A bimetallic additive and a method of making the same

Abstract

The application relates to a bimetallic additive and a preparation method thereof, and belongs to the technical field of additive manufacturing. The method comprises the following steps: obtaining a first metal, a gradient material and a second metal, the melting point of the second metal is higher than that of the first metal, and the melting point of the gradient material is between that of the first metal and that of the second metal; mixing the first metal, the gradient material and the second metal with a binder respectively to prepare first slurry, gradient slurry and second slurry; layer-by-layer printing the first slurry, the gradient slurry and the second slurry to obtain a green part containing a first metal layer, a gradient material layer and a second metal layer, and the gradient material layer is arranged between the first metal layer and the second metal layer; and performing degreasing and gradient sintering on the green part to obtain the bimetallic additive. The gradient material is arranged to realize the densification of the bimetallic material, is especially suitable for interfacial additive manufacturing of bimetals with a large melting point difference, and the gradient densification can effectively prevent the penetration between the bimetals from affecting the performance of a formed part.

Description

Technical Field

[0001] This application relates to the field of additive manufacturing technology, and in particular to a bimetallic additive and its preparation method. Background Technology

[0002] Bimetallic additive manufacturing adds a second metal to single-metal additive manufacturing to achieve different property distributions. It can combine material properties as needed to provide a wider range of performance and has higher economic efficiency. Current bimetallic additive manufacturing methods can be divided into direct and indirect methods. Direct additive manufacturing refers to using a heat source such as a laser, electron beam, or electric arc to melt the metal during additive manufacturing and then deposit it onto the top layer. Common examples include laser near-net-shape forming and powder bed fusion. Indirect additive manufacturing involves first creating a green part containing metal powder and binder, then debinding to remove the binder, and finally sintering it into a metal part. Common examples include binder jetting and extrusion printing.

[0003] Existing bimetallic additive manufacturing methods mostly involve direct forming. For example, Chinese invention patent application CN114871452A proposes a method for forming bimetals using laser selective melting. However, the manufacturing equipment is expensive, making bimetallic manufacturing highly challenging. Chinese invention patent application CN116372315A proposes a copper / steel bimetallic material and its CMT arc additive manufacturing method. The addition of a high-energy heat source similar to a laser increases equipment costs and imposes additional requirements on the working environment. Direct forming methods are costly, have stringent environmental requirements, and involve high temperatures during additive manufacturing, resulting in significant stress after cooling. Furthermore, the bimetallic interface is prone to cracking and warping due to differences in thermal expansion coefficients. Switching between different metal powders is cumbersome, and there are certain safety hazards when processing metal powders. Indirect forming equipment is less expensive, has lower environmental requirements, uses a higher safety factor in the slurry during additive manufacturing, and allows for easy switching between different materials, making it more advantageous in bimetallic additive manufacturing. For example, Chinese invention patent application CN113500205B proposes a 3D printing method for bimetallic materials. This method uses an indirect forming approach, where copper and iron pastes are extruded using a syringe. High-temperature sintering with the same sintering parameters and shrinkage rate is achieved by adjusting the proportion of binder in the paste. However, adjusting the paste inevitably leads to changes in solid content, and for combinations of multiple metals, adjusting the formula is obviously an extremely time-consuming task. Furthermore, the sintered images show that the print is not dense, with many visible gaps, which has a very negative impact on the performance of the bimetallic parts. Summary of the Invention

[0004] The inventors discovered that the method provided by CN113500205B has a smaller degree of melting of iron particles and a higher degree of melting of copper particles during the densification stage. This is foreseeable because copper has a low sintering temperature. When copper particles begin to diffuse and fuse, iron particles have not yet begun to fuse. When copper particles have a higher degree of fusion, iron particles may have just begun to fuse. Therefore, the sintered parts are not dense, especially for iron, which has many pores inside.

[0005] This application provides a bimetallic additive manufacturing process and a method for preparing the same, to improve the density of bimetallic additive manufacturing.

[0006] In a first aspect, this application provides a method for preparing bimetallic additives, the method comprising:

[0007] A first metal, a gradient material, and a second metal are obtained, wherein the melting point of the second metal is higher than that of the first metal, and the melting point of the gradient material is between that of the first metal and the second metal.

[0008] The first metal, the gradient material, and the second metal are respectively mixed with a binder to prepare a first slurry, a gradient slurry, and a second slurry;

[0009] The first slurry, gradient slurry, and second slurry are printed layer by layer to obtain a green part containing a first metal layer, a gradient material layer, and a second metal layer, wherein the gradient material layer is disposed between the first metal layer and the second metal layer.

[0010] The green part is degreased and subjected to gradient sintering to obtain a bimetallic additive.

[0011] As an optional implementation, the gradient material layer includes at least one gradient sublayer; the melting point of the gradient material in the gradient sublayer gradually increases along the direction from the first metal layer to the second metal layer; the thickness of the gradient sublayer is 0.1 to 2 mm.

[0012] As an optional implementation, the number of gradient sub-layers is 1 to 5.

[0013] As an optional implementation, the gradient material has a particle size of 10-150 μm; and / or

[0014] In the gradient slurry, the volume percentage of the gradient material is 20% to 40%; and / or

[0015] The gradient material includes at least one of alloys and composite materials.

[0016] As an optional implementation, the particle size of the first metal is 10–80 μm; and / or

[0017] In the first slurry, the volume percentage of the first metal is 40% to 60%; and / or

[0018] The particle size of the second metal is 10–80 μm; and / or

[0019] In the second slurry, the volume percentage of the second metal is 40% to 60%.

[0020] As an optional implementation, the thickness of the second metal layer is 0.1 to 2 mm.

[0021] As an optional implementation, the method further includes removing the second metal layer of the bimetallic additive.

[0022] As an optional implementation, the peak temperature of the degreasing process is 120–600°C; and / or

[0023] The peak temperature of the gradient sintering is 700–1800℃.

[0024] As an optional implementation, the printing includes photopolymerization printing and extrusion printing.

[0025] Secondly, this application provides a bimetallic additive material, which is prepared using the method described in the first aspect.

[0026] The technical solutions provided in this application have the following advantages compared with the prior art:

[0027] The method provided in this application embodiment employs indirect additive manufacturing of bimetals. Two metal powders are separately mixed with a binder to form a metal slurry, and gradient material powder is mixed with a binder to form a gradient slurry. One or more layers of gradient material are added as needed around the low-melting-point metal in the model. After manufacturing the green part, the binder is removed by degreasing. The gradient material is introduced during the sintering process to achieve densification of the bimetal. During the gradual heating process of sintering, the low-melting-point metal powder gradually forms a sintering neck at the junction, reducing porosity and densifying. When it becomes dense, the surrounding gradient material powder begins to diffuse and fuse, forming a sintering neck. At this point, the high-melting-point metal has not yet begun to diffuse and fuse. When the temperature continues to rise above the melting point of the low-melting-point metal, the low-melting-point metal begins to melt. At this point, the surrounding gradient material has been basically sintered and densified, so the molten low-melting-point metal will not seep out. The gradient material densifies according to the sintering temperature gradient until the last layer of gradient material is sintered and dense, and the high-melting-point metal powder diffuses and fuses. When the temperature is further raised to the sintering temperature of the high-melting-point metal, the last layer of gradient material melts, but it will not penetrate the already basically dense high-melting-point metal. Sintering continues until the high-melting-point metal is dense, completing the entire sintering process. Throughout the process, the introduction of gradient materials prevents the low-melting-point metal from penetrating before the high-melting-point metal powder begins to diffuse and fuse, thus avoiding the penetration phenomenon that occurs during the sintering of bimetals with large melting point differences. This achieves the densification of the bimetal, and the low-melting-point metal, being melted into a liquid, becomes even denser. Attached Figure Description

[0028] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0029] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 A flowchart illustrating the method provided in the embodiments of this application;

[0031] Figure 2 This is a schematic diagram of the cross-section of the printed model provided in Embodiment 1 of this application;

[0032] Figure 3 This is a schematic diagram of powder changes during the sintering process provided in an embodiment of this application;

[0033] Figure 4 A comparative schematic diagram of the sintering process provided for embodiments of this application;

[0034] Figure 5This is a schematic diagram of the cross-section of the printed model provided in Embodiment 2 of this application. Detailed Implementation

[0035] 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.

[0036] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0037] Figure 1 A flowchart illustrating the method provided in the embodiments of this application, as shown below. Figure 1 As shown in the embodiment of this application, a method for preparing bimetallic additive manufacturing is provided, the method comprising:

[0038] S1. Obtain a first metal, a gradient material, and a second metal, wherein the melting point of the second metal is higher than that of the first metal, and the melting point of the gradient material is between that of the first metal and the second metal;

[0039] In some embodiments, the gradient material includes at least one of alloys and composite materials; the particle size of the gradient material is 10-150 μm; the particle size of the first metal is 10-80 μm; and the particle size of the second metal is 10-80 μm.

[0040] S2. Mix the first metal, the gradient material, and the second metal with the binder respectively to prepare the first slurry, the gradient slurry, and the second slurry;

[0041] In some embodiments, the gradient material accounts for 20% to 40% of the volume in the gradient slurry; the first metal accounts for 40% to 60% of the volume in the first slurry; and the second metal accounts for 40% to 60% of the volume in the second slurry.

[0042] Specifically, in this embodiment, the first metal powder and the second metal powder are respectively mixed with a binder, and then heated and mechanically stirred to prepare their respective homogeneous slurries. The gradient material powder is also mixed with a binder, and then heated and mechanically stirred to prepare their respective homogeneous slurries. It should be noted that the types and quantities of gradient materials can be selected according to actual needs, and different types of gradient materials are also prepared separately as slurries. The first slurry and the second slurry are respectively composed of a mixture of the first metal powder, the second metal powder, and the binder. The particle sizes of the first metal powder and the second metal powder are independently selected from 10-80 μm, accounting for 40-60% of the first slurry / second slurry, and the binder accounts for 40-60% of the metal slurry. The gradient slurry is composed of a mixture of gradient material powder and the binder. The materials include, but are not limited to, alloys and composite materials, and their melting points are between the melting points of the first metal and the second metal. The gradient material powder has a particle size of 10-150 μm, accounting for 20-40% of the gradient slurry, and the binder accounts for 60-80% of the gradient slurry.

[0043] S3. Print the first slurry, the gradient slurry and the second slurry layer by layer to obtain a green part containing a first metal layer, a gradient material layer and a second metal layer, wherein the gradient material layer is disposed between the first metal layer and the second metal layer;

[0044] In some embodiments, the gradient material layer includes at least one gradient sublayer; the melting point of the gradient material in the gradient sublayer gradually increases along the direction from the first metal layer to the second metal layer; the thickness of the gradient sublayer is 0.1 to 2 mm.

[0045] Furthermore, the number of gradient sub-layers is 1 to 5.

[0046] In some embodiments, the printing includes photopolymerization printing and extrusion printing.

[0047] Specifically, in this embodiment, one or more layers of gradient material are added as needed to the lower melting point metal of the bimetallic compound in the original CAD model. A green part is then manufactured by printing based on the model.

[0048] S4. The green part is degreased and subjected to gradient sintering to obtain a bimetallic additive.

[0049] In some embodiments, the peak temperature for degreasing is 120–600°C; the peak temperature for gradient sintering is 700–1800°C. Specifically, densification is achieved by rationally setting the gradient according to the properties of the added gradient materials.

[0050] If the low-melting-point metal model in the original CAD model of the bimetallic material is not encased by the high-melting-point metal in the bimetallic material during the manufacturing of the green part, an additional high-melting-point metal shell needs to be added outside the gradient material shell. In some embodiments, the thickness of the second metal layer is 0.1–2 mm. The method further includes removing the second metal layer of the bimetallic additive manufacturing. Specifically, this removal can be achieved through grinding.

[0051] This method employs indirect additive manufacturing of bimetals. Two metal powders are separately mixed with a binder to form a metal slurry, while gradient material powder is mixed with the binder to form a gradient slurry. One or more layers of gradient material are added as needed around the low-melting-point metal in the model. After fabricating the green part, the binder is removed by degreasing. The gradient material is introduced during sintering to achieve densification of the bimetal. During the gradual heating process of sintering, the low-melting-point metal powder gradually forms a sintering neck at the junction, reducing porosity and densifying. When it becomes dense, the surrounding gradient material powder begins to diffuse and fuse, forming a sintering neck. At this point, the high-melting-point metal has not yet begun to diffuse and fuse. When the temperature continues to rise above the melting point of the low-melting-point metal, the low-melting-point metal begins to melt. At this point, the surrounding gradient material has been basically sintered and densified, so the molten low-melting-point metal will not seep out. The gradient material densifies according to the sintering temperature gradient until the last layer of gradient material is sintered and dense, and the high-melting-point metal powder diffuses and fuses. When the temperature is further raised to the sintering temperature of the high-melting-point metal, the last layer of gradient material melts, but it will not penetrate the already basically dense high-melting-point metal. Sintering continues until the high-melting-point metal is dense, completing the entire sintering process. Throughout the process, the introduction of gradient materials prevents the low-melting-point metal from penetrating before the high-melting-point metal powder begins to diffuse and fuse, thus avoiding the penetration phenomenon that occurs during the sintering of bimetals with large melting point differences. This achieves the densification of the bimetal, and the low-melting-point metal, being melted into a liquid, becomes even denser.

[0052] Densification of bimetallic materials can be achieved by setting gradient material layers, which is especially suitable for bimetallic indirect additive manufacturing with large melting point differences. At the same time, gradient densification can also effectively prevent the penetration between bimetals from affecting the performance of the molded parts.

[0053] Based on a general inventive concept, embodiments of this application also provide a bimetallic additive material, which is prepared using the method provided above.

[0054] The bimetallic additive is prepared based on the above method. The specific steps of the method can be referred to the above embodiments. Since the bimetallic additive adopts some or all of the technical solutions of the above embodiments, it has at least all the beneficial effects brought by the technical solutions of the above embodiments, which will not be repeated here.

[0055] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards. If there is no corresponding national standard, then general international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0056] Example 1

[0057] The bimetallic materials used in additive manufacturing are copper and 17-4PH stainless steel, with gradient materials being B10 copper-nickel alloy and B30 copper-nickel alloy. Furthermore, the copper portion of the printed model is surrounded by 17-4PH stainless steel.

[0058] The preparation method is as follows:

[0059] Slurry preparation: The binder system in all slurries was a mixture of low-density polyethylene, paraffin wax, and stearic acid. Copper powder with an average particle size of 25 μm was mixed with the binder and heated and stirred for 2 hours to form a homogeneous slurry, wherein the volume fraction of copper was 60% and the volume fraction of binder was 40%. 17-4PH stainless steel powder with an average particle size of 15 μm was mixed with the binder and heated and stirred for 2 hours to form a homogeneous slurry, wherein the volume fraction of 17-4PH stainless steel was 60% and the volume fraction of binder was 40%. B10 copper-nickel alloy powder with an average particle size of 28 μm was mixed with the binder and heated and stirred for 2 hours to form a homogeneous slurry, wherein the volume fraction of B10 copper-nickel alloy was 40% and the volume fraction of binder was 60%. B30 copper-nickel alloy powder with an average particle size of 30 μm was mixed with the binder and heated and stirred for 2 hours to form a homogeneous slurry, wherein the volume fraction of B30 copper-nickel alloy was 40% and the volume fraction of binder was 60%.

[0060] Green part manufacturing: In the original CAD model, the entire copper model is shrunk inward by 0.4mm, and then two thin shells with a thickness of 0.2mm are added, corresponding to the graded materials B10 copper-nickel alloy and B30 copper-nickel alloy respectively. For example... Figure 2 The diagram shows a cross-section of the CAD model. The inner layer is copper, surrounded by a 0.2mm thick B10 copper-nickel alloy. This B10 alloy is then surrounded by a 0.2mm thick B30 copper-nickel alloy, and finally, the outermost layer is 17-4PH stainless steel. Based on the model, a multi-nozzle extrusion machine moves along the slicing path, extrudes the corresponding metal slurry under optimal printing parameters, and forms a green part.

[0061] Debinding and Sintering: The printed green parts are first debinded with solvent. The debinding time depends on the size of the printed parts. After complete solvent debinding, thermal debinding is performed at a peak temperature of 550 degrees Celsius and a heating rate of 0.8 degrees Celsius / min. After debinding, the binder in the green parts is expelled as gas or liquid, forming internal channels. The debinded sample is then placed in a sintering furnace to begin sintering. As the temperature continues to rise, the internal metal powder of the sample changes as follows: Figure 3 As shown, the sintering temperatures of the four materials are arranged in a gradient, with copper having the lowest sintering temperature and 17-4PH stainless steel having the highest. As the temperature in the sintering furnace increases at a rate of 3℃ / min to 1030℃, the copper powder gradually begins to form a sintering neck, and the powder particles begin to diffuse and fuse, reducing the porosity until it becomes dense. At this point, the B10 copper-nickel alloy, because its sintering temperature is close to that of copper, also begins to diffuse and fuse between the powder particles. Holding it at this temperature for 2 hours further densifies it. However, the B30 copper-nickel alloy and 17-4PH stainless steel, due to their sintering temperatures being different from those of copper, exhibit different densities. The initial temperature was relatively high, and most particles were not yet in powder form. The temperature was further increased to 1100℃, exceeding the melting point of copper. However, the molten copper could not penetrate the already dense B10 copper-nickel alloy. At this point, sintering necks began to form between the B30 copper-nickel alloy powders, which diffused and fused. Holding for 2 hours further densified the powder. The temperature was then increased to 1200℃, where the B10 copper-nickel alloy melted. However, because the B30 copper-nickel alloy was already basically dense, it could not penetrate. The outermost 17-4PH stainless steel powder began to form sintering necks, and holding for 2 hours further densified it. The temperature was finally increased to 1360℃, the sintering temperature of the outermost 17-4PH stainless steel. Copper and gradient materials melted, but because the 17-4PH stainless steel was already basically dense, the molten metal could not penetrate. Holding for 3 hours continued until the 17-4PH stainless steel was sintered and dense. The morphological changes throughout the process are as follows: Figure 4 As shown below, the internal copper is sintered and densified first. It melts as the temperature rises, but it is encased in the basically dense B10 copper-nickel alloy and does not seep out. As the temperature continues to rise, the B10 copper-nickel alloy also begins to melt, but it is again encased in the basically dense B30 copper-nickel alloy and does not seep out. As the temperature rises further to its peak, the molten gradient material and copper are encased in the basically dense 17-4PH stainless steel and do not seep out, until the 17-4PH stainless steel becomes dense, completing the densification of the bimetallic material. Figure 4 The above illustrates a method for directly densifying copper and 17-4PH stainless steel. Due to the significant difference in sintering temperatures, as the temperature increases, the copper melts while the 17-4PH stainless steel remains in the initial sintering stage. The molten copper seeps out along the channels formed after the degreasing of the 17-4PH stainless steel, and some un-sintered powder even diffuses into the liquefied copper, severely affecting the formation of the bimetallic compound and significantly impacting the performance of the sintered parts. By introducing a gradient layer, densification of the bimetallic compound can be achieved, and the liquefaction of the copper further densifies it, reducing porosity.

[0062] Example 2

[0063] The bimetallic materials used in additive manufacturing are copper and 17-4PH stainless steel, with gradient materials being B10 copper-nickel alloy and B30 copper-nickel alloy. Furthermore, the copper portion of the printed model is not surrounded by 17-4PH stainless steel.

[0064] The preparation method is as follows:

[0065] Slurry preparation: The binder system in all slurries was a mixture of low-density polyethylene, paraffin wax, and stearic acid. Copper powder with an average particle size of 25 μm was mixed with the binder and heated and stirred for 2 hours to form a homogeneous slurry, wherein the volume fraction of copper was 60% and the volume fraction of binder was 40%. 17-4PH stainless steel powder with an average particle size of 15 μm was mixed with the binder and heated and stirred for 2 hours to form a homogeneous slurry, wherein the volume fraction of 17-4PH stainless steel was 60% and the volume fraction of binder was 40%. B10 copper-nickel alloy powder with an average particle size of 28 μm was mixed with the binder and heated and stirred for 2 hours to form a homogeneous slurry, wherein the volume fraction of B10 copper-nickel alloy was 40% and the volume fraction of binder was 60%. B30 copper-nickel alloy powder with an average particle size of 30 μm was mixed with the binder and heated and stirred for 2 hours to form a homogeneous slurry, wherein the volume fraction of B30 copper-nickel alloy was 40% and the volume fraction of binder was 60%.

[0066] Green part manufacturing: In the original CAD model, the entire copper model is shrunk inward by 0.4mm, and then two thin shells with a thickness of 0.2mm are added, corresponding to graded materials B10 copper-nickel alloy and B30 copper-nickel alloy respectively. Then, a thin shell with a thickness of 0.2mm is added to the overall model, corresponding to material 17-4PH. For example... Figure 5 The diagram shows a cross-sectional view of the CAD model. The exposed copper is surrounded by a 0.2mm thick B10 copper-nickel alloy, which is then surrounded by a 0.2mm thick B30 copper-nickel alloy. The entire model is then encased in a 0.2mm thick layer of 17-4PH stainless steel. Based on the model, a multi-nozzle extrusion machine moves along the slicing path, extruding the corresponding metal slurry under optimal printing parameters to form a green part.

[0067] Debinding and Sintering: The printed green parts are first debinded with solvent. The debinding time depends on the size of the printed parts. After complete solvent debinding, thermal debinding is performed at a peak temperature of 550 degrees Celsius and a heating rate of 0.8 degrees Celsius / min. After debinding, the binder in the green parts is expelled as gas or liquid, forming internal channels. The debinded sample is then placed in a sintering furnace to begin sintering. As the temperature continues to rise, the internal metal powder of the sample changes as follows: Figure 3As shown, the sintering temperatures of the four materials are arranged in a gradient, with copper having the lowest sintering temperature and 17-4PH stainless steel having the highest. As the temperature in the sintering furnace increases at a rate of 3℃ / min to 1030℃, the copper powder gradually begins to form a sintering neck, and the powder particles begin to diffuse and fuse, reducing the porosity until it becomes dense. At this point, the B10 copper-nickel alloy, because its sintering temperature is close to that of copper, also begins to diffuse and fuse between the powder particles. Holding it at this temperature for 2 hours further densifies it. However, the B30 copper-nickel alloy and 17-4PH stainless steel, due to the difference in sintering temperature between them and copper, exhibit different densities. The particles were relatively large, and most were not yet in powder form. The temperature was further increased to 1100℃, exceeding the melting point of copper. However, the molten copper could not penetrate the already dense B10 copper-nickel alloy. At this point, sintering necks began to form between the B30 copper-nickel alloy powders, diffusing and fusing. Holding for 2 hours further densified the powder. The temperature was then increased to 1200℃, where the B10 copper-nickel alloy melted. However, because the B30 copper-nickel alloy was already basically dense, it could not penetrate. The outermost 17-4PH stainless steel powder began to form sintering necks, and holding for 2 hours further densified it. The temperature was finally increased to 1360℃, the sintering temperature of the outermost 17-4PH stainless steel. Copper and gradient materials melted, but because the 17-4PH stainless steel was already basically dense, the molten metal could not penetrate. Holding for 3 hours continued until the 17-4PH stainless steel was sintered and dense. The morphological changes throughout the process are as follows: Figure 4 As shown below, the internal copper first sintersects and densifies. As the temperature rises, it melts, but is encased in the nearly dense B10 copper-nickel alloy, preventing leakage. With further temperature increases, the B10 copper-nickel alloy also begins to melt, but is again encased in the nearly dense B30 copper-nickel alloy, preventing leakage. At the peak temperature, the molten gradient material and copper are encased in the nearly dense 17-4PH stainless steel, preventing leakage, until the 17-4PH stainless steel becomes dense, completing the densification of the bimetallic structure. If direct densification were used, this structure would clearly not achieve densification through sintering. At 1360℃, the copper would have already melted into a liquid and could not maintain its intended shape. The addition of the gradient layer allows the exposed copper to retain its original shape while remaining dense under the dense sintering of the 17-4PH stainless steel. Furthermore, because it has already liquefied, it becomes even denser, further reducing porosity. Finally, after the furnace cools, the part is removed, and the thin 17-4PH shell on the surface is polished off.

[0068] Comparative Example 1

[0069] The additively manufactured bimetallic materials are copper and 17-4PH stainless steel. They are prepared using a direct printing sintering method.

[0070] The preparation method is as follows:

[0071] Slurry preparation: The binder system in all slurries is a mixture of low-density polyethylene, paraffin wax, and stearic acid. Copper powder with an average particle size of 25 μm is mixed with the binder and heated and stirred for 2 hours to form a homogeneous slurry, wherein the volume fraction of copper is 60% and the volume fraction of binder is 40%. 17-4PH stainless steel powder with an average particle size of 15 μm is mixed with the binder and heated and stirred for 2 hours to form a homogeneous slurry, wherein the volume fraction of 17-4PH stainless steel is 60% and the volume fraction of binder is 40%.

[0072] Green part manufacturing: Based on the model, a multi-nozzle extrusion device moves along the slicing path and extrudes the corresponding metal slurry under optimal printing parameters to form a green part.

[0073] Debinding and Sintering: The printed green parts are first debinded with solvent. The debinding time depends on the size of the printed parts. After complete solvent debinding, thermal debinding is performed at a peak temperature of 550 degrees Celsius and a heating rate of 0.8 degrees Celsius / min. After debinding, the binder in the green parts is expelled as gas or liquid, forming internal channels. The debinded sample is then placed in a sintering furnace to begin sintering. As the temperature continues to rise, the internal metal powder of the sample changes as follows: Figure 3 As shown, as the temperature is increased to 1360℃ and held for 2 hours, the 17-4PH stainless steel densifies, but the copper has already melted into a liquid and seeps out through the channels formed after the degreasing of the 17-4PH stainless steel due to capillary action. Ultimately, the sintering results in a hollow part encased in a 17-4PH stainless steel shell, with copper seeping to the surface and accumulating to some extent at the bottom, leading to molding failure. If the sintering temperature is lowered to 1050℃ and held for 2 hours, a non-dense 17-4PH stainless steel shell encasing copper can be formed, but the 17-4PH portion has low strength.

[0074] Comparative Example 2

[0075] The additively manufactured bimetallic materials are copper and 17-4PH stainless steel, with the copper portion of the printed model not surrounded by 17-4PH stainless steel. It is prepared using a direct printing-sintering method.

[0076] Slurry preparation: The binder system in all slurries is a mixture of low-density polyethylene, paraffin wax, and stearic acid. Copper powder with an average particle size of 25 μm is mixed with the binder and heated and stirred for 2 hours to form a homogeneous slurry, wherein the volume fraction of copper is 60% and the volume fraction of binder is 40%. 17-4PH stainless steel powder with an average particle size of 15 μm is mixed with the binder and heated and stirred for 2 hours to form a homogeneous slurry, wherein the volume fraction of 17-4PH stainless steel is 60% and the volume fraction of binder is 40%.

[0077] Green part manufacturing: Based on the model, a multi-nozzle extrusion device moves along the slicing path and extrudes the corresponding metal slurry under optimal printing parameters to form a green part.

[0078] Debinding and Sintering: The printed green parts are first debinded with solvent. The debinding time depends on the size of the printed parts. After complete solvent debinding, thermal debinding is performed at a peak temperature of 550 degrees Celsius and a heating rate of 0.8 degrees Celsius / min. After debinding, the binder in the green parts is expelled as gas or liquid, forming internal channels. The debinded sample is then placed in a sintering furnace to begin sintering. As the temperature continues to rise, the internal metal powder of the sample changes as follows: Figure 3 As shown, as the temperature is increased to 1360℃ and held for 2 hours, the 17-4PH stainless steel becomes denser, but the copper has already melted into a liquid and cannot be formed; the copper portion melts and collapses directly. If the sintering temperature is lowered to 1050℃ and held for 2 hours, a non-dense 17-4PH stainless steel and copper part can be formed, but the 17-4PH portion has low strength.

[0079] The density of the bimetallic additives provided in Examples 1 to 2 and Comparative Examples 1 to 2 was tested using Archimedes' water displacement method. The results are shown in the table below: (where high-temperature sintering represents the highest sintering temperature of the high-melting-point metal, and low-temperature sintering represents the highest sintering temperature of the low-melting-point metal).

[0080] Density Example 1 97.5% (high-temperature sintering) Example 2 96.8% (high-temperature sintering) Comparative Example 1 90.3% (low-temperature sintering) / high-temperature sintering failure Comparative Example 2 89.9% (low-temperature sintering) / high-temperature sintering failure

[0081] As can be seen from the table above, the bimetallic additives prepared by the method provided in the embodiments of this application have high density.

[0082] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0083] In this application, unless otherwise stated, directional terms such as "upper" and "lower" specifically refer to the drawing directions in the accompanying drawings. Furthermore, in the description of this application, terms such as "comprising" and "including" mean "including but not limited to." In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this document, "and / or" describes the relationship between related objects, indicating that three relationships can exist; for example, A and / or B can represent: A alone, A and B simultaneously, or B alone. A and B can be singular or plural. In this document, "at least one" means one or more, and "more than one" means two or more. "At least one," "at least one of the following," or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c" or "at least one of a, b, and c" can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be a single or multiple.

[0084] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for preparing bimetallic additives, characterized in that, The method includes: A first metal, a gradient material, and a second metal are obtained, wherein the melting point of the second metal is higher than that of the first metal, and the melting point of the gradient material is between that of the first metal and the second metal. The first metal, the gradient material, and the second metal are respectively mixed with a binder to prepare a first slurry, a gradient slurry, and a second slurry; The first slurry, gradient slurry, and second slurry are printed layer by layer to obtain a green part containing a first metal layer, a gradient material layer, and a second metal layer, wherein the gradient material layer is disposed between the first metal layer and the second metal layer. The green part is degreased and subjected to gradient sintering to obtain a bimetallic additive; The gradient material layer includes at least one gradient sublayer; the melting point of the gradient material in the gradient sublayer gradually increases along the direction from the first metal layer to the second metal layer; the thickness of the gradient sublayer is 0.1~2mm; During the sintering process, as the green blank gradually heats up, the low-melting-point metal powder gradually forms a sintering neck at the joint, reducing porosity and densifying. When it becomes dense, the surrounding gradient material powder begins to diffuse and fuse, forming a sintering neck. At this point, the high-melting-point metal has not yet begun to diffuse and fuse. When the temperature continues to rise above the melting point of the low-melting-point metal, the low-melting-point metal begins to melt. At this point, the surrounding gradient material has been basically sintered and densified, so the molten low-melting-point metal will not seep out. The gradient material densifies according to the sintering temperature gradient until the last layer of gradient material is sintered and dense, and the high-melting-point metal powder diffuses and fuses. The temperature is further raised to the sintering temperature of the high-melting-point metal, and the last layer of gradient material melts, but it will not penetrate the already basically dense high-melting-point metal. Sintering continues until the high-melting-point metal is dense, completing the entire sintering process.

2. The method for preparing bimetallic additive manufacturing according to claim 1, characterized in that, The number of gradient sub-layers is 1 to 5.

3. The method for preparing bimetallic additive manufacturing according to claim 1, characterized in that, The gradient material has a particle size of 10-150 μm; and / or In the gradient slurry, the volume percentage of the gradient material is 20% to 40%; and / or The gradient material includes at least one of alloys and composite materials.

4. The method for preparing bimetallic additive manufacturing according to claim 1, characterized in that, The particle size of the first metal is 10~80 μm; and / or In the first slurry, the volume percentage of the first metal is 40% to 60%; and / or The particle size of the second metal is 10~80 μm; and / or In the second slurry, the volume percentage of the second metal is 40% to 60%.

5. The method for preparing bimetallic additive manufacturing according to claim 1, characterized in that, The thickness of the second metal layer is 0.1~2mm.

6. The method for preparing bimetallic additives according to claim 1, characterized in that, The peak temperature for degreasing is 120~600℃; and / or The peak temperature of the gradient sintering is 700~1800℃.

7. The method for preparing bimetallic additive manufacturing according to claim 1, characterized in that, The printing includes photopolymer printing and extrusion printing.

8. A bimetallic additive manufacturing process, characterized in that, The bimetallic additive is prepared by the method described in any one of claims 1 to 7.

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