Directional energy deposition forming method for high-temperature structural material easy to crack and difficult to weld

Abstract

The invention provides a directional energy deposition forming method for a high-temperature structural material easy to crack and difficult to weld, and relates to the technical field of additive manufacturing. The method comprises the following steps: firstly, adding a heating device at the bottom of a substrate, and heating the substrate until the substrate is obviously softened; secondly, additive manufacturing is carried out on the heated substrate through the directional energy deposition technology, and bottom heating is continuously carried out in the forming process so that the substrate and the lowermost base body can be kept in a softened state; and thirdly, after forming is completed, heating of the base plate and the bottom base body is slowly weakened, the temperature of the base body is reduced to 400 DEG C at the speed of 50 DEG C / min, and then air cooling is conducted to the room temperature. According to the method, the purpose of softening is achieved by increasing the temperature of the substrate and the bottom of the formed product in the forming process, so that thermal stress in the printing process and residual stress of the formed product are reduced, and cracks in the additive manufacturing process are prevented. And the common problems of difficulty in welding, difficulty in forming, easiness in cracking and the like in the high-temperature structural material additive manufacturing process are effectively solved.

Description

Technical Field

[0001] The invention relates to the technical field of additive manufacturing, and in particular to a directed energy deposition forming method for a high-temperature structural material that is easy to crack and difficult to weld. Background Art

[0002] High temperature structural materials include high temperature alloys, intermetallic compounds, etc. High temperature structural materials are widely used in extreme environments, especially in key temperature-bearing components such as aircraft engines and gas turbines, by adding alloying elements such as aluminum, chromium, niobium, etc. to improve their high temperature strength, thermal stability and corrosion resistance. However, the high alloying of high temperature metal materials will lead to low liquid fluidity and high thermal cracking sensitivity, making their formability, weldability and room temperature plasticity low in traditional forming and processing processes, and the difficulty of forming and processing and the high preparation cost.

[0003] Directed energy deposition is a new manufacturing method for additive manufacturing. In this process, raw materials in the form of powder or wire are melted by energy beams in a conveying manner and deposited layer by layer on a substrate to achieve the formation of complex parts. It has the advantages of short manufacturing cycle, low cost, and integrated formation of complex shapes. However, due to the characteristics of non-equilibrium solidification, high temperature gradient and thermal cycle effect of directed energy deposition technology, the forming window of this technology in the application of high-temperature and low-plasticity metal materials is extremely narrow, and cracks are easily generated during the additive process, especially high-temperature structural materials that are easy to crack and difficult to weld.

[0004] In order to solve the above problems, some methods have been proposed to improve the application scope of this technology, such as substrate preheating, controlling heat source input, adding composite processing devices, etc.

[0005] Chinese patent CN118287689A prevents the generation of cracks in high-temperature alloys during the forming process by preheating the substrate and controlling the temperature gradient; however, the control method is relatively complicated, requiring upper and lower cooling fixtures to cool down and finely controlling the cooling rate; and the substrate preheating temperature is low, which cannot guarantee the forming quality of the early forming process.

[0006] Chinese patent CN116967484A uses a composite processing device of laser directional energy deposition-impact rolling to achieve simultaneous impact and rolling during the deposition process, reduce deformation and inhibit cracking, and improve the surface quality and density of components; but it is not suitable for high-temperature structural metal materials and cannot solve the problem of condensation cracks. This type of technology improves the processing window of some alloys and has a certain effect in inhibiting the generation of cracks, but it is still difficult to solve the widespread application of additive manufacturing on high-temperature structural metal materials that are easy to crack and difficult to weld.

[0007] Chinese patent CN111957960A discloses a selective laser melting forming method for precipitation-strengthened high-temperature alloy without thermal cracks. The method includes mixing precipitation-strengthened high-temperature alloy powder with melting element particles before laser melting. Since the melting element particles are all high-cost particles, the cooling after their preparation is natural cooling. The natural cooling rate of laser additively manufactured products is usually between tens of degrees and hundreds of degrees per second. Obviously, the natural cooling rate is relatively high, and cracks will still occur.

[0008] Chinese patent CN107774997A discloses a method for laser directional additive of nickel-based directional high-temperature alloys. The method uses three powders, Ni-Cr-Mo, Ni-Cr-Nb and Co-Cr-Ni, and performs laser deposition in a vacuum glove box using a synchronous powder feeding method. At the same time, a liquid nitrogen continuous cooling method is used to cool the deposition platform to increase the temperature gradient of the deposition layer cooling; therefore, the cooling rate is very fast, which will cause a sharp increase in internal stress, thereby causing problems such as material rupture and deformation. Summary of the invention

[0009] In order to solve the technical defect that the traditional high-temperature alloy additive manufacturing process makes the prepared material easy to crack, and to solve this technical defect by adjusting the raw material powder, machining coordination, and controlling the cooling rate, the process will become more complicated, the operation will be difficult, the cost will be high, the efficiency will be low, and the quality will be poor; the present invention proposes a directed energy deposition forming method for high-temperature structural materials that are easy to crack and difficult to weld, which can solve the above problems. The technical solution is as follows:

[0010] A directed energy deposition forming method for a high-temperature structural material that is easy to crack and difficult to weld, the directed energy deposition forming method comprising the following steps:

[0011] S1. Heating and softening the substrate: adding a heating device to the bottom of the substrate, and heating and keeping the substrate warm until it is obviously softened;

[0012] S2. Heating the bottom forming substrate during additive manufacturing: using directed energy deposition technology to perform additive manufacturing on a heated substrate, in addition to maintaining the substrate temperature during the forming process, the bottom forming substrate is heated and kept warm until it softens;

[0013] S3. Slowly cool down and air cool to room temperature: After the forming is completed, slowly reduce the heating of the substrate and the bottom base to slowly reduce the temperature of the base, and then air cool to room temperature.

[0014] Optionally, the heating device for preheating the preformed substrate in S1 is placed at the bottom of the substrate, and includes a power supply and a sensor, and the sensor is arranged at the bottom of the substrate.

[0015] Optionally, the substrate material in S1 is selected to have a melting point that is the same as or close to that of the preformed product, and the thickness does not exceed 20 mm; the temperature of the substrate heating and insulation is 100-200° C. lower than the melting point.

[0016] Optionally, the temperature of the substrate heating and insulation in S1 is 1100-1600°C.

[0017] Optionally, the directed energy deposition technology in S2 is any one of laser, arc, electron beam, and plasma directed energy deposition forming.

[0018] Optionally, in S2, laser is used as the light source, the laser power used is 500-6000W, the laser spot diameter is 500-5000μm, the scanning speed is 1-15mm / s, the powder feeding amount is 5-30g / min, and the powder feeding gas flow rate is 6-20L / min; the bottom layer of the forming matrix is ​​the first 1-20 layers of the formed product, and the bottom layer of the forming matrix is ​​heated and kept warm until the temperature of the softened state is 1100-1600℃.

[0019] Optionally, the bottom area of ​​the formed substrate in S2 is 5×5mm-100×100mm, the single-layer forming height is 0.1-2mm, and the total forming height is 5-100mm.

[0020] Optionally, in S2, when the bottom area of ​​the forming substrate is 15×15mm, the single-layer forming height is 0.8mm, and the total forming height is 70mm, the laser power is 900W, the scanning speed is 7mm / s, the powder feeding amount is 8g / min, the scanning spacing is 0.86mm, the air flow rate is 15L / min, the bottommost forming substrate is the first 10 layers of the formed product, and the substrate temperature will be further increased to 1400°C.

[0021] Optionally, in S2, when the bottom area of ​​the forming substrate is 5×5mm, the single-layer forming height is 0.6mm, and the total forming height is 20mm, the laser power is 780W, the scanning speed is 6mm / s, the powder feeding amount is 5g / min, the scanning spacing is 0.54mm, the air flow rate is 8L / min, the bottommost forming substrate is the first 5 layers of the formed product, and the substrate temperature will be further increased to 1340°C.

[0022] Optionally, in S2, when the bottom area of ​​the forming substrate is 100×100mm, the single-layer forming height is 1.5mm, and the total forming height is 90mm, the laser power is 2000W, the scanning speed is 10mm / s, the powder feeding amount is 20g / min, the scanning spacing is 1.62mm, the air flow rate is 20L / min, the bottommost forming substrate is the first two layers of the formed product, and the substrate temperature will be further increased to 1500°C.

[0023] Optionally, after the forming in S3 is completed, the substrate temperature is determined by the temperature sensor of the heating device, and the temperature of the substrate is controlled to drop to 400°C at a rate of 50°C / min by weakening the induced current, and then the heating device is turned off to allow the substrate and the formed product to be air-cooled to room temperature.

[0024] Optionally, the high-temperature structural material that is easy to crack and difficult to weld includes, but is not limited to: Ti-Al intermetallic compounds, Ni-Al intermetallic compounds, nickel, iron, cobalt-based high-temperature alloys, molybdenum alloys, tantalum alloys, niobium alloys, tungsten alloys, etc.

[0025] Optionally, the additively manufactured Ti-Al intermetallic compound product has a porosity of 0.07-0.01%, a surface hardness of 270-530HV, a tensile strength of 500-900MPa, a yield strength of 350-800MPa, and an elongation at break of 0.1-0.8%; the additively manufactured Ni-Al intermetallic compound product has a porosity of 0.07-0.01%, a surface hardness of 450-600HV, a tensile strength of 1100-1400MPa, a yield strength of 1000-1200MPa, and an elongation at break of 1-15%; the additively manufactured molybdenum alloy product has a porosity of 0.07-0.01%, a surface hardness of 170-300HV, a tensile strength of 150-350MPa, a yield strength of 80-270MPa, and an elongation at break of 1-7%.

[0026] Compared with the prior art, the above technical solution has at least the following beneficial effects:

[0027] The above scheme, the present invention proposes a directed energy deposition forming method for high-temperature structural materials that are easy to crack and difficult to weld, which can solve the technical defect that the traditional additive manufacturing process of high-temperature structural materials in the prior art will make the prepared materials easy to crack. Solving this technical defect by adjusting the raw material powder, machining coordination, and controlling the cooling rate will result in technical problems such as the process flow becoming more complicated, the operation being difficult, the cost being high, the efficiency being low, and the quality being poor.

[0028] The present invention effectively improves the preheating temperature of the substrate by setting a substrate heating device and softening the substrate, and effectively improves the bonding strength between the forming material and the substrate by heating to soften the substrate.

[0029] The present invention effectively improves the thermal stress caused by heat input during the additive manufacturing process by softening the substrate and the first few layers of the forming material, and improves the deformation capacity of the substrate and the first few layers of the forming material through the softening effect to further weaken the deformation caused by stress.

[0030] The present invention achieves slow cooling by controlling the cooling rate after forming, effectively weakening the crack initiation and expansion caused by tensile and compressive stresses generated by contraction of the solid-liquid phase and the cooling process during and after the addition process, thereby improving the density of the formed part.

[0031] In summary, compared with other traditional methods, the method of the present invention achieves slow cooling by preheating the base plate, softening the base plate and the first few layers of the forming material, and controlling the cooling rate after forming, thereby reducing the thermal stress in the printing process and the residual stress of the product after forming, so as to prevent the generation of cracks in the additive manufacturing process and improve the welding performance and forming performance of the prepared product; the method is simple and easy to operate, green and environmentally friendly, low cost, short process, high efficiency, and is conducive to large-scale industrial production and promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] 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.

[0033] Figure 1 This is a process flow chart of a directed energy deposition forming method for a high-temperature structural material that is easy to crack and difficult to weld according to the present invention;

[0034] Figure 2 It is a structural schematic diagram of a product prepared by a directed energy deposition forming method for a high-temperature structural material that is easy to crack and difficult to weld according to the present invention;

[0035] Figure 3 This is a physical picture of a product prepared by a directed energy deposition forming method for a high-temperature structural material that is easy to crack and difficult to weld according to Example 1 of the present invention;

[0036] Figure 4 This is a physical picture of a product prepared by a directed energy deposition forming method for a high-temperature structural material that is easy to crack and difficult to weld according to Example 2 of the present invention. DETAILED DESCRIPTION

[0037] The technical solution of the present invention is described below in conjunction with the accompanying drawings.

[0038] In the embodiments of the present invention, words such as "exemplarily" and "for example" are used to indicate examples, illustrations or explanations. Any embodiment or design described as "example" in the present invention should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of the word "example" is intended to present the concept in a specific way. In addition, in the embodiments of the present invention, the meaning expressed by "and / or" can be both, or it can be either of the two.

[0039] In the embodiments of the present invention, "image" and "picture" may sometimes be used interchangeably. It should be noted that when the distinction between them is not emphasized, the meanings they intend to express are consistent.

[0040] In the embodiments of the present invention, sometimes a subscript such as W1 may be written as a non-subscript such as W1. When the difference is not emphasized, the meanings to be expressed are the same.

[0041] 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.

[0042] A directed energy deposition forming method for high temperature structural materials that are easy to crack and difficult to weld, the directed energy deposition forming method is combined with Figure 1 The steps are as follows:

[0043] S1. Heating and softening the substrate: adding a heating device to the bottom of the substrate, and heating and keeping the substrate warm until it is obviously softened;

[0044] S2. Heating the bottom forming substrate during additive manufacturing: using directed energy deposition technology to perform additive manufacturing on a heated substrate, in addition to maintaining the substrate temperature during the forming process, the bottom forming substrate is heated and kept warm until it softens;

[0045] S3. Slowly cool down and air cool to room temperature: After the forming is completed, slowly reduce the heating of the substrate and the bottom base to slowly reduce the temperature of the base, and then air cool to room temperature.

[0046] In particular, the heating device for preheating the preformed substrate in S1 is placed at the bottom of the substrate, and includes a power supply and an inductor, and the inductor is arranged at the bottom of the substrate.

[0047] In particular, the substrate material in S1 is selected to have a melting point that is the same as or close to that of the preformed product, and the thickness does not exceed 20 mm; the temperature of the substrate heating and insulation is 100-200° C. lower than the melting point.

[0048] In particular, the temperature of the substrate heating and insulation in S1 is 1100-1600°C.

[0049] In particular, the directed energy deposition technology in S2 is any one of laser, arc, electron beam, and plasma directed energy deposition forming.

[0050] In particular, in S2, laser is used as the light source, the laser power adopted is 500-6000W, the laser spot diameter is 500-5000μm, the scanning speed is 1-15mm / s, the powder feeding amount is 5-30g / min, and the powder feeding gas flow rate is 6-20L / min; the bottom layer forming matrix is ​​the first 1-20 layers of the formed product, and the bottom layer forming matrix is ​​heated and kept warm until the temperature of the softened state is 1100-1600℃.

[0051] In particular, the bottom area of ​​the forming substrate in S2 is 5×5 mm-100×100 mm, the single-layer forming height is 0.1-2 mm, and the total forming height is 5-100 mm.

[0052] In particular, in S2, when the bottom area of ​​the forming substrate is 15×15 mm, the single-layer forming height is 0.8 mm, and the total forming height is 70 mm, the laser power is 900 W, the scanning speed is 7 mm / s, the powder feeding amount is 8 g / min, the scanning spacing is 0.86 mm, the gas flow rate is 15 L / min, the bottommost forming substrate is the first 10 layers of the formed product, and the substrate temperature will be further increased to 1400°C.

[0053] In particular, in S2, when the bottom area of ​​the forming substrate is 5×5mm, the single-layer forming height is 0.6mm, and the total forming height is 20mm, the laser power is 780W, the scanning speed is 6mm / s, the powder feeding amount is 5g / min, the scanning spacing is 0.54mm, the gas flow rate is 8L / min, the bottom layer of the forming substrate is the first 5 layers of the formed product, and the substrate temperature will be further increased to 1340°C.

[0054] In particular, in S2, when the bottom area of ​​the forming substrate is 100×100mm, the single-layer forming height is 1.5mm, and the total forming height is 90mm, the laser power is 2000W, the scanning speed is 10mm / s, the powder feeding amount is 20g / min, the scanning spacing is 1.62mm, the gas flow rate is 20L / min, the bottommost forming substrate is the first two layers of the formed product, and the substrate temperature will be further increased to 1500℃.

[0055] In particular, after the forming in S3 is completed, the substrate temperature is determined by the temperature sensor of the heating device, and the temperature of the substrate is controlled to drop to 400°C at a rate of 50°C / min by weakening the induced current, and then the heating device is turned off to allow the substrate and the formed product to be air-cooled to room temperature.

[0056] In particular, the high-temperature structural materials that are easy to crack and difficult to weld include but are not limited to: Ti-Al intermetallic compounds, Ni-Al intermetallic compounds, nickel, iron, cobalt-based high-temperature alloys, molybdenum alloys, tantalum alloys, niobium alloys, tungsten alloys, etc.

[0057] In particular, the additively manufactured Ti-Al intermetallic compound products have a porosity of 0.07-0.01%, a surface hardness of 270-530HV, a tensile strength of 500-900MPa, a yield strength of 350-800MPa, and an elongation at break of 0.1-0.8%; the additively manufactured Ni-Al intermetallic compound products have a porosity of 0.07-0.01%, a surface hardness of 450-600HV, a tensile strength of 1100-1400MPa, a yield strength of 1000-1200MPa, and an elongation at break of 1-15%; the additively manufactured molybdenum alloy products have a porosity of 0.07-0.01%, a surface hardness of 170-300HV, a tensile strength of 150-350MPa, a yield strength of 80-270MPa, and an elongation at break of 1-7%.

[0058] Example 1

[0059] A directed energy deposition forming method for a high-temperature structural material that is easy to crack and difficult to weld, the directed energy deposition forming method comprising the following steps:

[0060] S1. Heating and softening the substrate: The substrate material is a TC4 alloy substrate with a thickness of 6 mm. A heating device is added to the bottom of the substrate. The heating device is an induction heating device, and the heating temperature can be adjusted by the current. The substrate is heated and kept warm until it is obviously softened. The temperature of the substrate heating and keeping warm is 200°C lower than the melting point.

[0061] S2. Heating of the bottom forming substrate during additive manufacturing: laser is used as the light source, the laser power is 950W, the scanning speed is 8mm / s, the powder feeding amount is 6g / min, the scanning spacing is 0.8mm, and the gas flow rate is 5L / min; the bottom area of ​​the formed product is 15×15mm, and the single-layer forming height is 1.7mm; due to the input of the laser heat source, the temperature of the first 5 layers of the formed product and the substrate will further increase to 1550℃; then continue to form, and finally obtain a formed TiAl alloy product; the product has uniform structure, no defects such as pores and cracks, and the formed product quality is high;

[0062] S3. Slowly cool down and air cool to room temperature: After forming, the temperature of the substrate is determined by the temperature sensor of the heating device. The temperature of the substrate is controlled to drop to 400°C at a rate of 50°C / min by weakening the induced current. Then the heating device is turned off to allow the substrate and the formed product to be air cooled to room temperature.

[0063] The prepared additively manufactured TiAl alloy product is as follows Figure 3 As shown, the porosity is 0.07-0.01%, the surface hardness is 270-530HV, the tensile strength is 500-900MPa, the yield strength is 350-800MPa, and the elongation at break is 0.1-0.8%.

[0064] Example 2

[0065] A directed energy deposition forming method for a high-temperature structural material that is easy to crack and difficult to weld, the directed energy deposition forming method comprising the following steps:

[0066] S1. Heating and softening the substrate: The substrate material is 45# steel with a thickness of 8mm. A heating device is added to the bottom of the substrate. The heating device is an induction heating device. The heating temperature can be adjusted by the current size, and the substrate is heated and kept warm until it is obviously softened. The temperature of the substrate heating and keeping warm is 150°C lower than the melting point.

[0067] S2. Heating of the bottom forming substrate during additive manufacturing: laser is used as the light source, the laser power is 2000W, the scanning speed is 10mm / s, the powder feeding amount is 10g / min, the scanning spacing is 0.7mm, and the gas flow rate is 20L / min; the bottom area of ​​the formed product is 30×45mm, and the single-layer forming height is 1.3mm; due to the input of the laser heat source, the temperature of the first two layers of the formed product and the substrate will further increase to 1400℃; then continue to form, and finally obtain a formed nickel-based high-temperature alloy product; the product has uniform structure, no defects such as pores and cracks, and the formed product quality is high;

[0068] S3. Slowly cool down and air cool to room temperature: After forming, the temperature of the substrate is determined by the temperature sensor of the heating device. The temperature of the substrate is controlled to drop to 400°C at a rate of 50°C / min by weakening the induced current. Then the heating device is turned off to allow the substrate and the formed product to be air cooled to room temperature.

[0069] The prepared additively manufactured nickel-based high-temperature alloy products are as follows Figure 4 As shown, the porosity is 0.07-0.01%, the surface hardness is 230-410HV, the tensile strength is 750-1000MPa, the yield strength is 700-750MPa, and the elongation at break is 20-40%.

[0070] Example 3

[0071] A directed energy deposition forming method for a high-temperature structural material that is easy to crack and difficult to weld, the directed energy deposition forming method comprising the following steps:

[0072] S1. Heating and softening the substrate: The substrate material is a pure molybdenum substrate with a thickness of 20 mm. A heating device is added to the bottom of the substrate. The heating device is an induction heating device, and the heating temperature can be adjusted by the current. The substrate is heated and kept warm until it is obviously softened. The temperature of the substrate heating and keeping warm is 110°C lower than the melting point.

[0073] S2. Heating of the bottom forming substrate during additive manufacturing: laser is used as the light source, the laser power is 3000W, the scanning speed is 15mm / s, the powder feeding amount is 24g / min, the scanning spacing is 1.4mm, and the gas flow rate is 8L / min; the bottom area of ​​the formed product is 30×30mm, and the single-layer forming height is 1.2mm; due to the input of the laser heat source, the temperature of the first 5 layers of the formed product and the substrate will further increase to 1600℃; then continue to form, and finally obtain a formed molybdenum alloy product; the product has uniform structure, no defects such as pores and cracks, and the formed product quality is high;

[0074] S3. Slowly cool down and air cool to room temperature: After forming, the temperature of the substrate is determined by the temperature sensor of the heating device. The temperature of the substrate is controlled to drop to 400°C at a rate of 50°C / min by weakening the induced current. Then the heating device is turned off to allow the substrate and the formed product to be air cooled to room temperature.

[0075] The prepared additively manufactured molybdenum alloy product has a porosity of 0.07-0.01%, a surface hardness of 170-300 HV, a tensile strength of 150-350 MPa, a yield strength of 80-270 MPa, and an elongation at break of 1-7%.

[0076] Example 4

[0077] A directed energy deposition forming method for a high-temperature structural material that is easy to crack and difficult to weld, the directed energy deposition forming method comprising the following steps:

[0078] S1. Heating and softening the substrate: The substrate material is a TA15 alloy substrate with a thickness of 10 μm. A heating device is added to the bottom of the substrate. The heating device is an induction heating device. The heating temperature can be adjusted by the current size, and the substrate is heated and kept warm until it is obviously softened. The temperature of the substrate heating and keeping warm is 100°C lower than the melting point.

[0079] S2. Heating of the bottom forming substrate during additive manufacturing: laser is used as the light source, the laser power is 1000W, the scanning speed is 9mm / s, the powder feeding amount is 9g / min, the scanning spacing is 1mm, and the gas flow rate is 6L / min; the bottom area of ​​the formed product is 20×20mm, and the single-layer forming height is 1.9mm; due to the input of the laser heat source, the temperature of the first 5 layers of the formed product and the substrate will further increase to 1530℃; then continue to form, and finally obtain a formed TiAl alloy product; the product has uniform structure, no defects such as pores and cracks, and the formed product quality is high;

[0080] S3. Slowly cool down and air cool to room temperature: After forming, the temperature of the substrate is determined by the temperature sensor of the heating device. The temperature of the substrate is controlled to drop to 400°C at a rate of 50°C / min by weakening the induced current. Then the heating device is turned off to allow the substrate and the formed product to be air cooled to room temperature.

[0081] The prepared additively manufactured TiAl alloy product has a porosity of 0.07-0.01%, a surface hardness of 270-530HV, a tensile strength of 500-900MPa, a yield strength of 350-800MPa, and an elongation at break of 0.1-0.8%.

[0082] Example 5

[0083] A directed energy deposition forming method for a high-temperature structural material that is easy to crack and difficult to weld, the directed energy deposition forming method comprising the following steps:

[0084] S1. Heating and softening the substrate: The substrate material is a GH4099 alloy substrate with a thickness of 11 mm. A heating device is added to the bottom of the substrate. The heating device is an induction heating device, which can adjust the heating temperature by the current size, and heat and keep the substrate warm until it is obviously softened. The temperature of heating and keeping the substrate warm is 130°C lower than the melting point;

[0085] S2. Heating of the bottom forming substrate during additive manufacturing: laser is used as the light source, the laser power is 1500W, the scanning speed is 8mm / s, the powder feeding amount is 15g / min, the scanning spacing is 0.65mm, and the gas flow rate is 5L / min; the bottom area of ​​the formed product is 5×5mm, and the single-layer forming height is 1.3mm; due to the input of the laser heat source, the temperature of the first 10 layers of the formed product and the substrate will further increase to 1230℃; then continue to form, and finally obtain a formed Ni3Al alloy product; the product has uniform structure, no defects such as pores and cracks, and the formed product quality is high;

[0086] S3. Slowly cool down and air cool to room temperature: After forming, the temperature of the substrate is determined by the temperature sensor of the heating device. The temperature of the substrate is controlled to drop to 400°C at a rate of 50°C / min by weakening the induced current. Then the heating device is turned off to allow the substrate and the formed product to be air cooled to room temperature.

[0087] The prepared additively manufactured Ni3Al alloy product has a porosity of 0.07-0.01%, a surface hardness of 450-600 HV, a tensile strength of 1100-1400 MPa, a yield strength of 1000-1200 MPa, and an elongation at break of 1-15%.

[0088] Example 6

[0089] A directed energy deposition forming method for a high-temperature structural material that is easy to crack and difficult to weld, the directed energy deposition forming method comprising the following steps:

[0090] S1. Heating and softening the substrate: The substrate material is 304 stainless steel with a thickness of 20 mm. A heating device is added to the bottom of the substrate. The heating device is an induction heating device. The heating temperature can be adjusted by the current size, and the substrate is heated and kept warm until it is obviously softened. The temperature of the substrate heating and keeping warm is 100°C lower than the melting point.

[0091] S2. Heating of the bottom forming substrate during additive manufacturing: laser is used as the light source, the laser power is 6000W, the scanning speed is 15mm / s, the powder feeding amount is 30g / min, the scanning spacing is 1.1mm, and the gas flow rate is 20L / min; the bottom area of ​​the formed product is 15×15mm, and the single-layer forming height is 2mm; due to the input of the laser heat source, the temperature of the first layer of the formed product and the substrate will further increase to 1410℃; then continue to form, and finally obtain a formed GH4099 alloy product; the product has uniform structure, no defects such as pores and cracks, and the formed product quality is high;

[0092] S3. Slowly cool down and air cool to room temperature: After forming, the temperature of the substrate is determined by the temperature sensor of the heating device. The temperature of the substrate is controlled to drop to 400°C at a rate of 50°C / min by weakening the induced current. Then the heating device is turned off to allow the substrate and the formed product to be air cooled to room temperature.

[0093] The prepared additively manufactured GH4099 alloy product has a porosity of 0.07-0.01%, a surface hardness of 230-410HV, a tensile strength of 750-1000MPa, a yield strength of 700-750MPa, and an elongation at break of 20-40%.

[0094] The above scheme, the present invention proposes a directed energy deposition forming method for high-temperature structural materials that are easy to crack and difficult to weld, which can solve the technical defect that the traditional additive manufacturing process of high-temperature structural materials in the prior art will make the prepared materials easy to crack. Solving this technical defect by adjusting the raw material powder, machining coordination, and controlling the cooling rate will result in technical problems such as the process flow becoming more complicated, the operation being difficult, the cost being high, the efficiency being low, and the quality being poor.

[0095] The present invention effectively improves the preheating temperature of the substrate by setting a substrate heating device and softening the substrate, and effectively improves the bonding strength between the forming material and the substrate by heating to soften the substrate.

[0096] The present invention effectively improves the thermal stress caused by heat input during the additive manufacturing process by softening the substrate and the first few layers of the forming material, and improves the deformation capacity of the substrate and the first few layers of the forming material through the softening effect to further weaken the deformation caused by stress.

[0097] The present invention achieves slow cooling by controlling the cooling rate after forming, effectively weakening the crack initiation and expansion caused by tensile and compressive stresses generated by contraction of the solid-liquid phase and the cooling process during and after the addition process, thereby improving the density of the formed part.

[0098] In summary, compared with other traditional methods, the method of the present invention achieves slow cooling by preheating the base plate, softening the base plate and the first few layers of the forming material, and controlling the cooling rate after forming, thereby reducing the thermal stress in the printing process and the residual stress of the product after forming, so as to prevent the generation of cracks in the additive manufacturing process and improve the welding performance and forming performance of the prepared product; the method is simple and easy to operate, green and environmentally friendly, low cost, short process, high efficiency, and is conducive to large-scale industrial production and promotion.

[0099] It should be understood that the term "and / or" in this article is only 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 at the same time, and B exists alone. A and B can be singular or plural. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship, but it may also indicate an "and / or" relationship. Please refer to the context for specific understanding.

[0100] In the present invention, "at least one" means one or more, and "plurality" means two or more. "At least one of the following" or similar expressions refers 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 mean: a, b, c, ab, ac, bc, or abc, where a, b, and c can be single or multiple.

[0101] It should be understood that in various embodiments of the present invention, the size of the serial numbers of the above-mentioned processes does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0102] 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 directed energy deposition forming method for high-temperature structural materials that are easy to crack and difficult to weld, characterized in that: The directed energy deposition forming method comprises the following steps: S1. Heating and softening the substrate: adding a heating device to the bottom of the substrate, and heating and keeping the substrate warm until it is obviously softened; S2. Heating the bottom forming substrate during additive manufacturing: using directed energy deposition technology to perform additive manufacturing on a heated substrate, in addition to maintaining the substrate temperature during the forming process, the bottom forming substrate is heated and kept warm until it softens; S3. Slowly cool down and air cool to room temperature: After the forming is completed, slowly reduce the heating of the substrate and the bottom base to slowly reduce the temperature of the base, and then air cool to room temperature.

2. The directed energy deposition forming method for high-temperature structural materials that are easy to crack and difficult to weld according to claim 1, characterized in that: The heating device for preheating the preformed substrate in S1 is placed at the bottom of the substrate, and includes a power supply and a sensor, and the sensor is arranged at the bottom of the substrate.

3. The directed energy deposition forming method for high temperature structural materials that are easy to crack and difficult to weld according to claim 1, characterized in that: In S1, the substrate material is selected to have a melting point that is the same as or close to that of the preformed product, and the thickness does not exceed 20mm; the temperature of the substrate heating and insulation is 100-200℃ lower than the melting point.

4. The directed energy deposition forming method for high temperature structural materials that are easy to crack and difficult to weld according to claim 1, characterized in that: The temperature of the substrate heating and insulation in S1 is 1100-1600°C.

5. The directed energy deposition forming method for high temperature structural materials that are easy to crack and difficult to weld according to claim 1, characterized in that: The directed energy deposition technology in S2 is any one of laser, arc, electron beam, and plasma directed energy deposition forming.

6. The directed energy deposition forming method for high temperature structural materials that are easy to crack and difficult to weld according to claim 1, characterized in that: In S2, laser is used as the light source, the laser power adopted is 500-6000W, the laser spot diameter is 500-5000μm, the scanning speed is 1-15mm / s, the powder feeding amount is 5-30g / min, and the powder feeding gas flow rate is 6-20L / min; the bottom layer forming matrix is ​​the first 1-20 layers of the formed product, and the bottom layer forming matrix is ​​heated and kept warm until the temperature of the softened state is 1100-1600℃.

7. The directed energy deposition forming method for high temperature structural materials that are easy to crack and difficult to weld according to claim 1, characterized in that: The bottom area of ​​the forming substrate in S2 is 5×5mm-100×100mm, the single-layer forming height is 0.1-2mm, and the total forming height is 5-100mm.

8. The directed energy deposition forming method for high temperature structural materials that are easy to crack and difficult to weld according to claim 1, characterized in that: In S2, when the bottom area of ​​the forming substrate is 15×15mm, the single-layer forming height is 0.8mm, and the total forming height is 70mm, the laser power is 900W, the scanning speed is 7mm / s, the powder feeding amount is 8g / min, the scanning spacing is 0.86mm, the gas flow rate is 15L / min, and the bottom layer of the forming substrate is the first 10 layers of the formed product, and the substrate temperature will be further increased to 1350℃.

9. The directed energy deposition forming method for high temperature structural materials that are easy to crack and difficult to weld according to claim 1, characterized in that: After the forming in S3 is completed, the substrate temperature is determined by the temperature sensor of the heating device, and the temperature of the substrate is controlled to drop to 400°C at a rate of 50°C / min by weakening the induced current. Then the heating device is turned off to allow the substrate and the formed product to be air-cooled to room temperature.

10. The directed energy deposition forming method for high temperature structural materials that are easy to crack and difficult to weld according to claim 1, characterized in that: The high-temperature structural materials that are easy to crack and difficult to weld include, but are not limited to: Ti-Al intermetallic compounds, Ni-Al intermetallic compounds, nickel, iron, cobalt-based high-temperature alloys, molybdenum alloys, tantalum alloys, niobium alloys, and tungsten alloys.

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