Tungsten-containing / high-entropy alloy slurry for inkjet direct additive manufacturing and application thereof

Abstract

The application aims to provide a slurry containing tungsten / high-entropy alloy for ink direct writing additive manufacturing and application thereof, and belongs to the technical field of 3D printing forming, characterized in that the slurry is composed of polyvinyl alcohol, glycerol and tungsten / high-entropy alloy mixed powder, and polyvinylpyrrolidone, cellulose and deionized water can be added to the slurry. The slurry is particularly suitable for preparing additive manufacturing samples of high-melting-point metals at room temperature. Compared with existing room-temperature additive manufacturing technologies, the application effectively improves the stability of the slurry, reduces the production cost, is simple to operate, has low requirements for protective facilities, is very safe and environmentally friendly.

Description

TECHNICAL FIELD

[0001] The application discloses a slurry for additive manufacturing of tungsten / high-entropy alloy composite material based on ink direct writing technology and a method for preparing high-melting-point metal additive manufacturing products by using the slurry, and belongs to the technical field of 3D printing forming. BACKGROUND

[0002] At present, additive manufacturing technology is developing rapidly, and laser cladding, electron beam cladding and high-energy directional deposition technology are becoming more and more mature, but they also have their limitations, including residual stress in the part, removal of excess powder, and microstructure gradient and defects (pores and cracks) in the part due to thermal gradient after electron beam or laser sintering. The method of realizing additive manufacturing by melting method is considered as a rapid solidification process, and the melting of high-melting-point metals in the additive manufacturing process will inevitably produce a large temperature gradient, accompanied by a large internal stress, making it difficult to realize the melting additive manufacturing of high-melting-point metals.

[0003] Based on the shortcomings of the direct melting additive manufacturing method, in recent years, a room-temperature additive manufacturing technology, namely "ink direct writing additive manufacturing", has emerged. This method mixes metal powder with dispersants, solvents, surfactants and other organic matters in a certain proportion to form additive manufacturing slurry. The slurry is extruded and stacked into a specific geometric shape through the needle of the ink direct writing additive manufacturing equipment. During the preparation process, the solvent volatilizes, and then the residual organic matter is heated and decomposed. Finally, the additive manufacturing sample is sintered (or sintered after reduction), thereby obtaining an ideal design material with certain strength.

[0004] The existing room-temperature additive manufacturing technology mainly uses volatile solvent dichloromethane (DCM) and dispersant polylactic acid-hydroxyacetic acid copolymer (PLGA) based additive manufacturing slurry. DCM, as a volatile solvent, is beneficial to the drying of the sample during the preparation process, so that the bottom layer has a certain strength and ensures that the upper layer will not collapse during continuous stacking. However, this is also the disadvantage of DCM, because it is toxic, which requires high safety measures for the additive manufacturing equipment and additive manufacturing site. In addition, due to the volatile nature of DCM, the properties of this kind of additive manufacturing slurry are very unstable. The volatilization of the slurry that is not extruded during the additive manufacturing process will directly affect the viscosity of the slurry, and then affect the quality of the additive manufacturing sample. PLGA has good dispersibility for metal and metal oxide powders, and can be completely removed during heating. However, due to its high cost, it is difficult to be widely used.

[0005] In general, the existing melting additive manufacturing technology is difficult to prepare additive manufacturing products of high-melting-point metals (such as W). The existing room-temperature additive manufacturing technology has many limitations in actual production process due to the instability of the slurry, the toxicity of the volatile solvent and the high cost of PLGA. SUMMARY

[0006] In order to overcome the deficiencies in the prior art, the present application provides a slurry containing tungsten / high-entropy alloy for ink direct writing additive manufacturing, which can be used to prepare tungsten / high-entropy alloy composite additive manufacturing products with specific shapes and certain strength. Another object of the present application is to provide a low-cost, easy-to-operate and safe and environmentally friendly room temperature additive manufacturing method.

[0007] The technical scheme of the present application is as follows:

[0008] A slurry A containing tungsten / high-entropy alloy for ink direct writing additive manufacturing, characterized in that the composition of the slurry comprises polyvinyl alcohol (PVA), glycerol (Gl), tungsten (W) powder or tungsten / high-entropy alloy mixed powder. The slurry is suitable for a preparation method of additive manufacturing with a temperature control device on the cartridge followed by debinding and sintering.

[0009] Among them, the addition amount of glycerol is 15-20 parts by weight, and the addition amount of polyvinyl alcohol is 0.9-1.6 parts by weight, relative to 100 parts by weight of the mixed powder of tungsten / cobalt-chromium-iron-nickel high-entropy alloy.

[0010] The preparation method of the slurry A is as follows: first, prepare a polyvinyl alcohol / glycerol solution, the concentration of polyvinyl alcohol in the solution is 80-100 mg / mL; heat the mixed polyvinyl alcohol / glycerol to 130-160 DEG C in an oil bath and stir at the same time for 3-5 h, so that the polyvinyl alcohol is completely dissolved, then mix the tungsten / high-entropy alloy mixed powder with the polyvinyl alcohol / glycerol solution at 80 DEG C to obtain the slurry for ink direct writing additive manufacturing.

[0011] The present application also provides another slurry B containing tungsten / high-entropy alloy for ink direct writing additive manufacturing, characterized in that the slurry is composed of polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), cellulose, glycerol, deionized water and tungsten / high-entropy alloy mixed powder. The slurry is suitable for a preparation method of room temperature additive manufacturing followed by debinding and sintering.

[0012] Among them, the addition amount of glycerol is 10-20 parts by weight, the addition amount of polyvinyl alcohol is 0.35-1.08 parts by weight, the addition amount of deionized water is 1-6 parts by weight, the addition amount of polyvinylpyrrolidone is 0.07-0.54 parts by weight, and the addition amount of cellulose is 0.08-0.9 parts by weight, relative to 100 parts by weight of the powder of tungsten / cobalt-chromium-iron-nickel high-entropy alloy.

[0013] As a preferred technical scheme, the cellulose is prepared from loofah sponge as raw material by bleaching, acid washing, alkali washing and freeze-drying.

[0014] The preparation method of the slurry B is: first, prepare a polyvinyl alcohol / glycerol solution, the concentration of polyvinyl alcohol in the solution is 50-70 mg / mL; the mixed polyvinyl alcohol / glycerol is heated to 130-160℃ in an oil bath and stirred at the same time for 3-5h, so that the polyvinyl alcohol is completely dissolved; then prepare a cellulose / polyvinylpyrrolidone / water solution, the concentration of cellulose in the solution is 80-150 mg / mL, and the concentration of polyvinylpyrrolidone is 70-90 mg / mL; finally, mix tungsten / high-entropy alloy mixed powder, polyvinyl alcohol / glycerol solution and cellulose / polyvinylpyrrolidone / water solution to prepare the slurry for ink direct writing additive manufacturing.

[0015] In the above-mentioned slurry A and slurry B, the particle size of the tungsten / high-entropy alloy mixed powder is 2-4 μm. The system of the high-entropy alloy is not particularly limited, and is preferably equiatomic high-entropy alloy FeCoNi, FeCoNiCr, FeCoNiCrMn, FeCoNiAlMn, FeCoNiCuAl, FeCoNiCrAlMnCu.

[0016] In the above-mentioned slurry A and slurry B, the tungsten / high-entropy alloy mixed powder is most preferably made of tungsten, cobalt, chromium, iron and nickel powder, and their atomic ratio is 55:11.25:11.25:11.25:11.25.

[0017] The above-mentioned slurry A and slurry B can be used to prepare high-melting-point metal additive manufacturing products, and the printing error can be controlled within 0.3 mm.

[0018] In which, due to the too high powder content of the slurry A, the slurry is too dry to be extruded, so it needs to be applied with a temperature control device cartridge, which softens the slurry by heating the cartridge, so that the high powder content slurry is smoothly extruded. The temperature of the cartridge during printing is between 130-160℃, and the slurry extruded through the heated cartridge has excellent formability, and its properties are close to rubber.

[0019] Working principle: PVA is dissolved in Gl to form a jelly-like mixture, PVA plays a role in improving the viscosity of the slurry, Gl plays a role in lubrication and thickening, and PVP and cellulose act as dispersants. The metal powder / PVA / Gl slurry is placed in the tube of the ink direct writing additive manufacturing equipment, and is extruded from the needle under the action of air pressure to form a printing filament. The printing filament is stacked layer by layer to obtain an additive manufacturing product with a preset shape. For A slurry, the A slurry is softened and extruded through a cartridge with heating function; for B slurry, it can be directly extruded at room temperature. The subsequent evaporation process selects 120℃ to slowly evaporate Gl, and the evaporation temperature cannot be higher than 120℃, otherwise the product will collapse due to softening. Then remove PVA, PVP and cellulose at 800℃ and sinter at a suitable temperature.

[0020] The present application has the following significant features compared with the prior art:

[0021] 1. The present application can prepare additive manufacturing samples of high melting point metals (such as tungsten) at room temperature. The stress generated by the post-additive manufacturing sintering process is greatly reduced compared with the direct melting additive manufacturing method, making the additive manufacturing of high melting point metals more simple.

[0022] 2. The slurry A described in the present application is non-volatile and can be stored for a long time without sealing. Both the slurry A and the slurry B have good stability and will not delaminate during printing. The extruded filaments are uniform and stable.

[0023] 3. The slurry described in the present application does not contain toxic substances, has good safety compared with the slurry using DCM as the solvent, and is very environmentally friendly, only producing waste gas during debinding, and the collection of waste gas is also very convenient.

[0024] 4. The additive manufacturing slurry described in the present application has higher stability, lower requirements for additive manufacturing equipment, and simple operation. The requirement for protective facilities is very low, and it is very safe and environmentally friendly, which reduces the production cost of the product.

[0025] 5. Various high melting point metal additive manufacturing products can be prepared using the slurry described in the present application, such as metal lusterous reticular porous structure products. The compressive fracture limit of the tungsten reticular porous printing product is 296 MPa, and the compressive fracture limit of the tungsten / high-entropy alloy reticular porous printing product is 300 MPa. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 It is the tungsten / high-entropy alloy slurry additive manufacturing product of Example 1 just after printing.

[0027] Figure 2 It is the dried green body of the additive manufacturing product of Example 1.

[0028] Figure 3 It is the tungsten / high-entropy alloy slurry additive manufacturing product of Example 1 sintered at 1450℃.

[0029] Figure 4 It is the tungsten / high-entropy alloy slurry additive manufacturing product of Example 2 sintered at 1500℃.

[0030] Figure 5 It is the microstructure of the tungsten / cobalt-chromium-iron-nickel additive manufacturing product of Example 2 after sintering.

[0031] Figure 6 It is the tungsten / cobalt-chromium-iron-nickel additive manufacturing product of Example 4 (the left picture is the product just after printing, and the right picture is the tungsten 3D printing product sintered at 1450℃).

[0032] Figure 7 This is a microstructure diagram of the tungsten / cobalt-chromium-iron-nickel additively manufactured product of Example 4 after sintering.

[0033] Figure 8 This is the microstructure diagram of the tungsten / cobalt-chromium-iron-nickel additively manufactured product in Example 4.

[0034] Figure 9 This is a solid sheet structure printed for the tungsten / cobalt-chromium-iron-nickel additive manufacturing product of Example 4.

[0035] Figure 10 The product of Comparative Example 1 was printed. DETAILED DESCRIPTION

[0036] The preferred embodiments of the present invention will be described in detail below. Although the following description is of a preferred embodiment of the present invention, it should be understood that the present invention can be implemented in other ways and should not be limited by this method.

[0037] Example 1

[0038] (1) A PVA / Gl solution mixture with a concentration of 90 mg / ml was prepared. The PVA / Gl mixture was heated to 150°C in an oil bath and stirred for 3 h to fully dissolve the PVA to obtain a jelly-like PVA / Gl solution mixture.

[0039] (2) Tungsten, cobalt, chromium, iron, and nickel powders (W / CoCrFeNi powders) with a particle size of 2 to 4 μm were mixed in an atomic ratio of 55:11.25:11.25:11.25:11.25 to obtain a tungsten / high entropy alloy mixed powder.

[0040] (3) The mixed W / CoCrFeNi powder and PVA / Gl solution were mixed at 80°C. The mass ratio of W / CoCrFeNi powder, PVA, and Gl was 100:20:1.38. After mixing evenly, W / CoCrFeNi / PVA / Gl slurry was obtained (the properties were close to rubber when cooled to room temperature).

[0041] (4) Draw a porous cube using Cinema 4D software and export it as an STL format model. Import the STL format model into Cura slicing software and set the printing parameters using Cura software. The specific additive manufacturing parameters are as follows: layer height 0.2mm, shell thickness 0mm, bottom / top thickness 0mm, filling density 50%, running speed 20mm / s, wire diameter 0.4mm, nozzle size 0.4mm, initial layer thickness 0.4mm, moving speed 50mm / s, bottom execution speed 20mm / s, internal filling execution speed 20mm / s. After setting all additive manufacturing parameters, export it as a Gcode format model and import it into the additive manufacturing equipment for use.

[0042] (5) Print the porous network structure in the ink direct writing 3D printer equipped with a temperature-controlled cartridge (temperature 130℃), and then dry, debind, and sinter to obtain the final product. The just-manufactured product does not have strength, as shown in Figure 1 .

[0043] (6) The additively manufactured sample is heated to 120℃ in an air atmosphere and kept for 48 hours. After a long time of keeping, most of the Gl is slowly evaporated, and then the sample is heated to 800℃ in an argon atmosphere for debinding. The final sintering is performed using an MRF5299 high-temperature high-vacuum hot-pressing furnace. The dried network structure is as shown in Figure 2 , and the debound product is sintered at 1450℃ in an argon atmosphere for 1h, and finally the tungsten / high-entropy alloy composite material additively manufactured product is obtained, as shown in Figure 3 .

[0044] Example 2

[0045] The tungsten / high-entropy alloy slurry preparation, printing, drying, debinding, and sintering method refers to Example 1, except that the sintering temperature is controlled to be 1500℃, and it can be known from Figure 4 that the sample sintered at 1500℃ in this embodiment still maintains the designed structure and does not collapse in the sintering process. The microstructure of the product after sintering is as shown in Figure 5 .

[0046] Example 3

[0047] The difference from Example 1 is that the slurry also contains polyvinylpyrrolidone, cellulose, and deionized water, specifically:

[0048] A cellulose / PVP / water solution is prepared, in which the concentration of cellulose is 100mg / mL and the concentration of PVP is 80mg / mL. The tungsten / high-entropy alloy mixed powder, PVA / glycerol solution (concentration 60mg / ml), and cellulose / PVP / water solution are mixed to prepare the slurry for ink direct writing additive manufacturing. The weight fractions of the components are as shown in the following table:

[0049] Table 1 Slurry composition table

[0050]

[0051] The slurry is used to print a porous network structure in an ink direct writing 3D printer, and then dried, debound, and sintered to obtain the final product. The additive manufacturing product prepared using the slurry described in this embodiment can control the printing error to be within 0.3mm.

[0052] Example 4

[0053] (1) PVA / Gl solution mixture with a concentration of 90 mg / ml was heated to 150°C in an oil bath and stirred for 3 h to fully dissolve PVA, obtaining a jelly-like PVA / Gl solution mixture.

[0054] (2) Tungsten powder, cobalt powder, chromium powder, iron powder, nickel powder with a particle size of 2-4 μm were mixed with the PVA / Gl mixture at 80°C, and the mass ratio of W:Co:Cr:Fe:Ni:Gl:PVA was 85.83:3.7:3.27:3.51:3.69:20:1.38 (i.e. tungsten accounts for 65 at% of the metal powder) to obtain a W / PVA / Gl slurry (cooled to room temperature, the shape is close to rubber).

[0055] (3) Refer to Example 1 for model drawing, printing parameter setting and file format.

[0056] (4) Refer to Example 1 for printing process, and the sample just printed has toughness.

[0057] (5) The additively manufactured sample was heated to 120°C in air atmosphere and kept for 48 hours, and after a long time of keeping, most of the Gl was slowly evaporated, and then the sample was heated to 800°C in argon atmosphere for debinding. MRF5299 high temperature and high vacuum hot press furnace was used for final sintering, the heating rate from room temperature to 1000°C was 10°C / min, the heating rate from 1000°C to 1450°C was 5°C / min, and the sample was kept at 1450°C for 60 min and then cooled in the furnace. The final additively manufactured product is shown in Figure 6 , the printing error can be controlled within 0.3 mm, and the microstructure is shown in Figure 7 , 8 .

[0058] The slurry described in this example was used to print a solid sheet structure, and the product printed after the slurry was heated in the temperature-controlled barrel was cooled to room temperature and had a shape close to rubber, as shown in Figure 9 .

[0059] Example 5

[0060] The difference from Example 3 is that the metal powder is W / FeCoNiCrCu, and the atomic ratio is 55:9:9:9:9:9. A porous network structure was printed in an ink direct writing 3D printer using the slurry, and then dried, debound and sintered to obtain the final product. The slurry described in this example was used to prepare an additively manufactured product, and the printing error can be controlled within 0.3 mm.

[0061] Comparative Example 1

[0062] The difference from Example 1 is that the mass ratio of W / CoCrFeNi powder, PVA and Gl is 100:33:2.2, and the printing is directly performed at room temperature by using an ink direct writing 3D printer without a temperature control cartridge, the product has poor formability compared with Examples 1 and 2, the layers are fused, and the designed model cannot be realized, such as Figure 10

[0063] The details of the present application are known.

[0064] The above examples are only for illustrating the technical concept and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the content of the present application and to implement it, and it cannot limit the protection scope of the present application. Any equivalent changes or modifications made in accordance with the spirit and essence of the present application shall be covered within the protection scope of the present application.​

Claims

1. A slurry containing tungsten / high entropy alloy for ink direct writing additive manufacturing, characterized by: The slurry is composed of polyvinyl alcohol, polyvinyl pyrrolidone, cellulose, glycerol, deionized water and tungsten / high entropy alloy mixed powder; the high entropy alloy is a cobalt-chromium-iron-nickel high entropy alloy, and for every 100 parts by weight of the tungsten / cobalt-chromium-iron-nickel high entropy alloy mixed powder, the amount of glycerol added is 10 to 20 parts by weight, the amount of polyvinyl alcohol added is 0.35 to 1.08 parts by weight, the amount of deionized water added is 1 to 6 parts by weight, the amount of polyvinyl pyrrolidone added is 0.07 to 0.54 parts by weight, and the amount of cellulose added is 0.08 to 0.9 parts by weight; The preparation method comprises the following steps: firstly preparing a polyvinyl alcohol / glycerol solution, wherein the concentration of the polyvinyl alcohol in the solution is 50-70 mg / mL; heating the mixed polyvinyl alcohol / glycerol in an oil bath to 130-160° C. and stirring for 3-5 hours to completely dissolve the polyvinyl alcohol; A cellulose / polyvinyl pyrrolidone / deionized water solution is then prepared, wherein the concentration of cellulose in the solution is 80-150 mg / mL, and the concentration of polyvinyl pyrrolidone is 70-90 mg / mL. Finally, the tungsten / high entropy alloy mixed powder, polyvinyl alcohol / glycerol solution, and cellulose / polyvinyl pyrrolidone / deionized water solution are mixed to prepare a slurry for ink direct writing additive manufacturing.

2. The tungsten / high entropy alloy slurry for ink direct writing additive manufacturing according to claim 1, characterized in that: The particle size of the tungsten / high entropy alloy mixed powder is 2-4 μm.

3. The tungsten / high entropy alloy slurry for ink direct writing additive manufacturing according to claim 1, characterized in that: The tungsten / high entropy alloy mixed powder is made of tungsten, cobalt, chromium, iron and nickel powder, and their atomic ratio is 55:11.25:11.25:11.25:11.

25.

4. A method for preparing the slurry containing tungsten / high entropy alloy for ink direct writing additive manufacturing according to claim 1, characterized in that: First, prepare a polyvinyl alcohol / glycerol solution with a polyvinyl alcohol concentration of 50-70 mg / mL; heat the mixed polyvinyl alcohol / glycerol in an oil bath to 130-160°C while stirring for 3-5 hours to completely dissolve the polyvinyl alcohol; A cellulose / polyvinyl pyrrolidone / deionized water solution is then prepared, wherein the concentration of cellulose in the solution is 80-150 mg / mL, and the concentration of polyvinyl pyrrolidone is 70-90 mg / mL. Finally, the tungsten / high entropy alloy mixed powder, polyvinyl alcohol / glycerol solution, and cellulose / polyvinyl pyrrolidone / deionized water solution are mixed to prepare a slurry for ink direct writing additive manufacturing.

5. A method for preparing a high-melting-point metal additive manufacturing product using the slurry according to claim 1, characterized in that: The ink direct writing additive manufacturing equipment is used for manufacturing, and then debonding and sintering are performed. The temperature of the barrel during the printing process is between 130 and 160 degrees Celsius.

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