A heat treatment system and method for aircraft rivets

Abstract

A heat treatment system and method for aerospace rivets are disclosed. The system, based on a vacuum heat treatment furnace, adds a controllable atmosphere introduction system, an oxygen partial pressure sensor, and a control unit. The controllable atmosphere introduction system includes an inert gas source, an active gas source, and a gas mixing and proportioning device. The control unit stores preset values ​​for the segmented mixed gas proportions corresponding to rivets of different materials. The heat treatment method employs a combination of vacuum heating and controllable atmosphere cooling. After heat treatment, a mixed protective gas is introduced into the furnace. Based on the material microstructure transformation characteristics, differentiated proportions and cooling rates are segmentally controlled in at least two temperature ranges, with closed-loop feedback regulation achieved through the oxygen partial pressure sensor. This invention effectively suppresses the formation of a brittle oxide layer on the rivet surface, resulting in a silvery-white metallic luster on the rivet surface after treatment. No subsequent pickling or shot blasting processes are required, significantly improving the surface quality and mechanical property consistency of aerospace rivets.

Description

Technical Field

[0001] This invention belongs to the field of heat treatment technology, specifically referring to a heat treatment system and method for aerospace rivets. Background Technology

[0002] To meet the stringent requirements for comprehensive mechanical properties and surface quality of aerospace rivets, vacuum heat treatment is a commonly used process in the industry. However, existing vacuum heat treatment technology faces significant challenges in actual production: even at 10... -3 ~10 -4 Under high vacuum conditions, the high affinity of titanium alloys for oxygen and the residual trace amounts of oxygen in the furnace still lead to the formation of an extremely thin but highly hard and brittle grayish-yellow oxide layer on the rivet surface. High-temperature alloy rivets are prone to forming a brittle surface contamination layer and microcracks during prolonged heat treatment. These two types of brittle surface layers become the initiation sites for microcracks during subsequent cold heading or riveting processes, severely reducing the fatigue life and connection reliability of the rivets.

[0003] To remove this surface defect, existing processes generally rely on adding pickling or shot blasting steps after heat treatment. However, pickling carries the risk of hydrogen embrittlement and environmental pollution, while shot blasting may damage the surface precision of the rivets, prolonging the production cycle, increasing manufacturing costs, and fundamentally affecting the quality consistency of aerospace fasteners.

[0004] More importantly, existing vacuum heat treatment equipment lacks the ability to monitor and dynamically control the composition of the furnace atmosphere during the cooling stage. The vacuum level only adopts a set value holding mode and cannot be adaptively adjusted according to changes in the oxidation state of the rivet surface, resulting in blindness and unreliability in surface quality control. Summary of the Invention

[0005] In view of the above situation and to overcome the defects of the prior art, the present invention provides a heat treatment system and method for aerospace rivets, which at least partially solves the above problems.

[0006] In a first aspect, the present invention provides a heat treatment system for aerospace rivets, comprising a vacuum heat treatment furnace, a controllable atmosphere introduction system, an oxygen partial pressure sensor, and a control unit. The controllable atmosphere introduction system is connected to the inlet of the vacuum heat treatment furnace and includes an inert gas source, an active gas source, and a gas mixing and proportioning device. The oxygen partial pressure sensor is installed inside the vacuum heat treatment furnace near the workpiece. The control unit is electrically connected to the controllable atmosphere introduction system and the oxygen partial pressure sensor, and internally stores preset values ​​for the mixed gas proportions in at least two temperature ranges corresponding to the cooling stages of rivets made of different materials. During the cooling stage, the control unit controls the controllable atmosphere introduction system to adjust the proportion and / or flow rate of the mixed protective gas based on the oxygen partial pressure value fed back by the oxygen partial pressure sensor.

[0007] Furthermore, the inert gas source is either argon or helium, and the active gas source is either hydrogen or a carbon-containing gas source. When the mixed protective gas is a mixture of argon and hydrogen, the hydrogen volume ratio is 0.1%–1.0%, and the furnace pressure during the cooling stage is 10. -1 ~10 -2 Pa.

[0008] Furthermore, the system also includes a surface temperature monitoring device, which is electrically connected to the control unit, for acquiring the surface temperature of the rivet workpiece during the heating and cooling process; the control unit adjusts the ratio of the mixed protective gas in segments according to the preset temperature range during the cooling stage based on the temperature signal fed back by the surface temperature monitoring device.

[0009] Secondly, the present invention also provides a heat treatment method for aircraft rivets, comprising the following steps: S1: Load the aerospace rivet workpiece into a vacuum heat treatment furnace and evacuate to 10°C. -3 Below Pa; S2: Heating and heat preservation are carried out according to the process requirements of the rivet material, maintaining the furnace pressure below 10. -2 Pa; S3: After the heat preservation is completed, the cooling stage begins. A mixed protective gas consisting of inert gas and active gas is introduced into the furnace. During the cooling process, according to the microstructure transformation characteristics of the rivet material, different mixed gas ratios and / or cooling rates are used for segmented control in at least two temperature ranges. At the same time, the oxygen partial pressure in the furnace is monitored by an oxygen partial pressure sensor. When the oxygen partial pressure exceeds the preset threshold, the proportion of active gas is increased or the total flow rate is increased. S4: After the workpiece has cooled to the preset temperature, shut off the atmosphere introduction system and remove it from the furnace.

[0010] As a preferred method, the protective gas mixture in step S3 is a mixture of argon and hydrogen, and the furnace pressure is maintained at 10. -1 ~10 -2 Pa. The segmented control specifically includes: a first cooling stage, cooling from the holding temperature to the first temperature node, using a first cooling rate and a first mixing ratio with a higher hydrogen content; a second cooling stage, cooling from the first temperature node to the second temperature node, using a second cooling rate and a second mixing ratio with a lower hydrogen content, the second cooling rate being higher than the first cooling rate; and a third cooling stage, cooling from the second temperature node to below 200°C, using a third cooling rate, and shutting off the active gas source while only introducing inert gas, or maintaining the active gas volume ratio at no more than 0.1%.

[0011] In one specific implementation, for TC16 titanium alloy rivets, the heat preservation temperature is 800–850℃, the first temperature node is 700℃, and the second temperature node is 550℃. In the first cooling section, the mixed gas ratio is argon and 0.5%–1.0% hydrogen, and the cooling rate is 2–5℃ / min; in the second cooling section, the hydrogen ratio in the mixed gas is reduced to 0.1%–0.3%, and the cooling rate is 10–20℃ / min; in the third cooling section, pure argon or argon containing less than 0.1% hydrogen is introduced, and the cooling rate is 5–10℃ / min.

[0012] As another specific implementation, for GH2132 or GH4169 high-temperature alloy rivets, the mixed protective gas consists of argon, hydrogen, and methane. The cooling stage is divided into two temperature zones: the first temperature zone is from the holding temperature to 600°C, in which the mixed protective gas is introduced; and the second temperature zone is from 600°C to 300°C, in which a mixed gas consisting of argon and hydrogen is introduced.

[0013] Furthermore, after step S3, an aging process is also included: the cooled rivet is heated to 500-600°C under vacuum or inert gas protection and held for 2-6 hours.

[0014] Compared with existing technologies, this invention effectively suppresses the formation of brittle oxide layers on the surface of titanium alloy and high-temperature alloy rivets by introducing a controllable atmosphere and implementing closed-loop feedback segmented regulation of oxygen partial pressure during the cooling stage of vacuum heat treatment. The rivet surface exhibits a silvery-white metallic luster, eliminating the need for subsequent pickling or shot blasting processes, thus mitigating the risk of hydrogen embrittlement, significantly shortening the production cycle, and reducing manufacturing costs. The segmented atmosphere regulation strategy is based on the material microstructure transformation characteristics, achieving precise control of microstructure transformation while ensuring the suppression of surface oxidation, thereby ensuring batch-to-batch consistency of rivet mechanical properties. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the heat treatment system for aerospace rivets according to an embodiment of the present invention; Figure 2 This is a flowchart of a heat treatment method for aviation rivets according to an embodiment of the present invention.

[0016] The components include: 1. Vacuum heat treatment furnace; 2. Controlled atmosphere introduction system; 3. Oxygen partial pressure sensor; 4. Air inlet; 5. Control unit; and 6. Surface temperature monitoring device.

[0017] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof. Detailed Implementation

[0018] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0019] In the description of this invention, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0020] like Figure 1 As shown in the figure, an embodiment of the present invention provides a heat treatment system for aerospace rivets, including a vacuum heat treatment furnace 1, a controllable atmosphere introduction system 2, an oxygen partial pressure sensor 3, and a control unit 5. The vacuum heat treatment furnace 1 is used to perform heat treatments such as solution treatment, aging, or annealing on aerospace rivet workpieces, and includes a furnace body, heating elements, a vacuum extraction system, and a cooling system. The furnace body is equipped with a platform for placing the rivet workpieces. The platform can be a multi-layer mesh belt type or a basket type structure to adapt to the small-size, high-volume production characteristics of rivets.

[0021] The controllable atmosphere introduction system 2 is connected to the air inlet 4 of the vacuum heat treatment furnace 1, and includes an inert gas source, an active gas source, and a gas mixing and proportioning device. The inert gas source provides high-purity inert gas, and can be either argon or helium, with argon purity preferably above 99.999%. The active gas source provides active gas with reducing or modifying functions, and can be either hydrogen or carbon-containing gas, such as methane, with hydrogen purity preferably above 99.999%. The gas mixing and proportioning device precisely mixes gases from different gas sources according to a preset ratio to form a mixed protective gas with the required proportions.

[0022] In practical implementation, the gas mixing and proportioning device can employ a mass flow controller with a control accuracy of ±0.1% of full scale. Precise proportioning control is achieved through independent adjustment of the mass flow rate of each gas path. An oxygen partial pressure sensor 3 is installed inside the vacuum heat treatment furnace 1 near the workpiece to monitor the residual oxygen partial pressure in the furnace atmosphere in real time.

[0023] Because high-temperature alloys and titanium alloys have extremely low tolerance to oxygen, the measurement accuracy of the oxygen partial pressure sensor 3 is preferably not less than 10. -18 The Pa level is applicable. In practical implementation, a zirconia-type high-temperature oxygen probe can be used, with a measurement range covering 10 Pa. -20Pa to 10 -5 Pa is sufficient to meet the needs of process monitoring.

[0024] The control unit 5 is electrically connected to the controllable atmosphere introduction system 2 and the oxygen partial pressure sensor 3. Internally, it stores preset values ​​for the mixed gas ratios in at least two temperature ranges corresponding to different material rivets during the cooling stage. During the cooling stage, the control unit 5, based on the oxygen partial pressure value fed back by the oxygen partial pressure sensor 3, controls the controllable atmosphere introduction system 2 to adjust the ratio and / or flow rate of the mixed protective gas, thereby achieving closed-loop feedback control of the furnace atmosphere.

[0025] To further improve the accuracy of temperature monitoring, the system may also include a surface temperature monitoring device 6, which is electrically connected to the control unit 5 and is used to acquire the surface temperature of the rivet workpiece during the heating and cooling processes. The surface temperature monitoring device 6 can utilize a dual-color infrared thermometer and a multi-point armored thermocouple for combined monitoring. The infrared thermometer is used for non-contact, rapid acquisition of the workpiece surface temperature field distribution, while the thermocouples are used for precise temperature calibration at critical locations. Based on the temperature signal fed back by the surface temperature monitoring device 6, the control unit 5 adjusts the ratio of the mixed protective gas in segments according to preset temperature ranges during the cooling stage, thereby achieving coordinated control of temperature and atmosphere during the cooling process.

[0026] This invention also provides a heat treatment method for aerospace rivets, the process flow of which is as follows: Figure 2 As shown, it includes the following steps: Step S1: Loading and Initial Vacuum Establishment. Load the aerospace rivet workpieces to be processed onto the stage inside the vacuum heat treatment furnace. The workpieces can be TC16 titanium alloy rivets, TC4 titanium alloy rivets, GH2132 high-temperature alloy rivets, or GH4169 high-temperature alloy rivets, etc. After closing the furnace door, start the vacuum pumping system to evacuate the furnace, raising the pressure inside to 10... -3 The pressure is below 100 Pa to remove most of the oxygen from the furnace. The vacuuming process can be achieved in stages by sequentially starting the mechanical pump, Roots pump, and diffusion pump to reach rough vacuum, medium vacuum, and high vacuum.

[0027] Step S2: Vacuum heating and heat preservation. Set the heating temperature profile according to the process requirements of the rivet material, and heat and preserve the workpiece. Maintain the furnace pressure below 10℃ during the heating and heat preservation process. -2 Taking the solution treatment of TC16 titanium alloy rivets as an example, the furnace temperature can be raised to the solution temperature of 800-850℃ at a rate of 5-10℃ / min, and held for 60-120min. During the holding process, the oxygen partial pressure sensor continuously monitors the residual oxygen partial pressure, and the control unit records the data in real time to ensure the traceability of the heat treatment process.

[0028] Step S3: Controlled atmosphere synergistic cooling, this is the core innovative step of the present invention. After the heat preservation stage, the cooling stage begins, and a mixed protective gas composed of inert and active gases is introduced into the furnace. The introduction of the mixed protective gas reduces the furnace pressure from 10°C during the heat preservation stage to 10°C during the heat preservation stage. -2 Pa is increased to 10. -1 ~10 -2 The cooling process is controlled in stages within at least two temperature ranges by using different mixed gas ratios and / or cooling rates, based on the microstructure transformation characteristics of the rivet material.

[0029] Specifically, taking TC16 titanium alloy rivets as an example, its β-phase transformation point is approximately 875℃. The cooling process after solution treatment needs to control the morphology and quantity of α-phase precipitation to obtain ideal mechanical properties. Based on these material characteristics, the cooling stage can be divided into three temperature ranges for differentiated atmosphere control.

[0030] The first cooling section cools from the holding temperature to the first temperature node of 700℃, employing a first cooling rate of 2–5℃ / min and a first mixing ratio with a high hydrogen content. The mixed gas ratio is a mixture of argon and 0.5%–1.0% hydrogen. Within this temperature range, the rivet is located in the high-temperature section of the β-phase region to the initial section of the α-phase and β-phase two-phase region. The slower cooling rate is beneficial for temperature field homogenization. At the same time, the higher hydrogen content can effectively reduce trace oxides that may form in the high-temperature section. Hydrogen reacts with residual oxygen to generate water vapor, which is then removed by the vacuum pumping system, thereby actively eliminating residual oxygen in the furnace.

[0031] The second cooling section cools from the first temperature node of 700℃ to the second temperature node of 550℃, employing a second cooling rate of 10–20℃ / min and a second mixing ratio with a reduced hydrogen content. The hydrogen content in the mixed gas is reduced to 0.1%–0.3%, and the second cooling rate is higher than the first cooling rate. This temperature range is the main temperature range of the α-phase and β-phase two-phase region and is the key stage for α-phase precipitation and growth. Rapid cooling can suppress the formation of coarse lamellar α-phase and obtain a fine and uniform α / β phase two-state structure. The purpose of reducing the hydrogen content is to avoid interference from active hydrogen atoms on the migration of the α / β phase interface during the active phase transition stage.

[0032] The third cooling stage cools from the second temperature node of 550℃ to below 200℃ at a third cooling rate of 5-10℃ / min. At this stage, the microstructure transformation is essentially complete, and the active gas source can be shut off, allowing only pure argon gas to be introduced for protection. Alternatively, depending on the surface gloss requirements, the active gas volume ratio can be maintained at no more than 0.1%. Below 200℃, the furnace door can be opened for air cooling to room temperature.

[0033] Throughout the cooling process, the oxygen partial pressure sensor continuously monitors the oxygen partial pressure inside the furnace in real time. When the oxygen partial pressure exceeds a preset threshold, the control unit automatically increases the proportion of active gas or increases the total flow rate until the oxygen partial pressure returns to a safe range. When the oxygen partial pressure remains below the threshold and the rivet surface temperature has dropped to a safe temperature, the gas flow rate can be appropriately reduced to save gas consumption. This closed-loop feedback regulation mechanism ensures optimal protection and economical gas consumption.

[0034] Regarding the question of whether the introduction of hydrogen in this embodiment will cause the risk of hydrogen embrittlement, the following explanation is provided. The concentration of hydrogen introduced during the cooling stage is controlled within a low range of 0.1% to 1.0%, and the total pressure inside the furnace is maintained at 10... -1 ~10 -2 At a low pressure of Pa, the partial pressure of hydrogen is extremely low, approximately 10 Pa. -3 ~10 -4 The hydrogen content is on the order of Pa. Theoretical calculations based on Sivez's law show that the equilibrium hydrogen content of the titanium alloy under this low hydrogen partial pressure condition is less than 10 ppm, far from sufficient to cause hydrogen embrittlement. Furthermore, hydrogen is mainly consumed through two pathways: first, it reacts with residual oxygen to generate water vapor, which is then removed by the vacuum system; second, it is directly discharged by the vacuum pumping system at high temperatures, with very little adsorption and dissociation from the workpiece surface to penetrate the matrix. Therefore, the method of this invention does not introduce the risk of hydrogen embrittlement.

[0035] Step S4: Unloading from the furnace. After the rivet workpiece has cooled to below the preset temperature of 150°C, turn off the controlled atmosphere introduction system, open the furnace door, and remove the workpiece. Perform surface quality inspection and mechanical property testing on the heat-treated rivets. Surface quality inspection includes visual inspection and metallographic examination, and mechanical property testing includes hardness testing and room temperature tensile testing.

[0036] In another embodiment, after step S3, an aging treatment step may be included: heating the cooled rivet to 500–600°C under vacuum or inert gas protection and holding for 2–6 hours. Taking TC16 titanium alloy rivets as an example, the process is 550°C for 4 hours. The aging treatment, on the one hand, causes the metastable structure obtained from the solution treatment to precipitate fine and dispersed strengthening phases, increasing the rivet strength to a target value of over 1030 MPa. On the other hand, at this temperature, the diffusion coefficient of hydrogen in titanium alloy is relatively high, approximately 10. -7 Hydrogen atoms that may have slightly penetrated into the workpiece surface during the solution cooling stage can escape fully from the surface during the aging and heat preservation process, thus playing a role in in-situ dehydrogenation.

[0037] In another embodiment, the rivet workpiece is a GH2132 or GH4169 high-temperature alloy rivet. These high-temperature alloys are prone to forming a brittle and hard contamination layer on their surface after vacuum heat treatment, and water or oil cooling according to relevant process standards can easily lead to workpiece deformation. In this embodiment, the mixed protective gas consists of argon, hydrogen, and methane. The cooling stage is divided into two temperature ranges for atmosphere control based on the microstructure of the high-temperature alloy. In the first temperature range, cooling is performed from the holding temperature of 980–1000°C to 600°C, during which a mixed protective gas consisting of argon, hydrogen, and methane is introduced into the furnace, and furnace cooling is carried out at a relatively slow cooling rate of 3°C / min. During this process, trace amounts of methane decompose at high temperatures to produce active carbon atoms, forming an extremely thin carburized layer of approximately 0.5–1 μm on the rivet surface, enhancing the wear resistance of the rivet surface; hydrogen acts as a reducing protective gas to prevent surface oxidation; argon serves as a carrier gas and dilution gas, maintaining the furnace pressure at a stable 10... -1 ~10 -2 Within the Pa range, slow cooling ensures minimal product deformation and dimensional accuracy, while also resulting in uniform grain structure after annealing. In the second temperature range, cooling from 600℃ to 300℃ involves shutting off the methane gas source and introducing only a mixture of argon and hydrogen for continued protective cooling; the cooling rate can be appropriately increased to 5℃ / min. Below 300℃, the controlled atmosphere introduction system is shut off, and the furnace is air-cooled to room temperature.

[0038] In the above embodiments, the preset parameters stored inside the control unit can be flexibly configured and recalled according to different rivet materials and specifications. When changing product specifications, it is only necessary to recall the corresponding preset temperature nodes, mixed gas ratios, and cooling rates to achieve process switching, adapting to the characteristics of multi-variety, small-batch production of aerospace fasteners.

[0039] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0040] The present invention and its embodiments have been described above. This description is not restrictive, and the accompanying drawings are only one embodiment of the present invention; the actual structure is not limited thereto. In conclusion, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the invention, such designs should fall within the protection scope of the present invention.

Claims

1. A heat treatment system for aircraft rivets, comprising a vacuum heat treatment furnace (1), characterized in that, Also includes: A controllable atmosphere introduction system (2) is connected to the air inlet (4) of the vacuum heat treatment furnace (1), and includes an inert gas source, an active gas source and a gas mixing and proportioning device; An oxygen partial pressure sensor (3) is installed inside the vacuum heat treatment furnace (1) near the workpiece. The control unit (5) is electrically connected to the controllable atmosphere introduction system (2) and the oxygen partial pressure sensor (3), and stores preset values ​​of mixed gas ratios for at least two temperature ranges corresponding to the cooling stages of rivets made of different materials. During the cooling phase, the control unit (5) controls the controllable atmosphere introduction system (2) to adjust the ratio and / or flow rate of the mixed protective gas based on the oxygen partial pressure value fed back by the oxygen partial pressure sensor (3).

2. The heat treatment system for aerospace rivets according to claim 1, characterized in that: The inert gas source is an argon gas source or a helium gas source, and the active gas provided by the active gas source is a hydrogen gas source or a carbon-containing gas source.

3. The heat treatment system for aerospace rivets according to claim 2, characterized in that: The mixed protective gas is a mixture of argon and hydrogen, wherein the volume ratio of hydrogen is 0.1% to 1.0%; the pressure in the cooling stage furnace is 10 -1 ~10 - 2 Pa.

4. The heat treatment system for aerospace rivets according to claim 1, characterized in that, It also includes a surface temperature monitoring device (6), which is electrically connected to the control unit (5) to obtain the surface temperature of the rivet workpiece during the heating and cooling process; the control unit (5) adjusts the ratio of the mixed protective gas in segments according to the preset temperature range based on the temperature signal fed back by the surface temperature monitoring device (6) during the cooling stage.

5. A heat treatment method for aircraft rivets, characterized in that, Includes the following steps: S1: The aviation rivet workpiece is loaded into a vacuum heat treatment furnace (1), vacuumized to 10 -3 Pa or below; S2: Heating and heat preservation are carried out according to the process requirements of the rivet material, maintaining the furnace pressure below 10. -2 Pa; S3: After the heat preservation is completed, the cooling stage begins. A mixed protective gas consisting of inert gas and active gas is introduced into the furnace. During the cooling process, according to the microstructure transformation characteristics of the rivet material, different mixed gas ratios and / or cooling rates are used for segmented control in at least two temperature ranges. At the same time, the oxygen partial pressure in the furnace is monitored by the oxygen partial pressure sensor (3). When the oxygen partial pressure exceeds the preset threshold, the proportion of active gas is increased or the total flow rate is increased. S4: After the workpiece has cooled to the preset temperature, shut off the atmosphere introduction system and remove it from the furnace.

6. The method according to claim 5, characterized in that, The protective gas mixture in step S3 is a mixture of argon and hydrogen, and the furnace pressure is maintained at 10. -1 ~10 -2 Pa.

7. The method according to claim 6, characterized in that, The segmented control includes: First cooling section: Cooling from the insulation temperature to the first temperature node, using a first cooling rate and a first mixing ratio with a high proportion of hydrogen; Second cooling section: Cooling from the first temperature node to the second temperature node, using a second cooling rate and a second mixing ratio with a reduced hydrogen content, wherein the second cooling rate is higher than the first cooling rate; Third cooling stage: Cooling from the second temperature node to below 200℃, using the third cooling rate, and shutting off the active gas source to allow only inert gas to be introduced, or keeping the volume ratio of active gas no higher than 0.1%.

8. The method according to claim 7, characterized in that, For TC16 titanium alloy rivets, the heat preservation temperature is 800-850℃, the first temperature node is 700℃, and the second temperature node is 550℃. In the first cooling section, the mixed gas ratio is argon and 0.5% to 1.0% hydrogen, and the cooling rate is 2 to 5 °C / min; In the second cooling section, the proportion of hydrogen in the mixed gas is reduced to 0.1% to 0.3%, and the cooling rate is 10 to 20 °C / min; In the third cooling section, pure argon or argon containing less than 0.1% hydrogen is introduced, and the cooling rate is 5-10℃ / min.

9. The method according to claim 5, characterized in that, The mixed protective gas consists of argon, hydrogen, and methane; the rivet workpiece is a GH2132 or GH4169 high-temperature alloy rivet; the cooling stage is divided into two temperature ranges, the first temperature range from the holding temperature to 600°C is through which the mixed protective gas is introduced, and the second temperature range from 600°C to 300°C is through which a mixed gas consisting of argon and hydrogen is introduced.

10. The method according to claim 5, characterized in that, After step S3, an aging process is also included: the cooled rivet is heated to 500-600°C under vacuum or inert gas protection and held for 2-6 hours.

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