Heat treatment method for additive manufacturing of high-temperature alloy

Abstract

The invention relates to a heat treatment method for additive manufacturing of high-temperature alloy, and relates to the technical field of additive manufacturing of high-temperature alloy. According to the main technical scheme, the heat treatment method for the additive manufacturing high-temperature alloy comprises the following steps that (1) the printing-state additive manufacturing high-temperature alloy is heated to the annealing temperature, heat preservation is conducted for the first set time, stress relief annealing treatment is conducted, and the alloy subjected to stress relief annealing treatment is obtained; and (2) the alloy obtained after stress relief annealing treatment is heated to the temperature of long-term aging treatment from the annealing temperature, long-term aging treatment is carried out, and after cooling, the additive manufacturing high-temperature alloy obtained after heat treatment is obtained. Wherein the temperature of the long-term aging treatment ranges from 950 DEG C to 1050 DEG C, and the time of the long-term aging treatment ranges from 80 h to 200 h. A traditional solid solution and aging heat treatment system is abandoned, a novel heat treatment process is adopted, and the high-temperature tensile strength and ductility of the additive manufacturing high-temperature alloy are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of additive manufacturing of superalloys, and particularly to a heat treatment method for additive manufacturing of superalloys. Background Art

[0002] Superalloys are a class of metallic materials with excellent high-temperature resistance. They are usually composed of a solid solution of matrix metal and superalloy elements, interstitial compounds, and γ'-strengthening phases. These alloys exhibit excellent mechanical properties, heat-resistant corrosion properties, and oxidation resistance under high-temperature environments, and are thus widely used in high-temperature conditions in the fields of aerospace, energy, chemical engineering, etc.

[0003] Due to the disadvantages of long production cycles, low material utilization rates, and low design freedoms of traditional cast superalloys and forged superalloys, the development of additive manufacturing of superalloys has gradually received attention. Additive manufacturing of superalloys can achieve the rapid manufacturing of complex shapes and structures, such as hollow blades, etc. Compared with traditional machining methods, there is almost no waste of materials; there is no need for additional assembly processes, reducing the number of components and the manufacturing cycle.

[0004] However, the additive manufacturing process is a rapid cooling process, which forms large internal stresses inside the alloy, easily causing component deformation and warping, and reducing mechanical properties. In addition, due to the too-fast cooling rate, the γ'-strengthening phase does not have enough time to precipitate and grow. Therefore, compared with traditional cast superalloys, the strength and plasticity of as-printed additive manufacturing superalloys may not be high. Therefore, the reasonable design of the heat treatment process is crucial for the mechanical properties of additive manufacturing superalloys, that is, while removing internal stresses and maintaining grain boundary strength (no grain boundary cracking) through heat treatment, precipitating γ'-strengthening phases with reasonable morphology and quantity to meet the high-temperature service requirements of the alloy.

[0005] In summary, it is very important to regulate the microstructure of additive manufacturing superalloys through a suitable heat treatment system, improve the tensile strength and plasticity of additive manufacturing superalloys at high temperatures, and ensure the safe use of the alloy. Summary of the Invention

[0006] In view of this, the present invention provides a heat treatment method for additive manufacturing of superalloys, and the main purpose is to improve the high-temperature strength and plasticity of additive manufacturing superalloys.

[0007] To achieve the above object, the present invention mainly provides the following technical solutions:

[0008] On the one hand, an embodiment of the present invention provides a heat treatment method for additive manufacturing of superalloys, which includes the following steps:

[0009] Step 1), heat the as-printed additive manufacturing superalloy to the annealing temperature, hold for the first set time, and perform stress relief annealing treatment to obtain the alloy after stress relief annealing treatment;

[0010] Step 2), heat the alloy after the stress relief annealing treatment from the annealing temperature to the temperature for long-term aging treatment, perform long-term aging treatment, and after cooling, obtain the heat-treated additive manufacturing superalloy;

[0011] Among them, the temperature for long-term aging treatment is 950 - 1050 °C, and the time for long-term aging treatment is 80 - 200 h.

[0012] Preferably, by weight percentage, the additive manufacturing superalloy includes the following chemical components: Al 5 - 6 wt%, B 0.01 - 0.02 wt%, C 0.05 - 0.15 wt%, Co 9 - 10 wt%, Cr 8 - 10 wt%, Hf 0 - 1.5 wt%, Mo 0 - 0.6 wt%, Ta 3 - 4 wt%, Ti 0.5 - 1 wt%, W 9 - 11 wt%, Zr 0 - 0.02 wt%, and the balance is Ni.

[0013] Preferably, the as-printed additive manufacturing superalloy is prepared by the SLM process of laser powder bed fusion metal 3D printing technology.

[0014] Preferably, in the step 1): the annealing temperature is 600 - 650 °C; the first set time is 6 - 10 h, preferably 8 - 10 h.

[0015] Preferably, in the step 1): the heating rate of heating the as-printed additive manufacturing superalloy to the annealing temperature is 5 - 10 K / min.

[0016] Preferably, in the step 2): the heating rate of heating the alloy after the stress relief annealing treatment from the annealing temperature to the temperature for long-term aging treatment is 5 - 10 K / min; and / or after the long-term aging treatment, the cooling rate is 5 - 10 K / min. And / or after the long-term aging treatment, take out the alloy after the long-term aging treatment from the heating furnace and perform air cooling to obtain the heat-treated additive manufacturing superalloy.

[0017] Preferably, in the step 2): the temperature for long-term aging treatment is 1000 °C ± 10 °C, and the time for long-term aging treatment is 100 h ± 5 h.

[0018] Preferably, both the step 1) and the step 2) are carried out in a muffle furnace.

[0019] Preferably, the as-printed additive manufacturing superalloy has a columnar crystal structure with a <001> orientation; preferably, the size of the columnar crystals is 50-100 μm; preferably, in the as-printed additive manufacturing superalloy: more than 90% (area fraction) of the carbides are distributed within the grains and are spherical particles; preferably, the size of the carbides within the grains is 50 nm-100 nm.

[0020] On the other hand, an embodiment of the present invention provides a heat-treated additive manufacturing superalloy, wherein the heat-treated additive manufacturing superalloy is obtained by heat-treating the as-printed additive manufacturing superalloy using the heat treatment method of the additive manufacturing superalloy described in any one of the above.

[0021] Preferably, the grain boundaries of the heat-treated additive manufacturing superalloy remain intact, and nano-sized carbides are distributed both at the grain boundaries and within the grains; the γ'-strengthening phase is distributed throughout the alloy, with a size of 500 nm-1 μm and a volume fraction of 57-63%; preferably, the number of nano-sized carbides at the grain boundaries is greater than the number of nano-sized carbides within the grains; preferably, the grain size is 100-200 μm.

[0022] Compared with the prior art, the heat treatment method of an additive manufacturing superalloy of the present invention has at least the following beneficial effects:

[0023] 1. An embodiment of the present invention provides a heat treatment method for an additive manufacturing superalloy. First, stress relief annealing is performed on the as-printed additive manufacturing superalloy to eliminate the internal stress of the alloy and homogenize the alloy structure. On this basis, by combining stress relief annealing with subsequent long-term aging, while retaining the integrity of the grain boundaries (no cracking occurs at the grain boundaries), the precipitation position of the carbides is adjusted to strengthen the grain boundaries, and the precipitation of the γ'-strengthening phase is promoted, thereby significantly improving the high-temperature mechanical properties of the alloy.

[0024] 2. Due to the rapid solidification process, the internal stress level of the additive manufacturing superalloy is high, which easily causes the alloy to crack and seriously affects the mechanical properties of the alloy. By using the stress relief annealing of the embodiment of the present invention, the internal stress of the alloy can be effectively reduced or eliminated. In addition, the higher the stress relief annealing temperature, the better the stress elimination effect; the longer the holding time, the more significant the stress elimination effect. However, if the temperature is too high, it is easy to reach the recrystallization temperature of the alloy, resulting in recrystallization and reducing the alloy properties. Therefore, the annealing temperature of the present invention is set to 600-650 °C; the holding time is set to 6-10 h, preferably 8-10 h.

[0025] 3. During the long-term aging process of the embodiments of the present invention, due to the relatively low aging temperature, the reduction of the grain boundary strength under high-temperature solution treatment is prevented. While ensuring that the original grain boundary strength is not weakened, segregation can also be eliminated to achieve the homogenization of the alloy. Long-term aging can not only precipitate γ′ strengthening phases to strengthen the alloy, but also promote the precipitation of nano-scale carbides at grain boundaries, modify the grain boundaries, and enhance the strength and stability of grain boundaries at high temperatures.

[0026] 4. For the alloy using the heat treatment method of the embodiments of the present invention, the tensile strength at a high temperature of 1100 °C reaches 280 MPa, the yield strength is 173 MPa, the elongation is 18.0%, and the reduction of area is 14.0%, showing excellent high-temperature strength and plasticity.

[0027] 5. The heat treatment method of the embodiments of the present invention is simple to operate and has low equipment requirements, and has great popularization value.

[0028] The above description is only an overview of the technical solution of the present invention. In order to be able to understand the technical means of the present invention more clearly and implement it according to the content of the specification, the following takes the preferred embodiments of the present invention and describes them in detail in conjunction with the accompanying drawings as follows. Description of the Drawings

[0029] Figure 1 It is the metallographic structure of the additive manufacturing superalloy after heat treatment in Example 1 and Comparative Example 1; among them, (a) is the metallographic structure of the additive manufacturing superalloy after heat treatment in Example 1; (b) is the metallographic structure of the additive manufacturing superalloy after heat treatment in Comparative Example 1.

[0030] Figure 2 It is the SEM structure of the as-printed additive manufacturing superalloy and the additive superalloy after heat treatment in Example 1 after corrosion; among them, (a) is the SEM structure of the as-printed additive manufacturing superalloy after corrosion; (b) is the SEM structure of the additive superalloy after heat treatment in Example 1 after corrosion.

[0031] Figure 3 It is the microstructure of the as-printed additive manufacturing superalloy, the additive superalloy after heat treatment in Example 1, and the additive superalloy after heat treatment in Comparative Example 1; among them, (a) is the microstructure of the as-printed additive manufacturing superalloy; (b) is the microstructure of the additive superalloy after heat treatment in Example 1; (c) is the microstructure of the additive superalloy after heat treatment in Comparative Example 1. Detailed Embodiments

[0032] To further elaborate on the technical means and effects adopted by the present invention to achieve the intended invention purpose, the following will, in conjunction with the accompanying drawings and preferred embodiments, elaborate in detail on the specific implementation manners, structures, features, and their effects of the application according to the present invention. In the following description, different "one embodiment" or "embodiments" do not necessarily refer to the same embodiment. In addition, the specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0033] The present invention provides a heat treatment method for additively manufactured superalloys, mainly aiming to adjust carbides and precipitate γ'-strengthening phases while maintaining the grain boundary strength, thereby improving the high-temperature strength and plasticity of additively manufactured superalloys.

[0034] The inventive concept of the present invention is as follows: The present invention adopts a method combining stress relief annealing and long-term aging to replace the heat treatment method of solution + aging in the traditional heat treatment of superalloys. The present invention improves the mechanical properties of the alloy while maintaining the grain boundary strength and suppressing pores.

[0035] On the one hand, an embodiment of the present invention provides a heat treatment method for additively manufactured superalloys, which includes the following steps:

[0036] Step 1), heating the as-printed additively manufactured superalloy to the annealing temperature, holding for the first set time, and performing stress relief annealing treatment to obtain the alloy after stress relief annealing treatment.

[0037] In this step, the annealing temperature is 600 - 650 °C; the first set time is 8 - 10 h. The heating rate for heating the as-printed additively manufactured superalloy to the annealing temperature is 5 - 10 K / min, preferably 5 K / min. Here, if the heating rate is too fast, recrystallization will occur.

[0038] Specifically, place the as-printed additively manufactured superalloy in a ceramic tray and place it in a muffle furnace. Heat and raise the temperature of the muffle furnace, controlling the heating rate at 5 - 10 K / min, preferably 5 K / min, and raise the temperature to 600 - 650 °C, preferably 600 °C.

[0039] Regarding this step, it should be noted that stress relief annealing of the as-printed additively manufactured superalloy at a lower temperature can effectively reduce the internal stress level of the additively manufactured superalloy while avoiding recrystallization. The longer the holding time, the lower the internal stress level. The above heating rate and cooling rate can prevent cracking of the alloy caused by the rapid release of stress.

[0040] Preferably, in terms of weight percentage, the additive manufacturing superalloy comprises the following components: Al 5-6 wt%, B 0.01-0.02 wt%, C 0.05-0.15 wt%, Co 9-10 wt%, Cr 8-10 wt%, Hf 0-1.5 wt%, Mo 0-0.6 wt%, Ta 3-4 wt%, Ti 0.5-1 wt%, W 9-11 wt%, Zr 0-0.02 wt%, and the balance is Ni.

[0041] Preferably, the as-printed additive manufacturing superalloy is prepared by the SLM process of laser powder bed fusion metal 3D printing technology.

[0042] Step 2), heating the alloy after stress relief annealing from the annealing temperature to the temperature for long-term aging treatment, performing long-term aging treatment, and after cooling, obtaining the heat-treated additive manufacturing superalloy; wherein, the temperature for long-term aging treatment is 950-1050 °C, and the time for long-term aging treatment is 80-200 h.

[0043] Specifically, in this step, after stress relief annealing, the alloy does not need to be taken out, and the muffle furnace is continuously heated at a heating rate of 5-10 K / min until the temperature reaches the temperature for long-term aging treatment. After the temperature is stabilized, it enters the heat preservation stage. After the heat preservation is completed, the alloy is taken out of the muffle furnace and air-cooled.

[0044] Preferably, the temperature for long-term aging treatment is 1000 °C ± 10 °C, and the time for long-term aging treatment is 100 h ± 5 h.

[0045] Here, the present invention adopts long-term aging treatment (instead of solution treatment plus aging) to effectively reduce the following problems existing in the high-temperature solution process: the increase of solution holes due to the Kirkendall effect; at the same time, it avoids the reduction of the grain boundary strength under high-temperature solution, that is, at too high a temperature, some grain boundary strengthening elements diffuse into the grains, causing the alloy to fracture along the grain boundaries.

[0046] In summary, the present invention provides a new idea for exploring the heat treatment system of additive manufacturing superalloys by combining stress relief annealing and long-term aging heat treatment processes to replace the traditional solution treatment plus aging heat treatment system. By performing stress relief annealing on the as-printed additive manufacturing superalloy, the internal stress of the alloy is eliminated, and the alloy structure is homogenized. By combining stress relief annealing with subsequent long-term aging, on the basis of retaining the integrity of the grain boundaries (no grain boundary cracking), the precipitation position of carbides is adjusted to strengthen the grain boundaries; the precipitation of γ'-strengthening phases is promoted, significantly improving the high-temperature mechanical properties of the alloy.

[0047] In addition, it should be noted that for the printed state additive manufacturing superalloy of the present invention, carbides are mainly distributed in the grains, and there are few carbides precipitated at the grain boundaries. The size of the intragranular carbides is about 50 nm - 100 nm, and they are uniformly distributed in the grains in the form of spherical particles. After the heat treatment of the alloy according to the present invention: the number of intragranular carbides is slightly reduced compared with the printed state alloy, a large number of nano-sized carbides are precipitated at the grain boundaries, and the grain size increases after heat treatment, increasing to 100 - 200 μm.

[0048] The present invention will be further described below through specific examples as follows:

[0049] Example 1

[0050] This example provides a heat treatment method for an additive manufacturing superalloy. The chemical composition of the additive manufacturing superalloy is shown in Table 1, and it includes the following steps:

[0051] Step 1) Stress relief annealing treatment: Place the printed state additive manufacturing superalloy (prepared by the laser powder bed fusion metal 3D printing technology SLM process) in a ceramic tray and place it in the working cavity of a muffle furnace. Heat up the muffle furnace, and control the heating rate at 5 K / min to make the printed state additive manufacturing superalloy heat up to 600 °C with the furnace. Calibrate the temperature in the furnace using a standard thermocouple to ensure that the temperature difference is within ±2 °C. After holding for 6 h, the alloy after stress relief annealing treatment is obtained.

[0052] Step 2) Long-term aging treatment: After stress relief annealing, there is no need to take out the alloy after stress relief annealing treatment. Continue to heat up the muffle furnace at a heating rate of 5 K / min until it reaches 1000 °C. After the temperature stabilizes, enter the holding stage. Calibrate the temperature in the furnace using a standard thermocouple to ensure that the temperature difference is within ±2 °C. The holding time is 100 h. After the holding is completed, take it out of the muffle furnace and air cool it to obtain the heat-treated additive manufacturing superalloy.

[0053] Example 2

[0054] This example provides a heat treatment method for an additive manufacturing superalloy. The chemical composition of the additive manufacturing superalloy is shown in Table 1, and it includes the following steps:

[0055] Step 1) Stress relief annealing treatment: Place the printed state additive manufacturing superalloy (prepared by the laser powder bed fusion metal 3D printing technology SLM process) in a ceramic tray and place it in the working cavity of a muffle furnace. Heat up the muffle furnace, and control the heating rate at 5 K / min to make the printed state additive manufacturing superalloy heat up to 600 °C with the furnace. Calibrate the temperature in the furnace using a standard thermocouple to ensure that the temperature difference is within ±2 °C. After holding for 8 h, the alloy after stress relief annealing treatment is obtained.

[0056] Step 2) Long-term aging treatment: After stress relief annealing, without removing the alloy after stress relief annealing treatment, continue to heat up the muffle furnace at a heating rate of 5 K / min until it reaches 1010 °C. After the temperature stabilizes, enter the heat preservation stage. Calibrate the temperature in the furnace using a standard thermocouple to ensure that the temperature difference is within ±2 °C. The heat preservation time is 100 h. After the heat preservation is completed, take it out of the muffle furnace and air cool it to obtain the heat-treated additive manufacturing superalloy.

[0057] Example 3

[0058] This example provides a heat treatment method for an additive manufacturing superalloy. The chemical composition of the additive manufacturing superalloy is shown in Table 1 and includes the following steps:

[0059] Step 1) Stress relief annealing treatment: Place the as-printed additive manufacturing superalloy (prepared by the laser powder bed fusion metal 3D printing technology SLM process) in a ceramic tray and place it in the working cavity of the muffle furnace. Heat up the muffle furnace, control the heating rate at 5 K / min, and heat the as-printed additive manufacturing superalloy to 650 °C with the furnace. Calibrate the temperature in the furnace using a standard thermocouple to ensure that the temperature difference is within ±2 °C. After heat preservation for 10 h, obtain the alloy after stress relief annealing treatment.

[0060] Step 2) Long-term aging treatment: After stress relief annealing, without removing the alloy after stress relief annealing treatment, continue to heat up the muffle furnace at a heating rate of 5 K / min until it reaches 1000 °C. After the temperature stabilizes, enter the heat preservation stage. Calibrate the temperature in the furnace using a standard thermocouple to ensure that the temperature difference is within ±2 °C. The heat preservation time is 100 h. After the heat preservation is completed, take it out of the muffle furnace and air cool it to obtain the heat-treated additive manufacturing superalloy.

[0061] Comparative Example 1

[0062] Comparative Example 1 provides a heat treatment method for an additive manufacturing superalloy. The chemical composition of the additive manufacturing superalloy is shown in Table 1 and includes the following steps:

[0063] Step 1) High-temperature solution treatment: Heat up the muffle furnace to 1300 °C, and then place the as-printed additive manufacturing superalloy (prepared by the laser powder bed fusion metal 3D printing technology SLM process) in a ceramic tray and put it into the muffle furnace together. Calibrate the temperature in the furnace using a standard thermocouple to ensure that the temperature difference is within ±2 °C. After heat preservation for 2 h, take it out and air cool it to obtain the alloy after high-temperature solution treatment.

[0064] Step 2) Primary aging treatment: Heat up the muffle furnace to 1080 °C. Then place the alloy after high-temperature solution treatment in a ceramic tray and put it into the muffle furnace together. Calibrate the temperature in the furnace using a standard thermocouple to ensure that the temperature difference is within ±2 °C. After heat preservation for 4 h, take it out and air cool it to obtain the alloy after primary aging treatment.

[0065] Step 3) Secondary aging treatment: Heat the muffle furnace to 870 °C. Then place the alloy after the primary aging treatment on a ceramic tray and put them into the muffle furnace together. Calibrate the temperature in the furnace using a standard thermocouple to ensure that the temperature difference is within ±2 °C. After holding for 20 h, take it out and air cool to obtain the heat-treated additive manufacturing superalloy.

[0066] Comparative Example 2

[0067] Comparative Example 2 provides a heat treatment method for an additive manufacturing superalloy. The chemical composition of the additive manufacturing superalloy is shown in Table 1, and it includes the following steps:

[0068] Step 1) High-temperature solution treatment: Heat the muffle furnace to 1260 °C. Then place the as-printed additive manufacturing superalloy (prepared by the laser powder bed fusion metal 3D printing technology SLM process) on a ceramic tray and put them into the muffle furnace together. Calibrate the temperature in the furnace using a standard thermocouple to ensure that the temperature difference is within ±2 °C. After holding for 2 h, take it out and air cool to obtain the alloy after high-temperature solution treatment.

[0069] Step 2) Primary aging treatment: Heat the muffle furnace to 1080 °C. Then place the alloy after high-temperature solution treatment on a ceramic tray and put them into the muffle furnace together. Calibrate the temperature in the furnace using a standard thermocouple to ensure that the temperature difference is within ±2 °C. After holding for 4 h, take it out and air cool to obtain the alloy after primary aging treatment.

[0070] Step 3) Secondary aging treatment: Heat the muffle furnace to 870 °C. Then place the alloy after primary aging treatment on a ceramic tray and put them into the muffle furnace together. Calibrate the temperature in the furnace using a standard thermocouple to ensure that the temperature difference is within ±2 °C. After holding for 20 h, take it out and air cool to obtain the heat-treated additive manufacturing superalloy.

[0071] Comparative Example 3

[0072] Comparative Example 3 provides a heat treatment method for an additive manufacturing superalloy. The chemical composition of the additive manufacturing superalloy is shown in Table 1, and it includes the following steps:

[0073] Step 1) Stress relief annealing treatment: Place the as-printed additive manufacturing superalloy (prepared by the laser powder bed fusion metal 3D printing technology SLM process) on a ceramic tray and put it into the working cavity of the muffle furnace. Heat the muffle furnace, and control the heating rate at 5 K / min to make the as-printed additive manufacturing superalloy heat up to 600 °C with the furnace. Calibrate the temperature in the furnace using a standard thermocouple to ensure that the temperature difference is within ±2 °C. After holding for 10 h, obtain the alloy after stress relief annealing treatment.

[0074] Step 2) Long-term aging treatment: After stress relief annealing, without removing the alloy after stress relief annealing treatment, continue to heat up the muffle furnace at a heating rate of 5 K / min until it reaches 1100 °C. After the temperature stabilizes, enter the holding stage. Calibrate the temperature in the furnace using a standard thermocouple to ensure that the temperature difference is within ±2 °C. The holding time is 100 h. After the holding is completed, take it out of the muffle furnace and air cool it to obtain the heat-treated additive manufacturing superalloy.

[0075] Table 1 shows the chemical compositions (wt%) of the additive manufacturing superalloys in the examples and comparative examples.

[0076] Table 1

[0077] Al B C Co Cr Hf Mo Ta Ti W Zr Ni 5.5 0.017 0.06 9.24 8.5 1.37 0.53 3.08 0.73 9.93 0.006 Bal.

[0078] Effect verification:

[0079] Samples were taken from the heat-treated additive manufacturing superalloys of the examples, the heat-treated additive manufacturing superalloys of the comparative examples, and the as-printed additive manufacturing superalloys, and microstructure characterization and high-temperature tensile mechanical property tests were carried out. Since the microstructure of the additive manufacturing superalloy changes with the printing height, considering that the mechanical property test is taken from the middle of the specimen, we only compare the alloy microstructure in the middle.

[0080] Figure 1 Fig. 19 shows the metallographic microstructures of the heat-treated additive manufacturing superalloys of Example 1 and Comparative Example 1; among them, Fig. (a) shows the metallographic microstructure of the heat-treated additive manufacturing superalloy of Example 1; Fig. (b) shows the metallographic microstructure of the heat-treated additive manufacturing superalloy of Comparative Example 1. It can be seen that: through reasonable stress relief annealing in Example 1, the internal stress of the alloy was effectively eliminated, and no recrystallization occurred during the subsequent heat treatment process. Due to the large internal stress and high solution temperature in the alloy of Comparative Example 1, a large amount of recrystallization occurred in the alloy.

[0081] Figure 2 Fig. 23 shows the SEM microstructures of the as-printed additive manufacturing superalloy and the heat-treated additive superalloy in Example 1 after corrosion; among them, Fig. (a) shows the SEM microstructure of the as-printed additive manufacturing superalloy after corrosion; Fig. (b) shows the SEM microstructure of the heat-treated additive superalloy in Example 1 after corrosion. It can be seen that: due to the rapid cooling process of additive manufacturing, no γ′ strengthening phase precipitated in the as-printed additive manufacturing superalloy (as shown in Fig. (a) in Figure 2 . The alloy is in a supersaturated state. After stress relief annealing at 600 °C / 6 h and long-term aging at 1000 °C / 100 h, a γ′ strengthening phase appeared in the alloy (as shown in Fig. (b) in Figure 2 .

[0082] Figure 3The microstructures of the additively manufactured high-temperature alloy in the printed state, the additively manufactured high-temperature alloy after heat treatment in Example 1, and the additively manufactured high-temperature alloy after heat treatment in Comparative Example 1 are shown in Figure (a); Figure (b) shows the microstructure of the additively manufactured high-temperature alloy after heat treatment in Example 1; Figure (c) shows the microstructure of the additively manufactured high-temperature alloy after heat treatment in Comparative Example 1. It can be seen that:

[0083] Printed additive manufacturing of high temperature alloys has <001> Oriented columnar crystal structure; the size of the columnar crystal is 50-100μm; in the printed additive manufacturing high-temperature alloy: the carbides with an area fraction of more than 90% are distributed in the crystals and are in the form of spherical particles; the size of the carbides in the crystals is 50nm-100nm.

[0084] In the additive high-temperature alloy after heat treatment in Comparative Example 1: carbides are distributed between dendrites, and there are few carbides at the grain boundaries.

[0085] In the additive high-temperature alloy after heat treatment in Example 1, the number of carbides in the grains is slightly reduced, but a large number of nano-scale carbides are precipitated at the grain boundaries (about 2-3 carbides with a size of 100-200 nm are precipitated on a 1 μm grain boundary), which modify the grain boundaries and play a role in strengthening the grain boundaries.

[0086] from Figure 3 It can also be seen that there are no obvious holes in the printed additively manufactured high-temperature alloy. In the additive high-temperature alloy after heat treatment in Comparative Example 1, more holes appeared. This is because at high temperatures, the diffusion of elements intensified, and the solid solution micropores produced by the Kirkendall effect. Subsequent aging cannot eliminate these micropores, which may affect the mechanical properties of the alloy. However, no similar holes appeared in the additive high-temperature alloy after heat treatment in Example 1. In addition, the additive high-temperature alloy after heat treatment in Example 1 eliminated element segregation, homogenized the alloy, and no obvious dendritic structure was observed.

[0087] The printed additively manufactured high-temperature alloy, the additively manufactured high-temperature alloy after heat treatment in Examples 1 to 3, and the additively manufactured high-temperature alloy after heat treatment in Comparative Examples 1 to 3 were processed with tensile test bars at the center position for mechanical property testing. The results are shown in Table 2.

[0088] Table 2 shows the tensile mechanical properties of the original printed additively manufactured high-temperature alloy and the additively manufactured high-temperature alloy specimens after heat treatment in Example 1 at 1100°C.

[0089] Table 2

[0090] <![CDATA[σ b / MPa]]> <![CDATA[σ 0.2 / MPa]]> δ / % Ψ / % As-printed state 259 155 16.0 15 Example 1 280 173 18.0 14 Example 2 276 175 17.5 14 Example 3 273 171 19.0 15 Comparative Example 1 218 114 11.5 13 Comparative Example 2 198 103 5.0 4 Comparative Example 3 225 150 15.0 14

[0091] As can be seen from Table 2: (1) In Examples 1-3, the tensile properties, tensile strength and yield strength of the heat-treated additive high-temperature alloy at 1100 °C are 8-10% higher than those of the as-printed additive manufacturing high-temperature alloy, the plasticity is slightly improved, and it is significantly better than the heat-treated additive high-temperature alloys in Comparative Example 1 and Comparative Example 2 as a whole. (2) Although stress relief annealing and long-term aging treatment were also carried out in Comparative Example 3, the temperature of the long-term aging treatment is not within the protection scope of the present invention, resulting in the performance of the heat-treated additive manufacturing high-temperature alloy being inferior to that of the examples of the present invention (the long-term aging temperature in Comparative Example 3 is reduced, resulting in a slower decomposition and re-precipitation rate of carbides, and it is impossible to form a microstructure with a dispersed distribution of intragranular and intergranular carbides).

[0092] Combined with Figure 1 , Figure 2 and Figure 3 , through the heat treatment method combining stress relief annealing and long-term aging in the examples of the present invention, stress is effectively eliminated, the occurrence of recrystallization is prevented, the alloy structure is homogenized, γ′ strengthening phase is precipitated, and the carbide precipitation position is adjusted, so that the precipitation amount at the grain boundary increases, the grain boundary strength is strengthened, and the high-temperature mechanical properties of the alloy are improved. In the traditional heat treatment process, solution treatment has two functions: on the one hand, it makes γ′ remelt into the matrix, and on the other hand, it makes the alloy homogenized. However, since the additive manufacturing high-temperature alloy does not precipitate γ′ due to rapid solidification, and rapid solidification also inhibits the diffusion of elements, resulting in a lower segregation level, the role of traditional high-temperature solution treatment in additive manufacturing high-temperature alloys is not so important. On the contrary, using the traditional heat treatment method of solution plus aging increases pores and weakens grain boundaries, instead reducing the mechanical properties of the alloy. In addition, the traditional heat treatment system does not consider the high internal stress level of additive manufacturing, so it is easy to cause recrystallization, destroy the original fine columnar crystal state of the alloy, and reduce the mechanical properties of the alloy.

[0093] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A heat treatment method for an additive manufacturing superalloy, characterized in that, It includes the following steps: Step 1), heating the as-printed additive manufacturing superalloy to the annealing temperature, holding for the first set time, and performing stress relief annealing treatment to obtain the alloy after stress relief annealing treatment; Step 2), heating the alloy after the stress relief annealing treatment from the annealing temperature to the temperature for long-term aging treatment, performing long-term aging treatment, and after cooling, obtaining the heat-treated additive manufacturing superalloy; Among them, the temperature for long-term aging treatment is 950 - 1050 °C, and the time for long-term aging treatment is 80 - 200 h.

2. The heat treatment method of the additive manufacturing superalloy according to claim 1, characterized in that, In terms of weight percentage, the additive manufacturing superalloy includes the following chemical components: Al 5 - 6 wt%, B 0.01 - 0.02 wt%, C 0.05 - 0.15 wt%, Co 9 - 10 wt%, Cr 8 - 10 wt%, Hf 0 - 1.5 wt%, Mo 0 - 0.6 wt%, Ta 3 - 4 wt%, Ti 0.5 - 1 wt%, W 9 - 11 wt%, Zr 0 - 0.02 wt%, and the balance is Ni.

3. The heat treatment method of the additively manufactured superalloy according to claim 1 or 2, characterized in that The as-printed additive manufacturing superalloy is prepared by the SLM process of laser powder bed fusion metal 3D printing technology.

4. The heat treatment method of the additively manufactured superalloy according to any one of claims 1-3, characterized in that, In the said Step 1): The annealing temperature is 600 - 650 °C; the first set time is 6 - 10 h, preferably 8 - 10 h.

5. The heat treatment method of the additive manufacturing superalloy according to any one of claims 1-4, characterized in that, In the said Step 1): The heating rate for heating the as-printed additive manufacturing superalloy to the annealing temperature is 5 - 10 K / min.

6. The heat treatment method of the additive manufacturing superalloy according to any one of claims 1-5, characterized in that, In the said Step 2): The heating rate for heating the alloy after the stress relief annealing treatment from the annealing temperature to the temperature for long-term aging treatment is 5 - 10 K / min; and / or After the long-term aging treatment, the cooling rate is 5 - 10 K / min; and / or After the long-term aging treatment, take out the alloy after long-term aging treatment from the heating furnace and perform air cooling to obtain the heat-treated additive manufacturing superalloy.

7. The heat treatment method of the additively manufactured superalloy according to any one of claims 1-6, characterized in that, In the said Step 2): The temperature for long-term aging treatment is 1000 °C ± 10 °C, and the time for long-term aging treatment is 100 h ± 5 h.

8. The heat treatment method of the additively manufactured superalloy according to any one of claims 1-7, characterized in that, Both the said Step 1) and the said Step 2) are carried out in a muffle furnace.

9. The heat treatment method of the additively manufactured superalloy according to any one of claims 1-8, characterized in that, The as-printed additive manufacturing superalloy has a columnar crystal structure with <001> orientation; preferably, the size of the columnar crystals is 50 - 100 μm; Preferably, in the as-printed additive manufacturing superalloy: more than 90% of the carbides are distributed in the grains and are in the shape of spherical particles; preferably, the size of the carbides in the grains is 50 nm - 100 nm.

10. An additively manufactured superalloy after heat treatment, characterized in that, The heat-treated additive manufacturing superalloy is obtained by heat-treating the as-printed additive manufacturing superalloy using the heat treatment method of the additive manufacturing superalloy according to any one of claims 1 - 9; Preferably, the grain boundaries of the heat-treated additive manufacturing superalloy remain intact, and nano-sized carbides are distributed at both the grain boundaries and in the grains; γ′ strengthening phases are distributed throughout the alloy, with a size of 500 nm - 1 μm and a volume fraction of 57 - 63%; Preferably, the number of nano-sized carbides at the grain boundaries is greater than the number of nano-sized carbides in the grains; preferably, the grain size is 100 - 200 μm.

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