Heat treatment method of nickel-based superalloy for additive manufacturing

Abstract

The invention relates to the technical field of additive manufacturing, and particularly provides a heat treatment method of a nickel-based superalloy for additive manufacturing. The heat treatment method comprises the following steps: S1, preparing a nickel-based high-temperature alloy forming part by adopting a selective laser melting process; s2, the formed part is subjected to homogenizing annealing treatment at the temperature ranging from 1000 DEG C to 1200 DEG C; s3, the formed part subjected to homogenizing annealing treatment is subjected to water quenching treatment and cooled to the room temperature; and S4, the formed part subjected to water quenching treatment is subjected to primary aging treatment at the temperature of 700-800 DEG C, then cooled to 600-700 DEG C, subjected to secondary aging treatment and then air-cooled to the room temperature. According to the method, the effect of simultaneously regulating and controlling the grain structure and the precipitated phase of the SLM-GH4169 alloy is achieved by increasing the homogenizing annealing heat treatment time, combining a water quenching cooling mode and cooperating with two-stage aging, and the strength and plasticity of the alloy are successfully and synergistically improved. According to the prepared SLM-GH4169 alloy, not only can the tensile strength reach 1400 MPa, but also the elongation at break can reach 22% or above.

Description

Technical Field

[0001] The present invention relates to the technical field of additive manufacturing, and in particular to a heat treatment method for a nickel-based high-temperature alloy used in additive manufacturing. Background Art

[0002] GH4169 alloy is a precipitation-strengthened nickel-based high-temperature alloy. As a core material in the field of aero-engines, it has a long-term service temperature of up to 650°C and has good corrosion resistance, weldability, oxidation resistance, and high-temperature mechanical properties. It is widely used in key load-bearing components such as turbine disks, blades, casings, and shafts. With the increasing demand for lightweight and complex structures in aviation equipment, additive manufacturing technologies represented by selective laser melting have become an important supplement to traditional casting and forging processes due to their near-net-shape forming capabilities. Selective laser melting (SLM) uses a high-energy laser beam to melt metal powder layer by layer. Therefore, the microstructure of the GH4169 alloy produced by it exhibits multi-level and multi-scale characteristics, which is essentially different from the homogeneity of traditional casting and forging structures. This makes it difficult for traditional heat treatment systems designed based on homogenized structures to fully realize the potential of the alloy's mechanical properties.

[0003] Currently, the commonly used heat treatment schedules for GH4169 alloys are ASTM 5662 to ASTM 5664. During homogenization heat treatment, these schedules primarily utilize air cooling, which results in slow cooling rates. This prevents the Laves phase (a Nb-rich brittle phase) from dissolving completely at grain boundaries, leading to segregation and formation of continuous banded structures, which severely hinders grain boundary sliding. Furthermore, the short holding time prevents the complete elimination of SLM residual stresses and compositional segregation, resulting in a low degree of recrystallization and significant anisotropy. This leads to an imbalance in the alloy's strength-ductility balance, particularly in tensile plasticity perpendicular to the printing direction, which is lower than that of forged parts. This severely limits the application of additively manufactured high-temperature alloys in load-bearing aerospace engine components. Some studies have attempted to improve the plasticity of SLM-GH4169 alloys by modifying the precipitated phases, while others have attempted to achieve a uniform grain structure by optimizing heat treatment parameters. However, these approaches have failed to synergistically adjust the grain structure and precipitated phases, and thus remain unable to meet the high-performance requirements of GH4169 alloys for aerospace applications. Therefore, it is of great significance to study a heat treatment method that can simultaneously improve the strength and plasticity of additively manufactured nickel-based high-temperature alloys. Summary of the Invention

[0004] To address the above issues, the present invention provides a heat treatment method for nickel-based high-temperature alloys for additive manufacturing. By increasing the homogenization annealing treatment time, combining water quenching cooling with double-stage aging, the grain structure and precipitation phase of the SLM-GH4169 alloy can be simultaneously regulated, achieving a synergistic improvement in strength and plasticity.

[0005] To solve the above technical problems, in a first aspect, the present invention provides a heat treatment method for a nickel-based high-temperature alloy for additive manufacturing, comprising the following steps: S1. Fabrication of nickel-based high-temperature alloy parts using selective laser melting; S2. The formed part is homogenized and annealed at 1000°C to 1200°C for 1 to 5 hours; S3. The formed part after homogenization annealing is water quenched and cooled to room temperature; S4. The formed part after water quenching is subjected to primary aging treatment at 700°C to 800°C, then cooled to 600°C to 700°C for secondary aging treatment, and then air-cooled to room temperature.

[0006] In response to the multi-level microstructural characteristics of the nickel-based high-temperature alloy (SLM-GH4169) prepared by selective laser melting, the present invention extends the homogenization heat treatment time and uses water quenching to increase the cooling rate, fully eliminating residual stress and composition segregation, promoting complete recrystallization, increasing the proportion of equiaxed grains, and effectively eliminating the banded Laves phase at the grain boundaries. Combined with bipolar aging treatment, the grain structure and precipitation phase of the SLM-GH4169 alloy are precisely controlled to stimulate high-density nanoscale γ'' strengthening phases, thereby improving the plasticity of the alloy while ensuring alloy strength. This successfully achieves a synergistic improvement in the alloy's strength and plasticity, allowing the SLM-GH4169 alloy to achieve a tensile strength of 1400 MPa and an elongation at break of over 22%.

[0007] Preferably, in step S2, the homogenization annealing treatment time is 2.5 to 4 hours.

[0008] Preferably, in step S3, the cooling rate of the water quenching treatment is 100-120°C / s.

[0009] Preferably, in step S4, the holding time of the primary aging treatment is 8 to 10 hours.

[0010] Preferably, in step S4, the holding time of the secondary aging treatment is 8 to 10 hours.

[0011] Preferably, in step S4, the cooling rate is 50-60°C / h.

[0012] Preferably, the nickel-based high-temperature alloy is GH4169 alloy.

[0013] Preferably, the chemical composition of the nickel-based high-temperature alloy formed part is: Ni: 50.0wt%~55.0wt%, Cr: 17.0wt%~21.0wt%, Mo: 2.80wt%~3.30wt%, Nb: 4.75wt%~5.5wt%, Mn≤0.35wt%, Si≤0.35wt%, Ti: 0.65wt%~1.15wt%, Al: 0.20wt%~0.80wt%, and the balance is Fe.

[0014] In a second aspect, the present invention provides a nickel-based high-temperature alloy for additive manufacturing, which is prepared by the above-mentioned heat treatment method of the nickel-based high-temperature alloy for additive manufacturing.

[0015] In a third aspect, the present invention provides applications of the above-mentioned nickel-based high-temperature alloy for additive manufacturing in the field of aerospace.

[0016] Compared with the prior art, the present invention has the following beneficial effects: Based on the multi-level microstructural characteristics of SLM-GH4169, this paper proposes a new heat treatment method. By increasing the homogenization heat treatment duration, combining water quenching with dual-stage aging, and simultaneously regulating the grain structure and precipitation phase of the SLM-GH4169 alloy, the alloy's strength and plasticity are successfully improved. The resulting SLM-GH4169 alloy not only achieves a tensile strength of 1400 MPa but also an elongation at break exceeding 22%. This provides theoretical guidance for designing personalized heat treatment regimes based on the microstructural characteristics of alloys formed by selective laser melting to achieve a synergistic improvement in alloy strength and plasticity. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The grain structure and main precipitation phase diagram of the GH4169 nickel-based high-temperature alloy for additive manufacturing after heat treatment in Example 1 of the present invention; (a) is the grain structure diagram, and (b) is the γ′′ phase distribution diagram. DETAILED DESCRIPTION

[0018] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the specific implementation methods will be briefly introduced below. Obviously, the embodiments described below are some implementation methods of the present invention. For ordinary technicians in this field, other implementation methods can be obtained based on these embodiments without paying creative work.

[0019] If specific experimental steps or conditions are not specified in the examples, the procedures or conditions of conventional experimental steps described in the literature in the field can be followed. All raw materials and instruments used are commercially available, including but not limited to those used in the examples of this application.

[0020] Example 1 This embodiment provides a heat treatment method for GH4169 nickel-based high-temperature alloy for additive manufacturing, comprising the following steps: (1) GH4169 nickel-based high-temperature alloy powder is pre-placed in the cylinder in the forming chamber for forming. The forming substrate is placed in a sealed forming chamber with inert gas protection. High-purity argon gas with a purity of not less than 99.99% is filled into the forming chamber. The substrate is preheated to 80°C and the laser beam is started for forming. The laser beam melts the laid nickel-based high-temperature alloy powder layer by layer according to the pre-set trajectory. During forming, the energy of the beam is regulated by adjusting the forming process parameters to obtain a forming material with better internal quality and microstructure properties. After one layer is melted, the forming platform is lowered and the powder is re-laid for the next layer of forming until the part is formed and a GH4169 nickel-based high-temperature alloy formed part is obtained. The forming process parameters are: laser power 285W, scanning speed 960mm / s, melt channel spacing 110μm, powder laying thickness 40μm, and rotation angle 67°.

[0021] (2) After the prepared GH4169 nickel-based high-temperature alloy formed part is cooled to below 50°C, the forming chamber is opened and taken out. The formed part is placed in a heat treatment furnace and heated to 1065°C for homogenization annealing for 4 hours.

[0022] (3) The homogenized molded parts are rapidly cooled to room temperature by water quenching at a cooling rate of 100~120℃ / s.

[0023] (4) The molded part after water quenching was placed in a heat treatment furnace, heated to 760℃ and kept at this temperature for 10h, and then subjected to primary aging treatment. Then, it was cooled to 650℃ at a cooling rate of 55℃ / h and kept at this temperature for 8h, and then subjected to secondary aging treatment. It was then air-cooled to room temperature. Scanning electron microscopy and electron backscatter diffraction analysis (EBSD) were used to characterize the laser selectively melted GH4169 nickel-based superalloy after heat treatment. The results are shown in Figure 2. Figure 1 shown.

[0024] Example 2 This embodiment provides a heat treatment method for GH4169 nickel-based high-temperature alloy for additive manufacturing, comprising the following steps: (1) GH4169 nickel-based high-temperature alloy powder is pre-placed in the cylinder in the forming chamber for forming. The forming substrate is placed in a sealed forming chamber with inert gas protection. High-purity argon gas with a purity of not less than 99.99% is filled into the forming chamber. The substrate is preheated to 80°C and the laser beam is started for forming. The laser beam melts the laid nickel-based high-temperature alloy powder layer by layer according to the pre-set trajectory. During forming, the energy of the beam is regulated by adjusting the forming process parameters to obtain a forming material with better internal quality and microstructure properties. After one layer is melted, the forming platform is lowered and the powder is re-laid for the next layer of forming until the part is formed and a GH4169 nickel-based high-temperature alloy formed part is obtained. The forming process parameters are: laser power 285W, scanning speed 960mm / s, melt channel spacing 110μm, powder laying thickness 40μm, and rotation angle 67°.

[0025] (2) After the prepared GH4169 nickel-based high-temperature alloy formed part is cooled to below 50°C, the forming chamber is opened and taken out. The formed part is placed in a heat treatment furnace and heated to 1065°C for homogenization annealing for 2.5 hours.

[0026] (3) The homogenized molded parts are rapidly cooled to room temperature by water quenching, with a cooling rate of >100℃ / s.

[0027] (4) The molded parts after water quenching are placed in a heat treatment furnace, heated to 760℃ and kept at this temperature for 10h for primary aging treatment, then cooled to 650℃ at a cooling rate of 55℃ / h and kept at this temperature for 8h for secondary aging treatment, and then air-cooled to room temperature.

[0028] Example 3 The difference between this embodiment and embodiment 1 is that the homogenization annealing time in step (2) is 1 hour. Other steps are the same as those in embodiment 1.

[0029] Comparative Example 1 The difference between this comparative example and Example 1 is that air cooling is used instead of water quenching in step (3). Other steps are the same as in Example 1.

[0030] Comparative Example 2 In this comparative example, the conventional heat treatment process standard ASTM 5663 of nickel-based high-temperature alloy GH4169 was used to heat treat the GH4169 nickel-based high-temperature alloy formed parts.

[0031] Performance Testing The performance tests were performed on the GH4169 nickel-based superalloy for additive manufacturing after heat treatment in Examples 1-3 and Comparative Examples 1-2. The test standards for tensile strength and elongation were based on GB / T 228.1-2021. The results are shown in Table 1 below.

[0032] Table 1 As can be seen from the data in Table 1, the heat treatment method for nickel-based high-temperature alloys for additive manufacturing provided by the present invention adopts a homogenization heat treatment method with a long holding time and water quenching, combined with a double-stage aging process to control the microstructure of the material. This significantly improves the tensile strength of the alloy without sacrificing elongation, exceeding the performance standard of traditional forgings after heat treatment, and achieves a strength-plasticity synergistic effect.

[0033] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A heat treatment method for nickel-based high-temperature alloys for additive manufacturing, characterized in that: The following steps are included: S1. Fabrication of nickel-based high-temperature alloy parts using selective laser melting; S2. The formed part is homogenized and annealed at 1000°C to 1200°C for 1 to 5 hours; S3. The formed part after homogenization annealing is water quenched and cooled to room temperature; S4. The formed part after water quenching is subjected to primary aging treatment at 700°C to 800°C, then cooled to 600°C to 700°C for secondary aging treatment, and then air-cooled to room temperature.

2. The heat treatment method of nickel-based high-temperature alloy for additive manufacturing according to claim 1, characterized in that: In step S2, the homogenization annealing treatment time is 2.5 to 4 hours.

3. The heat treatment method of nickel-based high-temperature alloy for additive manufacturing according to claim 1, characterized in that: In step S3, the cooling rate of the water quenching treatment is 100-120°C / s.

4. The heat treatment method of nickel-based high-temperature alloy for additive manufacturing according to claim 1, characterized in that: In step S4, the holding time of the primary aging treatment is 8 to 10 hours.

5. The heat treatment method of nickel-based high-temperature alloy for additive manufacturing according to claim 1, characterized in that: In step S4, the holding time of the secondary aging treatment is 8 to 10 hours.

6. The heat treatment method of nickel-based high-temperature alloy for additive manufacturing according to claim 1, characterized in that: In step S4, the cooling rate is 50-60°C / h.

7. The heat treatment method of nickel-based high-temperature alloy for additive manufacturing according to claim 1, characterized in that: The nickel-based high-temperature alloy is GH4169 alloy.

8. The heat treatment method of nickel-based high-temperature alloy for additive manufacturing according to claim 1, characterized in that: The chemical composition of the nickel-based high-temperature alloy formed part is: Ni: 50.0wt%~55.0wt%, Cr: 17.0wt%~21.0wt%, Mo: 2.80wt%~3.30wt%, Nb: 4.75wt%~5.5wt%, Mn≤0.35wt%, Si≤0.35wt%, Ti: 0.65wt%~1.15wt%, Al: 0.20wt%~0.80wt%, and the balance is Fe.

9. A nickel-based high-temperature alloy for additive manufacturing, characterized in that: The nickel-based high-temperature alloy is prepared by the heat treatment method for additive manufacturing according to any one of claims 1 to 8.

10. Application of the nickel-based high-temperature alloy for additive manufacturing according to claim 9 in the field of aerospace.

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