Method for additive manufacturing of large-size crack-free titanium-aluminum alloy

Abstract

The invention provides a method for additive manufacturing of a large-size crack-free titanium-aluminum alloy, and relates to the technical field of additive manufacturing of titanium-aluminum alloy composite materials. The method comprises the steps of setting of a medium-frequency induction heating device, deposition, rapid remelting, in-situ remelting and in-situ heat treatment. According to the method disclosed by the invention, the density of a deposited layer and the integrity of a workpiece are creatively and synergistically improved through an induction heating technology, high-speed remelting scanning of each layer of double laser beams, in-situ remelting and in-situ heat treatment, and the fatigue property, the mechanical property and other properties of the prepared large-size titanium-aluminum alloy are improved; the occurrence probability of thermal stress cracks is greatly reduced; the method is high in resource utilization rate, low in production cost, short in process, easy to operate, high in efficiency, uniform in component distribution of each deposition layer and beneficial to industrial large-scale production and popularization.

Description

Technical Field

[0001] The present invention relates to the technical field of additive manufacturing of titanium aluminide composites, and particularly to a method for additive manufacturing of large-size crack-free titanium aluminide alloys. Background Art

[0002] Titanium aluminide alloys are widely used in aerospace, automotive, and military fields due to their excellent mechanical properties and low density. In particular, the γ-TiAl phase in titanium aluminide alloys has attracted much attention due to its high-temperature strength and good oxidation resistance. However, the manufacturing of large-size titanium aluminide alloy components faces many challenges, especially in crack-free production.

[0003] Currently, laser additive manufacturing technology has made significant progress in the production of small titanium aluminide alloy components, such as aeroengine blades and high-performance structural components. However, when it comes to large-size titanium aluminide alloy components, problems such as cracks and pores are often encountered. Especially during the rapid cooling process of the material, the incidence of cracks increases significantly, which is mainly due to the thermal stress generated during the rapid solidification of the molten pool.

[0004] Laser melting in the prior art usually cannot perform remelting treatment within an appropriate time, resulting in stress cracks in the rapidly solidified molten pool. These cracks not only affect the mechanical properties of the material but also reduce the reliability of the final product. Therefore, there is a lack of effective in-situ repair technology to deal with the microcracks generated during the additive manufacturing process. Although traditional heat treatment methods can alleviate some problems, their adaptability and effectiveness for large-size components are still limited.

[0005] For example: Chinese Patent CN118080853A discloses a post-treatment method for improving the tensile properties of selective laser melted titanium aluminide alloys. This method uses pulsed current, external pressure, and high temperature to eliminate thermal cracks and reduce pores. However, although the process can refine grains, the range of grain size control is limited at different sintering temperatures, generally not exceeding the original powder size, and this powder metallurgy process will significantly increase the oxygen content, which will seriously reduce the mechanical properties of titanium aluminide alloys.

[0006] Chinese Patent CN103495729A discloses a laser solid forming method for large-size titanium aluminide-based alloys. This method first establishes a three-dimensional model of the titanium aluminide-based alloy and performs dissection, and then compiles a cladding control program; there are many control processes and process parameters. In order to avoid the increase of thermal stress, the structure of the basic cladding layer is adopted. Obviously, this method only reduces the thermal stress, but with the increase of the number of cladding layers, new thermal stress will inevitably be generated.

[0007] Chinese Patent CN107812941A discloses an in-situ preparation method and product of laser additive manufacturing aluminum alloy. This method involves adding other alloying elements and mixing and grinding them evenly with the raw alloy powder, screening and drying after spheroidizing to prepare an alloy substrate, and then performing laser additive manufacturing on this substrate. Although the metallurgical defects such as pores and cracks in the prepared aluminum alloy are few, the cost of the raw material powder consumed in the preparation process is high, and preheating the substrate will make the process complex. Summary of the Invention

[0008] In order to solve the technical problems in the prior art that there are cracks, pores in laser additive manufacturing of large-sized titanium aluminum alloy, the thermal stress caused by high cooling rate cannot be released well, the thermal stress defects are initially solved and gradually accumulate as the process progresses, the improvement of the composition of the raw material powder and preheating the substrate will result in high cost, it is difficult to effectively release the subsequent thermal stress, and the process becomes complex; therefore, the embodiments of the present invention provide a method for additive manufacturing of large-sized crack-free titanium aluminum alloy that can synergistically improve the density of the deposited layer and the integrity of the workpiece. The technical solution is as follows:

[0009] A method for additive manufacturing of large-sized crack-free titanium aluminum alloy, and the method for additive manufacturing of large-sized crack-free titanium aluminum alloy comprises the following steps:

[0010] S1. Setting of the intermediate frequency induction heating device: Set the intermediate frequency induction heating device around the titanium aluminum alloy block to be prepared, and adjust the working temperature of the induction heating device according to the heat treatment characteristics of the titanium aluminum alloy and the size of the titanium aluminum alloy block; and gradually lift the coil according to the deposition speed during the printing process.

[0011] S2. Deposition, rapid remelting, and in-situ remelting: The dual laser beam cooperative device includes a main laser beam scanning device for melting the titanium aluminum alloy powder and an auxiliary laser beam scanning device for rapid remelting. The main laser beam scanning device and the auxiliary laser beam scanning device are used in combination to deposit and rapidly remelt a layer of titanium aluminum alloy powder, and then the laser beam automatically performs the in-situ remelting process. The key to remelting lies in the setting of the laser power and the scanning speed, and then layer-by-layer additive manufacturing of the titanium aluminum alloy is repeated to finally obtain the additive manufactured titanium aluminum alloy.

[0012] S3. In-situ heat treatment: Perform in-situ heat treatment on the additive manufactured titanium aluminum alloy block to obtain large-sized crack-free titanium aluminum alloy.

[0013] Optionally, the heating power of the intermediate frequency induction heating device in S1 is 3 - 10 kW according to the size of the titanium aluminum alloy block to be prepared, and the induction heating coil is deformed into a cylindrical, square, or special-shaped shape according to the size of the titanium aluminum alloy block.

[0014] Optionally, when the size of the titanium-aluminum alloy block in S1 is below 3 cm × 3 cm × 3 cm, the heating power of the intermediate frequency induction heating device is not greater than 500 W, and the induction heating coil is deformed into a square shape and placed at the bottom; when the size of the titanium-aluminum alloy block is below 8 cm × 8 cm × 8 cm, the heating power of the intermediate frequency induction heating device is not greater than 2000 W, and the induction heating coil is deformed into a ring shape and placed around the sample; when the size of the titanium-aluminum alloy block is below 15 cm × 15 cm × 15 cm, the heating power of the intermediate frequency induction heating device is not greater than 5000 W, and the induction heating coil is deformed into the shape of the sample contour.

[0015] Optionally, the operating temperature of the induction heating device in S1 is 700 - 1000 °C. The specific temperature is adjusted according to the specific phase region of the titanium-aluminum alloy and the size of the block, and the lifting coil is lifted by a stepping motor.

[0016] Optionally, the average particle size of the titanium-aluminum alloy powder in S2 is between 45 - 100 μm; during the laser additive manufacturing process, the temperature of the block is monitored in real time, and a thermocouple or an infrared temperature sensor is used to ensure the uniformity of the temperature distribution; the fluctuation of the temperature gradient should not exceed ±200 °C, and the temperature feedback by the sensor is transmitted to the induction heating power supply through a PID control circuit to control its power to avoid cracks caused by local undercooling.

[0017] Optionally, in the main laser beam scanning device of S2, the main laser beam and in the auxiliary laser beam scanning device, the auxiliary laser beam perform energy management through different scanning speeds and powers; in the main laser beam scanning device, the main laser beam is protected by argon, the gas flow rate is 5 - 20 L / min, the laser power is 600 - 1200 W, the laser beam diameter is 1 - 3 mm, the scanning speed is 500 - 1000 mm / s, the main laser beam adopts an oscillation scanning frequency of 100 - 1000 Hz, and when the main laser beam turns, a corner acceleration strategy is adopted to avoid cracking, and a rounded corner scan is used for transition and the power is reduced by 50%; in the auxiliary laser beam scanning device, the auxiliary laser beam uses large defocusing and a small gas flow of 3 - 5 L / min; the laser power is 400 - 500 W, the laser beam diameter is 0.5 - 1 mm, and the scanning speed of the auxiliary laser beam in the scanning device is 1000 - 1500 mm / s; the power setting of in-situ remelting is 60 - 80% of the maximum laser power, and the scanning speed is set to 1500 mm / s to avoid stress cracks in the molten pool through rapid remelting.

[0018] Optionally, the power setting of in-situ remelting in S2 is set to 720 W to 960 W in a 1200 W system.

[0019] Optionally, in the main laser beam scanning device of S2, the path of the main laser beam and the path of the auxiliary laser beam in the auxiliary laser beam scanning device are consistent with the deposition path of the previous layer of material to avoid excessive path interference and ensure complete contact with the previous deposited layer during the remelting process; the main working area of the auxiliary laser beam is the middle and rear section of the melting path of the main laser beam, and the distance between the two laser beams is 2 - 5 mm to ensure that the molten pool undergoes secondary melting immediately after initial solidification and suppress microcracks caused by rapid solidification; the depth of in-situ remelting should be controlled within 0.5 - 0.2 mm to ensure a flat molten pool surface and full release of thermal stress; during the remelting process after each layer of material is deposited, the intermediate frequency induction heating device maintains a stable heating temperature, and the laser beam performs local heating on this basis. This strategy avoids remelting in areas that have not been fully melted, thus ensuring a reasonable distribution of laser energy and preventing excessive heat input from causing overheating or local undercooling of the molten pool.

[0020] Optionally, the path planning of the main laser beam and the auxiliary laser beam in S2 should ensure that no area is missed while avoiding excessive repeated scanning. During the remelting process after each layer of material is deposited, the induction heating device maintains a stable heating temperature, and the laser beam performs local heating on this basis. Induction heating can help maintain an appropriate material temperature before remelting and reduce the influence of thermal gradients on in-situ remelting.

[0021] Optionally, the main laser beam in the main laser beam scanning device of S2 and the auxiliary laser beam in the auxiliary laser beam scanning device need to cooperate closely. The scanning path of the main laser beam advances first, and then the auxiliary laser beam follows and performs repeated scanning of the same area. The main working area of the auxiliary laser beam is the path that has started to solidify but not fully solidified after being scanned by the main laser beam. The main laser beam adopts a serpentine or parallel linear scanning path, whose function is to evenly cover the area to be melted and ensure uniform melting of the material. The scanning path of the auxiliary laser beam should deviate from the path of the main laser beam by no more than 10%.

[0022] Optionally, in S2, the dual laser beams perform energy management through different scanning speeds and powers. The main laser beam provides a large amount of heat during initial melting, while the auxiliary laser beam reduces the power relatively (usually 60% - 80% of the power of the main laser beam), and only performs secondary melting on the areas that have been initially solidified, controlling the heat input not to be excessive to prevent overburning or grain coarsening.

[0023] Optionally, the in-situ heat treatment of S3 is annealing or aging treatment, with a temperature of 500 - 800 °C and a time of 2 - 4 h. This operation aims to further release residual stress and optimize the microstructure of the alloy through temperature-controlled annealing or aging treatment; the specific temperature depends on the composition of the titanium-aluminum alloy and the stress level generated during the additive manufacturing process. Generally, the initial treatment temperature is 650 °C, and the duration is 2 h to 4 h.

[0024] Optionally, during the additive manufacturing process, the heating rate of the intermediate frequency induction heating device is 5-10 °C / min to prevent new stresses from being generated due to rapid heating; after the in-situ heat treatment is completed, the cooling rate is 3-5 °C / min to ensure that the alloy does not develop thermal cracks or other defects due to sudden temperature changes during cooling.

[0025] The above technical solution has at least the following beneficial effects compared with the prior art:

[0026] In the above solution, the present invention proposes a method for additive manufacturing of large-sized crack-free titanium aluminide alloys, which can solve the technical problems in the prior art of laser additive manufacturing of large-sized titanium aluminide alloys, such as cracks, pores, the inability to effectively release the thermal stress caused by high cooling rates, the gradual accumulation of thermal stress defects that were initially solved as the process progresses, the high cost due to the improvement of raw material powder composition and preheating of the substrate, the difficulty in effectively releasing subsequent thermal stress, and the complexity of the process.

[0027] The present invention uses induction heating technology to raise the overall temperature of the printed block and adopts a dual-laser beam rapid remelting technology to successfully suppress the cracks generated due to stress concentration during the additive manufacturing process. The coordinated operation of the dual-laser beams effectively controls the cooling rate of the molten pool, avoids the stress crack problem during traditional rapid solidification, and greatly improves the integrity and service life of the workpiece.

[0028] The high-speed remelting scan of the dual-laser beams in the present invention can fully stir the surface molten pool, promote the further uniform distribution of materials in the surface molten pool, and perform an in-situ remelting process after the path that has started to solidify but not completely solidified after the main laser beam scans each layer of material, quickly repairing microcracks in a timely manner, improving the density of the deposited layer, and thus forming a high-quality crack-free titanium aluminide alloy.

[0029] The present invention uses an induction heating device to keep the substrate and the deposited layer at a suitable preheating temperature, effectively reducing the thermal stress caused by the temperature gradient during the cooling process, further reducing the risk of crack generation, and is particularly suitable for the manufacture of large-sized titanium aluminide alloy workpieces.

[0030] The present invention combines technologies such as induction heating, dual-laser beam high-speed remelting, and in-situ remelting to achieve an efficient additive manufacturing process for large-sized titanium aluminide alloys. The process of in-situ remelting to repair cracks is carried out synchronously with material deposition, reducing heat loss and time loss, avoiding additional post-treatment steps, simplifying the process flow, and improving production efficiency.

[0031] Through in-situ heat treatment, the present invention can further effectively eliminate the stress defects brought about by the high-efficiency additive manufacturing process inside the material, that is, by controlled-temperature annealing or aging treatment, further release the residual stress of large-sized titanium aluminide alloys and optimize the microstructure of the alloy.

[0032] In the present invention, the temperature is slowly increased and decreased by using induction heating or a heating furnace, ensuring that no new stress cracks or other defects are generated in the alloy during the heating and cooling processes due to rapid temperature changes.

[0033] In summary, compared with other traditional methods, the method of the present invention creatively synergistically improves the density of the deposited layer and the integrity of the workpiece through induction heating technology, high-speed remelting scanning and in-situ remelting, and in-situ heat treatment of each layer of the double laser beam, improves the fatigue performance, mechanical properties and other properties of the prepared large-size titanium aluminide alloy, and greatly reduces the occurrence probability of thermal stress cracks; this method has high resource utilization rate, low production cost, short process, easy operation, high efficiency, and uniform composition distribution of each deposited layer, which is conducive to large-scale industrial production and popularization. Description of the Drawings

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following-described drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0035] Figure 1 It is a schematic structural diagram of the device used in the method for additive manufacturing of a large-size crack-free titanium aluminide alloy of the present invention;

[0036] Figure 2 It is a physical diagram of the additive manufacturing of a large-size crack-free titanium aluminide alloy in Embodiment 1 of the present invention;

[0037] Figure 3 It is a physical diagram of the additive manufacturing of a large-size crack-free titanium aluminide alloy in Embodiment 2 of the present invention;

[0038] Figure 4 It is a physical diagram of the laser additive manufacturing of a large-size crack-free titanium aluminide alloy in Embodiment 3 of the present invention. Detailed Embodiments

[0039] The following will describe the technical solutions in the present invention with reference to the drawings.

[0040] In the embodiments of the present invention, words such as "exemplarily" and "for example" are used to represent examples, illustrations or explanations. Any embodiment or design solution described as "example" in the present invention should not be construed as being more preferred or having more advantages than other embodiments or design solutions. Exactly, the use of the word "example" is intended to present concepts in a specific manner. In addition, in the embodiments of the present invention, the meaning expressed by "and / or" can be both, or either one of the two can be selected.

[0041] In the embodiments of the present invention, "image" and "picture" can sometimes be used interchangeably. It should be noted that when the difference is not emphasized, their intended meanings are the same. "Of", "corresponding", and "corresponding to" can sometimes be used interchangeably. It should be noted that when the difference is not emphasized, their intended meanings are the same.

[0042] In the embodiments of the present invention, sometimes a subscript such as W1 may be written in a non-subscript form such as W1. When the difference is not emphasized, their intended meanings are the same.

[0043] To make the technical problems, technical solutions, and advantages to be solved by the present invention clearer, the following will be described in detail with reference to the accompanying drawings and specific embodiments.

[0044] A method for additive manufacturing of a large-sized crack-free titanium aluminum alloy, the method for additive manufacturing of a large-sized crack-free titanium aluminum alloy comprises the following steps:

[0045] S1. Setting of the intermediate frequency induction heating device: The intermediate frequency induction heating device is arranged around the titanium aluminum alloy block to be prepared, and the working temperature of the induction heating device is adjusted according to the heat treatment characteristics of the titanium aluminum alloy and the size of the titanium aluminum alloy block; and the coil is gradually lifted according to the deposition speed during the printing process;

[0046] S2. Deposition, rapid remelting, and in-situ remelting: The dual laser beam cooperation device includes a main laser beam scanning device for melting titanium aluminum alloy powder and an auxiliary laser beam scanning device for rapid remelting. The main laser beam scanning device and the auxiliary laser beam scanning device are used in combination to deposit and rapidly remelt a layer of titanium aluminum alloy powder, and then the laser beam automatically performs the in-situ remelting process. The key to remelting lies in the setting of the laser power and the scanning speed, and then the additive manufacturing of titanium aluminum alloy layer by layer is repeated to finally obtain the additively manufactured titanium aluminum alloy;

[0047] S3. In-situ heat treatment: The additively manufactured titanium aluminum alloy block is subjected to in-situ heat treatment to obtain a large-sized crack-free titanium aluminum alloy.

[0048] Specifically, the heating power of the intermediate frequency induction heating device in S1 is 3-10 kW according to the size of the titanium aluminum alloy block to be prepared, and the induction heating coil is deformed into a cylindrical shape, a square shape, or a special shape according to the size of the titanium aluminum alloy block.

[0049] In particular, when the size of the titanium-aluminum alloy block in S1 is below 3 cm × 3 cm × 3 cm, the heating power of the intermediate frequency induction heating device is not greater than 500 W, and the induction heating coil is deformed into a square and placed at the bottom; when the size of the titanium-aluminum alloy block is below 8 cm × 8 cm × 8 cm, the heating power of the intermediate frequency induction heating device is not greater than 2000 W, and the induction heating coil is deformed into a ring and placed around the sample; when the size of the titanium-aluminum alloy block is below 15 cm × 15 cm × 15 cm, the heating power of the intermediate frequency induction heating device is not greater than 5000 W, and the induction heating coil is deformed into the shape of the sample contour.

[0050] In particular, the operating temperature of the induction heating device in S1 is 700 - 1000 °C. The specific temperature is adjusted according to the specific phase region of the titanium-aluminum alloy and the size of the block, and the lifting coil is lifted by a stepping motor.

[0051] In particular, the average particle size of the titanium-aluminum alloy powder in S2 is between 45 - 100 μm; during the laser additive manufacturing process, the temperature of the block is monitored in real time, and a thermocouple or an infrared temperature sensor is used to ensure the uniformity of the temperature distribution; the fluctuation of the temperature gradient should not exceed ±200 °C, and the temperature feedback by the sensor is transmitted to the induction heating power supply through a PID control circuit to control its power, so as to avoid cracks caused by local supercooling.

[0052] In particular, in the main laser beam scanning device of S2, the main laser beam and in the auxiliary laser beam scanning device, the auxiliary laser beam perform energy management through different scanning speeds and powers; in the main laser beam scanning device, the main laser beam is protected by argon, the gas flow rate is 5 - 20 L / min, the laser power is 600 - 1200 W, the laser beam diameter is 1 - 3 mm, the scanning speed is 500 - 1000 mm / s, the main laser beam adopts an oscillation scanning frequency of 100 - 1000 Hz, and when the main laser beam turns, a corner acceleration strategy is adopted to avoid cracking, and a rounded corner scan is used for transition and the power is reduced by 50%; in the auxiliary laser beam scanning device, the auxiliary laser beam uses large defocusing and a small gas flow of 3 - 5 L / min; the laser power is 400 - 500 W, the laser beam diameter is 2 - 4 mm, and the scanning speed of the auxiliary laser beam in the scanning device is 1000 - 1500 mm / s; the power setting of in-situ remelting is 60 - 80% of the maximum laser power, and the scanning speed is set to 1500 mm / s to avoid stress cracks in the molten pool through rapid remelting.

[0053] In particular, the power setting of in-situ remelting in S2 is set to 720 W to 960 W in a system with a maximum laser power of 1200 W.

[0054] Specifically, in the main laser beam scanning device of S2, the path of the main laser beam coincides with the path of the auxiliary laser beam in the auxiliary laser beam scanning device, which is the same as the deposition path of the previous layer of material, to avoid excessive path interference and ensure full contact with the previous deposition layer during the remelting process; the main working area of the auxiliary laser beam is the middle and rear section of the melting path of the main laser beam, and the distance between the two laser beams is 2-5 mm to ensure that the molten pool undergoes secondary melting immediately after initial solidification and suppress microcracks caused by rapid solidification; the depth of in-situ remelting should be controlled within 0.5-0.2 mm to ensure a flat molten pool surface and full release of thermal stress; during the remelting process after each layer of material is deposited, the intermediate frequency induction heating device maintains a stable heating temperature, and the laser beam performs local heating on this basis. This strategy avoids remelting in areas that have not been fully melted, thus ensuring a reasonable distribution of laser energy and preventing excessive heat input from causing overheating or local undercooling of the molten pool.

[0055] Specifically, the path planning of the main laser beam and the auxiliary laser beam in S2 should ensure that no area is missed while avoiding excessive repeated scanning. During the remelting process after each layer of material is deposited, the induction heating device maintains a stable heating temperature, and the laser beam performs local heating on this basis. Induction heating can help maintain an appropriate material temperature before remelting and reduce the influence of thermal gradients on in-situ remelting.

[0056] Specifically, the main laser beam in the main laser beam scanning device of S2 and the auxiliary laser beam in the auxiliary laser beam scanning device need to cooperate closely. The scanning path of the main laser beam advances first, followed by the auxiliary laser beam, and repeated scanning of the same area is performed. The main working area of the auxiliary laser beam is the path that has started to solidify but not fully cured after being scanned by the main laser beam. The main laser beam adopts a serpentine or parallel linear scanning path, whose function is to evenly cover the area to be melted and ensure uniform melting of the material. The scanning path of the auxiliary laser beam should deviate from the path of the main laser beam by no more than 10%.

[0057] Specifically, in S2, the dual laser beams manage energy through different scanning speeds and powers. The main laser beam provides a large amount of heat during initial melting, while the auxiliary laser beam relatively reduces the power (usually 60%-80% of the power of the main laser beam), and only performs secondary melting on the areas that have been initially solidified, controlling the heat input so as not to be excessive and preventing overburning or grain coarsening.

[0058] Specifically, the in-situ heat treatment of S3 is annealing or aging treatment, with a temperature of 500-800 °C and a time of 2-4 h. This operation aims to further release residual stress and optimize the microstructure of the alloy through temperature-controlled annealing or aging treatment; the specific temperature depends on the composition of the titanium-aluminum alloy and the stress level generated during the additive manufacturing process. Generally, the initial treatment temperature is 650 °C, and the duration is 2 h to 4 h.

[0059] In particular, during the additive manufacturing process, the heating rate of the intermediate frequency induction heating device is 5-10 °C / min to prevent the generation of new stresses caused by rapid heating. After the in-situ heat treatment is completed, the cooling rate is 3-5 °C / min to ensure that no thermal cracks or other defects are caused by sudden temperature changes during the cooling of the alloy.

[0060] Example 1

[0061] A method for additive manufacturing of large-sized crack-free titanium aluminide alloys, preparing a cubic 4822 titanium aluminide alloy specimen with a specimen size of 50 50 50 mm, using the equipment as Figure 1 shown, the method for additive manufacturing of large-sized crack-free titanium aluminide alloys is as follows:

[0062] S1. Setting of the intermediate frequency induction heating device: The intermediate frequency induction heating device is arranged around the titanium aluminide alloy block to be prepared. The heating power is set to 3 kW according to the size of the titanium aluminide alloy sample to be prepared. The induction heating coil is deformed into a square according to the sample size, and the induction coil is sleeved around the sample. The coil is gradually lifted according to the deposition speed during the printing process, and the induction coil is lifted by a stepping motor. The operating temperature range of the induction heating device is 900 °C. After setting the temperature, the PID circuit will perform feedback adjustment according to the real-time temperature measured by the infrared thermometer.

[0063] S2. Setup of the dual-laser beam collaboration device: The dual-laser beam collaboration device includes a main laser beam scanning device for melting titanium-aluminum alloy powder and an auxiliary laser beam scanning device for rapid remelting. The main laser beam in the main laser beam scanning device and the auxiliary laser beam in the auxiliary laser beam scanning device perform energy management through different scanning speeds and powers. The main laser beam in the main laser beam scanning device is protected by argon gas. The gas flow rate is 5 L / min, the laser power is 700 W, the laser beam diameter is 1.5 mm, the scanning speed is 600 mm / s, the main laser beam adopts an oscillation scanning frequency of 300 Hz, and the main laser beam adopts a corner acceleration strategy to avoid cracking at the corner, uses rounded corner scanning for transition and reduces the power by 50%. The auxiliary laser beam in the auxiliary laser beam scanning device adopts large defocusing and a small gas flow rate of 3 L / min; the laser power is 200 W, the laser beam diameter is 2 mm, and the scanning speed of the auxiliary laser beam in the scanning device is 1000 mm / s. Then the laser beam automatically performs an in-situ remelting process. The key to remelting lies in the setting of the laser power and scanning speed. Then layer-by-layer additive manufacturing of titanium-aluminum alloy is repeated, and finally additive manufactured titanium-aluminum alloy is obtained. The laser power for in-situ remelting is 60% of the maximum laser power, and the scanning speed is 1500 mm / s. Among them, the average particle size of the titanium-aluminum alloy powder is 80 μm. During the laser additive printing process, the temperature of the block is monitored in real time, and a thermocouple or an infrared temperature sensor is used to ensure the uniformity of the temperature distribution. The fluctuation of the temperature gradient should not exceed ±200 °C, and the temperature feedback by the sensor is transmitted to the induction heating power supply through a PID control circuit to control its power.

[0064] The path of the main laser beam in the main laser beam scanning device and the path of the auxiliary laser beam in the auxiliary laser beam scanning device are consistent with the deposition path of the previous layer of material. The scanning path of the main laser beam advances first, and the auxiliary laser beam follows. The distance between the two laser beams is 3 mm, and repeated scanning of the same area is performed. The main working area of the auxiliary laser beam is the path that has started to solidify but not completely solidified after being scanned by the main laser beam. The main laser beam adopts a serpentine scanning path to ensure complete contact with the previous deposition layer during the remelting process. The scanning path of the auxiliary laser beam should deviate from the path of the main laser beam by no more than 10%. The depth of in-situ remelting should be controlled within 0.2 mm. During the in-situ remelting process after each layer of material deposition, the intermediate frequency induction heating device maintains a stable heating temperature, and the laser beam performs local heating on this basis.

[0065] S3. In-situ heat treatment: The additive manufactured titanium-aluminum alloy block is subjected to in-situ heat treatment. The temperature of the in-situ heat treatment is 600 °C and the time is 3 h to obtain a large-size crack-free titanium-aluminum alloy. The physical object is as Figure 2 shown.

[0066] During the additive manufacturing process of this embodiment, the heating rate of the intermediate frequency induction heating device is 5 °C / min, and after the in-situ heat treatment is completed, the cooling rate is 3 °C / min.

[0067] The density of the large-size crack-free titanium aluminide alloy prepared in this embodiment is 3.8 g / cm 3 , the tensile strength is 744 MPa, the yield strength is 681 MPa, the elongation is 1.2%, the tensile strength at 800 °C is 617 MPa, the yield strength is 504 MPa, and the elongation is 5%.

[0068] Example 2

[0069] A method for additive manufacturing of a large-size crack-free titanium aluminide alloy, preparing a square TNM titanium aluminide alloy specimen with a specimen size of 60 60 70 mm, using the equipment as Figure 1 shown, the method for additive manufacturing of the large-size crack-free titanium aluminide alloy is as follows:

[0070] S1. Setting of the intermediate frequency induction heating device: Set the intermediate frequency induction heating device around the titanium aluminide alloy block to be prepared. The heating power is set to 5 kW according to the size of the titanium aluminide alloy sample. The induction heating coil is deformed into a square according to the sample size, and the induction coil is sleeved around the sample, and the coil is gradually lifted according to the deposition speed during the printing process. The induction coil is lifted by a stepping motor; the working temperature range of the induction heating device is 950 °C. After setting the temperature, the PID circuit will perform feedback adjustment according to the real-time temperature measured by the infrared thermometer;

[0071] S2. Setup of the dual-laser beam collaborative device: The dual-laser beam collaborative device includes a main laser beam scanning device for melting titanium-aluminum alloy powder and an auxiliary laser beam scanning device for rapid remelting. The main laser beam in the main laser beam scanning device and the auxiliary laser beam in the auxiliary laser beam scanning device perform energy management through different scanning speeds and powers. The main laser beam in the main laser beam scanning device is protected by argon gas, with an air flow rate of 9 L / min, a laser power of 900 W, a laser beam diameter of 2 mm, a scanning speed of 800 mm / s, a 500 Hz oscillation scanning frequency, and a corner acceleration strategy to avoid cracking when turning the corner, and a fillet scanning transition with a 50% power reduction. The auxiliary laser beam in the auxiliary laser beam scanning device uses large defocusing and a small air flow rate of 4 L / min, a laser power of 350 W, a laser beam diameter of 2.5 mm, and a scanning speed of 1200 mm / s for the auxiliary laser beam in the scanning device. Then, the laser beam automatically performs an in-situ remelting process. The key to remelting lies in the setting of the laser power and scanning speed. Then, layer-by-layer additive manufacturing of titanium-aluminum alloy is repeated, and finally, additive manufacturing titanium-aluminum alloy is obtained. The laser power for in-situ remelting is 70% of the maximum laser power, and the scanning speed is 1500 mm / s. Among them, the average particle size of the titanium-aluminum alloy powder is 60 μm. During the laser additive printing process, the temperature of the block is monitored in real-time, and a thermocouple or an infrared temperature sensor is used to ensure the uniformity of the temperature distribution. The fluctuation of the temperature gradient should not exceed ±200 °C, and the temperature feedback by the sensor is transmitted to the induction heating power supply through a PID control circuit to control its power.

[0072] The path of the main laser beam in the main laser beam scanning device and the path of the auxiliary laser beam in the auxiliary laser beam scanning device are consistent with the deposition path of the previous layer of material. The main laser beam uses a serpentine scanning path. The scanning path of the main laser beam advances first, and the auxiliary laser beam follows. The distance between the two laser beams is 4 mm, and repeated scanning of the same area is performed. The main working area of the auxiliary laser beam is the path that has started to solidify but not fully solidified after being scanned by the main laser beam to ensure complete contact with the previous deposition layer during the remelting process. The scanning path of the auxiliary laser beam should deviate from the path of the main laser beam by no more than 10%. The depth of in-situ remelting should be controlled within 0.35 mm. During the remelting process after each layer of material deposition, the intermediate frequency induction heating device maintains a stable heating temperature, and the laser beam performs local heating on this basis.

[0073] S3. In-situ heat treatment: The additive manufacturing titanium-aluminum alloy block is subjected to in-situ heat treatment at a temperature of 700 °C for 3.5 h to obtain a large-sized crack-free titanium-aluminum alloy. The physical object is as Figure 3 shown.

[0074] During the additive manufacturing process of this embodiment, the heating rate of the intermediate frequency induction heating device is 8 °C / min, and after the in-situ heat treatment is completed, the cooling rate is 4 °C / min.

[0075] The density of the large-sized crack-free titanium aluminide alloy prepared in this embodiment is 4.1 g / cm 3 , the tensile strength is 708 MPa, the yield strength is 611 MPa, the elongation is 1.8%, the tensile strength at 800 °C is 629 MPa, the yield strength is 490 MPa, and the elongation is 6%.

[0076] Example 3

[0077] A method for additive manufacturing of a large-sized crack-free titanium aluminide alloy, preparing a square Ti45Al8Nb titanium aluminide alloy specimen with a specimen size of 90 90 70 mm, using the equipment as Figure 1 shown, the method for additive manufacturing of the large-sized crack-free titanium aluminide alloy is as follows:

[0078] S1. Setting of the intermediate frequency induction heating device: Set the intermediate frequency induction heating device around the titanium aluminide alloy block to be prepared. The heating power is set to 6 kW according to the size of the titanium aluminide alloy sample. The induction heating coil is deformed into a square according to the sample size, and the induction coil is sleeved around the sample, and the coil is gradually lifted according to the deposition speed during the printing process. The induction coil is lifted by a stepping motor; the working temperature range of the induction heating device is 1000 °C. After setting the temperature, the PID circuit will perform feedback adjustment according to the real-time temperature measured by the infrared thermometer;

[0079] S2. Setup of the dual-laser beam collaboration device: The dual-laser beam collaboration device includes a main laser beam scanning device for melting titanium-aluminum alloy powder and an auxiliary laser beam scanning device for rapid remelting. In the main laser beam scanning device, the main laser beam and in the auxiliary laser beam scanning device, the auxiliary laser beam perform energy management through different scanning speeds and powers. The main laser beam in the main laser beam scanning device is protected by argon gas, with an air flow rate of 10 L / min, a laser power of 1100 W, a laser beam diameter of 2.5 mm, a scanning speed of 1000 mm / s, a 700 Hz oscillation scanning frequency. When the main laser beam turns, a corner acceleration strategy is adopted to avoid cracking, and a rounded corner scanning transition is used with a 50% reduction in power. The auxiliary laser beam in the auxiliary laser beam scanning device uses large defocusing and a small air flow of 5 L / min; the laser power is 400 W, the laser beam diameter is 3 mm, and the scanning speed of the auxiliary laser beam in the scanning device is 1400 mm / s. Then the laser beam automatically performs an in-situ remelting process. The key to remelting lies in the setting of the laser power and scanning speed. Then layer-by-layer additive manufacturing of titanium-aluminum alloy is repeated, and finally additive manufactured titanium-aluminum alloy is obtained. The laser power for in-situ remelting is 80% of the maximum laser power, and the scanning speed is 1500 mm / s. Among them, the average particle size of the titanium-aluminum alloy powder is 100 μm. During the laser additive printing process, the temperature of the block is monitored in real time, and a thermocouple or an infrared temperature sensor is used to ensure the uniformity of the temperature distribution. The fluctuation of the temperature gradient should not exceed ±200 °C, and the temperature feedback from the sensor is transmitted to the induction heating power supply through a PID control circuit to control its power.

[0080] The path of the main laser beam in the main laser beam scanning device and the path of the auxiliary laser beam in the auxiliary laser beam scanning device are consistent with the deposition path of the previous layer of material. The main laser beam uses a serpentine scanning path. The scanning path of the main laser beam advances first, and the auxiliary laser beam follows. The distance between the two laser beams is 5 mm, and repeated scanning of the same area is performed. The main working area of the auxiliary laser beam is the path that has started to solidify but not completely solidified after being scanned by the main laser beam to ensure complete contact with the previous deposition layer during the remelting process. The scanning path of the auxiliary laser beam should deviate from the path of the main laser beam by no more than 10%. The depth of in-situ remelting should be controlled within 0.4 mm. During the remelting process after each layer of material deposition, the intermediate frequency induction heating device maintains a stable heating temperature, and the laser beam performs local heating on this basis.

[0081] S3. In-situ heat treatment: The additive manufactured titanium-aluminum alloy block is subjected to in-situ heat treatment at a temperature of 700 °C for 4 h to obtain a large-size crack-free titanium-aluminum alloy. The physical object is as Figure 4 shown.

[0082] During the additive manufacturing process of this embodiment, the heating rate of the intermediate frequency induction heating device is 10 °C / min, and after the in-situ heat treatment is completed, the cooling rate is 5 °C / min.

[0083] The density of the large-sized crack-free titanium aluminide alloy prepared in this embodiment is 4.2 g / cm 3 , the tensile strength is 853 MPa, the yield strength is 711 MPa, the elongation is 5%, the tensile strength at 800 °C is 740 MPa, the yield strength is 668 MPa, and the elongation is 7%.

[0084] For the above solution, the present invention proposes a method for additive manufacturing of large-sized crack-free titanium aluminide alloy, which can solve the technical problems in the prior art that laser additive manufacturing of large-sized titanium aluminide alloy has cracks, pores, the thermal stress caused by high cooling rate cannot be well released, the thermal stress defects are initially solved and gradually accumulate as the process progresses, the improvement of the composition of the raw material powder and the preheating substrate will increase the cost, it is difficult to effectively release the subsequent thermal stress, and the process becomes complicated.

[0085] The present invention uses induction heating technology to increase the overall temperature of the printed block, and adopts the double laser beam rapid remelting technology to successfully suppress the cracks generated due to stress concentration during the additive manufacturing process. The collaborative work of the double laser beams effectively controls the cooling rate of the molten pool, avoids the stress crack problem during traditional rapid solidification, and greatly improves the integrity and service life of the workpiece.

[0086] The high-speed remelting scan of the double laser beams in the present invention can fully stir the surface molten pool, promote the further uniform distribution of the materials in the surface molten pool, and perform an in-situ remelting process after the path that has started to solidify but not completely solidified scanned by the main laser beam of each layer of material, repair the micro-cracks in a timely and rapid manner, improve the density of the deposited layer, and thus form a crack-free high-quality titanium aluminide alloy.

[0087] The present invention uses an induction heating device to keep the substrate and the deposited layer at a suitable preheating temperature, effectively reduces the thermal stress caused by the temperature gradient during the cooling process, and further reduces the risk of crack generation, which is particularly suitable for the manufacturing of large-sized titanium aluminide alloy workpieces.

[0088] The present invention combines technologies such as induction heating, double laser beam high-speed remelting, and in-situ remelting to achieve an efficient additive manufacturing process for large-sized titanium aluminide alloy. The process of in-situ remelting and repairing cracks is synchronized with the material deposition, reducing heat loss and time loss, avoiding additional post-treatment steps, simplifying the process flow, and improving production efficiency.

[0089] Through in-situ heat treatment, the present invention can further effectively eliminate the stress defects brought about by the high-efficiency additive manufacturing process inside the material, that is, by controlled-temperature annealing or aging treatment, further release the residual stress of the large-size titanium-aluminum alloy, and optimize the microstructure of the alloy.

[0090] The present invention controls the temperature to rise and fall slowly by using induction heating or a heating furnace, ensuring that no new stress cracks or other defects are generated in the alloy during the heating and cooling processes due to rapid temperature changes.

[0091] In summary, compared with other traditional methods, the method of the present invention creatively synergistically improves the density of the deposited layer and the integrity of the workpiece through induction heating technology, high-speed remelting scanning and in-situ remelting, and in-situ heat treatment of each layer of the dual laser beam, improves the fatigue performance, mechanical properties and other properties of the prepared large-size titanium-aluminum alloy, and greatly reduces the occurrence probability of thermal stress cracks; this method has high resource utilization rate, low production cost, short process, easy operation, high efficiency, and uniform composition distribution of each deposited layer, which is conducive to large-scale industrial production and promotion.

[0092] It should be understood that the term "and / or" in this article is merely a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. Among them, A and B can be singular or plural. In addition, the character " / " in this article generally represents an "or" relationship between the associated objects before and after, but it may also represent an "and / or" relationship, which can be specifically understood with reference to the context before and after.

[0093] In the present invention, "at least one" means one or more, and "a plurality" means two or more. "At least one of the following items" or its similar expressions refer to any combination of these items, including any combination of single items or plural items. For example, at least one of a, b, or c can represent: a, b, c, a - b, a - c, b - c, or a - b - c, where a, b, and c can be single or multiple.

[0094] It should be understood that in various embodiments of the present invention, the magnitudes of the serial numbers of the above processes do not mean the sequence of execution. The execution sequence of each process should be determined by its function and internal logic, and should not constitute any limitation to the implementation process of the embodiments of the present invention.

[0095] The above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of changes or substitutions, which should all be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A method for additive manufacturing of large-size crack-free titanium aluminum alloy, characterized in that: The method for additive manufacturing of large-size crack-free titanium aluminum alloy comprises the following steps: S1. Setting of medium frequency induction heating device: Setting the medium frequency induction heating device around the titanium aluminum alloy block to be prepared, and adjusting the working temperature of the induction heating device according to the heat treatment characteristics of the titanium aluminum alloy and the size of the titanium aluminum alloy block; and gradually increasing the coil according to the deposition speed during the printing process; S2, deposition and rapid remelting, and in-situ remelting: The dual laser beam collaborative device includes a main laser beam scanning device for melting titanium aluminum alloy powder and an auxiliary laser beam scanning device for rapid remelting. The main laser beam scanning device and the auxiliary laser beam scanning device are used together to deposit and rapidly remelt a layer of titanium aluminum alloy powder, and then the laser beam automatically performs the in-situ remelting process. The key to remelting lies in the setting of laser power and scanning speed, and then the titanium aluminum alloy additive manufacturing is repeated layer by layer to finally obtain the additively manufactured titanium aluminum alloy; S3. In-situ heat treatment: The additively manufactured titanium-aluminum alloy block is subjected to in-situ heat treatment to obtain a large-sized crack-free titanium-aluminum alloy.

2. The method for additive manufacturing of large-size crack-free titanium aluminum alloy according to claim 1, characterized in that: The heating power of the medium frequency induction heating device of S1 is 3-10kW according to the size of the titanium aluminum alloy block to be prepared, and the induction heating ring deforms the titanium aluminum alloy block into a cylindrical, square or special shape according to the size of the titanium aluminum alloy block.

3. The method for additive manufacturing of large-size crack-free titanium aluminum alloy according to claim 2, characterized in that: When the size of the titanium-aluminum alloy block in S1 is less than 3cm×3cm×3cm, the heating power of the medium frequency induction heating device is not more than 500W, and the induction heating coil is deformed into a square and placed at the bottom; when the size of the titanium-aluminum alloy block is less than 8cm×8cm×8cm, the heating power of the medium frequency induction heating device is not more than 2000W, and the induction heating coil is deformed into a ring and placed around the sample; when the size of the titanium-aluminum alloy block is less than 15cm×15cm×15cm, the heating power of the medium frequency induction heating device is not more than 5000W, and the induction heating coil is deformed into the shape of the sample outline.

4. The method for additive manufacturing of large-size crack-free titanium aluminum alloy according to claim 1, characterized in that: The operating temperature of the induction heating device of S1 is 700-1000℃, and the lifting coil is lifted by a stepper motor.

5. The method for additive manufacturing of large-size crack-free titanium aluminum alloy according to claim 1, characterized in that: The average particle size of S2's titanium-aluminum alloy powder is between 45 and 100 μm. During the laser additive printing process, the block temperature is monitored in real time, and a thermocouple or infrared temperature sensor is used to ensure the uniformity of the temperature distribution. The fluctuation of the temperature gradient should not exceed ±200 °C, and the temperature feedback from the sensor is transmitted to the induction heating power supply through the PID control circuit to control its power.

6. The method for additive manufacturing of large-size crack-free titanium aluminum alloy according to claim 1, characterized in that: The main laser beam in the main laser beam scanning device of S2 and the auxiliary laser beam in the auxiliary laser beam scanning device perform energy management through different scanning speeds and powers; the main laser beam in the main laser beam scanning device is protected by argon gas, the air flow speed is 5-20L / min, the laser power is 600-1200W, the laser beam diameter is 1-3mm, the scanning speed is 500-1000mm / s, the main laser beam adopts an oscillation scanning frequency of 100-1000Hz, the main laser beam adopts a corner acceleration strategy to avoid cracking when turning a corner, and adopts a rounded corner scanning over-scanning and reduces the power by 50%; the auxiliary laser beam in the auxiliary laser beam scanning device adopts large defocusing and a small air flow of 3-5L / min; the laser power is 400-500W, the laser beam diameter is 0.5-1mm, and the scanning speed of the auxiliary laser beam in the scanning device is 1000-1500mm / s; the power of in-situ remelting is set to 60-80% of the maximum laser power, and the scanning speed is set to 1500mm / s.

7. The method for additive manufacturing of large-size crack-free titanium aluminum alloy according to claim 1, characterized in that: The paths of the main laser beam in the main laser beam scanning device of S2 and the auxiliary laser beam in the auxiliary laser beam scanning device are consistent with the deposition path of the previous layer of material. The main working area of ​​the auxiliary laser beam is the middle and rear sections of the melting path of the main laser beam. The distance between the two laser beams is 2-5mm, and the depth of in-situ remelting should be controlled at 0.5-0.2mm; during the remelting process after the deposition of each layer of material, the medium frequency induction heating device maintains a stable heating temperature, and the laser beam performs local heating on this basis.

8. The method for additive manufacturing of large-size crack-free titanium aluminum alloy according to claim 1, characterized in that: The main laser beam in the main laser beam scanning device of S2 and the auxiliary laser beam in the auxiliary laser beam scanning device need to work closely together. The scanning path of the main laser beam advances first, and the auxiliary laser beam follows, and repeats the scanning of the same area. The main working area of ​​the auxiliary laser beam is the path that has begun to solidify but not completely solidified after being scanned by the main laser beam. The main laser beam adopts a serpentine or parallel linear scanning path, and the scanning path of the auxiliary laser beam should deviate from the path of the main laser beam by no more than 10%.

9. The method for additive manufacturing of large-size crack-free titanium aluminum alloy according to claim 1, characterized in that: The in-situ heat treatment of S3 is annealing or aging treatment at a temperature of 500-800°C and a time of 2-4h.

10. The method for additive manufacturing of large-size crack-free titanium aluminum alloy according to claim 1, characterized in that: During the additive manufacturing process, the heating rate of the medium frequency induction heating device is 5-10℃ / min, and after the in-situ heat treatment is completed, the cooling rate is 3-5℃ / min.

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