A method for preparing TiAl alloy 3D printed blank isothermal forging formed aviation parts

Abstract

The present invention provides a method for preparing a TiAl alloy 3D printed blank isothermal forging formed aviation parts, which belongs to the field of material processing technology and comprises the following steps: step one, 3D printing to prepare the blank: using TiAl alloy powder as raw material, printing layer by layer according to a preset CAD model to obtain a TiAl alloy blank that is close to the final shape of the part; step two, isothermal forging to prepare the aviation part: the forging temperature is the α+γ dual phase region of the TiAl alloy. The present invention combines 3D printing technology with isothermal forging technology to achieve efficient and high-precision preparation of TiAl alloy materials. And the prepared TiAl alloy aviation parts have good comprehensive mechanical properties, which is convenient for subsequent machining. Large-sized TiAl alloy aviation key parts with fine grain structure and good high-temperature mechanical properties can be obtained at the same time.

Description

Technical Field

[0001] The invention relates to the technical field of material processing, and in particular to a method for preparing a TiAl alloy 3D printed blank isothermal forging formed aviation parts. Background Art

[0002] In recent years, with the upgrading of aircraft engines, advanced and new aircraft engines, such as high thrust-to-weight ratio turbofan engines, have put forward higher requirements on the organizational performance, dimensional accuracy, manufacturing cost and service life of large integral disks. TiAl alloy is a lightweight and high-temperature resistant alloy material with high strength, low density, good corrosion resistance and high temperature performance. It is widely used in aerospace, automobile, energy and other fields. Traditional TiAl alloy preparation processes mostly use casting, forging or machining, but these methods have the disadvantages of low material utilization, long processing cycle and high manufacturing cost.

[0003] Large TiAl alloy disks for aircraft engines, such as compressor disks, turbine disks, or ring-shaped parts, often require excellent organization and performance to adapt to extremely harsh working environments such as high temperature, high stress, high speed, and high-speed airflow due to the harsh working environment and complex forces. 3D printing TiAl alloy technology is an advanced additive manufacturing technology that builds three-dimensional objects by stacking materials layer by layer. It uses computer-aided design software to create a digital model of TiAl alloy parts, then slices the model into thin layers, and uses a 3D printer to accurately melt and solidify the TiAl alloy powder layer by layer according to the slice file, and finally builds the desired object.

[0004] However, although the existing 3D printing technology can realize the preparation of TiAl alloy, it still has the following technical deficiencies. The organization and performance of TiAl alloy integral disks that rely solely on 3D printing cannot meet the design and use requirements of aircraft engines. The main reasons are as follows:

[0005] 1. Insufficient printing accuracy and low surface quality: Due to the high melting point and high strength characteristics of TiAl alloy, cracking and other problems are prone to occur during the printing of complex parts due to concentrated thermal stress. Although selective laser melting (SLM) has high printing accuracy, TiAl is very easy to crack during the printing process due to the lack of a preheating process, and is not suitable for printing TiAl alloys. Laser directed energy deposition (DLD) and electron beam powder bed fusion (EB-PBF) can provide an insulating environment and can control the printing process so that TiAl does not crack, but the printing accuracy is not high. When the energy input of the laser or electron beam is unstable (insufficient capacity or excessive energy), the printing accuracy is difficult to guarantee.

[0006] 2. Influence of environmental protection gas powder blowing: In the argon protection environment during the layer-by-layer printing process, the central protection gas is easily mixed into the TiAl alloy powder, resulting in incomplete fusion of the powder and metallurgical defects such as pores. Hot isostatic pressing (HIP) is required for subsequent processing, and the process is complicated.

[0007] 3. Difficulty in releasing residual stress: The cooling rate during 3D printing is fast, and the residual stress inside 3D printed parts is large and difficult to release, which causes parts to crack easily or reduce their service life and poor service stability. Heat treatment is required to release internal stress. Even after a long period of annealing, the residual stress level is still higher than that of traditional forgings.

[0008] 4. Difficulty in subsequent processing: The blanks obtained through 3D printing often need to undergo subsequent machining to reach the final size requirements, which increases the difficulty and cost of processing.

[0009] Isothermal forging technology is a high-precision forming technology for difficult-to-deform materials such as TiAl alloys. This technology effectively solves the problems of uneven material deformation and cracking caused by temperature changes in the traditional forging process by forging at a specific constant temperature, so that difficult-to-process materials such as TiAl alloys can be precisely formed. In the isothermal forging process of TiAl alloys, the key is to control the deformation of the billet within a specific temperature range. This temperature range is usually determined based on the thermoplastic properties of the material to ensure that the material has sufficient plasticity and low deformation resistance during the deformation process. By precisely controlling the forging temperature and deformation rate, isothermal forging technology can achieve high-precision forming of TiAl alloys while ensuring the excellent performance of the material.

[0010] However, isothermal forging also has some disadvantages:

[0011] 1. During the forging process, the grains tend to grow larger, resulting in coarse grains and reduced mechanical properties of parts.

[0012] 2. Forging blanks are required: Compressor and other discs or ring parts have an internal through hole in the center after being processed into parts. If parts are prepared by forging alone, the blank waste rate is high, the production cycle is long, and the processing efficiency is low. The deformation rate selected for isothermal forging is low, and it is usually carried out within a lower range of the working speed of the movable crossbeam, which leads to low processing efficiency.

[0013] Therefore, the present invention combines the above two material preparation processes, quickly forms a near-net-size billet through 3D printing, and forms the final parts by isothermal forging, making full use of the advantages of isothermal forging, eliminating the residual stress inside large parts, saving raw material billets, and the prepared TiAl alloy aviation parts have good comprehensive mechanical properties, which is convenient for subsequent machining. Large-sized TiAl alloy aviation key parts with fine grain structure and good high-temperature mechanical properties can be obtained at the same time. Summary of the invention

[0014] The present invention provides a TiAl alloy preparation method using a combination of 3D printing technology and isothermal forging technology, which combines the characteristics of the two technologies and aims to achieve efficient and high-precision preparation of TiAl alloys. It can solve the problems of insufficient 3D printing accuracy and difficulty in releasing residual stress in the prior art, and improve the preparation efficiency and comprehensive performance of large TiAl alloy aviation parts.

[0015] To achieve the above object, the present invention provides the following technical solutions:

[0016] A method for preparing a TiAl alloy 3D printed blank isothermal forging formed aviation parts, comprising the following steps:

[0017] Step 1: Prepare the blank by 3D printing: Use TiAl alloy powder as raw material and print layer by layer according to the preset CAD model to obtain a TiAl alloy blank that approximates the final shape of the part.

[0018] Optionally, the TiAl alloy blank is printed by electron beam powder bed fusion (EB-PBF) or laser directed energy deposition (DLD). The two process steps and their corresponding process parameters are as follows:

[0019] Optionally, the TiAl alloy blank is printed by an electron beam powder bed fusion (EB-PBF) process, which specifically includes the following steps:

[0020] 1) Place the TiAl pre-alloyed powder into the powder bin of the EB-PBF equipment and set the powder feeding mode to single-side powder feeding;

[0021] 2) Mark the center position on the surface of the base plate and level the base plate;

[0022] 3) Make the forming chamber and high-voltage electron gun in a high vacuum state, and calibrate, calibrate and center the high-voltage electron beam after reaching the set vacuum degree;

[0023] 4) Import the printed model into the slicing software for slicing optimization;

[0024] 5) Select TiAl pre-alloyed powder corresponding to the equipment process parameters and set the melting parameters;

[0025] 6) Start printing after preheating, and take out the titanium aluminum alloy billet after printing is completed.

[0026] Optionally, the particle size distribution of the TiAl pre-alloyed powder in step 1) is 45-150 μm. The material of the TiAl pre-alloyed powder in the embodiment is Ti45Al8Nb or Ti48Al2Cr2Nb. Selecting single-side powder feeding can effectively avoid powder adhesion caused by powder splashing during printing.

[0027] Optionally, the printing base plate described in step 2) has a size of 210 mm×210 mm and is made of stainless steel. The reason is that stainless steel has fast heat conduction and does not deform during the forming process below 1150°C.

[0028] Optionally, in step 3), the vacuum pressure of the molding chamber is 2-3×10 -3 mbar, electron gun vacuum pressure ≥5×10 - 5 mbar. The above vacuum environment can effectively prevent the material from oxidation.

[0029] Optionally, in step 4), the selected profile melt width d 熔道 =0.2-1mm, L 补偿 =0.1-0.3mm; filling channel width d 填充 =0.5-2mm, β overlap coefficient is 0.5-1.2, l 搭接 =0.1-0.2mm. The slicing optimization method can ensure the compactness of the filling and contour overlap.

[0030] Optionally, in step 5), the specific melting parameters are as follows: layer thickness is 50 μm, base plate preheating temperature: 1050-1150°C, powder bed preheating temperature: 950-1050°C, scanning speed (v) is 300-12000 mm / s, beam current (I) is 2-20 mA. Different scanning line lengths can be used to use the optimal energy density per unit distance according to the slice size of the model to prevent bulges and holes caused by excess and insufficient energy.

[0031] Optionally, a TiAl alloy blank is printed by laser directed energy deposition (DLD) process, which specifically includes the following steps:

[0032] 1) Preparation of pre-alloyed powder: TiAl round rod ingots were prepared by suspension melting method, and then TiAl pre-alloyed powder was obtained by rotating electrode method;

[0033] 2) Preparation before printing: First clean the surface of the substrate, then dry the pre-alloyed powder in step 1), and finally put the alloy material powder with a thermal expansion coefficient similar to that of the TiAl alloy and easy to form and the dried TiAl alloy powder into two powder feeding tubes respectively;

[0034] 3) Substrate preheating: Before starting pre-printing, the substrate cleaned in step 2) is heated in situ by laser, and when it reaches a red-hot state, a red-hot substrate is obtained;

[0035] 4) Pre-printing: feeding the alloy material powder having a thermal expansion coefficient similar to that of the TiAl alloy and being easy to form in step 2), and performing laser printing on the substrate in the red-hot state in step 3) to obtain a pre-printed material;

[0036] 5) Post-printing and cutting: When the residual stress in step 4) is completely released, switch the powder feeding tube, stop feeding the alloy material powder with a thermal expansion coefficient similar to that of the TiAl alloy and easy to form in step 2), and switch to feeding the dried TiAl alloy powder in step 2), continue laser printing on the pre-printed material, and finally use wire cutting to remove the pre-printed material at the bottom to obtain a high-tensile strength TiAl alloy billet with a desired shape and no macro cracks on the surface.

[0037] Optionally, in step 1), the diameter of the TiAl round rod ingot is 100 mm. The material of the TiAl pre-alloyed powder in the embodiment is Ti45Al8Nb or Ti48Al2Cr2Nb.

[0038] Optionally, in step 2), the material of the substrate is TC4 titanium alloy. The alloy material powder that is similar in thermal expansion coefficient to TiAl alloy and easy to form is TC4 or other titanium alloy powder. The surface cleaning of the substrate includes: grinding the substrate with an angle grinder to remove the oxide film, then wiping the surface with acetone to remove oil stains; then placing the cleaned substrate into a coaxial powder feeding additive manufacturing device; the drying process is carried out in a vacuum drying oven, the drying temperature is 80-200°C, and the insulation time is 10-30h.

[0039] Optionally, in step 4), the process parameters of laser printing are: laser power 400-1200W, printing powder feeding rate 1.5-4g / min, printing rate 8-15mm / s; until the residual stress is completely released, at which time the height of the pre-printed material is 10mm.

[0040] Step 2: Isothermal forging to prepare aviation parts: The forging temperature is in the α+γ dual-phase region of TiAl alloy, such as 1160-1250°C. In this temperature range, the microstructure shows multi-phase coexistence, which is conducive to grain refinement by deformation, providing fine-grained pre-parts for subsequent production.

[0041] Optionally, the aviation parts are prepared by atmospheric isothermal forging or vacuum isothermal forging.

[0042] Optionally, the aviation parts are prepared by atmospheric isothermal forging, including placing the TiAl alloy billet obtained in the above step 1 (the billet can be prepared by the EB-PBF process or the DLD process) into an isothermal forging press, and controlling parameters such as the forging temperature and strain rate to keep the material under constant temperature conditions for plastic deformation, thereby obtaining a TiAl alloy part of the final shape.

[0043] Optionally, the aviation parts are prepared by atmospheric isothermal forging, which specifically includes the following steps:

[0044] (1) Material and mold preparation: Lubricating coating is sprayed on the periphery of the TiAl alloy blank obtained by 3D printing, and a release agent is sprayed on the inner surface of the molybdenum alloy mold. Both the lubricating material and the release agent are selected to be high-temperature resistant boron nitride powder.

[0045] (2) Material preheating: Place the blank into a heating furnace and heat it to the target temperature of 1160-1250°C at a heating rate of 10-50°C / s. Keep the temperature for 30-120 minutes to keep the temperature inside and outside the material uniform and consistent.

[0046] (3) Material loading: The preheated blank is quickly transferred to the lower die of the isothermal forging press, and asbestos is wrapped around the die for insulation.

[0047] (4) Forging process: By controlling the speed of the press head, the speed is 0.001-10s -1 The strain rate causes the TiAl alloy billet to undergo plastic deformation under isothermal conditions and is forged until the upper and lower dies are in contact, thereby obtaining a TiAl alloy forging billet with a target shape.

[0048] (5) Cooling annealing: After forging is completed, the TiAl alloy forging billet is placed in a heating furnace and cooled to room temperature along with the furnace.

[0049] (6) Subsequent processing: The TiAl alloy component forging blank parts after isothermal forging are post-processed, including cutting, grinding, polishing and other steps to obtain the final product. In addition, subsequent processes such as surface treatment and heat treatment can be carried out as needed to further improve the performance and service life of the parts to meet the requirements of the final product.

[0050] Optionally, vacuum isothermal forging is used to prepare aviation parts, including placing the TiAl alloy billet obtained in the above step 1 (the billet can be prepared by the EB-PBF process or the DLD process) into a vacuum isothermal forging device, and controlling parameters such as the forging temperature and strain rate to keep the material under constant temperature conditions for plastic deformation, thereby obtaining a TiAl alloy forging billet of a final shape.

[0051] Optionally, the aviation parts are prepared by vacuum isothermal forging, which specifically includes the following steps:

[0052] (1) Material and mold preparation: Lubricating coating is sprayed on the outer periphery of the blank obtained by 3D printing, and a release agent is sprayed on the inner surface of the mold. Both the lubricating material and the release agent are selected to be high-temperature resistant boron nitride powder.

[0053] (2) Material loading: Place the 3D printed blank and mold into the furnace chamber of the vacuum isothermal forging equipment, ensure that the position and placement of the materials are correct, and then close the furnace door.

[0054] (3) Vacuuming: Start the mechanical pump, open the roughing valve, and start vacuuming. Wait until the vacuum degree reaches 7.0×10 2 Pa, open the fore valve and molecular pump, and finally make the vacuum degree of the chamber reach 2~3×10 -2 Pa and hold.

[0055] (4) Material preheating: Start the heating power supply, heat up to the target temperature of 1160-1250℃ at a heating rate of 5-20℃ / s, and keep warm for 30-60 minutes to keep the temperature inside and outside the material uniform and consistent.

[0056] (5) Forging process: Start the forging press and control the speed of the forging head to ≤0.1s -1 The strain rate causes the TiAl alloy billet to undergo plastic deformation under isothermal conditions and be forged until the upper and lower dies are in contact to obtain a TiAl alloy forging billet of the desired part shape.

[0057] (6) Cooling annealing: After forging is completed, turn off the heating power supply, wait for the TiAl alloy forging billet and the mold to cool to room temperature with the furnace, and then take out the TiAl alloy forging billet.

[0058] (7) Subsequent processing: The TiAl alloy parts after isothermal forging are post-processed, including cutting, grinding, polishing and other steps to obtain the final product. In addition, subsequent processes such as surface treatment and heat treatment can be carried out as needed to further improve the performance and service life of the parts to meet the requirements of the final product.

[0059] Optionally, in step (1), the vacuum isothermal forging die is made of high-purity hard graphite, and includes an upper die, a lower die and a pad.

[0060] After completing steps 1 and 2 above, you can proceed to step 3: quality inspection and evaluation, including:

[0061] (1) Quality inspection: Comprehensive inspection and evaluation of TiAl alloy aviation parts obtained by isothermal forging to ensure that their dimensional accuracy, mechanical properties, surface quality, etc. meet the design requirements and usage standards.

[0062] (2) Finished product storage: Qualified TiAl alloy aviation parts are packaged, labeled and stored for subsequent use or shipment.

[0063] The present invention also provides TiAl alloy aviation parts prepared by the method.

[0064] The present invention combines 3D printing technology with isothermal forging technology to achieve efficient and high-precision preparation of TiAl alloy materials. The key points of the technology are:

[0065] 1. During the 3D printing process, it is necessary to select appropriate printing parameters and powder materials to ensure the dimensional accuracy and surface quality of the preform.

[0066] 2. During the isothermal forging process, the heating and cooling rates need to be strictly controlled to avoid excessive grain growth and defects.

[0067] The beneficial effects brought about by the technical solution provided by the present invention include at least:

[0068] 1. Improved printing accuracy: By optimizing 3D printing process parameters and selecting high-performance printing equipment, the printing accuracy of TiAl alloy can be significantly improved to meet the needs of high-precision applications.

[0069] 2. Improved production efficiency: The use of isothermal forging technology can achieve rapid forming while maintaining material properties, thereby improving production efficiency.

[0070] 3. High material utilization rate: 3D printing can produce blanks of similar shapes, reducing material waste and improving production efficiency.

[0071] 4. Reduce the difficulty and cost of subsequent processing: The final shape of titanium-aluminum alloy parts can be directly obtained through isothermal forging technology, which reduces the subsequent mechanical processing links and reduces the difficulty and cost of processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0072] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0073] Figure 1 The present invention provides a flow chart of a method for preparing a TiAl alloy 3D printed blank isothermal forging formed aviation parts. DETAILED DESCRIPTION

[0074] In order to make the technical problems, technical solutions and advantages to be solved by the present invention more clear, a detailed description will be given below with reference to the accompanying drawings and specific embodiments.

[0075] Figure 1 The present invention provides a flow chart of a method for preparing an aviation part formed by isothermal forging of a TiAl alloy 3D printed blank, comprising the following steps:

[0076] 1. Raw material preparation: storage and pretreatment of TiAl alloy powder. After pretreatment, the raw materials are ready to enter the 3D printing equipment.

[0077] 2. 3D printing blank: The raw materials are stacked layer by layer according to the preset model under the method of powder feeding or powder spreading, and 3D printing is performed to form a TiAl alloy blank of a preset shape.

[0078] 3. Isothermal forging parts: Isothermal forging equipment includes forging dies, heating systems and pressure control systems. The heating system ensures that the material maintains a constant temperature during the forging process, and the pressure control system controls the pressure during the forging process. This process requires ensuring that the material undergoes large plastic deformation under a certain temperature condition to obtain TiAl alloy forging billets.

[0079] 4. Post-processing: The TiAl alloy forging blank after forging is subjected to necessary post-processing, such as heat treatment and machining (such as grinding and polishing), etc., to meet the requirements of the final product and obtain TiAl alloy aviation parts.

[0080] Example 1: EB-PBF printing + vacuum isothermal forging

[0081]

Step 1: EB-PBF printing TiAl alloy billet

[0082] (1) Take 40 kg of Ti48Al2Cr2Nb pre-alloyed powder with a particle size distribution of 45-150 μm and put it into the powder bin of the EB-PBF equipment. Set the powder feeding mode to single-side powder feeding.

[0083] (2) Select a base plate with a size of 210 mm × 210 mm, mark the center position, and level it;

[0084] (3) The high vacuum state of the forming chamber and high-voltage electron gun is obtained, and the vacuum pressure of the forming chamber is 2-3×10 -3 mbar, the vacuum pressure of the electron gun is not less than 5×10 -5 mbar; after reaching the vacuum degree, the high voltage electron beam is calibrated, calibrated and centered.

[0085] (4) Import the printed STL model into Magics slicing software for slicing optimization, and select the contour melt width d 熔道 =0.5mm, L 补偿 =0.2mm; Filling channel width d 填充 =1mm, β overlap coefficient is selected as 0.8, l 搭接 =0.15mm.

[0086] (5) Select Ti48Al2Cr2Nb pre-alloyed powder corresponding to the equipment process parameters, and its specific parameters are as follows: layer thickness is selected as 50μm, base plate preheating temperature: 1050-1100℃, powder bed preheating temperature: 950-1000℃, scanning speed (v) is 1.8-2.3m / s, and beam current (I) is 5.4-8.6mA. The process parameters for setting different energy densities according to the scanning line length are shown in Table 1:

[0087] Table 1

[0088]

[0089] (6) Start preheating and printing. After printing is completed, take out the TiAl alloy billet. The billet structure is a dual-state structure (DP) with a layer size of 13 μm, and proceed to the next step.

[0090] [Step 2: Vacuum isothermal forging to prepare aviation parts]

[0091] (1) Material and mold preparation: The material of the vacuum isothermal forging mold is high-purity hard graphite, including the upper mold, the lower mold, and the pad. The lubricating coating is sprayed on the outer periphery of the blank obtained by 3D printing, and the mold release agent is sprayed on the inner surface of the mold. The lubricating material and the mold release agent are both selected as high-temperature resistant boron nitride powder.

[0092] (2) Material loading: Place the 3D printed blank, mold and pad into the furnace chamber of the vacuum isothermal forging equipment, ensure that the position and placement of the materials are correct, and then close the furnace door.

[0093] (3) Vacuuming: Start the mechanical pump, open the roughing valve, and start vacuuming. Wait until the vacuum degree reaches 7.0×10 2Pa, open the fore valve and molecular pump, and finally make the vacuum degree of the chamber reach 2~3×10 -2 Pa and hold.

[0094] (4) Material preheating: Start the heating power supply, heat up to 1160℃ at a heating rate of 10℃ / s, and keep warm for 45 minutes to keep the temperature inside and outside the material uniform and consistent.

[0095] (5) Forging process: Start the forging press and control the speed of the forging head at 0.001s -1 The strain rate causes the TiAl alloy billet to undergo plastic deformation under isothermal conditions and be forged until the upper and lower dies contact to obtain the desired shape of the TiAl alloy part.

[0096] (6) Cooling annealing: After forging is completed, turn off the heating power supply. After the TiAl alloy parts and molds are cooled to room temperature with the furnace, take out the TiAl alloy forging billet. The performance indicators are shown in Table 3.

[0097] (7) Subsequent processing: The TiAl alloy forging blank after isothermal forging is subjected to post-processing, including cutting, grinding, polishing and other steps to obtain the final product. In addition, subsequent processes such as surface treatment and heat treatment can be carried out as needed to further improve the performance and service life of the parts to meet the requirements of the final product.

[0098] Example 2: EB-PBF printing + atmospheric isothermal forging

[0099]

Step 1: EB-PBF printing TiAl alloy billet

[0100] (1) Take 40 kg of Ti48Al2Cr2Nb pre-alloyed powder with a particle size distribution of 45-150 μm and put it into the powder bin of the EB-PBF equipment. Set the powder feeding mode to single-side powder feeding.

[0101] (2) Select a base plate with a size of 210 mm × 210 mm, mark the center position, and level it;

[0102] (3) The high vacuum state of the forming chamber and high-voltage electron gun is obtained, and the vacuum pressure of the forming chamber is 2-3×10 -3 mbar, the vacuum pressure of the electron gun is not less than 5×10 -5 mbar; after reaching the vacuum degree, the high voltage electron beam is calibrated, calibrated and centered.

[0103] (4) Import the printed STL model into Magics slicing software for slicing optimization, and select the contour melt width d 熔道 =0.5mm, L 补偿 =0.2mm; Filling channel width d 填充=1mm, β overlap coefficient is selected as 0.8, l 搭接 =0.15mm.

[0104] (5) Select Ti48Al2Cr2Nb pre-alloyed powder corresponding to the equipment process parameters, and its specific parameters are as follows: layer thickness is selected as 50μm, base plate preheating temperature: 1050-1100℃, powder bed preheating temperature: 950-1000℃, scanning speed (v) is 1.8-2.3mm / s, and beam current (I) is 5.4-8.6mA. The process parameters for setting different energy densities according to the scanning line length are shown in Table 2:

[0105] Table 2

[0106]

[0107] (6) Start preheating and printing. After printing is completed, take out the TiAl alloy billet. The billet structure is a dual-state structure (DP) with a layer size of 13 μm, and proceed to the next step.

[0108] The preferred selection of single-sided powder feeding in step (1) can effectively avoid powder adhesion caused by powder splashing during the printing process.

[0109] [Step 2: Preparation of aviation parts by atmospheric isothermal forging]

[0110] (1) Material and mold preparation: Lubricating coating is sprayed on the periphery of the TiAl alloy blank obtained by 3D printing, and a release agent is sprayed on the inner surface of the molybdenum alloy mold. Both the lubricating material and the release agent are selected to be high-temperature resistant boron nitride powder.

[0111] (2) Material preheating: Place the blank in a heating furnace, heat it to 1160°C at a heating rate of 10°C / s, and keep it warm for 45 minutes to keep the temperature inside and outside the material uniform and consistent.

[0112] (3) Material loading: The preheated blank is quickly transferred to the lower die of the isothermal forging press, and asbestos is wrapped around the die for insulation.

[0113] (4) Forging process: By controlling the speed of the punch, the forging speed is 0.1s -1 The strain rate causes the TiAl alloy billet to undergo plastic deformation under isothermal conditions and is forged until the upper and lower dies contact to obtain a TiAl alloy part with a target shape.

[0114] (5) Cooling annealing: After forging, the TiAl alloy forging billet is placed in a heating furnace and cooled to room temperature. The performance indicators are shown in Table 3.

[0115] (6) Subsequent processing: The TiAl alloy forging blank after isothermal forging is subjected to post-processing, including cutting, grinding, polishing and other steps to obtain the final product. In addition, subsequent processes such as surface treatment and heat treatment can be carried out as needed to further improve the performance and service life of the parts to meet the requirements of the final product.

[0116] Example 3: DLD printing + vacuum isothermal forging

[0117]

Step 1: DLD printing TiAl alloy billet

[0118] (1) Preparation of pre-alloyed powder

[0119] A TiAl round rod ingot with a diameter of 100 mm is prepared by a suspension smelting method, and then a pre-alloyed powder is prepared by a rotating electrode method; the pre-alloyed powder is Ti45Al8Nb, wherein the Al content is 45%, the Nb content is 8%, and the balance is Ti and other inevitable impurities.

[0120] (2) Preparation before printing

[0121] The surface of the substrate is first cleaned. Specifically, before printing, the substrate is grinded with an angle grinder to remove the oxide film, and then the surface is wiped with acetone to remove oil stains; the cleaned substrate is then placed in a coaxial powder feeding additive manufacturing device; the pre-alloyed powder of (1) is then dried in a vacuum drying oven at a temperature of 200°C for 22 hours to obtain a dry TiAl alloy powder; finally, an alloy material powder having a thermal expansion coefficient similar to that of the TiAl alloy and being easy to form and a dry TiAl alloy powder are placed in two powder feeding tubes respectively; wherein: the material of the substrate is TC4 titanium alloy.

[0122] (3) Substrate preheating

[0123] Before starting pre-printing, the cleaned substrate (2) is in-situ heated by a laser, and when the substrate reaches a red-hot state, a substrate in a red-hot state is obtained;

[0124] (4) Pre-printing

[0125] The alloy material powder having a thermal expansion coefficient similar to that of the TiAl alloy and being easy to form, such as TC4 powder, in (2) is fed and laser printed on the red-hot substrate in (2). The process parameters of the laser printing are: laser power 900 W, printing powder feeding rate 2.5 g / min, and printing rate 12 mm / s; until the residual stress is completely released, the height of the pre-printed material is 10 mm, and the pre-printed material is obtained;

[0126] (5) Post-printing and cutting

[0127] When the residual stress in (4) is completely released, the powder feeding cylinder is switched to stop feeding the alloy material powder with a thermal expansion coefficient similar to that of the TiAl alloy and easy to form in (2), and switch to feeding the dry TiAl alloy powder in (2). Laser printing is continued on the pre-printed material, and finally the pre-printed material at the bottom is removed by wire cutting to obtain a high tensile strength TiAl alloy billet with a desired shape and no macro cracks on the surface. The organization is a full lamellar organization (NFL) with a lamellar size of 100 μm.

[0128] [Step 2: Vacuum isothermal forging to prepare aviation parts]

[0129] (1) Material and mold preparation: The material of the vacuum isothermal forging mold is high-purity hard graphite, including the upper mold, the lower mold, and the pad. The lubricating coating is sprayed on the outer periphery of the blank obtained by 3D printing, and the mold release agent is sprayed on the inner surface of the mold. The lubricating material and the mold release agent are both selected as high-temperature resistant boron nitride powder.

[0130] (2) Material loading: Place the 3D printed blank, mold and pad into the furnace chamber of the vacuum isothermal forging equipment, ensure that the position and placement of the materials are correct, and then close the furnace door.

[0131] (3) Vacuuming: Start the mechanical pump, open the roughing valve, and start vacuuming. Wait until the vacuum degree reaches 7.0×10 2 Pa, open the fore valve and molecular pump, and finally make the vacuum degree of the chamber reach 2~3×10 -2 Pa and hold.

[0132] (4) Material preheating: Start the heating power supply, heat up to 1250℃ at a heating rate of 5℃ / s, and keep warm for 60 minutes to keep the temperature inside and outside the material uniform and consistent.

[0133] (5) Forging process: Start the forging press and control the speed of the forging head at 0.001s -1 The strain rate causes the TiAl alloy billet to undergo plastic deformation under isothermal conditions and be forged until the upper and lower dies contact to obtain the desired shape of the TiAl alloy part.

[0134] (6) Cooling annealing: After forging is completed, turn off the heating power supply. After the TiAl alloy parts and molds are cooled to room temperature with the furnace, take out the TiAl alloy forging billet. The performance indicators are shown in Table 3.

[0135] (7) Subsequent processing: The TiAl alloy forging blank after isothermal forging is subjected to post-processing, including cutting, grinding, polishing and other steps to obtain the final product. In addition, subsequent processes such as surface treatment and heat treatment can be carried out as needed to further improve the performance and service life of the parts to meet the requirements of the final product.

[0136] Example 4: DLD printing + atmospheric isothermal forging

[0137]

Step 1: DLD printing TiAl alloy billet

[0138] (1) Preparation of pre-alloyed powder

[0139] A TiAl round rod ingot with a diameter of 100 mm is prepared by a suspension smelting method, and then a pre-alloyed powder is prepared by a rotating electrode method; the pre-alloyed powder is Ti45Al8Nb, wherein the Al content is 45%, the Nb content is 8%, and the balance is Ti and other inevitable impurities.

[0140] (2) Preparation before printing

[0141] The surface of the substrate is first cleaned. Specifically, before printing, the substrate is grinded with an angle grinder to remove the oxide film, and then the surface is wiped with acetone to remove oil stains; the cleaned substrate is then placed in a coaxial powder feeding additive manufacturing device; the pre-alloyed powder of (1) is then dried in a vacuum drying oven at a temperature of 200°C for 22 hours to obtain a dry TiAl alloy powder; finally, an alloy material powder having a thermal expansion coefficient similar to that of the TiAl alloy and being easy to form and a dry TiAl alloy powder are placed in two powder feeding tubes respectively; wherein: the material of the substrate is TC4 titanium alloy.

[0142] (3) Substrate preheating

[0143] Before starting pre-printing, the cleaned substrate (2) is in-situ heated by a laser, and when the substrate reaches a red-hot state, a substrate in a red-hot state is obtained;

[0144] (4) Pre-printing

[0145] The alloy material powder having a thermal expansion coefficient similar to that of the TiAl alloy and being easy to form, such as TC4 powder, in (2) is fed and laser printed on the red-hot substrate in (2). The process parameters of the laser printing are: laser power 900 W, printing powder feeding rate 2.5 g / min, and printing rate 12 mm / s; until the residual stress is completely released, the height of the pre-printed material is 10 mm, and the pre-printed material is obtained;

[0146] (5) Post-printing and cutting

[0147] When the residual stress in (4) is completely released, the powder feeding cylinder is switched to stop feeding the alloy material powder with a thermal expansion coefficient similar to that of the TiAl alloy and easy to form in (2), and switch to feeding the dry TiAl alloy powder in (2). Laser printing is continued on the pre-printed material, and finally the pre-printed material at the bottom is removed by wire cutting to obtain a high tensile strength TiAl alloy billet with a desired shape and no macro cracks on the surface. The organization is a full lamellar organization (NFL) with a lamellar size of 100 μm.

[0148] [Step 2: Preparation of aviation parts by atmospheric isothermal forging]

[0149] (1) Material and mold preparation: Lubricating coating is sprayed on the periphery of the TiAl alloy blank obtained by 3D printing, and a release agent is sprayed on the inner surface of the molybdenum alloy mold. Both the lubricating material and the release agent are selected to be high-temperature resistant boron nitride powder.

[0150] (2) Material preheating: Place the blank in a heating furnace, heat it to 1250°C at a heating rate of 20°C / s, and keep it warm for 120 minutes to keep the temperature inside and outside the material uniform and consistent.

[0151] (3) Material loading: The preheated blank is quickly transferred to the lower die of the isothermal forging press, and asbestos is wrapped around the die for insulation.

[0152] (4) Forging process: By controlling the speed of the punch, the forging speed is 0.1s -1 The strain rate causes the TiAl alloy billet to undergo plastic deformation under isothermal conditions and is forged until the upper and lower dies contact to obtain a TiAl alloy part with a target shape.

[0153] (5) Cooling annealing: After forging, the TiAl alloy forging billet is placed in a heating furnace and cooled to room temperature. The performance indicators are shown in Table 3.

[0154] (6) Subsequent processing: The TiAl alloy forging blank after isothermal forging is subjected to post-processing, including cutting, grinding, polishing and other steps to obtain the final product. In addition, subsequent processes such as surface treatment and heat treatment can be carried out as needed to further improve the performance and service life of the parts to meet the requirements of the final product.

[0155] Comparative Example 1

[0156] The ingot blank was obtained after smelting 3-5 times in a common vacuum magnetic levitation melting furnace, and then the ingot was subjected to a hot isostatic pressing process at 1200°C / 150MPa / 2h / furnace cooling for component homogenization, and then vacuum isothermal forging in step 2 was performed. Other aspects were the same as in Example 3. The organization and properties are detailed in Table 3.

[0157] Comparative Example 2

[0158] In the vacuum isothermal forging of step 2, the forging temperature is 1300°C, and the rest is the same as in Example 1. The microstructure and properties are detailed in Table 3.

[0159] Comparative Example 3

[0160] In the atmospheric isothermal forging of step 2, the temperature is raised to 1200° C. at a heating rate of 20° C. / s. The other steps and parameters are the same as those of Example 4. The microstructure and properties are detailed in Table 3.

[0161] Table 3 Performance of Examples and Comparative Examples

[0162]

[0163] The test results in Table 3 show that the TiAl alloys (Examples 1-4) obtained by 3D printing and then processed by isothermal forging are significantly better than TiAl (Comparative Example 1) obtained by ordinary smelting and then isothermal forging in terms of elongation and room temperature tensile strength. The technical solution proposed in the present invention improves the strength and plasticity of the material at the same time. Comparing Comparative Example 2 with Example 1, it can be seen that the forging temperature in the embodiment is selected at 1160-1250℃. The microstructure in this temperature range shows multi-phase coexistence, which is conducive to grain refinement by deformation, and provides fine-grained TiAl forging billets for subsequent production.

[0164] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for preparing a TiAl alloy 3D printed blank isothermal forging formed aviation parts, characterized in that: The following steps are involved: Step 1: 3D printing to prepare the blank: TiAl alloy powder is used as the raw material, and layer-by-layer printing is performed according to the preset CAD model to obtain a TiAl alloy blank that is close to the final shape of the part; Step 2: Prepare aviation parts by atmospheric isothermal forging or vacuum isothermal forging: the forging temperature is the α+γ dual phase region of TiAl alloy; Aircraft parts are prepared by atmospheric isothermal forging. Material preheating: put the billet into the heating furnace, heat it to the target temperature of 1160-1250℃ at a heating rate of 10-50℃ / s, and keep it warm for 30-120min to keep the temperature inside and outside the material uniform and consistent; forging process: control the speed of the punch at 0.001-0.1s -1 The TiAl alloy billet is plastically deformed under isothermal conditions at a strain rate until the upper and lower dies are in contact, thereby obtaining a TiAl alloy forging billet with a target shape; Aviation parts are prepared by vacuum isothermal forging. Material preheating: start the heating power supply, heat up to the target temperature of 1160-1250℃ at a heating rate of 5-20℃ / s, and keep warm for 30-60min to keep the internal and external temperatures of the material uniform and consistent; forging process: start the forging press, control the pressure head speed by ≤0.1s -1 The strain rate makes the TiAl alloy billet undergo plastic deformation under isothermal conditions and forged until the upper and lower dies are in contact to obtain a TiAl alloy forging billet with the required part shape; cooling annealing: after forging is completed, turn off the heating power supply, wait for the TiAl alloy forging billet and the die to cool to room temperature with the furnace, and then take out the TiAl alloy forging billet.

2. The method according to claim 1, characterized in that In step 1, the TiAl alloy blank is printed by electron beam powder bed fusion (EB-PBF) process or laser directed energy deposition (DLD) process.

3. The method according to claim 1, characterized in that The TiAl alloy blank was printed using the electron beam powder bed fusion (EB-PBF) process, which specifically includes the following steps: 1) Place the TiAl pre-alloyed powder into the powder bin of the EB-PBF equipment and set the powder feeding mode to single-side powder feeding; 2) Mark the center position on the surface of the base plate and level the base plate; 3) Make the forming chamber and the high-voltage electron gun in a high vacuum state, and calibrate, calibrate and center the high-voltage electron beam after reaching the set vacuum degree; 4) Import the printed model into the slicing software for slicing optimization; 5) Select TiAl pre-alloyed powder corresponding to the equipment process parameters and set the melting parameters; 6) Start printing after preheating, and take out the titanium aluminum alloy blank after printing is completed.

4. The method according to claim 3, characterized in that The particle size distribution of the TiAl pre-alloyed powder in step 1) is 45-150 μm; And / or in step 3), the vacuum pressure of the molding chamber is 2-3×10 -3 mbar, electron gun vacuum pressure ≥5×10 -5 mbar; and / or in step 4), the selected profile melt width d 熔道 =0.2-1mm, L 补偿 =0.1-0.3mm; Filling channel width d 填充 =0.5-2mm, β overlap coefficient is 0.5-1.2, l 搭接 =0.1-0.2mm; And / or in step 5), the specific melting parameters are as follows: layer thickness is selected as 50 μm, base plate preheating temperature: 1050-1150°C, powder bed preheating temperature: 950-1050°C, scanning speed (v) is 300-12000 mm / s, and beam current (I) is 2-20 mA.

5. The method according to claim 2, characterized in that: The TiAl alloy blank is printed by laser directed energy deposition (DLD) process, which specifically includes the following steps: 1) Preparation of pre-alloyed powder: TiAl round rod ingots are prepared by suspension smelting method, and then TiAl pre-alloyed powder is obtained by rotating electrode method; 2) Preparation before printing: First, clean the surface of the substrate, then dry the pre-alloyed powder in step 1), and finally put the alloy material powder with a thermal expansion coefficient similar to that of the TiAl alloy and easy to form and the dried TiAl alloy powder into two powder feeding tubes respectively; 3) Substrate preheating: before starting pre-printing, the substrate cleaned in step 2) is heated in situ by laser, and when it reaches a red-hot state, a red-hot substrate is obtained; 4) Pre-printing: feeding the alloy material powder having a thermal expansion coefficient similar to that of the TiAl alloy and being easy to form in step 2), and performing laser printing on the substrate in the red-hot state in step 3) to obtain a pre-printed material; 5) Post-printing and cutting: When the residual stress in step 4) is completely released, switch the powder feeding tube, stop feeding the alloy material powder with a thermal expansion coefficient similar to that of the TiAl alloy and easy to form in step 2), and switch to feeding the dried TiAl alloy powder in step 2), continue laser printing on the pre-printed material, and finally use wire cutting to remove the pre-printed material at the bottom to obtain a high-tensile strength TiAl alloy billet with a desired shape and no macro cracks on the surface.

6. The method according to claim 5, characterized in that In step 1), the diameter of the TiAl round rod ingot is 100 mm; And / or in step 2), the material of the substrate is TC4 titanium alloy; the alloy material powder with a thermal expansion coefficient similar to that of TiAl alloy and easy to form is TC4 or other titanium alloy powder; the drying process is carried out in a vacuum drying oven at a drying temperature of 80-200° C. and a holding time of 10-30 hours; And / or in step 4), the process parameters of laser printing are: laser power 400-1200W, printing powder feeding rate 1.5-4g / min, printing rate 8-15mm / s; until the residual stress is completely released, and the height of the pre-printed material is 10mm.

7. The method according to claim 1, characterized in that The atmospheric isothermal forging method is used to prepare aviation parts, which specifically includes the following steps: (1) Material and mold preparation: Spray lubricating coating on the outer periphery of the TiAl alloy blank obtained by 3D printing, and spray release agent on the inner surface of the molybdenum alloy mold. The lubricating material and release agent are both selected to be high temperature resistant boron nitride powder; (2) Material preheating: Place the blank into a heating furnace and heat it to the target temperature of 1160-1250°C at a heating rate of 10-50°C / s, and keep it warm for 30-120 minutes to keep the temperature inside and outside the material uniform and consistent; (3) Material loading: The preheated blank is quickly transferred to the lower die of the isothermal forging press, and asbestos is wrapped around the die for insulation; (4) Forging process: By controlling the speed of the press head, the speed is 0.001-0.1s -1 The TiAl alloy billet is plastically deformed under isothermal conditions at a strain rate until the upper and lower dies are in contact, thereby obtaining a TiAl alloy forging billet with a target shape; (5) Cooling annealing: After forging is completed, the TiAl alloy forging billet is placed in a heating furnace and cooled to room temperature to obtain a TiAl alloy forging billet; (6) Post-processing: The TiAl alloy forging billet after isothermal forging is post-processed, including cutting, grinding, polishing and other steps to obtain the final TiAl alloy aviation parts.

8. The method according to claim 1, characterized in that: The vacuum isothermal forging method is used to prepare aviation parts, which specifically includes the following steps: (1) Material and mold preparation: Spray lubricating coating on the outer periphery of the blank obtained by 3D printing, and spray release agent on the inner surface of the mold. Both the lubricating material and the release agent are selected to be high temperature resistant boron nitride powder; (2) Material loading: Place the blank and mold obtained by 3D printing into the furnace chamber of the vacuum isothermal forging equipment, ensure that the position and placement of the materials are correct, and then close the furnace door; (3) Vacuuming: Start the mechanical pump, open the roughing valve, and start vacuuming. Wait until the vacuum degree reaches 7.0×10 2 Pa, open the fore valve and molecular pump, and finally make the vacuum degree of the chamber reach 2~3×10 -2 Pa and hold; (4) Material preheating: Start the heating power supply, heat up to the target temperature of 1160-1250°C at a heating rate of 5-20°C / s, and keep warm for 30-60 minutes to keep the temperature inside and outside the material uniform and consistent; (5) Forging process: Start the forging press and control the speed of the forging head to ≤0.1s -1 The TiAl alloy blank is plastically deformed under isothermal conditions at a strain rate until the upper and lower dies are in contact, thereby obtaining a TiAl alloy forging blank of a desired part shape; (6) Cooling annealing: After forging is completed, turn off the heating power supply, wait for the TiAl alloy forging billet and the mold to cool to room temperature with the furnace, and then take out the TiAl alloy forging billet; (7) Post-processing: The TiAl alloy forging billet after isothermal forging is post-processed, including cutting, grinding, polishing and other steps to obtain the final TiAl alloy aviation parts.

9. The aviation part prepared by the method according to any one of claims 1 to 8.

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