A heat treatment process for relieving the warm brittleness of nickel-based cast equiaxed superalloy

Abstract

This invention discloses a heat treatment process to alleviate the intermediate-temperature brittleness of nickel-based cast equiaxed superalloys. The process involves sequentially subjecting the melted and solidified nickel-based cast equiaxed superalloy to high-temperature solution treatment, slow cooling treatment, and solution re-dissolution treatment. After heat treatment, the alloy exhibits tensile yield strength not less than [value missing], tensile strength not less than [value missing], and elongation not less than [value missing]. This invention employs a heat treatment regime combining high-temperature solution treatment, slow cooling, and solution re-dissolution, which causes phases to precipitate in a chain-like manner at grain boundaries, forming bent grain boundaries. Simultaneously, it controls the size and volume fraction of phases within the grains, further optimizing the balance between intragranular strength and grain boundary strength. This improves the yield strength, tensile strength, and elongation of the alloy under intermediate-temperature conditions, thus alleviating intermediate-temperature brittleness.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature alloy heat treatment technology, specifically relating to a heat treatment process for mitigating the mid-temperature brittleness of nickel-based cast equiaxed high-temperature alloys. Background Technology

[0002] Nickel-based superalloys, due to their excellent high-temperature strength and corrosion resistance, have been widely used in components such as turbine blades for industrial gas turbines. Industrial gas turbine blades are characterized by their large size, complex internal cavities, and thin-walled structures, and their manufacturing often employs precision casting processes to achieve near-net-shape forming. To improve the performance of cast superalloys, high-temperature solution treatment is needed to enhance the uniformity of the alloy's microstructure, and aging treatment is employed to precipitate... Strengthening phases are used to fully utilize the solid solution strengthening and precipitation strengthening effects of the alloy. However, with the continuous increase in turbine inlet temperature, higher requirements are placed on the heat resistance and comprehensive mechanical properties of cast high-temperature alloys. In order to pursue high-temperature strength and creep resistance, the alloy system usually needs to add a large amount of refractory solid solution strengthening elements such as W, Mo, and Ta, as well as a high content of precipitation strengthening elements such as Al and Ti, in order to obtain higher volume fractions and better thermal stability. Enhanced phase.

[0003] These highly alloyed nickel-based cast equiaxed superalloys in Under intermediate-temperature service or testing conditions, alloys are highly susceptible to premature fracture, leading to a sharp decrease in elongation and tensile strength, resulting in intermediate-temperature brittleness, which seriously threatens the safe operation of gas turbine blades. The occurrence of intermediate-temperature brittleness is mainly related to the deformation mechanism of the alloy within this temperature range and the poor strength matching between grains and grain boundaries. Under traditional conventional heat treatment, such as direct air cooling after high-temperature solution treatment, a large number of fine... The precipitation of phases within the grains leads to a sharp increase in intragranular strength; however, grain boundaries are often relatively straight and lack effective strengthening and toughening mechanisms. Under stress, deformation is difficult to occur uniformly within the grains, dislocation movement is hindered and accumulates at grain boundaries, causing stress to easily concentrate on the relatively weak, straight grain boundaries. This severe imbalance in microscopic strength easily promotes the initiation of microcracks at grain boundaries and their rapid propagation along the grain boundaries, ultimately manifesting as typical intergranular brittle fracture.

[0004] To address this issue, heat treatment processes can be used to create curved grain boundaries, altering the crack propagation path, increasing crack propagation resistance, and improving grain boundary strength. However, conventional temperature-controlled cooling processes struggle to simultaneously address grain boundary issues. Chain precipitation of phases and intracrystalline Phase size control often leads to insufficient grain boundary curvature or sacrifices excessive intragranular strength in pursuit of plasticity, resulting in decreased tensile strength. Therefore, designing a novel heat treatment process that balances engineering feasibility with synergistic optimization of microstructure, effectively promoting microstructure development while avoiding the risk of rapid cooling cracking in large, complex cast high-temperature alloy blades, is crucial. The phase precipitates in a chain-like manner at the grain boundaries and pins to form curved grain boundaries with a certain wavelength and amplitude, while the intragranular structure is reasonably controlled. Determining the optimal balance between intragranular and grain boundary strength to mitigate mid-temperature brittleness in the size and volume fraction of phases has become a pressing technical challenge in the field of nickel-based cast high-temperature alloys. Summary of the Invention

[0005] The purpose of this invention is to provide a heat treatment process to alleviate the mid-temperature brittleness of nickel-based cast equiaxed high-temperature alloys.

[0006] In order to achieve the above-mentioned objectives, the technical solution adopted by the present invention is as follows: a heat treatment process to alleviate the mid-temperature brittleness of nickel-based cast equiaxed superalloys, wherein the nickel-based cast equiaxed superalloys after melting and solidification are subjected to high-temperature solution treatment, slow cooling treatment and remelting treatment in sequence.

[0007] The chemical composition of the nickel-based cast equiaxed superalloy, by mass percentage, is as follows: , , The balance is Ni; the mass fraction ratio of Ti to Al is... The sum of the mass fractions of Ti and Al is The sum of the mass fractions of Ta, Mo, and W is The sum of the mass fractions of C, B and Zr elements .

[0008] After heat treatment, the alloy is in Tensile yield strength not less than Tensile strength not less than The elongation rate is not less than ;exist Tensile yield strength not less than Tensile strength not less than The elongation rate is not less than .

[0009] A further improvement of this invention is that the temperature of the high-temperature solution treatment is... Above the phase complete dissolution temperature The time is Hour.

[0010] A further improvement of the present invention is that the slow cooling treatment is performed by cooling the alloy that has undergone high-temperature solution treatment with... The cooling rate increases as the furnace cools slowly to The temperature range was then cooled to room temperature with water.

[0011] A further improvement of the present invention is that the melting-back treatment involves heating the alloy that has undergone slow cooling treatment to... Below the phase complete dissolution temperature The time is Hours, then air-cooled to room temperature.

[0012] A further improvement of this invention is that, after high-temperature solution treatment, the alloy grains are equiaxed, with an average grain size of [missing information]. .

[0013] A further improvement of this invention lies in that, after the alloy undergoes solution treatment followed by slow cooling and remelting, the chain-like... The phase is distributed at the grain boundaries, and the pinning formation has an average wavelength of not less than The average amplitude is not less than The curved grain boundaries; the interior of the grains The phase is spherical with an average size of less than 250 nm.

[0014] The technical advantage of this invention is that it proposes a... A synergistic heat treatment process is employed, achieving a balance between intragranular strengthening and grain boundary strengthening through the following specific stages of microstructural evolution:

[0015] During high-temperature solution treatment, the cast alloy is heated to... Above the temperature at which the phase completely dissolves, coarse particles form due to solidification. Phase, eutectic structure and elemental segregation dissolution The matrix improves the casting microstructure, resulting in a uniformly composed supersaturated solid solution that provides a homogeneous parent phase for subsequent precipitation control. Simultaneously, by controlling temperature and time, recovery, recrystallization, and appropriate grain growth are promoted, resulting in grains with an average size of [missing information]. The equiaxed crystal structure avoids the problem of insufficient strength due to excessively coarse grains or increased intergranular fracture tendency due to excessively fine grains.

[0016] During furnace slow cooling, the alloy is cooled slowly at a low cooling rate. Phases preferentially nucleate and grow heterogeneously at grain boundaries with higher energies. This is due to the slower cooling rate and moderate driving force at grain boundaries. The phase precipitates as dispersed chain-like particles, exerting a strong pinning effect on grain boundaries, locally hindering grain boundary migration, and causing the grain boundaries to further evolve into curved morphologies with larger amplitudes and wavelengths. Simultaneously, intragranular precipitation... The phases continue to grow, but due to diffusion control, some are larger in size, unevenly distributed, and have varied morphologies. This step establishes a chain-like grain boundary. Phase and bent grain boundaries are not completely eliminated in subsequent treatments, which can improve the grain boundary's resistance to crack propagation.

[0017] During the remelting process, the alloy is reheated to slightly below [temperature value missing]. The temperature is maintained within the range of the phase's complete dissolution temperature. At this point, the internal crystal size is too small and thermodynamically unstable. The phase preferentially dissolves back into the matrix, while those of moderate size... The phase partially dissolves and is retained; chain-like structures at grain boundaries Partial dissolution of the phase occurs, preserving the curved grain boundary morphology. By controlling the re-dissolution temperature and time, the intragranular phase is ultimately... The phase size is stably controlled below 250 nm. This intracrystalline structure provides sufficient precipitation strengthening to ensure strength without being affected by... Excessively dense and fine phases lead to a sharp increase in intragranular strength, causing stress concentration and premature cracking; at the same time, it can also alleviate the effects of slow cooling. The phenomenon of excessively coarse and uneven phases is further improved to enhance tissue uniformity.

[0018] The beneficial effects of the present invention are that, through the above... Synergistic effect, regulating grain size and intragranularity Phase size and volume fraction as well as grain boundaries The chain-like precipitation of the phase and the bending morphology of the grain boundaries enable the alloy to provide high yield and tensile strength within the grains during mid-temperature mechanical property testing, while the bending grain boundaries significantly increase the resistance to intergranular crack propagation. This improves elongation while achieving high strength, thus alleviating the mid-temperature brittleness problem of nickel-based cast equiaxed superalloys. Attached Figure Description

[0019] Figure 1 The grain boundaries of the alloy in the heat-treated state of Example 1 and the alloy in the heat-treated state of Comparative Example 1 in this invention. In comparison.

[0020] Figure 2 This is a comparison of the grain boundary morphology of the alloy in Example 1 and the alloy in Comparative Example 1 under heat treatment.

[0021] Figure 3 The intragranular structures of the alloy in the heat-treated state of Example 1 and the alloy in the heat-treated state of Comparative Example 1 are shown. In comparison. Detailed Implementation

[0022] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0023] A heat treatment process for mitigating the intermediate-temperature brittleness of nickel-based cast equiaxed superalloys includes the following steps:

[0024] Among them, the chemical composition of nickel-based cast equiaxed superalloys, by mass percentage, is... , , , , , , , , , , , The balance is Ni; the mass fraction ratio of Ti to Al is... The sum of the mass fractions of Ti and Al is The sum of the mass fractions of Ta, Mo, and W is The sum of the mass fractions of C, B and Zr elements .

[0025] Step 1: High-temperature solution treatment: The molten and solidified nickel-based cast equiaxed superalloy is heated to... Above the phase complete dissolution temperature The time is Hour;

[0026] Step 2: Slow cooling treatment: The alloy that has undergone high-temperature solution treatment is then cooled... The cooling rate increases as the furnace cools slowly to The temperature range was then water-cooled to room temperature.

[0027] Step 3: Remelting treatment: Heat the alloy that has undergone slow cooling treatment to... Below the phase complete dissolution temperature The time is Hours, then air-cooled to room temperature.

[0028] The following are specific embodiments and comparative examples:

[0029] Example 1

[0030] A nickel-based cast equiaxed superalloy within the composition range specified in the invention has the following chemical composition by mass percentage: , , , , , , , , , , , The balance is Ni. The mass fraction ratio of Ti to Al is 1.11, and the sum of the mass fractions of Ti and Al is... The sum of the mass fractions of Ta, Mo, and W is The sum of the mass fractions of C, B, and Zr is 0.065%. Alloy The temperature at which the phase completely dissolves is Solidus temperature is The solidified nickel-based cast equiaxed superalloy was subjected to high-temperature solution treatment at a temperature of [temperature value missing]. The heat treatment time is 3 hours; then a slow cooling process is performed to remove the alloy that has undergone high-temperature solution treatment. The cooling rate increases as the furnace cools slowly to The alloy was then water-cooled to room temperature; finally, a remelting process was performed, heating the slowly cooled alloy to... The heat treatment was carried out for 15 hours, followed by air cooling to room temperature. The microstructure characteristics after heat treatment are shown in Table 1, and the tensile properties are shown in Table 2. Figure 1 Demonstrating grain boundaries after heat treatment in Example 1 Mutually, Figure 2 The grain boundary morphology after heat treatment in Example 1 is shown. Figure 3 Demonstration of intragranular structures after heat treatment in Example 1 Mutually.

[0031] Example 2

[0032] A nickel-based superalloy with a composition within the range specified in the invention is selected, and the composition of this alloy is consistent with that of Example 1. The solidified nickel-based cast equiaxed superalloy is subjected to a high-temperature solution treatment at a temperature of [temperature missing]. The holding time is 4 hours; then a slow cooling treatment is performed to remove the alloy that has undergone high-temperature solution treatment. The cooling rate increases as the furnace cools slowly to The alloy was then water-cooled to room temperature; finally, a remelting process was performed, heating the slowly cooled alloy to... The heat treatment was carried out for 12 hours, followed by air cooling to room temperature. The microstructure characteristics after heat treatment are shown in Table 1, and the tensile properties are shown in Table 2.

[0033] Example 3

[0034] A nickel-based superalloy with a composition within the range specified in the invention is selected, and the composition of this alloy is consistent with that of Example 1. The solidified nickel-based cast equiaxed superalloy is subjected to a high-temperature solution treatment at a temperature of [temperature missing]. The heat treatment time is 5 hours; then a slow cooling process is performed to remove the alloy that has undergone high-temperature solution treatment. The cooling rate increases as the furnace cools slowly to The alloy was then water-cooled to room temperature; finally, a remelting process was performed, heating the slowly cooled alloy to... The heat treatment was carried out for 9 hours, followed by air cooling to room temperature. The microstructure characteristics after heat treatment are shown in Table 1, and the tensile properties are shown in Table 2.

[0035] Comparative Example 1

[0036] A nickel-based superalloy with a composition within the range specified in the invention is selected, and the composition of this alloy is consistent with that of Example 1. The solidified nickel-based cast equiaxed superalloy is subjected to a high-temperature solution treatment at a temperature of [temperature missing]. The holding time is 3 hours, followed by air cooling to room temperature; then the alloy that has undergone high-temperature solution treatment is heated to... The heat treatment was carried out for 15 hours, followed by air cooling to room temperature. The microstructure characteristics after heat treatment are shown in Table 1, and the tensile properties are shown in Table 2. Figure 1 Demonstrating grain boundaries after heat treatment in Comparative Example 1 Mutually, Figure 2 This shows the grain boundary morphology of Comparative Example 1 after heat treatment. Figure 3 Demonstration of Comparative Example 1 after heat treatment of intragranular structures Mutually.

[0037] Comparative Example 2

[0038] A nickel-based superalloy with a composition within the range specified in the invention is selected, and the composition of this alloy is consistent with that of Example 1. The solidified nickel-based cast equiaxed superalloy is subjected to a high-temperature solution treatment at a temperature of [temperature missing]. The holding time is 3 hours, followed by air cooling to room temperature; then the alloy that has undergone high-temperature solution treatment is heated to... The holding time is 15 hours, followed by air cooling to room temperature; then the alloy is heated to... The heat treatment time was 16 hours. The microstructure characteristics after heat treatment are shown in Table 1, and the tensile properties are shown in Table 2.

[0039] Comparative Example 3

[0040] A nickel-based superalloy with a composition within the range specified in the invention is selected, and the composition of this alloy is consistent with that of Example 1. The solidified nickel-based cast equiaxed superalloy is subjected to a high-temperature solution treatment at a temperature of [temperature missing]. The heat treatment time is 3 hours; then a slow cooling process is performed to remove the alloy that has undergone high-temperature solution treatment. The cooling rate increases as the furnace cools slowly to The alloy was then water-cooled to room temperature; finally, a remelting process was performed, heating the slowly cooled alloy to... The heat treatment was carried out for 15 hours, followed by air cooling to room temperature. The microstructure characteristics after heat treatment are shown in Table 1, and the tensile properties are shown in Table 2.

[0041] Table 1 shows the microstructure characteristics of the examples and comparative examples after heat treatment, and Table 2 shows the tensile properties of the examples and comparative examples after heat treatment. Figure 1 , Figure 2 , Figure 3 The statistical results in Tables 1 and 2 show that, compared with traditional heat treatment systems and cooling rates, Compared to other processes, the heat treatment process of this invention reduces the chain-like structures in the alloy. Phases are distributed at grain boundaries, pinning to form curved grain boundaries; within the grains... The phase size and morphology distribution are uniform. After employing the heat treatment process of this invention, the alloy exhibits... Tensile yield strength not less than Tensile strength not less than The elongation rate is not less than ;exist Tensile yield strength not less than Tensile strength not less than The elongation rate is not less than The tensile properties at medium temperature are improved.

[0042] The above specific embodiments are used to explain and illustrate the present invention, but not to limit the present invention. Any modifications and changes made to the present invention within the spirit and scope of the claims shall fall within the protection scope of the present invention.

[0043] Table 1. Microstructural characteristics of the embodiments and comparative examples

[0044]

[0045] Table 2 Tensile properties of the examples and comparative examples

[0046]

Claims

1. A heat treatment process for mitigating the intermediate-temperature brittleness of nickel-based cast equiaxed superalloys, characterized in that, The nickel-based cast equiaxed superalloy after melting and solidification is subjected to high-temperature solution treatment, slow cooling treatment and re-dissolution treatment in sequence. The chemical composition of the nickel-based cast equiaxed superalloy, by mass percentage, is as follows: , , The balance is Ni; the mass fraction ratio of Ti to Al is... The sum of the mass fractions of Ti and Al is The sum of the mass fractions of Ta, Mo, and W is The sum of the mass fractions of C, B and Zr elements .

2. The heat treatment process for mitigating the intermediate-temperature brittleness of nickel-based cast equiaxed superalloys according to claim 1, characterized in that: The temperature of the high-temperature solution treatment is: Above the phase complete dissolution temperature The time is Hour.

3. The heat treatment process for mitigating the intermediate-temperature brittleness of nickel-based cast equiaxed superalloys according to claim 1, characterized in that: The slow cooling process involves cooling the alloy that has undergone high-temperature solution treatment with... The cooling rate increases as the furnace cools slowly to The temperature range was then cooled to room temperature with water.

4. The heat treatment process for mitigating the intermediate-temperature brittleness of nickel-based cast equiaxed superalloys according to claim 1, characterized in that: The melting-back process involves heating the alloy, which has undergone slow cooling, to... Below the phase complete dissolution temperature The time is Hours, then air-cooled to room temperature.

5. The heat treatment process for mitigating the intermediate-temperature brittleness of nickel-based cast equiaxed superalloys according to claim 1, characterized in that: After high-temperature solution treatment, the alloy has equiaxed grains with an average grain size of [missing information]. .

6. The heat treatment process for mitigating the intermediate-temperature brittleness of nickel-based cast equiaxed superalloys according to claim 1, characterized in that: After solution treatment and slow cooling followed by dissolution remelting, the alloy exhibits chain-like structures. The phase is distributed at the grain boundaries, and the pinning formation has an average wavelength of not less than The average amplitude is not less than The curved grain boundaries; the interior of the grains The phase is spherical, with an average size smaller than 100 mm. .

7. The heat treatment process for mitigating the intermediate-temperature brittleness of nickel-based cast equiaxed superalloys according to claim 1, characterized in that: After heat treatment, the alloy is in Tensile yield strength not less than Tensile strength not less than The elongation rate is not less than ;exist Tensile yield strength not less than Tensile strength not less than The elongation rate is not less than .

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