Method for improving impact toughness of electric arc additive manufacturing titanium alloy

Abstract

The invention provides a method for improving impact toughness of electric arc additive manufacturing titanium alloy, and belongs to the technical field of additive manufacturing. The method comprises the steps that a pretreated forming base material is placed on a cooling device in a gas protection device, when the oxygen content in the gas protection device is smaller than 1000 ppm, the electric arc additive manufacturing process of the titanium alloy is started, meanwhile, the cooling device is started to cool the forming base material, the cooling device is placed in the gas protection device, and the cooling device is started to cool the forming base material. According to the method, the cooling device can cool the environment gas in the gas protection device while cooling the base material, printing can be conducted at a low temperature in the whole additive manufacturing process, and compared with an existing additive printing process in which the environment oxygen content needs to be controlled to be 100 ppm or below, due to the fact that the environment is low in the printing process, the printing efficiency is greatly improved. And the temperature of the formed base material is low all the time, so that the printing quality of the titanium alloy can be guaranteed even if printing is conducted under the high oxygen content, and the titanium alloy is not prone to being oxidized.

Description

Technical Field

[0001] The invention belongs to the technical field of additive manufacturing, and in particular relates to a method for improving the impact toughness of titanium alloys manufactured by arc additive manufacturing. Background Art

[0002] The demand for titanium alloys in aerospace, shipbuilding, medical and other fields is increasing, and most of the application scenarios of titanium alloys will be subjected to strong impact loads, requiring titanium alloys to have excellent impact toughness. For titanium alloy materials used in aerospace and other fields, impact toughness is one of its important mechanical performance indicators. Arc additive manufacturing technology uses metal wire as raw material, electric arc as heat source, CNC machine tools or robotic arms as motion systems, and manufactures three-dimensional parts through layer-by-layer deposition. It has the characteristics of high deposition efficiency, few forming size restrictions, and low manufacturing cost. It is suitable for manufacturing large-scale, integrated structural parts.

[0003] Due to the high chemical activity of titanium alloy, it starts to absorb hydrogen at about 250℃ and oxygen at about 400℃. At above 600℃, titanium absorbs oxygen to form an oxide layer on the surface. As the hydrogen content increases, a brittle layer will also be produced in the component, seriously affecting the performance of the component. When titanium alloy arc additive manufacturing is carried out in an atmospheric environment, only the area directly below the nozzle of the welding gun has a certain amount of argon protection. As the welding gun is removed, the molten pool will react violently with the oxygen in the atmosphere during the subsequent solidification process, resulting in the formation of a brittle oxide film on the surface of the weld. As the number of cladding layers increases, cracks that penetrate the entire component may even appear, resulting in the scrapping of the component. During the layer-by-layer deposition process, the oxide will be drawn into the molten pool by the arc, resulting in an increase in the oxygen content in the titanium alloy sample. The oxygen content will significantly affect the room temperature impact properties of the titanium alloy. The increase in oxygen content will significantly reduce the impact toughness and the ability of the titanium alloy to resist crack propagation.

[0004] There are still many shortcomings in titanium alloy metal parts directly formed by arc additive manufacturing technology. Different atmospheres and processes have a significant impact on the formed parts. Mismatched processes will make it difficult to form components, or the formed metal parts will be difficult to meet the corresponding production and performance requirements. Therefore, it is necessary to study suitable arc additive manufacturing processes to further improve the impact toughness of titanium alloys, which is of great significance to the subsequent application of titanium alloy parts. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art and provide a method for improving the impact toughness of arc additively manufactured titanium alloys, so as to solve the problems of poor forming quality, many pores and crack defects, and poor mechanical properties of arc additively manufactured titanium alloys in the prior art.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions: A method for improving the impact toughness of arc additively manufactured titanium alloy, comprising the following steps: S1, placing the formed substrate on a cooling device in a gas protection device, wherein a cooling medium is introduced into the cooling device; the gas protection device is a closed device; S2, insert the welding gun into the gas protection device and introduce the protective gas; S3, when the oxygen content in the gas protection device is less than 1000ppm, a cold metal transfer arc additive manufacturing is performed on the forming substrate through a welding gun. During the printing process, a cooling medium is continuously supplied to the cooling device until the printing is completed, and an additive part is formed on the forming substrate.

[0007] A further improvement of the present invention is: Preferably, in S3, during the printing process, the temperature of the forming substrate is 20°C.

[0008] Preferably, in S3, during the printing process, the outlet water temperature of the cooling device is 40-50°C.

[0009] Preferably, the welding gun and the gas protection device are simultaneously wrapped by a flexible film.

[0010] Preferably, the material of the flexible film is plastic, nylon or aluminum foil.

[0011] Preferably, in S1, the forming substrate is pre-treated before being placed in the gas protection device; and the connection method between the forming substrate and the cooling device includes slot connection, bolt connection and colloid bonding.

[0012] Preferably, in S3, the wire feeding speed of the printing process is 5-15 m / min, the scanning speed is 5-20 mm / s, the overlap is 30%-60%, the interlayer lift is 1-4 mm, and the interlayer cooling time is 0-30 min. A device for improving the impact toughness of titanium alloy manufactured by arc additive manufacturing, which is used to implement the above method, comprises a gas protection device and a welding gun, wherein the welding gun is inserted into the gas protection device, a cooling device is arranged at the bottom of the gas protection device, and an air intake pipeline is arranged in the gas protection device.

[0013] Preferably, a smoke processor is provided in the gas protection device.

[0014] Preferably, a detection circuit is provided in the gas protection device.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The present invention proposes a method for improving the impact toughness of titanium alloys produced by arc additive manufacturing. The main step is to place a pretreated formed substrate on a cooling device inside a gas protection device. When the oxygen content inside the gas protection device is below 1000ppm, the arc additive manufacturing process of the titanium alloy is started, and the cooling device is turned on to cool the formed substrate. This method places the cooling device in the gas protection device so that the cooling device can cool the ambient gas in the gas protection device while cooling the substrate, so that the entire additive manufacturing can be printed at a lower temperature. Compared with the existing process of additive printing that requires the ambient oxygen content to be controlled below 100ppm, this method has a lower printing process environment and the temperature of the formed substrate is always low, so that even if printing is performed under a higher oxygen content, the printing quality of the titanium alloy can be guaranteed, and the titanium alloy is not easily oxidized.

[0016] The present invention adopts a specific forming strategy to perform arc additive manufacturing of titanium alloy until the part manufacturing is completed, and then opens the gas protection device to take out the part after the titanium alloy part is completely cooled. The method can accurately control the additive forming atmosphere, effectively protect the titanium alloy additive parts from oxidation, and reduce the defect content to improve the forming quality; by reducing the oxygen content in arc additively manufactured titanium alloy parts and rapidly cooling and refining the structure, the mechanical properties of the titanium alloy can be further improved, especially its impact toughness can be greatly improved; by adjusting the cooling device to continuously cool the forming substrate, the continuous forming of large-sized parts can be achieved, the manufacturing time of titanium alloy parts can be shortened, the forming efficiency can be improved, and the cost of titanium alloy arc additive manufacturing can be further reduced. The method of the present invention can reduce the defects and oxygen content in arc additively manufactured titanium alloy parts, and the impact toughness of the prepared titanium alloy parts is as high as 94 J / cm 2 .

[0017] Furthermore, during the printing process, the temperature of the forming substrate is controlled at 20°C, which can continuously cool the printed additive parts.

[0018] Furthermore, during the printing process, the water outlet temperature of the cooling device is controlled to ensure that the temperature of the formed substrate is maintained within a set temperature range.

[0019] Furthermore, the welding gun and the gas protection device are simultaneously wrapped by a flexible film, so that the entire printing process is carried out in a closed environment.

[0020] Furthermore, the material of the flexible film is plastic, nylon or aluminum foil, which protects the entire printing process without affecting the movement of the welding gun.

[0021] Furthermore, the formed substrate is connected to the cooling device in a certain manner, so that the formed substrate can be closely connected to the cooling device, and the cooling device can continuously cool the formed substrate.

[0022] The present invention also discloses a device for improving the impact toughness of titanium alloy produced by arc additive manufacturing. The device integrates a printing welding gun and a cooling device in a gas protection device. While ensuring that the printing environment is under gas protection, the ambient temperature is only affected by the printing heat and the heat dissipation of the cooling device. The cooling device can cool the ambient gas in the gas protection device while cooling the substrate, so that the entire additive manufacturing can be printed at a lower temperature, effectively inhibiting the reaction of the titanium alloy surface with oxygen in the air at high temperature, avoiding the so-called "oxidation" phenomenon, and maintaining the excellent mechanical properties of the titanium alloy, especially the impact toughness. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Shown is a schematic diagram of the gas shielded arc additive manufacturing process in the present invention; Figure 2 The figure shows the nondestructive testing results of the TC4 titanium alloy parts manufactured by arc additive manufacturing in the embodiment of the present invention; Among them, 1. gas protection device, 2. smoke processor, 3. air intake pipe, 4. detection circuit, 5. cooling device, 6. forming substrate, 7. additive parts, 8. welding gun. DETAILED DESCRIPTION

[0024] The present invention is further described in detail below in conjunction with the accompanying drawings: As the problem raised in the background technology, titanium alloy, due to its high chemical activity, begins to absorb hydrogen when the temperature reaches about 250°C, and when the temperature rises to about 400°C, it will begin to react with oxygen. Especially when the temperature exceeds 600°C, titanium will absorb a large amount of oxygen and form an oxide layer on its surface. At the same time, as the hydrogen content continues to accumulate, a brittle layer may also be produced inside the component, which poses a serious threat to the overall performance of the component. When conducting arc additive manufacturing of titanium alloys in an atmospheric environment, although a certain degree of argon protection can be provided directly below the nozzle of the welding gun, once the welding gun moves, the molten pool will be directly exposed to the atmosphere in the subsequent solidification stage, and react violently with the oxygen in the air, thereby forming a fragile oxide film on the surface of the weld. As the number of deposited layers gradually increases, this oxidation phenomenon may even cause cracks to appear throughout the entire component, ultimately causing the component to be completely scrapped. In addition, during the layer-by-layer accumulation process, the oxide may also be drawn into the molten pool by the arc, causing the oxygen content in the titanium alloy sample to continue to rise. The increase in oxygen content will significantly weaken the impact properties of titanium alloy at room temperature, which is manifested in a significant decrease in impact toughness and a significant weakening of the ability to resist crack propagation.

[0025] In order to solve the above problems, the first aspect of the present invention discloses a method for improving the impact toughness of titanium alloy manufactured by arc additive manufacturing, comprising the following steps: S1. Place the pretreated forming substrate 6 on the cooling device 5 inside the gas protection device 1; the forming substrate 6 is used to receive the arc additive manufacturing titanium alloy sample, the gas protection device 1 is used to apply a constant arc additive gas environment, and the cooling device 5 is used to cool the forming substrate to stabilize it at a set temperature.

[0026] Preferably, the pretreatment includes but is not limited to grinding, polishing, cleaning, preheating and other steps. Preferably, the connection methods between the forming substrate 6 and the cooling device 5 include but are not limited to slot connection, bolt connection, colloid bonding and the like.

[0027] S2. Insert the welding gun into the gas protection device and keep a certain distance from the forming substrate. The welding gun and the gas protection device are wrapped by a flexible film. Shielding gas is introduced into the gas protection device, and an oxygen meter is used to monitor the oxygen content inside the gas protection device.

[0028] Preferably, the distance between the welding gun tip and the forming substrate is 10-30 mm.

[0029] Preferably, the material of the flexible film includes but is not limited to plastic, nylon, aluminum foil, etc.; preferably, the protective gas includes but is not limited to high-purity argon, mixed gas, etc.

[0030] S3. When the oxygen content inside the gas protection device is below 1000 ppm, the arc additive manufacturing process of the titanium alloy is started, and the cooling device is turned on to cool the formed substrate.

[0031] The use of cold metal transition arc additive manufacturing technology can effectively control the energy input process and metal transfer behavior. This intermittent arc starting method makes the CMT heat input much lower than ordinary TIG welding. The rapid heating, melting and rapid cooling stages of the wire in the CMT arc additive manufacturing process are a CMT cycle. The CMT cycle used in the present invention is within 60ms, and the output power is 4000-5000W. Through this process, the temperature of the additive part 7 during the printing process is less than 600°C. Further combined with the cooling device 5 and the low ambient temperature, the temperature of the additive part 7 during the printing process can be controlled at 100-200°C, which can significantly prevent the titanium alloy from being oxidized. In addition, the CMT process has a small heat input, the microstructure of the additive titanium alloy is fine, and the mechanical properties are excellent.

[0032] Due to the low heat output in the additive manufacturing process, the process parameters used in the arc additive manufacturing process are: wire feeding speed 5-15m / min, scanning speed 5-20mm / s, overlap 30%-60%, interlayer lifting 1-4mm, and interlayer cooling time 0-30min; compared with conventional additive manufacturing processes, the wire feeding speed and scanning speed are faster, making the forming efficiency higher.

[0033] During the printing process, the cooling medium is continuously introduced into the cooling device 5 until the printing is completed, and the additive part 7 is formed on the forming substrate 6. By continuously introducing the cooling medium into the cooling device 5, the cooling device 5 can continuously cool the printing environment while cooling the additive part 7 through the forming substrate 6.

[0034] By continuously introducing the cooling medium, the temperature of the forming substrate 6 can be maintained at 20° C., meeting the temperature setting requirement.

[0035] S4. Use a specific forming strategy to perform arc additive manufacturing of titanium alloy until the part is manufactured. When the titanium alloy part is completely cooled, open the gas protection device to take out the part, close the gas supply, and close the cooling device, thus ending the process.

[0036] In some preferred embodiments of the present invention, the forming substrate 6 and the cooling device 5 are connected via a slot, that is, a slot is provided on the cooling device so that the forming substrate 6 can be inserted into the cooling device 5, so that the forming substrate 6 can be better cooled by the cooling device 5.

[0037] The second aspect of the present invention discloses a device for improving the impact toughness of arc additively manufactured titanium alloy, the device comprising a gas protection device 1 and a welding gun 8, the welding gun 8 is inserted into the gas protection device 1, a cooling device 5 is provided at the bottom of the gas protection device 1; an air intake pipeline 3 is provided in the gas protection device 1.

[0038] The gas protection device 1 and the welding gun 8 are both wrapped by a flexible film to ensure that the printing process is in a closed environment to prevent the entry of air. On this basis, a smoke processor 2 is also provided in the device. Since the entire printing process is in a closed environment, smoke is not easy to disperse. The device is provided with a smoke processor 2, so that dust or impurities in the printing process can be discharged in time to prevent the titanium alloy in the printing process from being affected. The smoke processor 2 also has the function of exhausting.

[0039] As a preferred solution, the air inlet pipeline 3 is arranged at the bottom of the entire gas protection device 1, so that the introduced gas can spread upward from the bottom of the gas protection device 1 and fill the entire printing chamber.

[0040] The gas protection device 1 is also provided with a detection circuit 4, in which there are detection devices such as a temperature measuring device or an oxygen content detector.

[0041] The following is further described in conjunction with specific embodiments.

[0042] Example 1 The present invention provides a method for improving the impact toughness of titanium alloys manufactured by arc additive manufacturing, see Figure 1 , including the following steps: S1. Taking TC4 titanium alloy as an example, the polished and cleaned TC4 titanium alloy forming substrate 6 is placed on the cooling device 5 inside the gas protection device 1. The gas protection device 1 is used to apply a constant argon environment. The cooling device 5 is set at 20°C and is bonded to the forming substrate 6 by aluminum foil.

[0043] S2. Insert the welding gun 8 into the gas protection device 1 and keep a distance of 15 mm from the forming substrate 6. The welding gun 8 and the gas protection device 1 are wrapped with a flexible plastic film. High-purity argon gas is introduced into the gas protection device 1, and an oxygen meter is used to monitor the oxygen content inside the gas protection device. Preferably, the distance between the welding gun tip 1 and the forming substrate 6 is 15 mm.

[0044] S3. When the oxygen content inside the gas protection device 1 is below 1000 ppm, the arc additive manufacturing process of TC4 titanium alloy is started, and the cooling device 5 is turned on to cool the formed substrate 6; the process parameters used in the arc additive manufacturing process are: wire feeding speed 6 m / min, scanning speed 6 mm / s, overlap amount 50%, interlayer lifting amount 3 mm, and interlayer cooling time 2 min.

[0045] S4. Use a two-way reciprocating forming strategy to perform arc additive manufacturing of titanium alloy until the part is manufactured. When the titanium alloy part is completely cooled, open the gas protection device 1 to take out the part, close the gas supply, and close the cooling device 5, thus ending the process.

[0046] The nondestructive testing results of TC4 titanium alloy parts prepared by arc additive manufacturing technology are as follows: Figure 2 As shown, by comparison, it can be seen that the TC4 titanium alloy parts formed in air environment have a large number of holes, cracks, oxides and other defects inside, and the forming quality is poor; the TC4 titanium alloy parts prepared by the above steps have only a small amount of pores and oxides inside, with high density and good forming quality. The room temperature impact properties of the two TC4 titanium alloy samples were further tested. As shown in Table 1, the impact toughness of the TC4 titanium alloy samples prepared by the above steps of the present invention is 30% higher than the impact toughness value of the TC4 titanium alloy samples manufactured by general arc additive manufacturing. The impact toughness of the TC4 titanium alloy parts prepared by the method of the present invention is as high as 94 J / cm 2 .

[0047] Table 1 Room temperature impact properties of arc additively manufactured TC4 titanium alloy samples

[0048] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more. In the description of the present invention, the first feature "above" or "below" the second feature may include the first and second features being in direct contact, or the first and second features not being in direct contact but being in contact through another feature between them.

[0049] In the description of the present invention, “on”, “over” and “above” a first feature from a second feature includes the first feature being directly above and obliquely above the second feature, or simply means that the first feature is horizontally higher than the second feature.

[0050] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0051] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0052] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

[0053] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for improving the impact toughness of titanium alloy manufactured by arc additive manufacturing, characterized in that: The following steps are involved: S1, placing a formed substrate (6) on a cooling device (5) in a gas protection device (1), wherein a cooling medium is introduced into the cooling device (5); the gas protection device (1) is a closed device; S2, inserting the welding gun (8) into the gas protection device (1) and introducing the protective gas; S3, when the oxygen content in the gas protection device (1) is less than 1000 ppm, a cold metal transition arc additive manufacturing printing is performed on the forming substrate (6) through a welding gun (8), and during the printing process, a cooling medium is continuously supplied to the cooling device (5) until the printing is completed, thereby forming an additive part (7) on the forming substrate (6).

2. The method for improving the impact toughness of titanium alloy produced by arc additive manufacturing according to claim 1, characterized in that: In S3, during the printing process, the temperature of the forming substrate (6) is 20°C.

3. The method for improving the impact toughness of titanium alloy manufactured by arc additive manufacturing according to claim 2, characterized in that: In S3, during the printing process, the outlet water temperature of the cooling device (5) is 40-50°C.

4. The method for improving the impact toughness of titanium alloy manufactured by arc additive manufacturing according to claim 1, characterized in that: The welding gun (8) and the gas protection device (1) are simultaneously wrapped by a flexible film.

5. The method for improving the impact toughness of titanium alloy produced by arc additive manufacturing according to claim 4, characterized in that: The material of the flexible film is plastic, nylon or aluminum foil.

6. The method for improving the impact toughness of titanium alloy produced by arc additive manufacturing according to claim 1, characterized in that: In S1, the shaped substrate (6) is pre-treated before being placed in the gas protection device (1); the connection method between the shaped substrate (6) and the cooling device (5) includes slot connection, bolt connection and colloid bonding.

7. The method for improving the impact toughness of titanium alloy produced by arc additive manufacturing according to claim 1, characterized in that: In S3, the wire feeding speed of the printing process is 5-15m / min, the scanning speed is 5-20mm / s, the overlap is 30%-60%, the interlayer lifting amount is 1-4mm, and the interlayer cooling time is 0-30min.

8. A device for improving the impact toughness of titanium alloy produced by arc additive manufacturing according to the method of claim 1, characterized in that: It comprises a gas protection device (1) and a welding gun (8), wherein the welding gun (8) is inserted into the gas protection device (1), a cooling device (5) is provided at the bottom of the gas protection device (1), and an air intake pipeline (3) is provided in the gas protection device (1).

9. The device for improving the impact toughness of titanium alloy produced by arc additive manufacturing according to claim 8, characterized in that: The gas protection device (1) is provided with a smoke processor (2).

10. The device for improving the impact toughness of titanium alloy produced by arc additive manufacturing according to claim 8, characterized in that: The gas protection device (1) is provided with a detection circuit (4).

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