Thermal-electric coupled sintering apparatus for binder jetting 3d-printed metal powder green bodies, and sintering method therefor

Abstract

A thermal-electric coupled sintering method for binder jetting 3D-printed metal powder green bodies, comprising: adjusting a printing layer thickness, a powder spreading speed and a binder saturation parameter for printing, placing a printed green body into a curing furnace and heating to 120-200°C for curing, then placing the green body into a sintering furnace and heating to 400-900°C for debinding, and holding temperature; after debinding is completed, continuing to raise the temperature to a solid-phase sintering temperature for sintering densification, while simultaneously introducing an electric current of 1-500 A / cm2 to the sample, so that the metal green body undergoes sintering densification under thermal-electric coupling. This method can, without external pressure, enable the green body to be rapidly sintered at low temperature into a structure having smaller grains and higher density, improving the strength and plasticity of the sintered metal material. The present invention also relates to a thermal-electric coupled sintering apparatus for binder jetting 3D-printed metal powder green bodies.

Description

A thermo-electric coupling sintering apparatus and sintering method for binder jet 3D printing of metal powder green bodies Technical Field

[0001] This invention belongs to the field of additive manufacturing (3D printing), particularly the research direction of binder jetting 3D printing forming and sintering of metal powder. Background Technology

[0002] Binder Jetting 3D Printing (BJ3DP) is a high-efficiency, low-cost 3D printing technology that can form complex parts and has been widely used in the forming of materials such as ceramics, stainless steel, high-temperature alloys, and titanium alloys.

[0003] BJ3DP can be used to form porous and complex materials, as well as larger materials. Its forming process consists of several main steps: green body printing, curing, debinding, and densification sintering. The densification sintering process is similar to conventional powder metallurgy and MIM. Typically, metal parts formed by BJ3DP can achieve relatively dense samples after hot sintering (without external pressure), but it suffers from problems such as high sintering temperature, long sintering time, and coarse grains and high porosity.

[0004] In powder metallurgy and MIM forming processes for metallic materials, multi-field coupled sintering can solve the problems of rapid sintering and densification of green blanks. Spark plasma sintering (SPS) is a typical thermo-electric-mechanical multi-field coupled sintering method, utilizing pulsed discharge principles and mechanical pressure to achieve rapid densification of metal powder at low temperatures and in a short time, while simultaneously controlling grain growth. However, due to the complex shapes and porous structures of BJ3DP-formed green blanks, pressure cannot be applied during the sintering process. Therefore, thermo-electric-mechanical multi-field coupled sintering is not suitable for the densification sintering of BJ3DP-formed green blanks. Similarly, hot isostatic pressing (thermo-mechanical coupling) is only suitable for BJ3DP-formed green blanks with simple shapes and cannot meet the requirements for BJ3DP-formed green blanks with complex shapes. Currently, there are no reports on thermo-electric coupled sintering densification processes for BJ3DP green blanks made of metal powder. Summary of the Invention

[0005] This invention provides a thermo-electric coupling sintering apparatus and sintering method for binder jet 3D printing of metal powder green bodies. By utilizing the Joule heating effect, electromigration effect and electroplastic effect between metal powder and electric current, the 3DP printed green body can obtain metal materials with higher density, higher strength and better plasticity during the sintering process.

[0006] The present invention provides a thermo-electric coupling sintering device for 3D printing of metal powder green bodies by binder jetting, comprising: ①: furnace body, ③: electrode plate, ④: insulation device, ⑤: wire, ⑥: power supply.

[0007] The present invention provides a thermo-electric coupling sintering method for forming metal powder green bodies by binder jetting 3D printing, the specific steps of which are as follows:

[0008] Step (1): Green printing. Adjust printing parameters such as layer thickness and binder saturation to obtain a green blank by 3DP printing of metal or high-entropy alloy powder.

[0009] Step (2): Curing and degreasing. The green blank is placed in a curing furnace for curing and heat preservation, and then placed in a sintering furnace for degreasing and heat preservation.

[0010] Step (3): Thermo-electric coupling sintering of the green blank. The degreased green blank is placed on the electrode plate, and current is passed through it for thermo-electric coupling sintering, while vacuum or atmosphere protection is used. After sintering is completed, the sample is obtained after cooling.

[0011] Furthermore, in step (1), the metal powder includes, but is not limited to, aluminum alloys, copper alloys, nickel alloys, and titanium alloys.

[0012] Furthermore, in step (1), the high-entropy alloy powder includes, but is not limited to, AlFeCoCrNi. 2.1 , FeCoCrNi, TiZrNbHfNi, TiZrNbMoTa, CoCrFeMnNi, CoCrFeMnNiTi and Al 0.5 Cr 0.9 FeNi 2.5 V 0.2 wait.

[0013] Furthermore, in step (1), the metal powder has a particle size of 10-150 μm and a morphology of spherical or irregular.

[0014] Further, in step (1), the printing parameters are: layer thickness of approximately 60-200μm, binder saturation of 35%-80%, powder spreading speed of 5-20pps, and powder spreading shaft rotation speed of 10-30pps.

[0015] Furthermore, in step (2), the curing temperature is 120-200℃, the heating rate is 1-10℃ / min, and the holding time is 90-150min.

[0016] Furthermore, in step (2), the degreasing temperature is 400-900℃, the heating rate is 1-10℃ / min, and the holding time is 1-4h.

[0017] Furthermore, in step (3), the thermal-electric coupling sintering temperature is generally 10-100℃ lower than the melting point of the material, the heating rate is 1-10℃ / min, and the holding time is 1-8h.

[0018] Furthermore, in step (3), the current applied during the thermo-electric coupling sintering is 1-500 A / cm. 2 The type of current is direct current or alternating current.

[0019] Furthermore, in step (3), the thermo-electric coupling sintering is protected by vacuuming or by introducing inert gases such as nitrogen or argon.

[0020] The principle of this invention is as follows:

[0021] This invention employs the principle of thermo-electric coupling sintering, utilizing the Joule heating effect, electromigration effect, and electroplastic effect between metal powder and electric current. This enables the rapid bonding of contact necks between powder particles in the 3DP metal powder green body during the initial densification stage of sintering, thereby accelerating the densification process and achieving higher density. Simultaneously, under the influence of the electric current, the green body forms a smaller and denser grain structure, resulting in better strength and plasticity in the sintered metal material.

[0022] Compared with the prior art, the advantages of the present invention are as follows:

[0023] 1. Compared with ordinary hot sintering furnaces, the thermo-electric coupling sintering device of the present invention can achieve low-temperature sintering and forming with lower energy consumption.

[0024] 2. Compared with ordinary high-temperature sintering process, green blanks can form a structure with smaller and denser grains under the action of electric current, resulting in better strength and plasticity.

[0025] 3. Compared with ordinary high-temperature sintering process, the green body can be degreased more thoroughly under the action of electric current, which greatly reduces the impact of carbon residue in the binder on the material properties. Attached Figure Description

[0026] Figure 1 is a structural diagram of the thermo-electric coupling sintering device. ①: Furnace body; ②: Degreased green billet; ③: Electrode plate; ④: Insulation device; ⑤: Wire; ⑥: Power supply.

[0027] Figure 2 shows the metallographic structure of the thermo-electric sintered sample from Example 9. Embodiments of the present invention

[0028] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0029] The embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0030] As shown in Figure 1, the thermo-electric coupling sintering device in the following embodiment includes a furnace body ①, an electrode plate ③, an insulating device ④, a wire ⑤, and a power supply ⑥; the electrode plate ③ is disposed inside the furnace body ①, and the electrode plate ③ is connected to the power supply ⑥ through the wire ⑤; the degreased green blank ② is disposed in the middle of the electrode plate ③; the insulating device ④ is disposed at the contact part between the wire ⑤ and the furnace body ①.

[0031] Example 1

[0032] (1) Printing and shaping of green blanks

[0033] The printing process uses spherical 6061 aluminum alloy powder with a particle size of 13-53 μm and a median particle size of approximately 20 μm. The printing parameters are: layer thickness of 60 μm, binder saturation of 35%, powder spreading shaft rotation speed of 10 pps, and powder spreading shaft movement speed of 5 pps. The green body size is 24 mm × 12 mm × 10 mm.

[0034] (2)Curing degreasing

[0035] The printed green blank is placed in a curing oven for curing. The temperature is increased to 120℃ at a rate of 1℃ / min and held for 90 minutes. Then, the temperature is increased to 400℃ at a rate of 1℃ / min for degreasing and held for 1 hour.

[0036] (3) Thermal-electric coupling sintering of green body

[0037] Continue to increase the temperature at a rate of 1℃ / min to the densification temperature and hold for 1 hour for sintering and densification. A 1A / cm gas flow is then introduced into the sample. 2 The sample is subjected to an electric current while simultaneously being heated in the thermal field. After the holding period, the sample is cooled to room temperature at a rate of 5°C / min, and high vacuum is maintained throughout the sintering process.

[0038] Example 2

[0039] (1) Printing and shaping of green blanks

[0040] The printing process used spherical H62 copper alloy powder with a particle size of 13-53 μm and a median particle size of approximately 30 μm. The printing parameters were: layer thickness of 70 μm, binder saturation of 40%, powder spreading shaft rotation speed of 15 pps, and powder spreading shaft movement speed of 10 pps. The green size was 24 mm × 12 mm × 10 mm.

[0041] (2)Curing degreasing

[0042] The printed green blank is placed in a curing oven for curing. The temperature is increased to 130℃ at a rate of 2℃ / min and held for 100min. Then, the temperature is increased to 500℃ at a rate of 2℃ / min for degreasing and held for 1.5h.

[0043] (3) Thermal-electric coupling sintering of green body

[0044] Continue sintering and densification by increasing the temperature to the densification temperature at a rate of 2℃ / min and holding for 2 hours, while introducing 5A / cm gas into the sample. 2 The sample is subjected to an electric current while simultaneously being heated in the thermal field. After the holding period, the sample is cooled to room temperature at a rate of 5°C / min, and high vacuum is maintained throughout the sintering process.

[0045] Example 3

[0046] (1) Printing and shaping of green blanks

[0047] The printing process used spherical N6 nickel alloy powder with a particle size of 13-53 μm and a median particle size of approximately 40 μm. The printing parameters were: layer thickness of 80 μm, binder saturation of 50%, powder spreading shaft rotation speed of 20 pps, and powder spreading shaft movement speed of 15 pps. The green size was 24 mm × 12 mm × 10 mm.

[0048] (2)Curing degreasing

[0049] The printed green blank is placed in a curing oven for curing. The temperature is increased to 140℃ at a rate of 3℃ / min and held for 110 minutes. Then, the temperature is increased to 550℃ at a rate of 3℃ / min for degreasing and held for 2 hours.

[0050] (3) Thermal-electric coupling sintering of green body

[0051] Continue sintering and densification by increasing the temperature to the densification temperature at a rate of 3℃ / min and holding for 3 hours, while introducing 5A / cm into the sample. 2 The sample is subjected to an electric current while simultaneously being heated in the thermal field. After the holding period, the sample is cooled to room temperature at a rate of 5°C / min, and high vacuum is maintained throughout the sintering process.

[0052] Example 4

[0053] (1) Printing and shaping of green blanks

[0054] The printing process used spherical TC4 titanium alloy powder with a particle size of 25-60 μm and a median particle size of approximately 40 μm. The printing parameters were: layer thickness of 90 μm, binder saturation of 60%, powder spreading shaft rotation speed of 25 pps, and powder spreading shaft movement speed of 20 pps. The green body size was 24 mm × 12 mm × 10 mm.

[0055] (2)Curing degreasing

[0056] The printed green blank is placed in a curing oven for curing. The temperature is increased to 150℃ at a rate of 4℃ / min and held for 120 minutes. Then, the temperature is increased to 600℃ at a rate of 4℃ / min for degreasing and held for 3 hours.

[0057] (3) Thermal-electric coupling sintering of green body

[0058] Continue to increase the temperature at a rate of 4℃ / min to the densification temperature and hold for 4 hours for sintering and densification. A flow of 10 A / cm is then introduced into the sample. 2 The sample is subjected to an electric current while simultaneously being heated in the thermal field. After the holding period, the sample is cooled to room temperature at a rate of 5°C / min, and a nitrogen atmosphere is introduced throughout the sintering process.

[0059] Example 5

[0060] (1) Printing and shaping of green blanks

[0061] Printing uses spherical AlFeCoCrNi 2.1 High-entropy alloy powder with a particle size of 33-75μm and a median particle size of approximately 50μm was used. The printing parameters were: layer thickness of 100μm, binder saturation of 65%, powder spreading shaft rotation speed of 17pps, and powder spreading shaft movement speed of 7pps. The green body size was 24mm × 12mm × 10mm.

[0062] (2)Curing degreasing

[0063] The printed green blank is placed in a curing oven for curing. The temperature is increased to 160℃ at a rate of 5℃ / min and held for 130 minutes. Then, the temperature is increased to 700℃ at a rate of 5℃ / min for degreasing and held for 4 hours.

[0064] (3) Thermal-electric coupling sintering of green body

[0065] Continue sintering and densification by increasing the temperature to the densification temperature at a rate of 5℃ / min and holding for 5 hours, while introducing 20A / cm into the sample. 2 The sample is subjected to an electric current while simultaneously being heated in the thermal field. After the holding period, the sample is cooled to room temperature at a rate of 5°C / min, and a nitrogen atmosphere is introduced throughout the sintering process.

[0066] Example 6

[0067] (1) Printing and shaping of green blanks

[0068] The printing process used spherical FeCoCrNi high-entropy alloy powder with a particle size of 43-85 μm and a median particle size of approximately 60 μm. The printing parameters were: layer thickness of 110 μm, binder saturation of 70%, powder spreading shaft rotation speed of 22 pps, and powder spreading shaft movement speed of 13 pps. The green body size was 24 mm × 12 mm × 10 mm.

[0069] (2)Curing degreasing

[0070] The printed green body is placed in a curing oven for curing. The temperature is increased to 170℃ at a rate of 6℃ / min and held for 140 minutes. Then, the temperature is increased to 750℃ at a rate of 6℃ / min for degreasing and held for 1.5 hours.

[0071] (3) Thermal-electric coupling sintering of green body

[0072] Continue sintering and densification by increasing the temperature to the densification temperature at a rate of 6℃ / min and holding for 6 hours, while introducing 50A / cm into the sample. 2 The sample is subjected to an electric current while simultaneously being heated in the thermal field. After the holding period, the sample is cooled to room temperature at a rate of 5°C / min, and a nitrogen atmosphere is introduced throughout the sintering process.

[0073] Example 7

[0074] (1) Printing and shaping of green blanks

[0075] The printing process used spherical CoCrFeMnNi high-entropy alloy powder with a particle size of 80-160 μm and a median particle size of approximately 100 μm. The printing parameters were: layer thickness of 120 μm, binder saturation of 80%, powder spreading shaft rotation speed of 26 pps, and powder spreading shaft movement speed of 16 pps. The green body size was 24 mm × 12 mm × 10 mm.

[0076] (2)Curing degreasing

[0077] The printed green blank is placed in a curing oven for curing. The temperature is increased to 180℃ at a rate of 7℃ / min and held for 150min. Then, the temperature is increased to 800℃ at a rate of 7℃ / min for degreasing and held for 2.5h.

[0078] (3) Thermal-electric coupling sintering of green body

[0079] Continue sintering and densification by increasing the temperature to the densification temperature at a rate of 7℃ / min and holding for 7 hours, while introducing 100A / cm into the sample. 2The sample is subjected to an electric current while simultaneously being heated in the thermal field. After the holding period, the sample is cooled to room temperature at a rate of 5°C / min, and argon atmosphere is introduced throughout the sintering process.

[0080] Example 8

[0081] (1) Printing and shaping of green blanks

[0082] The printing process used irregularly shaped CoCrFeMnNiTi high-entropy alloy powder with a particle size of 160-200 μm and a median particle size of approximately 140 μm. The printing parameters were: layer thickness of 180 μm, binder saturation of 75%, powder spreading shaft rotation speed of 28 pps, and powder spreading shaft movement speed of 18 pps. The green body size was 24 mm × 12 mm × 10 mm.

[0083] (2)Curing degreasing

[0084] The printed green blank is placed in a curing oven for curing. The temperature is increased to 190℃ at a rate of 8℃ / min and held for 140 minutes. Then, the temperature is increased to 850℃ at a rate of 8℃ / min for degreasing and held for 3 hours.

[0085] (3) Thermal-electric coupling sintering of green body

[0086] Continue sintering and densification by increasing the temperature to the densification temperature at a rate of 8℃ / min and holding for 7.5 hours, while introducing 200 A / cm into the sample. 2 The sample is subjected to an electric current while simultaneously being heated in the thermal field. After the holding period, the sample is cooled to room temperature at a rate of 5°C / min, and argon atmosphere is introduced throughout the sintering process.

[0087] Example 9

[0088] (1) Printing and shaping of green blanks

[0089] Printing uses spherical Al 0.5 Cr 0.9 FeNi 2.5 V 0.2 High-entropy alloy powder with a particle size of 160-200μm and a median particle size of approximately 150μm was used. The printing parameters were: layer thickness of 200μm, binder saturation of 80%, powder spreading shaft rotation speed of 30pps, and powder spreading shaft movement speed of 20pps. The green body size was 24mm × 12mm × 10mm.

[0090] (2)Curing degreasing

[0091] The printed green body is placed in a curing oven for curing. The temperature is increased to 200℃ at a rate of 10℃ / min and held for 150min. Then, the temperature is increased to 900℃ at a rate of 10℃ / min for degreasing and held for 4 hours.

[0092] (3) Thermal-electric coupling sintering of green body

[0093] Continue sintering and densification by increasing the temperature to the densification temperature at a rate of 10℃ / min and holding for 8 hours, while introducing 500 A / cm into the sample. 2 The sample is subjected to an electric current while simultaneously being heated in the thermal field. After the holding period, the sample is cooled to room temperature at a rate of 5°C / min, and argon atmosphere is introduced throughout the sintering process.

[0094] (4) Metallographic sample preparation

[0095] The sintered sample was cut into 5x5x5mm cubes. One side was then successively polished with 600-grit, 1200-grit, and 2500-grit metallographic sandpaper, followed by polishing. A 1.5μm diamond polishing solution was then applied for 2 minutes of polishing, followed by etching with aqua regia for 7 seconds. After drying, the sample was observed under a metallographic microscope, and its morphology is shown in Figure 2. It is evident from the figure that the hot-sintered sample has coarse grains, mostly around 200μm, with numerous pores distributed between the grains, significantly affecting the sample's performance.

Claims

1. A thermo-electric coupled sintering method of binder jet 3D printed shaped metal powder green bodies, characterized by, The main steps of this thermo-electric coupling sintering method are as follows: Step (1): Green blank printing: Adjust the printing parameters to obtain a green blank by 3DP printing of metal powder or high entropy alloy powder; the printing parameters include layer thickness, binder saturation, powder spreading speed and powder spreading shaft rotation speed; Step (2): Curing and degreasing: The green blank is placed in a curing furnace for curing and heat preservation, and then placed in a sintering furnace for degreasing and heat preservation; Step (3): Thermo-electric coupling sintering of green blanks: Place the degreased green blanks on the electrode plate of the thermo-electric coupling sintering device, pass current through them, and perform thermo-electric coupling sintering. At the same time, use vacuum or atmosphere protection. After sintering is completed, the sample is obtained after cooling.

2. The thermo-electric coupling sintering method for forming metal powder green bodies by binder jetting 3D printing according to claim 1, in step (1), the metal powder includes aluminum alloy, copper alloy, nickel alloy or titanium alloy; the particle size of the metal powder is 10-150μm, and the morphology is spherical or irregular.

3. The thermal-electric coupling sintering method of binder jet 3D printed shaped metal powder green body according to claim 1, wherein the high-entropy alloy powder in step (1) comprises AlFeCoCrNi 2.1 , FeCoCrNi, TiZrNbHfNi, TiZrNbMoTa, CoCrFeMnNi, CoCrFeMnNiTi or Al 0.5 Cr 0.9 FeNi 2.5 V 0.2 .

4. The thermal-electric coupling sintering method for forming metal powder green bodies by binder jetting 3D printing according to claim 1, wherein the printing parameters in step (1) are: layer thickness of 60-200μm, binder saturation of 35%-80%, powder spreading speed of 5-20pps, and powder spreading shaft rotation speed of 10-30pps.

5. The thermo-electric coupling sintering method for forming metal powder green bodies by binder jetting 3D printing according to claim 1, in step (2), the curing temperature is 120-200℃, the heating rate is 1-10℃ / min, and the holding time is 90-150min.

6. In the thermo-electric coupling sintering method for forming metal powder green bodies by binder jetting 3D printing according to claim 1, in step (2), the degreasing temperature is 400-900℃, the heating rate is 1-10℃ / min, and the holding time is 1-4h.

7. The thermo-electric coupling sintering method for forming metal powder green blanks by binder jetting 3D printing according to claim 1, in step (3), the thermo-electric coupling sintering temperature is generally 10-100℃ lower than the melting point of the powder, the heating rate is 1-10℃ / min, and the holding time is 1-8h.

8. The thermo-electric coupling sintering method for forming metal powder green bodies by binder jetting 3D printing according to claim 1, wherein in step (3), the current applied during the thermo-electric coupling sintering is 1-500 A / cm. 2 The type of current is direct current or alternating current.

9. The thermo-electric coupling sintering method for forming metal powder green blanks by binder jetting 3D printing according to claim 1, wherein in step (3), the thermo-electric coupling sintering is protected by vacuuming or by introducing nitrogen or argon inert gas.

10. The thermoelectrically coupled sintering apparatus for use in the method of any one of claims 1 to 9, characterized in that It includes a furnace body, electrode plates, insulation devices, wires, and a power supply; the electrode plates are installed inside the furnace body and are connected to the power supply via wires; the degreased green blanks from step (2) are placed in the middle of the electrode plates; and the part of the wires that contacts the furnace body is equipped with an insulation device.

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