Method for improving performance of laser selective melting forming pure tungsten grid

Abstract

The application provides a method for improving the performance of laser selective melting forming pure tungsten grid. By adding rare earth tantalate RETaO4 as a nucleating agent, the strength and hardness of the tungsten grid are improved, and it is more durable. In addition, the use of double-layer glow plasma surface alloying technology can further improve its performance, making it more corrosion resistant and wear resistant. The tungsten grid sample prepared by the tungsten composite powder formula and surface modification of the application can effectively improve the tensile properties and elongation, and can improve its toughness and high temperature resistance. The toughness is increased by about three times, and the specific wear rate is reduced by one unit.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metal additive manufacturing, and relates to metallurgical mining, in particular to a method for improving the performance of laser selective melting forming pure tungsten grid. BACKGROUND

[0002] Laser selective melting technology (SLM) is an advanced additive manufacturing (AM) technology, also known as metal 3D printing technology. It uses a high-energy laser beam to melt metal powder layer by layer to build a three-dimensional object. It can manufacture complex three-dimensional structures, including internal cavities, threads, and mesh structures, without the need for traditional mechanical processing molds. Because it can manufacture complex whole parts at one time, reduce subsequent assembly processes, and shorten the manufacturing time of parts, compared with traditional cutting processing methods, SLM can improve the utilization rate of raw materials. Laser selective melting forming is a high-precision and high-efficiency manufacturing process, and is widely used in the fields of aerospace, automobile, and electronics. Pure tungsten grid, as an important structural material, has high strength, high hardness, high wear resistance, and corrosion resistance, and is widely used in laser forming field. However, in practical application, pure tungsten grid has some problems, such as brittleness, difficulty in forming, poor surface quality, etc., which limit its application in laser forming field.

[0003] The existing method for improving the performance of laser selective melting forming pure tungsten grid has the technical problems mainly related to the brittleness, low plasticity, and poor thermal stability of tungsten, and the sample is affected by cracks and hole defects, and the mechanical properties are poor, which cannot meet the requirements of industrial application. SUMMARY

[0004] The purpose of the present application is to provide a method for improving the performance of laser selective melting forming pure tungsten grid, which adds rare earth tantalate RETaO4 as a nucleating agent to improve the strength and hardness of tungsten grid, making it more durable. In addition, the use of double-layer glow plasma surface alloying technology can further improve its performance, making it more corrosion-resistant and wear-resistant. The tungsten grid sample prepared by the tungsten composite powder formula and surface modification of the present application can effectively improve the tensile properties and elongation, and can improve its toughness and high temperature resistance. The toughness is about three times higher, and the specific wear rate is reduced by one unit.

[0005] To achieve the above purpose, the present application adopts the following technical scheme:

[0006] A tungsten composite powder mass fraction ratio: 3.0 wt.% RETaO4 + 97.0 wt.% pure tungsten powder.

[0007] The present application also proposes a preparation method and a forming method of the above-mentioned composite powder, and the preparation and forming method comprises:

[0008] (1) Weigh the corresponding mass of RETaO4 powder and pure tungsten powder according to the proportion; wherein the RETaO4 powder is prepared by mixing 86.76 grams of Y2O3, 113.24 grams of Ta2O5, 8676 milliliters of anhydrous ethanol as an activator, and 20.3 grams of Li2SO4 fluxing agent, ball milling, and calcining at 1250 DEG C for 10 hours; and the pure tungsten powder is selected as a spherical, uniform and good flowability powder;

[0009] (2) Ball mill the two powders;

[0010] (3) Put the composite powder of step (2) into a drying oven;

[0011] (4) Put the dried composite powder in step (3) into an SLM Solution 125 metal additive manufacturing equipment to form a grid sample;

[0012] (5) Perform double-layer glow plasma surface alloying on the formed sample obtained in step (4).

[0013] In step (1), the pure tungsten powder is a solid sphere with a particle size of 15-40 mm; and the RETaO4 powder particles are solid spheres with a particle size of 5-25 mm.

[0014] In step (2), the jar mill rotates at 100-110 revolutions per minute, and the jar milling time is 10 hours. The powder jar is vibrated for 10-12 minutes every 1-2 hours.

[0015] In step (3), the drying oven is vacuumized, the drying temperature is 80 DEG C, and the drying time is 4 hours.

[0016] In step (4), the forming process parameters are as follows: the laser power is 250-370 W, the scanning speed is 250-400 mm / s, the scanning interval is 70-90 mm, the powder laying thickness is 20-30 mm, the substrate is a tungsten substrate, the substrate preheating temperature is 190-200 DEG C, the adjacent powder layer scanning angle is rotated by 90 DEG, the forming chamber uses argon, and the oxygen content is 100-150 ppm.

[0017] In step (5), a W-Ti-Zr-Cr alloy layer is formed on the surface of the tungsten grid sample by the double-layer glow plasma surface alloying process, and the thickness of the W-Ti-Zr-Cr alloy layer is 8 microns.

[0018] The advantages of the present application are:

[0019] Compared with the prior art, the solid spherical RETaO4 powder particle used in the application, in which Y2O3 is doped into tungsten as a second phase particle, improves the strength and thermal stability of tungsten through second phase dispersion strengthening, purifies the grain boundary, has a dispersion strengthening effect on pure tungsten material, and the dispersion of the oxide in the tungsten matrix can improve the strength and toughness of the tungsten matrix material. Ta2O5 has high hardness, high melting point, good thermal stability and chemical stability, can be effectively dispersed in the tungsten matrix, and can improve the hardness and wear resistance of the alloy; and can help to improve the performance and corrosion resistance of the tungsten alloy in a high-temperature environment, especially in an oxidizing environment.

[0020] The application eliminates the crack defects generated by laser selective melting of the tungsten-aluminum alloy, and the mechanical properties are greatly improved compared with the pure tungsten printed sample. The alloy layer prepared by adding the RETaO4 powder particle and the 1200℃+1000℃ (two-stage heating) process has a fracture toughness of 30.21 MPa·m^0.5, which is better than the fracture toughness KIC of 10 MPa·m^0.5 of pure tungsten. The specific wear rate of the alloy layer prepared by adding the RETaO4 powder particle and the 1200℃+1000℃ process is 5.60×10 -6 mm 3 / (N·m), which is one order of magnitude smaller than that of pure tungsten (4.66×10 -5 mm 3 / (N·m). BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 It is a macrograph of the sample formed by laser selective melting of Example 1 of the application;

[0022] Figure 2 It is an XRD spectrum of the tungsten powder and the pure tungsten sample of Comparative Example 2 of the application;

[0023] Figure 3 It is an XRD spectrum of RETaO4 of the application;

[0024] Figure 4 It is a microhardness curve of the sample formed by laser selective melting of Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3 of the application under different loads. It can be seen from Figure 4 that the addition of the RETaO4 powder particle and the double-layer glow plasma surface alloying process significantly improves the surface hardness of the substrate, and the hardness decreases with the increase of the load. DETAILED DESCRIPTION

[0025] In order to make the above features and advantages of the application more obvious and easy to understand, the following examples are used for detailed description. The method of the application is a conventional method in the art unless otherwise specified.

[0026] Example 1

[0027] The application discloses a method for improving the performance of a laser selective melting forming tungsten grid, and comprises the following steps.

[0028] S1. Two powders are weighed according to the proportion of 3.0 wt.% RETaO4+97.0 wt.% pure tungsten powder for standby;

[0029] S2. The mixed powder weighed in S1 is subjected to jar milling treatment, the jar milling time is 10 hours, the ball milling rotating speed is 100 r / min, every 1 hour, the powder jar is vibrated for 10 minutes; the composite powder is placed into a drying oven for drying, the drying oven is vacuumized, the drying temperature is 80 DEG C, and the drying time is 4 hours;

[0030] S3. The composite powder dried in S2 is subjected to laser selective melting forming: the forming process parameters are as follows: the laser power is 250 W, the scanning speed is 300 mm / s, the scanning interval is 70 mm, the powder laying thickness is 30 mm, the substrate is a tungsten substrate, the substrate preheating temperature is 200 DEG C, the adjacent powder layer scanning angle is rotated by 90 DEG, argon is used in the forming chamber, and the oxygen content is 100 ppm;

[0031] S4. The printed and formed tungsten grid sample is subjected to double-layer glow plasma surface alloying: an anode, a cathode and a source electrode are arranged in a vacuum container, the abnormal glow discharge phenomenon is used to accelerate the ion bombardment on the surfaces of the cathode and the source electrode, so that a W-Ti-Zr-Cr surface alloy diffusion layer with a thickness of about 8 microns is formed, the method has the advantages of fast diffusion speed, the ability to form a dense alloy layer structure, good surface quality, no environmental pollution and the like, and is a suitable method for improving the wear resistance and corrosion resistance of the tungsten grid.

[0032] The specific operation of the DGPSA technology is as follows: 1. Pretreatment: including degreasing, polishing and polishing of the tungsten grid sample to obtain a clean surface with a certain roughness. Ultrasonic cleaning is performed, and the sample is dried for standby. 2. Sample installation: place the tungsten grid sample on the sample table and ensure that it is fixed and stable. 3. Source preparation: prepare the W-Ti-Zr-Cr alloy target material to hang at a source position 15 mm away from the workpiece, wherein the target material refers to several W, Ti, Zr and Cr metal rods with a purity of 99.9% and a size of Φ1.5×40 mm. A pure titanium plate with a size of 100×100×3 mm is processed with several equidistant holes for fixing the four metal rods. The four metal rods are inserted into the holes in an equal proportion and arranged in a circular manner to obtain a target plate. 4. Vacuum and gas preparation: start the cooling water circulation system, use a mechanical pump to perform vacuum pumping, and when the vacuum degree is less than 1 Pa, fill in high-purity argon gas for cleaning and then pump to vacuum again. 5. Alloying process: adjust the mechanical valve and argon gas flow, and adjust the working gas pressure to 40 Pa. Perform pre-sputtering to remove contaminants on the surface of the target material. After reaching the preset alloying temperature, keep the temperature constant and start the alloying process. Start the temperature timer, and maintain the stability of the workpiece temperature by adjusting the optimal source voltage of 700-1000 V and the workpiece voltage of 300-600 V. 6. Cooling and sample removal: after the temperature holding is over, remove the sample after it cools to room temperature.

[0033] The main parameters of the DGPSA technology are as follows: metal penetration temperature: 1200℃+1000℃ (two-stage heating). Holding time: 3+3 hours (two-stage heating). Working gas pressure: 40 Pa. Inter-electrode distance: 15 mm. Workpiece pulse power parameters: duty cycle 62%, frequency 50 kHz. Two-stage heating process refers to first holding at 1200℃ for 3h, then cooling to 1000℃, and continuing to hold for 3h.

[0034] Comparative Example 1

[0035] S1, weigh two kinds of powders according to the proportion of 3.0 wt.% RETaO4+97.0 wt.% pure tungsten powder for standby;

[0036] S2, jar mill treatment is performed on the mixed powders weighed in S1, the jar mill time is 10 hours, the ball mill rotation speed is 100 revolutions / minute, every 1 hour, the powder jar is vibrated for 10 minutes; the composite powder is placed in a drying oven, the drying oven is vacuumized, the drying temperature is 80℃, and the drying time is 4 hours;

[0037] S3. Laser selective melting and forming of the composite powder dried in S2: Forming process parameters: laser power is 250W, scanning speed is 300mm / s, scanning interval is 70mm, powder thickness is 30mm, substrate is tungsten substrate, substrate preheating temperature is 200℃, adjacent powder layer scanning angle is rotated 90°, argon gas is used in the forming chamber, and oxygen content is 100ppm; double-layer glow plasma surface alloying treatment is not performed on the printed parts.

[0038] Comparative Example 2

[0039] S1. Weigh a certain amount of pure tungsten powder for later use; put the pure tungsten powder into a drying oven and dry it. The drying oven is vacuumed, the drying temperature is 80℃, and the drying time is 4 hours.

[0040] S2. Laser selective melting and forming of the dried pure tungsten powder from S1: Forming process parameters: laser power is 250W, scanning speed is 300mm / s, scanning interval is 70mm, powder thickness is 30mm, substrate is tungsten substrate, substrate preheating temperature is 200℃, adjacent powder layer scanning angle is rotated 90°, argon gas is used in the forming chamber, oxygen content is 100ppm, and double-layer glow plasma surface alloying treatment is not performed on the printed parts.

[0041] Comparative Example 3

[0042] S1. Weigh a certain amount of pure tungsten powder for later use; put the pure tungsten powder into a drying oven and dry it. The drying oven is vacuumed, the drying temperature is 80℃, and the drying time is 4 hours.

[0043] S2. Laser selective melting and forming of the dried pure tungsten powder from S1: Forming process parameters: laser power is 250W, scanning speed is 300mm / s, scanning interval is 70mm, powder thickness is 30mm, substrate is tungsten substrate, substrate preheating temperature is 200℃, adjacent powder layers are rotated 90°, and argon gas is used in the forming chamber with an oxygen content of 100ppm.

[0044] S3. Perform double-layer glow plasma surface alloying on the printed pure tungsten grid sample: The process is the same as in Example 1.

[0045] The fracture toughness and specific wear rate data of the samples obtained in Example 1 and Comparative Examples 1-3 are shown in the table below.

[0046]

[0047] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. A method for improving the performance of laser selective melting forming of pure tungsten grids, characterized in that, Includes the following steps: (1) Tungsten composite powder formulation: 3.0~3.5 wt.% RETaO4 powder, the balance being pure tungsten powder; weigh out the corresponding mass of RETaO4 powder and pure tungsten powder according to the proportion, and mix the two powders by ball milling; wherein the RETaO4 powder is prepared by mixing and ball milling 86.76 g of Y2O3, 113.24 g of Ta2O5, 8676 ml of anhydrous ethanol as activator and 20.3 g of Li2SO4 flux, and calcining at 1250℃ for 10 hours; (2) Place the composite powder obtained in step (1) into a drying oven and dry it; (3) Place the dried composite powder from step (2) into an SLM molding device to obtain a grid sample; (4) Perform double-layer glow plasma surface alloying on the grating sample obtained in step (3).

2. The method according to claim 1, characterized in that: The pure tungsten powder is solid spherical with a particle size of 15-40 mm; the RETaO4 powder particles are solid spherical with a particle size of 5-25 mm.

3. The method according to claim 1, characterized in that: In step (1), the ball mill speed is 100-110 rpm and the ball milling time is 10 hours. The powder jar is vibrated for 10-12 minutes every hour.

4. The method according to claim 1, characterized in that: In step (2), the drying oven is evacuated, the drying temperature is 80℃, and the drying time is 4 hours.

5. The method according to claim 1, characterized in that: In step (3), the laser selective melting forming process parameters are as follows: laser power is 250-370W, scanning speed is 250-400mm / s, scanning distance is 70-90mm, powder thickness is 20-30mm, substrate is tungsten substrate, substrate preheating temperature is 190-200℃, adjacent powder layer scanning angle is rotated 90°, forming chamber uses argon gas, and oxygen content is 100ppm-150ppm.

6. The method according to claim 1, characterized in that: In step (4), a W-Ti-Zr-Cr alloy layer is formed on the surface of the tungsten grid sample by a double-layer glow plasma surface alloying process, wherein the thickness of the W-Ti-Zr-Cr alloy layer is 8 μm.

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