CN111575619A - A method for rapid elimination of dendrite segregation in deformed superalloy ingots by pulsed current - Google Patents

Abstract

The invention relates to the technical field of turbine disk preparation, and provides a method for rapidly eliminating dendrite segregation (mainly aimed at the second stage of traditional homogenization heat treatment) in a nickel-based deformed superalloy ingot for a turbine disk by pulsed current. Under the coupling action of pulse current and Joule heat, the diffusion ability of segregated element atoms is greatly enhanced, thereby realizing the rapid elimination of dendrite segregation under pulse current external field. The parameter range of the pulsed external field treatment of the present invention is: frequency 30000Hz, voltage 0.1V-100V, current density 1A/mm ² -150A/mm ² , and treatment time 5min-20h. Compared with the traditional long-time high-temperature treatment in a single thermal field, the use of the present invention can quickly eliminate dendrite segregation under suitable pulse parameters, achieve uniform distribution of segregation elements, and the treated superalloy has lower strength, which is more conducive to subsequent Billet forging process. Not only that, the technical means of the present invention is a brand-new means of green energy saving, which conforms to the current concept and requirements of green development and has broad application prospects.

Description

A method for rapid elimination of dendrite segregation in deformed superalloy ingots by pulsed current

technical field

The invention belongs to the technical field of superalloy turbine disk preparation, and in particular relates to a new method for rapidly eliminating dendrite segregation in a nickel-based deformed superalloy ingot for a turbine disk by an external field of pulse current.

technical background

Since the birth of superalloys in the last century, the huge demand for high-temperature materials for aero-engine hot-end components has continuously promoted the rapid development of superalloys. Among the three types of superalloys: deformed, cast and powder, deformed superalloys are the most widely used. Deformed superalloys are mainly used to manufacture high-temperature components such as aero-engine turbine disks and combustion chambers. Turbine disk is an important part in the engine, not only the working temperature is high, but also the stress conditions of each part are extremely complex. Therefore, extremely high requirements are placed on superalloys for turbine disks, including extremely high strength, plasticity, long life, creep resistance, corrosion resistance, oxidation resistance, and long-term microstructure stability. However, due to the high degree of alloying of the deformed superalloy, it contains a large amount of insoluble elements. Serious dendrite segregation is likely to occur at the end of solidification of superalloys, resulting in uneven microstructure and mechanical properties, often resulting in turbine disk performance that does not meet service requirements. Therefore, dendrite segregation is not allowed in the finished material.

Under the existing smelting conditions, the existence of dendrite segregation in deformed superalloy ingots is inevitable. In order to obtain high-quality bars and improve the quality of turbine disks, dendrite segregation in alloy ingots should be completely eliminated. At present, the most effective way to eliminate dendrite segregation is homogenization heat treatment. The patent (CN 107523772 B) discloses a homogenization process of U720Li superalloy. In order to solve the problem of element segregation, the entire homogenization process described in the invention needs to keep the alloy ingot at 1200°C for 72 hours continuously. The patent (CN 103276333 A) discloses a GH4738 nickel-based superalloy ingot homogenization treatment method. In order to solve the problem of a large number of as-cast dendrites in the GH4738 ingot, the invention requires the ingot to be placed in an annealing furnace. Continuous annealing at high temperature of 1160℃～1200℃ for 20h～50h.

The grade of nickel-based deformed superalloy material used in the present invention is GH4169D. There are a large number of low melting point brittle phases and typical dendrite segregation in the GH4169D ingot obtained by triple smelting. The traditional homogenization method is divided into two stages: Stage 1, heat preservation above 1100°C for at least 20h to eliminate low melting point brittle Laves phase; Stage 2, heat preservation above 1160°C for at least 70h to eliminate interdendritic element segregation. In order to show the positive significance of the pulse current intervention method of the present invention to the elimination of dendrite segregation in the alloy ingot, the raw materials of the present invention are all processed in one stage of the traditional homogenization process to eliminate the low melting point phase (collectively referred to as one-stage homogenization heat treatment). state). At present, in order to achieve the complete elimination of dendrite segregation in the GH4169D alloy ingot, high temperature heat treatment with a temperature of 1100°C or more and a time of more than 70h is usually used. Although dendrite segregation can be better eliminated by the above methods, due to the high temperature, long processing time, complex process and high energy consumption of traditional heat treatment, it does not meet the requirements of the current industrial green development plan. Therefore, it is necessary to find a new treatment method to achieve the purpose of eliminating dendrite segregation with high efficiency and low energy consumption.

SUMMARY OF THE INVENTION

In traditional heat treatment, after dissolving the low melting point brittle phase in the GH4169D alloy ingot, it needs to be kept at high temperature for a long time for 70h to 80h to completely eliminate the segregation of dendritic elements. The technical means used in the present invention—pulse current is an instantaneous high-energy input method. Different from the single thermal field of traditional heat treatment, the pulse current external field accelerates the diffusion rate of segregated element atoms due to the coupling effect of pulse current and Joule heat, breaking the thermal diffusion limit, thereby significantly accelerating the elimination of dendrite segregation in the ingot. A new treatment method completely different from heat treatment.

Aiming at the deficiencies in the process of eliminating dendrite segregation by traditional heat treatment, the present invention provides a brand-new technical means for rapidly eliminating dendrite segregation in an ingot under a non-traditional pulse current external field. With the technical solution of the present invention, under suitable pulse parameters, the dendrite segregation can be completely eliminated in only 30 minutes. In addition, after applying a pulse current external field, the electronic wind force brought by high-speed drifting electrons can not only speed up the diffusion rate of segregated element atoms, but also improve the mobility of defects in metal materials, thereby improving the plasticity of materials. Therefore, compared with the conventional homogenization heat treatment, the homogenized state material obtained by the technical means of the present invention has a lower yield strength at room temperature. Considering the integrity of the process, the superalloy treated by the pulse current field is more conducive to the subsequent blanking and forging processes. The invention performs pulse external field treatment on the small-sized superalloy material subjected to one-stage homogenization heat treatment. For ingots of different sizes, it is only necessary to adjust the two parameters of voltage and current to ensure a constant current density in the ingot to achieve the same pulsed external field treatment effect as for small-sized superalloy materials.

The technical scheme of the present invention is as follows:

A new method for rapidly eliminating dendrite segregation in deformed superalloy ingots by pulsed current. The ingot is subjected to pulse current treatment, and the method greatly shortens the time required for the complete elimination of dendrite segregation in the ingot; the pulse treatment parameters: frequency 30000Hz, voltage 0.1V ~ 100V, current density 1A/mm ² ~ 150A/mm ^2. The treatment time is 5min～20h. To demonstrate the positive effect of the pulsed external field on the elimination of dendrite segregation, the temperature was measured by a K-type thermocouple welded in the center of the superalloy surface, and an equivalent heat treatment was performed in a muffle furnace.

The above-mentioned method for rapidly eliminating dendrite segregation in a deformed superalloy ingot by pulsed current, the specific steps are as follows:

(1) The nickel-based deformed superalloy material is fixed by a pure copper fixture and then connected to both ends of the pulse power supply by a pure copper wire;

(2) After setting the parameters, turn on the pulse power supply, and the temperature of the central area of the superalloy reaches the expected processing temperature in 10s; continue to apply the pulse for 5min to 20h, disconnect the power supply and air-cool to room temperature.

Further, the nickel-based deformed superalloy is a GH4169D alloy ingot, which is obtained by a triple smelting process: vacuum induction melting, electroslag remelting and vacuum self-consumption remelting, and undergoes a first-stage homogenization heat treatment to redissolve a low melting point. brittle phase.

Further, the pulse current output device is a high-frequency pulse power supply, and different processing effects can be obtained by adjusting the voltage and current.

Further, the whole process of pulse current external field treatment is carried out at room temperature.

Further, when the pulsed current is applied, the temperature rise caused by the generated Joule heat is considered to be uniform on the cross-section of the superalloy material.

Furthermore, after applying pulsed current, the rapid elimination of dendrite segregation benefits from the coupling effect of pulsed current and Joule heat; compared with pure thermal field, pulsed current has outstanding advantages in eliminating dendrite segregation in alloy ingots. .

Further, the size of the superalloy in the superalloy treated with pulsed current for the analysis of dendrite segregation elimination is 30×4×1.5 mm ³ ; the rectangular deformation area of the superalloy in the superalloy treated with pulsed current for the tensile strength test at room temperature is 20× 4×1.5mm ³ .

Further, due to the rapid heat dissipation of copper, the temperature of the clamping end parts on both sides of the superalloy is lower than the processing temperature. Therefore, in the subsequent microstructure observation process, the main focus is on the dendrite segregation in the central region of the superalloy treated with pulse current. Eliminate the situation.

Compared with the traditional heat treatment, the beneficial effects of the present invention are:

1. The time required for dendrite segregation elimination is greatly shortened. In order to diffuse the segregated elements in the alloy ingot to a uniform distribution, the traditional heat treatment needs to be kept at a high temperature in two stages for about 100 hours. Compared with the traditional heat treatment method, the pulse current breaks the thermal diffusion limit of the segregated element atoms, and the same effect can be achieved in only 30 minutes under suitable parameters. Therefore, the external field of pulsed current can obviously promote the elimination of dendrite segregation.

2. The temperature required to eliminate dendrite segregation is reduced. The dendrite segregation can be completely eliminated by applying a pulsed external field at 1050℃. Compared with the traditional heat treatment method, the pulse current external field treatment reduces the working temperature by more than 100℃.

3. The simplification of the treatment process, the shortening of the treatment time and the reduction of the treatment temperature will greatly reduce the energy consumption required for the entire process and bring unpredictable economic benefits.

4. The strength of the superalloy obtained by using the technical solution of the present invention is lower than that of the traditional homogenization method, which is more conducive to the subsequent blanking and forging processes.

Description of drawings

Figure 1 shows the metallographic photo. Among them, (a) is the metallographic photograph of the dendrite distribution in the first-stage homogenized heat-treated superalloy, (b) is the metallographic photograph of the dendrite distribution in Example 3, (c) is the metallographic photograph of the dendrite distribution in Comparative Example 3 Photo (d) is a metallographic photo of dendrite distribution in an industrial heat treatment example.

FIG. 2 shows the room temperature tensile strength results of the as-cast state, the one-stage homogenization heat treatment state, the industrial heat treatment example, Examples 1-3 and Comparative Examples 1-3.

Detailed ways

Hereinafter, specific embodiments 1 to 3 of the present invention will be described in detail with reference to the accompanying drawings, and the present invention will be further illustrated, but not limited to the present invention. At the same time, in order to verify the positive effect of the pulse current, an equivalent heat treatment was performed in a muffle furnace, as shown in Comparative Examples 1 to 3 for details.

The superalloy materials used in Examples 1 to 3, Comparative Examples 1 to 3 and industrial heat treatment examples are all obtained by heat treatment to dissolve the low melting point brittle phase (collectively referred to as the one-stage homogenization heat treatment state). The neglected dendrite structure is shown in Fig. 1(a). The industrial heat treatment example described in this paper is that the one-stage homogenized heat-treated superalloy is kept in a muffle furnace under high temperature conditions to achieve the elimination of dendrites.

The pulse parameters described in the following Examples 1 to 3 are all parameters when pulses are applied to materials with a size of 30 × 4 × 1.5 mm ³ for dendrite elimination analysis; pulse current external field for tensile strength test at room temperature The rectangular deformation area of the treated superalloy is 20×4×1.5mm ³ , and the same pulsed external field treatment effect as the sample used for tissue analysis can be achieved by adjusting the voltage and current parameters accordingly to keep the current density constant.

Example 1

In this embodiment, the pulse parameters are set as 30000Hz, 1.2V, and 14.721A/mm ² . Under this parameter, the temperature measured by a K-type thermocouple is 850°C. The pulse was continuously applied for 30 min, and then air-cooled to room temperature. Specific steps are as follows:

(1) Take the one-stage homogenized heat-treated material in the rectangular deformation area of 20×4×1.5mm ³ , and polish the surface with 180-mesh, 600-mesh, 1000-mesh, 1500-mesh and 2000-mesh sandpaper in turn until there are no visible defects to the naked eye to ensure that Good contact with pulse electrodes.

(2) Pulse current field treatment. Fix the high temperature alloy polished in step (1) on both ends of the pulse power supply with a copper fixture. Continuous pulse treatment at room temperature for 30min at the same time, the surface temperature of superalloy after applying pulse current external field measured by K-type thermocouple is 850℃.

(3) Test the tensile strength at room temperature of the treated tensile specimen at room temperature (23° C.).

Comparative Example 1

The heat treatment process of this comparative example was carried out in a muffle furnace. The temperature was raised to 850°C at a heating rate of 5°C/min, maintained for 30 minutes, and then air-cooled to room temperature. The treated tensile specimens were tested for room temperature tensile strength at room temperature (23°C).

Example 2

In this embodiment, the pulse parameters are set as 30000Hz, 1.45V, and 17.570A/mm ² . Under this parameter, the temperature is measured by a K-type thermocouple, and the temperature is 950 °C. The pulse was continuously applied for 30 min, and then air-cooled to room temperature.

(1) Take the one-stage homogenized heat-treated material in the rectangular deformation area of 20×4×1.5mm ³ , and polish the surface with 180-mesh, 600-mesh, 1000-mesh, 1500-mesh and 2000-mesh sandpaper in turn until there are no visible defects to the naked eye to ensure that Good contact with pulse electrodes.

(2) Pulse current field treatment. Fix the high temperature alloy polished in step (1) on both ends of the pulse power supply with a copper fixture. Continuous pulse treatment at room temperature for 30min at the same time, the surface temperature of superalloy after applying pulse current external field measured by K-type thermocouple is 950℃.

(3) Test the tensile strength at room temperature of the treated tensile specimen at room temperature (23° C.).

Comparative Example 2

The heat treatment process of this comparative example was carried out in a muffle furnace. The temperature was raised to 950°C at a heating rate of 5°C/min, kept for 30 min, and then air-cooled to room temperature. The treated tensile specimens were tested for room temperature tensile strength at room temperature (23°C).

Example 3

In this embodiment, the pulse parameters are set as 30000Hz, 1.6V, and 19.676A/mm ² . Under this parameter, the temperature is measured by a K-type thermocouple, and the temperature is 1050 °C. The pulse was continuously applied for 30 min, and then air-cooled to room temperature. Specific steps are as follows:

(1) Take 30×4×1.5mm ³ and rectangular deformation zone 20×4×1.5mm ³ of one-stage homogenized heat-treated material, and polish the surface with 180-mesh, 600-mesh, 1000-mesh, 1500-mesh and 2000-mesh sandpaper in turn To no visible defects, ensure good contact with the pulse electrode.

(2) Pulse current field treatment. Fix the high temperature alloy polished in step (1) on both ends of the pulse power supply with a copper fixture. Continuous pulse treatment at room temperature for 30min at the same time, the surface temperature of superalloy after applying pulse current external field measured by K-type thermocouple is 1050℃.

(3) Test the tensile strength at room temperature of the treated tensile specimen at room temperature (23° C.).

(4) The distribution of dendrites was observed with OLYMPUS GX71 metallographic optical microscope. Take one-stage homogenized heat treatment state and pulse current external field treated superalloy respectively, and use 180-mesh, 600-mesh, 1000-mesh, 1500-mesh and 2000-mesh sandpaper in turn to grind the surface to the same direction of scratches. Electrolytic corrosion is carried out after mechanical polishing: the etching solution is 16g CrO ₃ +10mLH ₂ SO ₄ +170mL H ₃ PO ₄ ; the DC voltage is 5V, and the electrolytic corrosion time is 5-7 seconds. The state of one-stage homogenization heat treatment and the distribution of dendrites in the superalloy in this example were observed by metallographic microscope. The metallographic results are shown in (a) and (b) of Figure 1 .

Comparative Example 3

The heat treatment process of this comparative example was carried out in a muffle furnace. The temperature was increased to 1050°C at a heating rate of 5°C/min, and the temperature was maintained for 30 minutes. The elimination of dendrite segregation was observed by means of a metallographic optical microscope, and the sample preparation method was shown in Example 3. The metallographic results are shown in Figure 1 (c). The treated tensile specimens were tested for room temperature tensile strength at room temperature (23°C).

Industrial heat treatment example

The entire heat treatment process was completed in a muffle furnace, and the temperature was raised to 1190 °C for 72 hours, and then air-cooled to room temperature. The elimination of dendrite segregation was observed by means of a metallographic optical microscope, and the sample preparation method was shown in Example 3. The metallographic results are shown in Figure 1 (d). The treated tensile specimens were tested for room temperature tensile strength at room temperature (23°C).

With the aid of a metallographic optical microscope, the elimination of dendrites in the one-stage homogenized heat-treated superalloy, implementation case 3, comparative example 3 and industrial heat treatment example was observed. The results are shown in Figure 1. Figure 1 shows that the external field of pulse current greatly accelerates the atomic diffusion rate of segregated elements, breaking the thermal diffusion limit of atoms. Under suitable pulse parameters (30000Hz, 1.6V, 19.676A/mm ² ), the effect of industrial long-term high-temperature heat treatment can be achieved with only 30 minutes of treatment.

The samples of as-cast state, one-stage homogenization heat treatment state, industrial heat treatment example, Examples 1-3 and Comparative Examples 1-3 were stretched at room temperature, and the test results of the yield strength of superalloys in each state were obtained, as shown in Figure 2 shown. The results show that, compared with the traditional heat treatment, the yield strength of the superalloy reaches 283MPa when treated with appropriate pulse parameters (30000Hz, 1.6V, 19.676A/mm ² ) for 30min, which is significantly lower than 386MPa after industrial heat treatment. In billet forging after homogenization, in order to avoid cracking, it is desirable for the superalloy to have lower strength. Therefore, the present invention is more beneficial to the subsequent blanking and forging processes while realizing the elimination of dendrite segregation.

The above descriptions are only specific implementations of the present invention for eliminating dendrite segregation in a nickel-based deformed superalloy ingot. The above embodiments are only exemplary, and should not be used as limitations on the scope of the present invention. It is also applicable to other metal ingots and other size products, and only needs to adjust the parameters, but the protection scope of the present invention is not limited to this, any person skilled in the art is within the technical scope disclosed by the present invention, According to the technical solution of the present invention and its inventive concept, equivalent replacement of similar materials, equipment or adjustment of relevant technical parameters shall be included within the protection scope of the present invention.

Claims (9)

1. a method for rapidly eliminating dendrite segregation in a deformed superalloy ingot by pulse current, it is characterized in that, described method carries out pulse current treatment to the nickel-based deformed superalloy ingot only through traditional one-stage homogenization heat treatment, so The method greatly shortens the time required for the elimination of dendrite segregation in the ingot; the pulse processing parameters: frequency 30000Hz, voltage 0.1V-100V, current density 1A/mm ² -150A/mm ² , processing time 5min-20h; The traditional one stage is to eliminate the low melting point phase, but there is still a stage of serious element segregation. 2. the method for rapidly eliminating dendrite segregation in the deformed superalloy ingot by pulse current according to claim 1, is characterized in that, concrete steps are as follows: (1) The nickel-based deformed superalloy material is fixed by a pure copper fixture and then connected to both ends of the pulse power supply by a pure copper wire; (2) After setting the parameters, turn on the pulse power supply, and the temperature of the central area of the superalloy reaches the expected processing temperature in 10s; continue to apply the pulse for 5min to 20h, disconnect the power supply and air-cool to room temperature. 3. pulse current according to claim 2 quickly eliminates the method for dendrite segregation in deformed superalloy ingot, it is characterized in that, described nickel-based deformed superalloy is GH4169D alloy ingot, is that triple smelting process obtains: vacuum induction Smelting, electroslag remelting and vacuum consumable remelting, and a first-stage homogenization heat treatment to redissolve the low melting point brittle phase. 4. The method for rapidly eliminating dendrite segregation in a deformed superalloy ingot by pulse current according to claim 2, wherein the pulse current output device is a high-frequency pulse power supply, and can be obtained by adjusting voltage and current Get different processing effects. 5 . The method for rapidly eliminating dendrite segregation in a deformed superalloy ingot by pulse current according to claim 2 , wherein the whole process of pulse current external field treatment is carried out at room temperature. 6 . 6. The method for rapidly eliminating dendrite segregation in a deformed superalloy ingot by pulse current according to claim 2, characterized in that, when the pulse current is applied, the temperature rise brought by the Joule heat that is produced is removed on the cross-section of the superalloy material. considered to be uniform. 7. The method for rapidly eliminating dendrite segregation in a deformed superalloy ingot by pulse current according to claim 2, characterized in that, after applying pulse current, the rapid elimination of dendrite segregation benefits from the coupling of pulse current and Joule heat Compared with pure thermal field, pulse current has outstanding advantages in eliminating dendrite segregation in alloy ingot. 8. The method for rapidly eliminating dendrite segregation in a deformed superalloy ingot by pulsed current according to claim 2, wherein the size of the superalloy in the external field treated state of the pulsed current used for the analysis of the dendrite segregation elimination is 30×4 ×1.5mm ³ ; the rectangular deformation zone of the superalloy treated with pulsed current in the external field for tensile strength test at room temperature is 20×4×1.5mm ³ . 9. The method for rapidly eliminating dendrite segregation in a deformed superalloy ingot by pulse current according to claim 2, characterized in that, due to the faster heat dissipation of copper, the temperature of the clamping end portion on both sides of the superalloy is lower than the processing temperature, Therefore, in the subsequent microstructure observation process, the main focus is on the elimination of dendrite segregation in the central region of the superalloy treated by the pulse current external field.

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