Method for achieving titanium-aluminum alloy additive manufacturing through electron beam spot melting process

Abstract

The invention discloses a method for achieving titanium-aluminum alloy additive manufacturing through an electron beam spot melting process. The method comprises the steps that firstly, after a three-dimensional CAD model of a target product is established, layering slicing is conducted; 2, preheating and heat preservation of the substrate; 3, spreading powder and preheating a powder bed; 4, additive manufacturing process parameters are set, powder melting and solidification are carried out point by point, and a single-layer solid sheet layer is obtained; 5, carrying out secondary preheating treatment on the powder bed and descending the forming platform; and 6, repeating the process to obtain the titanium-aluminum alloy. A discrete point melting technology is adopted to replace a traditional line scanning continuous melting technology, point melting and solidification are carried out on a target area in a powder bed one by one, the size of a molten pool is reduced, the cooling speed of the molten pool is increased, the heat affected zone range of the edge of the molten pool is reduced, the influence time of the heat affected zone is shortened, and the uneven structure caused by aluminum element volatilization and phase change is avoided; and meanwhile, single-process printing of the titanium-aluminum alloy complex part is achieved, the difficulty and cost of the additive manufacturing process are reduced, and the method is suitable for the field of titanium-aluminum alloy additive manufacturing.

Description

Technical Field

[0001] The invention belongs to the technical field of metal additive manufacturing, and specifically relates to a method for realizing titanium-aluminum alloy additive manufacturing by electron beam spot melting process. Background Art

[0002] As an important lightweight high-temperature structural material, titanium aluminum alloy has low density, high specific strength, high specific elastic modulus, excellent oxidation resistance, corrosion resistance, high temperature strength and creep resistance. Its operating temperature can reach 900℃. It is a 600℃ to 900℃ alternative to traditional nickel-based high-temperature alloys to achieve a significant weight reduction in aerospace vehicles. Traditional titanium aluminum alloy parts are mainly prepared by casting and high-temperature deformation. This method has problems such as element segregation, coarse grains, difficulty in eliminating B2 phase, and difficulty in forming complex components, which restricts the engineering application of titanium aluminum alloy parts. The additive manufacturing technology that has emerged in recent years has the advantage of integrated forming of complex components, opening up a new way for the manufacture of complex titanium aluminum alloy components.

[0003] Since titanium aluminum alloy is composed of intermetallic compounds, it has the disadvantage of being brittle at room temperature. The powder bed electron beam additive manufacturing technology can release stress by preheating the powder bed at high temperature to increase the substrate temperature and reduce the brittle cracking of titanium aluminum alloy. It is currently the most technologically mature titanium aluminum alloy additive manufacturing solution. However, the high melt pool temperature of electron beam additive manufacturing will cause the volatilization of aluminum elements. In the long melt pool mode of online scanning, this volatilization will cause uneven distribution of aluminum elements in the printed parts. At the same time, long-term high-temperature exposure around the molten pool will cause phase change, generate γ phase bands, and cause uneven organization. This composition and organizational unevenness are particularly prominent when printing parts with complex shapes. The current solution is to design different printing processes for the thin-walled parts, thick-walled parts, and edge parts of complex parts, which increases the difficulty and cost of printing. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for realizing titanium aluminum alloy additive manufacturing by electron beam spot melting process in view of the deficiencies of the above-mentioned prior art. The method adopts a discrete spot melting process to melt and solidify the target area in the powder bed one by one, which reduces the size of the molten pool and makes the molten pool smaller, increases the cooling rate of the molten pool, reduces the range and influence time of the heat-affected zone at the edge of the molten pool, avoids the volatilization of aluminum elements caused by high molten pool temperature and the uneven organization caused by phase change, and solves the problems of uneven volatilization of aluminum elements and γ phase change in the heat-affected zone caused by line scanning of a long molten pool.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for realizing titanium aluminum alloy additive manufacturing by electron beam spot melting process, characterized in that the method comprises the following steps:

[0006] Step 1: Establish a three-dimensional CAD model of the target product titanium aluminum alloy, then perform layered slicing processing in the forming height direction of the three-dimensional CAD model, and import the slice data of each layer into the additive manufacturing equipment;

[0007] Step 2: Put the titanium aluminum alloy powder into the powder bin of the additive manufacturing equipment, evacuate it, and then preheat and insulate the substrate on the forming platform in the additive manufacturing equipment;

[0008] Step 3: using a powder scraping device to spread the titanium aluminum alloy powder put into the powder bin in step 2 on the substrate that has been preheated and heat-insulated in step 2 to form a powder bed, and then preheating the powder bed;

[0009] Step 4: setting the additive manufacturing process parameters including the electron beam current size, point heating time, point spacing distance and minimum point spacing time, melting and solidifying the powder point by point in the target area of ​​the powder bed after the preheating treatment in step 3 to obtain a single-layer solid sheet;

[0010] Step 5: Perform secondary preheating on the powder bed formed into a single-layer solid sheet in step 4, and then lower the forming platform;

[0011] Step six, repeat the titanium aluminum alloy powder laying process and powder bed preheating process in step three, the powder melting and solidification process in step four, the powder bed secondary preheating process and the descending forming platform process in step five, so that each single layer of solid sheets is stacked to manufacture titanium aluminum alloy.

[0012] The above-mentioned method for realizing additive manufacturing of titanium-aluminum alloy by electron beam spot melting process is characterized in that the atomic percentage of aluminum element in the target product titanium-aluminum alloy in step one is above 45%.

[0013] The above-mentioned method for realizing titanium-aluminum alloy additive manufacturing by electron beam spot melting process is characterized in that the titanium-aluminum alloy powder in step 2 is a nearly spherical or spherical powder with a particle size less than 150 μm.

[0014] The above-mentioned method for realizing additive manufacturing of titanium aluminum alloy by electron beam spot melting process is characterized in that the additive manufacturing equipment in step 2 is a powder bed selective melting electron beam additive manufacturing equipment.

[0015] The above-mentioned method for realizing titanium aluminum alloy additive manufacturing by electron beam spot melting process is characterized in that the vacuum in step 2 is evacuated to a vacuum degree of no more than 5×10 -2 Pa.

[0016] The above-mentioned method for realizing additive manufacturing of titanium aluminum alloy by electron beam spot melting process is characterized in that the temperatures of the substrate preheating in step 2, the powder bed preheating treatment after powder spreading in step 3, and the powder bed secondary preheating treatment for forming a single-layer solid sheet in step 5 are not less than 1000°C.

[0017] The above-mentioned method for realizing titanium-aluminum alloy additive manufacturing by electron beam spot melting process is characterized in that the titanium-aluminum alloy powder is laid with a thickness of 50 μm to 100 μm in step three.

[0018] The above-mentioned method for realizing titanium aluminum alloy additive manufacturing by electron beam spot melting process is characterized in that the additive manufacturing process parameters in step 4 are: electron beam acceleration voltage is 60kV, electron beam current is 8mA-25mA, spot heating time is 3×10 -5 s~8×10 -4 s, the spacing between adjacent points is 75μm to 200μm, and the heating time interval between adjacent points is greater than 1×10 -3 s.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] 1. The present invention adopts a discrete point melting process to replace the traditional line scanning continuous melting process in the additive manufacturing process. The target area in the powder bed is melted and solidified one by one, thereby realizing the melting of the entire powder layer. The size of the molten pool is reduced and the molten pool is small. The molten pool cools quickly, reducing the range and impact time of the heat affected zone at the edge of the molten pool, and avoiding the problems of uneven volatilization of aluminum elements and γ phase transformation in the heat affected zone caused by the long molten pool of line scanning.

[0021] 2. The present invention controls the size of the molten pool by regulating the additive manufacturing process parameters including the electron beam current size, the point heating time, the point spacing distance and the minimum point spacing time, thereby improving the composition and organizational uniformity of the additively manufactured titanium aluminum alloy. There is no need to design printing processes separately for the thin-walled parts, thick-walled parts and edge parts of the complex titanium aluminum alloy parts, thus achieving single-process printing of complex titanium aluminum alloy parts and reducing the difficulty and cost of the additive manufacturing process.

[0022] 3. The present invention preheats the substrate and the powder bed during the additive manufacturing process and prolongs the powder bed preheating time, thereby reducing the temperature gradient and cooling rate during the solidification process, alleviating thermal stress, and further improving the structural uniformity of the additively manufactured titanium aluminum alloy.

[0023] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1Schematic diagram of the outline of adjacent point melting areas of titanium aluminum alloy formed by electron beam additive manufacturing point melting in Example 1 of the present invention.

[0025] Figure 2 Schematic diagram of the size of a single molten pool and the melting area of ​​titanium-aluminum alloy formed by line scanning in electron beam additive manufacturing in Comparative Example 1 of the present invention.

[0026] Figure 3 Schematic diagram of the outline of adjacent point melting areas of titanium aluminum alloy formed by electron beam additive manufacturing point melting in Example 2 of the present invention.

[0027] Figure 4 Schematic diagram of the outline of adjacent point melting areas of titanium aluminum alloy formed by electron beam additive manufacturing point melting in Example 3 of the present invention. DETAILED DESCRIPTION

[0028] Example 1

[0029] This embodiment includes the following steps:

[0030] Step 1, establishing a three-dimensional CAD model of the target product TiAl4822 alloy (Ti-48Al-2Cr-2Nb, at.%), then performing layered slicing processing in the forming height direction of the three-dimensional CAD model, and importing the slice data of each layer into the additive manufacturing equipment; the atomic percentage of aluminum element in the target product TiAl4822 alloy is 48%;

[0031] Step 2: Place the titanium aluminum alloy powder into the powder bin of the powder bed selection melting electron beam additive manufacturing equipment and evacuate it to a vacuum degree of no more than 5×10 -2 Pa, then preheating the substrate on the forming platform in the additive manufacturing equipment to 1000° C. and keeping the temperature for 20 minutes; the titanium aluminum alloy powder is a spherical powder with a particle size of 53 μm to 150 μm;

[0032] Step 3: using a powder scraping device, the titanium aluminum alloy powder placed in the powder bin in step 2 is laid on the substrate that has been preheated and heat-insulated in step 2, with a laying thickness of 100 μm to form a powder bed, and then the powder bed is preheated at 1000° C.;

[0033] Step 4: Set the additive manufacturing process parameters including electron beam acceleration voltage of 60 kV, electron beam current of 25 mA, and spot heating time of 3 × 10 -3 s, the spacing between adjacent points is 100 μm, and the heating time interval between adjacent points is 2×10 -3 s, discretely melting and solidifying the powder in the target area of ​​the powder bed after preheating in step 3 point by point to obtain a single-layer solid sheet;

[0034] Step 5: Perform a secondary preheating treatment at 1000°C on the powder bed formed into a single solid sheet in step 4, and then lower the forming platform;

[0035] Step six, repeat the titanium aluminum alloy powder laying process and powder bed preheating process in step three, the powder melting and solidification process in step four, the powder bed secondary preheating process and the descending forming platform process in step five, so that each single layer of solid sheets is stacked to manufacture titanium aluminum alloy.

[0036] Figure 1 Schematic diagram of the contour of the adjacent melting areas of the titanium aluminum alloy formed by electron beam additive manufacturing point melting in Example 1 of the present invention, Figure 1 It can be seen that the width and depth of the molten pools at the Nth and N+1th points in the adjacent point melting area are both more than 200 μm. The two molten pools overlap with each other by offsetting by 100 μm, achieving: (1) Vertical direction: The molten pool depth exceeds the powder bed height, achieving complete melting of the powder layer in the vertical direction and fusion with the substrate; (2) Horizontal direction: The two molten pools overlap with each other, ensuring that the powder bed between the two heat sources in the horizontal direction is completely melted and fused with the substrate; (3) The surface of the point melting molten pool is flat, which is conducive to the continuation of subsequent printing.

[0037] Comparative Example 1

[0038] This comparative example comprises the following steps:

[0039] Step 1, establishing a three-dimensional CAD model of the target product TiAl4822 alloy (Ti-48Al-2Cr-2Nb, at.%), then performing layered slicing processing in the forming height direction of the three-dimensional CAD model, and importing the slice data of each layer into the additive manufacturing equipment; the atomic percentage of aluminum element in the target product TiAl4822 alloy is 48%;

[0040] Step 2: Place the titanium aluminum alloy powder into the powder bin of the powder bed selection melting electron beam additive manufacturing equipment and evacuate it to a vacuum degree of no more than 5×10 -2 Pa, then preheating the substrate on the forming platform in the additive manufacturing equipment to 1000° C. and keeping the temperature for 20 minutes; the titanium aluminum alloy powder is a spherical powder with a particle size of 53 μm to 150 μm;

[0041] Step 3: using a powder scraping device, the titanium aluminum alloy powder placed in the powder bin in step 2 is laid on the substrate that has been preheated and heat-insulated in step 2, with a laying thickness of 100 μm to form a powder bed, and then the powder bed is preheated at 1000° C.;

[0042] Step 4: setting the additive manufacturing process parameters including the electron beam acceleration voltage of 60 kV, the electron beam current of 13.5 mA, and the scanning speed of 5 m / s, and performing continuous line scanning on the target area in the powder bed after the preheating treatment in step 3 to melt and solidify the powder to obtain a single-layer solid sheet;

[0043] Step 5: Perform a secondary preheating treatment at 1000°C on the powder bed formed into a single solid sheet in step 4, and then lower the forming platform;

[0044] Step six, repeat the titanium aluminum alloy powder laying process and powder bed preheating process in step three, the powder melting and solidification process in step four, the powder bed secondary preheating process and the descending forming platform process in step five, so that each single layer of solid sheets is stacked to manufacture titanium aluminum alloy.

[0045] Figure 2 Schematic diagram of the size of a single molten pool and the melting area of ​​a titanium aluminum alloy formed by electron beam additive manufacturing line scanning in this comparative example. Figure 2 It can be seen that when the comparative example adopts line scanning forming, the length of a single molten pool exceeds 2 mm, while when Example 1 adopts point melting forming, the width of a single point molten pool is only 200 μm to 300 μm, indicating that the electron beam electric melting process of the present invention is significantly different from the traditional line scanning printing forming process in comparative example 1.

[0046] Example 2

[0047] This embodiment includes the following steps:

[0048] Step 1, establishing a three-dimensional CAD model of the target product TiAl4822 alloy (Ti-48Al-2Cr-2Nb, at.%), then performing layered slicing processing in the forming height direction of the three-dimensional CAD model, and importing the slice data of each layer into the additive manufacturing equipment; the atomic percentage of aluminum element in the target product TiAl4822 alloy is 48%;

[0049] Step 2: Place the titanium aluminum alloy powder into the powder bin of the powder bed selection melting electron beam additive manufacturing equipment and evacuate it to a vacuum degree of no more than 5×10 -2 Pa, then preheating the substrate on the forming platform in the additive manufacturing equipment to 1000° C. and keeping the temperature for 20 minutes; the titanium aluminum alloy powder is a spherical powder with a particle size of 53 μm to 150 μm;

[0050] Step 3: using a powder scraping device, the titanium aluminum alloy powder placed in the powder bin in step 2 is laid on the substrate that has been preheated and heat-insulated in step 2, with a laying thickness of 100 μm to form a powder bed, and then the powder bed is preheated at 1000° C.;

[0051] Step 4: Set the additive manufacturing process parameters including electron beam acceleration voltage of 60 kV, electron beam current of 25 mA, and spot heating time of 6 × 10 -3 s, the spacing between adjacent points is 200 μm, and the heating time interval between adjacent points is 2×10 -3 s, discretely melting and solidifying the powder in the target area of ​​the powder bed after preheating in step 3 point by point to obtain a single-layer solid sheet;

[0052] Step 5: Perform a secondary preheating treatment at 1000°C on the powder bed formed into a single solid sheet in step 4, and then lower the forming platform;

[0053] Step six, repeat the titanium aluminum alloy powder laying process and powder bed preheating process in step three, the powder melting and solidification process in step four, the powder bed secondary preheating process and the descending forming platform process in step five, so that each single layer of solid sheets is stacked to manufacture titanium aluminum alloy.

[0054] Figure 3 Schematic diagram of the outline of the adjacent melting areas of the electron beam additive manufacturing spot melting titanium aluminum alloy in this embodiment, Figure 3 It can be seen that the width and depth of the molten pools at points N and N+1 in the adjacent point melting area are both more than 200μm, and the two molten pools overlap with each other by a 200μm offset, ensuring the complete melting of the powder bed and fusion with the substrate, which is a feasible printing process combination.

[0055] Example 3

[0056] Step 1, establishing a three-dimensional CAD model of the target product TiAl4822 alloy (Ti-48Al-2Cr-2Nb, at.%), then performing layered slicing processing in the forming height direction of the three-dimensional CAD model, and importing the slice data of each layer into the additive manufacturing equipment; the atomic percentage of aluminum element in the target product TiAl4822 alloy is 48%;

[0057] Step 2: Place the titanium aluminum alloy powder into the powder bin of the powder bed selection melting electron beam additive manufacturing equipment and evacuate it to a vacuum degree of no more than 5×10 -2 Pa, and then preheating the substrate on the forming platform in the additive manufacturing equipment to 1150° C. and keeping the temperature for 20 minutes; the titanium aluminum alloy powder is a spherical powder with a particle size of 20 μm to 53 μm;

[0058] Step 3: using a powder scraping device, the titanium aluminum alloy powder placed in the powder bin in step 2 is laid on the substrate that has been preheated and heat-insulated in step 2, with a laying thickness of 50 μm to form a powder bed, and then the powder bed is preheated at 1150° C.;

[0059] Step 4: Set the additive manufacturing process parameters including electron beam acceleration voltage of 60 kV, electron beam current of 8 mA, and spot heating time of 8 × 10 -4 s, the spacing between adjacent points is 75 μm, and the heating time interval between adjacent points is 2×10 -3 s, discretely melting and solidifying the powder in the target area of ​​the powder bed after preheating in step 3 point by point to obtain a single-layer solid sheet;

[0060] Step 5: Perform a secondary preheating treatment at 1150° C. on the powder bed formed into a single-layer solid sheet in step 4, and then lower the forming platform;

[0061] Step six, repeat the titanium aluminum alloy powder laying process and powder bed preheating process in step three, the powder melting and solidification process in step four, the powder bed secondary preheating process and the descending forming platform process in step five, so that each single layer of solid sheets is stacked to manufacture titanium aluminum alloy.

[0062] Figure 4 Schematic diagram of the outline of the adjacent melting areas of the electron beam additive manufacturing spot melting titanium aluminum alloy in this embodiment, Figure 4 It can be seen that the width and depth of the molten pools at the Nth point and the N+1th point in the adjacent point melting area are both more than 200μm, and the two molten pools overlap by offsetting 75μm, ensuring the complete melting of the powder bed and fusion with the substrate, which is a feasible printing process combination.

[0063] The above is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent change made to the above embodiment according to the technical essence of the invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for realizing additive manufacturing of titanium aluminum alloy by electron beam spot melting process, characterized in that: The method comprises the following steps: Step 1: Establish a three-dimensional CAD model of the target product titanium aluminum alloy, then perform layered slicing processing in the forming height direction of the three-dimensional CAD model, and import the slice data of each layer into the additive manufacturing equipment; Step 2: Put the titanium aluminum alloy powder into the powder bin of the additive manufacturing equipment, evacuate it, and then preheat and insulate the substrate on the forming platform in the additive manufacturing equipment; Step 3: using a powder scraping device to spread the titanium aluminum alloy powder put into the powder bin in step 2 on the substrate that has been preheated and heat-insulated in step 2 to form a powder bed, and then preheating the powder bed; Step 4: setting the additive manufacturing process parameters including the electron beam current size, point heating time, point spacing distance and minimum point spacing time, melting and solidifying the powder point by point in the target area of ​​the powder bed after the preheating treatment in step 3 to obtain a single-layer solid sheet; Step 5: Perform secondary preheating on the powder bed formed into a single-layer solid sheet in step 4, and then lower the forming platform; Step six, repeat the titanium aluminum alloy powder laying process and powder bed preheating process in step three, the powder melting and solidification process in step four, the powder bed secondary preheating process and the descending forming platform process in step five, so that each single layer of solid sheets is stacked to manufacture titanium aluminum alloy.

2. The method for realizing titanium aluminum alloy additive manufacturing by electron beam spot melting process according to claim 1, characterized in that: The atomic percentage of aluminum in the target product titanium-aluminum alloy in step 1 is above 45%.

3. The method for realizing titanium aluminum alloy additive manufacturing by electron beam spot melting process according to claim 1, characterized in that: The titanium aluminum alloy powder in step 2 is a spherical powder with a particle size less than 150 μm.

4. The method for realizing titanium aluminum alloy additive manufacturing by electron beam spot melting process according to claim 1, characterized in that: The additive manufacturing equipment described in step 2 is a powder bed selective melting electron beam additive manufacturing equipment.

5. The method for realizing titanium aluminum alloy additive manufacturing by electron beam spot melting process according to claim 1, characterized in that: The vacuum in step 2 is evacuated to a vacuum degree of no more than 5×10 -2 Pa.

6. The method for realizing titanium aluminum alloy additive manufacturing by electron beam spot melting process according to claim 1, characterized in that: The temperatures of the substrate preheating in step 2, the powder bed preheating after powder spreading in step 3, and the powder bed secondary preheating to form a single-layer solid sheet in step 5 are all not less than 1000°C.

7. The method for realizing titanium aluminum alloy additive manufacturing by electron beam spot melting process according to claim 1, characterized in that: The titanium aluminum alloy powder in step three is laid to a thickness of 50 μm to 100 μm.

8. The method for realizing titanium aluminum alloy additive manufacturing by electron beam spot melting process according to claim 1, characterized in that: The additive manufacturing process parameters described in step 4 are: electron beam acceleration voltage is 60 kV, electron beam current is 8 mA to 25 mA, and spot heating time is 3×10 -5 s~8×10 -4 s, the spacing between adjacent points is 75μm to 200μm, and the heating time interval between adjacent points is greater than 1×10 -3 s.

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