A directed energy deposition forming method to prevent cracking of high temperature high performance alloys

Abstract

This invention provides a directional energy deposition forming method to prevent cracking in high-temperature high-performance alloys. Before additive manufacturing, the substrate is preheated to 400-600°C using a heating device. Then, additive manufacturing is performed on the preheated substrate using directional energy deposition equipment. During additive manufacturing, cooling is achieved through lower cooling fixtures surrounding the substrate and / or upper cooling fixtures located on both sides of the additive part. The cooling height of the upper cooling fixtures on both sides of the additive part increases with the height of the additive part, maintaining the temperature of the additive part within the range of 600-1000°C. After additive manufacturing, the heating device is turned on for auxiliary heating, allowing the temperature of the additive part to slowly decrease to 200°C at a cooling rate of 100°C / 5min. Then, the heating device is turned off, and the part is air-cooled to room temperature. By controlling the thermal cycle and temperature gradient during the forming process, crack formation during additive manufacturing is prevented, effectively solving the problem of cracking in conventional methods for additive manufacturing of high-temperature high-performance alloys.

Description

Technical Field

[0001] This invention belongs to the field of additive manufacturing technology, and specifically relates to a directional energy deposition forming method for preventing cracking of high-temperature high-performance alloys. Technical Background

[0002] High-temperature alloys possess excellent high-temperature strength, fatigue resistance, oxidation resistance, and corrosion resistance, making them widely used in aerospace, weaponry, and petrochemical industries, particularly in critical components such as gas turbine blades, aircraft casings, and turbine disks. However, in traditional casting and welding processes, high-temperature alloys are prone to cracking due to high aluminum and titanium content, variations in forming processes and parameters, and post-processing methods, leading to increased manufacturing costs.

[0003] Additive manufacturing, as a novel manufacturing method, has significant advantages in the integrated manufacturing of complex-shaped components such as turbine blades. However, the strong non-equilibrium solidification behavior accompanying additive manufacturing, along with its high temperature gradient, high cooling rate, and cyclic heating-cooling effect, leads to elemental segregation, phase transformation, and residual stress accumulation in the alloy. This significantly increases the alloy's tendency to crack, severely limiting its widespread application in the aerospace field. Especially in high-strength, highly alloyed high-temperature alloys, the high Al and Ti content results in relatively poor weldability and a greater susceptibility to defects such as cracks during the manufacturing process. The main type of crack is liquefaction cracking, characterized by the formation of low-melting-point phases (low-melting-point nitrides, γ / γ′ eutectic structures) at grain boundaries. Due to the cyclic heating characteristic of additive manufacturing, the thermal effect of the upper layer causes the low-melting-point phases in the lower heat-affected zone to melt directionally, leading to cracking. The presence of these defects greatly affects the performance of additively manufactured high-temperature alloys and restricts their application in the fabrication and repair of components.

[0004] To address the aforementioned technical challenges, scholars both domestically and internationally have reported some exploratory studies. Examples include substrate preheating, reducing heat input, and optimizing the additive manufacturing path. While these methods offer some crack suppression, they still fall short of completely resolving the cracking problem in high-temperature high-performance alloy additive manufacturing. Therefore, researchers have had to explore costly and complex crack suppression and post-processing elimination methods. Patent CN113927028A utilizes micron- and nano-sized ceramic particles to modify high-alumina titanium-nickel-based superalloy powder through ball milling to prepare high-alumina titanium-nickel-based superalloys. However, the introduction of alloying elements inevitably alters the alloy composition, requiring recertification before industrial application, which increases the material's cost and hinders its widespread adoption. Patent CN113059159A addresses the cracking and inability to guarantee orientation during the repair or manufacturing process of directional solidified superalloy parts manufactured through cooling and heating of the molten pool. However, this method is not well-suited for non-directional solidified superalloys, and its narrow process range, large temperature gradient, and rapid cooling rate contribute to crack formation. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a directional energy deposition forming method for preventing cracking in high-temperature high-performance alloys. By controlling the thermal cycle and temperature gradient during the forming process, crack formation during additive manufacturing is prevented, effectively solving the problem of cracking in the additive manufacturing of high-temperature high-performance alloys using conventional methods. This saves the high cost of post-processing to eliminate cracks, significantly improves the mechanical properties of the resulting additive parts, and provides process guidance and quality assurance for the additive manufacturing of high-temperature high-performance alloys.

[0006] A method for preventing cracking in high-temperature high-performance alloys by directional energy deposition molding, characterized by the following steps:

[0007] S1: Substrate preheating: The substrate is preheated using a heating device to a temperature of 400-600℃, and then the heating device is turned off.

[0008] S2: Additive manufacturing: Additive manufacturing is performed on a preheated substrate using directional energy deposition equipment. During the additive manufacturing process, the substrate is cooled by a lower cooling fixture surrounding the substrate and / or an upper cooling fixture located on both sides of the additive part. The cooling height of the upper cooling fixture located on both sides of the additive part increases with the increase of the height of the additive part, so that the temperature of the substrate is maintained within the temperature range of 600-1000℃.

[0009] S3: Cooling process after additive manufacturing: After additive manufacturing is completed, turn on the heating device to assist heating, so that the temperature of the substrate is slowly reduced to 200℃ at a cooling rate of 100℃ / 5min, and then turn off the heating device and air cool to room temperature.

[0010] Furthermore, the heating device is disposed around the substrate to provide auxiliary heating during the preheating of the substrate before additive manufacturing and the cooling process of the substrate after additive manufacturing; it includes a heating coil and a controller, with the heating coil located around the substrate.

[0011] Furthermore, the cooling medium of the lower cooling fixture is liquid nitrogen, water, or gas, while the cooling medium of the upper cooling fixture is air or inert gas; flow meters are installed on the cooling circuits of the lower and upper cooling fixtures to control the cooling efficiency; the upper cooling fixture has several vents at different heights and metal plate switches that control the number of vents opening and closing.

[0012] Furthermore, the upper cooling fixture is spaced 20mm apart from the additive part, and the vents are arranged vertically in a row on the fixture, with a 10mm interval between two adjacent vents.

[0013] Furthermore, in step S2, after additive manufacturing begins, the lower cooling fixture directly connects to the cooling circuit for cooling. When the height of the additive part is higher than 7cm, the upper cooling fixture vents air, and the height of the air outlet of the upper cooling fixture should be 2-9mm lower than the current height of the additive part.

[0014] Furthermore, for every 7cm increase in the height of the additive component, the control metal plate switch opens one more vent hole upwards.

[0015] Furthermore, the substrate is selected as a metal system or copper or aluminum alloy that does not react with the alloy of the additive part being prepared; it is cleaned with acetone and alcohol before additive manufacturing.

[0016] Furthermore, in step S3, after the additive manufacturing is completed, the temperature sensor of the heating device that detects the substrate temperature displays that the temperature drops by 100°C, the heating device is turned on at 100W power to provide auxiliary heating to the substrate for 30 seconds until the temperature display shows that the temperature is below 200°C.

[0017] Furthermore, the directional energy deposition forming is one of electric arc, electron beam, or plasma directional energy deposition forming.

[0018] Furthermore, the directional energy deposition molding is laser directional energy deposition molding, with a laser power of 1000-6000W, a scanning speed of 5-15mm / s, a powder feed rate of 6-20g / min, and a gas flow rate of 6-10L / min.

[0019] The beneficial effects of this invention are:

[0020] This invention takes into account the effect of the upper layer on the heat-affected zone of the lower layer in additive manufacturing. It uses cooling fixtures to control the thermal cycle during additive manufacturing, avoiding the problem of liquefaction cracks caused by the melting of low-melting-point phases. Simultaneously, it solves the problem of a sharp decrease in material plasticity under cyclic heating, leading to a brittle temperature range and loss-of-plasticity cracks under residual stress. The heat treatment of the substrate controls the temperature gradient during the forming process, reducing residual stress and thus preventing crack formation. This improves printing efficiency and results in a more aesthetically pleasing finished product. The temperature control device provided by this invention is applicable to energy-directed energy deposition forming methods such as electric arc, electron beam, and plasma. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the tooling used in the additive manufacturing method for preventing cracking of high-temperature high-performance alloys according to the present invention.

[0022] Figure 2 This is a top view of the tooling used in the additive manufacturing method for preventing cracking of high-temperature high-performance alloys according to the present invention.

[0023] Figure 3 The results show that GH4169 high-temperature alloy was formed without using a laser-guided energy deposition system.

[0024] Figure 4 The results of laser-directed energy deposition forming of GH4169 high-temperature alloy were obtained using the device.

[0025] Explanation of markings in the diagram:

[0026] 1-Heating device, 2a-Upper cooling fixture, 2b-Gas flow meter, 3a-Lower cooling fixture, 3b-Flow meter, 4-Laser, 5-Substrate, 6-Temperature detection device Detailed Implementation

[0027] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures; however, the scope of protection of the present invention is not limited to the following embodiments.

[0028] The tooling structure used in the additive manufacturing method for preventing cracking of high-temperature high-performance alloys described in this invention is as follows: Figure 1 , Figure 2 As shown, it includes a heating device 1 capable of heating the substrate and a cooling device. The heating device includes a heating coil and a controller. The heating coil surrounds the substrate and provides auxiliary heating to the substrate during the preheating process before additive manufacturing and during the cooling process after additive manufacturing.

[0029] The cooling device includes a lower cooling fixture 3a surrounding the substrate and an upper cooling fixture 2a located on both sides of the additive part. The cooling medium of the lower cooling fixture 3a is liquid nitrogen, water, or gas, while the cooling medium of the upper cooling fixture 2a is air or an inert gas. Flow meters are installed on the cooling circuits of the lower cooling fixture 3a and the upper cooling fixture 2a to control the cooling efficiency. The flow meters can be gas flow meters or liquid flow meters, depending on the cooling composition. The upper cooling fixture 2a has several vents at different heights and metal plate switches that control the number of vents opening and closing.

[0030] The heating and cooling devices are used in the additive manufacturing process through the following steps:

[0031] S1: Preheating the substrate before additive manufacturing: Select a metal system or copper / aluminum alloy that does not react with the alloy of the additive part to be manufactured as the substrate, and clean it with acetone and alcohol. Preheat the substrate using a heating device to a temperature of 400-600℃, then turn off the heating device.

[0032] S2: Additive Manufacturing: Additive manufacturing is performed on the substrate 5 using a directional energy deposition equipment 4. During the additive manufacturing process, cooling is achieved through a lower cooling fixture surrounding the substrate and / or upper cooling fixtures located on both sides of the additive part. The cooling height of the upper cooling fixtures on both sides of the additive part increases with the height of the additive part, maintaining the substrate temperature within the range of 600-1000℃. Specifically, after additive manufacturing begins, the lower cooling fixture directly opens the cooling circuit for cooling. When the height of the additive part exceeds 7cm, the upper cooling fixture vents air to cool the additive part.

[0033] S3: Cooling process after additive manufacturing: After additive manufacturing is completed, turn on the heating device to assist in heating the substrate, so that the temperature of the substrate is slowly reduced to 200℃ at a cooling rate of 100℃ / 5min, and then turn off the heating device and air cool to room temperature.

[0034] In the above process, the heating device is positioned around the substrate to preheat the substrate before and after additive manufacturing, thereby reducing the temperature gradient and cooling rate, minimizing residual stress, and preventing crack formation. The cooling device is positioned on both sides of the additive part and around the substrate to cool the additive part in real time, controlling the thermal cycle of the additive part and the temperature gradient and cooling rate during the forming process. This avoids the directional energy melting of low-melting-point phases, preventing liquefaction cracks, and also reduces residual stress, thus preventing crack formation. The method described in this invention is applicable to directional energy deposition forming processes such as arc, electron beam, and plasma deposition.

[0035] Example 1:

[0036] This embodiment uses laser-directed energy deposition (LDED) as an example. LDED utilizes a high-power, high-density laser beam to locally melt the surface of the workpiece, forming a molten pool. Simultaneously, metal powder is fed into the molten pool, melting together with the substrate surface and then rapidly solidifying, thereby forming a dense deposition layer that is metallurgically bonded to the substrate and has a very low dilution rate. The LDED equipment used in this embodiment is existing equipment, and its details will not be elaborated further.

[0037] In this embodiment, the heating device is an induction heating device 1. The heating coil is located around the substrate and has a square structure, encircling the substrate twice. It uses electric heating and the heating temperature can be adjusted as needed. Both cooling fixtures use gas as the cooling medium, therefore gas flow meters are used for both. The upper cooling fixture is 20mm away from the additive part and is a cuboid 40mm*20mm*40mm in shape, with each layer being 10mm thick. Each layer has a vent in the middle and an outlet on the side. The vent in the middle can be controlled by pushing and pulling a metal plate. The bottom layer has an inlet on the other side. The lower cooling fixture 3a is close to the substrate and has an inlet and an outlet for air. An adjustable gas flow meter is located at the inlet of the lower cooling fixture 3a, allowing the gas flow rate to be adjusted according to the additive part temperature. The gas flow rate of the lower cooling fixture 3a can also be kept consistent with that of the upper cooling fixture to control the thermal circulation of the additive part and thus prevent cracking.

[0038] It also includes a temperature detection device 6 for detecting the temperature on both sides of the substrate. The temperature detection device is a contact thermometer, which includes a temperature probe and a temperature display. The temperature probe is used to detect the temperature on both sides of the substrate, and then transmits the detected temperature data to the temperature display. The temperature display calculates and controls the heating temperature of the heating coil and the flow rate of the cooling device in real time.

[0039] In this embodiment, a metal system that does not react with GH4169 is selected as the substrate. During the additive manufacturing process, the directional energy deposition layer adheres to the substrate after cooling, thus fixing the formed part to the substrate and improving the stability of the part during the forming process. After deposition is completed, the formed part is cut off from the substrate.

[0040] In step S1, before additive manufacturing, the substrate is cleaned with acetone and alcohol. Cleaning the substrate facilitates the adhesion between the molten layer and the substrate, improving the stability of the entire molded part. The substrate is preheated using a heating device with a heating power set to 300W. Heating is stopped when the temperature display reaches 500℃, and then the additive manufacturing experiment is conducted. After additive manufacturing is completed, the heating device is turned on at 100W for 30 seconds every time the temperature on the display drops by 100℃, until the temperature display shows a temperature below 200℃.

[0041] S2. In the additive manufacturing process, laser directional energy deposition equipment is used for additive manufacturing. The laser power is 3000W, the scanning speed is 10mm / s, the powder feed rate is 13g / min, and the gas flow rate is 8L / min. Helium is used for both protective and cooling gases. The cooling device synchronously cools the temperature of the additive part during printing to ensure that the substrate remains within a temperature range of 600-1000℃ during the printing process. This temperature can be controlled by the gas flow rate and the number of vents in the cooling fixture. The height of the vents in the fixture is 2-9mm lower than the current height of the printed part to prevent powder from being blown away and affecting the deposition quality. The specific number of vents and gas flow rate are shown in Table 1. The above printing steps are repeated to complete the additive manufacturing of the part. After manufacturing, the formed additive part is cut off from the substrate for fluorescence detection, wire cutting, heat treatment, and tensile testing. The heat treatment parameters are 980℃×1h + air cooling, 720℃×8h, furnace cooling at 50℃ / h to 620℃×8h, and air cooling.

[0042] Table 1 shows the relationship between printing height, number of vent holes, and gas flow rate.

[0043] 7～17 1 3 18～27 2 4 28～37 3 5 38～47 4 6

[0044] In the manufacturing process of additive parts of other sizes and materials, the actual cooling rate depends on the size of the printed structure and the thermal conductivity of the material, so the gas flow rate needs to be adjusted according to the actual situation.

[0045] S3: Cooling process after additive manufacturing: After additive manufacturing is completed, turn on the heating device to assist in heating the substrate, so that the temperature of the substrate is slowly reduced to 200℃ at a cooling rate of 100℃ / 5min, and then turn off the heating device and air cool to room temperature.

[0046] Example 2:

[0047] Additive manufacturing was performed using the same laser-directed energy deposition equipment as in Example 1, with a laser power of 1000W, a scanning speed of 5mm / s, a powder feed rate of 6g / min, and a gas flow rate of 6L / min. The process conditions described in the example—pre-additive heating, in-additive cooling, and post-additive cooling rate control—were used to perform GH4169 laser energy deposition to print an additive part 2 of the same size as in Example 1. The preheating temperature before additive manufacturing was 400℃, and other process parameters were consistent with those in Example 1, to verify the technical advantages of the above-described embodiments of the present invention in suppressing cracks and improving mechanical properties.

[0048] Example 3:

[0049] Additive manufacturing was performed using the same laser-directed energy deposition equipment as in Example 1, with a laser power of 6000W, a scanning speed of 15mm / s, a powder feed rate of 20g / min, and a gas flow rate of 10L / min. The GH4169 laser energy deposition was performed using the process conditions described in the example, which included pre-additive heating, in-additive cooling, and post-additive cooling rate control to prevent cracking. An additive part 3 of the same size as in Example 1 was printed. The pre-additive preheating temperature was 600℃, and other process parameters were consistent with Example 1, to verify the technical advantages of the above-described embodiments of the present invention in suppressing cracks and improving mechanical properties.

[0050] Comparative example:

[0051] Additive manufacturing was performed using the same laser-directed energy deposition equipment as in Example 1, with the process parameters remaining consistent. However, the process conditions described in the example, which involved pre-additive heating, in-additive cooling, and post-additive cooling rate control to prevent cracking, were not used for GH4169 laser energy deposition. An additive part of the same size as in Example 1 was printed to verify the technical advantages of the above-described embodiments of the present invention in suppressing cracks.

[0052] Results Comparison: The cracking conditions of Example 1 and the comparative example are as follows: Figure 3 and Figure 4 As shown, it can be observed that GH4169 printed using the method described in this invention shows no cracks under an optical microscope, while GH4169 printed without the method described in this invention shows cracks under an optical microscope. Furthermore, the GH4169 printed using this invention exhibits better forming characteristics. These results demonstrate that the method of this invention is significantly effective in suppressing cracks.

[0053] Tensile tests were conducted on the additive parts obtained in the examples. Since the comparative additive parts had cracks and could not be tested, the examples were compared with castings and forgings obtained by conventional methods. Table 2 compares the tensile properties of GH4169 castings, forgings, and the GH4169 additive parts obtained in the examples at room temperature (23°C). Table 3 compares the tensile properties of GH4169 forgings and the GH4169 additive parts obtained in the examples at high temperature (650°C). The additive parts of this example, used at both room temperature and high temperature, exhibit tensile strength, plasticity, and toughness similar to forgings, but superior to castings.

[0054] Table 2 Comparison of tensile properties of GH4169 castings and forgings with additive parts obtained in the examples at 23℃;

[0055]

[0056]

[0057] Table 3 Comparison of tensile properties of GH4169 forgings and additive parts obtained in the examples at 650℃;

[0058]

[0059] As can be seen from the above embodiments and comparative examples, the present invention effectively solves the problem of cracking in the additive manufacturing of high-temperature high-performance alloys by conventional methods, saves the high cost required for crack removal in the post-processing stage, provides process guidance and quality assurance for the additive manufacturing of high-temperature high-performance alloys, effectively improves the mechanical properties of additive parts, and is applicable to directional energy deposition forming such as electric arc, electron beam, and plasma.

[0060] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A directed energy deposition forming method to prevent cracking of high temperature high performance alloys, characterized by: Includes the following steps: S1: Substrate preheating: The substrate is preheated using a heating device to a temperature of 400-600℃, and then the heating device is turned off. S2: Additive manufacturing: Additive manufacturing is performed on a preheated substrate using directional energy deposition equipment. During the additive manufacturing process, the substrate is cooled by a lower cooling fixture surrounding the substrate and an upper cooling fixture located on both sides of the additive part. The cooling height of the upper cooling fixture located on both sides of the additive part increases with the increase of the height of the additive part, so that the temperature of the substrate is maintained within the temperature range of 600℃-1000℃. The cooling medium of the lower cooling fixture is liquid nitrogen, water, or gas, while the cooling medium of the upper cooling fixture is air or inert gas. Flow meters are installed on the cooling circuits of the lower and upper cooling fixtures to control the cooling efficiency. The upper cooling fixture has several air outlets at different heights and metal plate switches that control the number of air outlets opening and closing. The upper cooling fixture is 20mm apart from the additive part, and the air vents are arranged in a vertical row on the fixture, with a 10mm interval between two adjacent air vents. Specifically, after additive manufacturing begins, the lower cooling fixture directly opens the cooling circuit for cooling. When the height of the additive part is higher than 7mm, the upper cooling fixture vents air, and the height of the air outlet of the upper cooling fixture should be 2~9mm lower than the current height of the additive part. S3: Cooling process after additive manufacturing: After additive manufacturing is completed, turn on the heating device to assist in heating the substrate, so that the temperature of the substrate is slowly reduced to 200℃ at a cooling rate of 100℃ / 5min, and then turn off the heating device and air cool to room temperature.

2. The method of claim 1, wherein: The heating device is located around the substrate to provide auxiliary heating during the preheating of the substrate before additive manufacturing and the cooling process of the substrate after additive manufacturing; it includes a heating coil and a controller, with the heating coil located around the substrate.

3. The method of claim 1, wherein: For every 7mm increase in the height of the additive component, the control metal plate switch opens one more vent hole upwards.

4. The method of claim 1, wherein: The substrate is selected from metal systems or copper and aluminum alloys that do not react with the alloy of the additive parts to be manufactured; it is cleaned with acetone and alcohol before additive manufacturing.

5. The method of claim 1, wherein: In step S3, after the additive manufacturing is completed, the temperature display of the temperature detection device will turn on the heating device at 100W power for 30 seconds to assist heating of the substrate for every 100°C decrease in temperature, until the temperature display shows a temperature below 200°C.

6. The method of claim 1, wherein: The directional energy deposition forming is one of the following: electric arc, electron beam, and plasma directional energy deposition forming.

7. The directional energy deposition forming method for preventing cracking of high-temperature high-performance alloys according to claim 2, characterized in that: The directional energy deposition modeling is laser directional energy deposition modeling, with a laser power of 1000~6000W, a scanning speed of 5~15mm / s, a powder feeding rate of 6~20g / min, and a gas flow rate of 6~10L / min.

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