A method for improving the surface quality of m247 manufactured by electron beam selective melting technology

Abstract

The application belongs to the technical field of high-temperature alloy preparation and relates to a method for improving the surface quality of M247 manufactured by electron beam selective melting technology, wherein M247 parts are first deposited and formed by electron beam selective melting technology; during the deposition and forming process, the electron beam scanning speed is controlled at 0.4-0.6 m / s, the defocusing amount is controlled at 40-70 mA, and the current size is controlled at 8-15 mA, so that the electron beam line energy density in the printing process is within the range of 800-1200 J / mm; after the part printing is completed, the part is naturally cooled in a vacuum environment, and the part is taken out after cooling; the part is placed in an electrolyte plasma polishing equipment for surface treatment, the part is immersed in an electrolyte, electrolytic plasma polishing is performed, and the surface quality of the part is improved. The surface roughness of the M247 part manufactured by the application is greatly reduced, and the macro and micro cracks in the part and on the surface are basically eliminated, and the performance of the part is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high-temperature alloy preparation, and particularly relates to a method for improving the surface quality of M247 manufactured by electron beam selective melting technology. BACKGROUND

[0002] With the rapid development of aerospace and power energy technology, in order to meet the increasingly high reliability and stability requirements of core equipment, high-temperature alloys have been increasingly applied to the production and manufacturing of advanced aerospace engines and gas turbines. High-temperature alloy refers to a metal structural material that can withstand large and complex stress at a high temperature of 600 DEG C or above, and has certain surface stability and organizational stability. It has good high-temperature strength and high-temperature creep performance, excellent corrosion resistance and wear resistance, good organizational stability and process performance.

[0003] M247 high-temperature alloy is a typical gamma prime phase precipitation strengthened high-temperature alloy. Because it has higher high-temperature strength and creep strength and heat corrosion resistance than general high-temperature alloys, it is widely used in turbine parts of ships and ground industrial gas turbines and aircraft engines working below 900 DEG C. More importantly, M247 high-temperature alloy has a certain representativeness in high-strength nickel-based high-temperature alloys due to its multiple phase types and rich alloying elements. In this type of alloy, the gamma prime strengthening phase and the gamma matrix account for the vast majority of the composition phase, and the composition elements of the gamma prime strengthening phase are mostly also the composition elements of the low-melting eutectic, resulting in poor weldability of the alloy.

[0004] Electron beam selective melting technology is a digital manufacturing technology that accelerates electrons to 0.3-0.5 times the speed of light, uses electromagnetic field to control the focusing and trajectory of the electrons, and forms a layer-by-layer scanning and selective melting of alloy powder. Compared with laser selective melting technology, this technology uses electron beam with higher energy density as heat source, has higher working efficiency, and can complete the melting and forming of powder materials with higher melting point, so this process has more advantages in the additive manufacturing of high-temperature alloys.

[0005] However, because of its high energy density, the temperature gradient is large during the forming process, and the energy overflow is serious, so the surface quality of the formed parts is poor, and defects such as warping deformation may occur. At the same time, since M247 high-temperature alloy is sensitive to temperature and has poor weldability, the large temperature gradient in the electron beam selective melting additive manufacturing process will cause thermal stress in the part, which is easy to cause macro and micro cracks in the part during the forming process, seriously affecting the forming quality of the part. Especially in the long size direction, the macro and micro cracks produced will cause the part to fail, limiting the wide application of the technology.

[0006] Therefore, the electron beam selective melting additive manufacturing process of the nickel-based superalloy M247 should be explored, appropriate parameters should be developed to control the surface quality of the part, the generation of macro and micro cracks should be inhibited, and the overall process should be improved to further inhibit the generation of cracks. SUMMARY

[0007] The purpose of the present application is to provide a method for improving the surface quality of M247 manufactured by electron beam selective melting technology, which solves the problems of poor surface quality of nickel M247 manufactured by electron beam selective melting technology and the existence of macro and micro cracks.

[0008] The present application is realized by the following technical solutions:

[0009] A method for improving the surface quality of M247 manufactured by electron beam selective melting technology, comprising the following steps:

[0010] (1) depositing and forming M247 parts by using electron beam selective melting technology, and controlling the electron beam parameters during the deposition and forming process, specifically as follows: the electron beam scanning speed is controlled at 0.4-0.6 m / s, the defocusing amount is controlled at 40-70 mA, and the current size is controlled at 8-15 mA, so that the electron beam line energy density in the printing process is within the range of 800-1200 J / mm;

[0011] (2) after the part is printed, the part is naturally cooled in a vacuum environment, and the part is taken out after cooling;

[0012] (3) after the part is initially processed, it is placed in an electrolyte plasma polishing equipment for surface treatment, the part is immersed in an electrolyte, electrolytic plasma polishing is performed, and the surface quality of the part is improved.

[0013] Further, in step (1), the influence of the electron beam parameters on the part forming quality is in the order of defocusing amount> current> interaction of defocusing amount*current> interaction of current*electron beam scanning speed> electron beam scanning speed.

[0014] Further, step (2) is specifically:

[0015] After the part is printed, stop the protection gas, naturally cool the part in a vacuum environment, and after the part is fully cooled, air is introduced and the part is taken out.

[0016] Further, the vacuum environment requires a vacuum degree of 2*10 -3 mbar or less.

[0017] Further, the protection gas is helium.

[0018] Further, in step (3), the electrolysis voltage is controlled at 320-350V, the distance between the anode and the cathode is 20-30mm, the electrolyte temperature is 70-85 DEG C, and the electrolyte flow rate is 10-15L / min.

[0019] Further, after the electrolyte plasma polishing is completed, the final part is subjected to a tensile property test at room temperature, the tensile strength reaches 1100±100MPa, and the specified plastic elongation strength reaches 700±100MPa.

[0020] The tensile property test is performed at 900 DEG C, and the highest tensile strength reaches 750MPa, and the highest specified plastic elongation strength reaches 500MPa.

[0021] Further, in step (3), the preliminary treatment is to remove the excess powder on the surface of the part.

[0022] Compared with the prior art, the present application has the following beneficial technical effects:

[0023] The present application discloses a method for improving the surface quality of M247 manufactured by electron beam selective melting technology, which controls the line energy density range, reduces the overflow of electron beam energy when melting the powder bed powder, prevents excess powder from being melted and sintered, increases the size of the part, and reduces the surface quality; and after the part is formed, the device operation is manually modified, the cooling method is changed, natural cooling is adopted, the cooling rate after the part is formed is greatly reduced, the internal stress is reduced, and the generation of cracks is inhibited; and considering the working conditions of the parts, electrolyte plasma polishing technology is used in the post-processing, an electrolyte solution suitable for M247 high-temperature alloy and polishing conditions are developed, the surface material of the workpiece is removed by electrochemical reaction and plasma discharge, and the surface roughness is finally reduced because the plasma discharge occurs preferentially at the micro convex parts on the surface of the workpiece.

[0024] The nickel-based high-temperature alloy M247 part manufactured by the process route of the present application has improved surface quality, greatly reduced surface roughness, and basically eliminated macro and micro cracks in the part and on the surface, and the performance of the part is improved, and the deposited parts obtained by printing have good mechanical properties at room temperature and 900 DEG C high temperature conditions.

[0025] As the scanning speed increases, the surface quality of the sample becomes worse and worse. When the scanning speed is in the range of 0.8m / s to 2m / s, the surface of the sample is almost full of defects. This is because when the scanning speed is too fast, the electron beam flow passes through the powder bed, and the powder is not uniformly melted, which may cause unmelted and spheroidization forming defects, thereby making the surface quality of the sample worse. Therefore, the electron beam scanning speed of the present application is controlled at 0.5-0.8m / s.

[0026] With the increase of electron beam current, the surface quality of the sample piece is better and better. When the electron beam current is in the range of 3 to 6 mA, the surface of the sample piece is almost full of defects. This is because, with the gradual increase of the current, the electron beam power also gradually increases, the powder is more fully melted, and when the current is in a high state, the molten pool state during printing is more stable, and the surface forming quality of the sample piece after solidification is also better. Therefore, the current of the present application is controlled to be 5-15 mA.

[0027] With the increase of the defocus amount, the surface quality of the sample piece gradually deteriorates, but the overall change is small. When the defocus amount is greater than 70 mA, some partial defects appear on the surface of the sample piece. This is because when the defocus amount increases, the electron beam flow energy applied to the powder bed is dispersed, which may cause the powder not to be fully penetrated, thereby affecting the surface quality of the part. Therefore, the defocus amount of the present application is controlled to be 60-75 mA. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 is the permeation method result of example 1; figure (a) is the permeation method result of the sample piece obtained by changing the scanning speed; figure (b) is the permeation method result of the sample piece obtained by changing the electron beam current; figure (c) is the permeation method result of the sample piece obtained by changing the defocus amount; figure (d) is the permeation method result of the sample piece obtained by changing the line spacing;

[0029] Figure 2 is the room temperature mechanical property of the part obtained under different parameters;

[0030] Figure 3 is the 900 DEG C high temperature mechanical property of the part obtained under different parameters;

[0031] Figure 4 is the part obtained by conventional process route protection gas cooling; figure a is the macrograph of the front of the part; figure b is the macrograph of the top of the part;

[0032] Figure 5 is the part obtained by the process route of the present application natural cooling; figure a is the macrograph of the front of the part; figure b is the CT scan of the part;

[0033] Figure 6 is the part obtained by electrolyte plasma polishing; figure a is the part before polishing; figure b is the part after polishing. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical scheme and advantages of the present application more clear and obvious, the following will be further described in detail in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application, and are not used to limit the present application, that is, the described examples are only a part of the examples of the present application, but not all the examples.

[0035] The components described and illustrated in the accompanying drawings and embodiments of this invention can be arranged and designed in various different configurations. Therefore, the detailed description of the embodiments of the invention provided in the following drawings is not intended to limit the scope of the claimed invention, but merely to illustrate one selected embodiment of the invention. All other embodiments obtained by those skilled in the art based on the accompanying drawings and embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0036] It should be noted that the terms “comprising,” “including,” or any other variations are intended to cover non-exclusive inclusion, such that a process, element, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to the process, element, method, article, or apparatus.

[0037] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0038] Example 1

[0039] Nickel-based superalloy M247 samples were prepared using an Arcam A2X instrument. The input process parameters, including defocusing amount, line spacing, line speed, and current, were varied. The baseline values ​​for each input variable are shown in Table 1. Components with different process parameters were printed on the same substrate, and their surface quality was inspected using a penetrant method. After spraying penetrant and developer onto the sample surface sequentially, the appearance of a magenta color indicated surface defects, thus determining the forming quality of the sample surface.

[0040] Table 1. Baseline values ​​for each parameter

[0041] Scan speed V (m / s) Electron beam current I (mA) Scan pitch L (mm) Defocus D (mA) 0.6 8 0.125 30

[0042] A single-factor test was conducted based on the baseline value. With other parameters fixed, the test parameters were varied, and the results were printed to obtain several control cases. The corresponding results are as follows: Figure 1 As shown.

[0043] from Figure 1 The penetration effect in (a) shows that the surface quality of the sample deteriorates with increasing scanning speed. When the scanning speed is between 0.8 m / s and 2 m / s, the sample surface is almost entirely composed of defects. This is because when the scanning speed is too fast, the powder melts unevenly after the electron beam passes through the powder bed, which may lead to forming defects such as incomplete fusion and spheroidization, thus deteriorating the surface quality of the sample.

[0044] from Figure 1The penetration effect of (b) can be found that the surface quality of the sample piece is getting better and better with the increase of the electron beam current. When the electron beam current is in the range of 3 to 6 mA, the surface of the sample piece is almost full of defects. This is because, with the gradual increase of the current, the electron beam power also gradually increases, the powder is melted more fully, and when the current is in a higher state, the molten pool state during printing is more stable, and the surface forming quality of the sample piece after solidification is also better.

[0045] From Figure 1 The penetration effect of (c) can be found that the surface quality of the sample piece gradually deteriorates with the increase of the defocus amount, but the overall change is small. When the defocus amount is greater than 70 mA, some partial defects appear on the surface of the sample piece. This is because when the defocus amount increases, the electron beam flow energy applied to the powder bed is dispersed, which may cause the powder not to be penetrated, thereby affecting the surface quality of the part.

[0046] From Figure 1 The penetration effect of (d) can be found that the surface quality of the sample piece almost does not change with the increase of the line spacing. Because the change of the line spacing cannot essentially affect the change of the molten pool size of the electron beam heat source, it can only affect the scanning path of the electron beam heat source, and has little effect on the surface quality of the part.

[0047] Comprehensive Figure 1 Based on the results of Table 1, it is preliminarily determined that the printing parameter range of the part forming is that the electron beam scanning speed is in the range of 0.4-0.6 m / s, the defocus amount is in the range of 40-70 mA, and the current size is in the range of 8-15 mA, so that the electron beam line energy density in the printing process is in the range of 800-1200 J / mm.

[0048] Example 2

[0049] Based on the range obtained in Example 1, the intermediate suitable values are taken as the high and low levels to carry out a full-factor experiment, a mathematical model of the parameters and the surface roughness can be obtained, the mutual influence between the parameters can be further determined, and the suitable parameters can be finally analyzed. The selection of each factor and different level values in the experiment are as follows in Table 2.

[0050] Table 2 Parameter levels of full-factor experiment

[0051] Experimental parameters Scan speed (m / s) Electron beam current (mA) Scan pitch (mm) Defocus (mA) High level 0.6 12 0.135 70 Low level 0.4 8 0.120 60

[0052] The surface roughness of the printed sample piece is taken as the output result of the full-factor experiment, and the experimental results are as follows in Table 3.

[0053] Table 3 Results of full-factor experiment

[0054] Number Defocus (mA) Line pitch (mm) Speed (m / s) Current (mA) Roughness (pm) 1 70 0.135 0.6 12 71.23 2 60 0.12 0.6 8 106.2 3 60 0.135 0.4 12 226.5 4 70 0.12 0.4 12 113.8 5 60 0.12 0.6 12 168.6 6 70 0.12 0.6 12 91.89 7 70 0.12 0.4 8 53.2 8 60 0.135 0.6 8 93.13 9 70 0.135 0.4 12 104.8 10 70 0.12 0.6 8 83.86 11 60 0.135 0.4 8 94.82 12 70 0.135 0.6 8 101.7 13 60 0.12 0.4 8 109.5 14 70 0.135 0.4 8 61.15 15 60 0.135 0.6 12 142.2 16 60 0.12 0.4 12 128.1 17 65 0.125 0.5 10 73.85 18 65 0.125 0.5 10 78.88 19 65 0.125 0.5 10 79.01

[0055] Based on the results in Table 3, a mathematical model was established and fitted. The final result shows that the influence of each process parameter on the forming quality is as follows: defocusing amount > current > interaction of defocusing amount and current > interaction of current and speed > speed. This establishes the selection rules for each printing parameter in engineering applications.

[0056] Tensile properties were tested on 19 samples from Example 2 to obtain their tensile strength and elongation at break at room temperature. The test results are as follows: Figure 2 .observe Figure 2 Within the parameter range obtained from Example 1, the tensile strength of the printed sample is 1100±100MPa, and the specified plastic elongation strength is 700±100MPa, which basically meets the established engineering requirements.

[0057] Six samples with the best surface roughness were selected, specifically numbered 1, 7, 14, 17, 18, and 19. The parameters corresponding to these six samples were printed, and their tensile properties at 900℃ were tested. The test results are as follows: Figure 3 As shown. Observation Figure 3 It can be seen that within the optimal parameter range, the high-temperature tensile properties of the obtained samples are better. Among them, the tensile strength of half of the samples is above 700MPa, the highest tensile strength can reach 750MPa, and the highest specified plastic elongation strength can reach 500MPa.

[0058] Therefore, the process route parameter range proposed in this invention can produce parts with good mechanical properties and surface quality.

[0059] Example 3

[0060] Within the printing parameter range obtained in Example 1, parameters were selected according to the selection rules obtained in Example 2. Experiments were conducted at higher parameter levels, using a defocusing amount of 75mA, a current of 12mA, and a scanning speed of 0.7m / s for part printing. After deposition, conventional cooling methods were used, with helium protective gas introduced at the end of printing for cooling, allowing for rapid part cooling. After cooling, the printed parts were removed, and the surface quality and macroscopic crack conditions were observed. Figure 4 As shown, Figure 4 a is a macroscopic view of the front of the part. Figure 4 b is a macroscopic view of the top of the part, where a clear through-type macroscopic crack can be seen.

[0061] Example 4

[0062] The parts were printed using the same printing parameters as in Example 3. After deposition, natural cooling was employed, and the printing equipment was manually operated to stop the helium protective gas supply, ensuring the parts were in a vacuum of 2*10⁻⁶. -3Natural cooling was performed under a vacuum below mbar, resulting in a longer cooling time for the part compared to Example 3. After cooling, the printed part was removed, and its surface quality and macroscopic crack conditions were observed. Figure 5 As shown.

[0063] Observe Examples 3 and 4, from Figure 4 It can be seen that conventional cooling methods, when manufacturing tall parts, result in high residual stress levels within the parts due to the high cooling rate, making them prone to through-cracks. This severely affects the forming quality and usability of the parts, and subsequent processing is insufficient to eliminate these macroscopic cracks. Figure 5 a and Figure 5 As shown in Figure b, by using natural cooling and manually shutting off the protective gas supply, the parts cool naturally, resulting in good surface molding quality and no large macroscopic cracks. The process route proposed in this invention can significantly reduce the generation of macroscopic cracks during the printing process, giving the parts better surface quality and mechanical properties.

[0064] Example 5

[0065] The parts were printed and cooled using the parameters and processes described in Example 3. After cooling, the parts were removed and post-processed to remove excess powder sintered and adhered to the surface, and then separated from the substrate. Preliminary surface treatments, including grinding and shot peening, were performed. The parts were then placed in an electrolyte plasma polishing device, immersed in an electrolytic cell, with the electrolytic voltage controlled at 320-350V, the anode-cathode distance at 20-30mm, the electrolyte temperature at 70-85℃, and the electrolyte flow rate at 10-15L / min.

[0066] After polishing, the parts were removed and cleaned. The parts before and after polishing are shown below. Figure 6 a and Figure 6 As shown in b, the surface roughness of the polished sample was measured using a MarSurf linear roughness meter. From... Figure 6 b shows that after polishing, the parts have a metallic luster, good forming effect, no cracks on the outer surface, and high forming precision. At the same time, the surface quality is also greatly improved after polishing, and the roughness value of the outer curved surface can reach Ra9.53μm.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for improving the surface quality of M247 manufactured using electron beam selective melting technology, characterized in that, Includes the following steps: (1) Electron beam selective melting technology is used to deposit and form M247 parts. During the deposition process, the electron beam parameters are controlled as follows: the electron beam scanning speed is controlled at 0.4-0.6m / s, the defocusing amount is controlled at 40-70mA, and the current is controlled at 8-15mA, so that the electron beam line energy density during the printing process is in the range of 800-1200J / mm. (2) After the part is printed, allow the part to cool naturally in a vacuum environment, and then remove the part after cooling. (3) After the parts are initially treated, they are placed in an electrolyte plasma polishing equipment for surface treatment. The parts are immersed in the electrolyte and then subjected to electrolyte plasma polishing to improve the surface quality of the parts.

2. The method for improving the surface quality of M247 manufactured using electron beam selective melting technology according to claim 1, characterized in that, In step (1), the order of influence of electron beam parameters on part forming quality is as follows: defocusing amount > current > interaction of defocusing amount and current > interaction of current and electron beam scanning speed > electron beam scanning speed.

3. The method for improving the surface quality of M247 manufactured using electron beam selective melting technology according to claim 1, characterized in that, Step (2) specifically involves: After the part is printed, stop the protective gas supply and allow the part to cool naturally in a vacuum environment. After the part has cooled sufficiently, introduce air and remove the part.

4. The method for improving the surface quality of M247 manufactured using electron beam selective melting technology according to claim 3, characterized in that, The vacuum environment requires a vacuum level of 2*10. -3 Below mbar.

5. The method for improving the surface quality of M247 manufactured using electron beam selective melting technology according to claim 3, characterized in that, Helium is used as the protective gas.

6. The method for improving the surface quality of M247 manufactured using electron beam selective melting technology according to claim 1, characterized in that, In step (3), the electrolysis voltage is controlled at 320-350V, the distance between the anode and cathode is 20-30mm, the electrolyte temperature is 70-85℃, and the electrolyte flow rate is 10-15L / min.

7. The method for improving the surface quality of M247 manufactured using electron beam selective melting technology according to claim 1, characterized in that, After completing the electrolyte plasma polishing, the final part was tested for tensile properties at room temperature. The tensile strength reached 1100±100MPa, and the specified plastic elongation strength reached 700±100MPa. Tensile properties were tested at 900℃, with a maximum tensile strength of 750 MPa and a maximum specified plastic elongation strength of 500 MPa.

8. The method for improving the surface quality of M247 manufactured using electron beam selective melting technology according to claim 1, characterized in that, In step (3), the preliminary treatment is to remove excess powder from the surface of the parts.

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