Two-stage aging heat treatment process for optimizing medium-temperature brittleness of precipitation strengthening type high-temperature alloy

Abstract

The invention discloses a two-stage aging heat treatment process for optimizing medium-temperature brittleness of a precipitation strengthening type high-temperature alloy, and belongs to the technical field of heat treatment of heat-resistant materials. The two-stage aging heat treatment process for improving the medium-temperature brittleness of the precipitation strengthening type high-temperature alloy comprises the following steps: heating the precipitation strengthening type high-temperature alloy to 120-220 DEG C below the liquidus temperature of the alloy, and carrying out solution treatment, then carrying out primary aging treatment in a manner of cooling to 100-350 DEG C below the dissolution line temperature of a precipitation phase at the cooling rate of 0.25-8 DEG C / min, and then cooling to obtain an alloy intermediate; and the alloy intermediate is heated to 150-350 DEG C below the precipitation phase dissolution line temperature, secondary aging treatment is carried out, then cooling is carried out, and the precipitation strengthening type high-temperature alloy with the medium-temperature brittleness improved is obtained. According to the two-stage aging heat treatment process, the problems of premature failure and fracture and insufficient plasticity of the alloy in the medium-temperature tensile deformation process are inhibited, and the percentage elongation after fracture of the alloy in the medium-temperature tensile deformation process is effectively improved.

Description

Technical Field

[0001] The invention relates to the technical field of heat treatment of heat-resistant materials, and in particular to a double-stage aging heat treatment process for optimizing the medium-temperature brittleness of a precipitation-strengthened high-temperature alloy. Background Art

[0002] With the continuous development of heat-resistant materials science, how to ensure that the material maintains excellent high-temperature performance (including high-temperature endurance strength, thermal fatigue performance, oxidation resistance and room-temperature processing performance) while taking into account high specific strength and good room-temperature processing performance is still a key issue that needs to be solved in the current field of materials science. Among them, precipitation-strengthened high-temperature alloys have become an important material choice in high-temperature environments such as aerospace and energy due to their excellent high-temperature mechanical properties.

[0003] The strength characteristics of this type of alloy are closely related to the characteristic parameters of the microstructure of its γ′ phase. Specifically, when the γ′ phase particle size is small and the volume fraction is high, the alloy exhibits excellent tensile strength, but is accompanied by lower tensile plasticity and relatively poor endurance strength. On the contrary, when the particle size increases and the volume fraction decreases, the alloy's endurance strength and plasticity are significantly improved, but this is often at the expense of high-temperature tensile strength. At present, the low plasticity of alloys under high-temperature service environment has become a bottleneck restricting the further development of precipitation-strengthened high-temperature alloys, and the creep endurance performance of alloys has become an important challenge in the field of high-temperature materials. The creep endurance strength of the alloy can be effectively improved by improving the elongation after fracture of the alloy at the intermediate service temperature. Therefore, scholars at home and abroad have conducted in-depth research on the brittle behavior of such alloys at intermediate temperatures in the hope of solving the problem of instability of medium-temperature plasticity.

[0004] Journal article Achieving excellent elevated-temperature mechanical properties in dual-phase high-entropy alloys via nanoscale co-precipitation and heterostructure engineering (Acta Materialia, 2025, 284, 120634) Adding Nb element to Al-Co-Cr-Fe-Ni high entropy alloy triggers L12 phase precipitation and induces α' and Laves nanoprecipitates to co-precipitate in B2 phase to form a hierarchical heterogeneous structure. The precipitation strengthening of L12, α' and Laves nanoprecipitates and the strengthening induced by heterogeneous deformation increase the yield strength to 1076MPa at room temperature and 905MPa at 700℃, while maintaining a high ductility of 10-50% in this temperature range.

[0005] Journal paper: Designing nanoparticles-strengthened high-entropy alloys with simultaneously enhanced strength-ductility synergy at both room and elevated temperatures (Acta Materialia, 2022, 238, 118216). By adjusting the content of Cr in Ni 39.9 Co 20 Fe 30- x Cr x Al6Ti4B 0.1 the content, the instantaneous antioxidant behavior of the alloy during medium-temperature deformation is improved. The increase in Cr promotes the rapid formation of a dense protective Cr2O3 oxide film on the alloy surface, avoiding further erosion of grain boundaries by O elements, and effectively improving the mechanical properties of the alloy at 600 °C. The elongation after fracture increases from 3.4% of Cr0 to 25.2% of Cr20, and the strength increases from 913 MPa to 1136 MPa.

[0006] Although the above methods have developed high-temperature structural materials with high thermal stability, high strength and toughness, the existing means usually adopt long-term aging treatment, which is as short as 100 hours and as long as tens of thousands of hours, or alloying treatment with precious metal elements to regulate the phase composition of the alloy. These semi-empirical methods of the existing technology have a long production cycle, high cost and low efficiency, which limit their wide application in industrial production and still need to be further improved. Summary of the Invention

[0007] The purpose of the present invention is to provide a two-stage aging heat treatment process for optimizing the medium-temperature brittleness of precipitation-strengthened superalloys to solve the above problems in the background technology. The two-stage aging heat treatment process of the present invention inhibits the problems of premature failure fracture and insufficient plasticity during medium-temperature tensile deformation of the alloy, effectively improves the elongation after fracture of the alloy during intermediate-temperature deformation, and thus effectively improves the creep rupture strength of the alloy. This heat treatment process is applicable to γ'-phase strengthened nickel-based superalloys and L12-phase strengthened high-entropy alloys.

[0008] To achieve the above purpose, the present invention provides the following technical solutions:

[0009] One of the technical solutions of the present invention: Provide a process for two-stage aging heat treatment for optimizing the medium-temperature brittleness of precipitation-strengthened superalloys, including the following steps:

[0010] (1) Heat the precipitation-strengthened superalloy to a temperature 120 - 220 °C below the alloy liquidus temperature for solution treatment, and then perform primary aging treatment by cooling at a cooling rate of 0.25 - 8 °C / min to a temperature 100 - 350 °C below the precipitation phase dissolution line temperature, and then cool to obtain an alloy intermediate;

[0011] (2) Heat the alloy intermediate to a temperature 150 - 350 °C below the precipitation phase dissolution line temperature for secondary aging treatment, and then cool to 10 - 30 °C to obtain a precipitation-strengthened superalloy with improved medium-temperature brittleness.

[0012] Preferably, the morphology of the precipitation-strengthened superalloy is an alloy rod with a diameter of 90 - 100 mm.

[0013] Preferably, the precipitation-strengthened superalloy is a pre-treated precipitation-strengthened superalloy, specifically:

[0014] Remove the cladding from the precipitation-strengthened superalloy billet by milling, and then perform wire cutting according to a preset shape to obtain the cut alloy;

[0015] Perform surface cleaning treatment on the cut alloy to obtain the pre-treated precipitation-strengthened superalloy.

[0016] More preferably, the surface cleaning treatment is: grind the cut alloy with SiC sandpaper until the surface is smooth and shows a metallic color, and then soak it in an ethanol solution for ultrasonic cleaning.

[0017] Preferably, the solution treatment, primary aging treatment, and secondary aging treatment are carried out in an oxygen-free atmosphere.

[0018] Preferably, the heating rate of the heating in step (1) ≤ 16 °C / min; the time of the solution treatment is 1 - 6 h.

[0019] Preferably, the types of the precipitation-strengthened superalloy include γ'-phase strengthened nickel-based superalloys and L12-phase strengthened high-entropy alloys.

[0020] Performing solution treatment under the parameters defined in the present invention can ensure more uniform solid solution composition.

[0021] Preferably, the time of the secondary aging treatment is 0.5 - 48 h.

[0022] Preferably, the cooling method in step (1) is air cooling.

[0023] Preferably, the cooling method in step (2) is air cooling.

[0024] Preferably, the heating rate in step (2) is 10 °C / min.

[0025] The second technical solution of the present invention: Provide a precipitation-strengthened superalloy with improved intermediate-temperature brittleness prepared according to the above process.

[0026] The technical principle of the present invention is as follows:

[0027] The heat treatment process of the present invention precipitates precipitate phases with two size characteristics of coarser and finer through double-stage aging. Among them, the coarser precipitate phase can bow out the grain boundary to form a serrated grain boundary, improving the intermediate-temperature plasticity of the alloy; the finer precipitate phase plays a role in dispersion strengthening to maintain the high-temperature strength of the alloy. Compared with the standard heat treatment process, this method is simple and efficient, and has a significant effect in improving the intermediate-temperature plasticity of the alloy, and is applicable to alloy systems such as γ'-phase strengthened nickel-based superalloys and L12-phase strengthened high-entropy alloys.

[0028] The present invention discloses a process for double-stage aging heat treatment to optimize the intermediate-temperature brittleness of a precipitation-strengthened superalloy. After solution treatment, slow cooling is used to control the cooling rate within the range of 0.25 - 8 °C / min. This is more suitable for regulating the grain boundary morphology, will significantly change the grain boundary morphology, improve the elongation of the alloy during deformation at intermediate temperatures, and at the same time, slow cooling after solution treatment can effectively avoid the generation of thermal stress due to rapid cooling and prevent cracks from appearing in the alloy.

[0029] In the aging stage, continuous double-stage aging treatment is adopted. The first-stage aging treatment is high-temperature aging treatment (cooling from 120 - 220 °C below the liquidus temperature of the alloy to 100 - 350 °C below the precipitation phase dissolution line temperature). During this process, precipitation of strengthening phases and aggregation growth of dispersed strengthening phases will occur. At the same time, the strengthening phases squeeze and pin the grain boundaries during cooling, promoting the change of grain boundary morphology, thereby effectively improving the intermediate-temperature plasticity of the alloy. The second-stage aging treatment is low-temperature aging treatment. During this process, relatively finer strengthening phases will be further precipitated to effectively ensure the precipitation strengthening effect.

[0030] The present invention uses a double-stage aging process to control the size of the strengthening phases: relatively larger strengthening phases are generated through high-temperature aging and slow cooling rate, and then relatively finer strengthening phases are precipitated and stored in cooperation with low-temperature aging. The grain boundaries of the precipitation-strengthened superalloy treated conventionally generally show a straight-tooth type. During service at intermediate temperatures, cracks are likely to propagate along the grain boundaries, causing the alloy to fail prematurely; while the present invention uses the strengthening phases to bow out the grain boundaries to form serrated grain boundaries, reducing the stress borne by the grain boundaries during service, effectively inhibiting the propagation of grain boundary cracks, and thus suppressing the phenomenon of intermediate-temperature brittleness.

[0031] The heat treatment method of the present invention, combined with inert gas powder filling and hot isostatic pressing process, has unexpected effects in improving the strength of the alloy.

[0032] The beneficial technical effects of the present invention are as follows:

[0033] The present invention provides a two-step aging heat treatment process for optimizing the intermediate-temperature brittleness of precipitation-strengthened superalloys, aiming to inhibit the problems of premature failure fracture and insufficient plasticity during intermediate-temperature tensile deformation of the alloy, effectively improving the elongation after fracture of the alloy during intermediate-temperature deformation, and thus effectively enhancing the creep rupture strength of the alloy. This heat treatment process is applicable to γ'-phase strengthened nickel-based superalloys and L12-phase strengthened high-entropy alloys.

[0034] After heat treatment, the elongation after fracture of the alloy at 800 °C can be increased by 0.5 to 2 times compared with the standard heat treatment process, significantly improving the intermediate-temperature brittleness problem of precipitation-strengthened superalloys, while maintaining its strength without obvious reduction. The heat treatment method of the present invention is simple to operate, has a short production cycle, can effectively reduce traditional heat treatment processes, save energy consumption, and has good popularization value. Brief Description of the Drawings

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0036] Figure 1 It is the low-magnification scanning electron microscope result diagram of the precipitation-strengthened superalloy in Embodiment 2 of the present invention.

[0037] Figure 2 It is the high-magnification scanning electron microscope result diagram of the precipitation-strengthened superalloy in Embodiment 2 of the present invention.

[0038] Figure 3 It is the scanning electron microscope result diagram of the product in Comparative Example 1 of the present invention. Detailed Embodiments

[0039] Now, various exemplary embodiments of the present invention will be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention. It should be understood that the terms described in the present invention are only used to describe specific implementation modes and are not used to limit the present invention.

[0040] In addition, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0041] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Although this invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of this invention. It should be noted that the aspects not detailed in this invention are all conventional operating means in the art and are not the focus of this invention.

[0042] Regarding the use of "comprising", "including", "having", "containing", etc. in this invention, they are all open-ended terms, meaning including but not limited to.

[0043] Precipitation-strengthened nickel-based superalloys usually obtain the final microstructure through solution treatment followed by aging treatment. The solution treatment generally involves heating the alloy to a temperature at which the γ' phase or L12 phase (such as Ni3Al or Ni3(Ti,Al) type, etc.) is completely dissolved (usually between 1050°C and 1200°C), holding for a period of time, and then rapidly cooling (such as water quenching) to obtain a supersaturated solid solution. Subsequently, aging treatment is carried out, that is, the alloy after solution treatment is held at a lower temperature (usually between 700°C and 900°C) for a period of time to uniformly precipitate the γ' / L12 phase. After the alloy undergoes solution aging treatment, its microstructure mainly consists of a γ matrix and dispersed γ' phases; the γ' / L12 phase, as the main strengthening phase, has a small size and is uniformly distributed. However, this heat treatment process may cause the following problems: 1. The rapid cooling after solution treatment may induce thermal stress, resulting in cracks; 2. The γ' phases are dispersed inside the grains, and the grain boundaries are the weak areas during high-temperature deformation. The erosion of oxygen elements on the grain boundaries at high temperature leads to grain boundary embrittlement. At the same time, the grain boundaries bear higher stress compared to the interior of the grains, resulting in the initiation of cracks at the grain boundaries, causing the alloy to fail prematurely, that is, medium-temperature brittleness.

[0044] This invention provides a two-stage aging heat treatment process for optimizing the medium-temperature brittleness of precipitation-strengthened superalloys, including the following steps:

[0045] (1) Put the precipitation-strengthened superalloy into an atmosphere tube furnace, heat it at a heating rate not higher than 16°C / min to 120 - 220°C below the liquidus temperature of the alloy, hold for 1 - 6 h, and then perform the first-stage aging treatment by cooling at a cooling rate of 0.25 - 8°C / min to 100 - 350°C below the precipitation phase dissolution line temperature, and then air-cool to room temperature to obtain an alloy intermediate;

[0046] (2) Put the alloy intermediate into the atmosphere tube furnace, heat it to 150 - 350°C below the precipitation phase dissolution line temperature, hold for 0.5 - 48 h, and then air-cool to room temperature to obtain a precipitation-strengthened superalloy with improved medium-temperature brittleness.

[0047] The reason for defining the solution treatment temperature of the present invention to be 120 - 220 °C below the liquidus temperature of the alloy is that a relatively high solution temperature may cause rapid grain growth and affect the performance; the reason for defining the temperature of the first aging treatment to be 100 - 350 °C below the precipitation phase dissolution line temperature is that the growth of the precipitation phase requires temperature and time drive, and a lower temperature can effectively increase the volume fraction of the alloy precipitation phase.

[0048] The particle size range of the γ′ / L12 phase strengthened nickel-based superalloy pre-alloy powder used in the present invention is 15 - 100 μm; the alloy composition of the γ′ phase strengthened nickel-based superalloy pre-alloy powder used is (mass percentage) Ni 66.4%, Cr 17%, Fe 9%, Co 1%, Ti 2.7%, Al 1%, Nb 1.2%, Mn 0.8%, Cu 0.5%, Si 0.4%; the alloy composition of the L12 phase strengthened high-entropy alloy used is (mass percentage) Ni 44.7%, Co 23%, Cr 9.1%, Fe 8.8%, Ti 3.9%, Al 3.8%, Ta 2.9%, Nb 0.8%, W 1.6%, Mo 0.9%, Hf 0.2%, Zr 0.1%, B 0.2%.

[0049] In the present invention, "room temperature" is calculated as 10 - 30 °C unless otherwise specified.

[0050] All raw materials used in the following examples and comparative examples of the present invention are commercially available products.

[0051] Example 1

[0052] A process for two-stage aging heat treatment to optimize the mid-temperature brittleness of a precipitation-strengthened superalloy is as follows:

[0053] Step 1: Load the γ′ phase strengthened nickel-based superalloy pre-alloy powder into a stainless steel cladding through a vacuum glove box (the glove box is filled with high-purity argon with a purity of more than 99.99%), perform vacuum degassing and sealing welding to obtain the sealed alloy powder.

[0054] Step 2: Perform hot isostatic pressing on the sealed alloy powder (parameters: 1180 °C, 140 MPa, holding for 2 h) to obtain a cylindrical ingot blank.

[0055] Step 3: Remove the stainless steel cladding on the outer surface of the cylindrical ingot blank to obtain a γ′ phase strengthened nickel-based superalloy blank; after testing, the tensile strengths of this blank at room temperature and 800 °C are 1254 and 513 MPa respectively, and the elongation after fracture are 23.1% and 12.7% respectively.

[0056] Step 4: Heat the γ'-phase strengthened nickel-based superalloy billet at a heating rate of 16 °C / min to 112 °C below the alloy liquidus temperature (specifically 1200 °C), and perform solution treatment for 6 h;

[0057] Step 5: Cool the precipitation-strengthened alloy after the solution treatment in Step 4 at a set rate (cooling rate is 5 °C / min) to 162 °C below the precipitation phase dissolution line temperature (800 °C) to complete the first-stage aging treatment; then air-cool to room temperature;

[0058] Step 6: Heat the γ'-phase strengthened nickel-based superalloy after the treatment in Step 5 at a heating rate of 10 °C / min to 162 °C below the precipitation phase dissolution line temperature (800 °C), perform aging treatment for 0.5 h, and then air-cool to room temperature to obtain a precipitation-strengthened superalloy with improved intermediate-temperature brittleness.

[0059] Machine the γ'-phase strengthened nickel-based superalloy obtained in Step 6 into a dog-bone tensile specimen with a gauge length of 8 mm, a width of 3 mm, and a thickness of 2 mm, and conduct a tensile test on a universal mechanical testing machine at a rate of 1 mm / min; it is measured that its tensile strengths at room temperature and 800 °C are 1383 and 587 MPa respectively, and the elongation after fracture are 26.7% and 19.1% respectively.

[0060] Example 2 (replacing alloy type)

[0061] A process for two-stage aging heat treatment to optimize the intermediate-temperature brittleness of a precipitation-strengthened superalloy is as follows:

[0062] Step 1: Load the L12-phase strengthened high-entropy alloy pre-alloy powder into a stainless steel cladding through a vacuum glove box (the glove box is filled with high-purity argon with a purity of more than 99.99%), perform vacuum degassing and sealing welding to obtain the sealed alloy powder;

[0063] Step 2: Perform hot isostatic pressing on the sealed alloy powder (parameters: 1180 °C, 140 MPa, hold for 2 h) to obtain a cylindrical ingot blank;

[0064] Step 3: Remove the stainless steel cladding on the outer surface of the cylindrical ingot blank to obtain an L12-phase strengthened high-entropy alloy billet;

[0065] Step 4: Heat the L12-phase strengthened high-entropy alloy billet at a heating rate of 16 °C / min to 132 °C below the alloy liquidus temperature (1200 °C), and perform solution treatment for 6 h;

[0066] Step 5: Cool the precipitation-strengthened alloy after the solution treatment in Step 4 in the furnace (cooling rate is 5 °C / min) to 324 °C below the precipitation phase dissolution line temperature (800 °C) to complete the first-stage aging treatment; then air-cool to room temperature;

[0067] Step 6: Heat the L12 phase strengthened high-entropy alloy processed in Step 5 to 324 °C (800 °C) below the precipitation phase dissolution line temperature at a heating rate of 10 °C / min, perform aging treatment for 1 h, and then air cool to room temperature to obtain a precipitation strengthened high-temperature alloy with improved intermediate temperature brittleness.

[0068] Process the L12 phase strengthened high-entropy alloy obtained in Step 6 into a dog-bone tensile specimen with a gauge length of 8 mm, a width of 3 mm, and a thickness of 2 mm, and conduct a tensile test on a universal mechanical testing machine at a rate of 1 mm / min; it is measured that the tensile strengths at room temperature and 800 °C are 1387 and 857 MPa respectively, and the elongation after fracture are 27.9% and 9.6% respectively.

[0069] The SEM result diagram of the L12 strengthened high-entropy alloy of Example 2 is as Figure 1 shown, and it can be seen from Figure 1 that this alloy has a duplex FCC / L12 structure, with a high density of L12 phases uniformly distributed in the FCC matrix, many abnormal L12 phases existing at the grain boundaries, and many fine secondary L12 phases precipitating in the FCC matrix.

[0070] Figure 2 This is the high-magnification SEM result diagram of the precipitation strengthened high-temperature alloy in Example 2 of the present invention.

[0071] Figure 2 The grain boundary bowing situation of the product of Example 2 is shown in

[0072] Comparative Example 1

[0073] The difference from Example 1 is only that the alloy after solution treatment in Step 4 is directly air cooled to room temperature, then heated to 800 °C at a heating rate of 10 °C / min, subjected to aging treatment for 24 h, and then air cooled to room temperature.

[0074] It is measured that the tensile strengths of the product of Comparative Example 1 at room temperature and 800 °C are 1403 and 601 MPa respectively, and the elongation after fracture are 25.6% and 13.9% respectively.

[0075] Figure 3 This is the SEM result diagram of the product of Comparative Example 1 of the present invention.

[0076] Figure 3 It shows that there are fine strengthening phases dispersed inside the alloy.

[0077] Comparative Example 2

[0078] The difference from Example 2 is only that the alloy after solution treatment in Step 4 is directly air cooled to room temperature, then heated to 800 °C at a heating rate of 10 °C / min, subjected to aging treatment for 24 h, and then air cooled to room temperature.

[0079] It was measured that the tensile strengths of the product of Comparative Example 2 at room temperature and 800 °C were 1520 and 910 MPa respectively, and the elongation after fracture were 11.9% and 2.9% respectively.

[0080] Table 1 Product properties of the high-entropy alloys prepared in the examples and comparative examples

[0081]

[0082] In summary, the present invention provides a heat treatment process for a precipitation-strengthened superalloy. By optimizing the heat treatment process and the alloy microstructure, the medium-temperature plasticity of the alloy is significantly improved on the basis of the existing process, and the strength is not seriously damaged.

[0083] The above-described embodiments are only descriptions of the preferred modes of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A process for double-stage aging heat treatment to optimize the intermediate-temperature brittleness of a precipitation-strengthened superalloy, characterized in that, It includes the following steps: (1) Heat the precipitation-strengthened superalloy to 120 - 220 °C below the alloy liquidus temperature for solution treatment, and then perform primary aging treatment by cooling at a cooling rate of 0.25 - 8 °C / min to 100 - 350 °C below the precipitation phase dissolution line temperature, and then cool to obtain an alloy intermediate; (2) Heat the alloy intermediate to 150 - 350 °C below the precipitation phase dissolution line temperature for secondary aging treatment, and then cool to obtain a precipitation-strengthened superalloy with improved intermediate temperature brittleness.

2. The process according to claim 1, characterized in that, The heating rate of the heating in step (1) ≤ 16 °C / min; the time of the solution treatment is 1 - 6 h.

3. The process according to claim 1, characterized in that, The types of the precipitation-strengthened superalloy include γ'-phase strengthened nickel-based superalloy and L12-phase strengthened high-entropy alloy.

4. The process according to claim 1, characterized in that, The time of the secondary aging treatment is 0.5 - 48 h.

5. The process according to claim 1, characterized in that, The cooling method in step (1) is air cooling.

6. The process according to claim 1, characterized in that, The cooling method in step (2) is air cooling.

7. The process according to claim 1, characterized in that, The heating rate of the heating in step (2) is 10 °C / min.

8. A precipitation-strengthened superalloy with improved intermediate temperature brittleness prepared by the process according to any one of claims 1 - 7.

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