phase and bright white carbide structure.

[0025] In the following examples, the current parameters selected for sample processing have avoided the influence of the skin effect, and the pulsed current is applied to the entire sample. Example 1

[0026] This embodiment applies pulsed current treatment to small-sized single-crystal superalloys. The specific steps are as follows:

[0027] Step 1: Prepare pulse-treated samples.

[0028] Take a 30mm×5mm×1.5mm cast nickel-based single crystal high-temperature alloy sample and polish its surface with 180, 800, and 2000 grit sandpaper in sequence until there are no visible defects to ensure good contact with the pulse electrode.

[0029] Step 2: Determine the gradient pulse current processing parameters.

[0030] Set the parameter range for the gradient pulse current and determine the gradient pulse current parameters:

[0031] The parameters for the first-stage pulse current processing are: frequency 2000Hz, pulse width 100ms, and current density 30A / mm². 2 Processing time: 30 minutes;

[0032] The second-stage pulse current processing parameters are: frequency 2000Hz, pulse width 100ms, and current density 32A / mm². 2 Processing time: 30 minutes;

[0033] The parameters for the third-level pulse current processing are: frequency 2000Hz, pulse width 100ms, and current density 35A / mm². 2 Processing time: 60 minutes.

[0034] Step 3: Pulse current processing.

[0035] After polishing, the small sample is fixed to the output of the pulse power supply with a clamp, and pulse current is applied to it at room temperature according to the gradient pulse current parameters set in the second step.

[0036] Step 4: Use a scanning electron microscope to examine the material after pulsed current treatment.

[0037] Samples treated with pulsed current were subjected to SEM analysis, and the results were compared with those of samples before pulsed current treatment. Figure 2 As shown, after using the pulsed current treatment method of this embodiment, it is basically impossible to distinguish between dendrite trunks and dendrites in the sample. The original large black γ / γ′ eutectic structure is completely eliminated, and the white network carbides are also basically eliminated. Example 2

[0038] This embodiment applies pulsed current treatment to small-sized single-crystal superalloys. The specific steps are as follows:

[0039] Step 1: Prepare pulse-treated samples.

[0040] Take a 30mm×5mm×1.5mm cast nickel-based single crystal high-temperature alloy sample and polish its surface with 180, 800, and 2000 grit sandpaper in sequence until there are no visible defects to ensure good contact with the pulse electrode.

[0041] Step 2: Determine the gradient pulse current processing parameters.

[0042] Set the parameter range for the gradient pulse current and determine the gradient pulse current parameters:

[0043] The parameters for the first-stage pulse current processing are: frequency 1000Hz, pulse width 100ms, and current density 33A / mm². 2 Processing time: 30 minutes;

[0044] The second-stage pulse current processing parameters are: frequency 1000Hz, pulse width 100ms, and current density 35A / mm². 2 Processing time: 30 minutes;

[0045] The parameters for the third-level pulse current processing are: frequency 1000Hz, pulse width 100ms, and current density 40A / mm². 2 Processing time: 60 minutes.

[0046] Step 3: Pulse current processing.

[0047] After polishing, the small sample is fixed to the output of the pulse power supply with a clamp, and pulse current is applied to it at room temperature according to the gradient pulse current parameters set in the second step.

[0048] Step 4: Use a scanning electron microscope to examine the material after pulsed current treatment.

[0049] Samples treated with pulsed current were subjected to SEM analysis, and the results were compared with those of samples before pulsed current treatment. Figure 3 As shown, after using the pulsed current treatment method of this embodiment, it is basically impossible to distinguish between dendrite trunks and dendrites in the sample. The original large black γ / γ′ eutectic structure is completely eliminated, and the white network carbides are also basically eliminated. Example 3

[0050] This embodiment applies pulsed current treatment to small-sized single-crystal superalloys. The specific steps are as follows:

[0051] Step 1: Prepare pulse-treated samples.

[0052] Take a 30mm×5mm×1.5mm cast nickel-based single crystal high-temperature alloy sample and polish its surface with 180, 800, and 2000 grit sandpaper in sequence until there are no visible defects to ensure good contact with the pulse electrode.

[0053] Step 2: Determine the pulse processing parameters.

[0054] Set the parameter range for the gradient pulse current and determine the gradient pulse current parameters:

[0055] The parameters for the first-stage pulse current processing are: frequency 1000Hz, pulse width 200ms, and current density 29A / mm². 2 Processing time: 30 minutes;

[0056] The second-stage pulse current processing parameters are: frequency 1000Hz, pulse width 200ms, and current density 30A / mm². 2 Processing time: 60 minutes;

[0057] The parameters for the third-level pulse current processing are: frequency 1000Hz, pulse width 200ms, and current density 32A / mm². 2 Processing time: 60 minutes.

[0058] Step 3: Pulse current processing.

[0059] After polishing, the small sample is fixed to the output of the pulse power supply with a clamp, and pulse current is applied to it at room temperature according to the gradient pulse current parameters set in the second step.

[0060] Step 4: Use a scanning electron microscope to examine the material after pulsed current treatment.

[0061] Samples treated with pulsed current were subjected to SEM analysis, and the results were compared with those of samples before pulsed current treatment. Figure 4 As shown, after using the pulsed current treatment method of the present invention, it is basically impossible to distinguish between dendrite trunks and dendrites in the sample. The original large black γ / γ′ eutectic structure is completely eliminated, and the white network carbides are also basically eliminated.

[0062] The above are only some specific embodiments of single-crystal superalloy samples of the present invention. In the present invention, the time range of 10min-3h is based on the size range of laboratory single-crystal superalloy samples. In actual production, the pulse current treatment time for single-crystal superalloys varies with the size of the material itself.

[0063] The scope of protection of this invention is not limited to the above embodiments. Any person skilled in the art who, within the technical scope disclosed in this invention, makes equivalent substitutions for similar materials or equipment or adjusts relevant technical parameters according to the technical solution and inventive concept of this invention should be included within the scope of protection of this invention.

Claims

1. A method for homogenizing nickel-based single-crystal superalloys using pulsed current, characterized in that, Two or more gradient pulse currents were applied to a 30mm×5mm×1.5mm as-cast nickel-based single-crystal superalloy. The parameters of the gradient pulse currents were: frequency 1000~2000Hz, pulse width 100ms~200ms, and current density 30~40A / mm². 2 The action time is 10 min to 3 h, and the current density of the applied gradient pulse current increases step by step.

2. The method for homogenizing nickel-based single-crystal superalloys using pulsed current according to claim 1, characterized in that, A gradient pulse current of level 2 to 4 was applied to the as-cast nickel-based single-crystal superalloy.

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